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M. J. Mirzaali
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Investigating Polymer-Clad Photonic Force Sensors
A Numerical Study of Polymer Geometry, Three-Dimensional Modelling, and Mechanical Loading
Soft tissue engineering is a field focused on the regeneration and replacement of damaged tissues through the development of engineered constructs. These constructs should mimic the structure and mechanical behavior of the native tissue.
The uterus is a soft tissue with a complex layered structure. Due to this complexity and the limited clinical solutions available for uterine healing, tissue engineering has emerged as a promising alternative for the treatment of uterine disorders. However, only a limited number of studies have systematically investigated how scaffold pore architecture influences the mechanical and viscoelastic behavior required to mimic native uterine tissue. Therefore, the aim of this study was to investigate the effect of pore size on the mechanical behavior of scaffolds in order to fabricate a scaffold capable of mimicking native uterine tissue.
In this work, four 3D-printed alginate–gelatin scaffold geometries were designed and characterized: a homogeneous Bulk control and three macroporous architectures (Small Pores, Gradient Pores, and Large Pores). The four geometries were tested under quasi-static compression up to 50 % strain to evaluate scaffold stiffness and load-bearing capacity, ramp-and-hold stress relaxation at 15 % strain for 600 s to characterize viscoelastic behavior and time-dependent stress dissipation, and ten cycles of cyclic compression to investigate energy dissipation, recovery behavior, and structural stability under repeated loading. For the compression tests, all four geometries showed a similar Young’s modulus of 14–18 kPa. However, architecture had a much stronger and statistically significant effect on the time-dependent response. The Bulk scaffold retained 47 % of its initial peak stress after 600 s of relaxation, whereas the porous groups retained only 17–22 % (p < 0.001). The slow viscoelastic time constant τ2 was 470 s for the Bulk scaffold compared with 165–196 s for the porous groups (p = 0.031). During cyclic loading, the porous scaffolds dissipated up to three times more energy per cycle than the Bulk control, while the scaffold with Large-Pores accumulated the largest residual strain (p = 0.002).
The results of this study show that the bulk scaffold most closely matches the viscoelastic signature of native uterine tissue. However, because the bulk scaffold lacks pores and therefore cannot adequately support uterine tissue regeneration, it is not suitable for regenerative applications. In contrast, the gradient scaffold emerges as the most promising alternative, as tissue regeneration requires porosity to enhance cell infiltration and nutrient transport. The gradient design provides the most balanced mechanical performance and represents the most suitable candidate for further optimization. ...
The uterus is a soft tissue with a complex layered structure. Due to this complexity and the limited clinical solutions available for uterine healing, tissue engineering has emerged as a promising alternative for the treatment of uterine disorders. However, only a limited number of studies have systematically investigated how scaffold pore architecture influences the mechanical and viscoelastic behavior required to mimic native uterine tissue. Therefore, the aim of this study was to investigate the effect of pore size on the mechanical behavior of scaffolds in order to fabricate a scaffold capable of mimicking native uterine tissue.
In this work, four 3D-printed alginate–gelatin scaffold geometries were designed and characterized: a homogeneous Bulk control and three macroporous architectures (Small Pores, Gradient Pores, and Large Pores). The four geometries were tested under quasi-static compression up to 50 % strain to evaluate scaffold stiffness and load-bearing capacity, ramp-and-hold stress relaxation at 15 % strain for 600 s to characterize viscoelastic behavior and time-dependent stress dissipation, and ten cycles of cyclic compression to investigate energy dissipation, recovery behavior, and structural stability under repeated loading. For the compression tests, all four geometries showed a similar Young’s modulus of 14–18 kPa. However, architecture had a much stronger and statistically significant effect on the time-dependent response. The Bulk scaffold retained 47 % of its initial peak stress after 600 s of relaxation, whereas the porous groups retained only 17–22 % (p < 0.001). The slow viscoelastic time constant τ2 was 470 s for the Bulk scaffold compared with 165–196 s for the porous groups (p = 0.031). During cyclic loading, the porous scaffolds dissipated up to three times more energy per cycle than the Bulk control, while the scaffold with Large-Pores accumulated the largest residual strain (p = 0.002).
The results of this study show that the bulk scaffold most closely matches the viscoelastic signature of native uterine tissue. However, because the bulk scaffold lacks pores and therefore cannot adequately support uterine tissue regeneration, it is not suitable for regenerative applications. In contrast, the gradient scaffold emerges as the most promising alternative, as tissue regeneration requires porosity to enhance cell infiltration and nutrient transport. The gradient design provides the most balanced mechanical performance and represents the most suitable candidate for further optimization. ...
Soft tissue engineering is a field focused on the regeneration and replacement of damaged tissues through the development of engineered constructs. These constructs should mimic the structure and mechanical behavior of the native tissue.
The uterus is a soft tissue with a complex layered structure. Due to this complexity and the limited clinical solutions available for uterine healing, tissue engineering has emerged as a promising alternative for the treatment of uterine disorders. However, only a limited number of studies have systematically investigated how scaffold pore architecture influences the mechanical and viscoelastic behavior required to mimic native uterine tissue. Therefore, the aim of this study was to investigate the effect of pore size on the mechanical behavior of scaffolds in order to fabricate a scaffold capable of mimicking native uterine tissue.
In this work, four 3D-printed alginate–gelatin scaffold geometries were designed and characterized: a homogeneous Bulk control and three macroporous architectures (Small Pores, Gradient Pores, and Large Pores). The four geometries were tested under quasi-static compression up to 50 % strain to evaluate scaffold stiffness and load-bearing capacity, ramp-and-hold stress relaxation at 15 % strain for 600 s to characterize viscoelastic behavior and time-dependent stress dissipation, and ten cycles of cyclic compression to investigate energy dissipation, recovery behavior, and structural stability under repeated loading. For the compression tests, all four geometries showed a similar Young’s modulus of 14–18 kPa. However, architecture had a much stronger and statistically significant effect on the time-dependent response. The Bulk scaffold retained 47 % of its initial peak stress after 600 s of relaxation, whereas the porous groups retained only 17–22 % (p < 0.001). The slow viscoelastic time constant τ2 was 470 s for the Bulk scaffold compared with 165–196 s for the porous groups (p = 0.031). During cyclic loading, the porous scaffolds dissipated up to three times more energy per cycle than the Bulk control, while the scaffold with Large-Pores accumulated the largest residual strain (p = 0.002).
The results of this study show that the bulk scaffold most closely matches the viscoelastic signature of native uterine tissue. However, because the bulk scaffold lacks pores and therefore cannot adequately support uterine tissue regeneration, it is not suitable for regenerative applications. In contrast, the gradient scaffold emerges as the most promising alternative, as tissue regeneration requires porosity to enhance cell infiltration and nutrient transport. The gradient design provides the most balanced mechanical performance and represents the most suitable candidate for further optimization.
The uterus is a soft tissue with a complex layered structure. Due to this complexity and the limited clinical solutions available for uterine healing, tissue engineering has emerged as a promising alternative for the treatment of uterine disorders. However, only a limited number of studies have systematically investigated how scaffold pore architecture influences the mechanical and viscoelastic behavior required to mimic native uterine tissue. Therefore, the aim of this study was to investigate the effect of pore size on the mechanical behavior of scaffolds in order to fabricate a scaffold capable of mimicking native uterine tissue.
In this work, four 3D-printed alginate–gelatin scaffold geometries were designed and characterized: a homogeneous Bulk control and three macroporous architectures (Small Pores, Gradient Pores, and Large Pores). The four geometries were tested under quasi-static compression up to 50 % strain to evaluate scaffold stiffness and load-bearing capacity, ramp-and-hold stress relaxation at 15 % strain for 600 s to characterize viscoelastic behavior and time-dependent stress dissipation, and ten cycles of cyclic compression to investigate energy dissipation, recovery behavior, and structural stability under repeated loading. For the compression tests, all four geometries showed a similar Young’s modulus of 14–18 kPa. However, architecture had a much stronger and statistically significant effect on the time-dependent response. The Bulk scaffold retained 47 % of its initial peak stress after 600 s of relaxation, whereas the porous groups retained only 17–22 % (p < 0.001). The slow viscoelastic time constant τ2 was 470 s for the Bulk scaffold compared with 165–196 s for the porous groups (p = 0.031). During cyclic loading, the porous scaffolds dissipated up to three times more energy per cycle than the Bulk control, while the scaffold with Large-Pores accumulated the largest residual strain (p = 0.002).
The results of this study show that the bulk scaffold most closely matches the viscoelastic signature of native uterine tissue. However, because the bulk scaffold lacks pores and therefore cannot adequately support uterine tissue regeneration, it is not suitable for regenerative applications. In contrast, the gradient scaffold emerges as the most promising alternative, as tissue regeneration requires porosity to enhance cell infiltration and nutrient transport. The gradient design provides the most balanced mechanical performance and represents the most suitable candidate for further optimization.
Master thesis
(2026)
-
F. Mule', M. J. Mirzaali, A. Accardo, E.L. Fratila-Apachitei, A.M.A.A.A. Al-Sanea, R.P. Tas, A. Savva
The mechanical and topographical properties of the cellular micro environment play a crucial role in regulating bone cell behavior through mechano transduction. In this thesis, the synergistic influence of 3D-printed meta-biomaterial scaffolds with controlled Poisson’s ratio, and cellulose nano crystals (CNCs) surface coating, on the proliferation, osteogenic differentiation, and mineralization of MC3T3-E1 pre-osteoblasts was investigated. Auxetic and non-auxetic micro-architectures were fabricated via two-photon polymerization (2-PP), expressing similar morphological and mechanical properties, except for the Poisson's ratio. Scaffold surfaces were further functionalized with CNCs coatings at different concentrations to assess the contribution of nano-topographical, biochemical and mechanical cues.
Morphological characterization confirmed fabrication of the scaffolds, with dimensions within the 15\% variation from the designed structures, and homogeneous coating deposition. Cellular responses were evaluated over time period of 19 days performing various cellular staining, fluorescence imaging and scanning electron microscopy (SEM). The time steps considered were days 3, 7, 9 and 19. Results demonstrated that scaffold geometry alone significantly influenced cell organization and proliferation. Significant differences (p<0.05) were in the number of cells between the auxetic and non-auxetic structures at day 3, across all conditions. The introduction of CNCs coating enhanced cell adhesion and modulated osteogenic outcomes. Notably, coated auxetic scaffolds showed increased Alizarin red staining (ARS) expression compared to coated non-auxetic structures, indicating that auxetic mechanics combined with nano-topographical cues can enhance mineralization of pre-osteoblasts.
Overall, the findings reveal that osteogenic behavior is governed by a synergistic interaction between mechanical architecture and surface topography rather than by a single parameter. This work highlights the potential of mechanically tunable meta-biomaterials integrated with bioactive coatings to engineer microenvironments for bone tissue regeneration and advanced biomaterial design. ...
Morphological characterization confirmed fabrication of the scaffolds, with dimensions within the 15\% variation from the designed structures, and homogeneous coating deposition. Cellular responses were evaluated over time period of 19 days performing various cellular staining, fluorescence imaging and scanning electron microscopy (SEM). The time steps considered were days 3, 7, 9 and 19. Results demonstrated that scaffold geometry alone significantly influenced cell organization and proliferation. Significant differences (p<0.05) were in the number of cells between the auxetic and non-auxetic structures at day 3, across all conditions. The introduction of CNCs coating enhanced cell adhesion and modulated osteogenic outcomes. Notably, coated auxetic scaffolds showed increased Alizarin red staining (ARS) expression compared to coated non-auxetic structures, indicating that auxetic mechanics combined with nano-topographical cues can enhance mineralization of pre-osteoblasts.
Overall, the findings reveal that osteogenic behavior is governed by a synergistic interaction between mechanical architecture and surface topography rather than by a single parameter. This work highlights the potential of mechanically tunable meta-biomaterials integrated with bioactive coatings to engineer microenvironments for bone tissue regeneration and advanced biomaterial design. ...
The mechanical and topographical properties of the cellular micro environment play a crucial role in regulating bone cell behavior through mechano transduction. In this thesis, the synergistic influence of 3D-printed meta-biomaterial scaffolds with controlled Poisson’s ratio, and cellulose nano crystals (CNCs) surface coating, on the proliferation, osteogenic differentiation, and mineralization of MC3T3-E1 pre-osteoblasts was investigated. Auxetic and non-auxetic micro-architectures were fabricated via two-photon polymerization (2-PP), expressing similar morphological and mechanical properties, except for the Poisson's ratio. Scaffold surfaces were further functionalized with CNCs coatings at different concentrations to assess the contribution of nano-topographical, biochemical and mechanical cues.
Morphological characterization confirmed fabrication of the scaffolds, with dimensions within the 15\% variation from the designed structures, and homogeneous coating deposition. Cellular responses were evaluated over time period of 19 days performing various cellular staining, fluorescence imaging and scanning electron microscopy (SEM). The time steps considered were days 3, 7, 9 and 19. Results demonstrated that scaffold geometry alone significantly influenced cell organization and proliferation. Significant differences (p<0.05) were in the number of cells between the auxetic and non-auxetic structures at day 3, across all conditions. The introduction of CNCs coating enhanced cell adhesion and modulated osteogenic outcomes. Notably, coated auxetic scaffolds showed increased Alizarin red staining (ARS) expression compared to coated non-auxetic structures, indicating that auxetic mechanics combined with nano-topographical cues can enhance mineralization of pre-osteoblasts.
Overall, the findings reveal that osteogenic behavior is governed by a synergistic interaction between mechanical architecture and surface topography rather than by a single parameter. This work highlights the potential of mechanically tunable meta-biomaterials integrated with bioactive coatings to engineer microenvironments for bone tissue regeneration and advanced biomaterial design.
Morphological characterization confirmed fabrication of the scaffolds, with dimensions within the 15\% variation from the designed structures, and homogeneous coating deposition. Cellular responses were evaluated over time period of 19 days performing various cellular staining, fluorescence imaging and scanning electron microscopy (SEM). The time steps considered were days 3, 7, 9 and 19. Results demonstrated that scaffold geometry alone significantly influenced cell organization and proliferation. Significant differences (p<0.05) were in the number of cells between the auxetic and non-auxetic structures at day 3, across all conditions. The introduction of CNCs coating enhanced cell adhesion and modulated osteogenic outcomes. Notably, coated auxetic scaffolds showed increased Alizarin red staining (ARS) expression compared to coated non-auxetic structures, indicating that auxetic mechanics combined with nano-topographical cues can enhance mineralization of pre-osteoblasts.
Overall, the findings reveal that osteogenic behavior is governed by a synergistic interaction between mechanical architecture and surface topography rather than by a single parameter. This work highlights the potential of mechanically tunable meta-biomaterials integrated with bioactive coatings to engineer microenvironments for bone tissue regeneration and advanced biomaterial design.
Three-dimensional (3D) computer-assisted planning is increasingly used for long bone osteotomies. However, creating an optimal pre-surgical plan remains challenging due to the procedure’s many degrees of freedom, leading to high human workload and associated costs. To address this, we present a fast, interactive surgical planning tool that maximises bone contact and minimises bone protrusion, while favouring wedge-type corrections. It employs an evolutionary multi-objective optimisation algorithm to generate a set of Pareto-optimal osteotomy solutions. This allows users to choose an optimal trade-off solution based on clinical experience. The approach proposed in this work generates optimised plans in under fifteen minutes. It features a user interface, integrated in Siemens NX, making it readily integrable into existing pre-operative workflows. Quantitative validation on past cases showed that our tool produced solutions with better or equal objective values compared to manual plans in 10 of 12 cases, with an average increase of bone contact of 3 % (range: –0.7 % to 31 %). A blinded assessment by surgeons and experiments with 3D printed bones confirmed the clinical relevance and feasibility of the automatic plans. Incorporating this automatic osteotomy planning tool can therefore improve the quality of the selected pre-surgical plan, speed up the workflow and increase the volume of cases handled by the 3D lab.
...
Three-dimensional (3D) computer-assisted planning is increasingly used for long bone osteotomies. However, creating an optimal pre-surgical plan remains challenging due to the procedure’s many degrees of freedom, leading to high human workload and associated costs. To address this, we present a fast, interactive surgical planning tool that maximises bone contact and minimises bone protrusion, while favouring wedge-type corrections. It employs an evolutionary multi-objective optimisation algorithm to generate a set of Pareto-optimal osteotomy solutions. This allows users to choose an optimal trade-off solution based on clinical experience. The approach proposed in this work generates optimised plans in under fifteen minutes. It features a user interface, integrated in Siemens NX, making it readily integrable into existing pre-operative workflows. Quantitative validation on past cases showed that our tool produced solutions with better or equal objective values compared to manual plans in 10 of 12 cases, with an average increase of bone contact of 3 % (range: –0.7 % to 31 %). A blinded assessment by surgeons and experiments with 3D printed bones confirmed the clinical relevance and feasibility of the automatic plans. Incorporating this automatic osteotomy planning tool can therefore improve the quality of the selected pre-surgical plan, speed up the workflow and increase the volume of cases handled by the 3D lab.
Finite Element Modeling of NiTiNol in Transcatheter Aortic Valve Implantation: Assessing Material Influence on Simulation Reliability
Verification, Validation, and Uncertainty Quantification of NiTiNol Behavior in TAVI Computational Modeling
This study investigates the impact of shape-memory alloy (NiTiNol) parameter variability on the predictive reliability of finite element (FE) models for transcatheter aortic valve implantation (TAVI). A fully verified and validated FE model was developed following ASME V&V 40 guidelines, integrating experimental tests, numerical verification, and uncertainty quantification to isolate material effects from numerical artifacts. A Monte Carlo parameter fitting approach was employed using three independent tensile datasets to calibrate the NiTiNol model, resulting in a quantified uncertainty range of ±5.34%. Simulation results revealed that only Austenite Young’s modulus significantly influenced the mechanical response under physiological loading, while other transformation parameters had negligible effects. In contrast, literature-derived parameters introduced up to 30% deviation, highlighting the inadequacy of non-case-specific data. This work emphasizes the critical need for validated material parameters to ensure simulation credibility, particularly in clinical and regulatory contexts where simulation outcomes increasingly inform patient-specific treatment and device design.
...
This study investigates the impact of shape-memory alloy (NiTiNol) parameter variability on the predictive reliability of finite element (FE) models for transcatheter aortic valve implantation (TAVI). A fully verified and validated FE model was developed following ASME V&V 40 guidelines, integrating experimental tests, numerical verification, and uncertainty quantification to isolate material effects from numerical artifacts. A Monte Carlo parameter fitting approach was employed using three independent tensile datasets to calibrate the NiTiNol model, resulting in a quantified uncertainty range of ±5.34%. Simulation results revealed that only Austenite Young’s modulus significantly influenced the mechanical response under physiological loading, while other transformation parameters had negligible effects. In contrast, literature-derived parameters introduced up to 30% deviation, highlighting the inadequacy of non-case-specific data. This work emphasizes the critical need for validated material parameters to ensure simulation credibility, particularly in clinical and regulatory contexts where simulation outcomes increasingly inform patient-specific treatment and device design.
Reinforcement Learning-Based Path Planning for Additive Manufacturing of Homogenised Grid Structures
Optimising Toolpaths and Defect Distribution in 2D Voxel Grids
This study provides new insight into the mechanisms linking shrinkage to long-term degrad This thesis presents a methodology for designing and manufacturing highly tunable Repetitive volume element (RVE) with tunable isotropy and mechanical properties through homogenisation reinforcement learning-guided toolpath planning for material extrusion additive manufacturing.
Background and Motivation FDM is used to create highly adaptable objects with geometrically complex shapes and features. High anisotropic behaviour is measured in conventional methods of FDM, and by optimising the mechanical properties and a toolpath of a given RVE, the result becomes highly variable. Scaling the material properties using a combination of homogenisation and RL-based toolpath planning helps extend the uses of AM.
Methodology The approach consists of three main stages. First, 2D voxel-based grids with controlled infill densities of 63% to 93% are generated to create permeable structures. Homogenisation techniques are applied to determine effective mechanical properties, e.g. Young’s moduli, shear moduli and Poisson’s ratios, across multiple configurations varying in voxel size, 0.1-0.4 mm, and void distribution. Second, optimal grid designs are selected using sequential optimisation with a multi-objective function balancing mechanical stiffness, isotropy, shear performance, and geometric connectivity. Third, a Double Deep Q-Network (DDQN) reinforcement learning agent is trained on 50 diverse grids to generate void-aware toolpaths for a 0.4 mm nozzle. The agent learns to maximise material coverage while avoiding collisions with voids, minimising redundant motions, and ensuring printability.
Results The trained RL agent achieved 89.4% material coverage on test grids with infill ratios of 73%, demonstrating effective void avoidance and path continuity. The optimised grid design exhibited an improvement in isotropy compared to conventional raster patterns, with 1040% reduction in mechanical anisotropy. RVEs were fabricated via MEX and mechanically tested, validating the computational predictions within close accuracy based on the isotropic behaviour, yet tensile tests show lower Young’s moduli than expected from the computational model.
Significance and Future Work This work demonstrates that reinforcement learning can effectively optimise toolpath planning for complex, defect-containing structures, enabling the fabrication of FDMproduced objects with improved mechanical isotropy. Future work should extend the methodology to 3D homogenisation to eliminate plane-stress/plane-strain approximations, incorporate multi-directional AM for true 3D toolpaths, and explore non-planar geometries that more closely replicate native tissue architecture. These advances would optimise the tunable properties already existing in AM.ation in AAS and demonstrates that combining sodium silicate activation, gypsum addition, and early fog curing offers a practical route to durable, shrinkage-resistant, and sustainable AAS concretes suitable for structural applications.
...
Background and Motivation FDM is used to create highly adaptable objects with geometrically complex shapes and features. High anisotropic behaviour is measured in conventional methods of FDM, and by optimising the mechanical properties and a toolpath of a given RVE, the result becomes highly variable. Scaling the material properties using a combination of homogenisation and RL-based toolpath planning helps extend the uses of AM.
Methodology The approach consists of three main stages. First, 2D voxel-based grids with controlled infill densities of 63% to 93% are generated to create permeable structures. Homogenisation techniques are applied to determine effective mechanical properties, e.g. Young’s moduli, shear moduli and Poisson’s ratios, across multiple configurations varying in voxel size, 0.1-0.4 mm, and void distribution. Second, optimal grid designs are selected using sequential optimisation with a multi-objective function balancing mechanical stiffness, isotropy, shear performance, and geometric connectivity. Third, a Double Deep Q-Network (DDQN) reinforcement learning agent is trained on 50 diverse grids to generate void-aware toolpaths for a 0.4 mm nozzle. The agent learns to maximise material coverage while avoiding collisions with voids, minimising redundant motions, and ensuring printability.
Results The trained RL agent achieved 89.4% material coverage on test grids with infill ratios of 73%, demonstrating effective void avoidance and path continuity. The optimised grid design exhibited an improvement in isotropy compared to conventional raster patterns, with 1040% reduction in mechanical anisotropy. RVEs were fabricated via MEX and mechanically tested, validating the computational predictions within close accuracy based on the isotropic behaviour, yet tensile tests show lower Young’s moduli than expected from the computational model.
Significance and Future Work This work demonstrates that reinforcement learning can effectively optimise toolpath planning for complex, defect-containing structures, enabling the fabrication of FDMproduced objects with improved mechanical isotropy. Future work should extend the methodology to 3D homogenisation to eliminate plane-stress/plane-strain approximations, incorporate multi-directional AM for true 3D toolpaths, and explore non-planar geometries that more closely replicate native tissue architecture. These advances would optimise the tunable properties already existing in AM.ation in AAS and demonstrates that combining sodium silicate activation, gypsum addition, and early fog curing offers a practical route to durable, shrinkage-resistant, and sustainable AAS concretes suitable for structural applications.
...
This study provides new insight into the mechanisms linking shrinkage to long-term degrad This thesis presents a methodology for designing and manufacturing highly tunable Repetitive volume element (RVE) with tunable isotropy and mechanical properties through homogenisation reinforcement learning-guided toolpath planning for material extrusion additive manufacturing.
Background and Motivation FDM is used to create highly adaptable objects with geometrically complex shapes and features. High anisotropic behaviour is measured in conventional methods of FDM, and by optimising the mechanical properties and a toolpath of a given RVE, the result becomes highly variable. Scaling the material properties using a combination of homogenisation and RL-based toolpath planning helps extend the uses of AM.
Methodology The approach consists of three main stages. First, 2D voxel-based grids with controlled infill densities of 63% to 93% are generated to create permeable structures. Homogenisation techniques are applied to determine effective mechanical properties, e.g. Young’s moduli, shear moduli and Poisson’s ratios, across multiple configurations varying in voxel size, 0.1-0.4 mm, and void distribution. Second, optimal grid designs are selected using sequential optimisation with a multi-objective function balancing mechanical stiffness, isotropy, shear performance, and geometric connectivity. Third, a Double Deep Q-Network (DDQN) reinforcement learning agent is trained on 50 diverse grids to generate void-aware toolpaths for a 0.4 mm nozzle. The agent learns to maximise material coverage while avoiding collisions with voids, minimising redundant motions, and ensuring printability.
Results The trained RL agent achieved 89.4% material coverage on test grids with infill ratios of 73%, demonstrating effective void avoidance and path continuity. The optimised grid design exhibited an improvement in isotropy compared to conventional raster patterns, with 1040% reduction in mechanical anisotropy. RVEs were fabricated via MEX and mechanically tested, validating the computational predictions within close accuracy based on the isotropic behaviour, yet tensile tests show lower Young’s moduli than expected from the computational model.
Significance and Future Work This work demonstrates that reinforcement learning can effectively optimise toolpath planning for complex, defect-containing structures, enabling the fabrication of FDMproduced objects with improved mechanical isotropy. Future work should extend the methodology to 3D homogenisation to eliminate plane-stress/plane-strain approximations, incorporate multi-directional AM for true 3D toolpaths, and explore non-planar geometries that more closely replicate native tissue architecture. These advances would optimise the tunable properties already existing in AM.ation in AAS and demonstrates that combining sodium silicate activation, gypsum addition, and early fog curing offers a practical route to durable, shrinkage-resistant, and sustainable AAS concretes suitable for structural applications.
Background and Motivation FDM is used to create highly adaptable objects with geometrically complex shapes and features. High anisotropic behaviour is measured in conventional methods of FDM, and by optimising the mechanical properties and a toolpath of a given RVE, the result becomes highly variable. Scaling the material properties using a combination of homogenisation and RL-based toolpath planning helps extend the uses of AM.
Methodology The approach consists of three main stages. First, 2D voxel-based grids with controlled infill densities of 63% to 93% are generated to create permeable structures. Homogenisation techniques are applied to determine effective mechanical properties, e.g. Young’s moduli, shear moduli and Poisson’s ratios, across multiple configurations varying in voxel size, 0.1-0.4 mm, and void distribution. Second, optimal grid designs are selected using sequential optimisation with a multi-objective function balancing mechanical stiffness, isotropy, shear performance, and geometric connectivity. Third, a Double Deep Q-Network (DDQN) reinforcement learning agent is trained on 50 diverse grids to generate void-aware toolpaths for a 0.4 mm nozzle. The agent learns to maximise material coverage while avoiding collisions with voids, minimising redundant motions, and ensuring printability.
Results The trained RL agent achieved 89.4% material coverage on test grids with infill ratios of 73%, demonstrating effective void avoidance and path continuity. The optimised grid design exhibited an improvement in isotropy compared to conventional raster patterns, with 1040% reduction in mechanical anisotropy. RVEs were fabricated via MEX and mechanically tested, validating the computational predictions within close accuracy based on the isotropic behaviour, yet tensile tests show lower Young’s moduli than expected from the computational model.
Significance and Future Work This work demonstrates that reinforcement learning can effectively optimise toolpath planning for complex, defect-containing structures, enabling the fabrication of FDMproduced objects with improved mechanical isotropy. Future work should extend the methodology to 3D homogenisation to eliminate plane-stress/plane-strain approximations, incorporate multi-directional AM for true 3D toolpaths, and explore non-planar geometries that more closely replicate native tissue architecture. These advances would optimise the tunable properties already existing in AM.ation in AAS and demonstrates that combining sodium silicate activation, gypsum addition, and early fog curing offers a practical route to durable, shrinkage-resistant, and sustainable AAS concretes suitable for structural applications.
Master thesis
(2025)
-
L.P. d' Engelbronner, M. J. Mirzaali, N.S. Shahriari, A.T. ŞENSOY, J. Zhou, Brend P. Jonker
Mandibular reconstruction plates are essential for restoring function after segmental defects, but current designs often lead to stress shielding and long-term complications. New porous implant architectures may reduce these problems, yet their performance is insufficiently validated in an experimental test environment under realistic loading conditions. Existing experimental setups either oversimplify the physiological fidelity or are too complex to reproduce reliable results.
In this thesis, a new experimental setup that combines anatomically relevant loading conditions with rigid and reproducible boundary conditions is designed, manufactured, and validated. It features moulded condyle fixation cups that ensure precise and repeatable alignment of the mandibular condyles, and a modular loading platform capable of accurately reproducing various bite configurations. The platform allows controlled repositioning of occlusal contact points and accommodates diverse mandibular geometries, enabling both unilateral and bilateral loading scenarios. This configuration creates a mechanically robust environment while preserving essential biomechanical characteristics of mandibular function.
Structural performance of the setup was investigated through finite element analysis to assess stress distribution, deformation behaviour, and potential failure locations. Experimental validation was carried out using quasi-static and progressive cyclic loading, confirming that the setup maintains stable boundary conditions, realistic load paths, and high reproducibility under repeated testing. Using this setup, three metamaterial implant designs were assessed and strain distributions were quantified using Digital Image Correlation, revealing distinct differences in strain concentration around screw regions.
Overall, this work provides a robust, reproducible, and physiologically informed platform for the mechanical evaluation of mandibular reconstruction implants. The setup enables systematic comparison of implant architectures and supports future extensions toward cadaveric studies and clinically validated testing protocols, contributing to the development of implants with improved long-term clinical outcomes. ...
In this thesis, a new experimental setup that combines anatomically relevant loading conditions with rigid and reproducible boundary conditions is designed, manufactured, and validated. It features moulded condyle fixation cups that ensure precise and repeatable alignment of the mandibular condyles, and a modular loading platform capable of accurately reproducing various bite configurations. The platform allows controlled repositioning of occlusal contact points and accommodates diverse mandibular geometries, enabling both unilateral and bilateral loading scenarios. This configuration creates a mechanically robust environment while preserving essential biomechanical characteristics of mandibular function.
Structural performance of the setup was investigated through finite element analysis to assess stress distribution, deformation behaviour, and potential failure locations. Experimental validation was carried out using quasi-static and progressive cyclic loading, confirming that the setup maintains stable boundary conditions, realistic load paths, and high reproducibility under repeated testing. Using this setup, three metamaterial implant designs were assessed and strain distributions were quantified using Digital Image Correlation, revealing distinct differences in strain concentration around screw regions.
Overall, this work provides a robust, reproducible, and physiologically informed platform for the mechanical evaluation of mandibular reconstruction implants. The setup enables systematic comparison of implant architectures and supports future extensions toward cadaveric studies and clinically validated testing protocols, contributing to the development of implants with improved long-term clinical outcomes. ...
Mandibular reconstruction plates are essential for restoring function after segmental defects, but current designs often lead to stress shielding and long-term complications. New porous implant architectures may reduce these problems, yet their performance is insufficiently validated in an experimental test environment under realistic loading conditions. Existing experimental setups either oversimplify the physiological fidelity or are too complex to reproduce reliable results.
In this thesis, a new experimental setup that combines anatomically relevant loading conditions with rigid and reproducible boundary conditions is designed, manufactured, and validated. It features moulded condyle fixation cups that ensure precise and repeatable alignment of the mandibular condyles, and a modular loading platform capable of accurately reproducing various bite configurations. The platform allows controlled repositioning of occlusal contact points and accommodates diverse mandibular geometries, enabling both unilateral and bilateral loading scenarios. This configuration creates a mechanically robust environment while preserving essential biomechanical characteristics of mandibular function.
Structural performance of the setup was investigated through finite element analysis to assess stress distribution, deformation behaviour, and potential failure locations. Experimental validation was carried out using quasi-static and progressive cyclic loading, confirming that the setup maintains stable boundary conditions, realistic load paths, and high reproducibility under repeated testing. Using this setup, three metamaterial implant designs were assessed and strain distributions were quantified using Digital Image Correlation, revealing distinct differences in strain concentration around screw regions.
Overall, this work provides a robust, reproducible, and physiologically informed platform for the mechanical evaluation of mandibular reconstruction implants. The setup enables systematic comparison of implant architectures and supports future extensions toward cadaveric studies and clinically validated testing protocols, contributing to the development of implants with improved long-term clinical outcomes.
In this thesis, a new experimental setup that combines anatomically relevant loading conditions with rigid and reproducible boundary conditions is designed, manufactured, and validated. It features moulded condyle fixation cups that ensure precise and repeatable alignment of the mandibular condyles, and a modular loading platform capable of accurately reproducing various bite configurations. The platform allows controlled repositioning of occlusal contact points and accommodates diverse mandibular geometries, enabling both unilateral and bilateral loading scenarios. This configuration creates a mechanically robust environment while preserving essential biomechanical characteristics of mandibular function.
Structural performance of the setup was investigated through finite element analysis to assess stress distribution, deformation behaviour, and potential failure locations. Experimental validation was carried out using quasi-static and progressive cyclic loading, confirming that the setup maintains stable boundary conditions, realistic load paths, and high reproducibility under repeated testing. Using this setup, three metamaterial implant designs were assessed and strain distributions were quantified using Digital Image Correlation, revealing distinct differences in strain concentration around screw regions.
Overall, this work provides a robust, reproducible, and physiologically informed platform for the mechanical evaluation of mandibular reconstruction implants. The setup enables systematic comparison of implant architectures and supports future extensions toward cadaveric studies and clinically validated testing protocols, contributing to the development of implants with improved long-term clinical outcomes.
Meta(llic) Clay
Molding and Firing of Multibody Systems
Shape-morphing and shape-locking describe objects’ ability to transform their shape and stay in that state, respectively. These qualities often come into play when grabbing or supporting an object. The contact area is increased by changing the shape, after which sustaining the shape maintains the support over time. We can imagine several ways of implementing this in engineered structures. One way of implementing shape-morphing and -locking is using kinematic movement, where a structure comprises relatively rigid parts connected by joints that allow motion. This work focuses on this type and presents a framework for analyzing it.
We identified and studied the factors determining the performance of kinematic morphing and locking structures. Three distinct steps were employed that explore the envelope of possible designs by i) creating and verifying a morphing modeling approach based on multibody dynamics principles, ii) analyzing a morphing and locking structure by applying the model, designing and experimentation, and iii) analyzing the effects of design parameters on the morphing and locking qualities in the light of geometrical features such as curvature. Spanning these steps, we developed several structures and fabricated them with additive manufacturing. These structures are i) a 3D modular system that allows easy experimentation with layouts and joint types, ii) an essentially 2D system that deforms in-plane and is selectively and reversibly locked by applying magnetic fields, and iii) a 3D deforming non-assembly metallic structure that can follow single and double curvatures and is irreversibly locked as a whole by applying bone cement. To assess the performance of these structures, in addition to the presented simulation approach, we developed methods that test the physical morphing and locking qualities visually and mechanically. These methods included 3D-scanning and mechanical testing, accompanied by digital image correlation to measure full-field strain distribution.
The presented framework shows the potential of kinematic shapemorphing and -locking mechanisms to endow structures with new functionalities. Specifically, we showed that structures incorporating the mechanism can be rationally designed, manufactured, and assessed. A multibody model predicts the morphing behavior accurately. We can use such a method to design the structures for specific applications such as orthopedic implants or soft robotics. Locking the mechanism as a whole or per individual degree of freedom obstructed the morphing capability effectively, whether or not in a reversible manner. Simulations and experiments show that we can alter the transformation and load-bearing performance of the structures as desired by changing their design parameters. The matching capacities are affected by parameters like structural body shape, dimensional ratios, and the curvature of the to-be-attained shape. These principles can be further developed and tailored for specific needs in a variety of fields. ...
We identified and studied the factors determining the performance of kinematic morphing and locking structures. Three distinct steps were employed that explore the envelope of possible designs by i) creating and verifying a morphing modeling approach based on multibody dynamics principles, ii) analyzing a morphing and locking structure by applying the model, designing and experimentation, and iii) analyzing the effects of design parameters on the morphing and locking qualities in the light of geometrical features such as curvature. Spanning these steps, we developed several structures and fabricated them with additive manufacturing. These structures are i) a 3D modular system that allows easy experimentation with layouts and joint types, ii) an essentially 2D system that deforms in-plane and is selectively and reversibly locked by applying magnetic fields, and iii) a 3D deforming non-assembly metallic structure that can follow single and double curvatures and is irreversibly locked as a whole by applying bone cement. To assess the performance of these structures, in addition to the presented simulation approach, we developed methods that test the physical morphing and locking qualities visually and mechanically. These methods included 3D-scanning and mechanical testing, accompanied by digital image correlation to measure full-field strain distribution.
The presented framework shows the potential of kinematic shapemorphing and -locking mechanisms to endow structures with new functionalities. Specifically, we showed that structures incorporating the mechanism can be rationally designed, manufactured, and assessed. A multibody model predicts the morphing behavior accurately. We can use such a method to design the structures for specific applications such as orthopedic implants or soft robotics. Locking the mechanism as a whole or per individual degree of freedom obstructed the morphing capability effectively, whether or not in a reversible manner. Simulations and experiments show that we can alter the transformation and load-bearing performance of the structures as desired by changing their design parameters. The matching capacities are affected by parameters like structural body shape, dimensional ratios, and the curvature of the to-be-attained shape. These principles can be further developed and tailored for specific needs in a variety of fields. ...
Shape-morphing and shape-locking describe objects’ ability to transform their shape and stay in that state, respectively. These qualities often come into play when grabbing or supporting an object. The contact area is increased by changing the shape, after which sustaining the shape maintains the support over time. We can imagine several ways of implementing this in engineered structures. One way of implementing shape-morphing and -locking is using kinematic movement, where a structure comprises relatively rigid parts connected by joints that allow motion. This work focuses on this type and presents a framework for analyzing it.
We identified and studied the factors determining the performance of kinematic morphing and locking structures. Three distinct steps were employed that explore the envelope of possible designs by i) creating and verifying a morphing modeling approach based on multibody dynamics principles, ii) analyzing a morphing and locking structure by applying the model, designing and experimentation, and iii) analyzing the effects of design parameters on the morphing and locking qualities in the light of geometrical features such as curvature. Spanning these steps, we developed several structures and fabricated them with additive manufacturing. These structures are i) a 3D modular system that allows easy experimentation with layouts and joint types, ii) an essentially 2D system that deforms in-plane and is selectively and reversibly locked by applying magnetic fields, and iii) a 3D deforming non-assembly metallic structure that can follow single and double curvatures and is irreversibly locked as a whole by applying bone cement. To assess the performance of these structures, in addition to the presented simulation approach, we developed methods that test the physical morphing and locking qualities visually and mechanically. These methods included 3D-scanning and mechanical testing, accompanied by digital image correlation to measure full-field strain distribution.
The presented framework shows the potential of kinematic shapemorphing and -locking mechanisms to endow structures with new functionalities. Specifically, we showed that structures incorporating the mechanism can be rationally designed, manufactured, and assessed. A multibody model predicts the morphing behavior accurately. We can use such a method to design the structures for specific applications such as orthopedic implants or soft robotics. Locking the mechanism as a whole or per individual degree of freedom obstructed the morphing capability effectively, whether or not in a reversible manner. Simulations and experiments show that we can alter the transformation and load-bearing performance of the structures as desired by changing their design parameters. The matching capacities are affected by parameters like structural body shape, dimensional ratios, and the curvature of the to-be-attained shape. These principles can be further developed and tailored for specific needs in a variety of fields.
We identified and studied the factors determining the performance of kinematic morphing and locking structures. Three distinct steps were employed that explore the envelope of possible designs by i) creating and verifying a morphing modeling approach based on multibody dynamics principles, ii) analyzing a morphing and locking structure by applying the model, designing and experimentation, and iii) analyzing the effects of design parameters on the morphing and locking qualities in the light of geometrical features such as curvature. Spanning these steps, we developed several structures and fabricated them with additive manufacturing. These structures are i) a 3D modular system that allows easy experimentation with layouts and joint types, ii) an essentially 2D system that deforms in-plane and is selectively and reversibly locked by applying magnetic fields, and iii) a 3D deforming non-assembly metallic structure that can follow single and double curvatures and is irreversibly locked as a whole by applying bone cement. To assess the performance of these structures, in addition to the presented simulation approach, we developed methods that test the physical morphing and locking qualities visually and mechanically. These methods included 3D-scanning and mechanical testing, accompanied by digital image correlation to measure full-field strain distribution.
The presented framework shows the potential of kinematic shapemorphing and -locking mechanisms to endow structures with new functionalities. Specifically, we showed that structures incorporating the mechanism can be rationally designed, manufactured, and assessed. A multibody model predicts the morphing behavior accurately. We can use such a method to design the structures for specific applications such as orthopedic implants or soft robotics. Locking the mechanism as a whole or per individual degree of freedom obstructed the morphing capability effectively, whether or not in a reversible manner. Simulations and experiments show that we can alter the transformation and load-bearing performance of the structures as desired by changing their design parameters. The matching capacities are affected by parameters like structural body shape, dimensional ratios, and the curvature of the to-be-attained shape. These principles can be further developed and tailored for specific needs in a variety of fields.
The growing need for personalized medical solutions has highlighted the importance of advancements in designing and producing patient-specific medical devices. Conventional manufacturing processes are effective in producing generic devices but often struggle to accommodate the unique anatomical variations of individual patients. This limitation may increase the risk of unfavorable surgical results and complications. Introducing 3D printing, or additive manufacturing (AM), has created new opportunities for the rapid and precise fabrication of customized implants, prosthetics, and orthotics tailored to fit patient anatomies. This technology not only enhances the functionality and durability of these devices but also contributes to faster recovery and improved patient outcomes.
However, several challenges remain: how to streamline the design process to deliver these tailored solutions swiftly and efficiently without compromising functionality, longevity, or durability. This thesis addresses these challenges by exploring strategies for integrating advanced computational models, design optimization techniques, and workflow automation into medical device design and production. These approaches aim to reduce the time from the initial concept to the final product, ensuring patients receive customized solutions promptly.
In addition to exploring the benefits of customization, this thesis investigates the use of generic but adaptable implants that can be quickly tailored to individual patient needs. This approach balances the need for rapid production with maintaining high standards of implant performance and patient outcomes, staying in the one-design-fits-all approach... ...
However, several challenges remain: how to streamline the design process to deliver these tailored solutions swiftly and efficiently without compromising functionality, longevity, or durability. This thesis addresses these challenges by exploring strategies for integrating advanced computational models, design optimization techniques, and workflow automation into medical device design and production. These approaches aim to reduce the time from the initial concept to the final product, ensuring patients receive customized solutions promptly.
In addition to exploring the benefits of customization, this thesis investigates the use of generic but adaptable implants that can be quickly tailored to individual patient needs. This approach balances the need for rapid production with maintaining high standards of implant performance and patient outcomes, staying in the one-design-fits-all approach... ...
The growing need for personalized medical solutions has highlighted the importance of advancements in designing and producing patient-specific medical devices. Conventional manufacturing processes are effective in producing generic devices but often struggle to accommodate the unique anatomical variations of individual patients. This limitation may increase the risk of unfavorable surgical results and complications. Introducing 3D printing, or additive manufacturing (AM), has created new opportunities for the rapid and precise fabrication of customized implants, prosthetics, and orthotics tailored to fit patient anatomies. This technology not only enhances the functionality and durability of these devices but also contributes to faster recovery and improved patient outcomes.
However, several challenges remain: how to streamline the design process to deliver these tailored solutions swiftly and efficiently without compromising functionality, longevity, or durability. This thesis addresses these challenges by exploring strategies for integrating advanced computational models, design optimization techniques, and workflow automation into medical device design and production. These approaches aim to reduce the time from the initial concept to the final product, ensuring patients receive customized solutions promptly.
In addition to exploring the benefits of customization, this thesis investigates the use of generic but adaptable implants that can be quickly tailored to individual patient needs. This approach balances the need for rapid production with maintaining high standards of implant performance and patient outcomes, staying in the one-design-fits-all approach...
However, several challenges remain: how to streamline the design process to deliver these tailored solutions swiftly and efficiently without compromising functionality, longevity, or durability. This thesis addresses these challenges by exploring strategies for integrating advanced computational models, design optimization techniques, and workflow automation into medical device design and production. These approaches aim to reduce the time from the initial concept to the final product, ensuring patients receive customized solutions promptly.
In addition to exploring the benefits of customization, this thesis investigates the use of generic but adaptable implants that can be quickly tailored to individual patient needs. This approach balances the need for rapid production with maintaining high standards of implant performance and patient outcomes, staying in the one-design-fits-all approach...
A complex interplay of material, mechanical, and biological factors governs the performance of bone implants and scaffolds. Key determinants include surface functionalization, Young’s modulus of the base material (e.g., metals, or polymers), morphometric properties (e.g., curvature, porosity), mechanical features (e.g., effective elastic modulus, and Poisson’s ratio, defined as the negative ratio of transverse strain to longitudinal strain), and mass transport parameters (e.g., permeability). All these properties are often designed to enhance osseointegration significantly within the context of both bone replacement and regeneration. Regarding Poisson’s ratio, auxeticity (i.e., negative values of Poisson’s ratio) is a distinct property of trabecular bone, which assumes a high relevance for implant design.
To address these challenges, meta-biomaterials offer a unique opportunity to tune all the above-mentioned properties, enhancing the rate of tissue regeneration. These designer materials derive their effective properties mainly from their engineered microarchitecture rather than solely from their material composition. This has led to the development of meta-implants, a new generation of bone implants that exhibit rare or unprecedented functionalities. Conventional solid hip joint implants are mainly under mechanical bending, and due to their design, a physical gap may be created between the surrounding bone and the implant in such conventional implants. Under such circumstances, the particles released from the bearing surfaces may enter the gap and trigger an inflammatory response, replacing the bone tissue with fibrous tissue around the implant, a process known as osteolysis. On the other hand, meta-implants minimize the risk of such physical gaps between the surrounding bone and implants, thereby reducing the risk of implant loosening.
While the next generation of “hip meta-implants” addresses this issue by using auxeticity to minimize the risk of gaps forming, a fundamental challenge remains: “How can the effects of auxeticity on cell and tissue response be studied in isolation from many intrinsically coupled properties of meta-biomaterials (e.g., elastic/shear moduli, porosity, pore size, permeability)?” This question forms the core of my dissertation, which focuses on decoupling Poisson’s ratio from interdependent scaffold properties to achieve tunable auxetic behavior while preserving structural and functional integrity. Beyond structural design, understanding how Poisson’s ratio influences bone cell mechanobiology is vital for ensuring meta-implants promote healthy tissue regeneration. This leads to a key sub-question: “How does Poisson’s ratio affect bone cell response in meta-biomaterials?” Exploring this extends the research into the biological implications of meta-biomaterials.
Addressing these challenges demands an interdisciplinary approach, including i. mechanical design to isolate Poisson’s ratio from all other scaffold properties, ii.additive manufacturing (AM) of meta-biomaterials and their mechanical characterizations, iii. bone cell culture of meta-biomaterials and their cellular assessments, and iv. creating shape-morphing meta-biomaterials via 4D bioprinting for prospective dynamic cell culture studies. ...
To address these challenges, meta-biomaterials offer a unique opportunity to tune all the above-mentioned properties, enhancing the rate of tissue regeneration. These designer materials derive their effective properties mainly from their engineered microarchitecture rather than solely from their material composition. This has led to the development of meta-implants, a new generation of bone implants that exhibit rare or unprecedented functionalities. Conventional solid hip joint implants are mainly under mechanical bending, and due to their design, a physical gap may be created between the surrounding bone and the implant in such conventional implants. Under such circumstances, the particles released from the bearing surfaces may enter the gap and trigger an inflammatory response, replacing the bone tissue with fibrous tissue around the implant, a process known as osteolysis. On the other hand, meta-implants minimize the risk of such physical gaps between the surrounding bone and implants, thereby reducing the risk of implant loosening.
While the next generation of “hip meta-implants” addresses this issue by using auxeticity to minimize the risk of gaps forming, a fundamental challenge remains: “How can the effects of auxeticity on cell and tissue response be studied in isolation from many intrinsically coupled properties of meta-biomaterials (e.g., elastic/shear moduli, porosity, pore size, permeability)?” This question forms the core of my dissertation, which focuses on decoupling Poisson’s ratio from interdependent scaffold properties to achieve tunable auxetic behavior while preserving structural and functional integrity. Beyond structural design, understanding how Poisson’s ratio influences bone cell mechanobiology is vital for ensuring meta-implants promote healthy tissue regeneration. This leads to a key sub-question: “How does Poisson’s ratio affect bone cell response in meta-biomaterials?” Exploring this extends the research into the biological implications of meta-biomaterials.
Addressing these challenges demands an interdisciplinary approach, including i. mechanical design to isolate Poisson’s ratio from all other scaffold properties, ii.additive manufacturing (AM) of meta-biomaterials and their mechanical characterizations, iii. bone cell culture of meta-biomaterials and their cellular assessments, and iv. creating shape-morphing meta-biomaterials via 4D bioprinting for prospective dynamic cell culture studies. ...
A complex interplay of material, mechanical, and biological factors governs the performance of bone implants and scaffolds. Key determinants include surface functionalization, Young’s modulus of the base material (e.g., metals, or polymers), morphometric properties (e.g., curvature, porosity), mechanical features (e.g., effective elastic modulus, and Poisson’s ratio, defined as the negative ratio of transverse strain to longitudinal strain), and mass transport parameters (e.g., permeability). All these properties are often designed to enhance osseointegration significantly within the context of both bone replacement and regeneration. Regarding Poisson’s ratio, auxeticity (i.e., negative values of Poisson’s ratio) is a distinct property of trabecular bone, which assumes a high relevance for implant design.
To address these challenges, meta-biomaterials offer a unique opportunity to tune all the above-mentioned properties, enhancing the rate of tissue regeneration. These designer materials derive their effective properties mainly from their engineered microarchitecture rather than solely from their material composition. This has led to the development of meta-implants, a new generation of bone implants that exhibit rare or unprecedented functionalities. Conventional solid hip joint implants are mainly under mechanical bending, and due to their design, a physical gap may be created between the surrounding bone and the implant in such conventional implants. Under such circumstances, the particles released from the bearing surfaces may enter the gap and trigger an inflammatory response, replacing the bone tissue with fibrous tissue around the implant, a process known as osteolysis. On the other hand, meta-implants minimize the risk of such physical gaps between the surrounding bone and implants, thereby reducing the risk of implant loosening.
While the next generation of “hip meta-implants” addresses this issue by using auxeticity to minimize the risk of gaps forming, a fundamental challenge remains: “How can the effects of auxeticity on cell and tissue response be studied in isolation from many intrinsically coupled properties of meta-biomaterials (e.g., elastic/shear moduli, porosity, pore size, permeability)?” This question forms the core of my dissertation, which focuses on decoupling Poisson’s ratio from interdependent scaffold properties to achieve tunable auxetic behavior while preserving structural and functional integrity. Beyond structural design, understanding how Poisson’s ratio influences bone cell mechanobiology is vital for ensuring meta-implants promote healthy tissue regeneration. This leads to a key sub-question: “How does Poisson’s ratio affect bone cell response in meta-biomaterials?” Exploring this extends the research into the biological implications of meta-biomaterials.
Addressing these challenges demands an interdisciplinary approach, including i. mechanical design to isolate Poisson’s ratio from all other scaffold properties, ii.additive manufacturing (AM) of meta-biomaterials and their mechanical characterizations, iii. bone cell culture of meta-biomaterials and their cellular assessments, and iv. creating shape-morphing meta-biomaterials via 4D bioprinting for prospective dynamic cell culture studies.
To address these challenges, meta-biomaterials offer a unique opportunity to tune all the above-mentioned properties, enhancing the rate of tissue regeneration. These designer materials derive their effective properties mainly from their engineered microarchitecture rather than solely from their material composition. This has led to the development of meta-implants, a new generation of bone implants that exhibit rare or unprecedented functionalities. Conventional solid hip joint implants are mainly under mechanical bending, and due to their design, a physical gap may be created between the surrounding bone and the implant in such conventional implants. Under such circumstances, the particles released from the bearing surfaces may enter the gap and trigger an inflammatory response, replacing the bone tissue with fibrous tissue around the implant, a process known as osteolysis. On the other hand, meta-implants minimize the risk of such physical gaps between the surrounding bone and implants, thereby reducing the risk of implant loosening.
While the next generation of “hip meta-implants” addresses this issue by using auxeticity to minimize the risk of gaps forming, a fundamental challenge remains: “How can the effects of auxeticity on cell and tissue response be studied in isolation from many intrinsically coupled properties of meta-biomaterials (e.g., elastic/shear moduli, porosity, pore size, permeability)?” This question forms the core of my dissertation, which focuses on decoupling Poisson’s ratio from interdependent scaffold properties to achieve tunable auxetic behavior while preserving structural and functional integrity. Beyond structural design, understanding how Poisson’s ratio influences bone cell mechanobiology is vital for ensuring meta-implants promote healthy tissue regeneration. This leads to a key sub-question: “How does Poisson’s ratio affect bone cell response in meta-biomaterials?” Exploring this extends the research into the biological implications of meta-biomaterials.
Addressing these challenges demands an interdisciplinary approach, including i. mechanical design to isolate Poisson’s ratio from all other scaffold properties, ii.additive manufacturing (AM) of meta-biomaterials and their mechanical characterizations, iii. bone cell culture of meta-biomaterials and their cellular assessments, and iv. creating shape-morphing meta-biomaterials via 4D bioprinting for prospective dynamic cell culture studies.
This paper introduces a fully compliant spherical joint with an optimized stiffness profile specifically for balancing a pendulum. The design builds on previous work that has successfully created a fully compliant spherical joint using tetrahedron-shaped elements connected in series. To efficiently compute and optimize the balancing behaviour of these compliant joints, a novel algorithm is developed and presented. Using this algorithm, optimizations are conducted to obtain simulated pendulum balancers under five different conditions. The performances of these results are analysed to assess the potential and limitations of the algorithm and these spherical joints. Based on one of the optimized results, a prototype is fabricated and expermentally validated, achieving a moment reduction of 90.5%. The deformation calculated by the TetraFEM tool closely matches the prototype’s deformation with an accuracy of 89.6%, demonstrating its potential for application in the development of shoulder exoskeletons.
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This paper introduces a fully compliant spherical joint with an optimized stiffness profile specifically for balancing a pendulum. The design builds on previous work that has successfully created a fully compliant spherical joint using tetrahedron-shaped elements connected in series. To efficiently compute and optimize the balancing behaviour of these compliant joints, a novel algorithm is developed and presented. Using this algorithm, optimizations are conducted to obtain simulated pendulum balancers under five different conditions. The performances of these results are analysed to assess the potential and limitations of the algorithm and these spherical joints. Based on one of the optimized results, a prototype is fabricated and expermentally validated, achieving a moment reduction of 90.5%. The deformation calculated by the TetraFEM tool closely matches the prototype’s deformation with an accuracy of 89.6%, demonstrating its potential for application in the development of shoulder exoskeletons.
Multi-material 4D-printing of a Magneto-responsive Hydrogel Scaffold with Tuned Stiffness
An approach to locally stimulate a hydrogel scaffold using uniaxial static magnetic fields
Master thesis
(2024)
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Elio Çinar San Segundo, M. J. Mirzaali, E.L. Fratila-Apachitei, S. Safarloo, A.A. Zadpoor, A. Savva, P. Boukany, K. Tufekci
The physical, chemical, and biological versatility and high water content of hydrogels have been taken advantage of to fabricate hydrogels that mimic the extracellular matrix (ECM) structure of native tissues and applied in the field of cell and tissue engineering to provide the cells with a 3D scaffold structure. Especially in tissue engineering, the creation of a suitable hydrogel scaffold with hard and soft interfaces that is capable of both supporting cell growth and stimulation for guided differentiation for tissue interface studies is a primary concern for advancements in tissue engineering. The ideal scaffold with hard and soft interfaces can be achieved by finetuning its biological, biochemical, structural, and mechanical properties for optimal cell proliferation and differentiation.
In this thesis, a magneto-responsive hydrogel scaffold composed of gelatin (Gel, 2.5%), alginate (Alg, 5%), and iron oxide microparticles (10% w/v) was developed and mechanically and rheologically characterized before, during and after the application of a uniaxial static magnetic field. The magneto-responsive hydrogel scaffolds were created through multi-material 3D printing using magnetic and non-magnetic hydrogel inks. The magnetic inks contained magnetic particle (MP) inclusions within its polymer network while the non-magnetic hydrogel ink had no MPs. The 3D printing process allowed for a local control in the magnetic and non-magnetic hydrogel distribution to create hard and soft hydrogel interfaces. The printability and shape fidelity of various ink compositions were evaluated, so that the final composition of Gel:Alg ratio of 1:2 (2.5%:5.0%) with 10% MP was chosen for further mechanical and rheological characterization. The magnetic hydrogel scaffold exhibited magnetorheological properties as it mainly increased the effective Young’s modulus, storage modulus, and damping factor, and decreased viscosity under a uniaxial static magnetic field application.
In tissue engineering, the developed hydrogel scaffold, which is locally responsive to magnetic cues, shows great potential for creating scaffolds capable of continuously stimulating embedded cells in a non-contact manner. As a proof of concept, a bi-layered, multi-material hydrogel scaffold was created with increased surface area attachment points between each hydrogel material to mimic the osteochondral tissue interface. The increased surface area between both layers was achieved through a checkered pattern design with alternating magnetic and non-magnetic hydrogel sections printed alongside each other. ...
In this thesis, a magneto-responsive hydrogel scaffold composed of gelatin (Gel, 2.5%), alginate (Alg, 5%), and iron oxide microparticles (10% w/v) was developed and mechanically and rheologically characterized before, during and after the application of a uniaxial static magnetic field. The magneto-responsive hydrogel scaffolds were created through multi-material 3D printing using magnetic and non-magnetic hydrogel inks. The magnetic inks contained magnetic particle (MP) inclusions within its polymer network while the non-magnetic hydrogel ink had no MPs. The 3D printing process allowed for a local control in the magnetic and non-magnetic hydrogel distribution to create hard and soft hydrogel interfaces. The printability and shape fidelity of various ink compositions were evaluated, so that the final composition of Gel:Alg ratio of 1:2 (2.5%:5.0%) with 10% MP was chosen for further mechanical and rheological characterization. The magnetic hydrogel scaffold exhibited magnetorheological properties as it mainly increased the effective Young’s modulus, storage modulus, and damping factor, and decreased viscosity under a uniaxial static magnetic field application.
In tissue engineering, the developed hydrogel scaffold, which is locally responsive to magnetic cues, shows great potential for creating scaffolds capable of continuously stimulating embedded cells in a non-contact manner. As a proof of concept, a bi-layered, multi-material hydrogel scaffold was created with increased surface area attachment points between each hydrogel material to mimic the osteochondral tissue interface. The increased surface area between both layers was achieved through a checkered pattern design with alternating magnetic and non-magnetic hydrogel sections printed alongside each other. ...
The physical, chemical, and biological versatility and high water content of hydrogels have been taken advantage of to fabricate hydrogels that mimic the extracellular matrix (ECM) structure of native tissues and applied in the field of cell and tissue engineering to provide the cells with a 3D scaffold structure. Especially in tissue engineering, the creation of a suitable hydrogel scaffold with hard and soft interfaces that is capable of both supporting cell growth and stimulation for guided differentiation for tissue interface studies is a primary concern for advancements in tissue engineering. The ideal scaffold with hard and soft interfaces can be achieved by finetuning its biological, biochemical, structural, and mechanical properties for optimal cell proliferation and differentiation.
In this thesis, a magneto-responsive hydrogel scaffold composed of gelatin (Gel, 2.5%), alginate (Alg, 5%), and iron oxide microparticles (10% w/v) was developed and mechanically and rheologically characterized before, during and after the application of a uniaxial static magnetic field. The magneto-responsive hydrogel scaffolds were created through multi-material 3D printing using magnetic and non-magnetic hydrogel inks. The magnetic inks contained magnetic particle (MP) inclusions within its polymer network while the non-magnetic hydrogel ink had no MPs. The 3D printing process allowed for a local control in the magnetic and non-magnetic hydrogel distribution to create hard and soft hydrogel interfaces. The printability and shape fidelity of various ink compositions were evaluated, so that the final composition of Gel:Alg ratio of 1:2 (2.5%:5.0%) with 10% MP was chosen for further mechanical and rheological characterization. The magnetic hydrogel scaffold exhibited magnetorheological properties as it mainly increased the effective Young’s modulus, storage modulus, and damping factor, and decreased viscosity under a uniaxial static magnetic field application.
In tissue engineering, the developed hydrogel scaffold, which is locally responsive to magnetic cues, shows great potential for creating scaffolds capable of continuously stimulating embedded cells in a non-contact manner. As a proof of concept, a bi-layered, multi-material hydrogel scaffold was created with increased surface area attachment points between each hydrogel material to mimic the osteochondral tissue interface. The increased surface area between both layers was achieved through a checkered pattern design with alternating magnetic and non-magnetic hydrogel sections printed alongside each other.
In this thesis, a magneto-responsive hydrogel scaffold composed of gelatin (Gel, 2.5%), alginate (Alg, 5%), and iron oxide microparticles (10% w/v) was developed and mechanically and rheologically characterized before, during and after the application of a uniaxial static magnetic field. The magneto-responsive hydrogel scaffolds were created through multi-material 3D printing using magnetic and non-magnetic hydrogel inks. The magnetic inks contained magnetic particle (MP) inclusions within its polymer network while the non-magnetic hydrogel ink had no MPs. The 3D printing process allowed for a local control in the magnetic and non-magnetic hydrogel distribution to create hard and soft hydrogel interfaces. The printability and shape fidelity of various ink compositions were evaluated, so that the final composition of Gel:Alg ratio of 1:2 (2.5%:5.0%) with 10% MP was chosen for further mechanical and rheological characterization. The magnetic hydrogel scaffold exhibited magnetorheological properties as it mainly increased the effective Young’s modulus, storage modulus, and damping factor, and decreased viscosity under a uniaxial static magnetic field application.
In tissue engineering, the developed hydrogel scaffold, which is locally responsive to magnetic cues, shows great potential for creating scaffolds capable of continuously stimulating embedded cells in a non-contact manner. As a proof of concept, a bi-layered, multi-material hydrogel scaffold was created with increased surface area attachment points between each hydrogel material to mimic the osteochondral tissue interface. The increased surface area between both layers was achieved through a checkered pattern design with alternating magnetic and non-magnetic hydrogel sections printed alongside each other.
Prosthetic socket design and fit are key for a successful amputee rehabilitation and comfort, directly influencing patient satisfaction and quality of life. However, there is a lack of quantitative data on stump pressure distribution and how it changes over time, which could greatly contribute to the efforts of designers, prosthetists and doctors to improve patient comfort.
This study explores the use of Force Sensitive Resistors (FSRs) to measure and visualize stump pressure distribution, specifically for transtibial prosthetic sockets. The research involves testing an experimental prototype equipped with FSRs on a cyclic loading machine, followed by a comparison of the results with a simulation.
The findings indicate that the highest loads are registered by FSRs positioned at the bottom of the stump and below the knee. Some anomalies were observed, potentially due to specific geometric features of the prototype and the way the load was applied during testing.
Overall, the experimental data suggests that FSRs are effective for measuring stump pressure distribution. However, further testing with increasingly complex load cases is necessary to validate the sensors' reliability.
In conclusion, FSRs demonstrate significant potential for enabling knowledge-based designs focused on patient well-being. Through the course of this project, valuable design insights and requirements for integrating sensors into prosthetic sockets were identified. Moreover, this systematic sensor testing approach can be applied to explore and compare between other pressure sensors.
...
This study explores the use of Force Sensitive Resistors (FSRs) to measure and visualize stump pressure distribution, specifically for transtibial prosthetic sockets. The research involves testing an experimental prototype equipped with FSRs on a cyclic loading machine, followed by a comparison of the results with a simulation.
The findings indicate that the highest loads are registered by FSRs positioned at the bottom of the stump and below the knee. Some anomalies were observed, potentially due to specific geometric features of the prototype and the way the load was applied during testing.
Overall, the experimental data suggests that FSRs are effective for measuring stump pressure distribution. However, further testing with increasingly complex load cases is necessary to validate the sensors' reliability.
In conclusion, FSRs demonstrate significant potential for enabling knowledge-based designs focused on patient well-being. Through the course of this project, valuable design insights and requirements for integrating sensors into prosthetic sockets were identified. Moreover, this systematic sensor testing approach can be applied to explore and compare between other pressure sensors.
...
Prosthetic socket design and fit are key for a successful amputee rehabilitation and comfort, directly influencing patient satisfaction and quality of life. However, there is a lack of quantitative data on stump pressure distribution and how it changes over time, which could greatly contribute to the efforts of designers, prosthetists and doctors to improve patient comfort.
This study explores the use of Force Sensitive Resistors (FSRs) to measure and visualize stump pressure distribution, specifically for transtibial prosthetic sockets. The research involves testing an experimental prototype equipped with FSRs on a cyclic loading machine, followed by a comparison of the results with a simulation.
The findings indicate that the highest loads are registered by FSRs positioned at the bottom of the stump and below the knee. Some anomalies were observed, potentially due to specific geometric features of the prototype and the way the load was applied during testing.
Overall, the experimental data suggests that FSRs are effective for measuring stump pressure distribution. However, further testing with increasingly complex load cases is necessary to validate the sensors' reliability.
In conclusion, FSRs demonstrate significant potential for enabling knowledge-based designs focused on patient well-being. Through the course of this project, valuable design insights and requirements for integrating sensors into prosthetic sockets were identified. Moreover, this systematic sensor testing approach can be applied to explore and compare between other pressure sensors.
This study explores the use of Force Sensitive Resistors (FSRs) to measure and visualize stump pressure distribution, specifically for transtibial prosthetic sockets. The research involves testing an experimental prototype equipped with FSRs on a cyclic loading machine, followed by a comparison of the results with a simulation.
The findings indicate that the highest loads are registered by FSRs positioned at the bottom of the stump and below the knee. Some anomalies were observed, potentially due to specific geometric features of the prototype and the way the load was applied during testing.
Overall, the experimental data suggests that FSRs are effective for measuring stump pressure distribution. However, further testing with increasingly complex load cases is necessary to validate the sensors' reliability.
In conclusion, FSRs demonstrate significant potential for enabling knowledge-based designs focused on patient well-being. Through the course of this project, valuable design insights and requirements for integrating sensors into prosthetic sockets were identified. Moreover, this systematic sensor testing approach can be applied to explore and compare between other pressure sensors.
Thermo-responsive hydrogels are a class of smart material that show increasing promise and applications in the biomedical engineering industry. This thesis investigated a thermo-responsive hydrogel for 4D printing applications. A poly(N-isopropylacrylamide) (>97%) (pNIPAM) based hydrogel was developed and the concentration of NIPAM, as well as the molar ratio of crosslinker, N,N-methylenebis (acrylamide) (>99%) (Mbis), to monomer was investigated to determine an optimal resin composition, which was determined from the thermo-response of the hydrogel at the microscale.
The resins were used to print several bilayer beams with varying laser power, scanning speed and hatching angles. Once the optimal composition and printing parameters were determined, mechanical characterization of the hydrogel was performed to measure the Young’s modulus at various loading rates via nanoindentation.
The thermal expansion coefficient (TEC) of the hydrogel was measured in three orthogonal directions at different temperatures. Finally, based on the shape morphing behaviour of the bilayer beams, we developed shape morphing applications at the microscale including a thermo-responsive micro-gripper and thermo-responsive drug delivery valve. The purpose of this work was, therefore, to explore possible applications of such a hydrogel and the ability to print with it in the microscale via two photon polymerization. ...
The resins were used to print several bilayer beams with varying laser power, scanning speed and hatching angles. Once the optimal composition and printing parameters were determined, mechanical characterization of the hydrogel was performed to measure the Young’s modulus at various loading rates via nanoindentation.
The thermal expansion coefficient (TEC) of the hydrogel was measured in three orthogonal directions at different temperatures. Finally, based on the shape morphing behaviour of the bilayer beams, we developed shape morphing applications at the microscale including a thermo-responsive micro-gripper and thermo-responsive drug delivery valve. The purpose of this work was, therefore, to explore possible applications of such a hydrogel and the ability to print with it in the microscale via two photon polymerization. ...
Thermo-responsive hydrogels are a class of smart material that show increasing promise and applications in the biomedical engineering industry. This thesis investigated a thermo-responsive hydrogel for 4D printing applications. A poly(N-isopropylacrylamide) (>97%) (pNIPAM) based hydrogel was developed and the concentration of NIPAM, as well as the molar ratio of crosslinker, N,N-methylenebis (acrylamide) (>99%) (Mbis), to monomer was investigated to determine an optimal resin composition, which was determined from the thermo-response of the hydrogel at the microscale.
The resins were used to print several bilayer beams with varying laser power, scanning speed and hatching angles. Once the optimal composition and printing parameters were determined, mechanical characterization of the hydrogel was performed to measure the Young’s modulus at various loading rates via nanoindentation.
The thermal expansion coefficient (TEC) of the hydrogel was measured in three orthogonal directions at different temperatures. Finally, based on the shape morphing behaviour of the bilayer beams, we developed shape morphing applications at the microscale including a thermo-responsive micro-gripper and thermo-responsive drug delivery valve. The purpose of this work was, therefore, to explore possible applications of such a hydrogel and the ability to print with it in the microscale via two photon polymerization.
The resins were used to print several bilayer beams with varying laser power, scanning speed and hatching angles. Once the optimal composition and printing parameters were determined, mechanical characterization of the hydrogel was performed to measure the Young’s modulus at various loading rates via nanoindentation.
The thermal expansion coefficient (TEC) of the hydrogel was measured in three orthogonal directions at different temperatures. Finally, based on the shape morphing behaviour of the bilayer beams, we developed shape morphing applications at the microscale including a thermo-responsive micro-gripper and thermo-responsive drug delivery valve. The purpose of this work was, therefore, to explore possible applications of such a hydrogel and the ability to print with it in the microscale via two photon polymerization.
Master thesis
(2024)
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M.H. Zwart, N.E. Putra, Mohammad Mirzaali, Amir Zadpoor, Sara Panahkhahi, Peyman Taheri
Over two million bone grafts are performed worldwide, each year. The preferred method is using autografts, but there are two important downsides. There is often insufficient tissue to harvest and the scar at the harvesting side is painfull for the patient. Therefore there exists a great need to improve synthetic grafts.
Traditionally, synthetic bone scaffolds are made from only one material, this can either be a (bioactive) ceramic or metal. The former has the benefit of promoting bone growth, but has insufficient mechanical properties. Metals on the other hand have no issue competing with bone in terms of mechanical properties, but they may not be biocompatible nor aid osteo-induction.
In this study direct ink writing was used to produce multimaterial Ti6Al4V and akermanite scaffolds. The goal was to combine the favourable mechanical properties of Ti6Al4V alloy with the osteo-inductive properties of akermanite. Composites of Ti6Al4V and akermanite were evaluated as well, but similar to akermanite ceramic on itself, their mechanical performance was deemed insufficient. Akermanite and Ti6Al4V was found to react and form titanium silicide and a calicum compound, presumed to be calcium oxide. A core shell scaffold was designed which uses a Ti6Al4V shell and an akermanite composite core in order to achieve both adequate mechanical and improved bioactive properties. This scaffold performed comparable to cortical bone in stiffness, and boasted superior strength. ...
Traditionally, synthetic bone scaffolds are made from only one material, this can either be a (bioactive) ceramic or metal. The former has the benefit of promoting bone growth, but has insufficient mechanical properties. Metals on the other hand have no issue competing with bone in terms of mechanical properties, but they may not be biocompatible nor aid osteo-induction.
In this study direct ink writing was used to produce multimaterial Ti6Al4V and akermanite scaffolds. The goal was to combine the favourable mechanical properties of Ti6Al4V alloy with the osteo-inductive properties of akermanite. Composites of Ti6Al4V and akermanite were evaluated as well, but similar to akermanite ceramic on itself, their mechanical performance was deemed insufficient. Akermanite and Ti6Al4V was found to react and form titanium silicide and a calicum compound, presumed to be calcium oxide. A core shell scaffold was designed which uses a Ti6Al4V shell and an akermanite composite core in order to achieve both adequate mechanical and improved bioactive properties. This scaffold performed comparable to cortical bone in stiffness, and boasted superior strength. ...
Over two million bone grafts are performed worldwide, each year. The preferred method is using autografts, but there are two important downsides. There is often insufficient tissue to harvest and the scar at the harvesting side is painfull for the patient. Therefore there exists a great need to improve synthetic grafts.
Traditionally, synthetic bone scaffolds are made from only one material, this can either be a (bioactive) ceramic or metal. The former has the benefit of promoting bone growth, but has insufficient mechanical properties. Metals on the other hand have no issue competing with bone in terms of mechanical properties, but they may not be biocompatible nor aid osteo-induction.
In this study direct ink writing was used to produce multimaterial Ti6Al4V and akermanite scaffolds. The goal was to combine the favourable mechanical properties of Ti6Al4V alloy with the osteo-inductive properties of akermanite. Composites of Ti6Al4V and akermanite were evaluated as well, but similar to akermanite ceramic on itself, their mechanical performance was deemed insufficient. Akermanite and Ti6Al4V was found to react and form titanium silicide and a calicum compound, presumed to be calcium oxide. A core shell scaffold was designed which uses a Ti6Al4V shell and an akermanite composite core in order to achieve both adequate mechanical and improved bioactive properties. This scaffold performed comparable to cortical bone in stiffness, and boasted superior strength.
Traditionally, synthetic bone scaffolds are made from only one material, this can either be a (bioactive) ceramic or metal. The former has the benefit of promoting bone growth, but has insufficient mechanical properties. Metals on the other hand have no issue competing with bone in terms of mechanical properties, but they may not be biocompatible nor aid osteo-induction.
In this study direct ink writing was used to produce multimaterial Ti6Al4V and akermanite scaffolds. The goal was to combine the favourable mechanical properties of Ti6Al4V alloy with the osteo-inductive properties of akermanite. Composites of Ti6Al4V and akermanite were evaluated as well, but similar to akermanite ceramic on itself, their mechanical performance was deemed insufficient. Akermanite and Ti6Al4V was found to react and form titanium silicide and a calicum compound, presumed to be calcium oxide. A core shell scaffold was designed which uses a Ti6Al4V shell and an akermanite composite core in order to achieve both adequate mechanical and improved bioactive properties. This scaffold performed comparable to cortical bone in stiffness, and boasted superior strength.
A hard-soft interface refers to the boundary between two materials or regions with significantly different mechanical properties, where one is rigid or hard and the other is flexible or soft. These interfaces are common in both engineered and natural systems and are characterized by the contrast in how each material deforms, transfers loads, or responds to environmental stress. Engineered hard-soft interfaces often experience failure due to high interfacial stresses, poor adhesion, and localized stress concentrations caused by mismatched mechanical properties. An example of engineered hard-soft interfaces can be found in tissue engineering, where they are used to replicate natural transitions between tissues, such as those between bone and cartilage. In contrast, hard-soft interfaces in nature, such as the root-soil system, demonstrate remarkable strength and adaptability, efficiently distributing loads and reducing stress concentrations despite differences in material properties.
The pull-out force was chosen to assess the strength of the root-soil interface, capturing the mechanical interactions of roots with their environment. This study focused on barley and mung bean seeds, chosen for their distinct root structures, barley with a fibrous system and mung bean featuring a taproot system. Over a 15-day growth period, various root characteristics such as length, diameter, tortuosity, and branching patterns were analyzed across soil and hydrogel substrates, each with distinct material properties and stiffness. The methodology included measuring growth in terms of days and stem height, along with 2D root trait extraction to analyze characteristics such as length, diameter and number of branches. Additionally, 3D computed tomography (CT) scanning was used to visualize root architecture, while pull-out tests provided key data on resistance and force-displacement curves, and finite element method (FEM) simulations enabled sensitivity analyses of various root structure configurations in a non-destructive manner. Lastly, experiments with hydrogel tested its viability for root growth, involving detailed protocols for hydrogel composition and seed preparation.
Plant growth measurements revealed a consistent increase in stem height over time, effectively captured by the logistic growth model. Laboratory pullout tests and root extraction demonstrated that increases in root characteristics such as length, diameter, and branching significantly improve pullout force in both barley and mung bean seeds. Moreover, pullout test results showed that barley roots have greater mechanical resistance and higher maximum forces than mung bean roots, although with greater variability in the data. FEM simulations indicated that a 45° vertical branching angle yielded the highest pullout force for barley in soil (5.09 N), while an 80° angle was most effective in hydrogel (4.98 N). In contrast, radial branching angles had negligible effects in both substrates. Tortuous root configurations significantly increased pullout force in soil, nearly doubling it from 5.09 N for straight roots to 9.80 N, but only slightly improved it in hydrogel, from 3.20 N to 3.61 N. The addition of branches in mung beans significantly increased pullout forces in both substrates due to the greater surface area, which enhanced root-substrate interaction. The FEM simulations showed that pullout forces were generally higher in soil due to its rigidity, which leads to a rapid increase in pullout force until root failure. Hydrogel, with its elastic properties, allowed roots to stretch more under load, providing uniform and gradual resistance. The FEM model was also validated through energy history output results and mesh convergence analysis. Lastly, initial experiments growing roots in hydrogel show promise for this substrate as a soil alternative, however further research is required to optimize its properties for plant growth.
Overall, this study provides a better understanding of the factors optimizing root anchorage and interface strength, offering design strategies for bioinspired engineered hard-soft interfaces. It also emphasizes the need to tailor natural design principles to the specific material properties of substrates in engineered contexts. ...
The pull-out force was chosen to assess the strength of the root-soil interface, capturing the mechanical interactions of roots with their environment. This study focused on barley and mung bean seeds, chosen for their distinct root structures, barley with a fibrous system and mung bean featuring a taproot system. Over a 15-day growth period, various root characteristics such as length, diameter, tortuosity, and branching patterns were analyzed across soil and hydrogel substrates, each with distinct material properties and stiffness. The methodology included measuring growth in terms of days and stem height, along with 2D root trait extraction to analyze characteristics such as length, diameter and number of branches. Additionally, 3D computed tomography (CT) scanning was used to visualize root architecture, while pull-out tests provided key data on resistance and force-displacement curves, and finite element method (FEM) simulations enabled sensitivity analyses of various root structure configurations in a non-destructive manner. Lastly, experiments with hydrogel tested its viability for root growth, involving detailed protocols for hydrogel composition and seed preparation.
Plant growth measurements revealed a consistent increase in stem height over time, effectively captured by the logistic growth model. Laboratory pullout tests and root extraction demonstrated that increases in root characteristics such as length, diameter, and branching significantly improve pullout force in both barley and mung bean seeds. Moreover, pullout test results showed that barley roots have greater mechanical resistance and higher maximum forces than mung bean roots, although with greater variability in the data. FEM simulations indicated that a 45° vertical branching angle yielded the highest pullout force for barley in soil (5.09 N), while an 80° angle was most effective in hydrogel (4.98 N). In contrast, radial branching angles had negligible effects in both substrates. Tortuous root configurations significantly increased pullout force in soil, nearly doubling it from 5.09 N for straight roots to 9.80 N, but only slightly improved it in hydrogel, from 3.20 N to 3.61 N. The addition of branches in mung beans significantly increased pullout forces in both substrates due to the greater surface area, which enhanced root-substrate interaction. The FEM simulations showed that pullout forces were generally higher in soil due to its rigidity, which leads to a rapid increase in pullout force until root failure. Hydrogel, with its elastic properties, allowed roots to stretch more under load, providing uniform and gradual resistance. The FEM model was also validated through energy history output results and mesh convergence analysis. Lastly, initial experiments growing roots in hydrogel show promise for this substrate as a soil alternative, however further research is required to optimize its properties for plant growth.
Overall, this study provides a better understanding of the factors optimizing root anchorage and interface strength, offering design strategies for bioinspired engineered hard-soft interfaces. It also emphasizes the need to tailor natural design principles to the specific material properties of substrates in engineered contexts. ...
A hard-soft interface refers to the boundary between two materials or regions with significantly different mechanical properties, where one is rigid or hard and the other is flexible or soft. These interfaces are common in both engineered and natural systems and are characterized by the contrast in how each material deforms, transfers loads, or responds to environmental stress. Engineered hard-soft interfaces often experience failure due to high interfacial stresses, poor adhesion, and localized stress concentrations caused by mismatched mechanical properties. An example of engineered hard-soft interfaces can be found in tissue engineering, where they are used to replicate natural transitions between tissues, such as those between bone and cartilage. In contrast, hard-soft interfaces in nature, such as the root-soil system, demonstrate remarkable strength and adaptability, efficiently distributing loads and reducing stress concentrations despite differences in material properties.
The pull-out force was chosen to assess the strength of the root-soil interface, capturing the mechanical interactions of roots with their environment. This study focused on barley and mung bean seeds, chosen for their distinct root structures, barley with a fibrous system and mung bean featuring a taproot system. Over a 15-day growth period, various root characteristics such as length, diameter, tortuosity, and branching patterns were analyzed across soil and hydrogel substrates, each with distinct material properties and stiffness. The methodology included measuring growth in terms of days and stem height, along with 2D root trait extraction to analyze characteristics such as length, diameter and number of branches. Additionally, 3D computed tomography (CT) scanning was used to visualize root architecture, while pull-out tests provided key data on resistance and force-displacement curves, and finite element method (FEM) simulations enabled sensitivity analyses of various root structure configurations in a non-destructive manner. Lastly, experiments with hydrogel tested its viability for root growth, involving detailed protocols for hydrogel composition and seed preparation.
Plant growth measurements revealed a consistent increase in stem height over time, effectively captured by the logistic growth model. Laboratory pullout tests and root extraction demonstrated that increases in root characteristics such as length, diameter, and branching significantly improve pullout force in both barley and mung bean seeds. Moreover, pullout test results showed that barley roots have greater mechanical resistance and higher maximum forces than mung bean roots, although with greater variability in the data. FEM simulations indicated that a 45° vertical branching angle yielded the highest pullout force for barley in soil (5.09 N), while an 80° angle was most effective in hydrogel (4.98 N). In contrast, radial branching angles had negligible effects in both substrates. Tortuous root configurations significantly increased pullout force in soil, nearly doubling it from 5.09 N for straight roots to 9.80 N, but only slightly improved it in hydrogel, from 3.20 N to 3.61 N. The addition of branches in mung beans significantly increased pullout forces in both substrates due to the greater surface area, which enhanced root-substrate interaction. The FEM simulations showed that pullout forces were generally higher in soil due to its rigidity, which leads to a rapid increase in pullout force until root failure. Hydrogel, with its elastic properties, allowed roots to stretch more under load, providing uniform and gradual resistance. The FEM model was also validated through energy history output results and mesh convergence analysis. Lastly, initial experiments growing roots in hydrogel show promise for this substrate as a soil alternative, however further research is required to optimize its properties for plant growth.
Overall, this study provides a better understanding of the factors optimizing root anchorage and interface strength, offering design strategies for bioinspired engineered hard-soft interfaces. It also emphasizes the need to tailor natural design principles to the specific material properties of substrates in engineered contexts.
The pull-out force was chosen to assess the strength of the root-soil interface, capturing the mechanical interactions of roots with their environment. This study focused on barley and mung bean seeds, chosen for their distinct root structures, barley with a fibrous system and mung bean featuring a taproot system. Over a 15-day growth period, various root characteristics such as length, diameter, tortuosity, and branching patterns were analyzed across soil and hydrogel substrates, each with distinct material properties and stiffness. The methodology included measuring growth in terms of days and stem height, along with 2D root trait extraction to analyze characteristics such as length, diameter and number of branches. Additionally, 3D computed tomography (CT) scanning was used to visualize root architecture, while pull-out tests provided key data on resistance and force-displacement curves, and finite element method (FEM) simulations enabled sensitivity analyses of various root structure configurations in a non-destructive manner. Lastly, experiments with hydrogel tested its viability for root growth, involving detailed protocols for hydrogel composition and seed preparation.
Plant growth measurements revealed a consistent increase in stem height over time, effectively captured by the logistic growth model. Laboratory pullout tests and root extraction demonstrated that increases in root characteristics such as length, diameter, and branching significantly improve pullout force in both barley and mung bean seeds. Moreover, pullout test results showed that barley roots have greater mechanical resistance and higher maximum forces than mung bean roots, although with greater variability in the data. FEM simulations indicated that a 45° vertical branching angle yielded the highest pullout force for barley in soil (5.09 N), while an 80° angle was most effective in hydrogel (4.98 N). In contrast, radial branching angles had negligible effects in both substrates. Tortuous root configurations significantly increased pullout force in soil, nearly doubling it from 5.09 N for straight roots to 9.80 N, but only slightly improved it in hydrogel, from 3.20 N to 3.61 N. The addition of branches in mung beans significantly increased pullout forces in both substrates due to the greater surface area, which enhanced root-substrate interaction. The FEM simulations showed that pullout forces were generally higher in soil due to its rigidity, which leads to a rapid increase in pullout force until root failure. Hydrogel, with its elastic properties, allowed roots to stretch more under load, providing uniform and gradual resistance. The FEM model was also validated through energy history output results and mesh convergence analysis. Lastly, initial experiments growing roots in hydrogel show promise for this substrate as a soil alternative, however further research is required to optimize its properties for plant growth.
Overall, this study provides a better understanding of the factors optimizing root anchorage and interface strength, offering design strategies for bioinspired engineered hard-soft interfaces. It also emphasizes the need to tailor natural design principles to the specific material properties of substrates in engineered contexts.
The solute transport across the osteochondral (OC) interface is of crucial metabolic importance for a normal function of articular cartilage, and, therefore, for the OC interface as a whole. A better understanding how the mechanical- and physiological properties of the OC interface affect the solute transport across the OC interface could lead to new insights in repair strategies. The aim of this master’s thesis was to investigate how graded mechanical- and/or physiological properties of the OC interface affect the solute transport across the OC interface.
A combination of computational modelling and experimental diffusion tests on GelMA-based hydrogel plugs was used to approach the goal. Regarding the computational model, first, a multi-zone biphasic-solute finite element model that accurately replicates axial solute transport across the OC interface was designed and validated. Second, a power law function was used to apply several gradients on the initial values of the solid volume fraction (SVF), diffusion coefficient, and elastic modulus across the OC interface to study the effect of each parameter on the solute diffusion across the OC interface. On the experimental front, attempts were made to 3D-print GelMA-based hydrogel plugs but all failed. Alternatively, five groups (n = 3) of hydrogel plugs were created, each of which underwent different UV curing time, by casting GelMA into cylindrical plugs. Axial diffusion of an alizarin red solution through the hydrogel samples was recorded using a digital camera.
The results of the computational model show that only the SVF plays a small role in the height of the equilibrium concentration reached in the subchondral bone layer. However, the influence of both the SVF and diffusion coefficient on the time when the equilibrium concentration is reached in the subchondral bone is considerably large. It is shown that the elastic modulus has a negligible influence on the solute transport. Regarding the experimental diffusion tests, air bubbles and/or sincere light reflections made all but six hydrogel plugs unusable for further analysis. A relationship between sample thickness and diffusion is observed in the remaining hydrogel samples. The results of the SVF computational model and experimental diffusion tests were compared, but sufficient experimental data was lacking to draw any solid conclusions from this comparison.
This master’s thesis provides a new computational model of the OC interface which allows the implementation of graded parameters across the OC interface. It is concluded that the current experimental set-up is not suitable for obtaining consistent data on solute transport across hydrogel plugs. Suggestions to improve the experimental set-up are made.
...
A combination of computational modelling and experimental diffusion tests on GelMA-based hydrogel plugs was used to approach the goal. Regarding the computational model, first, a multi-zone biphasic-solute finite element model that accurately replicates axial solute transport across the OC interface was designed and validated. Second, a power law function was used to apply several gradients on the initial values of the solid volume fraction (SVF), diffusion coefficient, and elastic modulus across the OC interface to study the effect of each parameter on the solute diffusion across the OC interface. On the experimental front, attempts were made to 3D-print GelMA-based hydrogel plugs but all failed. Alternatively, five groups (n = 3) of hydrogel plugs were created, each of which underwent different UV curing time, by casting GelMA into cylindrical plugs. Axial diffusion of an alizarin red solution through the hydrogel samples was recorded using a digital camera.
The results of the computational model show that only the SVF plays a small role in the height of the equilibrium concentration reached in the subchondral bone layer. However, the influence of both the SVF and diffusion coefficient on the time when the equilibrium concentration is reached in the subchondral bone is considerably large. It is shown that the elastic modulus has a negligible influence on the solute transport. Regarding the experimental diffusion tests, air bubbles and/or sincere light reflections made all but six hydrogel plugs unusable for further analysis. A relationship between sample thickness and diffusion is observed in the remaining hydrogel samples. The results of the SVF computational model and experimental diffusion tests were compared, but sufficient experimental data was lacking to draw any solid conclusions from this comparison.
This master’s thesis provides a new computational model of the OC interface which allows the implementation of graded parameters across the OC interface. It is concluded that the current experimental set-up is not suitable for obtaining consistent data on solute transport across hydrogel plugs. Suggestions to improve the experimental set-up are made.
...
The solute transport across the osteochondral (OC) interface is of crucial metabolic importance for a normal function of articular cartilage, and, therefore, for the OC interface as a whole. A better understanding how the mechanical- and physiological properties of the OC interface affect the solute transport across the OC interface could lead to new insights in repair strategies. The aim of this master’s thesis was to investigate how graded mechanical- and/or physiological properties of the OC interface affect the solute transport across the OC interface.
A combination of computational modelling and experimental diffusion tests on GelMA-based hydrogel plugs was used to approach the goal. Regarding the computational model, first, a multi-zone biphasic-solute finite element model that accurately replicates axial solute transport across the OC interface was designed and validated. Second, a power law function was used to apply several gradients on the initial values of the solid volume fraction (SVF), diffusion coefficient, and elastic modulus across the OC interface to study the effect of each parameter on the solute diffusion across the OC interface. On the experimental front, attempts were made to 3D-print GelMA-based hydrogel plugs but all failed. Alternatively, five groups (n = 3) of hydrogel plugs were created, each of which underwent different UV curing time, by casting GelMA into cylindrical plugs. Axial diffusion of an alizarin red solution through the hydrogel samples was recorded using a digital camera.
The results of the computational model show that only the SVF plays a small role in the height of the equilibrium concentration reached in the subchondral bone layer. However, the influence of both the SVF and diffusion coefficient on the time when the equilibrium concentration is reached in the subchondral bone is considerably large. It is shown that the elastic modulus has a negligible influence on the solute transport. Regarding the experimental diffusion tests, air bubbles and/or sincere light reflections made all but six hydrogel plugs unusable for further analysis. A relationship between sample thickness and diffusion is observed in the remaining hydrogel samples. The results of the SVF computational model and experimental diffusion tests were compared, but sufficient experimental data was lacking to draw any solid conclusions from this comparison.
This master’s thesis provides a new computational model of the OC interface which allows the implementation of graded parameters across the OC interface. It is concluded that the current experimental set-up is not suitable for obtaining consistent data on solute transport across hydrogel plugs. Suggestions to improve the experimental set-up are made.
A combination of computational modelling and experimental diffusion tests on GelMA-based hydrogel plugs was used to approach the goal. Regarding the computational model, first, a multi-zone biphasic-solute finite element model that accurately replicates axial solute transport across the OC interface was designed and validated. Second, a power law function was used to apply several gradients on the initial values of the solid volume fraction (SVF), diffusion coefficient, and elastic modulus across the OC interface to study the effect of each parameter on the solute diffusion across the OC interface. On the experimental front, attempts were made to 3D-print GelMA-based hydrogel plugs but all failed. Alternatively, five groups (n = 3) of hydrogel plugs were created, each of which underwent different UV curing time, by casting GelMA into cylindrical plugs. Axial diffusion of an alizarin red solution through the hydrogel samples was recorded using a digital camera.
The results of the computational model show that only the SVF plays a small role in the height of the equilibrium concentration reached in the subchondral bone layer. However, the influence of both the SVF and diffusion coefficient on the time when the equilibrium concentration is reached in the subchondral bone is considerably large. It is shown that the elastic modulus has a negligible influence on the solute transport. Regarding the experimental diffusion tests, air bubbles and/or sincere light reflections made all but six hydrogel plugs unusable for further analysis. A relationship between sample thickness and diffusion is observed in the remaining hydrogel samples. The results of the SVF computational model and experimental diffusion tests were compared, but sufficient experimental data was lacking to draw any solid conclusions from this comparison.
This master’s thesis provides a new computational model of the OC interface which allows the implementation of graded parameters across the OC interface. It is concluded that the current experimental set-up is not suitable for obtaining consistent data on solute transport across hydrogel plugs. Suggestions to improve the experimental set-up are made.
Master thesis
(2023)
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AYMAN AHMED MUBEEN Ayman Ahmed Mubeen, M. J. Mirzaali, A. Accardo, E. Yarali, A. Hunt
Shape morphing is a prevalent feature in all living organisms. Incorporating shape-morphing capabilities into engineered scaffolds in the field of tissue engineering by virtue of 4D printing would allow for structures to closely mimic in-vivo conditions, and dynamically interact with changing cellular microenvironments. Engineered scaffolds subjected to external mechanical loads have recently drawn interest to study the impact of altering Poisson's ratio and pore size of cellular scaffolds on the properties of cells growing on it. However, this approach limits its applications to in-vitro environments. The ability to remotely actuate scaffolds would allow for precise, non-invasive, and controlled activation of these engineered structures. Towards this, the current research work aimed at the design and fabrication of a dynamic metamaterial-based unit cell microstructure capable of exhibiting a varying Poisson’s ratio in response to thermal stimulus. The microstructure was fabricated using a biocompatible Poly(N-isopropylacrylamide) (pNIPAM) based photoresist and a two-photon polymerization (2PP)-based direct laser writing technique. Systematic characterizations were first performed on a simplified model to evaluate the correlation between the printing parameters which include laser power, scanning speed, and hatching angles to the shape-morphing characteristics of the printed microstructures. The learnings were implemented to fabricate the proposed varying Poisson's ratio model. The fabricated microstructure exhibited a rapid and reversible change in Poisson’s ratio when subjected to a thermal stimulus by virtue of the inherent properties of hydrogels and heterogeneity introduced within the structures by varying the laser parameters during the printing process. In a broader context, this research serves as the first step towards the realization of a dynamic stimulus-responsive 3D scaffold for cell culture applications.
...
Shape morphing is a prevalent feature in all living organisms. Incorporating shape-morphing capabilities into engineered scaffolds in the field of tissue engineering by virtue of 4D printing would allow for structures to closely mimic in-vivo conditions, and dynamically interact with changing cellular microenvironments. Engineered scaffolds subjected to external mechanical loads have recently drawn interest to study the impact of altering Poisson's ratio and pore size of cellular scaffolds on the properties of cells growing on it. However, this approach limits its applications to in-vitro environments. The ability to remotely actuate scaffolds would allow for precise, non-invasive, and controlled activation of these engineered structures. Towards this, the current research work aimed at the design and fabrication of a dynamic metamaterial-based unit cell microstructure capable of exhibiting a varying Poisson’s ratio in response to thermal stimulus. The microstructure was fabricated using a biocompatible Poly(N-isopropylacrylamide) (pNIPAM) based photoresist and a two-photon polymerization (2PP)-based direct laser writing technique. Systematic characterizations were first performed on a simplified model to evaluate the correlation between the printing parameters which include laser power, scanning speed, and hatching angles to the shape-morphing characteristics of the printed microstructures. The learnings were implemented to fabricate the proposed varying Poisson's ratio model. The fabricated microstructure exhibited a rapid and reversible change in Poisson’s ratio when subjected to a thermal stimulus by virtue of the inherent properties of hydrogels and heterogeneity introduced within the structures by varying the laser parameters during the printing process. In a broader context, this research serves as the first step towards the realization of a dynamic stimulus-responsive 3D scaffold for cell culture applications.