S.J.P. Callens
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Shape-shifting of hyperbolic surfaces
Design and analysis of a shape-shifting method for complex hyperbolic surfaces, based on a passive frame in combination with an active shape-memory polymer
Almost every tissue in the human body is curved in a certain way. Examples are the extracellular matrix of different tissues such as trabecular bone, different acini and blood vessels. As such, the ability to create complex curved structures is crucial in the development of biomimetic biomaterials that could be used, for example, for tissue regeneration purposes. Currently, most of these different curved substrates and porous materials are fabricated with 3D-printing techniques. These techniques, however, have limitations. The 3D-printed structures, for example, have limited resolution and the production process is not compatible with planar functionality-inducing processes. A solution for these problems could be the concept of shape-shifting. Shape-shifting is the process through which an object transforms itself into a different shape under the influence of an external stimulus, such as temperature or light. A special interest goes to shape-shifting of initially flat materials (2D) into different complex 3D structures. This method has as main advantage that planar printing, patterning or other 2D processing techniques can be used on the planar (non-shape-shifted) state. In this research, the most important principles of shape-shifting of curved hyperbolic surfaces are explored. With this technique, the benefits of both hyperbolic surfaces and shape-shifting can be combined and exploited. A new way of hyperbolic shape-shifting is introduced. This is done by using a passive rigid frame and an active shape memory polymer (SMP). The passive material determines how and where the structure will fold, while the active SMP generates the force in order to fold and forms a curved (hyperbolic) surface spanned between the frame. A simple square patch design consisting of four rigid beams and an SMP was used as the basis of this research. When activated, this patch forms a saddle shaped (hyperbolic) surface. The design, activation and materials of the patch were changed and manipulated in different ways in order to perform a parametric study and to analyse different important aspects of the process. In order to quantify and assess the quality of the different patches and the effects of the manipulations, different test set-ups were made and the most valuable output parameters were chosen. Lastly, a finite element model of the principle was developed in order to further analyse the concept.
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Almost every tissue in the human body is curved in a certain way. Examples are the extracellular matrix of different tissues such as trabecular bone, different acini and blood vessels. As such, the ability to create complex curved structures is crucial in the development of biomimetic biomaterials that could be used, for example, for tissue regeneration purposes. Currently, most of these different curved substrates and porous materials are fabricated with 3D-printing techniques. These techniques, however, have limitations. The 3D-printed structures, for example, have limited resolution and the production process is not compatible with planar functionality-inducing processes. A solution for these problems could be the concept of shape-shifting. Shape-shifting is the process through which an object transforms itself into a different shape under the influence of an external stimulus, such as temperature or light. A special interest goes to shape-shifting of initially flat materials (2D) into different complex 3D structures. This method has as main advantage that planar printing, patterning or other 2D processing techniques can be used on the planar (non-shape-shifted) state. In this research, the most important principles of shape-shifting of curved hyperbolic surfaces are explored. With this technique, the benefits of both hyperbolic surfaces and shape-shifting can be combined and exploited. A new way of hyperbolic shape-shifting is introduced. This is done by using a passive rigid frame and an active shape memory polymer (SMP). The passive material determines how and where the structure will fold, while the active SMP generates the force in order to fold and forms a curved (hyperbolic) surface spanned between the frame. A simple square patch design consisting of four rigid beams and an SMP was used as the basis of this research. When activated, this patch forms a saddle shaped (hyperbolic) surface. The design, activation and materials of the patch were changed and manipulated in different ways in order to perform a parametric study and to analyse different important aspects of the process. In order to quantify and assess the quality of the different patches and the effects of the manipulations, different test set-ups were made and the most valuable output parameters were chosen. Lastly, a finite element model of the principle was developed in order to further analyse the concept.
Triply Periodic Minimal Surfaces (TPMS) have earned great popularity in porous meta- biomaterials by cause of unique mass transfer properties, tunable mechanical properties, large pore space and high surface to volume ratio. Numerical and experimental studies suggest a great potential for TPMS-based architectures in the treatment of segmental bone defects, where supporting scaffolds are crucial in bridging the gap unable to heal naturally. However, current studies are limited to investigating the properties of classic TPMS archi- tectures. In this thesis, I present the design, fabrication and characterisation of a novel type of meta-biomaterials inspired by TPMS morphology. I show a practical application of Weierstrass equations to define Schwarz P, Schwarz D and Gyroid surfaces, which pro- vides an opportunity to remove fundamental patches from the original surface and design unique structures. Moreover, one of the developed designs applied basics of graph theory to construct the material which mimics the randomness of the trabecular bone structure, while preserving the benefits of regular TPMS morphology. The results demonstrate the improved performance of the modified TPMS scaffolds compared to classic structures in terms of permeability and compliance properties, crucial for the materials applied in or- thopaedic implants. The porosity and permeability values of the developed metamaterial were found to be in the range of trabecular bone. Additionally, the possibilities to simulate the mass transfer properties of the novel material were examined in COMSOL and valu- able qualitative results, like fluid velocity distribution and flow-induced wall shear stress, retrieved. Overall my thesis introduces an innovative idea for biomaterial design and adds a strong argument in favour of TPMS morphology application in the orthopaedic material research field.
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Triply Periodic Minimal Surfaces (TPMS) have earned great popularity in porous meta- biomaterials by cause of unique mass transfer properties, tunable mechanical properties, large pore space and high surface to volume ratio. Numerical and experimental studies suggest a great potential for TPMS-based architectures in the treatment of segmental bone defects, where supporting scaffolds are crucial in bridging the gap unable to heal naturally. However, current studies are limited to investigating the properties of classic TPMS archi- tectures. In this thesis, I present the design, fabrication and characterisation of a novel type of meta-biomaterials inspired by TPMS morphology. I show a practical application of Weierstrass equations to define Schwarz P, Schwarz D and Gyroid surfaces, which pro- vides an opportunity to remove fundamental patches from the original surface and design unique structures. Moreover, one of the developed designs applied basics of graph theory to construct the material which mimics the randomness of the trabecular bone structure, while preserving the benefits of regular TPMS morphology. The results demonstrate the improved performance of the modified TPMS scaffolds compared to classic structures in terms of permeability and compliance properties, crucial for the materials applied in or- thopaedic implants. The porosity and permeability values of the developed metamaterial were found to be in the range of trabecular bone. Additionally, the possibilities to simulate the mass transfer properties of the novel material were examined in COMSOL and valu- able qualitative results, like fluid velocity distribution and flow-induced wall shear stress, retrieved. Overall my thesis introduces an innovative idea for biomaterial design and adds a strong argument in favour of TPMS morphology application in the orthopaedic material research field.