Context. In times where human kind is facing serious challenges due to global warming, scarcity of natural resources and inequality, to continue producing food, especially meat, as it is now done, does not seem sustainable. For people that want to continue enjoying their delicious piece of steak, the manner in which meat is sourced will need to be redesigned. One of the disruptive initiatives in this field is in vitro cultured meat. For the cultivation of muscle tissue, one needs cells, chemical factors and the appropriate biomaterials that function as a scaffold. Meatable B.V. is a food-technology startup that is a pioneer in the cultivation of steak-like meat using induced pluripotent stem cells. Aims. The aim of the study is to optimise the extracellular matrix (i.e. scaffold) mimicry of natural biomaterials to serve as a scaffold for 3D skeletal muscle tissue engineering, using iPSCs. The supplementary aim of this study is to determine the feasibility of the optimised scaffold as a proof of concept for cultured meat. Methods. The proof of concept model (Model A) was created in collaboration with researchers from the Loughborough University who demonstrated a scalable model for 3D human skeletal muscle tissue engineering. Their strategy was to use a hard plastic mould to confine and provide initial support for the viscoelastic hydrogel (matrigel and rat tail collagen) encapsulated with cells (C2C12 myoblasts). For the optimisation of the extracellular matrix for iPSCs for the production of cultured meat, this model was copied and repeated with different edible scaffold alternatives. The best alternative biomaterial (Model B) was further optimised in large scale tissue moulds and compared to the proof of concept model and meat. Lastly, Model C was created by seeding iPSCs in Model B. The qualitative and quantitative comparisons were based on different analytical parameters. Results. The hydrogel scaffolds of both models A and B were highly comparable in terms of permeability, scaffold compaction by cell activity and cell alignment. The improved model (B) resulted in a higher cell proliferation as seen by cell development and cell density. The stiffness of model A was half the stiffness of Model B, and the stiffness of Model B was more comparable with the higher stiffness of beef steak (factor 5 difference). Nevertheless, when the improved model was seeded with pre-differentiated iPSCs (Model C) instead of C2C12 myoblasts, the results were clearly less successful than the first models and were not comparable with beef steak. Conclusions. This research describes the successful improvements of an existing 3D in-vitro skeletal tissue engineering method, as prototype model for cultured meat, that was for the first time seeded with iPSCs. Model B should be set as the basis model to optimise for the culture of iPSCs. The bovine collagen model with C2C12s was not comparable to steak, but a longer culture period could result in more comparable tissue. The main reason for the limitations of Model C was the maturation of iPSCs, which could be improved in different ways. In addition, there remain certain requirements to be met for the hydrogel scaold, mainly connected with current developments for recombinant animal-free materials. It can still be concluded that the less successful Model C was a step in the right direction to becoming a feasible model for the culture of in vitro meat.

An acetabular revision is a very challenging intervention, due to moderate to severe bone deficiencies and poor bone quality. Current solutions for this intervention are associated with inconsistent and unreliable clinical outcomes. This leads to substantial complications, including implant migration and loosening. These complications are, among others, caused by the lack of biological fixation, a non-physiological stress distribution and stress shielding. To encounter these problems a novel concept for an acetabular revision has been presented. The aim of this new design is to plastically deform into massive acetabular bone deficiencies. This will stimulate the surrounding bone and therefore diminishes effect of stress shielding (Wolff’s Law). This study explored whether a porous layer made of pure titanium can achieve this space-filling behaviour. The infill of this porous layer is based on meta-biomaterials. The macro-scale properties of this type of materials are determined by their small-scale architecture. The aim of the first part of this study was therefore to systematically study the topology-property relationship of six topological designs, including the cube, truncated cube, truncated cuboctahedron, rhombic dodecahedron, diamond and body centred cubic. These designs were studied by experimentally determining their mechanical properties, including the Poisson’s ratio using the Digital Image Correlation (DIC) technique. Afterwards, three topological designs were selected to be implemented in the novel acetabular component, including the diamond, rhombic dodecahedron and body centred cubic. These unit cells showed the lowest stiffness and the highest positive Poisson’s ratio over the complete range of concerned porosities (80-98%). Besides, they showed bending-dominated deformation without the failure of struts. The results indicated that these unit cells have the highest capacity to plastically deform as well have the potential of space-filling behaviour. The porosity of the porous layer of the implant functionally graded from very porous at the bone-implant interface to very solid at the joint’s articulating surface, which corresponds to bone’s hierarchical structure. These implants were compressed inside a bone-mimicking mould, of which the appearance and mechanics resembled an acetabulum with large bone deficiencies. µCT images revealed that the implant based on the diamond unit cell showed the most promising deformability at the mould-implant interface. Although this deformation was promising, the push-in forces needed to compress the implant into the mould were very high (ranging from 3.33 kN to 14.8 kN). Future work is needed to diminish the need for these high push-in forces by making the porous outer layer even more deformable. This novel implant has the potential to increase the biological fixation, preserve the physiological stress distribution and diminish the effect of stress shielding in the acetabular component of a total hip replacement.

The incidence of osteoporotic vertebral compression fractures (VCFs) is rapidly increasing, necessitating the identification of the most appropriate treatment method. The well-established first and second generation surgical procedures are not capable of giving optimal outcomes. Moreover, my literature study has shown little to no improvements for four of the most prevailing third generation procedures. As a consequence, the med-tech company Amber Implants B.V. developed a new 3D-printed porous titanium implant that has the potential to resolve difficulties and drawbacks that were identified for all former procedures. Nonetheless, the performance of this implant has never been tested before. Thus, the aim of this study was to pre-clinically evaluate the biomechanical properties regarding the spinal deformities for this implant. For the quantification, the prevention of spinal deformities was subdivided into the anterior height restoration and the kyphotic angle correction. The pre-clinical evaluation was conducted on isolated vertebrae originating from three human cadaver specimens. First, the most abundant type of all osteoporotic VCFs, a wedge fracture, was generated on the vertebrae with 40% anterior height decrease. Thereafter, vertebral restoration was performed with the implants. Besides, vertebral restoration with the second generation surgical procedure, the Balloon Kyphoplasty procedure (BKP), was performed likewise to serve as a comparative. After vertebral restoration, half of the implant group and the total BKP group were tested in a cyclic loading test that mimicked the activity during the first week after surgical VCF repair, i.e. 10.000 cycles with loads ranging from 100N to 600N. The other half of the implant group was tested under higher loading conditions, i.e. 10.000 cycles with loads ranging from 100N to 1000N. At each test stage the spinal deformities, which were subdivided into the anterior height and the kyphotic angle, were evaluated from micro-CT (μCT) data. Eventually, the μCT scans were compared in order to quantify the implant's performance. The anterior height restoration after vertebral restoration with the implant was outstanding compared to the BKP procedure. Thereby, a statistical significance difference (p<0.05) was not only observed for the anterior height restoration, but also for the central and posterior height restorations, between the two surgical procedures. Additionally, the kyphotic angle correction of the implant procedure outperformed the outcomes observed for the BKP. Nonetheless, after cyclic loading various drawbacks for the implants were observed, resulting in substantial decreases in outcomes for the height restoration and the kyphotic angle correction. Regarding the height decrease, most was found in the trabecular bone inferior to the implant. Presumably, the plastic deformation was induced by high local stresses as a result of the minimal contact area between the implant and the trabecular bone. Complementary, the rotation of the implant was observed to effect the implant's performance. Ultimately, it was concluded that the implant in its current design could not compete with the BKP procedure, neither with the third generation surgical repair procedures for an osteoporotic VCF such as Vertebral Body Stenting (VBS) and SpineJack. Nevertheless, the outcomes after vertebral restoration were promising. Therefore, it was assumed that the implant has a decent chance of succeeding after implementing some adjustments on the implant's geometry and the corresponding surgical tools.

Massive acetabular bone defects are difficult to treat with the currently available implants. Advances in additive manufacturing create new design possibilities, which allow the production of patient specific implants. These endless possibilities will enable to tune the mechanical properties of porous implants and to distribute the loads in such a way that it mimics the natural load distribution. This technique will therefore be used in the design of a new type of implant, which is a deformable acetabular implant that will fully fit in a massive acetabular defect after plastic deformation. In this way, all remaining bone will be loaded, and the physiological load distribution will be restored to maximally reduce stress shielding and to prevent further loss of bone stock. To design this new implant, more information is required on the mechanical properties of the titanium porous structures. Therefore, the aim of this study is to examine the mechanical properties and deformation behaviour of highly porous pure titanium (grade 1) structures. The diamond unit cell was used to design three types of structures with different porosities (> 95%). A static compression test was performed on cylindrical samples. In addition, push-in and pull-out tests were performed on hemispherical shaped samples. The samples were compressed into specially designed moulds, which represent the acetabulum with defects, to test how these structures deform according to their surrounding shape. Micro-CT images were made during and after the test to analyse the deformation. The cylindrical samples continuously deformed during compression and large plastic strains were measured (> 57%). The hemispherical samples deformed conform the surrounding mould and even penetrated into the holes. The push-in and pull-out forces are positively correlated, and these forces are lower for more porous structures. The micro-CT scans show that all unit cells within the structure do not equally deform under compression, but show a gradual, layer-by-layer deformation. This study is a first step towards the design of a deformable implant. The results are quite promising and can function as a basis for future work.

BACKGROUND: Knee problems are the most common complaints of the lower extremity in the Netherlands. Osteoarthritis has the highest prevalence of all knee complaints. Knee osteoarthritis is likely to start at the patellofemoral joint and is associated with the aggravation of pain. Mechanical overloading is hypothesized to contribute to the development and progression of patellofemoral osteoarthritis (PFOA). Several studies have explored the mechanical loading pattern of the patellofemoral joint. Because different biomechanical models were used, vastly different estimations of the patellofemoral joint contact force (PFJCF) were concluded. This diversity prevents a clear understanding of the role of mechanical overloading in PFOA, since it is unknown how different biomechanical models affect the PFJCF estimation. OBJECTIVES: This study will explore how different biomechanical models of the patellofemoral joint affect the estimated PFJCF for common weight-bearing activities. METHODS: Ten healthy participants were included in this study. Common weight-bearing activities (walking, stair ascending, stair descending, sit-to-stand and stand-to-sit) were performed in the motion lab. Marker trajectory data and force plate data were collected. The data were input to biomechanical models used to estimate the quadriceps muscle force and subsequently the PFJCF. The quadriceps muscle force was estimated using the inverse dynamics and static optimization method. From there on, the PFJCF was estimated using three PFJCF to quadriceps muscle force ratios (P2QFRs), each based on a different patellofemoral joint model (i.e. van Eijden’s model, Yamaguchi’s model and Gill’s model). For each weight-bearing activity, the peak PFJCF was obtained and the magnitude of the difference among the biomechanical models was explored. RESULTS: The static optimization method resulted in a significantly higher peak PFJCF compared to the inverse dynamics method in walking (largest effect size was 0.10 BW). However, for stair descending, sit-to-stand and stand-to-sit, the inverse dynamics method resulted in a significantly higher peak PFJCF compared to the static optimization method (largest effect size was 0.45 BW, 1.17 BW, 1.25 BW, respectively). No significantly difference was found for stair ascending. For walking, Yamaguchi’s model resulted in a significantly higher peak PFJCF compared to van Eijden’s model and Gill’s model, and van Eijden’s model resulted in a significantly higher peak PFJCF compared to Gill’s model (largest effect size was 0.06 BW). For stair ascending, stair descending, sit-to-stand and stand-to-sit, Gill’s model resulted in a significantly higher peak PFJCF compared to van Eijden’s model and Yamaguchi’s model. For stair descending the van Eijden’s model resulted in a significantly higher peak PFJCF compared to Yamaguchi’s model. The largest effect size was 0.15 BW, 0.32 BW, 0.72 BW and 0.72 BW, for respectively stair ascending, stair descending, sit-to-stand and stand-to-sit. CONCLUSION: The choice of a biomechanical model has a critical effect on the estimation of the magnitude of the PFJCF. Its differences might reach half the clinical size effects when comparing control to symptomatic PF pain patients.

Introduction. To prevent burns from scar formation and contraction, the use of splinting therapy in the early phase of wound healing is considered as an effective non-surgical method. Splinting entails the application of a mechanical load in the opposite direction of the contractile force within the wound, based on the assumption that wound- or scar contraction will be prevented or reduced. However, clinical research provides conflicting evidence on its effectiveness and optimal treatment method. Therefore, the aim of this study was to design an in vitro model to investigate the mechanoresponsive cellular effects of stress on specifically Human Eschar Fibroblasts and their extracellular matrix, in order to confirm or disprove effects of burn splinting. Methods. The two major players of the burn wound model include (1) the fibroblasts, and (2) the novel extracellular matrix they produce. Outcome measures were chosen that directly relate to matrix organization, fibroblast functioning and matrix functioning. Three chronological sub-goals were defined to achieve the goal of designing a burn wound splinting model: (1) Formulating a suitable mechanical stress protocol; (2) Select a system that enables the selected mechanical stress of extensible substrates that facilitate the growth of fibroblasts and their derived extracellular matrix; (3) Create and optimize conditions to culture fibroblasts on an extensible substrate. To successfully reach these goals, the current literature on this subject was evaluated and comparative experiments were executed. Feasibility of the model was tested in a pilot study. Results. The MCB1 stretching apparatus was provided by Association of Dutch Burn Centre as a suitable device, which was modified to fulfill all predefined requirements. Human Eschar fibroblasts and dermal fibroblasts were cultured on custom made silicone culture wells. Cross-linked gelatin-A coating and vitamin C-supplemented culture medium were selected for optimal cell culturing results. A clinically relevant stretching regimen was chosen, given the paucity of available evidence in literature. A pilot study to test the feasibility of the model indicated that both dynamic and static stretching of eschar fibroblasts show a trend towards thicker, denser collagen matrices compared to unstretched conditions. These collagen fibers also showed a greater degree of alignment. However, no definitive conclusions can be drawn since sample size is limited. Conclusion. The model presented in this work constitutes a practical framework to test mechanotransducive processes in burn scars on a cellular and molecular level. A pilot study using this model showed excellent feasibility

Background Adolescent idiopathic scoliosis (AIS) with a Cobb angle larger than 45° is a spinal deformity that needs surgical treatment to stop progression and reduce pain. Spinal fusion is a surgical procedure where rods are attached to the spine through screws to diminish the Cobb angle. Objective The metal rods are pre-bent to correct the spinal deformity as much as possible. This rod shape is currently based on experience of the orthopedic surgeon. The aim of this thesis is to use Fi-nite element analysis (FEA) to predict a suitable rod shape for AIS patients that need to un-dergo surgery.  Method An FE model of an AIS spine was created based on high quality CT images. Rotation of ver-tebrae led to the optimal shape of the spine in the coronal plane. Vertebral bodies in this model were one by one rotated to a new position from top to bottom, to bring the spine to a new state and align it as much as possible to a normal physiological shape. However, alignment of the spine is an iterative process and rotation of every subsequent vertebra affects the shape of the entire spine. For each vertebral rotation, the reaction moments to maintain the new position is determined in the FE spine model. The acquired reaction moments are transferred to an FE rod model to provide the pre-bending of a rod that can bring the spine in its new state. Results The FE spine model was corrected to reduce the Cobb angle as much as possible. The highest stresses were found at the spinal apex. The reaction moments were transferred to a rod that became deformed in such a manner that straightened the spine model and corrected the Cobb angle to its pre-determined position with 33% reduction. Discussion This is an exploratory study that examines the possibility to predict ideal rod shapes pre-operatively to reduce surgical duration and improve the quality of the procedure. An accessory rod shape was accomplished but could not be validated due to lack of comparable studies. Improved FE spine models will lead to higher reliability of FE pre-bent rod models. This can be accomplished by, for example, inclusion of ligaments, muscles and other structures in the FE model and use of time-dependent material properties. The current model did not lead to a perfect aligned physiological spine and optimization algorithms should be developed in future models to further improve pre-bending of the rods. Conclusion Pre-operative prediction can improve the quality and reduce the time of spinal fusion. Im-provements to the FE spine- and rod model, such as automation, generalization, inclusion of more structures, and optimization algorithms will lead to optimal pre-bending of rods and bet-ter and quicker surgical outcome.

The management of large acetabular defects remains one of the most challenging aspects of revision total hip arthroplasties. Failure of frequently used acetabular reconstruction components are, among others, caused by the lack of biological fixation, a non-physiological stress distribution and stress-shielding. Attempting to diminish these drawbacks of current implants a new acetabular cup has been explored. The double layer of this new acetabular cup better fills the acetabular defect. According to Wolff’s law this should reduce stress shielding and stimulate bone ingrowth. Part one of this study explores the relationship between unit cell size of the titanium and mechanical properties for the body centred cubic unit cell. Three graded lattices using different unit cell sizes were designed and 3D-printed out of commercially pure titanium (Grade 1) using selective laser melting. An unconfined compression test with cylindrical samples as well as a confined compression test with hemispherical samples were performed to obtain mechanical properties. An additional finite element study was used to validate the confined compression test. Acetabular defects were made in five Sawbones hemipelves which served as the basis for the design of the ‘patient specific’ acetabular cups. Three triflange and two unflanged acetabular cups were designed and 3D-printed out of commercially pure titanium (Grade 1) using selective laser melting. Mechanical properties were obtained from the unconfined compression tests. All acetabular cups were inserted by two orthopaedic surgeons at the UMC Utrecht. Cyclic testing was performed up to 1000 cycles to assess femoral head penetration under load after insertion. Additional penetration of the femoral head was found to be between 0.1781 and 0.3793 mm. Future work is needed to prevent strut breakage upon insertion and more research is needed in the fatigue behaviour of these new cups and their biological effect on living bone tissue.

The fundamentals of the nanopatterned surface can be found on the wings of cicada. These bactericidal surfaces are artificially mimicked on the surface of the implant to reduce the infection rate, which is one of the main complication after joint replacement. The bactericidal properties of the nanopatterned surface are a promising feature. However, the non-cytotoxicity of the surface of the implants should not be compromised. So far, no optimal nanopatterned surface regarding the geometrical features has been found yet. This study focusses on the computational modeling of the nanopatterned surface using Finite Element approaches to simulate the interaction between bacterial cells (Staphylococcus aureus) and host cells (osteoblast) with the nanopatterned surface. The final aim of the project is to show how geometrical features of the nanopatterned surfaces can influence the bacteria’s and cell’s fate. The geometrical parameters of the nanopatterned surface are height, width, interspace, radius and the shape and are varied to create different types of nanopatterned surfaces. The simulations have been performed based on the experimental examination of the bactericidal and cytotoxicity properties of nanopatterned surfaces. From the numerical analysis, it is concluded that among different geometrical parameters of the nanopatterned surface, only width and interspace of the nanopillars have a direct bactericidal effect. The nanopatterned surface with a small/intermediate width (50 nm) in combination with a large interspace (300 nm) has been found as the most optimal nanopattern resulting in bactericidal properties and non-cytotoxic properties for host cells. The results of this project can be considered as a guideline for the proper design of geometry of nanopatterned surfaces and can be verified by further experimental investigations.