This thesis explores the impact of 3D femoral rotational effects on 2D X-ray femoral shapes using Statistical Shape Modeling (SSM). The study is driven by the clinical relevance of accurately diagnosing hip disorders from 2D radiographs, which are inherently influenced by the femur's position and rotation. The primary objective is to understand how these rotations affect the femur's apparent shape on radiographs and quantify the influence of rotation on shape variations observed in 2D SSMs.

The research was structured around two main experiments. The first experiment involves the creation of a 3D SSM of the whole femur using CT scans. This model was then used to explore how projections of the proximal femur change with different rotations. The second experiment focuses on the proximal femur and constructs two 2D SSMs. These were derived from Digitally Reconstructed Radiographs (DRRs) of the proximal femur, which are obtained by rotating the CTs (±30° in 5° increments) around the shaft axis of the femur. One 2D SSM is based solely on DRR data, while the other combines DRR data with the WorldCOACH dataset of hip X-rays. This approach aims to provide an understanding of how rotation influences the shape modes of the femur as described by the 2D SSMs. For the first five shape modes the resulting b-values presented in a boxplot. Lastly, Welch's Analysis of Variance (ANOVA) is performed on these b-values for both 2D SSMs. The ANOVA analysis is performed on the following independent values: the femur, which represents the natural bone shape of that specific femur, and the angle, which represents the angle of rotation at which the DRR was created.

Findings show that sensitivity to angle changes varies across SSM modes, with shape changes due to external rotation being more evident than those caused by internal rotation. The combined results from the plots and Welch's ANOVA analyses of the two models (DRR-only and combined WorldCOACH and DRR) indicate that modes 1 to 4 are more heavily influenced by rotation, while mode 5 is more influenced by natural shape differences. This suggests that higher modes, which describe more specific and less variable shapes, are less influenced by rotation and more by intrinsic anatomical variations.

Investigations into mechanotransduction in connective tissue extracellular matrix (ECM) have demonstrated that collagen networks show cell-independent mechanosensitive behavior. It has been suggested that mechanical strain could lead to conformational changes in the molecular structure of collagen, thereby influencing the susceptibility to other molecules. In the process of normal aging, the collagen fibrils in cartilage undergo a non-enzymatic process known as glycation. It involves the accumulation of advanced glycation end products (AGEs) after exposure to sugars, resulting in the formation of cross-links between the collagen fibrils. This process is correlated with increased stiffness and brittleness of the cartilage, making it more prone to mechanical damage. The goal of this thesis was to assess whether mechanical compression has any effects on the formation of non-enzymatic cross-links during the aging of articular cartilage. Two different models have been developed to mimic aging knees that undergo static and dynamic compression. Healthy cartilage explants were exposed to L-threose sugar to induce artificial aging. During incubation, these explants were submitted to either static or dynamic unconfined compression. Treatment with static compression consisted of a 5, 10 or 15\% strain throughout the whole incubation period, using a custom-made bioreactor. Treatment with dynamic compression consisted of multiple loading cycles at a frequency of either 0.01 Hertz (Hz) or 1 Hz, using a Dynamic Mechanical Analyzer (DMA). We conducted cartilage surface color analyses, micro‐indentation tests, dynamic mechanical analyses and biochemical measurements of pentosidine cross‐links to assess the effects of advanced glycation cross‐linking under these different conditions. Dynamic compression at a frequency of 1 Hz was found to affect the formation of non-enzymatic cross-links. Biomechanical and biochemical data showed a similar trend, namely, the average values for equilibrium modulus, dynamic moduli, phase shifts and pentosidine per collagen level were noticeably higher (or lower in case of phase shift) for the 1 Hz treated samples compared to samples of other treatment groups. The results of these studies suggest that compression at the physiological frequency of walking does affect the formation of cross-links in the articular cartilage during aging. These findings contribute to a better understanding of the mechanochemistry of collagen fibrils, which is necessary to develop future strategies against cartilage aging and deterioration.

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.

BACKGROUND.Implant-associated infection (IAI) is a rising complication in bone-related medical treatments using metal implants. Preventive measures, such as implant surfaces with integrated antibacterial properties, are hence required. The emergence of antibiotic-resistant pathogens has led to a growing interest in inorganic nanoparticles as antibacterial agents. In addition, implants should simultaneously stimulate bone tissue regeneration and integration to improve implant longevity. Additive manufacturing (AM) of orthopedic implants has attracted interest as improved bone tissue regeneration and integration was demonstrated by AM porous implants. AM porous implants, however, are at enhanced risks of IAIs; these porous implants require integrated antibacterial properties. This study focused on a systematic comparison of the antibacterial properties of AM porous Ti6Al4V implant surfaces with silver nanoparticles (Ag NPs), copper nanoparticles (Cu NPs) and/or zinc nanoparticles (Zn NPs) against methicillin resistant Staphylococcus aureus (MRSA). METHODS.Medical grade porous Ti6Al4V implants were additively manufactured using selective laser melting (SLM). Subsequently, the SLM Ti6Al4V implants were biofunctionalized by plasma electrolytic oxidation (PEO) using an electrolyte that consisted of Ca/P-based species and ratios of Ag NPs, Cu NPs and/or Zn NPs. Implants with 0, 25, 75 and 100% of Ag NPs, Cu NPs and/or Zn NPs were synthesized. After biofunctionalization, the surface morphology, structure and chemistry of the implants were investigated using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The antibacterial properties of the implants against MRSA were studied in vitro as well as ex vivo. The leachable antibacterial activity was studied in an agar diffusion assay, the minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) of Ag+, Cu2+ and Zn2+ ions was determined by a micro-dilution assay and the bactericidal activity of the implants was quantified by a colony-forming unit (CFU) count in vitro against surface-adherent and non-adherent MRSA. Furthermore, ex vivo antibacterial properties were determined using a femoral murine infection model mimicking the in vivo environment. RESULTS.Biofunctionalization of the porous SLM Ti6Al4V implants by PEO resulted in a uniform and homogeneous micro-/nano-porous oxide layer that covered the entire surface of the implants. SEM and EDS analysis demonstrated the presence of Ag NPs, Cu NPs and Zn NPs in the TiO2 surface layer. The agar diffusion assay demonstrated a strong leachable antibacterial activity for the implants with Ag NPs and Cu NPs or Zn NPs, while no leachable antibacterial activity was observed for implants without Ag NPs. Antibacterial testing showed that Ag+, Cu2+ and Zn2+ ions, as well the combinations of the ions, were growth inhibitory and bactericidal to MRSA. In addition, implants with ≥ 50% of Ag NPs and combinations of ≥ 75% of Ag NPs and Cu NPs or Zn NPs, fully eradicated surface-adherent and non-adherent MRSA within 24 h and prevented biofilm formation up to 24 h. Moreover, strong ex vivo bactericidal properties against MRSA were demonstrated for these implants within 24 h. CONCLUSION. Biofunctionalized surfaces with Ag NPs and Cu NPs or Zn NPs on porous SLM Ti6Al4V implants showed strong in vitro and ex vivo antibacterial properties against MRSA. The implants with 50% of Ag NPs and combinations of 75% of Ag NPs and 25% of Cu NPs or Zn NPs are promising for further development, to prevent IAIs and improve the longevity of the implants in clinical applications.