A multi-material structure combines diverse materials, allowing for precise tailoring of properties in specific regions. The integration of dissimilar materials leads to superior performance compared to single-material components. Bimetallic structures, a subset of multi-material systems, offer site-specific performance owing to the contrasting properties of the materials involved. This thesis focused on fabricating a thin, functionally graded bi-metallic wall using Wire Arc Additive Manufacturing (WAAM) with Inconel 625 and HSLA steel. Functional grading of metallic materials, like Inconel 625 and HSLA steel, enables precise customisation of component properties to fulfil distinct functions within a structure. Despite its promise, this combination presents challenges, notably the formation of intermetallic compounds that act as a catalyst for forming solidification cracks in combination with varying material composition and high heat input. Optimal process parameters, notably reduced heat input, are critical in mitigating these issues. The current study involved process parameters optimisation for Inconel 625 single bead-on-plate welds to control dilution levels at dissimilar interfaces. Extensive characterisation using Light Optical Microscopy (LOM) and Scanning Electron Microscopy (SEM) equipped with Energy Dispersive Spectroscopy (EDS) was conducted to study the microstructural evolution of the as-fabricated sandwich structure. Results indicated that interface 1 (Inconel 625/HSLA steel) exhibited minimal dilution and zero defects, while interface 2 (HSLA Steel/Inconel 625) exhibited substantial dilution and was prone to solidification cracks. The EDS results affirmed that the variations of elemental composition and heavy dilution at interface 2 lead to inhomogeneous microstructural features, elemental segregations and the formation of brittle intermetallic phases, thereby leading to a solidification crack at this particular interface. X-ray diffraction (XRD) measurements were conducted to identify phases at the dissimilar interfaces, corroborating the microstructural features observed using SEM and LOM. The identified phases confirm the presence of brittle intermetallics, such as the laves phase, extensively present at interface 2. Vickers hardness testing was performed to assess the mechanical behaviour at both interfaces, revealing a consistent trend of decreasing values with a sudden increase in hardness values at both interfaces due to microstructural transition. Based on the EDS results, an optimal range of elemental compositions was speculated, focusing primarily on the significant elements Fe, Ni, and Cr. These compositions, with Ni content of approximately 20-25 wt%, Fe content of around 70-75 wt%, and Cr content of approximately 5-10 wt%, are crucial in reducing cracking susceptibility at interface 2. This study elucidates the initiation and propagation of solidification cracks at interface 2, establishing a definitive link between microstructural evolution, mechanical behaviour, and crack formation. Ultimately, this thesis lays the foundation for future research to delve deeper into these insights, fine-tune process parameters, and fabricate compositionally graded multi-material structures with enhanced susceptibility to solidification cracking at dissimilar interfaces.

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.

Aim: This project aims to design a lightweight, inexpensive and easy to use upper arm prosthesis through improving the design of ARM3D, which is a 3D printed body-powered transhumeral arm prosthesis. This study will cover general shortcomings of body-powered arm prostheses as the weight, cost, amount of parts and limited accessibility of them. This study also focusses on a natural appearance of the prosthetic arm. Results: The improved design of ARM3D is made of six 3D printed and eight non-3D printed parts. It has three Degrees of Freedom (DOF’s), one control cable, a harness both to suspend and control the prosthesis, an active voluntary closing hand, a passive rotating wrist joint and a passive elbow hinge joint. The prosthesis costs €59,68 and weighs 403 g. It takes 3 days, 6 hours and 47 minutes to print and 15 minutes to assemble. The maximum open hand width is 64 mm and the prosthesis needs 15 N of tension force on the control cable to operate. Furthermore, it is possible to paint the prosthetic fingernails and to remove the nail polish. Conclusion: An improved design of the ARM3D prosthesis is presented in this paper. ARM3D is almost entirely 3D printed. It is a lightweight and inexpensive device. A field study is required to gather more information whether the prosthesis is easy to use.

Purpose As a result of the worldwide aging population, Vertebral Compression Fractures (VCF) are commonly detected in osteoporotic patients; these can originate from traumatic events or occur spontaneously. The existing VCF devices and their corresponding surgical instruments have their limitations in terms of short- and long-term performance, efficiency, safety, and complications. Amber Implants has developed an innovative new Titanium Implantable Vertebral Augmentation Device (TIVAD) that overcomes the shortcomings of the available state-of-the-art VCF devices. However, the specific surgical instruments required for the insertion and deployment of the TIVAD are yet to be developed. Methods A knowledge-driven iterative design process that includes extensive theoretical and empirical research together with spine surgeons, concept development, and experimental verification phases has been executed. Results The outcomes of the experiments have shown that the final TIVAD inserter and expander met the predefined requirements regarding efficiency, mechanical properties, and usability. These results lead to a significant contribution to the overall TIVAD procedure. Conclusions To summarize, it can be stated that the essential surgical instruments, the TIVAD inserter, and expander, enable the surgeon to insert and deploy the TIVAD to relieve the patient from its pain sensation and to restore the adequate spine curve while reducing the number of surgical steps, the overall surgery time, and thus costs. Additionally, the risk of infection and pulmonary embolisms is decreased significantly due to the TIVAD’s non-PMMA minimally invasive surgical procedure.

Treatment of liver diseases is often done by means of interventional radiology and thereby needles are widely used. These needles are under constant development and therefore needle-tissue interaction data are necessary. The goal of this study is to provide data on needle forces during puncturing of liver blood vessels. These data can be used to mimic blood vessels in a polyvinyl alcohol (PVA) liver phantom, intended for needle development and training purposes. Needle insertion experiments were done on human livers, by puncturing portal veins, hepatic veins, hepatic arteries and liver tissue. The resulting force data show that peak forces are higher during puncturing of liver veins (median=2.20 N, interquartile range=1.46 N to 3.67 N) than during puncturing of liver tissue (median=0.38 N, interquartile range=0.31 N to 0.51 N). The force data were used to find a blood vessel mimicking material. Silicone, with the addition of a mesh fabric, was found to mimic the peak forces of liver veins during needle insertion. A silicone blood vessel was created with use of a 3D-printed blood vessel structure made of water-soluble PVA. The addition of the mesh fabric, furthermore ensures proper bonding between the silicone blood vessel and the PVA liver tissue. The methods described in this study can be used to implant artificial veins in a PVA liver phantom.

Third-generation advanced high strength steels (AHSS) are a new class of steels that offer superior functional properties and significant weight savings in the body-in-white (BIW) structure of a car. Weight savings directly translate to reduced CO2 emissions from cars which aids automotive manufactures to meet the vehicle emission guidelines put forth by regulatory bodies around the world. Further increase in weight savings and productivity can be realised when BIW components are fabricated using laser beam welding (LBW). However, the phenomenon of solidification cracking of AHSS during LBW poses challenges to not only its application in the automotive industry, and also in the production lines of steel manufacturers. From the body of literature pertaining to solidification cracking two fundamental conditions can be identified that result in solidification cracking in alloys. First is the development of thermo-mechanical stresses/strains during liquid melt solidification and second, is the formation of a crack susceptible microstructure. In addition to this, the welding conditions can influence the susceptibility of alloys to solidification cracking. The objective of the present study is to understand the influence of variable processing conditions during LBW on solidification cracking tendency of AHSS and how to control these conditions to minimise it. In particular, an attempt is made to understand the effect of keyhole configuration, welding speed and laser beam spot size on solidification cracking. Furthermore, finite element analysis is used to predict the size and shape of the weld pool during LBW, and to determine the net process efficiency which in turn is compared with the calculated process efficiency from the existing analytical model. Bead-on-plate LBW following the testing procedure of the VDEh (German Steel Institute) standard hot cracking test was performed on three third-generation AHSS at two LBW facilities with different beam quality. Due to this, the keyhole during the tests at the two facilities was identified to exist in the closed keyhole configuration and more towards the open keyhole configuration. The susceptibility to solidification cracking was found to increase when the keyhole prevailed in the closed keyhole configuration during LBW. The keyhole configuration was varied by altering the process parameters (welding speed and spot size of the laser beam) in comparison to the parameters corresponding to the closed keyhole configuration. Reducing the welding speed, while keeping the laser power and spot size constant, resulted in the open keyhole configuration and subsequent reduction in the solidification cracking tendency but, until a limit. Similarly, reducing the spot size, while keeping the welding speed and laser power constant, also reduced the solidification cracking tendency as the open keyhole configuration was enforced. The macroscopic area of the fusion zone (weld size) was found to corroborate with the solidification cracking tendency of the alloys. Consequently, the spot size of the laser beam was varied to determine the critical spot size which resulted in a critical weld size at which solidification cracking did not occur. Corresponding to this, the critical process efficiency was determined which is representative of the critical heat input above which solidification cracking occurs. However, the magnitude of the critical spot size, weld size and process efficiency is dependent on the solidification cracking susceptibility of the alloy in question.

Composite constructs made from gelatin methylacrylamide (gelMA) and polycaprolactone (PCL) have been proven as promising materials to form tissue equivalents which can be used to alleviate the problems arising due to damage of articular cartilage. Despite exhibiting an increase of compressive stiffness (up to 54 - fold) by synergistic combination of the two materials, as compared to gelMA or PCL fiber scaffolds alone, determination of shear properties of the composite construct remains unprecedented. The current study was aimed to comprehend the shear properties of the tissue equivalents made from gelMA or PCL fiber scaffolds. Direct shear tests were performed on composite constructs made from gelMA and boxed architecture of PCL fiber scaffolds with different fiber spacings to generate a comparative basis for shear modulus followed by computational modeling and analysis of the constructs to obtain a better understanding of reinforcing effect of PCL fiber scaffolds in gelMA and validate the experimental results computationally. Results indicate that shear stiffness of the tissue equivalent is dominated by the membrane elements of the boxed architecture of PCL fiber scaffolds which are produced by melt electrowriting (MEW). An association of increase in shear stiffness with decrease in fiber spacing for a given architecture has been depicted.

Atherosclerotic plaque rupture is the main cause of acute myocardial infarction and stroke, the two leading causes of death worldwide. Rupture of plaque tissue is a mechanical event, where plaque stress or strain locally exceeds its strength. Biomechanical studies agree with histopathological findings that a large lipid pool and thin fibrous cap overlying the lipid pool increase the likelihood of rupture, by showing increased plaque stresses for these geometries. Another plaque morphological feature that is frequently encountered is calcification. However, its role in the vulnerability of plaques to rupture is not fully understood, and biomechanical modeling studies do not agree on the effect of calcifications on plaque stress. These studies used isotropic material properties for the anisotropic and collagen rich plaque tissue, and generally focused on the effect of calcification on lumen stress or cap stress. However, histopathological findings revealed tissue damage at the interface between calcification and surrounding tissue. This study investigated stresses and strains at the interface between calcification and fibrous tissue, how these stresses and strains are influenced by local anisotropy of the fibrous tissue and how geometric features of the calcification are related to these metrics. A morphometric study was conducted first, to investigate and categorize different patterns of fiber alignment around the calcifications, and to measure the calcification geometric features including its location in the plaque, its shape and its size. Biomechanical models including the local anisotropic material properties were constructed next, based on the observations and measurements made in the morphometric analysis. Stress and strain metrics were investigated at the calcification boundary, and subsequently related to fiber patterns and calcification geometric features. Hundred forty five calcifications were segmented and measured in the morphometric analysis, and surrounding fiber alignments were studied. The analysis revealed that four main fiber patterns in the fibrous tissue surrounding calcifications exist: the Attached pattern, Pushed Aside pattern, Encircling pattern and Random pattern. Collagen fibers are attached to the calcification in the Attached pattern, are pushed aside by the calcification in the second pattern, encircle the calcification in the third pattern, and show a disorganized alignment in the Random pattern. The Attached pattern was the most prevalent fiber pattern, and its corresponding calcifications had larger aspect ratios and were on average larger than the other three fiber patterns. Large peak stresses and strains at the calcification boundary were identified in the biomechanical models for the Attached pattern and Pushed Aside pattern, while these metrics showed generally lower peak values for the Encircling pattern and Random pattern. Peak values for all stress and strain metrics were attained at the tip of the calcifications. Multivariate analysis showed that stresses and strains are related to the calcification geometric features; calcification interface stress and strain increased if the calcification was closer to the lumen, had a larger length/width ratio and was larger in size. Histopathological examination of plaques evidenced damage at the interface between calcification and fibrous tissue, potentially caused by an adverse mechanical state at this boundary. Most studies focused on stresses at the lumen or in the cap however, and this study for the first time specifically investigated stresses and strains at the calcification boundary while simultaneously introducing local fibrous tissue anisotropy in the computational models. Results show that peak stresses and strains can develop at this boundary, which will remain undiscovered if isotropic materials are used. This study was also the first to extensively analyze calcification geometric features and surrounding fiber alignment in relation to these interface stresses and strains. Peak values were found to be dependent on these features and fiber alignment patterns, indicating a relation between these characteristics and mechanical stability of the plaque. The findings of this study further increase the clinical relevance of finite element modeling in rupture risk prediction by showing previously undiscovered peak stress and strain values for interfaces and geometric configurations which already were deemed to be destabilizing in clinical and histopathological studies.

Degenerative disc disorders are among the most commonly diagnosed conditions and the leading cause for back and neck pain, affecting more than 266 million individuals annually. Interbody fusion is the proposed surgical treatment whenever lighter approaches such as physiotherapy and painkillers fail to improve the patient’s condition. It consists of the total or partial removal of the damaged disc, followed by the insertion of a spinal implant, referred to as interbody fusion cage or spacer, to block the vertebral segment and restore disc height. Unfortunately, in some cases this treatment can fail due to a loss in disc height as a result of subsidence, that is the sinking of the cage in the adjacent vertebrae. The investigation conducted in this thesis work focused on the effects of porosity of selective laser melted (SLM) implants and bone mineral density on subsidence, by means of a biomechanical study and a finite element model. In previous works, it was demonstrated that the most influential factor for the occurrence of subsidence is the condition of bone mineral density. Therefore, it was hypothesized that by using an implant with high porosity, the overall stiffness of the bone-implant system would decrease, as well as the stresses at the bone-implant interface, reducing the risk of subsidence and bone damage. At the same time, osseointegration would benefit due to the increased porosity, which is an important factor in the design of orthopaedic implants. The biomechanical study consisted of compression tests according to the standard ASTM-F2267 for subsidence evaluation in interbody fusion implants, according to which polyurethane foams were used to simulate the mechanical behaviour of trabecular bone. Cages designated for the cervical and lumbar regions of the spine were tested in two different porosities, in terms of apparent density of the cage, in combination with three foam densities, low-, medium- and high-density, corresponding respectively to low, average and above-average quality of bone. The results confirmed the findings in the literature and revealed significantly different outcomes when the foam density was changed, while the change in porosity did not affect the stiffness of the foam-implant system. The finite element model of a simplified cervical cage was used to explore the influence of the thickness of the solid frame in porous implants, revealing changes in stiffness of the simulations with the cages alone, while almost no stiffness variations were detected in the simulations for the implant-foam systems. Although the reduction of the stiffness of the system could not be achieved by tuning porosity, it was demonstrated that the mechanical performance of the system was not affected by an implant with higher porosity. These findings opened new research opportunities in the study of osseointegration, since it could be concluded that the use of implants with higher porosity would not affect the overall stiffness, while allowing more bone ingrowth to avoid cage migration.

When inserting a flexible endoscope into a human colon during colonoscopy, limitations in the endoscope design can cause medical implications such as excessive colon stretching and buckling of the endoscope shaft. This thesis proposes a novel propulsion mechanism design for flexible endoscopes which changes the method of insertion as a way to prevent these implications. As inspiration for the design an analogy is drawn between plant roots growing through tortuous cracks in soil and flexible endoscopes moving through a tortuous human colon. The analogy was found to be relevant, resulting in eight biological features of which seven were suitable as a potential solution in the development of a flexible endoscope. Of these seven suitable solutions, apical extension and variable stiffness were implemented as functions in the proposed propulsion mechanism. The focus of the design process on these two functions ultimately culminated in a proof of concept flexible, extending endoscope design dubbed the Flextendoscope. The Flextendoscope consists of an inverted tube mechanism which can propel the endoscope through apical extension combined with a fiber jamming mechanism that can vary the bending stiffness. The concept design is found very promising as it theoretically allows insertion of a highly compliant shaft which is also able to provide the high tip rigidity required at the surgical location after insertion. Although evaluation of the Flextendoscope prototype validated the feasibility of the proposed proof of concept design, the performance of the apical extension function was of a more limited success. Due to internal frictional resistances the prototype shaft only extended under the lowest evaluated pressure (0.5 bar) and required a high manual force (up to 119 N) to do so. The behavior of the variable stiffness function on the other hand was found to be very desirable. The bending stiffness of the prototype increased with internal pressure level as well as radial deflection, showing initial elastic deformation followed by hysteresis. It showed considerable stiffening at a convenient threshold pressure of 0.7 bar, slightly above the pressure at which the shaft is extended. Future iterations of the Flextendoscope design should focus on overcoming the internal frictional resistances that limit the apical extension of the current design. They can do so by multiplying the number of inverted tubes inside the shaft. This multiplication would enclose the sliding shaft material of each inverted tube within their own central lumen thus avoiding contact between the sliding shaft material and other stationary components in the design, preventing frictional interactions. If the frictional resistance is overcome the Flextendoscope design could prevent colon stretching during insertion of an flexible endoscope and inherently prevent shaft buckling. The prevention of these implications by the Flextendoscope design could ultimately lead to colonoscopy becoming an easier, safer and less painful procedure with a higher success rate.

The treatment of largy bone defect remains challenging in clinics. All the clinically available bone grafts have their own limitations and are not ideal for the treatment. Therefore, developing a new generation of suitable bone substitutes is urgently needed. In the recent years, porous magnesium (Mg) has been extensively studied for orthopedic applications owing to its biodegradability, favorable mechanical properties, and osteopromotive ability. The recent advances in additive manufacturing (AM) provide unprecedented opportunities to design and fabricate porous Mg scaffolds with interconnected porous structures that are favorable for the adhesion and proliferation of bone cells. However, powder bed fusion AM, which is the most commonly used AM technique for fabricating metal structures, has encountered many difficulties in manufacturing Mg due to safety concerns, excessive oxidation, and undesirable compositional variation due to the low boiling temperature of Mg. To alleviate these difficulties, alternative AM techniques that can create highly porous structures at room temperature are highly sought after. The aim of this research was to develop a room-temperature AM technique for manufacturing porous Mg and to characterize the fabricated Mg-based scaffolds in different aspects relevant to their potential applications as bone implants. In this thesis work, we, for the first time, successfully employed extrusion-based 3D printing techniques to fabricate biodegradable porous Mg and Mg-based scaffolds for application in orthopedics. We started with the optimization of the formulated binder system, the printing process, and the subsequent liquid-phase sintering process for the AM of Mg and Mg-based scaffolds. On this basis, a series of Mg and Mg-based porous scaffolds, including Mg alloy and Mg matrix composite scaffolds were successfully fabricated. Then, we conducted comprehensive studies on the microstructure, geometrical characteristics, in vitro biodegradation behavior, mechanical properties, and the in vitro biodegradation and the responses of preosteoblast MC3T3-E1 cells to the fabricated scaffolds to evaluate the ability of the fabricated scaffolds to satisfy the requirements of ideal bone-substituting biomaterials. By modifying the alloy composition and adding bioceramic components, the properties of the Mg scaffolds required were significantly improved as compared to those of the pure Mg specimens. The fabricated Mg-matrix composite scaffolds were shown to be the most promising materials to be further developed for bone substitution. Surface modification could also contribute to bringing the fabricated Mg scaffolds closer to meeting the requirements. Therefore, with proper material design and surface modification, the Mg-based scaffolds fabricated using extrusion-based 3D printing technique constitute a new category of porous Mg-based biomaterials that hold great promise for application as bone substitutes.@en

Introduction: Amputees still experience problems with the use of their upper limb prostheses, mainly in the lack of comfort and functionality. This results in rejection of the prosthesis or overuse injuries due to compensatory movements. The comfort and functionality should be improved by reducing weight and increasing the degrees of freedom. The wrist is an important joint for increasing the mobility. And for reducing the weight, another actuation method than the most available and heavy electrically driven device should be used. Methods: This study designs a hydraulic curved cylinder for the application of a wrist joint. Because of the complex and curved shape the manufacturing method used is 3D printing. The functionality of three 3D printing methods (FDM, MJF and SLA) and three sealing techniques (O-ring, X-ring, and Conus) will be evaluated by testing the amount of friction and leakage to find which configuration performs best and whether it results in an efficient actuator. Results: The SLA-cylinders and the Conus allowed the least leakage. The combination of these two even resulted in zero leakage. For friction the SLA and FDM-cylinders performed equally, only the MJF-cylinder caused more friction. The SLAcylinder is the only cylinder that can hold a constant pressure without leakage for 5 out of 8 pistons, when a 4 kg weight is attached. Finally, only piston-cylinder combinations with piston O-25 or Cylinder X.MJF do not match the requirements for the maximum allowed leakage and adjustment torque. Conclusions: The piston-cylinder combination of SLA-parts and Conus perform the best. For the application of a wrist joint in prostheses more research needed for the repeatability, scalability and long-term performance.

Currently, measuring wear of the insert of knee implants can only be accurately done in vitro. There are yet no accurate in vivo techniques that can capture and deliver data in real time. Therefore, the main objective of the research reported in this thesis was to introduce and validate a polyethylene insert with integrated wear sensors into knee implants that could be used in vivo after total knee replacement surgery. The instrumented insert was expected to help physicians and patients to acquire accurate wear information about the knee implant for an objective outcome evaluation of the intervention and to help to prevent excessive implant deterioration over time. A mechanical test setup with different parts of a knee implant was built. First, the positions where the highest forces would act on the implants, were determined by integrating resistance sensors in the test setup. The results of this test were used to determine the positions of the wear sensors, since the tibiofemoral forces correlate with the amount of the wear of the insert. Then, the insert with integrated wear sensors was produced by filling six cutouts in the insert with silver conductive paint and creating six tracks in three different layers. When the resistance of the track would be infinite, the track should be worn-out. This prototype was tested in the same test setup. The resistance values of the conductive tracks were measured to range from 40.3 to 128.4 Ω. After 6732 and 9974 cycles, the highest track on the medial and lateral sides, respectively, became damaged by the moving femoral head. The resistance of the tracks rose immediately to be infinite. Measuring the wear track with a caliper gave a value of 0.65 mms, which was deeper than the pre-determined track depth. The following tracks gave similar results. One of the limitations of the present study concerned the movement of the knee. Since the test setup was only made of a hinge, it could not be compared with a whole knee movement that also contains translation. Thereby was the prototype only suited for in vitro tests due to the materials choice and lack of a data transmitter. Since the prototype was made by hand, the layer thickness could not exceed the minimum of 0.6 mm and were the layers glued on each other. This made the wear measuring method not as accurate as wished. Nevertheless, the wear pattern corresponded well with the expected wear caused by the tibiofemoral forces. All in all, the insert with integrated silver conductive tracks is a concept that can be translated into a good solution to measuring wear in vivo in the near future. For the further development of this concept, the insert should be printed completely on a 3D printer. Thereby, more research should be performed on materials that could be used as conductive tracks, the possibilities to integrate more wear sensors to measure wear more accurately and the transmission of signals.

Many manufacturing industries have been impacted by the innovation of additive manufacturing (AM), and biomaterials manufacturing is no exception. One group of biomaterials impacted by the innovation of 3D printing are degradable biomaterials. Degradable biomaterials could eliminate the need for surgery to remove the implant. 3D printed porous degradable biomaterials provide both mechanical support and space for bone ingrowth. As of today, there is an absence of materials for this application that are biodegradable, biocompatible and can be 3D printed. Magnesium can be used as a degradable biomaterial but its corrosion resistance is not yet adequate for application in the human body. Applying zinc as an alloying element to magnesium increases its corrosion resistance compared to pure magnesium. As the addition of alloying elements changes the microstructure, which in turn changes its corrosion behaviour. This thesis analysed the effect of microstructure on the corrosion behaviour of extrusion-based 3D printed porous Mg-4Zn (wt.%) scaffolds, using localised electrochemical techniques i.e. scanning Kelvin probe force microscopy (SKPFM) and scanning electrochemical microscopy (SECM). The microstructure of the Mg-4Zn scaffolds includes grains with secondary phases precipitated along the grain boundaries with the presence of micropores. The secondary phase particles showed increased Volta-potential compared to the magnesium-based matrix. Therefore, the addition of zinc caused micro-galvanic coupling between secondary phase particles and the matrix, but their contribution to corrosion is minimal due to postponed contact with the electrolyte and the protection by the corrosion products. Micropores in the Mg-4Zn scaffold increased the surface exposed to fluids and were pitting corrosion initiation sites. During corrosion however, the surface was covered with a more stable corrosion product compared to pure magnesium. As a result of this, the corrosion resistance of Mg-4Zn scaffolds is better than pure magnesium scaffolds.