Background and rationale
Total Disc Replacement (TDR) aims to replicate the rotational and translational qualities of the natural intervertebral disc (IVD), preserving motion and reducing the stress on adjacent segments [65], reducing Adjacent Segment Disease (ASD). While TDR offers a promising alternative to the current golden standard of spinal fusion, current designs exhibit limitations that compromise their effectiveness.

In this thesis, an improved design of a novel lumbar TDR design developed by Amber Implants BV was proposed and biomechanically tested in static and dynamic axial compression according to the standard ASTM F2346. Furthermore, an exploration of the performance of the design in grade 1 commercially pure titanium (CpTi) in contrast to the standard grade 23 Ti-6Al-4V was conducted to find out if CpTi is a suitable alternative to Ti-6Al-4V in orthopaedic applications for the IVD.

Experimental methods
Based on the design goal, an optimised design was proposed and compared to the original design by FEA. To test the performance of the new design against the original design, static and dynamic axial compression tests were executed according to the standard ASTMF2346. Five samples per design were tested until failure during static axial compression testing, with an acceptance
criterion of 5500 N. Dynamic axial compression was conducted with a maximum load of 3500 N (R=10), up to 2.5 million cycles, for three samples of each device.

Results
In static axial compression, all three designs passed according to the acceptance criterion, with yield loads of 5892.82 ± 140.8 for the original design, 17255.54 ± 3675.9 N for the new design in grade 23 titanium, and 7790.32 ± 1778.6 N for the new design in grade 1 titanium. The new design in grade 23 outperformed the other two designs (p<0.001). In dynamic axial compression, the new design in grade 23 was the only device to survive 2.5million cycles, without failure and a height decrease of only 0.5%. The original design failed after 60.000, 70.000 and 100.000 cycles, and the new design in grade 1 failed after 33.000 and 30.500 cycles.

Conclusion
The design goal was achieved, with varying degrees of evidence for the different facets
of the goal. In both static and dynamic axial compression, the new design in grade 23 outperformed the original design. It can also be concluded that, in the current configuration of the new design, grade 1 CpTi is not a suitable alternative for orthopaedic applications in the lumbar spine.
It must be noted that complications arose regarding the test set-up in both static and dynamic axial testing, compromising the reliability of the results.

Hip replacement surgery, also termed total hip arthroplasty, is a surgical intervention intended to substitute a deteriorated or dysfunctional hip joint with an artificial prosthesis. This procedure is commonly indicated for individuals experiencing severe hip discomfort resulting from conditions like osteoarthritis, rheumatoid arthritis, hip fractures, or other hip-related issues that significantly impair mobility.

Globally, more than 1 million total hip replacement surgeries are conducted annually. Given the substantial mechanical loads experienced by hip implants during regular activities, a thorough understanding and early identification of potential issues before implant failure are imperative. Continuous monitoring of strain is crucial to assess how the implant responds to various stresses over time. This monitoring aids in evaluating the implant’s durability and performance under diverse stress conditions, enabling proactive interventions, if necessary, to prevent critical failures.

Strain monitoring acts as a diagnostic tool to assess the implant’s status and the surrounding tissues. Deviations in strain patterns may signify problems such as implant loosening, wear, or bone loss around the implant. Moreover, this monitoring technique helps customize rehabilitation programs and recommend specific activities based on individual strain levels. Consequently, this tailored approach enhances recovery outcomes while mitigating associated risks.

This project involves the development of a passive wireless resonant circuit that will be used in the future in a sensor designed to detect strain on hip implants for early failure detection. The strain is anticipated to cause fluctuations in the frequency. To evaluate the LC (inductor-capacitor) resonator design at a specific frequency, a simulation model was established using the Computer Simulation Technology (CST) Microwave Studio as the simulation platform. The fabrication of this LC resonant circuit employs cleanroom techniques and protocols to ensure precision and reliability in its structure. Subsequent to fabrication, the resonator underwent characterization employing an antenna to ascertain resonance frequency alterations in accordance with theoretical expectations. The results indicated a detectable shift in resonant frequency corresponding to designs representing different strains.

The increase in the average human lifespan and the higher prevalence of extreme sports communities in the current society has led to an unfortunate increase in bone defect and fracture cases. Consequently, there is a growing demand for bone fracture therapy and technology. In the case of orthopaedic implants, research has been gradually inclining towards designing biodegradable, biologically integrative porous scaffolds, capable of providing a healthy environment for optimal bone regeneration. Moreover, by mimicking the interconnected porous structures of the natural bone matrix, these implants allow the flow of blood, oxygen and nutrients that are essential in the healing and maintenance of healthy osseous tissue. The gradual dissolution of the structure deems it a non-permanent implant, ultimately completely replaced by natural bone tissue. Pure Fe can offer suitable mechanical properties to support the applied loads of habitual human activities, however, it exhibits too slow biodegradation rates and fails to display satisfactory bone integrative characteristics. Fe-based bioceramic composites are reported to offer biocompatibility, biodegradation and mechanical properties ideal for bone substitution applications. Currently, additively manufactured (AM) Fe-bioceramic composites are one of the most promising material classes for biodegradable scaffold implants. This thesis investigates the extrusion-based AM Fe-akermanite (5 to 15 vol%) composite scaffolds. The fabrication method involved 3D printing printable Fe-akermanite inks followed by heat treatment in an inert environment. Static in vitro immersion testing was conducted to evaluate the degradation characteristics of the scaffolds. Furthermore, the as-sintered and degraded scaffolds were subjected to uniaxial compression testing to determine how the mechanical properties vary as the scaffold degrades. Cytotoxicity evaluations of the scaffolds were also conducted in the form of indirect and direct preosteoblast seeding and culture procedures. The addition of akermanite hastened the degradation rate, with the Fe-15 (vol%) akermanite scaffolds displaying the fastest degradation and most rapid formation of corrosion products containing bone-forming elements, e.g., Ca and P. The yield strength of the scaffolds decreased with increased akermanite content however remained within a suitable range even after degradation. Furthermore, the akermanite addition did not induce a shift towards brittle-like material behaviour. The scaffolds containing 15 vol% akermanite displayed superior cytocompatibility with preosteoblast cells. Therefore, Fe- akermanite composites exhibit great potential for use in biodegradable orthopaedic scaffold applications, with Fe-15 (vol%) akermanite displaying the most promising results.

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.

Back pain is a major economic problem that can dramatically affect the quality of life. There are many causes that can lead to back pain, but intervertebral disc (IVD) degeneration is a recognised cause. The harmful effect of whole-body vibration (WBV) environment on the human intervertebral disc has been demonstrated to have an increased relative risk of failure. One of the treatments for a degenerative disc is spinal fusion procedure, in which the human IVD is replaced by a spinal fusion cage. In this thesis, the influence of WBV on custom-made spinal fusion cages was investigated.
With the advent of additive manufacturing lattice-based scaffolds were designed as spinal fusion implants and manufactured using a Polyet 3D-printer. The influence of the unit cell design on the build quality and the quasi-static mechanical properties as well as the dynamic WBV reaction was observed. Therefore, four different unit cell types were designed: body-centered cube (BC-cube), face-centered cube (FX-cube), truncated octahedron (T-octa) and negative Poisson cube (NP-cube). The influence of 3D-printing direction and scaffold porosity on print quality and mechanical properties were also investigated.
The build quality was determined by measuring the nominal size, determining the beam diameter and using μCT. The quasi-static mechanical properties were determined with the compression test. The dynamic response to WBV was determined with a mechanical test setup that imitates a base excitation model. Two cylindrical bases were printed as one sample together with the scaffold. The bases were embedded and mounted in the testing cups. A constant sinusoidal displacement to the lower embedding cup was applied and the accelerations of the input and response were measured. The difference between the response and input was compared and observed at which frequency the sample broke or reached the highest gain. This was done for all samples and the influence of unit cell type, 3D-printing direction and porosity on the dynamic response was observed.
The direction of 3D-printing had the greatest influence on the build quality, while the type of unit cell and porosity had a less obvious influence.
The compression test provided insight into which unit cell types have a higher elastic modulus, that the 3D-printing direction perpendicular to the test direction achieved higher E values, and that higher porosity, which is desirable for implants, resulted in a lower Young's modulus.
In terms of the dynamic response, the results of this work indicate that the FX cube design is the most robust and would improve the safety of the implant when exposed to WBV.
For the 3D-printing direction, it may be concluded that the perpendicular direction, i.e. the layers are perpendicular to the test direction, can best withstand the dynamic forces. The increase in porosity from 50% to 70% showed a decrease in resistance to the dynamic loading, with scaffolds failing more often and at lower frequencies. Understanding how different designs and porosity of the spinal fusion scaffolds influence the resistance to WBV conditions will help to develop safe and resistant implants which replace degenerated natural IVD.

Back pain and back instability affect close to 80% of the population at some point during their life. One solution is to insert a spinal cage, which results in spinal fusion, meaning two vertebrae fuse together to create one big vertebra. This study focuses on the investigation of both the processing aspects as the design aspects of producing a functional spinal cage. The spinal cage investigated is made of 3D printed Ti6Al4V using selective laser melting (SLM). The original design showed some undesirable qualities, which are a higher apparent Young's modulus compared to the surrounding bone, causing stress shielding; and the creation of high stress concentrations due to the implant design, which reduces the fatigue life. A new design is created and tested using a combination of FEM software and mechanical testing. Comparing the new spinal cage to the original spinal cage it was found that the Young's modulus is 4 times lower; the yield strength 27% lower, but does not yield when a force of 4 kN is applied as required; and the fatigue life 2.2 times higher. Currently, implants are post treated using hot isostatic pressing (HIP), which is an expensive procedure. One of the objectives of this research is to investigate the effectiveness of a vacuum oven as an alternative heat treatment method. This is done with SLM 3D printed Ti6Al4V samples with a porosity of 59%, which are heat treated at 850 and 1050 degrees Celsius for 2 hours. When comparing the vacuum heat treatment performed at 1050 with 850 degrees Celsius, the alpha grain thickness is increased 2.8 times, the Young's modulus with 13% and the yield strength with 7%. The vacuum heat treatments increase the fatigue life with 20% due to the removal of residual stresses and the transformation of the 'alpha-martensite to an alpha + beta microstructure as is required. Between the two heat treatments no significant difference in fatigue life is found. Comparing the fatigue life of the vacuum heat treatments with HIP at 920 degrees Celsius for 2 hours, it was observed that at 10,000 cycles the fatigue life of HIP is 20% better and at 1,000,000 cycles 1% worse. The main difference between the heat treatments is the reduction of internal pore size after HIP. The internal porosity affects the fatigue life. However, the effect of internal porosity will reduce faster compared to the effect of surface quality resulting in a similar fatigue life at high cycle fatigue. For spinal cages high cycle fatigue is more interesting to look at. Finally, commercial spinal implants are universally designed based on the requirements and life-style of a 30 year old male. In order to improve the success-rate of spinal fusion, more patient-specific implants can be designed and produced using additive manufacturing. In this research five different patient specific groups are defined based on expected load and bone density. Using these requirements five different spinal cages are designed based on different porosities. Using FEM software the minimum apparent Young's modulus which can be achieved for every patient group is found. The apparent Young's modulus found for every group ranges between 1.40 and 3.17 GPa. Finally, the fatigue graph and apparent Young's modulus obtained from the mechanical tests are used to validate the simulation. The simulated fatigue life was around three times lower compared to the actual fatigue life and the apparent Young's modulus was 6.3% higher compared to the actual apparent Young's modulus. These findings are used to correct the simulations and the new apparent Young's modulus for every patient group lies between 1.32 and 2.98 GPa which is even closer to the Young's modulus of the surrounding bone.

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.

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.

Biodegradable materials such as polymers and magnesium and its alloys are gaining attention and approval for clinical use as osteosynthesis implants. However, polymers often lack the required mechanical strength and commercial Mg systems contain elements that are not naturally occurring in the body. Extra-high purity magnesium alloyed with 1 weight % zinc and 0.3 weight % calcium (ZX10) aims to confront these disadvantages to eventually emerge as an optimal material for fracture fixation.
In this thesis, ZX10 has been biomedically characterized using various tools to test its ability to function as a screw plate system in mandibular angle fractures. The material was analyzed after production using metallography techniques. Implants were designed and optimized using finite element techniques and mechanical tests were performed to compare strength against commercially available screw-plate Ti systems of the craniomaxillofacial (CMF) region. Cytotoxicity tests were undertaken to gain an insight into biocompatibility. All results indicate that ZX10 bone plate and screw can be designed within acceptable dimensions to match the flexural strength of a Ti plate in 4 point bending and a Ti screw in pull out tests. Cell cultures in 10 % concentrations of corrosion products show low cytotoxicity, 50 % concentrations show moderate cytotoxicity and 100 % concentrations of corrosion products show severe cytotoxicity. Viable cells were observed in the presence of the implant material.
With a corrosion rate of 1.08 mm/year in simulated body fluid, ZX10 behaves comparably to commercially available degradable systems such as the WE43 alloy and thus bespeaks further development and in vivo characterization to move towards clinical implementation.

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.

Although many studies have been performed on porous absorbable iron scaffolds created by the space holder method, no studies have considered the influence of variations in space holders on absorbable scaffolds. The present study aimed to clarify the effects of space holder particle size and volume fraction, on the pore structure, resultant mechanical properties and absorbability of iron scaffolds.
Spherical iron particles were used as the matrix powder and mixed with coarse and fine rectangular urea space holding particles in volume fractions of 20, 40 and 60%, to create six different scaffolds with the space holder method. Scanning electron microscopy and energy-dispersive X-ray spectroscopy were used to observe the scaffolds surface. Thereafter x-ray microtomography and Archimedes’ tests were used to characterize the scaffolds topology. The absorbability of scaffolds was characterized by potentiodynamic polarization measurements and weight loss measurements after 3 and 11 of days immersion in modified simulated body fluid (m-SBF). Mechanical properties were determined by performing diametral compression of the scaffolds, both before and after immersion in m-SBF. SEM images showed that morphology of the final pores was similar to that of space holder particles. Pores at lower porosities are isolated and become more connective or fully connected at higher porosities. Archimedes’ data showed that space holder fraction was directly related to porosity. Pore connectivity, measured by 휇CT, is higher for fine space holding particles. Until at 60% space holder volume fraction, the high amount of space holder particles agglomerated. Furthermore, it was observed that space holding particles had a large preference to move in a plane perpendicular to the applied compaction pressure. Diametral compression showed that increasing porosity resulted in lower yield strength and elastic modulus of scaffolds. The effects of space holder particle size and immersion time on mechanical properties were less pronounced. PDP measurements showed that the corrosion mechanism of scaffolds did not change due to change in space holder particle size or volume fraction. Weight loss measurements after 3 and 11 day immersion in m-SBF showed that increasing porosity resulted in higher weight loss of scaffolds. Weight loss was marginally affected by space holder particle size. Space holder particle size affected the created pore size and surface area yet also changed the pore connectivity. Similarly, the space holder volume fraction affected the created porosity and pore connectivity yet also changed the pore size and shape. This means that the pore structure not independently changes due to space holder particle size or fraction, but rather as a combination of both. Furthermore, in this study it was mainly the created porosity that influenced the mechanical properties and absorption rate of the scaffold. Space holder particle size did not show the same differentiating results, although this might be caused by agglomerating space holder particles and its dependency on volume fraction. Differentiating the created pore structure more and using a longer immersion time should be the next objectives in the determination of the effect of space holder particles on the performance of absorbable iron scaffolds for orthopedic applications.

Severe scoliosis is a deformity of the curvature of the spine, mostly occurring in children. It is currently treated by performing Halo Gravity Traction (HGT) to reduce the curvature prior to surgery. In this procedure, a Bremer halo ring is fitted around the child's head and connected to the skull with a numberof pins. During the 3-month treatment period, step-wise increased weight is applied to pull the ring upwards so as to elongate the spine. With the current design of the Bremer halo ring, the pins are tightened while measuring the amount of torque applied, influences each other during tightening, loosenover time and leave visible scars on the forehead. Furthermore, the Bremer halo ring is not customized.In the present project, a novel halo with a different tightening technique was designed, manufactured and evaluated with the aim of solving the above mentioned shortcomings of the Bremer halo.A Surface Tessellation Language (STL) file was generated from Computed Tomography (CT) images of a male cadaver head. Based on the desired ring stiffness and the geometry of a custom-designed halo for the cadaver head, a model was created in Solid Edge ST 10. The model was analyzed and adjustedby using the Finite Element Method (FEM). The customized halo ring was then produced by means of Selective Laser Sintering (SLS) and then equipped with strain gauges in order to derive the forces acting on the skull by the pins during tightening. The customized novel halo and the Bremer halo were compared with respect to moment arm and pin orientation, both influencing the local pin site behavior. The moment arms, pin positions and pin orientations of the 3D model of the novel halo were validated in reality by consecutive application of the halo to the cadaver head. The halo was analyzed by measuring the pin force degradation over a period of 24 h, which was hypothesized to be caused by the visco-elastic behavior of the skull of the cadaver head. The tightening procedure was analyzed on a block of steel to determine the influence on the axial pin reaction forces.The novel halo showed smaller and more consistent lengths of moment arm than the Bremer halo. Furthermore, one pin of the Bremer halo showed a difference of >15° from 90°, which has been regarded as contributor to pin loosening. The novel halo was predicted to be able to keep sufficient axial pin force without pin re-tightening during the traction period. The intended axial pin forces of the novel halo were achieved with an accuracy of 94.5%.With the customized novel halo, pins were tightened based on the displacement of the C-contours, resulting in an increased accuracy of pin force during tightening. The anterior pins were designed to be located in the musculus temporalis region, thereby leaving no visible scars and to be less prone to loosening due to a lower anterior ring stiffness. In conclusion, customizing the halo ring brings opportunities toengineer and control important parameters which contribute to better wearing comfort, higher pin force accuracy and less pin loosening, although it is yet a costly and time-consuming procedure.

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.