Designing robotic systems such as quadrupeds is challenging due to the intricate relationship between motion and design, particularly when aiming to replicate the agility, efficiency, and versatility of animals. Co-design simplifies robotic development by simultaneously optimizing physical design and control algorithms in an integrated way. While most prior work validates co-design approaches in simulation, our research bridges this gap by transitioning optimized designs to real-world implementation. To achieve this, we developed a modular quadruped platform with bio-inspired legs that enables the physical implementation of the optimized designs. Our design space, which includes leg segment lengths, spring stiffness, and engagement angle, was optimized to maximize energy efficiency for real-world tasks. We propose a simplified learning-based co-design framework that combines reinforcement learning to create a universal locomotion controller with Bayesian optimization to select the best design. Real-world tests demonstrate a significant reduction in the cost of transport—18.6% for inspection tasks and 35.7% for payload tasks—compared to the nominal design without springs. In simulations, the universal controller adapts well across robot configurations, and the optimization process remains consistent across runs. Although some discrepancies between simulation and real-world performance remain, our findings underscore the potential of co-design to address complex trade-offs in real-world robotic system design.

As virtual technology rapidly advances globally, the integration of the sense of touch into virtual environments to enhance realism is becoming increasingly urgent, drawing significant attention from scientists and researchers. This has led to the development of innovative haptic devices designed to replicate tactile sensations, further immersing users in virtual experiences. However, despite significant research in this field, most of the current haptic devices appear to lack the ability to provide direct, flexible, and natural interactions. To address these challenges, this study introduces the FlexCube, a novel flexible multimodal haptic display capable of delivering three tactile sensations: softness, roughness, and temperature. The FlexCube is developed through the creation of two modules—a hydraulic-actuated module for temperature and contact area rendering and a roughness module using the electrovibration effect. Then, they are combined together and integrated with an available stiffness rendering device into one device - the complete FlexCube. Subsequent experiments were conducted to evaluate the performance and behavior of each module individually. The results demonstrate that the FlexCube is capable of rendering a step profile and real texture’s temperature profile, tracking a sinusoid contact area profile of 0.2 Hz with neglectable delay, and able to deliver salient roughness sensations with the maximum generated electrovibration force of 0.028N regardless of the possible surface deformation. Overall, the FlexCube can simultaneously deliver all the expected tactile sensations and appears to be a promising tool for applications in E-commerce, telepresence, and interactive simulations.

Background: Ischemic stroke is a major cause of death worldwide. Atherosclerosis in the carotid arteries is an established predictor of these events. Ideally, patient-specific prevention plans can be developed that target advanced plaque development prior to events. Morphometry of advanced calcified plaque phenotypes can be assessed through Computed Tomography Angiography (CTA) but predicting progression on morphometry alone is insufficient as atherosclerosis is nonlinear and heterogeneous. Therefore, it was hypothesized that biomechanical triggers stimulate advanced plaque growth. The biomechanical response can be observed through structural stress and strain in the vessel wall as a response to plaque composition, blood pressure and tethering. So, the research aim of this study is to develop a framework that allows for local and global assessment of structural biomechanical stimuli and morphometrical changes in atherosclerotic carotid arteries

Methods Nine CTA scans paired at baseline and follow-up were selected from the Plaque At RISK study. The carotid bifurcation at the cervical spine was segmented by two independent observers using QAngioCT (Medis Medical Imaging, Leiden, The Netherlands). Contour data was reconstructed into a 3D geometry using a two-phase developed method in which 3D surface was computed first, and the second phase converted this to volumetric parts. Finite Element (FE) models were developed for baseline geometries where Neo-Hookean for calcified and Holzapfel-Gasser-Ogden for non-calcified materials were assigned.
For both timepoints, local morphometry was defined in wall thickness (WT), principal curvatures and calcium localization. Contour maps allowed the local association analysis between biomechanics and morphometry. Global plaque progression was computed using the morphometrical parameters and overall plaque burden (PB).


Results: This pipeline was successfully run for nine different carotid arteries, which proved overall robustness. The Dice similarity index computed an average segmentation observer similarity of 0.80 (St. Dev. 0.06) and 0.87 (St. Dev. 0.07) for surface reconstruction. Throughout reconstruction, the FE-modeling set the requirements for reconstruction outcome thus the focus was laid on connecting these phases. No patient data was made available during this study, so standardized systolic blood pressure resulted in an average maximum stress of 269.07 kPa and 0.14 strain.
Morphometrical analysis detected diseased WT in seven out of nine cases at baseline and all at follow-up. Local principal curvatures uncovered a relation with diseased thickening, indicating its success in detection of irregularities on a surface. Calcified tissue was found in all cases but one at baseline. The average morphometrical change increased 2.71 mm (St. Dev. 7.86 mm) in maximum WT, 0.69 % (St. Dev. 5.75 %) for maximum PB and 12.91 mm³ (St. Dev. 12.50 mm³) for calcium. These preliminary results highlighted the importance of multicomponent morphometry analysis. Moreover, correlations between calcium growth and stress (R² = 0.33) and WT increase (R² = 0.67) indicate that future studies should focus on comprehending atherosclerotic pathways involved in calcified plaque formation.

Conclusion: This developed method has laid the groundwork for future research and exposed important relations between analysis methods. The close dependency between reconstruction and FE-modeling, and anatomy and biomechanics emphasize that there is still a lot to discover.

Current membrane fabrication processes are not sustainable as they are energy-intensive and require hazardous solvents. Additive manufacturing, due to its low waste production and the absence of harmful chemicals, can provide a more sustainable membrane manufacturing process. Up to this point, there was no way to 3D-print a membrane that meets the microfiltration pore sizes (1-10 μm) required in today’s industry. In this work, we showcase for the first time that membrane with pore size < 10 μm can be 3D-printed via a dual wavelength 3D printer. Polyethylene Glycol Diacrylate (PEGDA) hydrophilic membranes with cylindrical pores were designed and printed.

A dual-wavelength micro-stereolithography 3D printer has been employed to print the membranes. Photopolymerizable resins containing PEGDA monomers, were polymerized into membranes via a mixed projection of UV and blue light, creating unpolymerized pores and polymerized matrix respectively.

Using a pixel size of 1.4 μm, we could produce hydrophilic membranes with cylindrical pores and a diameter < 10 μm. These membranes were compared with benchmarking commercial PTFE membranes (JCWP14225, Merck, Germany) with the same pore size range. The resulting membranes exhibited good oil-repellent properties, indicated by the higher oil contact angle values under water. The permeability and filtration results also provide valuable insights into the material used for membrane printing. All in all, a successful microfiltration membrane has been produced via a fast, user-friendly and sustainable method.

We have introduced the next-generation 3D printing method for printing microfiltration membranes with precise pore size, shape, configuration, and arrangement. With further improvements, this technology will provide a new era in membrane manufacturing.

Stroke, currently ranked as the second leading cause of mortality and the most prevalent source of enduring disability, imposes significant societal and economic consequences. These consequences encompass the necessity for extended care, rehabilitation, and the economic burdens associated with lost productivity. In the diagnostic process, physicians typically employ imaging techniques to assess cerebral blood vessels, ruling out alternative conditions when stroke is suspected. Subsequent to di agnosis, treatments like Intravenous Thrombolysis (IVT) and Endovascular Thrombectomy (EVT) are administered to either dissolve or retrieve thrombi. However, with EVT emerging as the new standard of stroke care and an increasing body of evidence indicating the substantial impact of thrombus me chanical properties on thrombectomy success, the use of clot analogues is gaining prominence as a means of facilitating efficient mechanical testing, both in terms of time and finances. By establishing a link between mechanical properties and image characteristic parameters, medical practitioners gain a better understanding of intracranial thrombi before embarking on surgical procedures. This knowledge can serve as a theoretical foundation for optimizing surgical instruments and devising effective surgical protocols in the future. In pursuit of these objectives, this study involved 29 patients and entailed several key steps: firstly, the extraction of imaging parameters from pre-EVT CT images; secondly, the creation of thrombus analogues from the patient’s blood; thirdly, the execution of five distinct mechanical tests to derive me chanical properties, encompassing cyclic compression, compression relaxation, tensile test to failure, tensile relaxation, and fracture testing. Additionally, the hyperelastic Yeoh model was utilized to simu late the behavior observed from cyclic compression and tensile to failure test. Prony series (n=2) was fitted to stress relaxation curves. In summary, this investigation revealed noteworthy observations pertaining to mechanical proper ties. Notably, hysteresis areas demonstrated robust and statistically significant correlations with com pression high-strain stiffness, low-strain stiffness, and tensile stiffness along with the ultimate tensile stress, implying that the thrombus analogue exhibits both hyperelastic and viscoelastic characteristics. In the domain of imaging parameters, the evident interdependence among the densities of the three regions of interest within both CTA and NCCT is apparent, respectively. However, it is essential to un derscore that the relationship between CTA and NCCT was not deemed statistically significant. Lastly, a noteworthy revelation was the strong negative monotonic correlation (ρ=-0.82, P=0.011) observed between the analogue contraction ratio of the thrombus analogue and the density of the middle part of NCCT in actual thrombi. This insight suggests that, in addition to thrombus composition, microstructure plays a pivotal role as well in determining their properties.

Atherosclerosis is an arterial condition characterized by the accumulation mainly of lipid tissue, resulting in the narrowing and stiffening of arteries. It is the leading cause of death among cardiovascular diseases and its development has been associated with wall shear (WSS) and wall mechanical stress (WMS). This study aimed to analyse WSS and WMS with two morphometric measurements, serving as indicators of the initiation and progression of atherosclerosis. 30 coronary arteries from 10 adult familial hypercholesterolaemic pigs fed a high-fat diet were imaged at 3 time points, using intravascular ultrasound and optical coherence tomography. Two-dimensional geometries of the arteries and their lipid components, in combination with their arterial pressure, were used to calculate WMS both at T1 and T2. WSS data was obtained at T1 and T2 by combining the 3D geometry of the arterial lumen and local flow velocity measurements. Arteries were segmented into 3 mm length and 45° sectors for analysis. It was observed that atherosclerosis developed in response to a high-fat diet, evidenced by a gradual increase in wall thickness over time even in the absence of lipidic components. Areas with thicker walls were predominantly found in regions exposed to low WSS and low WMS. Additionally, low WSS was found to promote atherosclerosis initiation and progression whereas high WMS appeared to support atherosclerosis progression. Throughout all time points, it was observed that WSS had a higher contribution to the development of atherosclerosis compared to WMS.

Vitrectomy is an often performed procedure during eye surgery and requires a high-precision vitreous cutter. The production of these precise and lightweight vitreous cutters sets high demands on the manufacturing process. Trained technicians must assemble the device step by step and continuously check and validate the manufacturing process. Additive manufacturing on the contrary allows for non-assembly mechanisms that can be printed at once without requiring any post-assembling steps. However, a high-speed vitreous cutter design suitable for 3D Printing is not yet presented. This research aimed to deliver a 3D Printed driving mechanism design for a high-speed reciprocating needle used during vitrectomy that does not require post assembly steps from trained technicians. It was established that the driving mechanism should reciprocate two concentric needles by air pressure to cut vitreous. Currently used actuators are investigated and a prior attempt for a non-assembly vitreous cutter is analysed. The diaphragm and bellow-based design were considered a potential solution path. A suitable design for both potential solution paths is made. The bellow design consists of an inner and outer bellow to allow the passage of the needle. The diaphragm concept is already used for the first and only attempt to produce a non-assembly vitreous cutter. This prior attempt is further analysed and it became clear the damping of the diaphragm needed to be decreased to increase the speed of the backward motion. Therefore, a planar spring is added to the dual flat diaphragm design. Finally, the spring-reinforced dual flat diaphragm concept is selected for continuation and tested by using PolyJet prototypes. Tests are executed to determine if the requirements could be met, especially focussing on the speed and force requirements. Different spring shapes and thicknesses are tested. It became clear that the behaviour of the spring-reinforced diaphragms is suboptimal. The return time is higher than preferred and damping is still present in a large extent due to hysteresis. To improve the design it was decided to continue with tests where the start position is relocated to form a pretension and overcome the damping seen especially at the last part of the return stroke. Pretension appeared successful and showed a 98% decrease in return time, but the requirements for the speed could not be obtained. Altering the thickness of the spring led to a sufficient high backward force but did not show direct influence on the speed of the backward motion. Overall, a non-assembly vitreous cutter driving mechanism is made but not all requirements could be met. Exploring design directions which do have some drawbacks should be considered to offer a solution in the near future. Designing a driving mechanism that also requires 3D Printed flexible material, first requires a thoroughly material investigation to identify the mechanical properties and time-dependent behaviour such that a trustworthy design optimization can be made. However, a design for a non-assembly high-speed vitreous cutter is made and with the upcoming developments in the 3D Printing techniques and materials the design might form the basis of a high-speed vitreous cutter. This research tested the most ideal case and gave further insight bringing us a step closer towards a non-assembly high-speed vitreous cutter.

The current standard for organ-on-chip substrate materials is polydimethylsiloxane (PDMS). PDMS has many beneficial properties such as biocompatibility, transparency, elasticity, and easy prototyping. The main disadvantages of PDMS are its hydrophobicity (reducing cell attachment and cell proliferation), quick hydrophobic recovery (within a few hours) after surface modification, and unselective absorption of small molecules, altering drug concentration during testing or causing cross-contamination between channels. To overcome these shortcomings, an alternative material lacking the disadvantages and retaining the advantages of PDMS is needed in the field. Ostemer 324, Ostemer 220 and a variation of PDMS (PDMS+) were characterized to determine whether they would be a suitable alternative to PDMS as substrate material. The materials were compared to PDMS and characterized for spin-coating and curing on silicon wafers, moulding, etching, surface wettability before and after surface modification (plasma treatment), stiffness, optical transparency, biocompatibility and absorption of small molecules. The results of this work show that Ostemer 324 appears to be a promising alternative, with similar characteristics to PDMS. The main advantage is its hydrophilic surface, which becomes even more hydrophilic after plasma treatment, and slow hydrophobic recovery rate. However, its curing time is longer, the material is stiffer and not easy to mould. Ostemer 220 shows very poor adhesion on Teflon coated silicon wafers, is hard to mould, and shows inconsistent results during biocompatibility testing. PDMS+ is very similar to PDMS, and improves upon the latter in terms of surface wettability after surface modification, hydrophobic recovery and small molecule absorption.

An acute ischemic stroke is one of the leading causes of death and is caused by a thrombus that occludes a cerebral artery. This thrombus reduces the cerebral blood flow and causes irreversible brain tissue damage. Mechanical thrombectomy is a safe and effective technique to remove the thrombus from the cerebral arteries and restore the brain's blood flow. The mechanical properties of the thrombus highly influence the success rate of mechanical thrombectomy. To investigate the mechanical behavior of the thrombus under different loading conditions, numerical simulations could be performed. The aim of this thesis is to develop an in silico thrombus model to investigate the mechanical behavior of the thrombus under compressive and tensile loading conditions using finite element analysis software LS-DYNA. Experimental data collected from the lab is used to describe the mechanical behavior in the numerical thrombus models.

The building process of the in silico models in this study is organized in three parts. Part one is the cube model, where the material properties and numerical stable settings are investigated. Also, a combination of compression and tension is applied to the cube model to capture both the compressive and tensile forces present during mechanical thrombectomy. Part two includes geometry models that mimic the clot analog samples' geometry used during the experimental compression and tensile tests. Part three includes a clot analog with an initial hole in the middle to understand the fracture behavior of the thrombus. Different approaches to model fracture of the thrombus are investigated.

Three different parts characterize this thesis, and each includes a method, results, and discussion section. The discussion section of each part is dedicated to the decisions that have been made in that specific chapter. A discussion section is also included in the chapter Experiments. The general discussion at the end of this study will include the findings of each model and the comparison with literature. Recommendations for further research are given at the end.

In conclusion, this study provides a framework for modeling the thrombus under tensile and compressive loading, where the thrombus is modeled as a hyperelastic material. Future work is advised to extend and improve the models developed in this study.

A broad range of bistable, multi-stable and neutrally stable compliant mechanisms have been developed over the years. These non-monostable systems show great potential for deployment in e.g. the medical, the manufacturing and the precision industry. Often the presence of prestress is a requirement for obtaining non-monostability within the realm of compliant mechanisms. This prestress is for example a strict necessity for neutrally stable behaviour, but also various types of bistable systems need it for correct operation. Systematic methods to induce prestress to these mechanisms do not yet exist. Currently, the application of prestress is most often achieved by manual assembly steps. The manual nature of these assembly steps poses problems onto the dimensional scalability, the production scalability and the design freedom of these mechanisms. In this research the possibilities of imposing prestress onto compliant mechanisms during their fabrication, solely by utilizing inherent features of the manufacturing method, are explored. With such a technique at hand, an accurate, scalable and tailorable method for prestressing is obtained. In this work the fused filament fabrication technique is used to create PLA monostable compliant mechanisms. By making use of the heat-induced shrinkage property of PLA, a distributed and variable material shrinkage field can be acquired. By the virtue of this variable shrinkage, elements within the system can selectively be prestressed. Results show that the mechanical stability behaviour of a demonstrator mechanism can permanently be changed from monostable to bistable. The influence of various design parameters on the shrinkage yield and the force-delivering potential of PLA is examined to tailor and maximize both factors. The result of this work provides the onset for the further creation of multi and neutrally stable compliant mechanisms in a systematic way.

Origami structures are found in mechanical technology more and more often. A less strict derivative of origami are Hinging Rigid Panel Structures, which are not bound to be developable from a single flat sheet of planar material. These Hinging Rigid Panel Structures can be applied to many fields of mechanical design, and moreover are interesting for their kinematic behaviour. The benefits of using a structure that originates from pieces of flat material include but are not limited to being able to surface treat uninterrupted sections of material that can subsequently be folded into part of the structure’s configuration. In order to describe and programmatically manipulate Hinging Rigid Panel Structures and their kinematics adequately and systematically, this research takes a new and specific approach on modelling them. The Hinging Rigid Panel Structures are modelled as 1-DOF mechanisms, consisting of a base pyramid, to which 2 arms of a variable amount of pairs of triangles are attached. To sufficiently test the versatility of this method of describing Hinging Rigid Panel Structures, a classification has been set up to cover a range of kinematic input-output relations, which will be used to test algorithms against. This classification differentiates by dimension and displacement distribution over both the input and output curves, and captures all kinematic transmissions in 1545 cases. With a sample size of np = 10 randomly generated versions of each of these input-output relations and a motion path resolution of rc = 25, a data set was generated using this classification method. An evolutionary algorithm was created to navigate the solution space more efficiently than using conventional algorithms like (gradient based) hill climber algorithms. The main variables of the evolutionary algorithm like generation size (sg = 60), amount of generations (ng = 75), mutation rate amount (nm = 180) and parent splicing methods have empirically been determined. Running the optimisation for all the categories of the previously mentioned classification was done by adapting the code to be able to be run in crowd computational capacity across 17 contributors’ computers. The results show that Hinging Rigid Panel Structure mechanisms are to a certain extend able to be synthesised to generate requested transmissions, but some cases are harder to reach than others. Complex compound 3D paths are harder to optimise for than other categories, such as planar circular motions. This research lays out a valuable basis that contains all aspects to create a reasonable performing optimiser for 3-D Hinging Rigid Panel Structures that follow requested input-output relations. This research could for example be used as a starting point for developing a software package that allows designers to implement Hinging Rigid Panel Structures in their CAD designs for mechanical transmissions.

Background Pneumatic actuators are widely used in applications like (medical) robots, or prosthetics. They require tight tolerances to keep them leakage-free. Over the last decade 3D-printing, or additive manufacturing, has emerged as a cost-effective production method in these applications.
Objective The goal of this research is to study the possibility of creating a pneumatic linear actuator with additive manufacturing. The focus is on finding sealing mechanisms which can have a positive influence on preventing leakage and friction force in the 3D-printed actuator. Furthermore we aimed to use the advantage of 3D-printing to create pneumatic actuators with a non-circular cross-section.
Methodology To evaluate the performance of a 3D-printed pneumatic actuator, a test setup is designed to measure the leakage and sliding friction force. Furthermore, we designed two pneumatic actuators with a non-conventional cross-sectional shape and validated their performance.
Results The choice for the optimal sealing mechanism in 3D-printed pneumatic actuators depends on the application in mind. For low-pressure situations the single-acting cup-shaped NAPN sealing is recommended, with a measured friction force of 6.7 N at a pressure of 0.1 MPa for one entire movement cycle (extending and retracting stroke together). For high pressure situations the double acting KDN sealing shows the lowest friction force while remaining leakage-free (13.5 N for the entire stroke at a pressure of 0.7 MPa). Furthermore, we have proven it possible to print pneumatic cylinders with a non-cylindrical cross section.
Conclusion We demonstrated a method to create leakage-free pneumatic linear actuators with additive manufacturing. For low pressure applications we showed first steps towards 3D-printed pneumatic actuators with non-circular cross-section of the piston, allowing more design freedom for these actuators.

Two major challenges in the field of agriculture are the need for increases in food production due to the ever-increasing world population and simultaneously climate change caused by global warming. The increasing world population requires more food, and the food needs to be of a higher standard. Currently, the increase and high quality food production by farming are becoming difficult due to more inconsistency of the climate. Plant breed companies use old-fashioned science in their attempts to overcome the agriculture challenges. For plant breeding, multiple plants are combined to develop a plant crop with desired characteristics that can withstand to the environmental challenges, produce high quality crops and provide the production volumes according to the required specifications. If such a crop is developed using breeding, a batch of plant seeds will be produced to sell the plant seeds all over the world. Two main problems do come from breeding and production of these newly developed crops, firstly breeders need information about the plants for efficient plant breeding, and secondly, the quality of the produced plant seeds has to be ensured. The quality of the plant seeds is an important factor to sell the produced plant seeds over the world to growers and farmers. To ensure the quality of the seeds, phenotype experts obtain the information and perform quality assessments of the seeds and grown plants. To obtain information on plants, the experts use plant phenotyping in which the characteristics of the plant are described and evaluated. The evaluation of the plant characteristics provides a quality assessment of the batch of produced plant seeds. The quality assessment is done by growing the plant seed to seedlings and compare the grown seedlings with each other. The visual comparison between the seedlings is used to give a quality label to the produced batch of seeds. At the moment this visualization and subjective comparison of seedlings is the state of the art. Experts did not believe it is possible to assess the seedlings otherwise. To move away from the subjective approach, Rijk Zwaan BV is looking into more objective measurement systems to obtain plant information. The objective plant information of the seedlings provides solutions of objectively assessing quality and inform plant breeders with extra information making the plant breeding process more efficient. In this study, the feasibility of a digital phenotyping system able to give plant information and a quality assessment of the seedlings was examined. To show the possibilities of the system a model of a digital seedling quality system was developed. By applying the literature of plant phenotyping systems, a phenotype and quality assessment data pipeline were established. The data pipeline was developed to be understandable and transparent for the experts to ensure acceptance of a digital system. The plant phenotype pipeline consists out of multiple components. Each component of the plant phenotype data pipeline has been developed to form the seedling quality system model. The developed model is called SeeQS (Seedling Quality System) and is able to seek out the quality of the seedlings and provide phenotype information of the seedlings. SeeQS was evaluated using multiple samples of pepper seedlings to show the performance and capabilities of a digital phenotyping-based quality system. The system performance shows to be very capable and accurate to assess the quality of seedlings and give plant measurements. The model shows that it is possible to assess the quality of seedlings using a digital phenotyping-based system. Due to the transparency of the developed model, the experts understand the versatility of the digital system. Now, the phenotype experts accept the possibility of a digital system to obtain plant information and give a quality assessment. Due to these positive results, the company wants to continue with the development and implementation of a digital seedling quality and phenotyping system.

Functional gradients in hard-soft interfaces are abundant in nature, and we often mimic them to create strong and tough composites. A powerful tool for the designs and fabrication of biomimetic composites is voxel-based multi-material 3D printing. Earlier researches mainly focused on using this technique in the creation of gradients based on morphology. While this is a great way to create a gradient, the outcome material properties are often unknown. In this research, we attempted to create a gradient based on the desired outcome material properties rather than morphology. We created a linear gradient in density using a voxel-based 3D printing technique and tested it through nanoindentation. Furthermore, we created a Finite Element Model based on this sample. Out of the nanoindentation and Finite Element Model results, we extracted the b-value for a power-law function in the form of E(x)= E_h 〖ρ(x)〗^b+E_s. With the inverse of this power-law function, we designed three different gradients based on the desired material properties: a linear, stepwise, and sigmoid gradient. Nanoindentation experiments and Finite Element analyses showed that we achieved the desired outcome in material properties with our newly created approach of designing gradients. However, the nanoindentation experiments showed that using a machine suitable for the wide range of Young’s moduli present in these kinds of composites is crucial. To display the possible applications of our new approach, we designed a knee model with graded ligaments and tested it with a tensile test and digital image correlation. Results of these tests showed an energy before failure that was twice as high as its non-graded counterpart. Furthermore, with the introduction of the gradient, we achieved to change to loading condition on the ligaments. Overall, our results show that our new approach can create gradients based on material properties rather than morphology and opens many new doors in creating biomimetic composites.

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.

During a vitrectomy procedure vitreous is removed from the eye with a vitreous cutter, called a vitrectome. This instrument is comprised of two needles that move to cut the vitreous into small pieces before aspirating them. Vitreous cutters are complex instruments that are light and small in size to increase their accuracy. Because of their small size, and complexity, they are assembled by trained technicians with the help of a microscope. It is believed that new technologies such as additive manufacturing (AM) might be able to reduce the manufacturing complexity associated with vitreous cutters. The goal of this study was therefore; "To create a non-assembly driving mechanism for a vitreous cutter that is designed for AM". In order to achieve this goal, the functions of a vitreous cutter were identified, as well as the mechanisms that fulfil these functions in current instruments. Furthermore, the general limitations of AM were researched and listed. Extensive research was done to identify examples in the scientific literature to find linear actuators that were made by means of AM as an integrated assembly. A diaphragm actuator was selected to drive the mechanism based on the limitations of AM, the requirements, and examples found in the scientific literature. An in depth analysis of diaphragm driven vitreous cutters revealed that it would be a challenge to seal the air chamber of the instrument. A new concept was created that used one of the strengths of AM to solve this problem, by creating a compliant interface between the moving needle and the air chamber. A proof of principle prototype was created to quickly test if it would be possible to create movement by sealing the air chamber with differently sized diaphragms. Based on the concept of sealing an air chamber with flexible diaphragms, four concept variations were created.
It was decided to make a series of prototypes of one of these concept variations to study its performance. In total, 9 prototypes were manufactured using material jetting, out of Agilus30 and Vero, without the need of post-assembly. The prototypes were tested by applying a range of air pressure pulses, while measuring the force, the displacement, the actuation time, and the spring properties of the mechanism. With the successful manufacturing of the prototypes, it has been shown that it is possible to produce the novel driving mechanism using current AM techniques without any assembly steps other than the sealing of a cleaning hole to remove support material.  The tests revealed that the spring force of the mechanism was not linear for all materials, and that there was hysteresis present in the mechanism.  Furthermore, it was shown that none of the samples were capable of operating at the desired speed of 8000 pulses per minute (PPM). The soft samples were seen to have the best response time during the backward motion of the mechanism. A new driving mechanism was created in this study that utilized one of the strengths associated with AM. To the knowledge of the author this mechanism is the first of its kind, and has not been previously applied in another instrument. Additional knowledge on the material properties of digital materials is needed to be able to design a diaphragm mechanism that has the appropriate performance characteristics. With additional design efforts and research it could be possible to produce vitreous cutters using AM in a non-assembly manner. This could lead to a future where surgical instruments are manufactured on site and on demand.

Elastic neutral stability involves elastic deformation without stiffness or loads. It is a remarkable appearance, since the deformation of materials is normally associated with an increase of potential energy and a resulting opposing reaction force or moment. Neutrally stable mechanisms can be used to overcome unnecessary actuation which makes them an interesting topic for the aerospace industry, space exploration and the development of wearable assistive devices. This last group benefits from the use of spatially-curved thin-walled elastic structures, called compliant shell mechanisms. A literature review aims to give an overview of occurrences of elastic neutral stability and aims to find methods for creating neutrally stable compliant shell mechanisms. Single element mechanisms are herein further emphasized and a division between the application of pre-stress and the application of geometrical boundary conditions is proposed. So far, all neutrally stable (shell) mechanisms require either of the two conditions to be imposed. A new type of compliant shell structure, featuring a neutrally stable deformation mode without requiring one of the aforementioned conditions, is presented. The structure is composed of two initially flat compliant facets that are connected via a curved crease. It can be reconfigured into a second zero-energy state without apparent effort via propagation of a transition region. Both the structure’s local width and the local crease curvature turn out to be effective parameters for tuning the behavior regarding stability during transition. This structure shows potential for combining geometric simplicity with complex and highly tune-able behavior. However, its discontinuity obstructs physical realization. Therefore, a monolithic variant of this structure is investigated. The transition of a double-curved distributed compliant shell towards its second equilibrium configuration forms the basis of this investigation. A varying material thickness profile, described by an ideal set of design parameters, is obtained using an optimization procedure. Numerical analysis of the resulting optimized shell structure predicts a significant region of near-constant energy and associated near-zero loads within this unique deformation mode. Prototypes are manufactured using a 3D-printing process and demonstrate the validity of the modelled results by featuring a continuous equilibrium within a significant range of motion. These results lay the foundation for compliant beam elements with an internal statically balanced bending degree of freedom. Finally, a different deformation mode, involving crease actuation of the same type of structure, is examined. Curved creases are characterized by the coupled facet deformation upon actuation. The forces exerted by the facets can be used to oppose the effects of crease stiffness during actuation to achieve an overall stiffness decrease. An analytical approach, based on a combination of a pseudo-rigid-body model (PRBM) and plate theory, predicts the potential for constant-force actuation around its second stable, or ‘inverted’ state. The accuracy of the model is validated by numerical simulations. However, due to prototype inaccuracies, the experimental results do not feature the desired constant force behavior. Nevertheless, a stiffness decrease, or ‘softening’ is experienced, verifying the concept and marking a first step towards statically balanced curved creases.

This thesis contains the design process of a compliant shape adaptive chicory gripper for robotic sorting processes. The robotic sorting line consists of an input and output conveyor-belt. The input line contains unsorted chicories which are scanned by a robotic vision system. Overhead FlexPicker robots, equipped with chicory grippers, sort the chicories size by size onto the output line. The output line can contain a transportation crate or flowpack in which the chicories will be packed and shipped after sorting. Chicories are vulnerable for internal and external damages when touching the outer skin which makes robotic sorting difficult. The acceleration forces performed by the robot requires a strong but gentle grip on the chicory without any damaging marks. By designing a specific compliant shape adaptive gripper, sorting can be done faster, cheaper and more accurate than manual sorting. Current patents, academic literature or business applications had no solution for this chicory gripping problem. The design process for a suitable gripper started with an analysis of current patents and literature within compliant gripping in general. This provided insights in the the possibilities of compliant gripping. Based on the design requirements for the robot sorting setup, several concepts are obtained and selected. The concepts have been translated into four working gripper prototype layouts which are evaluated on force and damage requirements. Based on the results of these experiments, a first iteration prototype was made. Three additional optimizing iterations were needed to result in a prototype which reached the damage and force requirements. Further evaluation of this prototype proved a sufficient performance on robustness, endurance, operational speed and food grade requirements. The iteration 4 prototype reached therefore 17 of the total 19 gripper design requirements. To be able to accomplish the two remaining requirements, several recommendations are provided for a final gripper end product which is ready for industrial application.

The use of allografts for the treatment of critical size cartilage defects holds disadvantages including the limited number of donors and the compromised chondrocyte viability. These limitations have prompted researchers to explore different options, such as cartilage engineering. Bioprinting, a promising tissue engineering technique, could be used to fabricate biomimetic constructs that can potentially replace allografts. The present study explores the generation of a biomimetic chondrocyte density gradient in full-thickness bioprinted Alginate/NFC scaffolds with a PCL framework and investigates the effect of this zonal distribution of cells on the production of cartilage matrix within the scaffolds. To this end, two types of scaffolds were bioprinted; one with a graded three-zone distribution of cells (bottom zone: 5×106 cells/ml, middle zone: 10×106 cells/ml, top zone: 20×106 cells/ml), and another with a homogeneous cell density (10×106 cells/ml) and cultured for 25 days. Furthermore, the mechanical properties of the multi-material scaffolds were evaluated. The results showed that a three-zone cell density gradient could be achieved using extrusion-based bioprinting. The gradient was maintained for 25 days in scaffolds cultured in non-chondrogenic media (absence of ascorbic acid) but was transformed into a two-zone gradient within the first 14 days, in cultures with chondrogenic media (presence of ascorbic acid in the medium), and maintained as such until the end of the experiment. The zonal distribution of cells led to a zonal distribution of sGAGs, after 14 days of culture, with the sGAGs deposition being increased in the areas of high cell density. However, there was no significant Collagen deposition within the scaffolds at any time point during the experiment. This study attempts to shed light into one of the gradients of the native cartilage tissue (cell density gradient), with the hope of contributing to the development of a biomimetic fully functional engineered cartilage scaffold in the future.