In the last two decades, it has been generally accepted that the interaction between bone and immune cells is critical in the process of bone healing and regeneration. Steering this immune response with the development of biomaterials could lead to implant acceptance in the long term. The understanding of osteoimmunological responses is of high importance in the development of new biomaterials. In order to validate these biomaterials, better in vitro techniques are required that could mimic this inflammatory response immediately after implantation in more detail. This study investigated the effect of a direct co-culture model on a prototype nanopattern. In addition the effect of microflows, that are normally present in vivo, induced inside a microfluidic chip, on mono and co-cultures was investigated in order to improve in vitro research. Static mono- and co-cultures with a 1:1 (CO11) and 1:2 (CO12) ratio of murine pre-osteoblasts MC3T3-E1s (OBs) and M1 stimulated murine Macrophages J774A.1 (+ LPS & IFN-gamma) were cultured under static conditions for 4 weeks to see the effect of co-culturing on inflammatory markers (TNF-alpha, PGE2, and IL-10) and osteogenic markers (ALP, Runx2 & Alizarin Red Staining). It was found that the use of a co-culture did not have a positive effect on OB differentiation. The introduction of a prototype nanopattern (500 nm height and 300 nm width) that induces a macrophage polarization shift towards an anti-inflammatory phenotype, did have a positive effect on Runx2 secretion in the co-cultures. Furthermore the effect of a dynamic flow, initiated 2 days after seeding, on osteogenic differentiation of OB and CO12 was investigated. After 7 days of dynamic culture, Runx2 levels of the mono-cultures were significantly higher than the static cultures. OBs were positively affected by forming dense cell layers throughout the entire microfluidic channel. For dynamic co-cultures, no to little cells were present inside the channel after 7 days. Finally we attempted to fabricate a microfluidic device that could "sandwich" the patterned waver inside, so the effect of both the nanopattern and microflow on mono- and co-cultures could be investigated. Cells were seeded inside the channel after 1 day, but unfortunately forces on the PMMA layer of this chip resulted in cracks and failure of this system. Our findings in the design and fabrication of the chip can help in future research towards the osteoimmunodulatory properties of biomaterials. The study on a direct co-culture model, presented in this work, opens possibilities for future research towards co-cultures inside microfluidic devices. It discusses the possibilities and the drawbacks of both the use of co-cultures as the development of microfluidic devices.

The widespread proliferation of cellular lattices in engineering design has entailed a revolution in the design of lightweight and multifunctional structures. Furthermore, the development of auxetic metamaterials has led to applications in fields ranging from biomedical to civil engineering. However, cellular lattices suffer from the development of localized concentrations of strains during deformation, which lead to sub-optimal mechanical performance. Furthermore, the mechanical properties of cellular lattices are dependent on their macro-scale geometries, limiting their design space. Thus, we seek to both enhance the mechanical properties of lattices by ameliorating strain concentrations and expand the design space of cellular lattices. In attempting to do so, we can turn to nature. The bio-inspired design motif of the hierarchical arrangement of composite materials has lead to exceptional mechanical characteristics in natural materials. Moreover, morphogenetic processes such as bone remodelling play a vital role in the structural development of natural materials and their hierarchical material arrangement. Motivated by these concepts, we developed an algorithm that optimised the hierarchical material arrangement of hard and soft voxels in an auxetic and non-auxetic unit cell. Our algorithm does so based on a bone remodelling-like approach of strain energy optimisation, whereby elements are transitioned to a hard or soft material based on local strain energy. Our finite element (FE) simulation results demonstrate the considerable expansion of the range of mechanical properties we can achieve simply by modifying material placement on a micron scale. We also observe clear mitigation of peak strain energies and more homogeneous distributions of strain energy density, which affirm the amelioration of strain concentrations. Furthermore, we were able to increase the stiffnesses of our unit cells without substantially affecting its Poisson’s ratio, disentangling previously interdependent mechanical properties. We further validated our FE simulations by additively manufacturing our optimised unit cells with state-of-the-art voxel-based printing. Both the mechanical properties predicted by our FE simulations and the strain distributions correlated well with digital image correlation recordings, validating our models. Our mechanical testing also revealed the considerable in- creases in ultimate tensile strength of our optimised designs, demonstrating the benefits of hierarchical material arrangement. To conclude, we demonstrate the efficacy of strain energy-based material optimisation to improve the mechanical properties of unit cells and mitigate strain concentrations. The design paradigms of hierarchical arrangement of composite materials remarkably improved the material space of a unit cell without changing its macro-scale geometry. Findings from this study could enable the optimisation of existing cellular lattices and the development of novel unit cell designs with distinct intrinsic mechanical properties.

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.

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.

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.

The fracture properties of natural materials often outperform artificial material properties. This could be explained by their complex multi-scale (anisotropic) hard-soft material structure, starting at a nano-scale. The interest in the fabrication of complex biomimetic hard-soft materials and interfaces is growing due to their high fracture properties, including stiffness, strength and fracture toughness. Additive manufacturing, in particular voxel-based additive manufacturing, enables the precise mimicking of complex natural three-dimensional (3D) structures at a micro-scale. Various studies have been performed on the fabrication of biomimetic materials with an Objet500 Connex3 polyjet printer which is able to print multiple materials at the same time. However, fundamental research on the influence of multiple biomimetic design parameters on the fracture properties of hard-soft materials was missing. In this study the isolated and modulated effects of three different biomimetic design parameters on the fracture properties of hard-soft material samples were analysed. The samples differed in length scale (40, 240, 480 and 960 µm), hard material ratio (0, 25, 38, 50, 63, 75 and 100 %) and hard-soft material arrangement (semi-ordered, random and ordered). These design parameters could be found among different natural materials and interfaces. The fracture properties of the single edge notched samples, including stiffness, fracture strength, final strain and fracture toughness, were obtained with a tensile test. The effect of the different design parameters on the fracture properties was further analysed with digital image correlation (DIC) measurements and a digital microscope. The results show that the biomimetic design parameters had a modulated effect on the fracture properties. The fracture properties were mostly affected by the hard material ratio and length scale compared to the hard-soft material arrangement. A higher amount of hard material resulted in a higher stiffness and fracture strength, but in a smaller final strain. A smaller length scale improved the fracture properties if a significant amount of soft material was present. An important result is that the fracture toughness of the hard-soft material samples could be increased by nearly two times compared to the toughness of the individual constituents, supporting the potential of using biomimetic design parameters. The effect of the biomimetic design parameters on the fracture properties can be explained by the DIC measurements and digital microscope images. The microscope images show that the fracture path tended to propagate through the soft material phases, which was more difficult at a smaller length scale. DIC measurements showed that the plasticity zone in front of the crack tip was larger for the samples printed at native resolution, resulting in a higher fracture toughness. This study shows that a wide range of fracture properties can be achieved by regulating the length scale, hard material ratio and hard-soft material arrangement of hard-soft materials. The fracture toughness of hard-soft materials can be improved in comparison to the fracture toughness of the individual constituents, which supports the potential of using biomimetic design parameters in improving the fracture properties of hard-soft materials.

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.

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.

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

Since the beginning of time, humans have been trying to replace the skeletal system in cases of trauma or disease. Medical devices were designed, manufactured, and implanted, to restore the function of the skeletal system. Fast forward to today and joint replacements are among the most common surgeries carried out in the world. Despite their success, a relatively large number of patients will eventually need a revision surgery. In most cases, the implant fails due to aseptic loosening. Aseptic loosening represents a range of implant loosening cases not associated with infection and is often linked to an inflammatory response. This kind of implant loosening is often associated with the mechanical failure of the load-bearing connection at the bone-implant interface, which could be caused by inadequate initial fixation, the loss of fixation over time, or bone tissue deterioration as a result of (wear) particles. The complexity of the bony tissue, with its hierarchical and anisotropic structure, complicates the development of life-lasting replacements. Metallic biomaterials have been introduced as promising bone substitutes but their stiffness is usually vastly higher than that of the native bone. As a result, the patient’s bone becomes shielded from mechanical stimuli (stress shielding). Prolonged reduction in the mechanical stimuli results in bone resorption and may cause implant loosening. With the introduction of additively manufactured (AM) porous structures, the mechanical properties of metallic biomaterials could be reduced to the level of the bony tissue. Additionally, porous biomaterials allow for the diffusion of nutrients and oxygen, the ingrowth of de novo bone tissue, and the formation of capillaries. While this may sound as the golden combination, close bone-implant contact is of critical importance and can only be guaranteed if the implant matches the patient’s anatomy. Recent advances in AM have enabled the development of patient-specific implants, but this does not necessarily guarantee a lasting fixation. In the most ideal situation, the geometry of the implant should be tailored at both micro- and macroscale to optimize both shape-matching and material properties of the porous structures. This often calls for an unusual set of properties and functionalities that are not usually found in nature. Materials of which the small-scale architecture can be designed to obtain certain mechanical, mass-transport, and biological properties are referred to as meta-biomaterials. The deformation of a material in directions perpendicular to the direction of loading is described by the Poisson’s ratio. A negative value would indicate that the material exhibits lateral expansion in response to axial tension, which can be observed in auxetic materials. This Poisson effect is usually guided by the internal structure of the material, or the micro-architecture of meta-biomaterials. Changing the building block (i.e., the unit cell) will, therefore, change the micro-architecture and, thus, the deformation behavior of the material as a whole... @en