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The ability of cells to respond to substrate-bound protein gradients is crucial for many physiological processes, such as immune response, neurogenesis and cancer cell migration. However, the difficulty to produce well-controlled protein gradients has long been a limitation to our understanding of collective cell migration in response to haptotaxis. Here we use a photopatterning technique to create circular, square and linear fibronectin (FN) gradients on two-dimensional (2D) culture substrates. We observed that epithelial cells spread preferentially on zones of higher FN density, creating rounded or elongated gaps within epithelial tissues over circular or linear FN gradients, respectively. Using time-lapse experiments, we demonstrated that the gap closure mechanism in a 2D haptotaxis model requires a significant increase of the leader cell area. In addition, we found that gap closures are slower on decreasing FN densities than on homogenous FN-coated substrate and that fresh closed gaps are characterized by a lower cell density. Interestingly, our results showed that cell proliferation increases in the closed gap region after maturation to restore the cell density, but that cell–cell adhesive junctions remain weaker in scarred epithelial zones. Taken together, our findings provide a better understanding of the wound healing process over protein gradients, which are reminiscent of haptotaxis.

Personalized or individualized medicine is considered as an innovative approach to deliver the right dose to the right person at the right time. However, current technologies producing pharmaceutical products do not address the growing need for these new therapies. The aim of this work was the preparation of long-acting implantable dosage forms in which the drug release is regulated by the polymer matrix and the design of the implant. Paliperidone palmitate (PP), was selected as model drug. Indeed, PP is sensitive to thermal degradation above its melting temperature and its amorphous state remains difficult to obtain and stabilize. The first part of this study focused on obtaining and stabilizing the amorphous form of PP. A ternary mixture based on two polymers was therefore selected to be printed as dosage forms. Following an in vitro dissolution test, different release profiles were obtained depending on the selected printing parameters. Then, the stability of the amorphous state of PP was assessed at two different temperatures. During this test, implants were placed at 4°C and 25°C ± 40% residual humidity for 3 months. In the 2nd part, a 3D printing technology reducing the number of steps required to produce a suitable formulation was studied. This technology was based on a pressure extrusion-based printing process. Polycaprolactone was chosen as biocompatible and bioresorbable polymer matrix. Two different designs have been studied, namely a ring and a disk. The goal was to compare the effect of the design on the release of PP. An in vitro dissolution test was performed over a period of 3 to 6 months. In the last part, the development of a proof of concept of a predictive model taking into account the design of the printed form was studied. The impact of different printing parameters on the drug release were studied through a Design of Experiments (DoE). Finally, a second DoE was used to predict the release of PP from complex dosage forms combining two formulati, Doctorat en Sciences biomédicales et pharmaceutiques (Pharmacie), info:eu-repo/semantics/nonPublished

Cell-based therapies are promising for tissue engineering and for treating various diseases. However, their development is impaired by the large cell doses required per patient, since the common method to expand cells is not well suited for large-scale production. Therefore, cell culture on microcarriers (MCs) emerges as an alternative, providing a larger surface-to-volume ratio. However, most commercially available MCs are not designed for stem cell expansion as they are frequently coated with animal-proteins and/or produced using toxic organic solvents. In this context, the aim of the thesis was to develop novel polymeric MCs produced by a green solvent-free process and free of animal protein. We also aim to obtain MC with tunable characteristics (size, porosity, etc.) in order to deal with the multiparameter nature of dynamic cell culture. The MC core is obtained thanks to a versatile and green fabrication process meeting the requirements described above. A polyelectrolyte film composed of poly(L-ornithine) and hyaluronic acid is deposited on MCs using the Layer-by-Layer technique, followed by a crosslinking step and the grafting of a bioadhesive peptide to ensure optimal cell adhesion. The ability of these new MCs to expand human adipose-derived mesenchymal stem cells in both static and dynamic conditions is demonstrated. More precisely, a range of parameters such as growth medium, cell seeding density, MC morphology and composition of coating are optimized in semi-static condition. We also show in semi-static condition that these new MCs offer similar performance in term of cell expansion compared to a widely used commercial MC while being superior in terms of detachment efficiency. Finally, the possibility of using these new MCs in dynamic condition as well as performing bead-to-bead transfer to improve cell yield is proven., (FSA - Sciences de l'ingénieur) -- UCL, 2020

Collective cell migration is fundamental throughout development, during wound healing and in many diseases. Although much effort has focused on cell–cell junctions, a role for physical confinement in collective cell migration remains unclear. Here, we used adhesive microstripes of varying widths to mimic the spatial confinement experienced by follower cells within epithelial tissues. Our results reveal that the substrate area confinement is sufficient to modulate the three-dimensional cellular morphology without the need for intercellular adhesive cues. Our findings show a direct correlation between the migration velocity of confined cells and their cell–substrate adhesive area. Closer examination revealed that adhesive area confinement reduces lamellipodial protrusive forces, decreases the number of focal complexes at the leading edge and prevents the maturation of focal adhesions at the trailing edge, together leading to less effective forward propelling forces. The release of follower confinement required for the emergence of leader cells is associated with a threefold increase in contractile stress and a tenfold increase in protrusive forces, together providing a sufficient stress to generate highly motile mesenchymal cells. These findings demonstrate that epithelial confinement alone can induce follower-like behaviours and identify substrate adhesive area confinement as a key determinant of cell velocity in collective migration.

We report on metal-assisted chemical etching of Si for the synthesis of mechanically stable, hybrid crystallographic orientation Si superstructures with high aspect ratio, above 200. This method sustains high etching rates and facilitates reproducible results. The protocol enables the control of the number, angle, and location of the kinks via successive etch-quench sequences. We analyzed relevant Au mask catalyst features to systematically assess their impact on a wide spectrum of etched morphologies that can be easily attained and customized by fine-tuning of the critical etching parameters. For instance, the designed kinked Si nanowires can be incorporated in biological cells without affecting their viability. An accessible numerical model is provided to explain the etch profiles and the physicochemical events at the Si/Au−electrolyte interface and offers guidelines for the development of finite-element modeling of metal-assisted Si chemical etching.

Additive manufacturing techniques are promising technologies to produce patient-specific and effective scaffolds for tissue engineering. Chemical and physical surface modifications are often performed on scaffolds to control cell behavior and foster tissue regeneration. On the other hand, surface mechanical properties are known to influence stem cell proliferation and to direct their differentiation. The aim of this work was to produce degradable poly(lactic acid) (PLA) and poly(epsilon-caprolactone) scaffolds using a so-called gyroid geometry, which features an isotropic and spring-shaped design. This was achieved by adapting the parameters to get closer to the resolution limit of fused deposition modeling, an easy-to-use and low-cost 3D printing technology. A semi-interpenetrating polymer network made with poly(dimethylsiloxane) crosslinked at different densities was then designed to modify the surface mechanical properties of PLA gyroid scaffolds. Finally, the effect of the coating mechanical properties on the proliferation and osteogenic differentiation of stem cells from the apical papilla was evaluated. The production of complex scaffolds was successfully achieved using 3D printing. The coating technology that was further developed paves the way towards the modification of the surface mechanical properties of macroporous scaffolds with a complex shape, with a view to control stem cell behavior., (AGRO - Sciences agronomiques et ingénierie biologique) -- UCL, 2019