Ruijter, Mylène de

ABSTRACT In cartilage tissue engineering, there is a growing interest in dynamic hydrogels that promote spheroid fusion and cartilaginous matrix deposition, while maintaining sufficient stability for long‐term construct maturation. In this study, Diels‐Alder click chemistry is employed as a dynamic‐covalent crosslinking method to create hydrogels composed of hyaluronic acid, gelatin, and PEG. By adjusting the pH during crosslinking, the tuneability of hydrogel stiffness and stability at pH values around the physiological pH of native cartilage is demonstrated. This pH modulation does not compromise hydrogel functionality, as encapsulated equine articular cartilage progenitor cell spheroids remain viable and functional for a culture period of 28 days. The hydrogel environment supports the deposition of cartilaginous extracellular matrix components, including collagens and sulphated glycosaminoglycans. Enhanced chondrogenesis and deposition of collagen type II are observed at higher spheroid concentrations, corresponding to inter‐spheroid distances of 100–150 µm following hydrogel swelling, compared to lower concentrations at a distance of >500 µm. To further improve construct robustness, the hydrogel constructs can be reinforced on day 1 with a melt electrowritten scaffold, increasing the compressive modulus 100‐fold by day 28 compared to non‐reinforced constructs, highlighting the potential of this system for engineering cartilage implants.

Meniscus injury and meniscectomy are strongly related to osteoarthritis, thus there is a clinical need for meniscus replacement. The purpose of this study is to create a meniscus scaffold with micro-scale circumferential and radial fibres suitable for a one-stage cell-based treatment. Poly-caprolactone-based scaffolds with three different architectures were made using melt electrowriting (MEW) technology and their in vitro performance was compared with scaffolds made using fused-deposition modelling (FDM) and with the clinically used Collagen Meniscus Implants® (CMI®). The scaffolds were seeded with meniscus and mesenchymal stromal cells (MSCs) in fibrin gel and cultured for 28 d. A basal level of proteoglycan production was demonstrated in MEW scaffolds, the CMI®, and fibrin gel control, yet within the FDM scaffolds less proteoglycan production was observed. Compressive properties were assessed under uniaxial confined compression after 1 and 28 d of culture. The MEW scaffolds showed a higher Young’s modulus when compared to the CMI® scaffolds and a higher yield point compared to FDM scaffolds. This study demonstrates the feasibility of creating a wedge-shaped meniscus scaffold with MEW using medical-grade materials and seeding the scaffold with a clinically-feasible cell number and -type for potential translation as a one-stage treatment.