Improved Mesenchymal Stem Cell Viability in High-Stiffness, Translational Cartilage Matrix Hydrogels.

Abstract

Scaffolds made from cartilage extracellular matrix are promising materials for articular cartilage repair, attributed to their intrinsic bioactivity that may promote chondrogenesis. While several cartilage matrix-based scaffolds have supported chondrogenesis <i>in vitro</i> and/or <i>in vivo</i>, it remains a challenge to balance the biological response (e.g., chondroinductivity) with structural (e.g., robust mechanical performance, >1 MPa in compressive stiffness) and translational (e.g., ease of surgical implantation) considerations. Few studies have evaluated encapsulated cell viability within high-stiffness (>1 MPa) hydrogels. We previously fabricated one formulation of a high-stiffness (>3 MPa) pentenoate-functionalized, solubilized, devitalized cartilage (PSDVC) hydrogel that possessed an injectable, paste-like precursor for easy surgical application. In the current study, the characterization of the PSDVC material was expanded by varying the degree of functionalization (i.e., 0.45-1.09 mmol/g) and amount of crosslinker, dithiothreitol (DTT), to improve the reproducibility of the high compressive moduli and evaluate the viability of encapsulated human bone marrow-derived mesenchymal stem cells (hBMSCs) in high-stiffness cartilage matrix hydrogels. Prior to crosslinking, specific formulations functionalized with 0.80 mmol/g or less of pentenoate groups retained a paste-like precursor rheology. After crosslinking, these formulations produced hydrogels with greater than 1 MPa compressive stiffness. However, hBMSCs encapsulated in PSDVC hydrogels with lower functionalization (i.e., 0.57 mmol/g, no crosslinker) had a higher stiffness (i.e., 1.4 MPa) but the lowest viability of encapsulated hBMSCs (i.e., 5%). The middle PSDVC functionalization (i.e., 0.70 mmol/g) with DTT (i.e., 0.50 mmol thiols/g) demonstrated high cell viability (77%), high mechanical performance (1.65 MPa, 31% failure strain), and translational features (i.e., paste-like precursor, 1.5 min crosslinking time). For future evaluations of PSDVC hydrogels in cartilage repair, a middle functionalization (i.e., 0.70-0.80 mmol/g) with the addition of a crosslinker (i.e., 0.50 mmol thiols/g) had a desirable balance of high mechanical performance (i.e., >1 MPa compressive stiffness), high viability, and paste-like precursor for surgical translation.