Mixed Composition Microribbon Hydrogels Induce Rapid and Synergistic Cartilage Regeneration by Mesenchymal Stem Cells in 3D via Paracrine Signaling Exchange.

Hydrogels are widely used matrices for mesenchymal stem cell (MSC)-based cartilage regeneration but often result in slow cartilage deposition with inferior mechanical strength. We recently reported a gelatin-based microribbon (μRB) scaffold, which contains macroporosity and substantially enhances the speed of cartilage formation by MSCs in 3D. However, our previous method cannot be used to fabricate different polymers into μRBs, and the effects of varying μRB compositions on MSC cartilage regeneration in 3D remain unknown. Here, we report a method that allows fabricating different polymers [gelatin, chondroitin sulfate, hyaluronic acid, and polyethylene glycol (PEG)] into μRB structures, which can be mixed in any ratio and cross-linked into 3D scaffolds in a modular manner. Mixing glycosaminoglycan μRBs with gelatin or PEG μRBs induced great synergy, resulting in fast cartilage deposition. After only 3 weeks of culture, leading mixed μRB composition reached high compressive strength on par with native cartilage. Such synergy can be recapitulated via exchange of soluble factors secreted by MSCs seeded in different μRB compositions in a dose-dependent manner. Tuning the ratio of mixed μRB compositions allowed further optimization of the quantity and speed of cartilage regeneration by MSCs. Together, our results validate mixed μRB compositions as a novel biomaterial tool for inducing synergy and accelerating MSC-based cartilage regeneration with biomimetic mechanical properties through paracrine signal exchange.