Mechanically robust polyvinyl alcohol/silk fibroin cryogels via freeze-thaw processing for cartilage defect repair

Developing macroporous hydrogels with enhanced mechanical strength and favorable cell adhesion is crucial for effective cartilage repair. The freeze-thaw (FT) technique, a simple, environmentally friendly, and non-toxic approach, is widely employed to fabricate biocompatible macroporous hydrogels. In this study, a water-insoluble polyvinyl alcohol/silk fibroin (PVA/SF) porous cryogel was successfully fabricated via a cyclic FT process. Four FT cycles facilitated the formation of intermolecular hydrogen bonds between PVA and SF, thereby yielding a stable porous network. Incorporation of SF significantly improved the structural characteristics of PVA cryogels, increasing the pore size from 89.6 ± 29.0 to 206.8 ± 49.9 μm and the porosity from approximately 35 % to 87 %, while enhancing the compressive modulus from 138.4 to 840.7 kPa, approaching the mechanical range of native cartilage. In vitro assays demonstrated that SF incorporation promoted cellular infiltration, migration, and spatial distribution within the cryogel matrix to a depth of 200-300 μm. Notably, P50S50 cryogels (PVA/SF = 50/50) exhibited approximately 2-fold higher depth of cell infiltration than pure PVA cryogels at day 7. Furthermore, in a rabbit cartilage defect model, the P50S50 cryogel effectively promoted defect repair and the regeneration of cartilage-like tissue within 10 weeks. This study provides a facile and biocompatible strategy for constructing bioactive, mechanically robust macroporous cryogels with substantial potential for clinical applications in cartilage tissue engineering.