Engineering Bioactive Interfaces: Hybrid Scaffolds Based on Oxidized Polyvinyl Alcohol and Natural Matrices for Osteochondral Tissue Regeneration

Osteochondral defects associated with osteoarthritis represent a major clinical challenge due to the poor intrinsic regenerative capacity of the osteochondral unit. Tissue engineering offers a promising strategy to restore joint function through the use of biomimetic scaffolds capable of supporting coordinated regeneration of cartilage and subchondral bone. In this context, this study aimed to develop and characterize novel bio-hybrid scaffolds based on oxidized polyvinyl alcohol (OxPVA) combined with two clinically established biological matrices: the collagen membrane Bio-Gide® and the deproteinized bovine bone mineral Bio-Oss®. Two scaffold configurations were fabricated: a bilayer structure consisting of an OxPVA support layered with the collagen membrane (OxPVA/Col_bilayer), and a blend structure incorporating bone granules directly into the OxPVA hydrogel (OxPVA/Bone_blend). Scaffolds were cross-linked via freeze-thawing cycles and characterized for ultrastructure (scanning electron microscopy, histology), mechanical properties (compression tests), permeability (FRAP), and in vitro biocompatibility using HM1-SV40 mesenchymal stromal cells. Results showed that OxPVA/Col_bilayer scaffolds exhibited a highly porous, fibrillar collagen surface that significantly enhanced cell adhesion and proliferation. After 7 days, cells formed a confluent monolayer with extensive cytoplasmic extensions. In contrast, OxPVA/Bone_blend scaffolds displayed a denser microstructure with reduced porosity; cells remained viable but preferentially formed spheroidal aggregates around exposed bone granules. These differences are ascribable to the distinct accessibility of bioactive cues due to the specific configuration. Importantly, all scaffold formulations were non-cytotoxic, preserving cell viability above the 70% ISO threshold. Mechanical testing demonstrated that bilayer scaffolds possess lower compressive stiffness, suitable for cartilage-mimicking applications, while blend scaffolds show significantly higher stiffness, appropriate for subchondral bone support. FRAP analysis indicated improved molecular diffusivity in all bio-hybrid constructs compared to OxPVA alone, suggesting that the integration of biological matrices into the hydrogel not only enhances polymer bioactivity but also positively modulates scaffold permeability. In conclusion, the scaffold architecture and spatial distribution of bioactive components critically regulate structural, mechanical, and biological performance, supporting the potential of OxPVA-based bio-hybrid scaffolds for stratified osteochondral tissue regeneration.