Functionalized Fluoropolymer-Compatibilized Elastomeric Bilayer Composites for Osteochondral Repair: Unraveling the Role of Substrate Stiffness and Functionalities

The osteochondral lesions and osteoarthritis-related complications continue to be clinically relevant challenges to be addressed by the biomaterials community. Hydrogel-based scaffolds have been widely investigated to enhance osteochondral regeneration, but the inferior mechanical properties together with poor functional stability are the major constraints in their clinical translation. The development of osteochondral implants with natural tissue-mimicking mechanical properties remains largely unexplored. In this perspective, the present study demonstrates a strategy to develop a bilayer osteochondral implant with an elastically stiff composite (poly(vinylidene difluoride)-reinforced BaTiO3, PVDF/BT) and elastically compliant composite (maleic anhydride-functionalized PVDF/thermoplastic polyurethane/BaTiO3, m-PVDF/TPU/BT). The compositional variation in polymer composites allowed the elastic modulus of the hybrid bilayer construct to vary from ∼2 GPa to ∼90 MPa, which enabled a better understanding of the substrate-stiffness-dependent cellular behavior and maturation of preosteoblasts and chondrocytes. The cellular functionalities on PVDF-based polymer matrices have been benchmarked against ultrahigh-molecular-weight polyethylene (UHMWPE), which is clinically used for a wide spectrum of orthopedic applications. The increased alkaline phosphatase (ALP) activity, collagen synthesis, and matrix mineralization confirmed the early differentiation of preosteoblasts on the PVDF/BT matrix with subchondral bone-like mechanical properties. On the contrary, the upregulated chondrogenic functionalities were recorded on m-PVDF/TPU/BT with an elevated level of collagen content, glycosaminoglycans, and proteoglycans. Emphasis has been laid on probing the regulation of the osteochondral behavior using tailored substrate stiffness and functionalities using compatibilized fluoropolymer-based elastomeric composites. Taken together, the results of this work conclusively establish the efficacy of the hybrid bilayer composite with natural tissue-mimicking mechanical properties for the functional repair of osteochondral defects.