Functionally Graded Bioactive Composites Based on Poly(vinyl alcohol) Made through Thiol-Ene Click Reaction

Functionally graded materials (FGMs) composed of a polymer matrix embedded with calcium phosphate particles are preferred for bone tissue engineering, as they can mimic the hierarchical and gradient structure of bones. In this study, we report the design and development of a FGM based on thiolated poly(vinyl alcohol) (TPVA) and nano-hydroxyapatite (nano-HA) with graded bioactivity, cell compatibility, and degradability properties that are conducive for bone regeneration. The polymer matrix comprises crosslinked poly(vinyl alcohol) with ester and thioether linkages formed via the thiol-ene click reaction, avoiding undesired additives and byproducts. Freshly precipitated and spray-dried HA was mixed with the TPVA hydrogel, and layers of varying concentrations were cast. Upon lyophilization, the hydrogel structure yielded porous sheets of the graded composite of TPVA and nano-HA. The new FGM showed higher values of tensile strength and degradation in phosphate buffer saline (PBS) in vitro, compared to bare TPVA. The bioactive nature of the FGM was confirmed through bioactivity studies in simulated body fluid (SBF), while cytocompatibility was demonstrated with human periodontal ligament cells in vitro. Cumulatively, our results indicate that based on the composition, mechanical properties, bioactivity, and cytocompatibility, the fabricated TPVA-HA composites can find potential use as guided bone regeneration (GBR) membranes.