Design and characterization of a biopolymer halloysite composite of the Sr(II) mediated regeneration of bone

The design of biocompatible materials with tunable functionalities, either as scaffold for bone tissue engineering or as platforms for regenerative medicine, is a challenging target. This study reports on the preparation, characterization, and cytotoxicity of a hybrid nanocomposite material made of Sr(II)-loaded halloysite nanotubes embedded within a thin film of a biopolymer (3-polyhydroxybutyrate-co-3-hydroxyvalerate). This composite could be of interest for multiple strategies in the growing field of bone medication. The inorganic scaffold is intended to provide mechanical resistance, multi-scale porosity, and to favor the in-situ regeneration of bone tissue thanks to its biocompatibility and bioactivity. Furthermore, the chemical composition of halloysite is identical to the biologically well-tolerated kaolin, representing a significant advantage over other fibrous nanostructures. For instance, carbon nanotubes display comparable mechanical properties but were shown to be toxic. The interaction of the hybrid with the physiological environment is mediated through the biopolymer coating that acts both as a biocompatible binder for the halloysite nanocontainers and as a diffusional barrier to the Sr(II) release. In particular, the degradation of the polymer leads to the exposure of the Sr(II)-loaded halloysite scaffold, eventually modulating its interaction with osteogenic cells. The biocompatibility was proven by in vitro cytotoxicity tests on L929 fibroblast cells.