Development of carbon reinforced polymer-ceramic composites for bone tissue engineering

Abstract

Carbon based materials have attracted tremendous attention owing to their captivating electronic, mechanical and thermal properties. These materials are also being introduced in biological systems, considering the fact that life on earth is carbon based. However, limited information is available concerning the potential effects of different structures of these carbon materials on biological systems. In the present study, carbon reinforced (i.e. carbon nanotubes (CNTs-1D), graphene nanoplatelets (GNPs-2D) and activated carbon (AC-3D)) polymer-ceramic (nano-hydroxyapatite (nHA)) composite scaffolds have been developed. Poly(vinyl alcohol) (PVA) and poly(lactic-co-glycolic acid) (PLGA) have been used as polymer matrix. Initially, four different reinforcements i.e. nHA, CNTs, GNPs and AC were reinforced in PVA matrix by varying their concentrations and characterized for their physicochemical, mechanical and biological properties to find an optimum concentration. The proper dispersion of reinforcement materials up to threshold concentration enhanced the mechanical properties of the composites and provided the most favorable microenvironment for cell attachment and growth. The threshold (optimum) concentrations of different reinforcements were found to be 3% w/v for nHA, 1 wt% for CNTs, 1 wt% for GNPs and 2.5 wt% for AC, respectively, above which the agglomeration of reinforcements had reduced effect on the scaffold properties.

The optimum concentrations of each carbon were then reinforced into PVA along with 3% w/v of nHA to develop 3 component composite systems (PVA-nHA-carbon). Further, the optimum concentrations of each carbon reinforcement were also added to PLGA matrix without (PLGA- carbon) and with hydroxyapatite (PLGA-nHA-carbon). These composites containing threshold concentration of reinforcements were then characterized for their physicochemical, mechanical and biological properties. Along with the hemocompatible nature, the composites also exhibited good swelling ratio, degradation percentage and in-vitro bioactivity. The effective stress transfer between the homogenously dispersed reinforcement materials and polymer matrix increased the tensile strength, Young’s modulus and energy at break for the composites many folds. A significant enhancement in cell attachment, viability and differentiation was observed in all the composites. The suitable surface properties i.e. wettability, surface roughness and surface charge stimulated the protein adsorption on the carbonaceous composites making them suitable for MG-63 cell attachment, proliferation and differentiation. The augmented collagen secretion, ALP activity and matrix mineralization confirmed the improved bone forming ability of the cells. Owing to their nanostructure, both CNTs and GNPs exhibited better results in comparison to the AC.

Amongst all composites, GNPs along with nHA showed the strongest effect on the properties of PVA and PLGA based composites due to the sheet like 2D structure of GNPs. More functional groups and larger area exposed in case of GNPs lead to highest protein adsorption and hence, improved its cellular responses. The larger interface directed effective load transfer between polymer matrix and GNPs. These results demonstrate the potential of carbonaceous composites of polymer-nHA for accelerating bone tissue regeneration.