Covalent modification of chemically converted graphene with polycaprolactone to produce conductive and biocompatible composites
Novel conducting and biodegradable composite materials have been synthesised by covalently linking chemically converted graphene to a range of polymers with known biocompatibility, in this case, polycaprolactone.
The materials were synthesised by two routes. First, a solution processing method was used to mix polycaprolactone with well-dispersed highly-reduced graphene oxide. Secondly, an esterification reaction was used to covalently link the polymer chains to free carboxyl groups on well-dispersed highly-reduced graphene. The synthesised biopolymers were processable using a number of techniques including melt extrusion, wet spinning and dip/spray coating. The addition of graphene enhanced the mechanical properties and conductivity of the synthesized biopolymers, indicating the excellent reinforcement ability and electrical properties of graphene sheets. Covalent attachment was found to produce more homogenous materials with better conductivity and mechanical properties.
The degradation and biocompatibility of the composite materials have also been investigated. An enzymatic degradation assay was undertaken in order to compare the degradation of the solution-processed and covalently-modified materials. It was determined that the rate of degradation was similar for PCL and all PCL composites tested with graphene content lower than 1%.
Biocompatibility of all materials was assessed using a fibroblast cell line, and cells were observed to adhere to and proliferate on materials. Varying the graphene content between 0% and 5% did not change the morphology of cells growing on the surfaces, or the rate of cell proliferation. Neural cells were also observed to adhere to and proliferate on all composite materials. This suggests that the increase graphene content that is required to achieve more highly conducting composites does not interfere with cell metabolism, and indicates that the graphene is non-cytotoxic within the composite materials.
The novel covalently-linked synthetic route used here can be applied across a wide range of polymers to enable fine-tuning of the composite material properties, allowing synthesis of biocompatible and highly conducting materials for a wide range of biological and medical applications.