Controlled surface modification of silicone rubber by gamma-irradiation followed by RAFT grafting polymerization

Abstract

The formation of biofilms on the surface of some biomaterials causes problems that can have a negative impact on human health. Various studies have been carried out for the modification of polymeric biomaterials; however, with conventional methods of modifying surfaces with radiation-induced grafts, obtaining uniformly distributed grafts over the entire surface is not facilitated, so the mechanical properties are strongly affected by the modification. In this study, silicone rubber (SR) films were modified with 2-hydroxyethyl methacrylate (HEMA) and with oligo(ethylene glycol) methyl ether methacrylate, Mn = 300 g mol−1 (OEGMA300) using the oxidative pre-irradiation method with gamma-irradiation followed by reversible addition-fragmentation chain transfer (RAFT) grafting polymerization. The copolymers of SR-g-PHEMA and SR-g-poly(HEMA-co-OEGMA300) were synthesized with various grafting percentages and these could be adjusted to obtain a thin grafted layer. The grafted samples were characterized by FTIR-ATR spectroscopy, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), light microscopy, swelling in water, contact angle, and dynamic mechanical analysis (DMA); in addition, the non-grafted polymer formed in the RAFT copolymerization reactions was analyzed by gel permeation chromatography (GPC) and nuclear magnetic resonance spectroscopy (NMR). The results confirmed the presence of PHEMA and poly(HEMA-co-OEGMA300) on the surface of SR films, uniformly grafted by the use of a chain transfer agent (CTA). The uniform layer of hydrophilic grafts in the SR films generates a surface capable of forming a water barrier on the surface, without significantly compromising the elastic properties of the SR; furthermore, the grafted thin layer was capable of loading biologically active molecules like curcumin. Modified SR films loaded with curcumin may decrease the possibility of biofilm formation. The described approach of oxidative gamma pre-irradiation followed by RAFT controlled grafting may be of interest for the modification of biomaterials in a controlled way, in the case of silicone for instance for catheters or aesthetic implants.