In vitro mineralization of dual grafted polytetrafluoroethylene membranes

The modification of biomaterials by radiation induced grafting is a promising method to improve their bioactivity. Successful introduction of carboxyl and amine functional groups on the surface of a polytetrafluoroethylene membrane was achieved by grafting of acrylic acid (AA) and 2-aminoethyl methacrylate hydrochloride (AEMA) using simultaneous gamma irradiation grafting. Chemical characterization by attenuated total reflectance Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy confirmed the presence of amine and carboxylate functionalities and indicated that all protonated amines formed ion pairs with carboxyl groups, but not all carboxyl are involved in ion pairing. It was found that the irradiation doses (2, 5, or 10 kGy) affected the grafting outcome only when sulfuric acid (0.5 or 0.9 M) was added as a polymerization enhancer. The use of the inorganic acid successfully enhanced the total graft yield (GY), but the changes in the graft extent (GE) were not conclusive. Dual functional films were produced by either a one- or a two-step process. Generally, higher GY and GE values were observed for the samples produced by the two-step grafting of AA and AEMA. The in vitro mineralization in 1.5× simulated body fluid (SBF) induced the formation of carbonated hydroxyapatite as verified by FITR. All samples showed an increase in weight after mineralization with significantly larger increases observed for the samples which had the 1.5× SBF changed every third day compared to every seventh. For the dual functional samples, it was found that the sample grafted by the one-step method shows a significantly higher increase in weight despite a much lower GY compared to the sample prepared by the two-step method and this was attributed to the different architecture of grafted chains.