In vitro mineralisation of grafted ePTFE membranes carrying carboxylate groups

In vitro mineralisation in simulated body fluid (SBF) of synthetic polymers continues to be an important area of research as the outcomes cannot be predicted. This study evaluates a series of ePTFE membranes grafted with carboxylate-containing copolymers, specifically using acrylic acid and itaconic acid for grafting. The samples differ with regards to graft density, carboxylate density and polymer topology. The type and amount of mineral produced in 1.5 × SBF was dependent on the sample characteristics as evident from XPS, SEM/EDX, and FTIR spectroscopy. It was found that the graft density affects the mineral phases that form and that low graft density appear to cause co-precipitation of calcium carbonate and calcium phosphate. Linear and branched graft copolymer topology led to hydroxyapatite mineralisation whereas crosslinked graft copolymers resulted in formation of a mixture of calcium-phosphate phases. This study demonstrates that in vitro mineralisation outcomes for carboxylate-containing graft copolymers are complex. The findings of this study have implications for the design of bioactive coatings and are important for understanding the bone-biomaterial interface.