Calcium ion‐mediated grafting of a phosphate‐containing monomer

Abstract

Grafting of monoacryloxyethyl phosphate onto expanded polytetrafluoroethylene was achieved using simultaneous grafting with the aim of improving the membrane wettability and mineralization capacity. This study explored the effect of adding calcium ions to the grafting solution and observed increased graft yield and wettability when compared with samples grafted in the absence of calcium ions. Fourier transform infrared spectroscopy mapping found the graft copolymer to be distributed in a patchy manner across the surface as well as throughout the membrane. Through X-ray photoelectron spectroscopy analysis, it was found that calcium ions were incorporated into the graft copolymer and could be extracted using a basic ethylenediaminetetraacetic acid solution without reduction in graft yield. This implies that the presence of calcium ions is affecting the graft yield by increasing the local concentration of monomer near the surface during the grafting process. Investigation of the mineralization capacity of the grafted membranes in simulated body fluid revealed that the increased wettability of the membranes rather than the presence of the calcium ions affected the mineralization outcome.

In vitro mineralisation of grafted ePTFE membranes carrying carboxylate groups

“…Considering the different topologies of the carboxylate-containing materials it can be seen that on samples with linear or branched topology (AA-P, AA(0.3)-R, AA/IA(3)-R) the mineral HAP can be identified, while on the samples with a crosslinked topology (AA(1.3)-R and PAA) a mixture of calcium-phosphate phases form. A similar finding has previously been made for ePTFE samples modified with phosphate-containing graft copolymers [11] , [21] . The reason for this effect of polymer topology could be due to many factors.…”

“…However, it could also indicate that the underlying graft copolymer is patchy (correlating with the relatively low graft extent observed in these samples) and that mineral formed exclusively on areas where the graft copolymer is exposed at the surface. This has previously been observed by micro-FTIR mapping of MAEP-grafted membranes [7] , [21] . SEM images of the two samples which displayed high graft extent, samples AA/IA(3.0)-R (graft extent of 84% and COO/F = 1.23) and AA-P (graft extent of 86% and a COOH/F of 1.03) after immersion for two weeks in 1.5 × SBF are displayed in Fig.…”