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Calcification Resistant Polyurethanes Modified with Geminal Bisphosphonate Groups
Published online by Cambridge University Press: 10 February 2011
Abstract
Non-esterified geminal bisphosphonate groups (0.06–0.12 mmol/g) were covalently attached to elastomeric polyurethanes (PU) based on 4,4′-methylenebis(phenyl isocyanate) (MDI) and represented by a polyether-urethane (PEU), a polyurethane-urea (PUU), and a polycarbonate-urethane (PCU). Auxiliary 6-bromohexyl or carboxylic groups were attached to PU via base-induced N-alkylation of urethane NH sites either with 1,6-dibromohexane or with lithium salts of ω-bromocarboxylic acids. An alternative method to introduce carboxylic groups into the polymers via reactions of bromoalkylated PU with thiol-containing carboxylic acids was found to be more suitable than the direct carboxyalkylation. The subsequent reactions either of thiol-containing bisphosphonates with the attached 6-bromohexyl groups or of 3-amino-Ihydroxypropylidene-1,1-bisphosphonate (pamidronate) with N-hydroxysuccinimide-activated carboxylic groups of PU led to the bisphosphonate-modified PU. The polymers do not undergo a significant degradation in the course of the modification reactions, their mechanical properties and elasticity remain mostly unaffected. Water uptake of the bisphosphonate-modified PU increased up to 26% depending on the extent of modification. Bisphosphonate-modified PUU showed a significantly lower in vivo calcification compared to the non-modified polymer.
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