Polyphosphazenes containing lactic acid ester and methoxyethoxyethoxy side groups — Thermosensitive properties and, in vitro degradation, and biocompatibility

Abstract

The thermosensitive and hydrolytic properties and biocompatibility of polyphosphazenes containing lactic acid ester and methoxyethoxyethoxy as co-substitutents were investigated. Depending on the type of lactic acid ester, these polyphosphazenes exhibited lower critical solution temperatures (LCST) (from 33 to 52 °C), which were almost concentration-independent in the range of 1.5 to 15 wt% of the polymers in aqueous solution. The salt effect on the thermosensitivity of the polymers was studied by measuring their LCST in aqueous solutions containing various salts. Bu 4 NBr and KI showed salting-in effects among the tested six salts, but NH 4 Br, NaBr, NH 4 Cl, and NaCl showed salting-out effects. Hydrolysis studies showed the rate of polymer hydrolysis decreased in the order of basic > acidic > neutral solution. The polyphosphazene with bulkier and more hydrophobic ester groups was more stable in hydrolysis. The results of a cytotoxicity study using an MTT assay method with HepG2 cell and K562/VCR cell showed that these polyphosphazenes and their degradation products were biocompatible. The thermoresponsiveness and biocompatibility of these biodegradable polyphosphazenes may favor the polymers as potential stimuli-responsive materials in biomedical applications.