Thermosensitive poly(organophosphazene) hydrogels for a controlled drug delivery

Thermosensitive poly(organophosphazenes) were synthesized for a controlled release of hydrophilic polymeric model drugs such as dextran and albumin in this study. The solutions of the present polymers bearing both hydrophobic side groups of l-isoleucine ethyl ester (IleOEt) and hydrophilic groups of α-amino-ω-methoxy-PEG (Mw 550) (AMPEG550) exhibited reversible sol–gel transition behaviors with changes of temperature. Viscometric measurement indicated that the thermosensitive hydrogels with good strength could be formed from the solutions in the range of the concentrations of 7–15 wt% around body temperature. For increasing their biodegradabililites, depsipeptides of ethyl-2-(O-glycyl)lactate (GlyLacOEt) were also introduced to the polymer, showing enhanced degradation of hydrogels. In vitro release behaviors of hydrophilic FITC-dextran (Mw 71,600) and human serum albumin from these polymer hydrogels were sustained for about 2 weeks while those from poloxamer (Pluronic F-127) hydrogel showed a distinct initial burst. The release of FITC-dextran exhibited concentration-dependent behavior ranging from 7 to 15 wt% of the polymer solution while it was almost independent of the concentration of FITC-dextran.