Degradable polyphosphazenes for biomedical applications

Abstract

Polyphosphazene derivatives having amino acid ester side groups were prepared by reaction of poly (dichloro phosphazene) with ethyl esters of amino acids and dipeptides. In vitro degradation studies demonstrated that the rate of degradation depends on the nature of the amino acids. Introducing small amounts of depsipeptide ester co-substituents resulted in a drastic increase of the degradation. The rate of hydrolytic degradation of the polyphosphazene materials could be controlled by the content of the depsipeptide ester side groups or by blending poly [amino acid ester) phosphazenes] with poly [(amino acid ester)-co-(depsipeptide ester) phosphazenes]. A more detailed study of the degradation process indicated that in the initial stage of polymer degradation the amino acid ethyl ester is released, with subsequent formation of amino acid, ethanol and polymer backbone cleavage. Polyphosphazenes substituted with ethyl glycinate (D.S. 99%) are partially crystalline. D.S.C. experiments demonstrated that the degree of crystallinity and the morphology of the crystalline phase depends on the storage conditions.