Poly[(amino acid ester)phosphazenes] as substrates for the controlled release of small molecules

Three different poly[(amino acid ester) phosphazenes] have been examined in order to investigate their possible use as drug delivery vehicles. The three polymers are poly[di(ethyl glycinato)phosphazene], poly[di(ethyl alanato)phosphazene] and poly[di(benzyl alanato)phosphazene]. These macromolecules either share the same amino acid residue or the same ester group, and this facilitated comparisons of the hydrolytic decomposition and the small molecule release profiles of the polymers. The polymers were synthesized by treatment of poly(dichlorophosphazene) with an excess of the appropriate amino acid ester. Tetrahydrofuran solutions of each polymer were then thoroughly mixed with ethacrynic acid, a diuretic, or Biebrich Scarlet, an azo dye. Films cast from these solutions were immersed in aqueous media (pH 7) at 25°C and at 37°C for approximately 1400 h. During these experiments, the release of the small molecules was monitored by UV/visible spectroscopy. The molecular weight decline and the mass loss of the polyphosphazene films were measured.