Shawn R. Pucher

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 degrees C and at 37 degrees 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.

Antibacterial activity and mutagenicity studies of water-soluble phosphazene high polymers

Eight water-soluble phosphazene high polymers, [NPR2]n (R, organic, water-solubilizing side-group; n, approx: 15,000) and the small-molecule counterparts of the polymers were examined for antibacterial activity against six different strains of bacteria (Escherichia coli, Salmonella typhimurium (TA 100), Salmonella pullorum, Streptococcus faecalis, Bacillus subtilis and Pseudomonas aeruginosa). Antibacterial testing was carried out by measuring zones of inhibition and changes in solution turbidity over time. In addition, the antibacterial activity of the surfaces of cross-linked poly[di(methoxyethoxyethoxy)phosphazene] (MEEP) hydrogels were investigated. A number of the high polymers, as well as the MEEP hydrogels, impeded bacterial growth. Only E. coli was unaffected by the phosphazenes. A possible explanation for the antibacterial character of the polymers is presented. The same compounds were monitored for potential mutagenic activity using the Salmonella typhimurium tester strains TA 100 and TA 98. None of the high polymers or their small-molecule analogues showed mutagenic activity in either strain of Salmonella at the concentrations tested. The use of these materials as coatings for artificial implants is discussed.

Activity of urea amidohydrolase immobilized within poly[di(methoxyethoxyethoxy)phosphazene] hydrogels.

Urea amidohydrolase (urease) was immobilized within poly[di(methoxyethoxyethoxy)phosphazene] (MEEP) hydrogels. This was accomplished by mixing an aqueous solution (pH 7) of the soluble polymer with the enzyme. Films of the conjugate were cast and the solvent removed to yield an MEEP/enzyme composite. The conjugate films were dried in a vacuum and were then cross-linked by exposure to 0.2 or 0.5 Mrad of 60Co gamma-radiation to give an MEEP network with the enzyme entrapped within its matrix. The cross-linked films were sectioned into strips and were washed with pH 7 buffer to remove enzyme adhering to the surface. The films were then allowed to swell to form a hydrogel in pH 7 buffer to which was added a 1.0 M aqueous urea solution. The increase in pH from the conversion of urea to ammonia was monitored over a 24 h period. The immobilized enzyme could be recycled at least five times without significant loss of activity. Several control experiments were also performed by monitoring the pH of buffer solutions that contained hydrogels devoid of entrapped urease, and by monitoring the pH of solutions of the free, non-irradiated and free, irradiated urease after the addition of the urea solution. The polymer-free, irradiated urease lost little to no activity compared with its non-irradiated counterpart. The MEEP gel-immobilized enzyme retained approximately 80% of the activity of the non-irradiated, polymer-free urease.