The design of drug-carrying elastomers based on poly(phosphoester-urethanes) (PPUs) is presented. Bis(2-hydroxyethyl)phosphite and bis(6-hydroxyhexyl)phosphite were used as the chain extenders and 1,4-butane diisocyanate was the basis of the hard segment. The labile phosphoester linkage in the backbone of the PPU confers biodegradability on the polymer. Using the reactive phosphite side chain in the PPUs, p -aminosalicylic acid and benzocaine were attached pendantly to the polymer with or without a spacer. In vitro release of both drugs was complete in several hours. In contrast, ethambutol incorporated into the backbone of the polymer was released in over 10 days. Preliminary cytotoxicity of the drug-carrier to a macrophage cell line was also assessed.

A novel set of putrescine-based segmented polyurethanes was synthesized using 1,4-butane-diisocyanate and phosphoester diols, and was characterized for its potential as a degradable biomaterial. These poly(phosphoester-urethanes) (PPU) were flexible polymers with ultimate tensile strength (UTS) from 2 to 3 MPa, elongations up to 80% and tan delta near 0.15. The incorporation of phosphoester bonds in the backbone of the polymer by using bis(2-hydroxyethyl)phosphite (BGP) and bis(6-hydroxyhexyl)phosphite (BHP) as chain extenders resulted in hydrolytic degradation which was evaluated in vitro. By varying the content of the phosphoester diol BGP, degradation rate, as followed by mass loss and GPC, could be modulated. Polymers based on the more hydrophobic monomer, BHP, showed slower degradation than corresponding BGP based polymers. Tensile properties of PPU-B2 after 22 days in vitro degradation show more than a 50% drop in UTS and ultimate elongation, likely caused by void spaces left behind in the polymer after mass loss and swelling. The attachment of a drug, PAS, pendant to the phosphoester group of the PPU was demonstrated. PAS was linked via the spacer 4-hydroxybenzaldehyde, and free, intact drug was released in about 5 h from a thin film.