Preparation and rapid degradation of nontoxic biodegradable polyurethanes based on poly(lactic acid)-poly(ethylene glycol)-poly(lactic acid) and L-lysine diisocyanate

To obtain rapid biodegradable biomaterials, a biodegradable triblock oligomer poly(lactic acid)-poly(ethylene glycol)-poly(lactic acid) (PLA-PEG-PLA) was designed and synthesized as a soft segment of polyurethane. Then new nontoxic biodegradable polyurethanes were prepared using the same stoichiometric ratio of PLA-PEG-PLA, L-lysine ethyl ester diisocyanate (LDI), and 1,4-butanediol (BDO). The molecular weights of polyurethanes were controlled by adjusting the polymerization temperature. The resulting polyurethanes were characterized by gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC). Furthermore, the biodegradability of the synthesized polyurethanes was evaluated at 37 degrees C in phosphate buffer solutions (PBS) under different pH values and enzymatic solution at pH 7.4. The results showed that these polyurethanes could be rapidly degraded in PBS and enzymatic solution, as demonstrated by weight loss measurements and scanning electron microscope (SEM) observations. The degradation rates of these polyurethanes were mainly regulated by microphase separation degree, and could be restrained in lower pH value PBS. Moreover, the degradation products did not significantly decrease the pH value of incubation media, which would be useful to improve biocompatibilities of these polyurethanes in vivo. The current work provides a more promising approach to prepare nontoxic biodegradable polyurethanes with rapid degradation rates. These new materials may find potential use for drug delivery systems and magnetic resonance imaging (MRI) contrast agents.