Preparation and tunable temperature sensitivity of biodegradable polyurethane nanoassemblies from diisocyanate and poly(ethylene glycol)

The development of temperature-responsive and biodegradable polymeric nanoparticles with tunable temperature sensitivity is of great interest. In this study, alternating polyurethanes were synthesized from diisocyanate (L-lysine ethyl ester diisocyanate (LDI) or hexamethylene diisocyanate (HDI)) and poly(ethylene glycol) (PEG) of different molecular weights. The resulting polyurethanes were then used to prepare nanoparticles either by direct dispersion in water or by nanoprecipitation. The temperature-responsive property of the polyurethane nanoparticles was evaluated by UV-visible transmittance experiments and dynamic light scattering. During the heating-cooling cycling, the LDI-PEG series showed almost no change except LDI-PEG600, but the HDI-PEG series exhibited reversible dispersion-aggregation changes. The nanoparticles were spherical at temperatures below or above the cloud point, as observed by transmission electron microscopy. The cloud point temperature of the alternative polymers was found to depend on both the hydrophilic-hydrophobic balance of the alternative chain and polymer concentration. The degradation test in vitro revealed a fall of less than 20% of polymer molecular weight within 12 days. The transition temperature was close to human body temperature, which could have great potential in biomedical fields.