| Biodegradable polymers play an important role in the biomedical field. Polyurethane has been widely studied as biodegradable polymers due to its biocompatibility and its controllable structures and properties. The polyurethanes are expected to exhibit tunable temperature-sensitivity by selecting proper hydrophilic and hydrophobic segments.Alternative 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 chemical structure and molecule weight of the polymers were examined by 1H NMR, FT-IR, gel permeation chromatography (GPC).The resulting polyurethanes were 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 experiment and dynamic light scattering. During the heating-cooling cycling, LDI-PEG series showed almost no change except LDI-PEG600, but HDI-PEG series exhibited reversible dispersion-aggregation changes. 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 nanoparticles were spherical at temperatures below or above the cloud point, as observed by transmission electron microscopy. The degradation test in vitro revealed a fall of less than 20% of polymer molecular weight within 12 days.HDI-PEG polyurethanes exhibit temperature-sensitivity. The transition temperature was close to human body temperature, which is expected to be used for drug delivery. An anti-cancer drug, driamycin (ADR), was encapsulated into polyurethane using dialysis method. The particle sizes of HDI-PEG600,HDI-PEG1500 and HDI-PEG2000 nanoparticles loading with ADR are 863nm, 827nm and 813nm, respectively, as determined by dynamic light scattering (DLS). The maximum drug loading and encapsulation efficiency are up to 37% and 74%, respectively. If the environmental temperature is lower than the cloud point temperature, the accumulate ADR release was less than 20% after three days incubation. When the temperature is higher than the cloud point temperature, over 80% of ADR was released in ten hours. The in vitro release behavior of ADR is temperature-sensitive. |
