Thermo-Responsive Injectable MPEG-Polyester Diblock Copolymers for Sustained Drug Release

Thermo-responsive diblock copolymers composed of hydrophilic methoxy poly(ethylene glycol) (MPEG) and hydrophobic biodegradable polyesters were prepared for application as injectable drug delivery systems, because they show a thermo-responsive sol-to-gel transition, especially around body temperature, when dispersed in aqueous solutions. The thermogelling hydrogels formed by hydrophobic aggregation could be varied by changing the components of the hydrophobic polyester part. For the polyester block in the present study, 95 mol% of [straight epsilon]-caprolactone (CL) was used for the main polyester chain and 5 mol% of p-dioxanone (DO) was copolymerized randomly by the MPEG initiator in the presence of HCl as the catalyst. By adding a small portion of DO into the poly [straight epsilon]-caprolactone (PCL) chains, the temperature range of gelation, the intensity of viscosity and the drug release behavior were changed. The MPEG-b-poly([straight epsilon]-caprolactone-ran-p-dioxanone) (MPEG-b-PCDO) hydrogel showed the enhanced drug release in vitro and in vivo compared to MPEG-b-PCL hydrogel. Therefore, MPEG-polyester hydrogels may serve as minimally invasive and therapeutic, injectable hydrogel systems with adjustable temperature-responsive and biodegradable windows, as well as sustained release of drugs over a certain time period.