Solvent-free preparation of caprolactone oligomer microspheres

Abstract Caprolactone ( M n ∼3000 Da, melting point ∼46 °C) oligomer microspheres were prepared by an organic solvent-free process, and were investigated as a delivery system of a hydrophobic model drug (estradiol). The drug was dissolved in a polycaprolactone/poly(ethylene glycol-b-caprolactone) mixture at 50 °C, which was above the melting points of both polymers. The mixture was homogenized in water for 10 min at 50 °C, then it was quenched in the ice bath for 10 min to harden the microsphere. The polycaprolactone of the poly(ethylene glycol-b-caprolactone) coaggregated into the microsphere, and poly(ethylene glycol) formed a shell layer of the microsphere that protects the microsphere from interparticle aggregation during the hardening process of the microsphere in water. The size of microsphere could be controlled by the amount of polycaprolactone relative to poly(ethylene glycol-b-caprolactone). Estradiol release from the microsphere was investigated.