Poly(hydroxybutyrate-co-hydroxyvalerate) Microspheres for the Encapsulation and Controlled Release of Heparin
Résumé
The water-in-oil-in-water double emulsion followed by solvent extraction and evaporation method was used to encapsulate heparin in poly(hydroxybutyrate-co-hydroxyvalerate) (PHB-HV) microspheres to provide sustained heparin release. The impact of the polymer molecular weight and formulation parameters on the microspheres' morphology, encapsulation efficiency and release is studied and physical interpretations were provided, by relating the polymer precipitation time and hardening of the microspheres to the viscosity of the organic phase, solvent extraction time and pores and microspheres sizes. High molecular weight PHB-HV allowed a convenient encapsulation of heparin, with a modulation of the encapsulation efficiency and release rate by changing the formulation parameters. Heparin release was found to be gradual over seven days with low burst effect. After release, large microspheres having visible porosity on their surface became flattened whereas small smooth microspheres remained unchanged. On the contrary, the structure of low molecular weight microspheres was completely deformed after 7 days in phosphate buffer due to the lack of mechanical properties.