Controlled release of amoxicillin from hydroxyapatite-coated poly(lactic-co-glycolic acid) microspheres

Negatively charged poly(lactic-co-glycolic acid) (PLGA) microspheres with an encapsulated hydrophilic antibiotic (amoxicillin) have been prepared by the solid-in-oil-in-water (s/o/w) method using the anionic surfactant, sodium dodecyl sulfate (SDS). Drug encapsulation efficiency is over 40%. Successful coating of hydroxyapatite (HA) on these negatively charged PLGA microspheres has been achieved by a dual constant composition method in 3-6 h. The HA-coated PLGA microspheres (HPLG) have been characterised by zeta-potential and particle size measurements and the coating has been confirmed to be calcium deficient HA by analysis of X-ray diffraction, Fourier transform infrared spectroscopy and wavelength dispersive spectroscopy. The morphology of HPLG was studied by scanning electron microscopy, and cross sections of HPLG microspheres were prepared and imaged using focused ion beam microscopy. In-vitro drug release experiments in PBS (pH7.4) showed a sustained release profile for at least 31 days with little initial burst release. It shows a triphasic drug release profile commonly observed for biodegradable polymers.