The disclosure provides a method to form sustained release drug-containing microparticles with a biodegradable polymer. The method involves forming a polymer-drug-organic solvent phase, and dispersing the polymer-drug-organic solvent phase in an aqueous suspension of an inorganic gel, which may be hydroxyapatite. The hydroxyapatite appears to coat the polymer-drug-solvent droplets to prevent them coalescing. The solvent then evaporates with stirring of the dispersion, at which time the droplets solidify to drug-containing microparticles. The inorganic gel allows suitably small microparticles to form without use of an organic emulsifier.
