Porous polylactide (PLA) microspheres were prepared by means of the modified double emulsion solvent evaporation. The organic solvents with different boiling points and aqueous solubility were used to prepare PLA microspheres with different porous structures. Microspheres prepared with methylene chloride

chloroform and toluene as solvents had the similar homogeneous porous structure

while those microspheres with ethyl acetate as solvent showed a hollow structure with a porous thin shell. The effects of solvent types on porous structure of microspheres were discussed. It was concluded that the removal rate of solvent plays the decisive role in determining the porous structure of microspheres. Accordingly

a formation mechanism of porous microspheres fabricated with different solvents was proposed.