The dissipative particle dynamics (DPD) simulation method and experimental study were used to investigate the mechanism of poly-lactic acid (PLA) microspheres formation.Nifedipine was used as the model drug

PLA as the carrier

and poly vinyl alcohol (PVA) as the stabilizer

respectively.The mechanism of PLA microspheres formation was developed.The forming process of PLA microspheres consisted of four steps: (1) high dispersion

(2) aggregation of PLA molecules

(3) nifedipine molecules dispersion into the PLA matrix

(4) formation and stabilization of PLA microspheres

sequentially.Based on the mechanism analysis

it was pointed out that there was a maximum of the nifedipine content that the PLA matrix could carry.If the content of nifedipine was below the maximum

almost all the nifedipine molecules dispersed into the PLA matrix.However

when the nifedipine content exceeded the maximum

some nifedipine molecules would be repulsed outside the microspheres

resulting in surplus nifedipine molecules aggregation.