Study On Preparation Of Drug-Loading PLA Microspheres And Nanospheres And Drug-Releasing Performance

In this paper, the D,L polylactic acid (PLA) was synthesized by the two-step polymerization.Then the PLA was purifized and the molecular weight was determined. The product was characteristized by using IR,HNMR and DSC spectrum .The influence of the amounts of octoate stannum on the molecular weight ,the recrystallization times on the molecular weight and the relationship between the molecular weight and Tg was discussed. The results showed that in the course of ring-opening polymerization of lactide the ratio of initiator to monomer was critical to the molecular weight of PLA. If the ratio of octoate stannum to lactide was too high or too low, the high molecular weight PLA would be unable to be got. When the ratio of the initator to the monomer was too high, the activate centers would be too many and it was hard to get a high molecular weight PLA,while the ratio of the initator to the monomer was too low and the activate centers were too few and then it would be hard to get a great monomer conversion. The more recrystallization times of raw lactide,the better its optical activity and then the higher its purity.Therefore it would be easier to controll the PLA molecular weight by varing the molar ratio of iniator to monomer.The PLA microsphere containg RFP or Hydrochloride Oxytetracycline was prepared by an oil-in-water and water-in-oil solvent evaporation method and the different process conditions of preparing the drug-loading polylactic acid microsphere were investigated. Influence of some factors such as the molecular weight of PLA, the content of drug,the microsphere size and the pH value of release media on the drug-releasing performance of the microspheres was studied.The result showed that the greater the molecular weight of PLA , the less it degraded and the slower the drug released. Again, the greater the content of the drug and the bigger the difference of drug concentration between in and out of the microsphere, and the more quickly the drug released. The smaller the microsphere size , the more quickly the drug released. In the alkali medium, the PLA degraded more quickly and RFP became more stable, resulting in faster release of drug.Finally the PLA nanospheres containing Griseofulvin were prepared by method of oil -in-water solvent evaporation and uniform designed experiment. The result shew that the nanospheres were good in spherical shape and narrow distribution of the particle sizes.Theparticle diameter was about 114nm , the comprehensive score(S) of the nanosphere was 95.59, the error was 3.66% and the drug content (DL%) was 13.55% by the linearity regression and the three-time-repeated experiments. The drug-releasing rate of the microsphere was slower, while that of the nanosphere could have an abrupt increase, which indicated the latter could have the function of solubilizing the drug.