Study On Preparation Of Drug-loaded Collagen-modified Polylactide Microspheres And Its Performance

Microspheres have been widely used in the field of drug controlled release anddrug targeting delivery as a main carrier of drug delivery system. Compared with thetraditional pharmaceutical preparations, it has advantages of improving drug stability,long-term controlled drug release, increasing drug targeting and reducing drug sideeffects. Polylactide (PLA) has become widely researched carrier material ofmicrospheres due to its nontoxicity and biodegradability. However, the hydrophilicity ofPLA needs to be improved since its high hydrophobicity retards cell attachment, reducesthe drug intake of cell and affect the drug efficiency. In addition, the drug release fromPLA particles is difficult to be controlled because of long-term acid autocatalyticdegradation of polymer matrix. These limit the clinical application of drug-loaded PLAmicrospheres.In order to improve the defects of PLA and meet the requirements of idealmaterials of drug vehicles, the method of graft modification was adopted to introducecollagen(riched in active groups) into PLA. The hydrophilicity and degradability ofcollagen modified-PLA(CPLA) was studied. After that, the blank microspheres andaspirin sustained release microspheres were prepared via the emulsion-solventevaporation technique, followed with its measurements of morphology, size, drugloading and encapsulation efficiency. Finally, the controlled release properties of theobtained microspheres and the mechanism of drug release from microspheres wereinvestigated.(1) PLA was synthesized by the method of direct melt polycondensation, then,CPLA was synthesized by means of acylation and dehydration condensation. Thecharacterization of CPLA were studied by infrared spectroscopy (FTIR), fluorescencespectroscopy, gel permeation chromatography (GPC) and by ninhydrin, which verifiedcollagen was successfully grafted to the PLA. Analysis of GPC showed that theweight-average molecular weight(MW) of CPLA(DCC) and CPLA(PCl5) was higherthan that of PLA. The collagen grafting rate of CPLA(DCC) and CPLA(PCl5) was6.19%and5.10%respectively, which was quantitatively determined by Ninhydrin.(2) The hydrophilicity and degradability of PLA and CPLA were studied. Theresults showed that the water absorption of CPLA was greater than that of PLA, namely,its hydrophility was obviously better than that of PLA. In the degradation process of CPLA, the pH value of degradation medium (distilled water) was not significantlydecreased, there was no obvious acid catalytic degradation phenomenon on the processof degradation, and the degradability was more stable. Whereas in the degradationprocess of PLA, the pH value of degradation medium was significantly decreased, theacidity of which was strong. The acid catalytic degradation of PLA was quite obvious.(3) CPLA microspheres were prepared by O/W emulsion solvent evaporationmethod, the influences of preparation conditions on the size of microspheres wereinvestigated through single factor experiment and orthogonal experiment. Throughcomprehensively consideration of size and morphology, the best preparation conditionsof CPLA-MS were determined as follows: stiring speed (800r/min), the concentrationof CPLA (5%), the concentration of PVA (0.75%), the concentration of Tween-80(0.5%). Analysis results of ESEM showed that microspheres exhibited well-definedmorphology with smooth spherical surface and hollow inner structure. The results ofsize analysis showed that the average size of CPLA (DCC)-MS and CPLA (PCl5)-MSwas (1.730±0.120) μm and (2.211±0.125) μm respectively, in addition, their sizedistributions were narrow.(4) The aspirin-loaded CPLA microspheres were prepared by O/W emulsionsolvent evaporation method. The influences of preparation conditions on the drugloading and encapsulation efficiency of microspheres were investigated. Throughcomprehensively consideration of size and encapsulation efficiency, the preparationconditions of ASP-CPLA-MS were determined as follows: oil phase solvent(dichloromethane), ASP: CPLA=20%. The volume ratio of oil phase to water phasewas1:10and1:15respectively. ASP-CPLA-MS exhibited well-defined morphologywith smooth spherical surface and honeycombed inner structure, the average size ofASP-CPLA (DCC)-MS and ASP-CPLA (PCl5)-MS was (3.738±0.225) μm and(4.816±0.257) μm, their average drug loading was (8.638±0.122)%and (7.86±0.24)%,the average encapsulation efficiency was (51.830±0.733)%and (47.16±1.45)%respectively. The results of thermal performance showed that the glass transitiontemperature (Tg) of the ASP-CPLA-MS was significantly higher than that of the blankmicrospheres, mixture of aspirin and blank microspheres. This indicated that the drug inmicrospheres was dispersed in or adsorbed on the skeleton of microspheres, rather thansimply adhered on the surface of microspheres in a form of physical blend.(5) In vitro cumulative drug release ratios of ASP-CPLA-MS and ASP-PLA-MSwere determined, the drug release kinetics were evaluated using mathematical modeland the mechanism of drug release from microspheres were preliminary investigated. The results showed that the drug sustained release time of ASP-CPLA(DCC)-MS andASP-CPLA(PCl5)-MS was480h and624h respectively, which was higher thanASP-PLA-MS(144h and168h), this exhibited the highlight of long-term sustainedrelease. In addiation, the release of aspirin from CPLA microspheres followed aHiguchi model, which indicated that the release of drug was based on fick’s law in theform of diffusion controlled release from polymer skeleton to medium. Collagenmodified polylactide showd a good application prospect in the field of drug sustainedrelease.