Preparation, Properties And Application Of Biodegradable Sustained Release Microspheres

Biodegradable sustained release microspheres have garnered much attention in the past few decades, sustained release microspheres can control the drug release rate and release time, thus, obtain long-term therapy, reduce the dosing frequency. It can also relieve drug stimulation, drug toxicity and side effects, and protect drug from degradation caused by the special environment in vivo, such as enzyme, thus, improving the therapeutic efficacy. Poly(lactide-co-glycolide)(PLGA) is the most common used biomaterial for microspheres, but the hydrophobicity of PLGA limits the types of drugs that can be encapsulated, and also, affects the drug release behavior. In this research, we synthesized the amphiphilic poly(dl-lactide-co-glycolide)-methoxypoly(ethyleneglycol)(PLGA-mPEG) copolymers by grafting the hydrophilic methoxypoly (ethyleneglycol)(mPEG) to PLGA molecular chain. Based on PLGA-mPEG, we prepared a series of drug-loaded microspheres by emulsion evaporation methods, optimized the microspheres preparation parameters and studied the microspheres degradation and drug release mechanisms. Finally, we evaluated the feasibility of sustained-release microspheres for the treatment of chronic skin disease.The main achievements were summarized as follows:1. PLGA-mPEG diblock copolymer was synthesized by bulk ring-opening polymerization method, achived by the coordination-insertion of glycolide (GA) and DL-lactide (LA) that triggered by the initiator of monomethoxypoly(ethylene glycol)(mPEG) and the catalyst of stannous octoate. A series of linear PLGA-mPEG diblock copolymer different in molecular weight and LA/GA ratio were systhesized by adjusting the ratio of GA, LA and mPEG in the polymerization. The molecular structure, molecular weight and molecular weight distribution of these diblock copolymers were analyzed via Fourier transform infrared spectrometer (FT-IR),1H nuclear magnetic resonance spectroscopy (1H NMR),13C nuclear magnetic resonance spectroscopy (13C NMR) and gel permeation chromatography (GPC). The results revealed that the LA/GA ratio error almost not exceeding5%, and the molecular weight error not exceeding5.3%2. Based on the linear PLGA-mPEG diblock copolymer, we prepared microspheres encapsulating hydrophobic and hydrophilic drugs by the single and double emulsion evaporation methods, respectively. By observing the microspheres forming process with the optical microscope, we found that the microspheres prepared by single emulsion evaporation method were sphere, with a smooth surface and very low broken percentage. Higher PVA concentration and faster emulsification rate would result in lower drug encapsulation efficiency, smaller particle size, severer burst release and faster release rate. The inner aqueous proporation is the key factor that affected the microspheres morphology prepared by double emulsion evaporation method. We found that250mg PLGA-mPEG can encapsulate0.1ml inner water phase and generated microspheres best in morphology, only4.33%broken percentage and67.74±1.87%encapsulation efficiency. As the inner phase increased (0.2ml,0.4ml), the broken percentage rised (46.67%,60.33%) and the encapsulation efficiency decline (32.66±3.21%,25.43±2.04%). The increase of inner phase also caused a severer burst release and faster release rate.(3). A series of mizolastin loaded PLGA-mPEG microspheres in different Mw and LA/GA ratio were prepared by single emulsion evaporation method. With degradation time increased, changes in weight loss, Mw, PI and microspheres morphology were investigated via weight method, GPC and SEM. Microsphere revealed a surface-to-bulk degradation manner due to its solid structure. Lower Mw of PLGA-mPEG resulted in faster microsphere erosion rate, faster mean size and mass reducing rate. PLGA-mPEG microspheres in different Mw did not show obvious difference of Mw reducing rate in the early degradation period, while, PLGA-mPEG in higher Mw showed a faster Mw reducing rate. The release rate of mizolsatine was controlled by the erosion rate of microspheres, lower PLGA-mPEG Mw resulted in faster release rate. Lower LA/GA ratio in PLGA-mPEG caused a faster degradation and release rate of microspheres.(4) vancomycin (VM), lysozyme (LZ) and bovine serum albumin (BSA) were chose as the modle drugs, encapsulated in PLGA-mPEG microspheres in different Mw and LA/GA ratio by double emusion evaporation method, and the effects of PLGA-mPEG Mw, LA/GA ratio, drug Mw on microspheres degradation and release behaviors were studied. Microspheres revealed a bulk degradation manner and showed a faster degradation rate than that prepared by single emulsion evaporation method, and the lower PLGA-mPEG Mw caused a faster degradation rate. The release rate of VM was much faster than LZ and BSA, and mainly controlled by drug diffusion, not by the microspheres degradation rate. LZ and BSA showed typical tri-phase release profiles, and were mainly controlled by the microspheres erosion rate. PLGA (9.5)-mPEG (5) microspheres showed the fastest erosion rate and release rate of LZ and BSA. PLGA (19.9)-mPEG (5) microspheres degradated faster than PLGA (31.6)-mPEG (5) in mass, but the degradation difference did not resulted in different erosion rate of microspheres, thus, the release rates of LZ and BSA were similar. Lower LA/GA ratio in PLGA-mPEG caused a faster degradation and release BSA rate of microspheres.(5) Water soluble fluorescent drugs were applied for studying the microspheres release mechanism. Small drug (fluorescein sodium) loaded microspheres revealed a persistent fluorescence in the microspheres surface during in vitro release, and the fluorescence got weaker as the fluorescein sodium released. The phenomenon proved the small drug relase mechanism that we proposed. To macromolecular drug (FITC-BSA) loaded microspheres, the fluorescence almost dispeared in the surface after the burst release, and after an obvious erosion happened in the microspheres surface, the fluorescence appeared again. The fluorescence got weaker as the FITC-BSA released and the phenomenon proved the macromolecular drug relase mechanism that we proposed.(6) The PLGA-mPEG microspheres were basically biocompatible with low cell cytotoxicity due to high cell viability at all culture concentration and time by an MTT assay and acute toxicity. Mizplastin was employed as medicine for the treatment of atopic dermatitis. Mizolastine microspheres got a high encapsulation efficiency of92.44±5.04%, drug loading of4.240±0.231%, particle size range from2to10μm and a sustained release last for2weeks. Mizolastine microparticles injection and daily mizolastine injection treatments were compared. Animal experimental results showed that mizolastineMP injection got a similar curative effect on inhibiting the ear swelling, dermatitis score, inflammatory cell infiltration and concentration of IgE compared to daily mizolastine injection treatment, indicating that drug-loaded microparticles treatment could provide an effective alternative therapy for the management of chronic endemic.