环糊精改性生物降解聚酯及其药物控制释放系统的研究

【作者】 郭颖志；

【导师】 顾忠伟；

【作者基本信息】 中国协和医科大学 ， 药物化学， 2006， 博士

【摘要】 聚-ε-己内酯、聚丙交酯由于具有良好的生物降解性、生物相容性和生物可吸收性,在生物医药领域得到广泛的应用。合成两种单体的无规或嵌段共聚物是改善各自性能的一种方法,另一种常用的改性方法是在分子链中引入支化结构。本研究用共聚方法,合成共聚组成为85/15(CL/LA)的聚-ε-己内酯-DL-丙交酯的嵌段共聚物,考查了共聚物作为埋植剂在动物体内、体外的降解行为及其相关性。结果表明,体内、体外降解行为基本相似,降解首先发生在无定形区,开始主要是PLA链段的降解,引起共聚组成发生变化,降解过程中聚合物的结晶度和热焓随降解的进行而升高。该嵌段共聚物形成的埋植剂在体内、体外降解三年后仍保持完好的形状,有望作为长效药物控释制剂的载体。由于环糊精是一类环状多糖化合物,具有特殊的结构和性能,并且是广为使用的药物载体。利用环糊精的亲水性和多羟基的特点,有望对聚酯从亲水性的改善和支化结构的形成两方面同时对聚酯性能加以改善。通过阴离子开环聚合,合成了β-CD为功能端基的聚-ε-己内酯,考查了单体/催化剂的比例、聚合反应温度和时间对聚合物分子量及其分布的影响。结果表明,聚合温度在60～70℃,反应8小时获得单体转化完全、分子量高并且分布较窄的聚合物。PCL链上β-环糊精的引入,使聚合物的吸水率提高,与水的接触角变小,提高了聚合物的亲水性。通过阴离子开环聚合,合成了β-CD为核的星型PCL、PDLLA、PLLA,研究了影响聚合物臂数的反应条件以及聚合物臂数对性能的影响。β-CD上羟基离子化数目决定聚合物臂数,同时影响聚合反应速率和单体的转化率:羟基离子化数目越多形成的臂数越多,引发活性越大,聚合速率也越快;星型结构的聚合物较线性聚合物有较低的熔融温度、结晶度、特性粘度,同时臂数越多,差别越大。相同的条件下,DLLA和LLA两种单体的手性差别对聚合反应速率、聚合结果没有影响。以BSA为模型蛋白,用W/O/W法制备了含药微球,考查了线性PCL和不同臂数星型PCL微球的降解行为和药物释放行为。结果表明,分子量相近的情况下,星型聚合物的降解速率较线性聚合物的降解速率快,而且臂数越多,降解越快;与线性聚合物相比,星型聚合物形成的微球载药量高,突释量小,释放速率快,而且支化程度越高,释放速率越趋于平缓。当分子量大于一定值后,降解释放速率主要受分子量影响,臂数的影响不明显。更多还原

【Abstract】 Due to their excellent biodegradability,biocompatibility and bioabsorbance, poly-ε-caprolactone(PCL) and polylactide(PLA) are widely used in biomedical fields.In order to improve their properties it is usually used to synthesize their block or random copolymer by adjust the molar ratio of the two monomers.Another method usually be used to modify their properties is introducing branch structure into the polymer chain.First,block copolymer of poly-ε-caprolactone-b-lactide with 85 to 15 mole ratio (CL:LA) was synthesized and the biodegradation behavior as implant were investigated in vitro and in vivo.The biodegradation behaviors of in vitro and in vivo were similar.PLA segment was degraded initially because it was amorphous so its mole ratio was decreased in the beginning period of degradation.The crystallinity and fusion enthalpy of the implant were increased in the process of degradation.The appearance form of the implants was also sustained after three years and the weight loss is only about 25%(in vivo),so the polymer maybe used for long-acting drug delivery system.Cyclodextrin is a kind of cyclic polysaccharides with special structure and properties,and it is also extensively used as drug carrier.By using its hydrophilicity property and multi-hydroxy in the molecules,it is possible to introduce hydrophilicity and branched structure to PCL or PLA to enhance their degradation rates.Using anionic ring-opening polymerization method,PCL withβ-cyclodextrin (β-CD)as the end functional group were synthesized and characterized.Some polymerization factors influence on the monomer conversion and molecular weight and distribution,such as the mole ratio of monomer and initiator,polymerization temperature and polymerization time were investigated.Polymerization with high monomer conversion and narrow polymer molecular weight distribution was obtained at 60～70℃and 8 hours reaction.Because of containingβ-CD unit at the end of PCL chain,the water uptake was enhanced and contact angle was decreased,so the hyrophilicity of PCL was improved.Star-shaped PCL,PDLLA and PLLA based onβ-CD as the core were also synthesized by using anionic ring-opening polymerization and characterized.The reactive conditions that controlled the number of the star-shaped polymer arms and the influence of number of arms on the polymer properties were evaluated.The number of anionic hydroxyl ofβ-CD determined not only the arms,but also the polymerization rate and the monomer conversion,the more the number of anionic hydroxyl ofβ-CD,the more the arms of the star-shaped polymer and the faster the polymerization rate with higher monomer conversion.Star-shaped polymer has lower melting temperature,crystallbility,intrinsic viscosity than linear polymer at the similar molecular weight.The chiral difference of DLLA and LLA had no effect on the ring-opening polymerization results.As model protein,by using W/O/W solvent evaporation method,bovine serum albumin(BSA) was encapsulated in linear PCL and star-shaped PCL microspheres. The degradation behavior and BSA release behavior were studied.It was obviously that the degradation rate of star-shaped polymer was faster than the linear polymer at the similar molecular weight,and the more the arms,the faster the degradation rate. Microspheres prepared from star-shaped PCL showed higher drug-loading amount, small burst effect and fast release rate compared to those prepared from linear PCL.更多还原