【作者】 罗坤；

【导师】 尹静波；

【作者基本信息】 上海大学 ， 材料学， 2009， 博士

【摘要】 带相反电荷的聚电解质尤其是弱聚电解质间的作用力在很大程度上会受到pH值、离子强度和温度等因素的影响,因此利用聚电解质间的静电作用制备出的药物载体一般具有环境敏感性、可控性等诸多优点。药物载体用生物可降解聚电解质大多是天然高分子,如海藻酸钠、壳聚糖（CS）和明胶等。而天然高分子种类少,分子量不可控,机械强度差、降解速度快等[1-3],无法满足作为药物载体的应用需要。与天然高分子相比,生物可降解合成高分子作为药物载体具有分子量和结构可调控等优点。本课题以生物可降解合成聚电解质聚谷氨酸（PGA）和聚乙二醇单甲醚-聚谷氨酸嵌段共聚物（mPEGGA）为主要组分,选用两种聚电解质体系PGA/CS与mPEGGA/CS,深入研究不同因素对mPEGGA与CS络合行为的影响,同时探讨了层层自组装制备弱聚电解质多层膜的增长机理及不同因素对多层膜生长的影响,为构建药物载体奠定理论基础。通过层层自组装技术制备新型载药微球。成功合成嵌段共聚物mPEGGA。将mPEG的端羟基改性为活性端氨基:第一步是对甲苯磺酰氯与mPEG进行酯化反应在端位上形成磺酸酯基;第二步是用邻苯二甲酰亚胺基团取代mPEG端位上的对甲苯磺酸酯基;最后一步则是利用水合肼脱去邻苯二甲酰亚胺基团,制得端氨基聚乙二醇单甲醚（mPEG-NH₂）。利用mPEG-NH₂引发γ-苄基-L-谷氨酸-N-羧酸酐（NCA）开环聚合,成功合成聚乙二醇单甲醚-聚谷氨酸苄酯嵌段共聚物（mPEGBG）。在HBr作用下,成功脱去共聚物中苄基保护基团,制得嵌段共聚物mPEGGA。改变引发剂和单体摩尔比,合成两种分子量的共聚物。详细研究了不同因素对mPEGGA与CS络合行为的影响,重点考察了共聚物中非离子亲水链段mPEG对聚电解质络合物（Polyelectrolyte complexes, PEC）结构性质的影响:通过溶液滴定法制备mPEGGA/CS聚电解质络合物。由于聚阴阳离子的链段长度差别大,同时共聚物中mPEG链段与CS可形成氢键,因此聚电解质络合物胶束（Polyion complex micelle）只能在非等化学配比条件下形成。粒度分析结果显示胶束直径在200nm左右,大大超过其它聚电解质络合物胶束以及PGA/CS胶束[4]的粒径。胶束的粒径随着mPEGGA分子量的增大而增大。透射电镜（TEM）显示胶束典型的核壳结构。在本体PEC （polyelectrolyte complexes in the solid state）中,mPEGGA与CS间存在较强的静电作用力,与聚电解质体系PGA/CS比较[4],共聚物中亲水链段mPEG削弱了两者的静电力。mPEG链段与CS间存在较强的氢键作用力,从而破坏了嵌段共聚物中原有的结晶结构。探讨了弱聚电解质多层膜的生长机理及不同因素对多层膜增长的影响。利用交替沉积技术在二维模板表面构筑多层膜PGA/CS和mPEGGA/CS。构建PGA/CS多层膜的主要驱动力是静电力。PGA/CS多层膜按照先指数后直线形式生长。pH值增大,多层膜增长速率降低。离子强度增加,一定程度上屏蔽了聚电解质的有效电荷,从而使聚电解质更趋向采取卷曲构象,使膜增长速率加快。聚电解质溶液浓度增加,提供了更多有效的聚电解质链,导致多层膜的增长速率加快。与PGA/CS体系相比,mPEGGA/CS多层膜增长速度较快,这是由于共聚物中柔性的链段mPEG所致,另外一种原因可能与共聚物中mPEG链段与CS形成的氢键作用有关。共聚物mPEGGA分子量越大,聚离子链段长度越长,多层膜增长速度也越快。首次提出以CS微球为模板采用层层自组装技术构建载药微球。以5-氟尿嘧啶为模型药物,乳化交联法制备表面带正电荷的CS载药微球,并以PGA和mPEGGA为聚阴离子,CS为聚阳离子在其表面层层组装。结果发现,交联剂浓度越大,CS微球表面电荷越小。模板电荷的改变并不对其表面聚电解质层的电位产生影响。共聚物分子量越大,聚离子链段越长,聚电解质电荷密度也越大,相应层的电位也就越高。对于mPEGGA/CS组装体系,静电力和氢键同时成为自组装的驱动力。以PGA/CS为内层,mPEGGA为最外层的载药微球有效地抑制了药物载体中常有的突释现象,与CS载药微球和载药微胶囊相比都显著地延长了药物的释放时间。更多还原

【Abstract】 Drug carriers driven by electrostatic force always possess pH, temperature-stimulative ability. Much related work has been devoted to natural polymers, like CS, alginate,glutin and so on. However, some disadvantages of natural polymers limit their broad application in controlled release. In the work, two polyelectrolyte systems PGA/CS and mPEGGA/CS were used to fabricate novel drug-loaded microspheres. Effect of different factors on polyelectrolyte complexation between neutral-block-polyanion and polycation in dilute solution and solid state were scrutinized. We also investigated alternate depostion of PGA （or mPEGGA） and CS on 2D template and the influence of different factors on layer-by-layer. Based on the theory on polyelectrolyte complexation and alternate deposition, novel drug carrier was fabricated.Amino-monomethoxypoly （ethylene glycol） （mPEG-NH₂） was synthesized by converting terminal hydroxyl groups of mPEG to primary amino groups. Monomethoxypoly （ethylene glycol） tosyalte （mPEG-oTs） was prepared at first, and then reaction with salt of phthalimide and finally hydrazinolysis. N-carboxy anhydride ofγ-benzyl-L-glutamate （NCA） was synthesized fromγ-benzyl-L-glutamate and triphosegen. Methoxy poly（ethylene glycol）-b-poly（γ-benzyl-L-glutamate） （mPEGBG） diblock copolymer was obtained by ring-opening polymerization NCA of using amino-terminated methoxy polyethylene glycol （mPEG） as macroinitiator. Theγ-benzyl protection groups were removed in the presence of HBr and the resultant polymer monomethoxy poly（ethylene glycol）-b-poly（γ-benzyl-L-glutamate） （mPEGGA） was obtained.Polyelectrolyte complexation between mPEGGA as neutral-block-polyanion and chitosan （CS） as polycation has been scrutinized in aqueous solution as well as in the solid state. Water-soluble polyelectrolyte complexes （PEC） can be formed only under nonstoichiometric condition while phase separation is observed when approaching 1:1 molar mixing ratio in spite of the existence of hydrophilic mPEG block. This is likely due to mismatch in chain length between polyanion block of the copolymer and the polycation or hydrogen bonding between the components. Hydrodynamic size of primary or soluble PEC is determined to be about 200nm, which is larger than those reported in some literature. The increase in polyion chain length of the copolymer leads to the increase in the hydrodynamic size of the water-soluble PEC. Formation of spherical micelles by the mPEGGA/CS complex at nonstoichiometirc condition has been confirmed by the scanning electron microscopy observation （SEM） and transmission electron microscopy （TEM） observations. The homopolymer CS experiences attractive interaction with both mPEGA and PGA blocks within the copolymer. Competition of hydrogen bonding and electrostatic force in the system or hydrophilic mPEG segments weakens the electrostatic interaction between the oppositely charged polyions. The existence of hydrogen bonding restrains the mobility of mPEG chains of the copolymer and completely prohibits crystallization of mPEG segments.Multilayer films based on PGA and CS were fabricated by Layer-by-Layer Assembly technique. The growths of CS and PGA deposition are both exponential to the deposition steps at first,although at different steep growth. We further studied the factors of the growth by UV-vis spectroscopy. QCM measurements combined with UV-vis spectra revealed the increase of the multilayer film growth at different pHs: pH=4.4>pH=5.0>pH=5.5. When at pH=6.5, the build-up of the multilayer stoped after the deposition of a few layers. Meanwhile, the （PGA/CS） multilayer film grows more rapidly with increasing concentration of the polyelectrolytes’solutions and ionic strength. The multilayer films of mPEGGA/CS grew exponentially as the function of the deposition steps. The molecular weight of the block copolymer could significantly influence the growth of films. The film of mPEGGA/CS with high molecular weight of PGA segment grows faster than that of low molecular weight.We described an approach to fabricate microspheres by a combination of emulsion-crosslinking method and LbL assembly technique. Firstly, bare CS microspheres were obtained by a typical emulsion-crosslinking method. The multilayer microspheres were fabricated by a template-assisted assembly in a LbL manner, using poly（α, L-glutamic acid） and its copolymer methoxy poly（ethylene glycol）-b-Poly（α, L-glutamic acid） as polyanion and CS as polycation. The results determined byξ-potential measurement show thatξ-potential at the same layer does not depend on the surface charge of the template. For polyelectrolytes of a lower charge density, lower values ofξ-potential can be obtained. The system is believed to be effective to entrap hydrophilic ionic drug as shown in the paper. Using 5-Fu as model drug, controlled release behaviour of novel drug-loaded microspheres using （PGA/CS）4 as inner layers and mPEGGA as outmost layer were investigated. It is found that the release rate is slower than that of typical CS microspheres and microcapusles.更多还原