壳聚糖/聚乙烯醇微球吸附脲酶的特性及其动力学

目的制备壳聚糖/聚乙烯醇(PVA)微球脲酶,探讨其最适温度、最适pH、热稳定性及其动力学。方法用微乳法制备壳聚糖/PVA微球,采用电子扫描电镜表征其形态;用吸附法获得壳聚糖/PVA微球脲酶;运用Berthlot测定其活力。结果壳聚糖/PVA微球脲酶酶活性保持率是原酶的91.93%,最适温度为47℃,最适pH6.5,热稳定性明显高于溶液脲酶;壳聚糖/PVA微球脲酶的动力学参数KM=11.8 mmo.lL-1,Vm ax=37.1μmo.lm in-.1mg-1。结论壳聚糖/PVA微球脲酶可制备成用于尿毒症患者的口服制剂。     

新型胺基壳聚糖微球的制备及对黄酮类物质的吸附性能

目的制备1种新型胺基壳聚糖微球,并以山楂叶中的黄酮类化合物为吸附模型,研究其吸附性能。方法采用反相悬浮交联法制备壳聚糖微球,甲醛为预交联剂,经羟丙基化、胺基化,并通过红外光谱,扫描电镜测定其结构。结果改性壳聚糖微球对游离黄酮的吸附量大于壳聚糖的吸附量,9 h后基本达到吸附平衡,通过此法得到的最优的多孔壳聚糖吸附剂对黄酮类化合物的吸附量在600 mg/g以上。结论该法制得的壳聚糖微球是1种良好的多孔吸附剂,有较好的工业化前景。     

卡铂碳包铁纳米壳聚糖微球的制备和特征

目的制备卡铂碳包铁纳米壳聚糖微球,检测其性能,并与卡铂纯铁纳米壳聚糖微球进行比较。方法以吸附药物的碳包铁纳米磁粉为磁性内核,壳聚糖为基质,卡铂为负载药物,采用反相微乳法制备卡铂碳包铁纳米壳聚糖微球。卡铂纯铁纳米壳聚糖微球的制备方法相似,不同的是以无吸附药物能力的纯铁纳米磁粉为磁性内核。检测和比较两种纳米药物微球的形态、粒径、磁响应性、载药量、包封率和体外释药。结果两种药物微球的球形圆整,平均粒径(210±26)nm,粒径分布150~300nm,磁响应性强。碳包铁纳米微球的载药量(11.15±1.03)%,纯铁纳米微球载药量(9.21±1.10)%。碳包铁纳米微球1,2,3,4d的体外释药量分别为60%、74%、84%、92%;纯铁纳米微球1,2d的释药量分别为81%,91%。结论通过活性碳吸附和物理基质包裹双重物理机制载药载药的卡铂碳包铁纳米壳聚糖微球不但载药量高,而且释药速度平稳。多重机制的有机结合是优化纳米微球性能的有效方法。     

交联壳聚糖微球偶联胰蛋白酶研究

采用反相悬浮交联法,制备交联壳聚糖微球(CCTS),再以戊二醛为偶联剂,偶联胰蛋白酶.研究了胰蛋白酶偶联的最佳条件和偶联后酶的理化性质.结果表明:用终浓度为0.6%的戊二醛,在50℃下,先处理CCTS 6 h,再置冰浴加酶为12 mg/g,搅拌24 h,固定化酶活性回收率达63.4%.胰蛋白酶与壳聚糖微球偶联的最适温度为80℃、最适pH值为7、表观米氏常数(Km)为3.16 mmol/L.与壳聚糖载体相比,CCTS具有机械强度好、粒度均匀、耐酸性能好、对牛血清白蛋白非特异性吸附较弱的优点.     

壳聚糖-聚丙烯酸磁性微球的制备

目的研究壳聚糖-聚丙烯酸磁性微球的制备及吸附性能。方法在Fe3O4磁流体与分散剂聚乙二醇存在下,壳聚糖与丙烯酸通过戊二醛进行接枝共聚制得表面具有两性基团(-COOH和-NH2)的磁性壳聚糖-聚丙烯酸微球,探讨了聚乙二醇、磁流体、戊二醛交联时间对其制备的影响。结果 20%聚乙二醇量为20mL,0.2g.mL-1磁流体为20mL,25%戊二醛为4mL、反应交联时间为30min。合成的磁性微球粒径约为200nm;磁性微球的饱和磁化强度约为0.5emu.g-1,磁化率可达2.8×10-4;其对胸腺五肽及鸡卵清蛋白有较好的吸附效果,饱和吸附量分别约460mg·g-1和550mg·g-1。结论制备的壳聚糖-聚丙烯酸磁性微球具有较好的吸附性能及磁化强度。     

pH值调节法制备壳聚糖空白微球

目的：介绍一种壳聚糖空白微球的制备方法。方法：将溶有氨水的异丙醇加入到壳聚糖乳液中，使得壳聚糖液滴由酸性变为碱性，壳聚糖凝固析出。结果：制得了粒径在3～8μm左右，粒径分布均匀的壳聚糖微球。结论：使用改变pH值的方法来制备壳聚糖微球，避免了传统固化剂的使用及其缺点。     

汉防已甲素壳聚糖微球的制备和质量研究

目的 对汉防己甲素壳聚糖微球的制备工艺和制得的微球的质量进行研究.方法 以壳聚糖为载体,采用乳化交联法制备汉防己甲素壳聚糖微球.在单因素考察的基础上,利用正交试验设计优化汉防己甲素壳聚糖微球制备工艺,并对制得微球的粒径,形态,工艺重复性,稳定性,体外突释情况等进行研究.结果 制得的微球的形态圆整,微球的平均粒径为(9.73±1.34)μm,粒径在9～12 μm的占总数的85%以上,载药量为(32.21±3.21)%,包封率为(40.33±5.32)%,最佳工艺条件重复性良好.结论 筛选的最佳处方工艺可制备性质优良的微球.     

头孢曲松壳聚糖-海藻酸钠(钙)微球制备及性能研究

以壳聚糖-海藻酸钠为基质材料，在乳化体系中以复凝聚法制备头孢曲松壳聚糖-海藻酸钠（钙）微球，研究了成球的最佳工艺条件及载药微球性能。结果显示，最佳工艺制备条件为壳聚糖浓度：海藻酸钠浓度：1：1，pH4.0，反应温度25℃，搅拌速度200r／min。体外实验表明形态圆整的载药微球具有良好溶胀和缓释性能。     

金钱草壳聚糖微球制备工艺研究

目的：对金钱草壳聚糖微球的制备工艺和包封率、粒径等特性进行初步研究。方法：以生物降解材料壳聚糖为载体,采用乳化一交联法制备金钱草壳聚糖微球,并采用正交试验优化制备工艺。结果：所制备的金钱草壳聚糖微球外观圆整,平均粒径为48．34μm,载药量为15．11％,包封率为59．55％。结论：所制备的金钱草壳聚糖微球重现性良好,载药量较高,制备工艺可行。     

牛血清白蛋白阳离子微球的制备及体外评价

目的 制备牛血清白蛋白(BSA)口服阳离子微球,考察天然阳离子物质壳聚糖(CHS)的加入对蛋白微球的粒径、电动电势、包封率、载药量及体外释放情况的影响。方法 以乳酸/羟基乙酸共聚物(PLGA)和壳聚糖(CHS)为载体材料,采用W/O/W复乳-溶剂挥发法制备牛血清白蛋白乳酸/羟基乙酸共聚物-壳聚糖(PLGA/CHS)阳离子微球。通过正交设计优化制备工艺,确定最佳处方。建立准确而简便的蛋白含量测定方法,并对微球进行体外评价。结果 最佳处方为：BSA浓度为150 g·L^-1、PLGA浓度为8%、外水相体积为80 mL、壳聚糖浓度为0.2%。制得的微球形态圆整,平均粒径为(6.9±5.5)μm,为表面荷正电的阳离子微球[ζ电势=(10.0±0.6)mV],包封率为(75.4±4.6)%,载药量为(9.3±0.2)%。体外释放结果表明,在模拟胃液和模拟肠液中,壳聚糖的加入均能减少突释,延缓药物的释放。结论 与PLGA微球相比,制得的PLGA/CHS阳离子微球表面带正电,具有较高的包封率和载药量,可以延缓药物释放,同时减少突释现象。     

In vitro evaluation of the mucoadhesive properties of chitosan microspheres

The mucoadhesive properties of chitosan and chitosan microspheres were evaluated by studying the interaction between mucin and chitosan in aqueous solution by turbidimetric measurements and the measurement of mucin adsorbed on the microspheres. A strong interaction between chitosan microspheres and mucin was detected. Adsorption studies were carried out for the adsorption of mucin to chitosan microspheres with different crosslinking levels. The adsorption of type III mucin (1% sialic acid content), to chitosan microspheres followed Freundlich or Langmuir adsorption isotherms. When the contents of sialic acid was increased (i.e. type I-S mucin, 12% sialic acid content), the adsorption type followed more closely an electrostatic attraction type of isotherm. The heat of the adsorption was found to be 13–23 kJ/mol. A salt-bridge effect has been proposed for the interaction of the positively charged mucoadhesive chitosan microspheres with the negatively charged mucus glycoprotein. The extent of mucus adsorption was proportional to the absolute values of the positive zeta potential of chitosan microspheres and negative `zeta potential' of mucus glycoprotein. Factors leading to a reduction or a reversal of these absolute values (e.g. different crosslinking levels of chitosan microspheres, different types of mucin, different pH, or ionic strength of the medium used) led to a reduction in the amount adsorbed. The extent of this reduction depended upon the decreasing extent of the repective zeta potentials. Biological studies showed that chitosan microspheres were retained by a biological tissue; rat small intestine.     

5-Fluorouracil-loaded chitosan coated polylactic acid microspheres as biodegradable drug carriers for cerebral tumours

The development of injectable microspheres for anticancer drug delivery into the brain is a major challenge. The possibility of entrapping 5-fluorouracil (5-FU) in chitosan coated monodisperse biodegradable microspheres with a mean diameter of 10-25 um was demonstrated. An emulsion of 5-FU (in water) and polylactic acid (PLA) dissolved in acetone-dichloromethane mixture was poured into an aqueous solution of chitosan (or poly-vinyl alcohol) with stirring using a high-speed homogenizer, for the formation of microspheres. 5-FU recovery in microspheres ranged from 44-66% depending on the polymer and emulsification systems used for the preparation. Scanning electron microscopy revealed that the chitosan coated microspheres had less surface micropores compared to PVA based preparations. The drug release behaviour from microspheres suspended in phosphate buffered saline exhibited a biphasic pattern. The amount of drug release was much higher initially (approximately 25%), followed by a constant slow release profile for a 30 days period of study. This chitosan coated PLA/PLGA microsphere formulation may have potential for the targeted delivery of 5-FU to treat cerebral tumours.     

5-Fluorouracil-loaded chitosan coated polylactic acid microspheres as biodegradable drug carriers for cerebral tumours

The development of injectable microspheres for anticancer drug delivery into the brain is a major challenge. The possibility of entrapping 5-fluorouracil (5-FU) in chitosan coated monodisperse biodegradable microspheres with a mean diameter of 10-25um was demonstrated. An emulsion of 5-FU (in water) and polylactic acid (PLA) dissolved in acetone-dichloromethane mixture was poured into an aqueous solution of chitosan (or poly-vinyl alcohol) with stirring using a high-speed homogenizer, for the formation of microspheres. 5-FU recovery in microspheres ranged from 44-66% depending on the polymer and emulsification systems used for the preparation. Scanning electron microscopy revealed that the chitosan coated microspheres had less surface micropores compared to PVA based preparations. The drug release behaviour from microspheres suspended in phosphate buffered saline exhibited a biphasic pattern. The amount of drug release was much higher initially (25%),followed by a constant slow release profile for a 30 days period of study. This chitosan coated PLA/PLGA microsphere formulation may have potential for the targeted delivery of 5-FU to treat cerebral tumours.     

Preparation and characterisation of poly(vinyl alcohol)/cyclodextrin microspheres as matrix for inclusion and separation of drugs

Poly(vinyl alcohol) (PVA) microspheres containing cyclodextrin (CD) were obtained by chemical cross-linking with glutaraldehyde of an acidified mixture solution of PVA and alpha-, beta- or gamma-CD. The amount of linked CD in microspheres, estimated by tetrazolium blue method, decreases in the order beta- > gamma- > alpha-CD. The dimensions of PVA/gamma-CD microspheres are much higher than those of PVA/alpha- and beta-CD. The cross-linking density of microspheres was estimated by the amount of iodine retained by the polymer matrix. The pore size as well as the porous volume of PVA/CD microspheres decrease significantly on increasing the amount of glutaraldehyde, but are enough large to permit the access of drugs to the CD cavity. In order to test the PVA/CD microsphere inclusion ability, the microspheres were packed in a glass column and the liquid chromatographic behaviour by isocratic elution of different drugs or typical organic compounds, taken as model drugs, was investigated.     

Colon-specific delivery of mesalazine chitosan microspheres

Mesalazine (5-ASA) is a cyclo-oxygenase inhibitor and anti-inflammatory drug effective in Crohn's disease and ulcerative-colitis. As 5-ASA is rapidly absorbed from the small intestine and it is necessary to develop a colon-specific delivery system for it. Coated chitosan microspheres were used for this purpose by an emulsion-solvent evaporation technique based on a multiple w/o/w emulsion. Four hundred milligrams of chitosan solution (3%) in dilute acetic acid (0.5 M) containing 12% 5-ASA was dispersed into 2 ml solution of cellulose acetate butyrate (CAB) in methylene chloride. The primary induced w/o emulsion was dispersed into a 1% PVA aqueous solution to produce a w/o/w multiple emulsion and was stirred for approximately 2.5 h. The produced microspheres were separated, washed and dried. Release of 5-ASA from microspheres was studied in different pHs 1.2, 7.4, 6.8 and 6.8 in the presence of caecal contents of rat. The average size of microspheres was 200 microm. The highest yield efficiency (80%) was seen in medium molecular weight (MW) chitosan with a 1 : 2 core/coat ratio and the greatest loading efficiency (85%) related to the microspheres of the same type of chitosan but with a 1 : 1 core/coat ratio. Decreasing the coat content and increasing chitosan Mw increased the bioadhesion significantly (p < 0.05). Microspheres of chitosan with medium Mw and 1 : 1 core/coat that showed the greatest release of drug (near 80%) in the presence of caecal secretions with a zero-order mechanism, near zero per cent in pH 1.2 after 2 h, max 20% in pH 7.4 after 3 h and near 60% in pH 6.8 after 8 h seem suitable for site-specific delivery of 5-ASA in vitro.     

Chitosan microspheres enhance the immunogenicity of an Ag85B-based fusion protein containing multiple T-cell epitopes of Mycobacterium tuberculosis.

To develop novel delivery system for tuberculosis (TB) subunit vaccine, biodegradable chitosan microspheres were prepared and used to deliver a fusion protein, Ag85B-MPT64(190-198)-Mtb8.4 (AMM for short), made from three Mycobacterium tuberculosis genes. AMM-loaded microspheres were first characterized for their morphology, size, zeta potential, loading efficiency, and in vitro release of AMM. C57BL/6 mice were immunized at weeks 1, 3 and 5 subcutaneously with AMM formulated in chitosan microspheres, in incomplete Freund's adjuvant (IFA), or in phosphate-buffered saline (PBS), respectively. Three weeks after the last immunization, humoral and cell-mediated immune responses were examined. It was shown that the microspheres bound AMM quite efficiently (loading efficiency: >99%). AMM-loaded chitosan microspheres were observed as aggregated shapes with the average particle size of 5.78+/-0.65 microm and zeta potential of 32.77+/-1.51 mV. In vitro release studies revealed that only small amount of antigen was released in 16 days. Following subcutaneous administration, splenocytes immunized with AMM in chitosan microspheres produced higher levels of IFN-gamma compared to administration of AMM in PBS upon stimulation with Ag85B and synthetic peptide MPT64(190-198). The levels of Ag85B-specific IgG (H+L), IgG1 and IgG2a in sera of mice immunized with AMM in chitosan microspheres were also higher than those with AMM in PBS. These results indicate that chitosan microspheres when used as a carrier for fusion protein AMM could elicit strong humoral and cell-mediated immune responses.     

Plasmid-DNA loaded chitosan microspheres for in vitro IL-2 expression.

Interleukin-2 (IL-2) expression plasmid (pCXWN-hIL-2) loaded chitosan microspheres were evaluated for using in gene-based immunotherapy. Chitosan microspheres containing pCXWN-hIL-2 were prepared by using a precipitation technique. In addition, the effects of different factors such as the concentration (0.35-0.70%) and the molecular weight of chitosan (low and medium molecular weights), the plasmid amount (5-10 microg/ml) and the presence of glutaraldehyde during the encapsulation process, on microsphere characteristics were investigated. The size of microspheres changed between 1.45 and 2.00 microm. All the formulation factors affected the size of microspheres. The structure of plasmid remained unchanged during the encapsulation process and the release studies. Plasmid encapsulation efficiency of chitosan microspheres was high (82-92%). The zeta potential values of microspheres was approximately +5.2 to +12.4 mV. In vitro release properties of microspheres changed with formulation variables. In vitro release of DNA changed with the concentration and molecular weight of chitosan and initial plasmid amount. Addition of glutaraldehyde is not necessary for a formulation. MAT-LyLu, the rat prostate adenocarcinoma cell line, was used for the determination of the in vitro transfectional activity of IL-2 encoding plasmid DNA loaded chitosan microspheres and the level of IL-2 expressed into the cells was assayed using a ELISA kit. High level of IL-2 expression was obtained with plasmid-loaded chitosan microspheres. Microspheres showed similar IL-2 production as lipofectin. The molecular weight of chitosan used and the amount of plasmid influenced the in vitro IL-2 production in the cells. Encapsulation of IL-2 encoding gene into chitosan microspheres might be a useful strategy to increase the expression and to control the delivery of cytokine gene to cells.     

Cellulose acetate butyrate-pH/thermosensitive polymer microcapsules containing aminated poly(vinyl alcohol) microspheres for oral administration of DNA.

The aim of this work is to safely transport bioadhesive microspheres loaded with DNA to intestine and to test their bioadhesive properties. Poly(vinyl alcohol) (PVA) microspheres were prepared by dispersion reticulation with glutaraldehyde and further aminated. These microspheres were firstly loaded with plasmid DNA by electrostatic interactions and then entrapped in cellulose acetate butyrate (CAB) microcapsules for gastric protection. The entrapped PVA microspheres do not have enough force by swelling to produce the rupture of CAB shell, therefore the resistance of microcapsules was weakened by incorporating different amount of the pH/thermosensitive polymer (SP) based on poly(N-isopropylacrylamide-co-methyl methacrylate-co-methacrylic acid) (NIPAAm-co-MM-co-MA). This polymer is insoluble in gastric juice at pH 1.2 and 37 degrees C, but quickly solubilized in intestinal fluids (pH 6.8 and pH 7.4). Therefore, DNA loaded PVA microspheres were not expelled in acidic media but were almost entirely discharged in small intestine or colon. The integrity of DNA after entrapment was tested by agarose gel electrophoresis indicating that no DNA degradation occurs during encapsulation. The percentage of adhered microspheres on the mucus surface of everted intestinal tissue was 65+/-18% for aminated PVA microspheres without DNA and almost 50+/-15% for those loaded with DNA. Non-aminated PVA microspheres display the lowest adhesive properties (33+/-12%). In conclusion DNA loaded microspheres were progressively discharged in intestine. The integrity of DNA was not modified after entrapment and release, as proved by agarose gel electrophoresis. Both loaded and un-loaded aminated microspheres display good bioadhesive properties.     

Colon-specific delivery of mesalazine chitosan microspheres

Mesalazine (5-ASA) is a cyclo-oxygenase inhibitor and anti-inflammatory drug effective in Crohn's disease and ulcerative-colitis. As 5-ASA is rapidly absorbed from the small intestine and it is necessary to develop a colon-specific delivery system for it. Coated chitosan microspheres were used for this purpose by an emulsion-solvent evaporation technique based on a multiple w/o/w emulsion. Four hundred milligrams of chitosan solution (3%) in dilute acetic acid (0.5?M) containing 12% 5-ASA was dispersed into 2?ml solution of cellulose acetate butyrate (CAB) in methylene chloride. The primary induced w/o emulsion was dispersed into a 1% PVA aqueous solution to produce a w/o/w multiple emulsion and was stirred for ～2.5?h. The produced microspheres were separated, washed and dried. Release of 5-ASA from microspheres was studied in different pHs 1.2, 7.4, 6.8 and 6.8 in the presence of caecal contents of rat. The average size of microspheres was 200?µm. The highest yield efficiency (80%) was seen in medium molecular weight (MW) chitosan with a 1?:?2 core/coat ratio and the greatest loading efficiency (85%) related to the microspheres of the same type of chitosan but with a 1?:?1 core/coat ratio. Decreasing the coat content and increasing chitosan Mw increased the bioadhesion significantly (p?<?0.05). Microspheres of chitosan with medium Mw and 1?:?1 core/coat that showed the greatest release of drug (near 80%) in the presence of caecal secretions with a zero-order mechanism, near zero per cent in pH 1.2 after 2?h, max 20% in pH 7.4 after 3?h and near 60% in pH 6.8 after 8?h seem suitable for site-specific delivery of 5-ASA in vitro.     

Preparation and characterization of Mitomycin-C loaded chitosan-coated alginate microspheres for chemoembolization

Mitomycin-C loaded and chitosan-coated alginate microspheres were prepared for use in chemoembolization studies. In this respect, first alginate microspheres were prepared by using a spraying method using an extrusion device with a small orifice and following suspension cross-linking in an oil phase. Chitosan-coating onto the alginate microspheres was achieved by polyionic complex formation between alginate and chitosan. CaCl(2) was used as a cross-linker for alginate microspheres. The obtained chitosan-coated alginate microspheres were spherical shaped and approximately 100-400 microm average size. The microspheres were evaluated based on their swellability and the swelling ratio was changed between 50-280%. CaCl(2) concentration, stirring rate, chitosan molecular weight, chitosan concentration and time for coating with chitosan were selected as the effective parameters on microsphere size and swelling ratio. Equilibrium swellings were achieved in approximately 30 min. On the other hand, chitosan molecular weight, chitosan concentration and time for coating with chitosan were found as the most effective parameters on both drug loading ratio and release studies. Maximum drug loading ratio of 65% was achieved with high molecular weight (HMW) chitosan, highest chitosan concentration (i.e. 1.0% v/v) and shortest time for coating with chitosan (i.e. 1 h) values.