高纯度、高收率L-丙交酯的制备

以L-乳酸为单体,在催化剂作用下用乳酸先缩聚再解聚制备L-丙爻酯(LLA),讨论了温度、压强对制备丙交酯的影响。采用水洗加重结晶的方法制得高纯度的LLA,LLA的收率达到40.6％。用旋光度、红外光谱、色谱质谱对所制得的LLA进行了检测,结果表明,提纯后LLA的纯度较高。     

稀土催化剂在聚乳酸合成中的应用研究

生物降解材料聚乳酸(Poly1actic acid,PLA)可由丙交酯(lactide,LA)在催化剂引发下开环聚合。近年来有研究者开发了稀土催化剂用于聚乳酸的合成,稀土催化剂具有的独特结构赋予了它独特的催化性能,对聚合反应有良好的催化活性,以高反应速率和高转化率引发丙交酯开环聚合,合成分子量和立体结构可控的聚乳酸。本文介绍了稀土催化剂的分类、特点以及引发丙交酯开环聚合的催化机理,综述了各类稀土催化剂的优势和不足、以及多种单组分稀土催化剂和多组分稀土催化体系在引发丙交酯开环聚合中的应用,分析了各应用的优点和存在的问题,并对稀土催化剂的发展以及需进一步解决的问题进行了探讨。     

PLGA材料仿生改性的最新进展

聚乳酸-乙交酯（PLGA）因具有优良的可降解性而在医用生物材料中得到了广泛应用，然而由于其表面缺乏细胞识别位点，以及存在亲水性和细胞亲和性不足等缺点，影响了细胞在其表面的粘附生长。为了得到生物功能和亲水性均较理想的聚乳酸类生物降解高分子，通过物理或者化学的方法在材料中引入胶原或多肽对其进行改性，赋予材料生物信号，以提高其生物功能，使其在组织工程支架的研究和临床应用更加广泛。该文主要对PLGA仿生改性的最新进展进行综述。     

Spinel增强HAP·TCP复合生物材料研究

采用化学共沉淀法制得羟基磷灰石(Ca_(10)(PO_4)_6(OH)_2)粉体和铝镁尖晶石(MgAl_2O_4)粉体,并以羟基磷灰石(HAP)粉体和铝镁尖晶石(Spinel)粉体为原料采用粉末冶金方法制得HAP·TCP-Spinel复合生物材料;采用X射线衍射分析、金相分析、红外光谱分析、烧结收缩性能分析和力学性能测试等对制备的材料进行了表征。研究结果表明:HAP·TCP-Spinel复合生物材料的烧结收缩率约为45％;HAP·TCP与Spine两相分布均匀,且界面结合良好;该复合材料表现出优良的抗弯强度和抗压强度性能;羟基磷灰石的含量为62.5％时该复合材料性能达到最佳,其抗弯强度和抗压强度分别为189MPa和352MPa。     

羟基磷灰石复合材料对地下水中铀吸附去除研究进展

铀矿山尾矿库周边地下水在铀矿的风化、淋滤、渗漏等作用下,给地下水和人类带来长期的健康隐患。可渗透反应墙(PRB)作为一种原位修复技术,具有无动力运行、环境影响小和成本低等优点,已经在地下水污染修复中得到了应用。羟基磷灰石(HAP)因具有成本低、原料广泛、生物相容性等优点,成为去除地下水中铀废水的最具潜力介质材料。综述了羟基磷灰石在处理含铀废水中的影响因素,主要包括羟基磷灰石制备方法、改性方法,对含铀废水去除影响研究。并对羟基磷灰石除铀进行机理分析,包括羟基磷灰石形貌、铀溶液pH、共存阴离子等对铀的去除影响。羟基磷灰石(HAP)因具有成本低、原料广泛、生物相容性等优点,成为去除地下水铀的最具潜力介质材料。     

纳米羟基磷灰石晶体的制备及表征

采用化学沉淀法合成纳米羟基磷灰石(HA),并采用X-射线衍射和透射电镜(TEM)对其结构和晶粒尺寸进行了分析。制备的纳米HA主要为柱状晶体,平均尺寸为70 nm。这说明在常温常压水-乙醇反应体系下,可获得纯度、结晶度较好的纳米HA晶体材料,且晶体完整,具有与人体骨羟基磷灰石晶体相似的结构特征。     

微弧氧化和碱处理对钛的细胞黏附和骨植入行为的影响研究

<正>海南大学与南京理工大学的科研工作者联合考察了微弧氧化处理和碱处理对钛表面形貌、涂层成分、羟基磷灰石沉积能力、细胞黏附性、骨内植入效果的影响。结果表明,经微弧氧化和碱复合处理后,钛表面TiO2薄膜呈现大量裂缝,表现出表面含大量OH-极性基团的纳米多孔网状结构,此微观结构和组成使材料诱导羟基磷灰石生成能力显著,利     

高晶度医用羟基磷灰石(HAP)生物材料制备及表征

论述了制备高晶度医用生物陶瓷涂层材料羟基磷灰石粉末(HAP)方法,用SEM和XRD对粉末进行表征,结果表明经过重熔处理的羟基磷灰石粉末具有更好的晶体化程度,粉末表面致密光滑,具有优异的热喷涂使用性能.     

水热法合成不同形貌羟基磷灰石

羟基磷灰石由于具有良好的生物相容性和生物活性而应用广泛,形貌控制对其应用至关重要。本文分别以Ca(NO3)2.4H2O、KH2PO4.3H2O为Ca源和P源,采用水热法制备不同形貌的羟基磷灰石。用X射线衍射(XRD)和扫描电镜(SEM)对反应产物进行表征,研究水热反应温度、水热反应时间和反应物浓度对羟基磷灰石形貌的影响。结果表明,不同条件下,产物为长径比不同的片状、带状及花状羟基磷灰石(HA),其长度为1~100μm、宽1~5μm、厚约100 nm、长径比为1~100,并从晶体生长动力学方面探讨不同合成条件对羟基磷灰石形貌的影响机理。     

稀土硼氢化合物合成及其在有机聚合反应中应用

综述了稀土硼氢化合物的合成、表征及其应用研究现状,稀土硼氢化合物用于有机合成具有结构多样性和高催化活性,不仅作为内酯、丙交酯和甲基丙烯酸甲酯聚合反应催化剂,还可以催化单、双组分烯烃聚合反应,特别是以大基团作为骨架的稀土硼氢化合物作为有机聚合反应催化剂,配体骨架通常以多齿模式与稀土金属中心配位,其多变的空间立体结构对稀土硼氢化合物的性能产生很大的影响,引发不同单体聚合具有较高的催化活性,有利于对聚合物分子量及分布控制,为合成高度立体选择性聚合物及对功能材料的改性提供了非常有效的催化剂,阐述了稀土硼氢化合物对聚合反应催化性能,并对其在有机合成应用前景进行了展望。     

Controlled drug delivery by biodegradable poly(ester) devices: different preparative approaches

There has been extensive research on drug delivery by biodegradable polymeric devices since bioresorbable surgical sutures entered the market two decades ago. Among the different classes of biodegradable polymers, the thermoplastic aliphatic poly(esters) such as poly(lactide) (PLA), poly(glycolide) (PGA), and especially the copolymer of lactide and glycolide referred to as poly(lactide-co-glycolide) (PLGA) have generated tremendous interest because of their excellent biocompatibility, biodegradability, and mechanical strength. They are easy to formulate into various devices for carrying a variety of drug classes such as vaccines, peptides, proteins, and micromolecules. Most importantly, they have been approved by the United States Food and Drug Administration (FDA) for drug delivery. This review presents different preparation techniques of various drug-loaded PLGA devices, with special emphasis on preparing microparticles. Certain issues about other related biodegradable polyesters are discussed.     

Manufacture of porous biodegradable polymer conduits by an extrusion process for guided tissue regeneration

We have fabricated porous, biodegradable tubular conduits for guided tissue regeneration using a combined solvent casting and extrusion technique. The biodegradable polymers used in this study were poly(DL-lactic-co-glycolic acid) (PLGA) and poly(L-lactic acid) (PLLA). A polymer/salt composite was first prepared by a solvent casting process. After drying, the composite was extruded to form a tubular construct. The salt particles in the construct were then leached out leaving a conduit with an open-pore structure. PLGA was studied as a model polymer to analyze the effects of salt weight fraction, salt particle size, and processing temperature on porosity and pore size of the extruded conduits. The porosity and pore size were found to increase with increasing salt weight fraction. Increasing the salt particle size increased the pore diameter but did not affect the porosity. High extrusion temperatures decreased the pore diameter without altering the porosity. Greater decrease in molecular weight was observed for conduits manufactured at higher temperatures. The mechanical properties of both PLGA and PLLA conduits were tested after degradation in vitro for up to 8 weeks. The modulus and failure strength of PLLA conduits were approximately 10 times higher than those of PLGA conduits. Failure strain was similar for both conduits. After degradation for 8 weeks, the molecular weights of the PLGA and PLLA conduits decreased to 38% and 43% of the initial values, respectively. However, both conduits maintained their shape and did not collapse. The PLGA also remained amorphous throughout the time course, while the crystallinity of PLLA increased from 5.2% to 11.5%. The potential of seeding the conduits with cells for transplantation or with biodegradable polymer microparticles for drug delivery was also tested with dyed microspheres. These porous tubular structures hold great promise for the regeneration of tissues which require tubular scaffolds such as peripheral nerve, long bone, intestine, or blood vessel.     

Safety assessment of polylactide (PLA) for use as a food-contact polymer

This report constitutes a safety assessment of polylactide (PLA), a polymer of lactic acid intended for use in fabricating various food-contact articles. Migration studies were conducted on samples of the polymer following guidelines issued by the Food and Drug Administration. Potential migrants from PLA include lactic acid, lactide (the monomer), and lactoyllactic acid (the linear dimer of lactic acid). The studies were designed to model reasonable 'worst' case extraction situations when the polymer is used (a) in houseware articles for short and intermediate time periods at various temperatures and (b) in food-packaging materials. The limited migration observed during the trials represents no significant risk since migrating species are expected to convert to lactic acid, a safe food substance. It is concluded that PLA is safe and 'Generally Recognized As Safe' for its intended uses as a polymer for fabricating articles that will hold and/or package food.     

Characterization of poly(glycolide-co-D,L-lactide)/poly(D,L-lactide) microspheres for controlled release of GM-CSF

PURPOSE: This study describes the preparation and characterization of a controlled release formulation of granulocyte-macrophage colony-stimulating factor (GM-CSF) encapsulated in poly(glycolide-co-D,L-lactide) (PLGA) and poly(D,L-lactide) (PLA) microspheres. METHODS: GM-CSF was encapsulated in PLGA/PLA microspheres by a novel silicone oil based phase separation process. Several different blends of PLGA and low molecular weight PLA were used to prepare the microspheres. The microspheres and the encapsulated GM-CSF were extensively characterized both in vitro and in vivo. RESULTS: Steady release of GM-CSF was achieved over a period of about one week without significant "burst" of protein from the microspheres. Analysis of microsphere degradation kinetics by gel permeation chromatography (GPC) indicated that low molecular weight PLA enhanced the degradation of the PLGA and thereby affected release kinetics. GM-CSF released from the microspheres was found to be biologically active and physically intact by bioassay and chromatographic analysis. Analysis of serum from mice receiving huGM-CSF indicated that the GM-CSF was biologically active and that a concentration of greater than 10 ng/mL was maintained for a period lasting at least nine days. MuGM-CSF was not detected following in vivo administration of muGM-CSF microspheres. The tissues of mice receiving muGM-CSF microspheres were characterized by infiltration of neutrophils, and macrophages which were in significant excess of those found in mice administered with placebo controls (i.e. microspheres without GM-CSF). CONCLUSIONS: This study demonstrates the influence of formulation parameters on the encapsulation of GM-CSF in PLGA/PLA microspheres and its controlled release in biologically active form. The intense local tissue reaction in mice to muGM-CSF microspheres demonstrates the importance of the mode of delivery on the pharmacologic activity of GM-CSF.     

Retinal pigment epithelium cell culture on thin biodegradable poly(DL-lactic-co-glycolic acid) films

Thin films of 50:50 and 75:25 poly(DL-lactic-co-glycolic acid) (PLGA) were manufactured with a controlled thickness of less than 10 microm. The effect of PLGA copolymer ratio on in vitro cell attachment, proliferation, morphology, and tight junction formation was evaluated using a human D407 retinal pigment epithelium (RPE) cell line. Almost complete cell attachment was achieved on both PLGA films after 8 h of cell seeding, which was comparable to that on tissue culture polystyrene (TCPS) controls. The initial cell seeding density affected attachment, and the optimal value for 50:50 PLGA was 25000 cells cm(-2). After 7 days of in vitro culture, cell density on 50:50 and 75:25 PLGA films increased 45 and 40 folds, respectively, and a 34-fold increase was observed on TCPS. The RPE cells cultured on PLGA films at confluence had a characteristic cobblestone morphology. Confluent RPE cells also developed normal tight junctions in vitro which were concentrated mainly at the apical surfaces of cell-cell junctions. These results demonstrated that thin biodegradable PLGA films can provide suitable substrates for human RPE cell culture, and may serve as temporary carriers for subretinal implantation of organized sheets of RPE.     

Preservation of alveolar bone in extraction sockets using bioabsorbable membranes

The purpose of this study was to evaluate the clinical effectiveness of a bioabsorbable membrane made of glycolide and lactide polymers in preserving alveolar ridges following tooth extraction using a surgical technique based on the principles of guided bone regeneration. Sixteen patients requiring extractions of 2 anterior teeth or bicuspids participated in the study (split-mouth design). Following elevation of buccal and lingual full-thickness flaps and extraction of teeth, experimental sites were covered with bioabsorbable membranes; control sites did not receive any membrane. Titanium pins served as fixed reference points for measurements. Flaps were advanced in order to achieve primary closure of the surgical wound. No membrane became exposed in the course of healing. Reentry surgeries were performed at 6 months. Results showed that experimental sites presented with significantly less loss of alveolar bone height, more internal socket bone fill, and less horizontal resorption of the alveolar bone ridge. This study suggests that treatment of extraction sockets with membranes made of glycolide and lactide polymers is valuable in preserving alveolar bone in extraction sockets and preventing alveolar ridge defects.     

PLGA nanoparticles prepared by nanoprecipitation: drug loading and release studies of a water soluble drug

The nanoprecipitation technique for preparation of nanoparticles suffers the drawback of poor incorporation of water soluble drugs. The aim of this study was therefore to assess various formulation parameters to enhance the incorporation of a water soluble drug (procaine hydrochloride) into poly(dl-lactide-co-glycolide) (PLGA) nanoparticles prepared by this technique. Approaches investigated for drug incorporation efficiency enhancement included the influence of aqueous phase pH, replacement of procaine hydrochloride with procaine dihydrate and the inclusion of excipients: poly(dl-lactide) (PLA) oligomers, poly(methyl methacrylate-co-methacrylic acid) (PMMA-MA) or fatty acids into the formulation. The nanoparticles produced were submicron size (<210 nm) and of low polydispersity. It was found that an aqueous phase pH of 9.3, replacement of procaine hydrochloride with procaine dihydrate and the incorporation of PMMA-MA, lauric and caprylic acid into the formulation could enhance drug incorporation efficiency without the size, morphology and nanoparticle recovery being adversely influenced. For instance changing the aqueous phase pH from 5.8 to 9.3 increased nanoparticle recovery from 65.1 to 93.4%, drug content from 0.3 to 1.3% w/w and drug entrapment from 11.0 to 58.2%. However, the presence of high ratios of lauric acid and procaine dihydrate in the formulation adversely affected the morphology and size of the nanoparticles. Also, PLA oligomers were not considered a feasible approach since it decreased drug entrapment from 11.0 to 8.4% and nanoparticle recovery from 65.1 to 19.6%. Drug release from nanoparticles appears to consist of two components with an initial rapid release followed by a slower exponential stage. This study has demonstrated that formulation variables can be exploited in order to enhance the incorporation of a water soluble drug into PLGA nanoparticles by the nanoprecipitation technique.     

Minimally invasive coronary surgery at the beginning of the new millennium

Several formulations of poly(epsilon-caprolactone) (PCL), poly(lactic acid) (PLA), and poly(lactic-co-glycolic acid) (PLGA) nanocapsules containing phenylbutazone were prepared according to the interfacial deposition technique. These formulations differed in the type of polymer used to form the shell of the nanocapsules. Analysis of particle size distribution and encapsulation efficiency of the nanocapsules revealed that the type and molecular weight of polyester used were the main factors influencing these properties. PLA had the highest encapsulation efficiency with the best reproducibility. From in vitro release studies, a small amount of drug release was observed at pH 7.4. However, in the gastric medium, an important burst effect occurred and was highest with the PLGAs and lowest with PCL, suggesting that drug release from these systems is affected by the type of polymer and the environmental conditions. The two formulations of phenylbutazone-loaded nanocapsules should be evaluated based on PCL and PLA in vivo in order to determine to what extent they are able to reduce the local side effects of this drug.     

Effects of fluorides on titanium and other dental alloys in dentistry

Polymers issued from glycolic acid and lactic acids (PLAGA) are now used worldwide as bioresorbable devices in surgery and in pharmacology. Their abiotic hydrolytic degradation has been shown to depend on diffusion-reaction phenomena and to proceed homogeneously or heterogeneously, depending on many factors. Two initiators are presently used industrially to make PLAGA polymers by ring opening polymerisation of lactide and/or glycolide in the bulk, namely Sn octanoate and zinc metal. In this contribution, attention is paid to the differences generated by the use of these two initiator systems in the case of the polymerisation of DL-lactide. Various poly(DL-lactide)s were prepared and characterised by size-exclusion chromatography (SEC), differential scanning calorimetry (DSC) and nuclear magnetic resonance spectroscopy (NMR). These polymers were allowed to age in pH=7.4 isoosmolar phosphate buffer at 37 degrees C. Under these conditions, polymers prepared by the two initiator systems showed dramatic differences when the fates of parallel sided specimens of rather large dimensions were considered. These differences were related to the esterification of some of the OH chain ends by octanoic acid and to the presence of rather hydrophobic low molecular weight by-products which were insoluble in the solvent generally used to purify the crude PLAGA polymers. These new findings should be of great interest in the case of PLAGA based matrices aimed at drug delivery.     

Use of encapsulated single chain antibodies for induction of anti-idiotypic humoral and cellular immune responses

The use of biodegradable poly(lactic-co-glycolic acid) (PLGA) microspheres as a cancer vaccine delivery system for induction of anti-idiotypic responses has been investigated using a single chain antibody scFv-pDL10, which recognizes the human ovarian cancer antigen CA125. Immunization of mice with scFv-pDL10 encapsulated in PLGA microspheres resulted in enhanced humoral and cellular immune responses when compared to scFv-pDL10 alone. Induced anti-idiotypic antibodies (Ab2) which mimic the original antigen CA125 compete with CA125 for the epitope. A cellular response (T2 induction) was also observed. These results raise the possibility of anti-idiotypic antibody induction by a single chain antibody, encapsulated in biodegradeble microspheres, as a potential vaccine for ovarian carcinoma.