聚乙二醇改性聚乳酸类材料研究进展

为了改善聚乳酸类生物降解高分子的性能,聚乳酸的改性工作越来越引人注目,尤其是聚乙二醇改性的聚乳酸类生物降解材料.介绍了聚乙二醇改性聚乳酸的各种方法,以及各种聚乙二醇改性聚乳酸材料的性能与应用,展望了聚乙二醇改性聚乳酸类生物降解材料的未来,降低合成成本是广泛应用的关键,因此简单易行的以聚乙二醇、乳酸等为原料的直接聚合法合成值得关注.     

聚乳酸合成方法的研究进展

聚乳酸具有良好的生物相容性和生物降解性，无毒，可吸收，在各个领域尤其是医药领域得到越来越广泛的应用，因此聚乳酸的研制与开发日益受到人们的重视。综述了聚乳酸合成的直接法、间接法、反应挤出法和微波辐射法的研究现状，指出了聚乳酸合成研究的发展趋势。     

聚乳酸的聚合方法

本文探讨了聚乳酸的现有聚合方法 ,同时对聚乳酸的另一直接 -固相新聚合方法进行了研究 ,分析了聚乳酸固相聚合机理 ,通过实验验证了固相聚合方法的有效性     

绿色高分子材料聚乳酸的制备工艺研究进展

可再生资源、可生物降解绿色高分子材料聚乳酸(PLA)应用前景广阔.从聚合设备、聚合条件以及聚合材质3个方面着重总结了丙交酯开环聚合工艺,产品中低分子杂质的脱除是高聚物生产工艺难点,分析了再沉淀、溶剂萃取、真空熔融及无催化反应等脱挥方法,重点推荐了Hitomi Ohara脱挥工艺流程.     

聚乳酸合成研究进展

针对直接法和二步法合成聚乳酸的共性,从单体纯度、催化剂选择到共沸脱水、微波辅助、超临界流体介质,以及到固相聚合、反应挤出、扩链等各个方面,对近年来聚乳酸合成研究的新进展进行了综述,指出各种新方法、新技术的复合应用是提高聚乳酸分子量、降低其成本的关键。     

POSS为核的高臂数星型杂化聚乳酸的合成

首先合成了含有8个羟基、结构极为对称的八聚[2-(2-羟基乙氧基)二甲基硅氧基]倍半硅氧烷,再以其为核引发D,L-丙交酯发生开环聚合,制备了含有八臂聚乳酸的星型有机-无机杂化POSS-PDLLA材料,通过FTIR、1H-NMR、GPC、DSC和TGA等手段对八羟基倍半硅氧烷和POSS-PDLLA杂化材料的化学结构和性能等进行了表征。结果表明,成功合成了单分散性的八羟基倍半硅氧烷,而POSS-PDLLA杂化聚合物分子量分布极窄(小于1.1)、玻璃化转变温度为43.6℃、热稳定性良好,具有与线性聚乳酸截然不同的特性。     

钛(IV)配合物催化合成Ti-P聚乳酸材料微观结构分析

以双(烷氧-亚胺芳氧)基钛(IV)配合物为催化剂,催化D,L-丙交酯开环聚合合成Ti-P聚乳酸材料,为分析材料的微观结构和性能,采用IR、1HNMR、13C NMR、TG/DSC、拉伸/压缩以及扫描电镜等方法,对聚乳酸材料进行表征及测试。实验结果表明:该钛(IV)配合物催化D,L-丙交酯的加成反应不是随机加成聚合,存在中等程度的等规加成立构选择性,并能明显阻止分子内的酯交换,对D,L-丙交酯显示出可控开环聚合的特征;与Sn-P聚乳酸相比,采用具有烷氧-亚胺芳氧基大体积空间位阻的钛(IV)配合物为催化剂,可得窄分散度、规整度好的Ti-P聚乳酸,并能提高其热稳定性、抗拉伸和压缩的力学性能。     

聚乳酸合成及其共聚物在可降解骨材料领域的应用

在广泛的文献调研和实验工作基础上，对近年来聚乳酸及其共聚物的合成机理，材料结构和性能以及在骨材料中的应用等作了广泛而深入的总结和归纳。     

功能分子共聚改性聚乳酸的研究进展

为了获得降解性能、亲水性能和力学性能等更好的生物材料,各种功能分子改性聚乳酸的研究日益受到重视.本文按照官能团的不同,综述了近年来功能分子共聚改性聚乳酸的研究情况,指出利用新颖的功能分子改性聚乳酸和利用直接熔融共聚法降低共聚改性聚乳酸是未来的发展方向.     

医用聚乳酸材料的化学改性研究进展

聚乳酸是一种常用的可生物降解的医用材料,但单纯聚乳酸并不能满足临床需要.对聚乳酸的改性工作一直都备受关注.综述了近几年聚乳酸生物降解材料的化学改性研究进展,重点论述了共聚、接枝、星型、表面改性4个方面.经改性后聚乳酸的力学性能、降解性能和亲水性能可以得到某些改善,从而更好地满足了生物医用需要.并展望了未来聚乳酸的发展.     

Time-dependent failure in load-bearing polymers: a potential hazard in structural applications of polylactides

With their excellent biocompatibility and relatively high mechanical strength, polylactides are attractive candidates for application in load-bearing, resorbable implants. Pre-clinical studies provided a proof of principle for polylactide cages as temporary constructs to facilitate spinal fusion, and several cages already made it to the market. However, also failures have been reported: clinical studies reported considerable amounts of subsidence with lumbar spinal fusion cages, and in an in vivo goat study, polylactide spinal cages failed after only three months of implantation, although mechanical testing had predicted sufficient strength for at least eight months. The failures appear to be related to the long-term performance of polylactides under static loading conditions, a phenomenon which is common to all glassy polymers and finds its origin in stress-activated molecular mobility leading to plastic flow. This paper reviews the mechanical properties and deformation kinetics of amorphous polylactides. Compression tests were performed with various strain rates, and static stress experiments were done to determine time-to failure. Pure PLLA appeared to have a higher yield strength than its co-polymers with d-lactide, but the kinetic behaviour of the polymers was the same: an excellent short-term strength at higher loading rates, but lifetime under static stress is rather poor. As spinal implants need to maintain mechanical integrity for a period of at least six months, this has serious implications for the clinical application of amorphous polylactides in load bearing situations. It is recommended that standards for mechanical testing of implants made of polymers be revised in order to consider this typical time-dependent behaviour.     

Crystallinity assessment and in vitro cytotoxicity of polylactide scaffolds for biomedical applications

Bioresorbable polylactides are one of the most important materials for tissue engineering applications. In this work we have prepared scaffolds based on the two optically pure stereoisomers: poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA). The crystalline structure and morphology were evaluated by DSC, AFM and X-ray diffraction. PLLA and PDLA crystallized in the α form and the equimolar PLLA/PDLA blend, crystallized in the stereocomplex form, were analyzed by a proliferation assay in contact with mouse L-929 and human fibroblasts and neonatal keratinocytes for in vitro cytotoxicity evaluation. SEM analysis was conducted to determine the cell morphology, spreading and adhesion when in contact with the different polymer surfaces. The preserved proliferation rate showed in MTT tests and the high colonization on the surface of polylactides observed by SEM denote that PLLA, PDLA and the equimolar PLLA/PDLA are useful biodegradable materials in which the crystalline characteristics can be tuned for specific biomedical applications.     

In vitro biocompatibility testing of polylactides

Four high-molecular weight polylactides, three poly-l-lactides of 100, 250 and 500 kDa and a poly-dl-lactide of 400 kDa, were tested qualitatively in vitro. Cells were cultured on polylactide films and with media based on the artificially aged polylactides, as well as with different concentrations of the final degradation products (monomers). Implant site-related cell types were selected. Three kinds of epithelial cells (middle ear, ear canal and nasal septum) as well as fibroblasts and osteosarcoma cells were used. Characteristic of all four polylactides was the normal morphology of cells when cultured on polylactide films and with the artificially ageing media. Although the polylactide films revealed still uncovered spots after 14 days culture, the control cultures were already confluent. The different concentrations of monomers revealed normal cell morphologies except for the 10 mg ml^-1 concentration, which showed larger fibroblasts, and the nasal septum epithelium showed more signs of terminal differentiation for the 10 mg ml^-1 d-monomer than was seen for the l-monomer even if the osmolarity was adjusted. The degradation products of polylactide are not expected to cause adverse reactions when implanted, since cell cultures with monomer concentrations up to 1 mg ml^-1 resulted in normal morphologies. In the present study the cells were not able to cover the polylactide films completely.     

稀土固体超强酸SO_4~(2-)/TiO_2-Ce~(4 )直接法催化合成聚乳酸及其机理的研究

对稀土固体超强酸SO_4~(2-)/TiO_2-Ce~(4 )催化剂直接法催化合成聚乳酸反应机理进行了研究,实验结果表明:SO_4~(2-)/TiO_2-Ce~(4 )直接法催化剂合成聚乳酸的聚合机理是酸性聚合,酸性越强所合成聚乳酸的分子量越高。     

聚乳酸材料的仿生修饰研究进展

聚乳酸是生物可降解、生物相容性材料,但由于存在亲水性差、缺乏细胞识别位点等缺陷,限制了其在生物医学工程中的应用.模拟细胞与基质相互作用的特点以及细胞外基质的特性,通过表面修饰、本体改性和复合加工的方法在聚乳酸中引入蛋白胶原、活性肽、多糖以及羟基磷灰石等生物活性分子,实现聚乳酸的仿生修饰,能够有效提高聚乳酸材料的生物学功能.综述了利用这些生物活性分子对聚乳酸进行仿生修饰的研究进展.     

Crystallization and thermal behaviour of optically pure polylactides and their blends

Lactic acid based polymers of medical grade were crystallized under isothermal and non-isothermal conditions from the melt. Optically pure enantiomeric polylactides, Poly(L-lactide) (PLLA) and Poly(D-lactide) (PDLA), are found to crystallize as crystalline form. PLLA/PDLA blends were prepared by a melt mixing process and during solidification yielded both lower melting homocrystallites and higher melting stereocomplex crystallites. The effects of isothermal and non-isothermal crystallization conditions on developed polymorphism and degree of crystallinity are evaluated for PLLA/PDLA blends.     

超临界二氧化碳渗透成核剂至聚乳酸的分散及对基体性能的影响

通过超临界二氧化碳渗透的方法将成核剂分子输运到聚乳酸基体中,使其达到与传统挤出共混方法相比更为均匀、粒度更小的分散,从而进一步细化聚乳酸的球晶尺寸,改善其结晶行为。球晶尺寸的降低增加了球晶界面的结合强度,提高了聚乳酸的冲击强度。     

生物降解型交联PVP材料的制备和性能

合成了一种具有双烯丙基的聚乙二醇和聚乳酸三嵌段共聚物(PLA-b-PEG-b-PLA)的生物可降解交联剂,并以偶氮二异丁氰(AIBN)为引发剂与N-乙烯基吡咯烷酮(NVP)交联制备了一种新型可降解交联膜材料.研究了丙交酯和PEG的投料比对交联剂粘度的影响和交联剂含量和分子量对膜材料的吸水率、接触角和力学强度的影响,初步研究了交联膜材料的降解性能.结果表明:随着丙交酯含量的增加,交联剂的特性粘度增加;随着交联剂含量的增加,膜材料的吸水率减小,接触角增大,拉伸模量增加,断裂伸长率先增加后减小;随着交联剂分子量的增加,膜材料的吸水率和接触角均有增加;对降解性能的研究表明,在降解初期膜材料的质量损失率线性地增加,在降解后期剧烈增加.     

Long-term soft tissue reaction to various polylactides and their in vivo degradation

Cylindrical pins made from poly(L-lactide), poly(L/D-lactide) 95/5% and poly(L/DL-lactide) 95/5% were implanted in the subcutaneous tissue of sheep. The tissue reaction to the implanted materials and their in vivo degradation was investigated at 1,3,6 and 12 months. The capsule formed around the polylactide implants consisted of fibroblasts, fibrocytes, phagocytes, a few foreign body giant cells and polymorphonuclear cells. For all three polylactides used, the cellular response was most intensive during the first 6 months of implantation and significantly subsided at 1 year. The thickness of the capsule was 200 m at 1 month, increased to 200–600 m at 6 months, and decreased to 100 to 200 m at 1 year, depending on the material used. The tissue reaction was more intense for poly(L/D-lactide) than for poly(L/DL-lactide) and poly(L-lactide). The drop in molecular weight of the implants was highest after 1 month of implantation (70 to 95%). Irrespective of the extensive reduction of the molecular weight at 1 month, none of the polymers used was completely resorbed at 1 year. The most advanced resorption was observed for poly(L/D-lactide). Despite molecular weight reduction, the poly(L-lactide) implants had maintained 70% of their initial bending strength and 95% of their shear strength at 3 months. The poly (L/D-lactide) and poly(L/DL-lactide) had maintained only 26 to 27% of their initial bending strength and 26 to 31% of the initial shear strength, respectively. The crystallinity of all the materials increased after implantation as compared with nonimplanted materials. The overall crystallinity increase and the final crystallinity reached by the materials at 1 year was, however, lowest for poly(L/DL-lactide) as compared with the other two polylactides.     

In vitro biocompatibility testing of polylactides Part I Proliferation of different cell types

Four polylactides, P-L-LAs 100 KD, 240 KD, 500 KD and a P-DL-LA 400 KD, were testedin vitro by using five cell types. Middle ear, ear canal and nasal septum epithelial cells were used as well as fibroblasts and osteosarcoma cells. The proliferation of cells was studied by culturing on polylactide films and by culturing with media based on artificially aged PLA. The fibroblasts and the osteosarcoma cells were also cultured with media containingL- orD-monomers in different concentrations. Significant differences in cell numbers of polylactide cultures and/or controls were observed. These differences varied per cell type and experimental setting. In general the biocompatibility of the PLAs was satisfactory. Some inhibitory effect on the proliferation of high (10 mg ml^–1) monomer concentrations in culture media was seen.