Construction of functional aliphatic polycarbonates for biomedical applications

Aliphatic polycarbonates are one important kind of biodegradable polymers and have been commonly used as integral components of engineered tissues, medical devices and drug delivery systems. As far as the biomedical application is concerned, traditional aliphatic polycarbonates usually suffer from the strong hydrophobicity, deficient functionality, and insufficient compatibility with cell/organs. Consequently, the application is quite limited in scope. Due to the imparted appealing properties, aliphatic polycarbonates bearing specifically designed functional/reactive groups attract great interest from researchers in the recent years. The present review outlines the development up to date concerning the design and biomedical application of functional aliphatic polycarbonates, with an emphasis on their ring-opening (co)polymerization preparation.     

Mesoporous Silicon‐PLGA Composite Microspheres for the Double Controlled Release of Biomolecules for Orthopedic Tissue Engineering

In this study, poly(dl ‐lactide‐co‐glycolide)/porous silicon (PLGA/pSi) composite microspheres, synthesized by a solid‐in‐oil‐in‐water (S/O/W) emulsion method, are developed for the long‐term controlled delivery of biomolecules for orthopedic tissue engineering applications. Confocal and fluorescent microscopy, together with material analysis, show that each composite microsphere contained multiple pSi particles embedded within the PLGA matrix. The release profiles of fluorescein isothiocyanate (FITC)‐labeled bovine serum albumin (FITC‐BSA), loaded inside the pSi within the PLGA matrix, indicate that both PLGA and pSi contribute to the control of the release rate of the payload. Protein stability studies show that PLGA/pSi composite can protect BSA from degradation during the long term release. We find that during the degradation of the composite material, the presence of the pSi particles neutralizes the acidic pH due to the PLGA degradation by‐products, thus minimizing the risk of inducing inflammatory responses in the exposed cells while stimulating the mineralization in osteogenic growth media. Confocal studies show that the cellular uptake of the composite microspheres is avoided, while the fluorescent payload is detectable intracellularly after 7 days of co‐incubation. In conclusion, the PLGA/pSi composite microspheres offer an additional level of controlled release and could be ideal candidates as drug delivery vehicles for orthopedic tissue engineering applications.     

Poly(para‐dioxanone)/poly(D,L‐lactide) blends compatibilized with poly(D,L‐lactide‐co‐para‐dioxanone)

The effect of poly(D ,L ‐lactide‐co‐para‐dioxanone) (PLADO) as the compatibilizer on the properties of the blend of poly(para‐dioxanone) (PPDO) and poly(D ,L ‐lactide) (PDLLA) has been investigated. The 80/20 PPDO/PDLLA blends containing from 1% to 10% of random copolymer PLADO were prepared by solution coprecipitation. The PLADO component played a very important role in determining morphology, thermal, mechanical, and hydrophilic properties of the blends. Addition of PLADO into the blends could enhance the compatibility between dispersed PDLLA phase and PPDO matrix; the boundary between the two phases became unclear and even the smallest holes were not detected. On the other hand, the position of the T_g was composition dependent; when 5% PLADO was added into blend, the T_g distance between PPDO and PDLLA was shortened. The blends with various contents of compatibilizer had better mechanical properties compared with simple PPDO/PDLLA binary polymer blend, and such characteristics further improved as adding 5% random copolymers. The maximum observed tensile strength was 29.05 MPa for the compatibilized PPDO/PDLLA blend with 5% PLADO, whereas tensile strength of the uncompatibilized PPDO/PDLLA blend was 14.03 MPa, which was the lowest tensile strength. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

希夫碱镍金属催化对L-丙交酯的开环聚合

该文合成了3种希夫碱镍金属催化剂:NiL1〔乙二胺缩香草醛Ni(Ⅱ)〕、NiL2〔邻苯二胺缩3,5-二叔丁基水杨醛Ni(Ⅱ)〕、NiL3(1S,2S-二苯基乙二胺缩水杨醛Ni(Ⅱ)),并用1HNMR、X-ray单晶衍射等方法对新合成的催化剂NiL3进行了表征。以NiL1为催化剂通过单因素分析,选择合适的L-LA(左旋丙交酯)本体开环聚合条件,在该聚合条件下,对比不同配体结构特点的催化剂NiL1、NiL2、NiL3的催化聚合效果,结果表明,催化剂配体结构中引入供电子基团甲氧基有利于提高催化剂活性;配体结构中在金属活性中心周围增大位阻效应有利于得到相对分子质量(简称分子量,下同)分布较窄的聚合产物。     

PLA复合材料降解性能研究进展

概述了聚乳酸(PLA)的降解理论,重点综述了PLA复合材料水解和热降解的国内外研究进展,并展望了PLA复合材料降解研究的发展方向。     

聚乳酸的性能、合成方法及应用

本文对聚乳酸的性能、合成方法及在药物控制释放体系、接骨材料、手术缝合线等生物医学领域的应用作了综述 ,并讨论了聚乳酸类材料的开发前景     

利用有机催化剂合成分子量可控聚乳酸

利用有机催化剂--1,8-二氮杂双环[5.4.0]-7-十一碳烯(DBU),以异丙醇为引发剂,实现丙交酯在常温、常压下的活性开环聚合反应,合成可作为医用材料的分子量可控的聚乳酸.反应机理为有机催化剂DBU与引发剂异丙醇通过氢键形成中间体,中间体中呈负电性的氧对丙交酯羰基中的碳进行亲核进攻,使丙交酯单体通过酰氧键断裂,进行开环聚合反应.通过FT-IR和1H NMR对聚乳酸的结构进行了表征.通过调节丙交酯和异丙醇的摩尔比来调控产品聚乳酸的分子量,GPC分析表明该聚合方法能够实现聚乳酸分子量的有效控制,且聚乳酸分子量分布很窄.通过分析聚合反应时间对聚乳酸产率的影响,确定了poly-lactide-3000、polylactide-5000、polylactide-7000 和polylactide-10000的适宜聚合反应时间分别为20、30、40和50min.     

超临界CO2中聚乳酸的开环沉淀聚合反应研究

以L-丙交酯为原料、辛酸亚锡为引发剂,在超临界CO2中运用开环沉淀聚合法成功地制备了聚L-乳酸。用粘度法测定了所得聚合物的相对分子质量,用红外光谱和核磁共振分析了聚合物的结构,同时初步探索了反应温度、时间以及CO2压力对聚合物相对分子质量的影响。     

链转移剂对D,L-乳酸聚合的影响

采用两步法合成了聚D,L-乳酸,即以D,L-乳酸为原料。先制得高纯度聚合单体丙交酯,再以辛酸亚锡为引发剂,月桂醇为链转移剂(即相对分子质量调节剂),高真空条件下开环聚合制得了一系列不同相对分子质量的乳酸均聚物。分别以引发剂用量、链转移剂用量、聚合温度和聚合时间为因素进行正交实验设计,确定了制备较高相对分子质量聚乳酸的反应条件：辛酸亚锡质量分数为0．1％,月桂醇质量分数为0．04％,聚合温度为130℃,聚合时间为10h。在170℃下,考察了链转移剂用量对聚乳酸相对分子质量的影响．得到了聚乳酸相对分子质量与链转移剂用量的定量关系式。用凝胶渗透色谱、红外光谱、核磁共振氢谱等对聚乳酸的结构和性质进行了表征。     

Miscibility and phase structure of binary blends of poly(L‐lactide) and poly(vinyl alcohol)

Blend films of poly(L ‐lactide) (PLLA) and poly(vinyl alcohol) (PVA) were obtained by evaporation of hexafluoroisopropanol solutions of both components. The component interaction, crystallization behavior, and miscibility of these blends were studied by solid‐state NMR and other conventional methods, such as Fourier transform infrared (FTIR) spectra, differential scanning calorimetry (DSC), and wide‐angle X‐ray diffraction (WAXD). The existence of two series of isolated and constant glass‐transition temperatures (T_g's) independent of the blend composition indicates that PLLA and PVA are immiscible in the amorphous region. However, the DSC data still demonstrates that some degree of compatibility related to blend composition exists in both PLLA/atactic‐PVA (a‐PVA) and PLLA/syndiotactic‐PVA (s‐PVA) blend systems. Furthermore, the formation of interpolymer hydrogen bonding in the amorphous region, which is regarded as the driving force leading to some degree of component compatibility in these immiscible systems, is confirmed by FTIR and further analyzed by ¹³C solid‐state NMR analyses, especially for the blends with low PLLA contents. Although the crystallization kinetics of one component (especially PVA) were affected by another component, WAXD measurement shows that these blends still possess two isolated crystalline PLLA and PVA phases other than the so‐called cocrystalline phase. ¹³C solid‐state NMR analysis excludes the interpolymer hydrogen bonding in the crystalline region. The mechanical properties (tensile strength and elongation at break) of blend films are consistent with the immiscible but somewhat compatible nature of these blends. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 762–772, 2001