Electrospun poly(D,L)‐lactide nonwoven mats for biomedical application: Surface area shrinkage and surface entrapment

Nanofibrous poly(D,L )‐lactide mats prepared by electrospinning are useful for numerous biomedical applications. However, it was observed that these mats tend to shrink under physiological conditions. In this research, a physical entrapment method to modify the polymer surface with poly(ethylene glycol) was developed to ensure dimensional stability and to increase the hydrophilicity of the surface of the mats. Nanofiber morphology was characterized by scanning electron microscopy. Surface element analysis was performed by high resolution X‐ray photoelectron spectroscopy. Water contact angles were determined to identify surface properties before and after surface entrapment. Canine fibroblasts were prepared and seeded onto the poly(D,L)‐lactide mats, followed by cell morphology study by SEM and cell viability tests by MTT assay, which confirmed the improvement of biocompatibility by surface modification. Taking the results into account, hydrophilic and area‐stable nanofibrous nonwoven mats were successfully produced, with potential applications as in vivo biomedical material. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Decomposition rate control of PLLA plate by heat treatment

It is difficult to control the decomposition rate and the mechanical property of scaffolds after forming the poly(L ‐lactide) (PLLA) scaffolds. The purpose of this study is to control the decomposition rate and mechanical properties of the PLLA plate after forming. We carried out accelerated decomposition experiments using the enzyme on the (PLLA) with various crystallinity, which were prepared by changing the heat treatment condition, and elucidated the relationship between the crystallinity and the decomposition rate. A high positive correlation was observed between the heat treatment temperature and the crystallinity. A high negative correlation was observed between the crystallinity and the decomposition rate. Using the obtained empirical formula, it became possible to calculate the required period to decompose a certain amount of the PLLA if the heat treatment temperature was known. Changing the crystallinity of the PLLA plate could arbitrarily control the decomposition rate of the PLLA plate after forming. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

固体超强酸SO4^2—／ZnO—SnO2／La^3＋催化合成丙交酯

研究了在乳酸合成丙交酯的实验中,以三种不同类型金属氧化物(ZnO,SnO2,La2O3)的固体超强酸作催化剂对反应产物收率,反应温度和时间的影响。实验表明,双金属固体超强酸SO2-4/ZnO-SnO2/La3+催化效果最佳。使用该催化剂,减压(5 0×103Pa)条件下在120～130℃下脱水2h生成乳酸低聚物。然后在150～210℃下分解低聚物,收集丙交酯,反应时间90min。丙交酯的平均收率达58%。     

超临界CO_2中左旋丙交酯的开环聚合反应

以辛酸亚锡为催化剂,用超临界CO2作溶剂,实现了左旋丙交酯的开环聚合,系统地研究了催化剂用量、单体浓度、聚合时间、聚合温度、CO2纯度和压力等因素对单体转化率、聚合产物相对分子质量及其分布的影响。研究结果表明,在超临界状态下聚合温度、催化剂用量和CO2纯度是影响聚合的几个最重要的因素。超临界状态下的丙交酯开环聚合与本体丙交酯开环聚合相似,聚合过程符合配位插入聚合反应的机理。     

Dramatic improvements in toughness in poly(lactide-co-glycolide) nanocomposites

Poly(lactide-co-glycolide) (PLG), a biocompatible and biodegradable polymer, is dramatically toughened by adding small amounts of surface modified clay nanoparticles. The elongation during tensile tests increases from 7% for the pure polymer to 210% for the nanocomposite, accompanied with a modest increase in modulus. In contrast, PLG nanocomposites based on fumed silica treated with hexamethyldisilazane show only modest improvements in toughness. Electron microscopy, X-ray scattering, rheometry, and dielectric relaxation spectroscopy are used to investigate the toughening mechanism. Multiple crazing occurs in the clay nanocomposite after yielding. Small angle X-ray scattering studies show significant orientation of the clay nanoparticles along the tensile stress direction during deformation. The clay nanocomposites show a new, slow relaxation mode, most likely due to interfacial adsorbption of PLG chains on the surface of the clay nanoparticles. The dramatic increase in toughness is attributed to physical crosslinks introduced by the clay nanoparticles, a mechanism absent in the PLG/silica nanocomposites. The physical crosslinks increase the brittle fracture strength of the polymer and, consequently, trigger a toughening mechanism via multiple crazing and shear yielding.     

Synthesis and characterization of an amphiphilic pluronic‐poly(D,L‐lactide‐co‐glycolide) copolymer and their nanoparticles as protein delivery systems

A new amphiphilic Pluronic (F68)‐PLGA copolymer, which can be used to prepare the stealth or long‐circulating nanoparticles, was synthesized with Pluronic (F68), DL ‐Lactide, and glycolide. The structures of Pluronic (F68)‐PLGA copolymer as the products were characterized with infrared spectrometry, nuclear magnetic resonance and their molecular weights were determined by gel permeation chromatography. Two methods, double emulsion (DE) and nanoprecipitation (NP), were employed to fabricate the polymeric nanoparticles. Bovine serum albumin (BSA) was loaded into nanoparticles as a model protein. Influence of the preparation conditions on the nanoparticles size, encapsulation efficiency, and release profile in vitro was investigated. They showed the entrapment efficiency of 42.9–63.4% and the average diameter of 119.1–342.8 nm depending on the fabrication technique of nanoparticles and the type of copolymer. The stability maintenance of BSA in the nanoparticle release in vitro was also measured via sodium dodecyl sulfate‐polyacrylamide gel electrophoresis (SDS‐PAGE), circular dichroism (CD), and fluorescence spectrometry. The results showed that the new copolymer could load BSA effectively and BSA kept stable after it was released from the nanoparticles. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Compatibility of liquid deproteinized natural rubber having epoxy group (LEDPNR)/poly (L‐lactide) blend

Reaction after mixing of liquid epoxidized natural rubber/poly(L ‐lactide) blend was performed to enhance the compatibility of the blend. The liquid epoxidized natural rubber was prepared by epoxidation of deproteinized natural rubber with peracetic acid in latex stage followed by depolymerization with peroxide and propanal. The resulting liquid deproteinized natural rubber having epoxy group (LEDPNR) was mixed with poly(L ‐lactide) (PLLA) to investigate the compatibility of the blend through differential scanning calorimetry, optical light microscopy, and NMR spectroscopy. After heating the blend at 473 K for 20 min, glass transition temperature (T_g) of LEDPNR in LEDPNR/PLLA blend increased from 251 to 259 K, while T_g and melting temperature (T_m) of PLLA decreased from 337 to 332 K and 450 to 445 K, respectively, suggesting that the compatibility of LEDPNR/ PLLA blend was enhanced by a reaction between the epoxy group of LEDPNR and the ester group of PLLA. The reaction was proved by high‐resolution solid‐state ¹³C NMR spectroscopy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Ring‐opening graft polymerization of L‐lactide onto starch granules in an ionic liquid

A room temperature ionic liquid 1‐allyl‐3‐methylimidazolium chloride ([AMIM]Cl) was a promising direct solvent for starch and nonderivitizing solvent for starch‐effective dissolution, in which the ring‐opening graft polymerization (ROGP) of L ‐lactide (L ‐LA) onto starch chains was carried out homogeneously. The obtained starch grafted poly(L ‐lactide) (starch‐g‐PLLA) was characterized by FTIR, ¹³C NMR, DSC, and WAXD, and the good adhesion between the two components was evidenced by SEM observations although the chains of grafted PLLA were not long. The grafting efficiency of PLLA reached 30% when the ROGP proceeded at 100°C for 10 h with L ‐LA/starch 0.5 : 1 (wt/wt) and stannous octoate (Sn(Oct)₂) as a catalyst, which was calculated according to a standard curve newly created by FTIR method. The homopolymerization of L ‐LA and the disconnection of grafted PLLA from starch‐g‐PLLA were the main competition reactions. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Morphology and Properties of Poly(L‐Lactide) (PLLA) Filled with Hollow Glass Beads

The morphology, crystalline behavior, and mechanical and thermal properties of poly(L ‐lactide)/hollow glass beads (PLLA/HGBs) composites were investigated. The incorporation of HGBs enhanced the crystallization rate and crystallinity of PLLA, but slightly decreased its elongation at break. In addition, HGBs acted as stress concentration points inducing the plastic deformation of PLLA, leading to increased Izod impact strength. Differential scanning calorimetry results show that annealed PLLA eliminated cold crystallization phenomenon in the region of 100–140 °C and presented a double melting peak around 150 °C. Moreover, annealing was demonstrated to be effective for the improvement of tensile modulus, strength, Izod impact strength and heat distortion temperature of the composites due to the increased crystallinity and more perfect crystals. Silane coupling agents can enhance the interfacial adhesion of the composites, and lead to better mechanical properties. Compared to neat PLLA, the HGBs filled PLLA composites did not exhibit an obvious increase of the density.

     

镍金属催化剂对L-丙交酯的开环聚合效果分析

本文合成了三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镍),并用IH NMR、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,在此聚合条件下,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分子量分布较窄的聚合产物。