Biodegradable poly(lactic acid) microspheres containing total alkaloids of Caulis sinomenii

The fabrication of biodegradable poly(lactic acid) (PLA) microspheres containing total alkaloids of Caulis sinomenii was investigated. The formation, diameter, morphology and properties of the microspheres were characterized using Fourier transform infrared spectroscopy (FT-IR), laser particle size analyser and scanning electron microscopy (SEM), etc. In vitro releasing behaviour was also investigated using UV-Vis spectrometer. As a result, the drug-loaded microspheres with a narrower distributive, rounder and smoother surface were prepared. Drug-releasing behaviour from microspheres was affected by the concentration of emulsifier and the stirring rate. The results demonstrated that a medicated system, which can be potentially applied within a drug delivery system, was designed. This system acts in a systematic manner for the treatment of rheumatoid arthritis.     

Electrospinning highly oriented and crystalline poly(lactic acid) fiber mats

In recent years, there has been an increased focus on sustainable, green alternatives with similar properties to conventional petroleum-based polymers. Poly(lactic acid) (PLA) is a biodegradable biopolymer which exhibits mild piezoelectric properties and has good processability which gives it potential for use in numerous existing and novel applications. The purpose of this study was to produce highly oriented and crystalline PLA electrospun fiber mats for piezoelectric applications. In order to yield a high piezoelectric constant, high crystallinity and fiber orientation are necessary. A two parallel collector set up was used to mechanically orient the fibers in the space between two copper electrodes. Voltage and feed rate were adjusted to produce smooth, oriented fibers with average diameters ranging 0.73–1.19 μm. Crystallinity and orientation were increased via hot drawing of the fiber mats and were maximized between 40 and 50 % and greater than 50 %, respectively.     

Fabrication and characterization of fully biodegradable natural fiber-reinforced poly(lactic acid) composites

Polymer composites were fabricated with poly(lactic acid) (PLA) and cellulosic natural fibers combining the wet-laid fiber sheet forming method with the film stacking composite-making process. The natural fibers studied included hardwood high yield pulp, softwood high yield pulp, and bleached kraft softwood pulp fibers. Composite mechanical and thermal properties were characterized. The incorporation of pulp fibers significantly increased the composite storage moduli and elasticity, promoted the cold crystallization and recrystallization of PLA, and dramatically improved composite tensile moduli and strengths. The highest composite tensile strength achieved was 121 MPa, nearly one fold higher than that of the neat PLA. The overall fiber efficiency factors for composite tensile strengths derived from the micromechanics models were found to be much higher than that of conventional random short fiber-reinforced composites, suggesting the fiber–fiber bond also positively contributed to the composites’ strengths.     

Nanostructured medical device coatings based on self-assembled poly(lactic-co-glycolic acid) nanoparticles

Here we present a new method for providing nanostructured drug-loaded polymer films which enable control of film surface morphology and delivery of therapeutic agents. Silicon wafers were employed as models for implanted biomaterials and poly(lactic-co-glycolic acid) (PLGA) nanoparticles were assembled onto the silicon surface by electrostatic interaction. Monolayers of the PLGA particles were deposited onto the silicon surface upon incubation in an aqueous particle suspension. Particle density and surface coverage of the silicon wafers were varied by altering particle concentration, incubation time in nanoparticle suspension and ionic strength of the suspension. Dye loaded nanoparticles were prepared and assembled to silicon surface to form nanoparticle films. Fluorescence intensity measurements showed diffusion-controlled release of the dye over two weeks and atomic force microscopy (AFM) analysis revealed that these particles remained attached to the surface during the incubation time. This work suggests that coating implants with PLGA nanoparticles is a versatile technique which allows drug release from the implant surface and modulation of surface morphology.     

Nanodiamond/poly (lactic acid) nanocomposites: Effect of nanodiamond on structure and properties of poly (lactic acid)

Nanodiamond (ND)/poly (lactic acid) (PLA) nanocomposites with potential for biological and biomedical applications were prepared by using melting compound methods. By means of transmission electron microscopy (TEM), Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), Thermogravimetric analyses (TGA), Dynamic mechanical analyses (DMA), Differential scanning calorimetry (DSC) and Tensile test, the ND/PLA nanocomposites were investigated, and thus the effect of ND on the structural, thermal and mechanical properties of polymer matrix was demonstrated for the first time. Experimental results showed that the mechanical properties and thermal stability of PLA matrix were significantly improved, as ND was incorporated into the PLA matrix. For example, the storage modulus (E′) of 3 wt% ND/PLA nanocomposites was 0.7 GPa at 130 °C which was 75% higher than that of neat PLA, and the initial thermal decomposition was delayed 10.1 °C for 1 wt% ND/PLA nanocomposites compared with the neat PLA. These improvements could be ascribed to the outstanding physical properties of ND, homogeneous dispersion of ND nanoclusters, unique ND bridge morphology and good adhesion between PLA matrix and ND in the ND/PLA nanocomposites.     

聚乳酸纤维的研究进展

聚乳酸是一种新型的生态环保型高分子材料.本文主要介绍了世界各国对聚乳酸纤维研究及生产的相关情况,对聚乳酸的生产工艺作了深入的探究,并介绍了聚乳酸的应用及发展前景.     

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     

聚乳酸的增塑改性

采用溶液共混法,以聚乙二醇(PEG)、邻苯二甲酸二丁酯(DBP)、邻苯二甲酸二辛酯(DOP)作为增塑剂,对聚左旋乳酸(PLA)进行增塑改性.用综合热分析仪对改性PLA的热性能进行了表征.讨论了不同的增塑剂及其用量对改性PLA性能的影响:当增塑剂的含量增加时,改性PLA的强度下降,伸长率增加,并逐渐由脆性向韧性转变;玻璃化转变温度(Tg)和熔点(Tm)下降.当增塑剂的质量比≤20%时,共混物各组分间有较好的相容性.PEG400改性的PLA效果较好.     

Preparation and properties of self-reinforced poly(lactic acid) composites based on oriented tapes

The inherent brittleness and poor thermal resistance of poly(lactic acid) (PLA) are two main challenges toward a wider industrial application of this bioplastic. In the present work, through the development of self-reinforced PLA (SR-PLA) or “all-PLA” composites, the high brittleness and low heat deflection temperature (HDT) of PLA have been overcome, while simultaneously improving the tensile strength and modulus of SR-PLA. The obtained composites are fully biobased, recyclable and under the right conditions compostable. For the creation of SR-PLA composites, first a tape extrusion process was optimized to ensure superior mechanical properties. The results show that SR-PLA composites exhibited enhanced moduli (2.5 times) and tensile strengths (2 times) and showed 14 times increase in impact energy compared to neat PLA. Finally, the HDT of SR-PLA was also increased by about 26 °C compared to neat PLA, mainly as a result of an increase in modulus and crystallinity.     

Synthesis of multiblock thermoplastic elastomers based on biodegradable poly (lactic acid) and polycaprolactone

A new biodegradable (AB)_n type of multiblock copolymers derived from poly (ε-caprolactone) (PCL) and poly (lactic acid) (PLA) was prepared via the method of the chain extending reaction among PCL oligomers, PLA oligomers and hexamethylene diisocyanate (HDI). Fourier transform infrared spectra (FTIR), ¹H NMR, thermal gravity analysis (TGA) and derivative thermograms (DTG) were used to characterize the copolymers and the results showed that PCL and PLA were coupled by the reaction between –NCO groups and terminal –OH and –COOH groups of PCL and PLA, respectively. The material displayed enhanced mechanical properties: Young's modulus was as low as 2.7 ± 0.7 MPa and elongation at break value was above 790% at the composition of PCL/PLA = 80/20 (w/w). Moreover, according to SEM micrographs interfacial adhesion of the composites was improved. Thermal degradation temperature of the composites was higher than PLA but was lower than PCL, which is an advantage for industry process.     

Highly ordered poly(thiophene)s prepared in mesoporous silica nanoparticles

Nanostructured PEDOT was synthesized using mesoporous silica as a nano-template. The polymerization of thiophene monomers was performed with an oxidant and mesoporous silica nanoparticles. The silica particles took essential role in absorbing monomers and oxidant molecules, and growth of polymers inside their pores. As prepared polymer/silica composite was treated with HF solution to remove silica template to result in 1D wire structure and mesh type porous 3D structures from SBA-15 and KIT-6 template, respectively. The average size of the poly(thiophene) wires was 10 15 nm, which was matched well to the pores size of the silica templates, as determined from an electron microscopy. At optimized condition, the room temperature electrical conductivities of the PEDOT grown from SBA-15 and KIT-6 template were similar as 1.1 and 1.0 S/cm, respectively. However, the evolution of the PEDOT conductivity versus temperature was different depending on the templates. These results gave a unique chance to tailor made 3 dimensional structure as well as properties of conductive polymer.     

Fabrication of poly(lactic acid)-poly(ethylene oxide) electrospun membranes with controlled micro to nanofiber sizes

Biodegradable poly(L-lactide acid) (PLLA) nanofiber membranes were prepared by electrospinning of PLLA and poly(ethylene oxide) (PEO). The selective removal of PEO by water allows to obtain smaller fiber diameters and to increase the porosity of the membranes in comparison to PLLA membranes obtained under the same electrospinning conditions. After removal of PEO membranes with fiber sizes of 260 nm and average porosity close to 80% are obtained. Thermal and infrared results confirm the poor miscibility of PLLA and PEO, with the PEO randomly distributed along the PLLA fibers. On the other, PLLA and PEO mixing strongly affect their respective degradation temperatures. The influence of the PEO in the electrospinning process is discussed and the results are correlated to the evolution of the PLLA fiber diameter.     

基于非平衡现象的聚乳酸聚氧化乙烯复合材料梯度结构的自组织制备

基于热力学非平衡现象,将聚乳酸(PLA)-聚氧化乙烯(PEO)-CHCl₃溶液置于远离热力学平衡状态的开放系中干燥,自组织构筑了PLA-PEO复合体系内部的梯度相分离结构.通过偏光显微镜(POM)和衰减全反射傅里叶变换红外(ATR-FTIR)光谱对复合材料共混膜试样内部的梯度结构进行了表征.结果表明:在热力学非平衡状态下,复合体系内部形成了梯度结构;随着体系远离平衡状态,PLA富集在能量流出的空气侧,PEO则富集在能量流入的底部,膜的组成在能量流动方向上形成梯度分布,并随体系远离平衡状态呈增大的趋势,而热力学平衡状态是影响梯度结构形成的主要因素.     

Fabrication of microwell arrays based on two-dimensional ordered polystyrene microspheres for high-throughput single-cell analysis

This paper describes a method of fabricating rounded bottom microwell arrays (MA) in poly(dimethylsiloxane) (PDMS) by molding a monolayer of ordered polystyrene (PS) microspheres. PS microspheres were self-assembled on a glass slide and partially melted mainly from the bottom at 240 °C to increase adhesive force with the substrate. The partially melted PS arrays were used as master to generate MA. Microwell sizes are tunable in the 10-20 μm range with rounded bottoms; such a 3D structure is not readily obtainable through conventional soft lithography. Both adherent and nonadherent cell types can be retained in the microwells with high efficiency. As a demonstration of the advantage of real-time cell screening with this MA, single cell enzyme kinetic analysis was also carried out on trapped single cells. The PDMS MA may find applications in high-throughput drug screening, guided formation of cell clusters, and multicellular communication.     

Effect of phosphate-based glass fibre surface properties on thermally produced poly(lactic acid) matrix composites

Incorporation of soluble bioactive glass fibres into biodegradable polymers is an interesting approach for bone repair and regeneration. However, the glass composition and its surface properties significantly affect the nature of the fibre-matrix interface and composite properties. Herein, the effect of Si and Fe on the surface properties of calcium containing phosphate based glasses (PGs) in the system (50P₂O₅-40CaO-(10-x)SiO₂-xFe₂O₃, where x = 0, 5 and 10 mol.%) were investigated. Contact angle measurements revealed a higher surface energy, and surface polarity as well as increased hydrophilicity for Si doped PG which may account for the presence of surface hydroxyl groups. Two PG formulations, 50P₂O₅-40CaO-10Fe₂O₃ (Fe10) and 50P₂O₅-40CaO-5Fe₂O₃-5SiO₂ (Fe5Si5), were melt drawn into fibres and randomly incorporated into poly(lactic acid) (PLA) produced by melt processing. The ageing in deionised water (DW), mechanical property changes in phosphate buffered saline (PBS) and cytocompatibility properties of these composites were investigated. In contrast to Fe10 and as a consequence of the higher surface energy and polarity of Fe5Si5, its incorporation into PLA led to increased inorganic/organic interaction indicated by a reduction in the carbonyl group of the matrix. PLA chain scission was confirmed by a greater reduction in its molecular weight in PLA-Fe5Si5 composites. In DW, the dissolution rate of PLA-Fe5Si5 was significantly higher than that of PLA-Fe10. Dissolution of the glass fibres resulted in the formation of channels within the matrix. Initial flexural strength was significantly increased through PGF incorporation. After PBS ageing, the reduction in mechanical properties was greater for PLA-Fe5Si5 compared to PLA-Fe10. MC3T3-E1 preosteoblasts seeded onto PG discs, PLA and PLA-PGF composites were evaluated for up to 7 days indicating that the materials were generally cytocompatible. In addition, cell alignment along the PGF orientation was observed showing cell preference towards PGF.     

基于水溶性稀释剂复合相分离法制备聚乳酸分离膜的研究

以可降解聚乳酸为膜材料,采用水溶性稀释剂二甲基亚砜(DMSO),实现了复合相分离法制备结构可调控的聚乳酸分离膜.重点考察了铸膜液温度和凝固浴温度对其结构及渗透性能的影响.结果表明,当凝固浴温度接近浊点温度时,相分离过程中主要以NIPs过程为主,形成了指状孔和大空腔结构,聚乳酸分离膜的纯水通量较小;牛血清蛋白的截留率较高.当凝固浴温度低于浊点温度时,体系发生TIPs和NIPs复合相分离过程,制备的聚乳酸分离膜具有双连续和指状孔结构,聚乳酸分离膜纯水通量较大,牛血清蛋白的截留率略有降低,但都在66%以上.当铸膜液温度接近浊点温度时,体系发生TIPs和NIPs复合相分离过程,制备的聚乳酸膜具有多孔的表面膜结构,表面膜孔与支撑层之间的连通性较高;随着铸膜液温度的增加,膜表面孔径减小,聚乳酸分离膜纯水通量降低,由610L/(m2·h)降低至27.6L/(m2·h);牛血清蛋白截留率增加,由61%提高至84%.     

Improvement of surface bioactivity of poly(lactic acid) biopolymer by sandblasting with hydroxyapatite bioceramic

This study communicates a simple and effective method for modification of the surface of synthetic biopolymer poly(lactic acid) (PLA) with bioactive ceramic hydroxyapatite (HA) using a sandblasting technique. The sandblasting particles were bombarded onto the PLA, covering the surface quite evenly. The HA-sandblasted PLA showed good in vitro apatite forming ability in a simulated body fluid within a few days, which was rarely observed for pure PLA. Moreover, the HA-sandblasted PLA enhanced the initial cell adhesion and further proliferation, and up-regulated bone cell functions such as the alkaline phosphatase activity. This novel method of surface modification of the biopolymer with bioactive ceramic has the potential for use in developing bone bioactive implantable materials.     

聚乳酸类组织工程支架材料的设计

聚乳酸无毒、易加工、可生物降解、生物相容性好,是目前医学界作为组织工程支架最有开发和应用潜力一类材料。从材料的制备、支架的加工、生物学评价三方面出发,结合本课题组的研究,论述了聚乳酸类支架的设计,并对今后的研究做了进一步展望。     

新型生物降解材料聚乳酸的微孔发泡技术研究进展

介绍了新型生物可降解材料聚乳酸(PLA)微孔塑料的最新研究进展,并详细介绍了PLA微孔塑料的泡孔形态和力学性能的影响因素.