Preparation of a biodegradable matrix through polyion complex formation by mixing polylactide-based microspheres having oppositely charged surfaces

The aggregation of polyions into microsphere (MS) complexes was studied as a preparative method for the construction of a biodegradable matrix. Aqueous suspensions of polylactide (PLA)-based MSs with positively and negatively charged surfaces, MS(K(3)(4+)-PLA) and MS(E(3)(4-)-PLA), respectively, immediately formed aggregates when mixed. The effects of the stoichiometry of the charged groups on the surfaces of the MSs and the ionic strength of the medium on aggregate formation, as well as the degradation behavior of the polyion complex (PIC) matrix over time, were investigated.     

Applications of life cycle assessment to NatureWorks™ polylactide (PLA) production

NatureWorks™ polylactide (PLA)¹ is a versatile polymer produced by Cargill Dow LLC. Cargill Dow is building a global platform of sustainable polymers and chemicals entirely made from renewable resources. Cargill Dow's business philosophy is explained including the role of life cycle assessment (LCA), a tool used for measuring environmental sustainability and identifying environmental performance-improvement objectives. The paper gives an overview of applications of LCA to PLA production and provides insight into how they are utilized. The first application reviews the contributions to the gross fossil energy requirement for PLA (54 MJ/kg). In the second one PLA is compared with petrochemical-based polymers using fossil energy use, global warming and water use as the three impact indicators. The last application gives more details about the potential reductions in energy use and greenhouse gasses. Cargill Dow's 5–8 year objective is to decrease the fossil energy use from 54 MJ/kg PLA down to about 7 MJ/kg PLA. The objective for greenhouse gasses is a reduction from +1.8 down to −1.7 kg CO₂ equivalents/kg PLA.     

可生物降解的聚乳酸弹性体的性能研究

对制备的聚乳酸（聚醚）酯型聚氨酯弹性体进行了动态力学、力学性能和降解性能的测试．结果表明，弹性体的强度和弹性都较好，它们受交联度、ＰＥＧ含量和ＰＥＧ分子量的影响．该弹性体的降解速度较快．降解过程中存在自催化效应，而且是从表面开始由表及里逐渐降解的．但材料降解过程中也会出现内部降解较快的现象．动物实验表明，该弹性体是一种能满足尿道支撑管要求的有实际应用价值的材料．     

Synthesis of Sulfated Polysaccharides and Oligosaccharide Derivatives with Potent Anti-Aids Virus Activity

Abstract

Sulfated synthetic polysaccharides (with both high anti-AIDS virus activity and high anticoagulant activity) were prepared by sulfating such synthetic polysaccharides as ribopyranan, ribofuranans, and dextrans. Sulfated natural polysaccharides with high anti-AIDS virus activity but low anticoagulant activity were synthesized from lentinan and curdlan. It is assumed that curdlan sulfate will be helpful as an AIDS drug. In addition, sulfated alkyl oligosaccharides with high anti-AIDS virus activity were prepared.     

Improving Impact Toughness of Polylactide/Ethylene-co-vinyl-acetate Blends via Adding Fumed Silica Nanoparticles: Effects of Specific Surface Area-dependent Interfacial Selective Distribution of Silica

Adding fumed silica(SiO_2) has been considered as an effective method for tailoring the phase morphology and performance of elastomer-toughened plastic binary blends. It has been demonstrated that the selective distribution of SiO_2 plays a decisive role in the mechanical properties of plastic/elastomer/SiO_2 nanocomposites, especially for the impact toughness. In this work, we aim to illuminate the role of specific surface area in controlling their selective distribution of fumed SiO_2 and consequent mechanical properties of plastic/elastomer binary blends. Three types of SiO_2 with different specific surface areas were incorporated into polylactide/ethylene-co-vinyl-acetate(PLA/EVA) model blends by melt blending directly. It was found that the selective distribution of SiO_2 is largely determined by their specific surface areas, i.e. SiO_2 nanoparticles with low specific surface area has a stronger tendency to be located at the interface between PLA matrix and EVA dispersed phase as compared to those with high specific surface area. The specific surface area-dependent interfacial selective distribution of SiO_2 is mainly attributed to the extent of increased viscosity of EVA dispersed phase in which SiO_2 nanoparticles are initially dispersed and resultant migration rate of SiO_2 nanoparticles. The interfacial localized SiO_2 nanoparticles induce an obvious enhancement in the impact toughness with strength and modulus well maintained. More importantly, in the case of the same interfacial distribution, toughening efficiency is increased with the specific surface area of SiO_2. Therefore, this is an optimum specific surface area of SiO_2 for the toughening. This work not only provides a novel way to manipulate the selective distribution of SiO_2 in elastomer-toughened plastic blends toward high-performance, but also gives a deep insight into the role of interfacial localized nanoparticles in the toughening mechanism.     

Synthesis,Characterization, and Hydrolytic Degradation of Polylactide/Poly(ethylene glycol)/Nano-silica Composite Films

Poly(lactic acid) (PLA)/PEG/nano-silica composite degradable films have been prepared by solvent casting method. IR measurements showed that vibration of C–O–C group was confined by silica network. SEM results showed that nano-silica particles were dispersed uniformly in the PLA/PEG matrix. TGA results indicated that the thermal decomposition temperature rose with the increase of nano-silica content. The tensile strength of composite film increased by the addition of nano-silica particles into PLA/PEG matrix. The degradation rate of PLA/PEG/nano-silica composites increased with the acidic medium of degradation. On the other hand, the slower degradation was obtained in the neutral buffer solution. PLA/PEG/nano-silica composites were found to exhibit almost similar degradation behavior as that of PLA/PEG films.     

负载紫杉醇的聚乳酸纳米纤维对宫颈癌的抑制作用

从细胞水平和动物模型两个层次上研究了负载紫杉醇的聚乳酸纤维毡诱导U14宫颈癌细胞凋亡和抑制小鼠U14皮下移植瘤生长的能力.将U14细胞在纤维毡存在下孵育48 h,经Annexin V-FITC及PI双染后行流式细胞分析.结果表明,载药纤维(折合紫杉醇浓度40)g/mL)组总凋亡细胞比例(25.6%)明显高于对照组(1.0%)和未载药纤维组(1.5%).建立U14宫颈癌皮下移植瘤小鼠模型,将其随机分为3组.A组为对照组,不做任何处理.B、C组小鼠以纳米纤维毡覆盖于肿瘤表面,覆盖率约为70%～75%.其中B组纤维毡为纳米聚乳酸电纺丝纤维,不载药,C组为同种材料纤维毡,载有33 wt%紫杉醇.经处理后第7、14天每组各处死动物5～7只,剥离肿瘤,照相,称重,计算抑瘤率.结果表明,载药纤维对U14宫颈癌皮下移植瘤有明显抑制作用(48%～56%).用未载药聚乳酸纤维包裹肿瘤表面,肿瘤质量与对照组无显著差别,说明聚乳酸纤维本身对肿瘤没有抑制作用,载药纤维组所观察到的抑瘤效果为紫杉醇从纤维毡中释放所致.     

聚乳酸在生物医药领域的改性研究进展

聚乳酸类材料是一种用途广泛的生物降解高分子材料,已经成为生物医用材料中最受重视的材料之一。但由于聚乳酸本身的缺陷,限制了其在生物医学工程中的应用。对聚乳酸的改性工作就一直备受关注。本文综述了近几年聚乳酸生物降解材料的物理改性和化学改性研究进展,经改性后聚乳酸的力学性能、降解性能、亲水性能和生物活性得到有效改善,从而更好地满足了生物医用需要。     

可降解聚氨酯丙烯酸酯生物材料的制备及其表征

以端羟基聚丙交酯(PLLA)为软段,六亚甲基二异氰酸酯(HDI)和甲基丙烯酸羟乙酯(HEMA)为硬段聚合得到端基为双键的低聚物,再在UV照射下固化得到可生物降解的聚氨酯丙烯酸酯(PUA)生物组织工程材料.PLLA由1,4-丁二醇引发L-丙交酯(L-LA)开环得到.PLLA和低聚物的组成结构用NMR和GPC进行了表征.对固化聚合物PUA的热性能(DSC和TGA)、力学性能(DMA和拉伸)和亲水性(接触角和溶胀)的研究表明增加PLLA软段会增加材料的Tg,但降低材料的亲水性和交联度.PLLA500-HDI的拉伸强度为6.7 MPa,可以满足生物材料的力学性能要求.通过体外降解实验,发现增加PUA材料的软段,降解速率下降.降解16周后,PLLA500-HDI降解最快,失重15.8%,而PLLA2000-HDI的降解速率最慢,失重5.5%,可能与其微相分离的结构有关.红外(ATR)分析表明降解的PUA膜中N—H的伸缩吸收峰(3364 cm-1)变宽和C O吸收峰变尖锐,说明主链中酯键和氨基甲酸酯键都发生了水解.热失重(TGA)曲线上PLLA500-HDI和PLLA1000-HDI降解后的PUA材料热稳定性下降,而PLLA2000-HDI变化不大.此外,在SEM图中发现降解的PLLA500-HDI膜表面出现裂纹和孔洞,PLLA2000-HDI材料表面也形成相分离结构.细胞实验说明材料支持细胞的黏附,有较好的生物相容性,具有应用于组织工程的潜力.     

Thermal,morphological, mechanical and aging properties of polylactide blends with poly(ether urethane) based on chain-extension reaction of poly(ethylene glycol) using diisocyanate

Poly(ether urethane)s(PEU), including PEUI15 and PEUH15, were prepared through chain-extension reaction of poly(ethylene glycol)(PEG-1500) using diisocyanate as a chain extender, including isophorone diisocyanate(IPDI) and hexamethylene diisocyanate(HDI). These PEUs were used to toughen polylactide(PLA) by physical and reactive blending.Thermal, morphological, mechanical and aging properties of the blends were investigated in detail. These PEUs were partially compatible with PLA. The elongation at break of the reactive blends in the presence of triphenyl phosphate(TPP)for PLA with PEUH15 or PEUI15 was much higher than that of the physical blends. The aging test was carried out at-20 °C for 50 h in order to accelerate the crystallization of PEUs. The PEUs in the PLA/PEU blends produced crystallization and formed new phase separation with PLA, resulting in the declined toughness of blends. Fortunately, under the aging condition,although PEUH15 in blends could also form crystallization, the reactive blend of PLA/PEUH15/TPP(80/20/2) had higher toughness than the other blends. The elongation at break of PLA/PEUH15/TPP(80/20/2) dropped to 287% for the aging blend from 350% for the original blend. The tensile strength and modulus of PLA/PEUH15/TPP blend did not change obviously because of the crystallization of PEUH15.