一种成核剂对聚乳酸结晶行为的影响

通过示差扫描量热法研究了一种新型成核剂对聚乳酸结晶行为的影响,并通过Avrami方程对其结晶动力学进行分析。结果显示,当聚乳酸中加入0.3%质量分数的成核剂,即可使其半结晶时间由61.4 min缩短至9.2 min。通过偏光显微镜对聚乳酸及含成核剂的聚乳酸的晶体形貌观察,发现成核剂可以显著的提高聚乳酸的结晶速率,相同时间内,球晶数量显著增多,晶粒尺寸明显减小。     

Engineering proteolytically-degradable artificial extracellular matrices

Hydrogels are widely used as provisional matrices for tissue engineering and regenerative medicine, showing also great promise as platforms for 3D cell culture. Different bio-functionalization strategies have been proposed to enhance the biological performance of hydrogels, particularly when they lack intrinsic bioactivity. In this context, the design of artificial materials that mimic structural and functional features of the natural extracellular matrix (ECM) has been pursued. This review presents an overview on bioengineering approaches of integrating protease-sensitive motifs into hydrogels, for the creation of cell-responsive biomimetic scaffolding materials that degrade in response to their proteolytic microenvironment. The successful incorporation of protease-sensitive motifs in several synthetic and natural polymers, which has been achieved using various chemical routes, is described. In each case, the selected peptide sequences and their target proteases are highlighted, along with the main achievements of the study. A critical analysis of current limitations and recent advances is also provided, along with suggestions for further improvements.     

β-偏磷酸钙晶须增强左旋聚乳酸材料的体外降解

对用于骨折内固定的β-偏磷酸钙晶须/左旋聚乳酸(β-CMP_W/PLLA)复合材料在体外降解过程中强度的变化、 分子量和微观形貌进行了初步研究。结果表明: 在人体模拟体液(SBF)中浸泡, 前8周材料的强度变化较小, 25wt%β-CMP_W/75wt%PLLA降解20周后的抗压强度值仍高达103MPa; 45wt%β-CMP_W/55wt%PLLA降解12周后抗压强度约为初始值的88%。扫描电镜图表明, 随降解时间的延长, 因聚乳酸溶解而在样品中形成孔洞。在降解周期内, SBF溶液的pH值随β-CMP_W/PLLA降解时间的延长基本保持稳定。凝胶渗透色谱检测结果表明, PLLA的数均相对分子质量和重均相对分子质量随降解时间的延长而降低, 降解20周后数均相对分子质量约为20万, 重均相对分子质量下降了32%。     

A series of rare earth phenolates substituted by alkyl groups for D,L-lactide ring-opening polymerization

Single component rare earth phenolates substituted by various alkyl groups have been prepared and the correlation between the aryloxides’ structure and catalytic activity in the ring-opening polymerization of D,L-lactide has also been investigated.The catalytic activity of all rare earth aryloxides,characteristics of the ring-opening polymerization as well as polymerization kinetics and mechanism were investigated.The results showed that both phenolates’ catalytic activities and polymerization characteristics changed regularly,keeping in good concordance with variations in substitutents’ number on phenol and structure of aryloxide ligands.The stronger ability of electron-donation of alkyl groups,the higher catalytic activity.Moreover,the more numbers of substituted alkyl on phenyl ring,the higher catalytic activity.The analyses of polymer ends revealed that the polymerization proceeded via a coordination-acyl-oxygen bond cleavage-insertion mechanism.     

Optimization of Process Parameters for Controlled Ring-Opening Polymerization of Lactide to Produce Poly(L-Lactide) Diols as Precursor for Polyurethanes

Series of poly(L-Lactide) diols with molecular weights (M_n) in 2,069–4,811?g mol^?1 were synthesized from L-Lactide using stannous octoate catalyst and 1,4-butanediol chain extender. Operating conditions, i.e., temperature, catalyst concentration, chain extender concentration, and reaction time, were optimized. Maximum monomer conversion and M_n were observed at 0.5?mol% SnOct₂ and 1.0?mol% 1,4 butanediol (BDO) at 145°C. Poly(L-Lactide) diols were analyzed by Fourier transform infrared, proton nuclear magnetic resonance, end-group analysis, and X-ray diffraction techniques. Fourier transform infrared confirmed the formation of poly(L-Lactide) diols. Poly(L-Lactide) diols’ % degree of crystallinity was determined by X-ray diffraction. M_n was calculated by proton nuclear magnetic resonance and end-group analysis.     

Compatibilizers of a purposely designed graft copolymer for hydrolysate/PLLA blends

A wood hydrolysate derived hemicellulose-rich fraction was functionalized with L-lactide oligomers through a ring opening polymerization mediated grafting-from reaction. The graft copolymer was designed to act as a compatibilizer in hydrolysate/poly(L-lactide) (PLLA) blend films. The PLLA addition improved the tensile behavior of the hydrolysate matrix and this effect was enhanced further by the addition of minor amounts of the synthesized compatibilizer. With only 1% (w/w) of compatibilitzer the compatibility between the components and the homogeneity of the resulting films were greatly improved with an increase of strain-at-break with up to 400%. The oxygen permeability of the blend films was markedly reduced with the addition of wood hydrolysate, compared to the barrier properties of pure PLLA, an effect that is not significantly compromised when compatibilizer amounts are kept small.     

PHB/PLLA聚酯材料与PHB/PLLA/PEO聚酯材料的体外降解性

对聚β-羟基丁酸酯/聚乳酸（PHB/PLLA）及聚β-羟基丁酸酯/聚乳酸/聚氧乙烯（PHB/PLLA/PEO）膜状样品在37 ℃磷酸缓冲溶液（PBS）/溶菌酶中的降解行为进行了研究,通过定期观察质量损失、降解过程中的热力学性质及样品表面形态变化,发现PHB/PLLA共混未能提高PHB的降解速度,而PEO加入到PHB/PLLA体系中显著提高了PHB、PLLA的降解速度,进而提高了PHB/PLLA共混体系的降解速度。     

熔融分步结晶提纯L-丙交酯

以实验室制备的粗丙交酯为原料,采用熔融分步结晶法对提纯丙交酯进行了实验研究,考察了熔融分步结晶过程中结晶时间、结晶温差、发汗时间等参数对产品质量分数、结晶率、母液质量分数、组分收率以及提纯能力的影响,同时,对结晶和发汗过程的提纯能力进行了对比研究。结果表明:在给定的原料组成下,较适宜的结晶时间为60 min,结晶温差为20℃,发汗时间为50 min,发汗过程提纯能力是结晶过程的1.77倍。     

聚D,L-丙交酯的常压微波辐射合成

研究了常压下微波辐射开环聚合制备聚D,L-丙交酯(PDLLA)。考察了单体纯度、微波辐射时间、催化剂用量和体系真空度对聚合反应的影响。采用气相色谱(GC)测定丙交酯纯度;FTIR和1H-NMR表征产物结构;GPC测定分子量分布。实验结果表明:重结晶4次后的丙交酯,在催化剂辛酸亚锡用量为0.15%,常压下经微波辐射30min,可获得分子量为21.87×104的PDLLA。反应时间与传统法相比大大缩短。与传统合成法的不同还表现为,随丙交酯纯度的提高,最佳聚合时间延长;体系真空度对反应无影响。GPC结果表明聚合产物的分子量分布较窄。     

Phase behaviour of l-lactic acid based polymers of low molecular weight in supercritical carbon dioxide at high pressures

The results of investigations of phase behaviour in the systems l-lactic acid based polymers + carbon dioxide at high pressures are presented. The measurements have been performed in wide temperature and composition ranges. Two samples of the polymer differing in molecular weight (M_n: 1080 and 3990 g/mol) have been investigated. Both samples of the polymer were characterized with the gel permeation chromatography and NMR spectroscopy. The influence of the structure of the polymer on the solubility in supercritical carbon dioxide has been discussed. The results obtained suggest that the solubility of low molecular weight l-lactic acid based polymers in supercritical carbon dioxide is not controlled by its size, but to a large extent by the character of its terminal groups. The phase behaviour in the system l-lactic acid + carbon dioxide has been also investigated and the results were compared with those for the systems composed of l-lactic acid based polymers and carbon dioxide.