聚乳酸立构复合物规整度对其降解性能的影响

通过开环聚合法,利用D,L-丙交酯合成不同规整度(XD)的左旋聚乳酸PLLA和右旋聚乳酸PDLA。用溶液浇铸法制得不同规整度的聚乳酸立构复合物SC-PLA,并在50℃缓冲溶液中进行降解。通过分析剩余质量、溶液pH值、热性能(DSC)、表面形貌(SEM)、电离子喷雾质谱(ESI-MS)等评价SC-PLA的降解性能。结果表明:相同规整度时,SC-PLA降解速率小于PLLA,但pH值变化大于PLLA,立构复合物SC的存在使材料比常见PLLA更耐水解;立构规整度下降会使SC-PLA的结晶度降低,材料的降解速率加快;降解使材料的结晶度上升,立构复合物晶体SC与均聚物晶体HC熔点降低;高规整度SC-PLA相对于相同规整度PLLA及低规整度SC-PLA,其降解产物分子链长度更短。     

添加剂对聚乳酸湿热降解性的影响

文中研究了聚乳酸在日常使用温度、湿度条件下的降解行为。实验发现,聚乳酸热氧降解几乎可以忽略,主要的降解形式是吸湿后的水解。采用熔融共混添加剂的方法,加入憎水性添加剂二甲基硅油降低聚乳酸的吸湿性,加入碱性添加剂改变聚乳酸的pH值,都可以降低聚乳酸的湿热降解率。加入0.5%~1.5%硬脂酸钠效果最好,其中加入1.0%的聚乳酸树脂在60℃,70%相对湿度条件下24 h仅降解16.96%,而没有添加剂的树脂降解高达68.16%。     

环糊精改性聚乳酸及其体外降解性研究

环糊精改性聚乳酸(PLA-β-CD)是一种全生物降解的新型生物材料.考察了环糊精改性聚乳酸基生物材料的体外降解行为,包括材料在蒸馏水中的pH值变化和在pH=7.4 PBS中的失重率变化.结果表明,PLA-β-CD与PLA的降解行为相似,PLA-β-CD的分子主链没有被破坏,没有出现引入酸酐导致材料酸性进一步增强的现象.     

PEG改性聚乳酸嵌段共聚物降解性能研究

辛酸亚锡催化下开环聚合制备聚乳酸(DL-PLA)-聚乙二醇(PEG)-聚乳酸三嵌段共聚物.用GPC、DSC、1 H-NMR、质量损失、静态接触角等方法在pH=7.4磷酸盐缓冲液中,37℃下研究了分子量Mn=400、1000和4000的PEG改性DL-PLA的降解行为.结果表明,PEG嵌段增强了共聚物的亲水性,降低了共聚物Tg,加速了共聚物降解,随着PEG分子量增加及两端DL-PLA链段增长,共聚物分子量下降速率加快.由研究结果得出,共聚物降解期间DL-PLA链段中的酯键随机断裂,PEG两端DL-PLA链段逐渐变短;降解后期DL-PLA链段进一步变短,并有短链DL-PLA均聚物产生,当PEG两端DL-PLA链段足够短时,共聚物在介质中溶解.     

聚(D,L-乳酸)基仿生聚合物材料的合成与表征

探索一种新型聚乳酸基仿生聚合物材料的制备新方法.具体实验步骤是:利用聚乳酸上叔碳原子的自由基反应活性,在过氧化二苯甲酰的催化作用下,将马来酸酐引入聚乳酸侧链上,以此提供高反应活性的酸酐键;然后利用酸酐基团与-NH2发生N-酰化反应这一特点,将脂肪族二胺引入聚乳酸侧链上,从而克服聚乳酸降解产物的体液环境呈酸性的缺陷;再用碳二亚胺作缩合剂,在二胺改性聚乳酸材料中共价引入一种细胞粘附肽段Arg-Gly-Asp-Ser(RGDS),赋予材料生物活性和生物特异性,这样就制备了一种新型聚乳酸基仿生材料.采用MALLS、FTIR和XPS对仿生材料进行结构表征;采用罗丹明比色法、茚三酮显色法和氨基酸分析仪检测法对仿生材料中的马来酸酐、二胺和粘附肽RGDS进行定量测定.结果表明,按文中所述之制备技术,在不改变聚乳酸材料主链结构的前提下,该仿生材料中粘附肽RGDS的含量是5.12μmol/g.这就形成了一种具有类似细胞外基质的新型仿生材料.     

新型改性聚乳酸及其亲/疏水性研究

合成了基于马来酸酐改性聚乳酸（MPLA）和丁二胺的新型改性聚乳酸（BM-PLA），旨在提高聚乳酸的亲水性，克服乳酸和MPLA在降解过程中的酸性，并为进一步引入多肽和胶原等生物信号分子提供活性基团。通过红外光谱测定到了丁二胺已成功引入到MPLA中，利用接触角和吸水率评价了BMPLA的亲/疏水性变化，表明丁二胺改性所得BMPLA的亲水性相对于PDLLA和MPLA已大大改善，测定了材料在12周降解过程中的pH变化。表明丁二胺改性聚乳酸不表现酸致自加速降解特征，未出现pH陡降现象，已完全克服了聚乳酸和马来酸酐改性聚乳酸降解过程中的酸性，上述研究结果提示，丁二胺改性聚乳酸是一族新型的具有优良亲水性和良好降解行为的组织工程材料，预示着它可望具有优良的细胞亲和性，在组织工程中具有重要的应用潜力。     

亚磷酸三苯酯调控聚乳酸/氯化铁共混体系的降解行为和性能

用熔融共混法制备了氯化铁(FeCl₃)催化聚乳酸(PLA)快速降解材料。PLA材料降解的速率提高了10倍,但是PLA/FeCl₃在加工过程中分子量大幅度减小,使力学性能和可加工性能降低。为了减小PLA/FeCl₃在熔融加工中的过度降解,将有优良扩链和增塑效果的亚磷酸三苯酯(TPPi)引入PLA/FeCl₃体系中,用熔融共混制备TPPi改性PLA/FeCl₃材料,使其具有一定的综合力学性能。通过碱溶液降解实验和多种测试研究了样品的降解速率和综合性能。结果表明,TPPi和FeCl₃ 的添加量之比为3∶1的P3-1样品性能最优,拉伸强度和弯曲强度分别达到43.78 MPa和99.04 MPa,在碱液中降解8d其质量损失率为65.76%,远大于纯聚乳酸的4.67%。含2.95 phr FeCl₃的样品能在碱液中产生高降解速率,加工时不发生过度降解,由此制备出一种可快速降解并保持良好力学性能的聚乳酸改性材料。     

可降解碳纳米管/聚乳酸复合材料的制备及性能

利用丙交酯的开环聚合反应成功地制备了单壁碳纳米管/聚乳酸复合材料, 研究了其降解性和热稳定性。通过红外光谱(FTIR)、 Raman光谱、 热失重分析(TGA)和扫描电子显微镜(SEM)研究, 证明乙二醇功能化的单壁碳纳米管能够参与丙交酯的开环聚合反应, 并在碳纳米管侧壁成功接枝聚乳酸链, 得到的复合材料在碱性溶液中容易降解。差示热分析(DSC)表明, 功能化单壁碳纳米管/聚乳酸复合材料的玻璃化转变温度与纯聚乳酸相比有所提高。      

聚乳酸的降解研究

探讨了聚乳酸水解以及超声波降解情况,利用傅立叶红外光谱(FT-IR)和凝胶渗透色谱仪测定其基团及相对分子质量变化。研究结果表明:聚乳酸超声波降解同其水解均为酯键断裂导致的,并且是酯键的任意断裂,在水解过程中聚乳酸质量损失快慢为盐酸溶液>磷酸缓冲液>去离子水;聚乳酸在水解过程中,相对分子量随降解时间的延长而减小,但在超声波作用30min下其质量有一定程度的损失而相对分子量反而增大,推断其可能发生了部分交联反应。     

氨基酸改性聚乳酸共聚物的合成及降解研究进展

为了改善聚乳酸的降解速率,提高其与细胞的亲和性,氨基酸对聚乳酸的改性研究引起了人们的关注。综述了聚(乳酸-氨基酸)共聚物的各种合成路线及产物降解性能的研究进展。在聚乳酸(PLA)分子中引入氨基酸,可以使产物的大分子侧链获得氨基、羟基、羧基等活性基团。与PLA相比,此类聚合物的降解性能有所提高,具有两亲性和良好的细胞相容性,可用于药物缓释体系及组织工程。     

苎麻纤维/聚乳酸复合材料在不同pH环境下的水解行为

以生物基树脂聚乳酸为基体,以植物纤维苎麻为补强剂,利用熔融共混法制备了苎麻纤维/聚乳酸(RF/PLA)复合材料,考查了RF/PLA复合材料在不同pH环境下的水解行为,并以力学性能测试、SEM、DSC和维卡软化温度检测为手段对其降解行为进行了评估。结果表明:RF/PLA复合材料在碱性(pH=12.0)环境中的降解比在酸性(pH=2.0)和中性(pH=7.0)环境中的更快,界面侵蚀空化是其性能劣化的主要原因。RF的加入提高了PLA的结晶度和维卡软化温度,同时也加快了PLA的降解速度,降解导致材料的力学强度下降。随着降解过程的加剧,RF/PLA复合材料的结晶度和维卡软化温度因材料内部产生缺陷而有所降低;而纯PLA树脂的结晶度却随碱液处理时间的延长而增加,但其维卡软化温度没有发生明显的变化。     

Organizational Structure and Electronic Decoupling of Surface Bound Chiral Domains and Biomolecules

For the development of reagentless biological and chemical species detection at the single molecule level using external fields, including terahertz radiation, it is paramount to study model systems that uncover how intermolecular and molecule-surface interactions dictate monolayer ordering and electronic properties. This paper addresses two types of molecule-surface interactions and two distinct molecular systems, both of which impact our fundamental understanding of confined molecular domains and single molecule detection. We will first discuss the ordering and electronic characteristics of a chiral molecule, tartaric acid , weakly bound to an achiral metal surface, Ag(111), as studied with low temperature scanning tunneling microscopy (STM). This particular molecule-surface system contains many key elements, including hydrogen bonding interactions and stereochemical features, that would be common to other functional detection schemes. This paper will also treat the characterization of isolated, thiolated DNA molecules chemically bound to Au(111) terraces. Ambient STM and atomic force microscopy (AFM) measurements of both short and long DNA structures in both single and double strand configurations will be discussed with particular attention paid to imaging mechanisms involved. These results are particularly relevant to systems involving biomolecules anchored to inert metal surfaces, such as those used in external field-based assays.     

The Stability of Drug Adsorbates on Silica

Colloidal and porous silicas are used as carriers in solid, semisolid and liquid dosage forms. Adsorption of active ingredients onto their large surface areas can be used to regulate drug release or for the uniform distribution of drug in single dose units with a very low drug content. In the adsorbates the contact between drug and carrier surface on the molecular level can be of great importance for the chemical stability of drug preparations. This is demonstrated by the following examples:

Hydrolytic degradation of acetyl salicylic acid in dry silica adsorbates is mainly determined by alkaline impurities of the carrier and strongly adsorbed water on the silica surface. The “catalytic” action of silicas is, therefore, directly dependent on the preparation technique of the carrier. Propantheline a cationic ester compound is adsorbed on silica from aqueous solution. In aqueous silica suspensions and in dry adsorbates the ester hydrolysis is controlled by the pH, the neutral salt content, and buffer substances, due to different adsorption mechanisms.

The oxidative degradation of butylhydroxyanisole in silica adsorbates was also found to be enhanced in the presence of alkaline impurities. The oxidation of linoleic acid methylester in oleogels of colloidal silica proved to be influenced both by carrier impurities and the specific adsorption of intermediates (peroxides) onto the surface.     

不同聚乳酸对聚乳酸/淀粉共混复合膜的影响

目的探究不同聚乳酸基材对聚乳酸/热塑性淀粉共混复合膜基础性能的影响,筛选最适合的聚乳酸基材。方法选取REVODE 101,REVODE 110,REVODE 711B等3种聚乳酸原材料作为基材,与热塑性淀粉共混,采用热压法制备复合膜,并对复合膜进行动态热力学性能、力学性能、透湿性、水溶性及水分含量的表征。结果以REVODE110为基材制备的复合膜玻璃化转变温度(tg)最高,在增塑剂乙酰柠檬酸三丁酯质量分数为20%时tg为36.16℃,室温下稳定性最佳;其力学性能、透湿性以及水溶性与REVODE101复合膜相近,且显著优于REVODE 711B复合膜,3种复合膜透光性无显著差异,透光率T600均在14%左右。结论 3种聚乳酸材料中,REVODE 110是最适宜制备聚乳酸/淀粉复合膜的聚乳酸基材。     

Ultrasensitive detection of DNA sequences in solution by specific enzymatic labeling

We present a newly developed technique for the direct detection of very low concentrations of specific nucleic acid sequences in homogeneous solution based on a polymerase extension reaction. This method consists of synthesizing a highly fluorescent nucleic acid reporter molecule using a sequence of the target as a template. Synthesis of the reporter molecule is accomplished by hybridizing a short complementary oligonucleotide primer to the target and extending the reporter using a polymerase and free nucleotides. One of these nucleotides is partially labeled with a fluorophore. The reaction sample is then flowed through the capillary cell of a single molecule detector. Detection of the reporter signifies the presence of the target being sought. Under carefully selected conditions, fluorescence from the reporter molecule is much stronger than that of the free nucleotide background over the detection time. We have derived practical equations that allow us to determine an optimal range of values for the relative reporter and free-nucleotide concentrations. This method allows for the rapid, direct detection of individual targets at femtomolar concentrations without the use of an amplification procedure, such as the polymerase chain reaction.     

Controllable nanoreactor confined to atomic force microscopy tips and its application in low copy DNA ligation

Less molecules reaction, especially at the single molecule level, plays an important role in biochemical or chemical research. It is also significant to achieve low copy or single molecule DNA ligation during the whole genome project. In this paper, a new type of nanoreactor was constructed around atomic force microscopy (AFM) tips under certain humidity, where DNA molecules can be limited to a special space through water meniscus, so the probability of molecules collision was increased and the efficiency of DNA ligation was greatly enhanced. Combined with the nanomanipulation based on AFM, controllable nanoreactor may provide a new tool to single molecule reaction. Low copy DNA ligation was successfully achieved by this method. Results showed the number of DNA molecules involved in the nanoreactor can not be more than sixty. This method will found a base for the ultimate realization of single-molecule DNA ligation.     

Measuring adhesion forces between model polysaccharide films and PLA bead to mimic molecular interactions in flax/PLA biocomposite

Natural fiber-reinforced polymers or biocomposites are becoming increasingly popular as an environment friendly alternative to traditional glass fiber-reinforced thermoplastics. The mechanical properties of reinforced biocomposites, such as flax/polylactic acid (PLA), are largely governed by the level of interfacial interactions between the two constituents apart from their intrinsic properties. The hierarchical organization of various polysaccharides present in natural fibers results in complex mechanisms at the interface which are still poorly understood and difficult to analyze through a traditional approach that rely on indirect assessments. The possibility of measuring direct adhesion force between individual particles using the colloidal force microscopy has been exploited here by developing an experimental set-up in which a micrometer colloidal PLA bead is brought into close contact with molecularly smooth polysaccharide surfaces that mimic the main constituents of flax fibers, cellulose, hemicellulose, and pectins. Adhesion force measurements performed under ambient and low relative humidity conditions indicate that cellulose/PLA is the weakest interface in the biocomposite. Moreover, the results emphasize the important role of water molecules for the more hydrophilic polymers in flax fibers that takes place in the fundamental forces involved in the adhesion phenomena at the biocomposite interface.     

Kinetics of Hydrolysis of Succinimides

The neutral and alkaline hydrolyses of three substituted succinimides, phensuximide, methsuximide and ethosuximide, were followed spectrophotometrically. The rate-pH profile for phensuximide and methsuximide were similar and implicated both water attack and hydroxyl-ion catalyzed degradation of the neutral molecule. A different profile was observed for ethosuximide due to the presence of a pK'₂ in the alkaline pH region. The ethosuximide profile shows hydroxyl-ion catalyzed degradation of both the un-ionized and the mono-ionized species. A mechanism for hydrolysis of the succinimides is postulated based on ring-opening to produce substituted succinamic acids which may undergo further decomposition. Ionic strength effects on the alkaline hydrolysis of phensuximide show a decrease in the first-order rate constant as ionic strength is increased. Similarly, borate buffer inhibits hydrolysis as the buffer concentration is increased. The Arrhenius parameters for all compounds were determined.     

钛金属薄膜上两种短链自组装分子膜的制备与摩擦特性

采用自组装技术在钛金属薄膜上制备了两种分子链长相同、官能团不同的自组装分子膜,并对其进行了不同时间的紫外照射,对钛金属薄膜和自组装分子膜进行了表征和摩擦特性测试,研究了紫外照射、官能团、滑动速度和载荷对自组装分子膜摩擦特性的影响,结果表明:通过紫外照射钛金属薄膜表面羟基化、自组装分子水解及自组装分子缩合可在钛金属薄膜上制备结构致密的自组装分子膜,制备的两种短链自组装分子膜可降低钛金属薄膜的摩擦特性,APS自组装分子膜的摩擦特性优于MPS自组装分子膜的摩擦特性,紫外照射5 min的自组装分子膜表面吸附的有机杂质被蒸发掉,对针尖的黏着力减小,从而导致针尖的变形减小,摩擦力最低,而紫外照射15 min的自组装分子膜致密的网状结构被破坏,减弱了自组装分子膜的润滑效应,两种自组装分子膜的摩擦力随着滑动速度的增加略呈上升趋势,随着载荷的增加略呈下降趋势,但是变化不大.     

High density single-molecule-bead arrays for parallel single molecule force spectroscopy

The assembly of a highly parallel force spectroscopy tool requires careful placement of single-molecule targets on the substrate and the deliberate manipulation of a multitude of force probes. Since the probe must approach the target biomolecule for covalent attachment, while avoiding irreversible adhesion to the substrate, the use of polymer microspheres as force probes to create the tethered bead array poses a problem. Therefore, the interactions between the force probe and the surface must be repulsive at very short distances (<5 nm) and attractive at long distances. To achieve this balance, the chemistry of the substrate, force probe, and solution must be tailored to control the probe-surface interactions. In addition to an appropriately designed chemistry, it is necessary to control the surface density of the target molecule in order to ensure that only one molecule is interrogated by a single force probe. We used gold-thiol chemistry to control both the substrate's surface chemistry and the spacing of the studied molecules, through binding of the thiol-terminated DNA and an inert thiol forming a blocking layer. For our single molecule array, we modeled the forces between the probe and the substrate using DLVO theory and measured their magnitude and direction with colloidal probe microscopy. The practicality of each system was tested using a probe binding assay to evaluate the proportion of the beads remaining adhered to the surface after application of force. We have translated the results specific for our system to general guiding principles for preparation of tethered bead arrays and demonstrated the ability of this system to produce a high yield of active force spectroscopy probes in a microwell substrate. This study outlines the characteristics of the chemistry needed to create such a force spectroscopy array.