A novel laser light-scattering study of enzymatic biodegradation of poly(epsilon-caprolactone) nanoparticles

A successful micronization of water-insoluble poly(epsilon-caprolactone) (PCL) into narrowly distributed nanoparticles stable in water has not only enabled us to study the enzymatic biodegradation of PCL in water at 25 degrees C by a combination of static and dynamic laser light scattering (LLS), but also to shorten the biodegradation time by a factor of more than 10(3) compared with using a thin PCL film, i.e. a 1 week conventional experiment becomes a 4 min one. The time-average scattering intensity decreased linearly. It was interesting to find that the decrease of the scattering intensity was not accompanied by a decrease of the average size of the PCL nanoparticles, indicating that the enzyme, Lipase Pseudomonas (PS), ''eats'' the PCL nanoparticles one-by-one, so that the biodegradation rate is determined mainly by the: enzyme concentration. Moreover, we found that using anionic sodium lauryl sulphate instead of cationic hexadecyltrimethylammonium bromide as surfactant in the micronization can prevent the biodegradation, suggesting that the biodegradation involves two essential steps: the adsorption of slightly negatively charged Lipase PS onto the PCL nanoparticles and the interaction between Lipase PS and PCL. (C) 1999 Elsevier Science Ltd. All rights reserved.

A novel method of studying polymer biodegradation

A novel combination of laser light scattering (LLS) and the micronization of a water-insoluble polymer into narrowly distributed nanoparticles stable in water has provided not only an accurate, reliable and microscopic method to study polymer biodegradation, but also a novel and fast way to evaluate the biodegradability of a given polymer. Using poly(epsilon-caprolactone) (PCL) as a typical example, we have shown that its biodegradation time can be shortened by a factor of more than 10(3) times in comparison with the time required to biodegrade a thin film (10 x 10 x 0.1 mm(3)). Moreover, the biodegradation kinetics can be in-situ monitored in terms of the decrease of the time-average scattering intensity and the particle number. A comparison of static and dynamic LLS results revealed that the enzyme, Lipase Pseudomonas, ''eats'' the PCL nanoparticles in an one-by-one manner and the enzymatic biodegradation of PCL follows a zero-order kinetics. (C) 1998 Elsevier Science Ltd. All rights reserved.

A novel rare earth coordination catalyst for polymerization of biodegradable aliphatic lactones and lactides

A novel rare earth coordination system composed of lanthanide trifluoroacetates Ln(CF3COO)(3) (Ln = Y, Yb, Nd, Tm, Ho, La, Pr) and triisobutylaluminium Al(i-Bu)(3) was used as catalyst for the polymerization of epsilon-caprolactone (CL), D,L-lactide (DLLA) and their copolymerization. The influence of temperature, time and catalyst concentration on polymerization yields and molecular weights of the polyesters have been studied. It was shown that the ring-opening polymerization of cyclic esters catalysed by Ln(CF3COO)(3)/Al(i-Bu)(3) has some living character and the molecular weight of the polyester could be controlled by adjusting the molar ratio of monomer to catalyst. The DLLA/CL copolymer was synthesized by sequential addition of monomers and the structure of the copolyester was characterized by GPC, NMR and DSC. (C) 1998 SCI.

Ansa-metallocene derivatives .2. Syntheses and structures of tetramethyldisiloxandiyl bis(1-indenyl and tetrahydroindenyl) zirconium dichlorides

The ansa-zirconocene derivative tetramethyldisiloxandiyl bis(1-indenyl) zirconium dichloride (1) has been prepared by the reaction of the dilithium salt of 1,3-bis(l-indenyl) tetramethyldisiloxane with ZrCl4 . 2THF, After catalytic hydrogenation, the corresponding tetrahydroindenyl complex (2) has been formed. Both 1 and 2 have been shown by H-1 NMR spectra to be the mixture of the cis(meso) and trans(rac) isomers, The pure trans isomers 1(l), 2(l) and cis isomer 2(c) were obtained by recrystallization, The crystal structures of 1(l) and 2(c) were determined by X-ray diffraction. Both crystals of 1(l) and 2(c) are monoclinics, belonging to space groups P2(1)/n(1(l)) and P2(1)/c(2(c)). In the unit cell of 2(c), one of the six-membered rings of the tetrahydroindenyl Ligands has two different conformations which have the same probabilities.

面向月面探测作业的双目立体视觉测量及三维环境生成技术研究

星球漫游车技术是一项跨学科的综合性技术，它反映了一个国家整体科技水平和高技术产业的发展水平，对漫游车进行研究具有长远的战略意义。漫游车一般都工作在特殊的环境中，综合考虑功耗和有效载荷等问题，可以发现，非视觉传感器与视觉传感器相比在环境感知能力和综合性能方面都不甚理想，因此，基于视觉传感器的立体视觉定位也一直是各类漫游车用以感知环境所首选的技术。基于立体视觉可以构建相应的地面人机交互系统。该交互系统具有实现离线示教功能，通过虚拟现实和立体视觉技术实现虚拟漫游车在虚拟地形中行走，虚拟机械臂对虚拟物体进行研磨等功能。操作人员在虚拟环境中对月球车的各种运动进行验证以后，再将数据上传给真实的漫游车以实现真实的漫游和考察工作。因此，立体视觉系统性能的好坏将直接影响到漫游车的后续工作情况，它是漫游车自主导航和进行科学考察的基础，直接关系到漫游车的安全，是一项关键的技术。 本文的研究依托于中国科学院知识创新工程方向性项目“月球车月面探测作业支撑技术研究”，旨在探索立体视觉系统的实现及其与车载机械臂配合工作的问题。从理论和实践两个方面，对其中的若干关键技术，如双摄像机标定、对极几何恢复、图像校正、图像匹配、三维重建和车载机械臂视觉定位等进行了研究。主要研究成果如下： 1．提出一种基于坐标排序的标定特征点存储算法，使得两幅图像中的标定特征点能够快速准确的对应存储。基于径向一致约束（RAC）模型优化方法与直接光学法的优点，提出一种改进的光心确定方法，实验表明该方法有效地提高了Tsai两步法的标定与测量精度。以上两种方法为实现双摄像机的高精度标定奠定了基础。 2．在双摄像机的标定阶段，提出一种新的以三维重投影误差为优化目标的双摄像机两步标定算法，实验证明该方法的标定与测量精度要高于传统的基于二维重投影误差的方法。提出一种考虑多个畸变系数基于三维重投影误差的两步标定算法，实验证明该方法比只考虑一个畸变系数的Tsai两步法能够获得更高的标定与测量精度。研究了基于遗传算法和粒子群算法的双摄像机内、外参数的整体优化问题，实验证明可以获得比传统梯度下降法更高的标定与测量精度。以上改进方法可以使标定精度达到工程要求，并为后续的图像校正和三维测量奠定基础。 3．从简单背景和复杂背景两种情况对对极几何的离线恢复问题进行了研究。对于对极几何的离线恢复问题，提出了基于正确匹配标定特征点进行基础矩阵高精度估计的算法。该算法的特点是与标定共用同一组数据，其有效性得到了实验的验证。对于对极几何的在线恢复问题，基于摄像机成像几何原理证明了图像坐标系下存在的一种左右图像坐标间的约束关系，并设计了相应的稀疏匹配算法，采用两阶段鲁棒稀疏匹配算法对基础矩阵进行了高精度的估计，实现了对极几何的在线恢复。与传统方法相比，本文的方法速度更快，精度更高。 4．研究了标定与非标定图像的极线校正算法，利用上述改进方法求得的高精度的投影矩阵和基础矩阵，获得了令人满意的校正效果，为稠密匹配奠定了坚实的基础。研究并实现了四种稠密匹配算法，并进行了算法性能的比较。针对稠密匹配后的初始候选匹配点对，研究了三种误匹配的剔除方法。实验结果表明这些方法能够有效剔除误匹配点对，提高三维重建的效果。 5．研究了基于最小二乘法和立体成像几何法的三维重建算法，研究了一种集成上述多种改进算法的欧式三维重建算法。研究开发了三维重建软件，基于真实图像进行了欧式三维重建实验研究，取得了良好的重建效果。 6．以月球车为应用对象，研究了虚拟机械臂和车载机械臂的平面定位机理，构建了基于立体视觉的虚拟机械臂定位仿真平台。基于虚拟环境下验证好的数据，进行了月球车车载机械臂平面定位的实验，结果证明车载机械臂具有良好的视觉定位精度。