Enzymatic cross-linking of human recombinant elastin (HELP) as biomimetic approach in vascular tissue engineering

The use of polymers naturally occurring in the extracellular matrix (ECM) is a promising strategy in regenerative medicine. If compared to natural ECM proteins, proteins obtained by recombinant DNA technology have intrinsic advantages including reproducible macromolecular composition, sequence and molecular mass, and overcoming the potential pathogens transmission related to polymers of animal origin. Among ECM-mimicking materials, the family of recombinant elastin-like polymers is proposed for drug delivery applications and for the repair of damaged elastic tissues. This work aims to evaluate the potentiality of a recombinant human elastin-like polypeptide (HELP) as a base material of cross-linked matrices for regenerative medicine. The cross-linking of HELP was accomplished by the insertion of cross-linking sites, glutamine and lysine, in the recombinant polymer and generating ε-(γ-glutamyl) lysine links through the enzyme transglutaminase. The cross-linking efficacy was estimated by infrared spectroscopy. Freeze-dried cross-linked matrices showed swelling ratios in deionized water (≈2500%) with good structural stability up to 24 h. Mechanical compression tests, performed at 37°C in wet conditions, in a frequency sweep mode, indicated a storage modulus of 2/3 kPa, with no significant changes when increasing number of cycles or frequency. These results demonstrate the possibility to obtain mechanically resistant hydrogels via enzymatic crosslinking of HELP. Cytotoxicity tests of cross-linked HELP were performed with human umbilical vein endothelial cells, by use of transwell filter chambers for 1-7 days, or with its extracts in the opportune culture medium for 24 h. In both cases no cytotoxic effects were observed in comparison with the control cultures. On the whole, the results suggest the potentiality of this genetically engineered HELP for regenerative medicine applications, particularly for vascular tissue regeneration.     

Phase transition of thermosensitive amphiphilic cellulose esters bearing olig(oxyethylene)s

Summary A series of cellulose esters bearing olig(oxyethylene)s with different degree of substitution (DS) and different length of the oxyethylene chain were synthesized by a homogeneous reaction of cellulose with corresponding monofunctional acid chloride in a 10% LiCl-dimethyl acetoamide (DMAc) solution. The effect of total DS value on the solubility of the derivatives in aqueous solution was investigated. It was found that the lower limit DS value for both water-soluble and amphiphilic derivatives decreases with increasing length of oxyethylene chains. The amphiphilic derivatives, which are soluble in both water and chloroform, precipitate out of aqueous solution on heating without gel forming, such a phase transition behavior was studied in terms of DS value, length of oxyethylene and concentration. The precipitation temperature (T_p) of the amphiphilic derivatives is range from 54°C to 96°C. It decreases with increasing the total DS value, and increases with an increase in the length of oxyethylene chains. The T_p value of the derivatives was found to be almost independent in the concentration range of 1–15 wt %, however the T_p value increases sharply with decreasing polymer concentration when the concentration is lower than 1 wt%. Received: 29 August 2000/Revised version: 16 October 2000/Accepted: 31 October 2000     

碳纤维布预应力施加装置改进设计研究

对原有碳纤维布施加装置进行了分析,归纳了其施工中存在的缺点,针对其缺点对装置进行了改进,改进后的装置能有效克服原有装置的缺点,达到了较好的张拉效果,改进后的装置不需要经过任何改进即可用于现场施工,最后指出了该装置在施工中的注意事项,从而推广该装置的应用.     

Quantitative evaluation of reheat cracking susceptibility by in situ observation and measurement using laser confocal microscope*

In the post-weld heat treatment process, the reheat cracking which might occur in the weldments of low-alloy steels has been a serious problem. So, it is considered to be important to predict the possibility of occurrence of reheat cracking in these steels. It is however recognized as a time-consuming procedure to evaluate quantitatively the susceptibility to this type of cracking. In the present study, a new quantitative evaluation method of reheat cracking susceptibility by in situ observation and measurement using a laser confocal microscope has been proposed. Through this new method, the reheat cracking susceptibility of any kind of steels can be evaluated with the same standard. Moreover, because the position of the initial crack can be focused and the critical ductility to initiate the crack is measured by in situ observation, the reheat cracking susceptibility can be evaluated using only one specimen. So the newly developed method can provide efficient quantitative assessment of the reheat cracking sensitivity with high accuracy.     

放化分离-液闪测量联合分析核电厂废树脂中的^(55)Fe和^(63)Ni北大核心CSCD

建立了一种核电厂放射性废离子交换树脂中^(55)Fe和^(63)Ni的联合分析方法。将废树脂样品经芬顿氧化消解后,先用氢氧化钠沉淀法沉淀^(55)Fe和^(63)Ni,再用阴离子交换树脂联合丁二酮肟沉淀对杂质离子进行分离纯化,纯化后用液体闪烁计器测量。本方法对废树脂中^(60)Co、^(65)Zn、^(54)Mn等干扰核素的去污因子均大于10^(3)。本方法对^(55)Fe和^(63)Ni的平均化学回收率分别为86%和90%,对废树脂中^(55)Fe和^(63)Ni的检测限分别为5.7 Bq/g、6.8 Bq/g。用加标样品对分析方法进行验证,预期值和测量值的偏差小于±10%。实验测得某核电厂一组一回路实际废树脂样品中^(55)Fe和^(63)Ni的平均活度浓度分别为(76.2±1.4)kBq/g和(120.0±5.1)kBq/g。     

Toughened composites prepared from castor oil based polyurethane and soy dreg by a one‐step reactive extrusion process

A series of water‐resistant composites were successfully prepared from a mixture of soy dreg (SD), castor oil, and 2,4‐toluene diisocyanate (TDI) by a one‐step reactive extrusion (REX) process. The structure and properties of the composites were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, differential scanning calorimetry, dynamic mechanical analysis, tensile testing, and swelling experiments. The results indicated that the toughness of the composites prepared from castor oil based polyurethane and SD was significantly improved. In this case, TDI played an in situ compatibilization role through the crosslinking reaction of ? NCO groups with ? NH₂, ? NH? , and ? OH groups in SD and castor oil. With an increase in the molar ratio of ? NCO groups of TDI and ? OH groups of castor oil, the degree of crosslinking, tensile strength, glass‐transition temperature, water resistivity, and solvent resistivity of the composites increased. With an increase in the SD content of the composites, the tensile strength and solvent resistivity of the composites increased because of the reinforcement of the cellulose component in SD. This work provided a simple and effective way of preparing SD‐based composites by a REX process. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 953–960, 2006     

Facile purification of colloidal NIR-responsive gold nanorods using ions assisted self-assembly

Anisotropic metal nanoparticles have been paid much attention because the broken symmetry of these nanoparticles often leads to novel properties. Anisotropic gold nanoparticles obtained by wet chemical methods inevitably accompany spherical ones due to the intrinsically high symmetry of face-centred cubic metal. Therefore, it is essential for the purification of anisotropic gold nanoparticles. This work presents a facile, low cost while effective solution to the challenging issue of high-purity separation of seed-mediated grown NIR-responsive gold nanorods from co-produced spherical and cubic nanoparticles in solution. The key point of our strategy lies in different shape-dependent solution stability between anisotropic nanoparticles and symmetric ones and selective self-assembly and subsequent precipitation can be induced by introducing ions to the as-made nanorod solution. As a result, gold nanorods of excellent purity (97% in number density) have been obtained within a short time, which has been confirmed by SEM observation and UV-vis-NIR spectroscopy respectively. Based on the experimental facts, a possible shape separation mechanism was also proposed.     

Phase-controllable synthesis of nanosized nickel phosphides and comparison of photocatalytic degradation ability

In this paper, we employed a facile hydrothermal route to successfully synthesize nanosized nickel phosphide particles with controlled phases via selecting different surfactants at different temperatures and times. The phases of the as-obtained products were determined by X-ray powder diffraction (XRD) patterns and Rietveld refinement of XRD data. The morphologies of the products were characterized by (high resolution) transmission electron microscopy (HR/TEM) and field emission scanning electron microscopy (FESEM). Experiments indicated that pure Ni2P phase could be prepared when nontoxic red phosphorus and nickel dichloride were used as starting materials in the presence of polyvinylpyrrolidone (PVP, 30 K), sodium dodecylbenzene sulfonate (SDBS), cetyltrimethylammonium bromide (CTAB) or polyethylene glycol 10000 (PEG-10000) at 160 °C for 10 h. When acrylamide (AM) was selected as the surfactant, however, pure Ni12P5 phase could be prepared by prolonging the reaction time to 20 h at 160 °C, or enhancing the reaction temperature to 180 °C for 10 h. Furthermore, the experiments indicated that the pure Ni2P phase possessed a stronger photocatalytic degradation ability than the pure Ni12P5 phase.     

A novel conductivity composite based on polyaniline/zirconium phenylphosphonate

A novel conductivity composite from polyaniline (PANI) and layered zirconium phenylphosphonate (ZrPP) was carried out through in situ chemical oxidation polymerization by the addition of an appropriate amount of ammonium peroxodisulfate solution, and the relevant structure and properties were investigated. The composites were characterized by Fourier transform infrared spectroscopy, X‐ray diffraction, and scanning electron microscopy. The electrical conductivity was measured by the four‐probe technique. The electrical conductivity of the composites improved with increasing ZrPP loading, and the materials had reasonably good electrical properties, even with 40 wt % loadings of ZrPP in the polymer matrix. The results reveal that π–π interaction was formed in the composites, which enhanced the electrical conductivity of the composites compared to that in neat PANI. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preparation of raspberry‐like poly(methyl methacrylate) particles by seeded dispersion polymerization

The facile preparation of nonspherical raspberry‐like poly(methyl methacrylate) (PMMA) particles by seeded dispersion polymerization of methyl methacrylate (MMA) on micron‐sized PMMA seed particles was described. Various polymerization parameters influencing the particle morphology, as well as the polymerization kinetic and morphological stability, were investigated in detail. It was found that the following polymerization conditions were necessary to prepare this kind of nonspherical particles: a relatively low temperature, an appropriate ratio of seed/MMA, an initiator with a relatively low decomposition rate, and a relatively low initiator concentration. These particles showed very good morphological stability at room temperature, but they changed to the spherical ones when heat treated at 60°C in methanol solution of MMA. The experimental results suggest that the prepared PMMA particles were kinetically favored and the localized polymerization of the MMA monomer on PMMA seed particle surface was responsible for the formation of the raspberry‐like particles. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011