pH-Compensation Effect of Lysine on the Acidic Degradation of Electrospun Poly（ lactide-co-glycolide） Fibers in PBS

Electrospun aligned ultrafine fibers of poly（ lactide-coglycolide）（ PLGA） can be used to construct biomimetic scaffolds for engineering those structurally anisotropic and dense tissues（ e. g.,tendon,ligament,etc.）. But the acidic degradation products of the PLGA could result in p H decrease in the vicinity of the scaffolds,which may give rise to biocompatibility concerns. To address the noted problem, this study was designed to evaluate the p Hcompensation capacity of using Lysine（ Lys） —a kind of basic amino acid on the acidic degradation products of PLGA. Ultrafine PLGA（ 50∶ 50） fibers with 0,10%,20%,and 30% by weight of Lys loadings were prepared by a stable jet electrospinning（ SJES）approach. The morphology,structure,and mechanical properties of the electrospun aligned fibrous mats of Lys-incorporated PLGA（ 50∶50） were characterized by scanning electron microscope（ SEM）,Fourier transform infrared spectroscopy（ FTIR）,and tensile testing,respectively. Thereafter,the fibrous PLGA（ 50 ∶50） scaffolds were subjected to degradation by being immersed in phosphate buffered saline（ PBS,p H 6. 86） solution at 37 ℃ for 5weeks. Our results show that the formed Lys / PLGA composite ultrafine fibers have a well-aligned and uniform morphology with a fineness of ca. 1 #m in diameter. Introduction of Lys led to increased mechanical performance; that is,when the Lys loading is less than 30%,tensile strength and Young＇s modulus of the aligned Lys / PLGA fibers reached up to the impressive values of 84. 5 MPa and 2. 4 GPa,respectively. Degradation results show that the p H of the PLGA group fell to 5. 6 in 5 weeks while the p H of the Lys /PLGA groups with 10%,20%, and 30% of Lys loadings was maintained at 6. 3, 6. 5 and 6. 7, respectively. This work demonstrated that incorporation of Lys into electrospun PLGA fibers could be an effective approach in mediating the p H decrease caused by the acidic degradation products of the PLGA.     

喀斯特石山上的精灵——黑叶猴

759年2月，唐代诗人李白乘一叶扁舟进入长江三峡，有感于两岸群山和滔滔江水，吟咏出了千古传诵的《早发白帝城》：“朝辞白帝彩云间，千里江陵一日还。两岸猿声啼不住，轻舟已过万重山。”据考证，李白诗中的“猿”即为黑叶猴（Trach3pithccusfrancoisi）。     

浅析节能玻璃在建筑设计中的应用

在全球能源危机的大环境下，建筑节能已成为人们关注的焦点，本文对节能玻璃的分类及特性的做了简要介绍，井对其在建筑工程中实际的应用进行了浅析。     

安泽县三次产业结构研究

本文首先从地区生产总值和产业结构的变化特征、三次产业结构的比例分析两个方面对安泽县三次产业结构的现状进行了研究,分析得出安泽县三次产业结构比例不协调,第二产业比重过高,第三产业比重逐年下降,且三产结构内部也不合理,最后针对存在的问题提出了三次产业结构调整和优化的对策.     

探访阿诗玛故乡的白犀牛

白犀牛又称白犀,名虽如此,但其浑身灰色;因其嘴巴扁平宽阔,故又名方吻犀、宽吻犀。白犀体长可达4米以上,质量可达3吨多,体型浑圆硕大,体态粗壮威武,是现存五种犀牛（白犀牛、黑犀牛、印度犀牛、苏门答腊犀牛和爪畦犀牛）中体型和角最大的,     

Electrospun Nanofibers of Hydroxyapatite/Collagen/Chitosan Promote Osteogenic Differentiation of BMSCs

Bone tissue engineering, aiming at developing bone substitutes for repair and regeneration of bone defects instead of using autologous bone grafts, has attracted wide attention in the field of tissue engineering and regenerative medicine. Developing biomimetic biomaterial scaffolds able to regulate osteogenic differentiation of stem cells could be a promising strategy to improve the therapeutic efficacy. In this study, clectrospun composite nanofibers of hydroxyapatite/collagen/chitosan （ HAp/Col/CTS ） resembling the fibrous nanostructure and constituents of the hierarchically organized natural bone, were prepared to investigate their capacity for promoting bone mesenchymal stem cells （BMSCs） to differentiate into the osteogenic lineage in the absence and presence of the osteogenlc supplementation, respectively. Call morphology, proliferation and quantified specific osteogenic protein expression on the electrospun HAp/Coi/CTS scaffolds were evaluated in comparison with different controls including dectrospun nanofibrous CTS, HAp/CTS and tissue culture plate. Our remits showed that the nanofibrous HAp/Col/CTS scaffolds supported better spreading and proliferation of the BMSCs than other substrates （ P 〈 0.01 ）. Expressions of osteogenesis protein markers, alkaline phosphatase （ALP） and Col, were significantly upregulated on the HAp/Col/CTS than those on the CTS （P 〈0.01） and HAp/ CTS （P 〈 0. 05 ） scaffolds in the absence of the osteogeulc supplementation. Moreover, presence of osteogeulc supplementation also proved to enhance osteogeule differentiation of BMSCs on HAp/ Col/CTS scaffolds, indicative of a synergistic effect. This study highlights the potential of BMSCs/HAp/Col/CTS cell-scaffold system for functional bone repair and regeneration applications.     

FRFT在水声信道时延频移联合估计中的应用

由于水声信道的复杂性和多变性,信号在水声信道传播中将伴随着多径时延与多普勒频移,二者是水声信道估计中两个重要的参数。基于分数阶傅里叶变换(fractional Fourier transform, FRFT)的时延和频移特性,提出一种采用多分量线性调频(linear frequency modulated, LFM)信号的水声信道估计方法,通过分析分数阶傅里叶域上峰值的偏移,联立不同阶次的时延和频移方程,可得到水声信道的时延和频移值。理论推导及仿真结果表明,该方法计算量小,且随着LFM信号分量数和调频率差值的增大,能在一定程度上减小估计的时延误差和频移误差。水池实验中选用具有相反调频率的双LFM信号作为估计信号,估计出多径时延与运动目标的多普勒频移,并给出了水下目标的运动速度。实验结果表明,FRFT估计法简单有效,在水声信道多径时延与多普勒频移估计上具有较好的实际应用价值。     

五一桥水电站高压开关柜测温系统的优化设计

本文对五一桥水电站高压开关柜封闭设备系统的测温系统进行了优化设计。分析表明,五一桥水电站高压开关柜内测温系统存在能效低、可靠性差等缺点。此外,在实际运行过程中,多次出现测温不准确,运行不可靠等情况。为此,笔者对五一桥水电站高压开关柜测温系统提出了改造意见。通过合理选择配置测温系统,利用无线测温技术改进原本不合理的测温系统。     

Fabrication of Dex-Loaded Shape Memory Polymer Based Composite Nanofibers ：for Potential Bone Tissue Engineering

Biodegradable shape memory polymers （SMPs） are a class of intelligent materials with great potential for imparting biomaterial scaffolds multifunetionality in the field of tissue engineering and regenerative medicine. In this study, the biodegradable SMP poly（ D, L-lactide-co-trimethylene carbonate） （PLMC） incorporated with the ,dexamethasone （Dex）, which was a kind of synthetic bone-formation inducing factor, was fabricated into nanofibers via dectrospinning. The morphology, constituent, thermal and mechanical properties of the produced Dex/PLMC composite nanofibers were characterized by scanning electron microscopy （SEM）, Fourier transform ：infrared spectroscopy （ FTIR ）, differential scanning calorimetry （DSC）, and tensile testing, respectively. Then, ultrasound was ,employed as a remote stimulus to regulate the Dex releasing behavior from the composite nanofibers. It was found that the generated Dex/ PLMC composite nanofibers had a uniform and smooth morphology with a diameter of ca. 564 nm. Mechanical testing results showed that incorporation of the Dex gave rise to improved mechanical performance with the tensile strength, Young＇ s modulus and strain- at-break increased by 18.2 %, 20. 0 % and 64.4 %, respectively. DSC data revealed that the glass transition temperature （ Tg ） of the composite nanofibers, i. e., the thermal transition temperature （Ttrans） for activating shape memory effect, was 39. 7 ℃. Moreover, the release kinetics of the encapsulated Dex in the aanofibers could be manipulated by varying the acoustic power and insonation duration. These results suggested that the newly developed Dex/PLMC nanofibers could be a promising drug delivery system for applications in bone tissue engineering （BTE）.