超临界CO2反复循环萃取法制备PLA/TCP多孔组织工程支架材料

相对于传统的超临界CO2（SC—CO2）一次性升压法，采用SC—CO2反复循环萃取法制备了聚乳酸（PLA）／磷酸三钙（TCP）复合多孔支架材料，以提高材料的孔洞连通率。本文研究了材料的开孔率，不同PLA和TCP配比材料的孔洞形态以及材料的力学性能。结果表明，反复循环萃取法制备的材料比传统的一次性升压法制备的材料的开孔率可以提高10%左右，孔径在200-300μm之间，孔壁上有丝网型等几种适合细胞种植的特殊微隙形态；TCP在PLA支架中的分散性很好；材料压缩模量和压缩强度分别可达71.8和7．1MPa，比单纯的PLA材料明显增加。     

微囊化壳聚糖/纳米羟基磷灰石/胶原/聚乳酸复合材料

以多聚磷酸钠(TPP)为交联剂,采用乳化交联法制备了牛血清白蛋白(BSA)壳聚糖控释微球(CMs)。将微球与纳米羟基磷灰石/胶原(nHAC)、聚乳酸(PLA)按不同比例混合,采用热致分相法制备了CMs/nHAC/PLA复合支架材料。利用扫描电镜、激光粒度分析仪、压汞仪和力学性能测试仪考察了微球与复合支架的性能。结果表明：所制备的壳聚糖微球形态良好,呈规则球形,粒径主要分布在20～50μm;随 BSA 初始用量的增加,微球的载药量从0.78%增大到2.74%,但包封率从86.9%下降到78.4%;控制CMs用量不超过PLA 质量的30%,则可保证微球在CMs/nHAC/PLA中的均匀分布,此时复合材料的孔径主要分布在100～200μm,孔隙率不低于83.1%,压缩强度在1～2 MPa。这种复合支架材料可望作为人体非承重部位的植入骨修复体和组织工程支架使用。     

用超临界CO2法制备聚乳酸三维多孔支架材料

在超临界CO2(SC—CO2)条件下制备了生物相容性良好的聚乳酸(PLA)多孔材料，研究了PLA的分子量、SC—CO2的压力、温度和处理时间对多孔材料的结构形态、孔隙率和玻璃化温度的影响。结果表明：支架材料的孔洞分布、结构形态和孔隙率不仅与聚乳酸的分子量有关，而且与处理样品的压力、温度和时间关系密切；经超临界CO2处理后材料的玻璃化温度(Tg)有所升高，与传统的方法所制得的材料相比较，多孔材料不仅杂质少，孔径孔率分布均匀，孔洞表面粗糙，而且在大孔之间几乎布满了直径为10—20μm的微孔，该结构提供了营养物质和新陈代谢的通道，且细胞和生长因子也能通过。     

多孔再生纤维素/聚乳酸复合材料的制备与性能

通过简易、绿色环保的方法,将纤维素用NaOH/尿素体系进行溶解、再生、冷冻干燥获得再生纤维素(RC)多孔材料,再浸渍聚乳酸(PLA)获得多孔RC/PLA复合材料。该复合材料具有与多孔RC材料相同的开孔结构,超轻,高孔隙率等特性。随PLA的引入,多孔复合材料的三维纤维网络结构向密实片层结构转变,缺陷结构逐渐完善,其压缩强度大幅度提高。RC/PLA的压缩强度和模量相比于RC分别提高了369.8%和633.6%。     

超临界CO_2辅助工艺制备三维组织工程支架的研究进展

组织工程的主要目的是利用高分子生物材料构建类似细胞外基质的三维支架,用于诱导细胞粘附、生长、迁移和分化,从而修复受损组织或器官。超临界二氧化碳(SC-CO2)辅助工艺制备三维组织工程支架能克服传统制备工艺中支架有机溶剂残留量高的问题,在组织工程领域具有广阔的应用前景。综述了国内外SC-CO2辅助技术,如SC-CO2辅助发泡、SC-CO2辅助相分离、SC-CO2辅助干燥、SC-CO2辅助静电纺丝等在三维组织工程支架制备方面的研究进展及存在的问题。     

PEO/CaC03/PLA复合材料开孔结构的制备

采用聚乳酸(PLA)、聚氧化乙烯(PEO)、碳酸钙(CaCO3)熔融共混制备具有开孔结构的PLA多孔材料,借助于扫描电镜、孔隙率、热分析和压缩性能的测试方法,研究了连续混炼工艺对多孔材料结构和性能的影响.结果表明,过高或过低的转子转速和加料量都会导致多孔材料孔隙率的下降.当转子转速为600 r/min,加料量为2.61 kg/h时,孔隙率达到最大值76.8％.压缩模量和压缩强度分别为4.3 MPa和2.9 MPa.提高转子转速有利于多孔材料结晶性能的提高.     

胶原/壳聚糖管状支架材料的改性及物理特性

用冷冻干燥-蒸汽挤压法制备了猪胶原/壳聚糖管状支架,并用戊二醛对其进行改性。扫描电镜(SEM)观察到改性后的支架为多孔-三维网络结构;傅立叶-红外光谱(FT-IR)表明改性对胶原的三股螺旋结构影响不大;细胞增殖实验证明,改性后的材料基本保持了胶原生物活性优点,而其力学性能和吸水性大大改善。说明GTA交联改性方法,在保持胶原/壳聚糖支架材料优点的基础上,使导管承受外力作用时抵抗变形能力大大提高,但同时使材料的弹性下降。     

PEO/CaCO_3/PLA复合材料开孔结构的制备

采用聚乳酸(PLA)、聚氧化乙烯(PEO)、碳酸钙(CaCO_3)熔融共混制备具有开孔结构的PLA多孔材料,借助于扫描电镜、孔隙率、热分析和压缩性能的测试方法,研究了连续混炼工艺对多孔材料结构和性能的影响。结果表明,过高或过低的转子转速和加料量都会导致多孔材料孔隙率的下降。当转子转速为600 r/min,加料量为2.61 kg/h时,孔隙率达到最大值76.8%,压缩模量和压缩强度分别为4.3 MPa和2.9 MPa。提高转子转速有利于多孔材料结晶性能的提高。     

导电复合相变储能材料的制备及温敏响应性能

为探究相变储能材料聚乙二醇(PEG)的加入对多壁碳纳米管/聚乳酸(PLA/MWCNTs)复合材料的热力学稳定性、导电性能、力学性能和温敏响应行为的影响,采用溶液-熔融共混的方法制备了PLA/MWCNTs/PEG复合材料。PEG的加入能够提高PLA/MWCNTs/PEG复合材料的结晶性能和韧性,添加30%的PEG时,复合材料的起始结晶温度从109.2℃提升至126.5℃,断裂伸长率从11.2%提升到160.6%。等温-电阻测试数据表明,PLA/MWCNTs/PEG复合材料具有较高的导电稳定性能,并随着等温温度的提高,PLA/MWCNTs/PEG复合材料实现了从PTC到NTC效应的转变。此外,在不同温度的循环电阻测试中发现,随着热处理温度(T_end)的提升,复合材料的最大电阻值呈现上升趋势,复合材料的灵敏性得到改善;复合材料在热处理温度T_end=140～150℃的循环温度区间内,PEG的储能效果在降温过程中变得尤为显著,能够释放能量维持复合材料电阻性能的稳定。为制备具有柔性的高灵敏性的温度传感器提供了借鉴。     

氨基化改性生物玻璃/明胶/胶原复合支架的研究

利用溶胶-凝胶技术制备生物活性玻璃,并将其与明胶、胶原蛋白复合制备生物活性玻璃/明胶/胶原复合支架。力学性能研究表明,该复合支架形变量50%时的抗压强度为5.97 MPa;将生物活性玻璃氨基化改性后,制备的复合支架形变量50%时的抗压强度略有增加(6.15 MPa)。傅立叶红外光谱显示,氨基化改性生物玻璃与明胶、胶原之间生成酰胺键,增强了复合支架的结构稳定性。将生物活性玻璃/明胶/胶原复合支架置于模拟体液中矿化,在扫描电镜下可观察到其表面生成了羟基磷灰石,且随着矿化时间的延长,生成的羟基磷灰石颗粒逐渐增多。生物活性玻璃/明胶/胶原复合支架于磷酸盐缓冲液(PBS)中降解28d后,其质量剩余25.25%,而氨基化改性生物活性玻璃/明胶/胶原复合支架的质量剩余32.96%,表明氨基化改性能够提高其无机相与有机相的界面相容性,从而提高复合支架的结构稳定性。细胞毒性研究表明,氨基化改性生物活性玻璃/明胶/胶原复合支架和生物活性玻璃/明胶/胶原复合支架反应级为0级或1级,可满足生物医用材料的要求。氨基化生物活性玻璃/明胶/胶原复合支架有望在骨组织工程修复中得到应用。     

Structural and optical properties of AlxOy/Pt/AlxOy multilayer absorber

We report on the microstructure and optical properties of Al_xO_y–Pt–Al_xO_y interference-type multilayer films, deposited by electron beam (e-beam) deposition onto corning 1737 glass, silicon (1 1 1) and copper substrates. The structural properties were investigated by Rutherford backscattering spectrometry, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy and atomic force microscopy. The optical properties were extracted from specular reflection/transmission, diffuse reflectance and emissometer measurements. The stratification of the coatings consists of a semi-transparent middle Pt layer sandwiched between two layers of Al_xO_y. The top and bottom Al_xO_y layers were non-stoichiometric with no crystalline phases present. The Pt layer is in the fcc crystalline phase with a broad size distribution and spheroidal shape in and between the rims of Al_xO_y. The surface roughness of the stack was found to be comparable to the inter-particle distance. The optical calculations confirm a high solar absorptance of ∼0.94 and a low thermal emittance of ∼0.06 for the multilayer stack, which is attributed not only to the optimized nature of the multilayer interference stacks, but also to the specific surface morphology and texture of the coatings. These optical characteristics validate the spectral selectivity of the Al_xO_y–Pt–Al_xO_y interference-type multilayer stack for use in high temperature solar-thermal applications.     

Optimization of AlxOy/Pt/AlxOy multilayer spectrally selective coatings for solar-thermal applications

Spectrally selective Al_xO_y/Pt/Al_xO_y multilayer absorber coatings were deposited onto corning 1737 glass, Si (111) and copper substrates using electron beam (e-beam) vacuum evaporator at room temperature. The employment of ellipsometric measurements and optical simulation was proposed as an effective method to optimize and deposit multilayer solar absorber coatings. The optical constants (n and k) measured using spectroscopic ellipsometry, showed that both Al_xO_y layers, which used in the coatings, were dielectric in nature and the Pt layer was semi-transparent. The optimized multilayer coatings exhibited high solar absorptance α ∼ 0.94 ± 0.01 and low thermal emittance ? ∼ 0.06 ± 0.01 at 82 °C. The Rutherford backscattering spectroscopy (RBS) data of Al_xO_y/Pt/Al_xO_y multilayer absorber indicated the Al_xO_y layers present in the coating were nearly stoichiometry. The scanning electron microscope analysis (SEM) result indicated that the average diameter and inter-particles distance of Pt grains were statistically about 146 ± 0.17 nm and 6-10 ± 0.2 nm respectively.     

Interfacial microstructure of NiSix/HfO2/SiOx/Si gate stacks

Integration of NiSi_x based fully silicided metal gates with HfO₂ high-k gate dielectrics offers promise for further scaling of complementary metal-oxide- semiconductor devices. A combination of high resolution transmission electron microscopy and small probe electron energy loss spectroscopy (EELS) and energy dispersive X-ray analysis has been applied to study interfacial reactions in the undoped gate stack. NiSi was found to be polycrystalline with the grain size decreasing from top to bottom of NiSi_x film. Ni content varies near the NiSi/HfO_x interface whereby both Ni-rich and monosilicide phases were observed. Spatially non-uniform distribution of oxygen along NiSi_x/HfO₂ interface was observed by dark field Scanning Transmission Electron Microscopy and EELS. Interfacial roughness of NiSi_x/HfO_x was found higher than that of poly-Si/HfO₂, likely due to compositional non-uniformity of NiSi_x. No intermixing between Hf, Ni and Si beyond interfacial roughness was observed.     

Tc trend in high-Tc superconductors

In our previous works, we have shown that most existing ceramic superconductors can be considered to be built of superconductor-semiconductor composite and we have estimated the change in phonon spectrum of the intrinsic superconductor unit if a semiconductor unit is attached to it. Moreover, the proximity effect under the size quantization condition has been examined in the superconductor-semiconductor composite. Each of the stated effects by itself could causeT _c enhancement in general as more semiconductor blocks are added to the system. We extend our study in this paper to analyze the combined actions of phonon spectral change and proximity effect without size quantization condition onT _c variation in members of the Tl₁ series of high-T _c superconductors. Our results indicate that an optimumT _c is obtained if the stated effects are included in the idealized unit cells of the superconductors made up of a superconductor-semiconductor array.     

Anomalous Hall Effect in Sn1?x?yMnxEuyTe and Sn1?x?yMnxEryTe Mixed Crystals

The Anomalous Hall Effect (AHE) was investigated in IV–VI ferromagnetic semimagnetic semiconductors of Sn_1–x Mn _x Te codoped with either Eu or Er. The analysis of experimental data is as follows. Hall resistivity and magnetization showed that AHE coefficient R _s depends on temperature and its value decreases with thetemperature increase. We observe that above ferromagnet–paramagnet transition temperature R _s changes sign. We discuss the possible physical mechanisms responsible for observed temperature dependence of R _s , particularly change of the sign.     

Synthesis of a new perovskite Pb(Li14Nb34)O3

A high-pressure technique was adopted to obtain perovskite-type $\text{Pb(Li}{}_{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}\text{Nb}{}_{\mathrm{<mtext>3</mtext><mtext>4</mtext>}}\text{)}\text{O}{}_3$. A new perovskite $\text{Pb(Li}{}_{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}\text{Nb}{}_{\mathrm{<mtext>3</mtext><mtext>4</mtext>}}\text{)}\text{O}{}_3$ was characterized to have a cubic symmetry with $\text{a}{}_{\mathrm{<mtext>o</mtext>}}\text{= 4.069}\text{A}\text{?}$; Li and Nb ions in the B-site of perovskite lattice may be in a random arrangement.     

Bulk crystalline BaPb34Bi14O3: A ceramic superconductor

The preparation conditions of the high T_C ceramic superconductor Ba(Pb,Bi)O₃ is correlated with the superconducting transition. Transition onsets of all materials are similar, but transition widths and transition completeness is strongly dependent on firing temperature. Only materials prepared over a narrow temperature range, resulting in a nearly ideal weight loss, have a complete and narrow transition.     

Electrostriction in Pb (Zn13Nb23)O3

The electrostriction in $\text{Pb (Zn}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{Nb}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{)}\text{O}{}_3$ crystals has been investigated using a strain gauge method. In the ferroelectric phase below 140 C, the strain vs the electric field shows a hysteresis, which is ascribed to the effect of ferroelectric domains. A quadratic relation holds between the strain x and the electric polarization P as x = QP² above about 170 C in the paraelectric phase. Values of the electrostrictive Q coefficients are determined from the measurements near 190 C, as Q₁₁ = 1.6·10^?2m⁴/C², Q₁₂ = ?0.86·10^?2m⁴/C², and Q₄₄ = 0.85·10^?2m⁴/C².     

Effect of pressure onTc in La2-xBaxCuO4 withx=0.125

The superconducting transition temperature,T _c , of La_2–x Ba _x CuO₄ has been measured under high pressure up to 8 GPa.T _c is found to change drastically at the pressure where the structural phase transition takes place. This finding clearly indicates that there exists an intimate relation between the crystal structure and superconductivity.