海藻酸钙/明胶微胶珠的制备、检测及神经干细胞相容性分析

研究制备了海藻酸钙/明胶微胶珠,并探讨了此种微胶珠的机械和渗透性能及作为细胞载体用于神经干细胞体外培养的可行性。使用自制穿刺力测试仪检测不同浓度的海藻酸钠、明胶和Ca Cl2对微胶珠机械强度的影响;采用DMEM(Dulbecco's Modified Eagle Media)培养基浸泡法测试微胶珠的耐浸泡能力;试验以微胶珠为对象建立扩散模型以研究葡萄糖和牛血清蛋白(Bovine serum albumin BSA)在微胶珠中的扩散情况,并模拟得扩散系数与物质浓度之间的关系,此后,通过包埋培养昆明小鼠神经干细胞探索微胶珠用于神经干细胞体外培养的可行性。通过综合分析强度和扩散性能以及培养细胞的状况等,得出海藻酸钙/明胶微胶珠的最佳制备参数:海藻酸钠1.5%(wt)、明胶0.5%(wt)、Ca Cl24%(wt),并发现所研究制备的海藻酸钙/明胶微胶珠具有良好的细胞相容性,适于作为细胞载体用于神经干细胞的体外培养。     

硝化细菌的固定化及其处理氨氮污水的研究

通过富集培养硝化细菌,使污泥中硝化细菌数量增加,成为优势菌,再将硝化细菌包埋固定化在海藻酸钙凝胶胶珠中,并用于污水的处理,通过正交实验法确定了适宜的包埋固定化条件。结果表明,通过富集培养,硝化细菌数量从1.1×104个.g-1增加到2.1×108个.g-1,固定化的硝化细菌胶球对人工污水和实验污水的氨氮去除率均为90%。     

单分散海藻酸钙凝胶微球的制备及其缓释研究

利用表面张力和重力的平衡,采用悬滴-凝胶化法制备了均一的、直径在1 mm左右海藻酸钙微球颗粒。采用紫外-可见光谱分析法对一种模型分子(甲基绿)在该微球中的缓释过程进行了研究,并建立了扩散传质的数学模型。粒径的均一性使该模型只需要针对单个微球而设立,并具有严格的分析解,由此我们计算出了该分子在海藻酸钙凝胶微球中的扩散系数D。这一研究对药物控缓释动力学的研究具有借鉴意义。     

粒径相关的海藻酸盐/壳聚糖微球膜性能

粒径是评价微尺度凝胶载体性能的重要参数。文中以3种不同粒径(202,413,809μm)的海藻酸钙(Ca-Alg)凝胶珠为研究对象,以维生素B_(12)(VB_(12))、牛血清白蛋白(BSA)和壳聚糖(CS)为模型分子,实验考察了胶珠粒径对海藻酸钙/壳聚糖(Ca-Alg/CS)微球性能的影响。采用电子扫描显微镜(SEM)、傅里叶红外光谱仪(FTIR)和激光共聚焦显微镜(CLSM)等方法表征膜结构与形貌,采用膨胀率表征膜稳定性。结果表明:Ca-Alg/CS微球的凝胶结构、分子扩散性能和聚电解质复合膜性能与Ca-Alg胶珠粒径具有相关性。随着胶珠粒径减小,凝胶结构趋于致密,对分子扩散阻力增大。在成膜反应过程中,小粒径胶珠表面为成膜反应提供了更多的反应交联位点,在胶珠表面形成更致密连续和更厚的聚电解质复合膜。Ca-Alg/CS微球具有优异的膜强度和稳定性,在细胞固定化培养中具有显著应用优势。     

人工肝生物反应器中溶解氧浓度动态分布的模型与数值分析

研究了人工肝生物反应器的结构特点,并在对反应器内部液体流动与气液传质规律进行分析的基础上,结合反应器的实际需要,建立了基于一维轴向扩散模型的人工肝专用生物反应器溶解氧浓度动态分布的数学机理模型. 利用有限差分方法对模型离散化求解,得到了流动速度、氧传质系数及细胞耗氧速率对反应器内部溶解氧浓度分布的影响规律. 通过对模型数值解的分析得到了特定条件下反应器内的优化参数为液体流速0.55 mm/s,传质系数0.31 s-1,扩散系数0.02 mm2/s. 最后,通过仿真数据与实测实验的对比验证了该模型的正确性,其平均误差在±5%以内. 本模型的建立在理论上验证了该专用生物反应器可以提供稳定且均匀的溶解氧浓度分布,同时也为下一代新型反应器的优化设计提供了参考数据和理论依据.     

海藻酸钙/几丁聚糖微胶囊载胰蛋白酶研究

采用乳化固化法制备出平均粒径为820 nm的海藻酸钙空白微胶珠,并以几丁聚糖为膜材进一步制备了海藻酸钙/几丁聚糖微胶囊。以胰蛋白酶(Trypsin)为模型药物,采用两步法制备了载胰蛋白酶/几丁聚糖-海藻酸钙微胶囊,考察了几丁聚糖分子量、几丁聚糖浓度、成膜时间、投药浓度等工艺参数对微胶囊载药性能的影响,结果表明几丁聚糖-海藻酸钙微胶囊对胰蛋白酶具有较好的负载性能。     

海藻酸钠-壳聚糖复合膜中溶氧扩散性能研究

氧气在微胶囊膜中的扩散行为将直接决定微囊内细胞的生长代谢行为.以海藻酸钠-壳聚糖聚电解质复合平板膜为研究模型,利用渗透池法,重点考察溶氧在膜中的扩散行为及其影响因素.结果显示:复合膜的扩散系数和孔隙率均低于海藻酸钙,复合膜中溶氧扩散系数为(7～13)×10-10m2·s-1,为水中的23.3％～43.3％,孔隙率为93％～97％;扩散系数随海藻酸钠特性黏度的增大而减小,随壳聚糖分子量的增大而减小.微胶囊膜是氧传质主要的阻力部位,孔隙率、三维结构和材料极性是影响扩散性能的重要因素,改变海藻酸钠特性黏度和壳聚糖分子量可以改变膜孔隙率、结构和材料极性,进而调节膜扩散性能.     

多通道微胶囊制备系统规模化制备海藻酸钙微胶珠

利用自制多通道强制电场微胶囊制备系统制备海藻酸钙微胶珠,分析了微胶囊制备系统中电极电场分布规律,考察了进料气压、脉冲电压、脉冲频率、脉冲宽度、辅助电压等系统调节参数对微胶珠制备过程的影响,发现制备过程中微胶珠粒径大小与产率主要由进料气压决定,而微胶珠的分散性则是由多个因素共同作用的结果。通过优化条件制备的微胶珠分散系数较小（CV<20%）,球形度良好,表面光洁,并且产率是传统静电法的20~40倍,使海藻酸钙微胶珠大规模制备成为可能。     

ZrO2陶瓷注射成型超临界CO2流体脱脂动力学研究

用传统扩散方程建立了描述ZrO2陶瓷注射成型超临界流体脱脂过程的传质模型,研究分析了陶瓷注射成型超临界流体脱脂行为和脱脂的动力学过程。研究结果表明：有机粘合剂的溶解和扩散是陶瓷注射成型超临界脱脂过程关键因素,其中扩散为控制步骤。当脱脂时间足够长,模型计算曲线与实验结果吻合。通过实验数据,利用简单的理论模型可以得到相应的扩散系数。利用传质模型可以预测陶瓷注射成型超临界脱脂过程传质速率和萃取动力学。     

固定床内径向扩散研究

在直径为２６７ｍｍ的５Ａ分子筛固定床上，采用稳态有限源示踪技术，利用计算机数据采集系统，测定了不同流速下床层内部截面上示踪气体的浓度分布数据。并分别利用稳态有限源和稳态点源示踪条件下扩散模型的解析解，获得床层内的径向扩散系数值。结果表明，两种处理方法所获得的径向扩散系数值大致相等，且在实验条件范围内，当Ｒｅ数较小时，径向扩散系数值与分子扩散系数值相当，随着Ｒｅ数的增加，径向扩散系数值逐渐增大，最后几乎与流速成正比。文中还讨论了轴向扩散系数值对径向扩散系数计算结果的影响。     

Investigation of diffusivity in nanometer-thick yttria-stabilized zirconia by chronoamperometry and its formalism

This work aims to demonstrate that chronoamperometry is a valuable tool for determining diffusivities in all-solid-state nanometer-thick cells. The transient current in chronoamperometry of electrochemical cells under constant voltage is described by firstly considering purely capacitive processes, defined by RC circuit equations, and then purely diffusive processes, by Cottrell's equations. The physical meaning of the equations has been amply described in liquid cells with porous electrodes but scarcely in solid-state cells. Thus, we studied Metal/Insulator/Metal nano-cells with Ru and Au electrodes, Yttria Stabilized Zirconia (YSZ) electrolyte at temperatures between 50 and 170°C and voltages between 0.5 V and 1.5 V, where non-Faradaic processes occur. The calculated diffusive and capacitive contributions at different temperatures obey the Arrhenius law. The activation energy was associated with vacancies, the major carrier during electrical transport. The analysis discusses other parameters, such as capacitance, effective concentration, and leakage current. The experimental diffusivity of YSZ electrolytes was compared with diffusivity values obtained by the statistical moment method.     

Finite element analysis of oxygen transport in microfluidic cell culture devices with varying channel architectures, perfusion rates, and materials

Numerical simulations were done both as an exploration into the nature of oxygen transport within microfluidic cell culture devices and an investigation of the relative importance of various design parameters. A rectangular channel comprised of an oxygen permeable polymer layer bonded to a glass substrate seeded with a monolayer of oxygen-consuming cells was modeled. Oxygen transport by both convection and diffusion within the cell culture media and by diffusion in the polymer layer were explored using finite element analysis. Stiff spring analysis was applied at the interface between these two regions to ensure a continuous flux of O₂ across the boundary. The O₂ utilization of the cells was approximated by a constant flux of oxygen from the bottom of the channel. The model was verified against an analytical solution from the literature. Design parameters including flow rate, diffusive layer thickness, and material selection were manipulated within the model to determine their relative importance in ensuring adequate supplies of oxygen for cell growth. The solubility and diffusivity of oxygen within the polymer layer were found to be key parameters in determining the amount of oxygen available to the cells, along with the flow rate of the media perfusing the system. These explorations will enable rational design choices to be undertaken during the implementation of microfluidic devices for cell culture.     

湍流搅拌槽中原油-水分散体系的液滴破碎

对搅拌槽内原油-水分散体系中液滴的破碎过程进行了实验和理论分析。实验测定了在不同温度和转速条件下油滴的粒径分布以及最大稳定粒径,并采用以Voigt模型为基础的理论对最大稳定粒径进行了计算。在温度较低时,原油表现出了具有触变性的流变学性质,经过计算和数量级分析,液滴破碎时间与粘度达到平衡的时间相比非常短,可认为在破碎过程中液滴的粘度始终为初始粘度。实验结果与以初始粘度计算的理论值吻合较好。     

Effect of the interconnecting window diameter of hydroxyapatite scaffolds on vascularization and osteoinduction

The interconnectivity of the scaffold determines oxygen and nutrients transmission, and metabolic waste discharge, which plays a crucial role in cell migration, blood vessel, and tissue regrowth. In the present study, three types of porous hydroxyapatite scaffolds (HAS) with the same pore sizes but different interconnecting window diameters were fabricated by sugar spheres-leaching and heat treatment technique and were used to investigate the effect of interconnecting window diameter on ectopic angiogenesis and osteogenesis. In vitro cell culture experiments showed that the interconnectivity did not influence the performance of cells, while in vivo animal experiments revealed that the interconnecting window diameter of HAS impacted not only angiogenesis but also osteogenesis. The mean diameter of blood vessels was increased with the increase of interconnecting window diameter after 4 weeks of implantation, and the sample of mHAS (with about 0.25 w/m ratio of interconnecting window diameter to macro-pore diameter) exhibited the best osteogenesis after 12 weeks of implantation. This study provides a new reference for designing the porous structure of HAS effectively to enhance the new bone formation of bone tissue engineering scaffolds via vascularization in clinic application.     

用高效廉价载体培养CHO细胞生产rHuEPO的研究

研究了以自制胶原蛋白载体及C-DISK载体培养CHO细胞生产rHuEPO蛋白的过程,并以进口A-DISK载体作为对照培养。对培养过程中细胞贴壁过程、葡萄糖代谢速率、rHuEPO浓度及葡萄糖代谢速率与rHuEPO的浓度变化关系进行了实验研究分析和对比。结果表明:自制胶原蛋白载体培养细胞具有良好的生物代谢活力和蛋白表达能力,葡萄糖代谢速率高达14.2mmol?mL?1?h?1,比自制C-DISK载体高16.4%,比进口A-DISK载体高12.7%;在自制胶原蛋白载体上培养CHO细胞时EPO表达量也最高,培养10天后EPO浓度达到282U?mL?1,比自制C-DISK载体高30%,也比进口A-DISK载体高18%。自制胶原蛋白载体具有较佳的性价比,是一种高效、廉价的动物细胞培养载体。细胞的葡萄糖代谢水平对蛋白表达有着重要的影响,但两者又不同步,因此可用葡萄糖的代谢速率变化对该培养过程和目的蛋白表达进行适当监测和调控。     

Penetration of Monodisperse,Singly Charged Nanoparticles through Polydisperse Fibrous Filters

The article presents experimental results and theoretical analysis of aerosol nanoparticle penetration through fibrous filters with a broad fiber diameter distribution. Four fibrous filters were produced using the melt-blown technique. The analysis of the filters’ SEM images indicated that they had log-normal fiber diameter distribution. Five kinds of proteins and two types of silica particles were generated by electrospraying and were then classified using a Parallel Differential Mobility Analyzer to obtain well-defined, monodisperse, singly charged challenge aerosols with diameters ranging from 6.3 to 27.2 nm. Particle penetration through the filters was determined using a water-based CPC. Experimental results were compared first with predictions derived from the classical theory of aerosol filtration. It is demonstrated that it is inappropriate to apply it to the arithmetic mean fiber diameter, as this results in turn in a huge underestimation of nanoparticle penetration. A better, but still unsatisfactory agreement is observed when that theory was used together with the pressure drop equivalent fiber diameter or when the Kirsch model of nonuniform fibrous media was applied. We show that the classical theory applied to any fixed fiber diameter predicts a stronger dependence of nanoparticle penetration on the Peclet number as compared to experimental data. All these observations were successfully explained by using our original partially segregated flow model that accounts for the filter fiber diameter distribution. It was found that the parameter of aerosol segregation intensity inside inhomogeneous filters increases with the increase in particle size, when the convective transport becomes more pronounced in comparison to the diffusive one.     

Recent progress in preparation of functional capsule membranes based on co-extrusion minifluidic technique

As a kind of encapsulation system, the capsule membrane has a unique internal cavity structure, which can encapsulate and protect active substances and is widely used in the fields of substance encapsulation and controlled release of drugs. Capsule membranes fabricated with calcium alginate (Ca-Alg) as shells process notable advantages such as good biocompatibility and degradability. Compared with other fabrication methods, co-extrusion minifluidic technique has the advantages of facile fabrication process and mild conditions for fabrication of Ca-Alg capsule membranes with uniform size and regulated structures. This paper reviews recent progress in fabrication and functionalization of Ca-Alg capsule membranes by co-extrusion minifluidic technique. Fabrication of Ca-Alg capsule membranes with single and multi-compartment, factors affecting mass transfer of Ca-Alg capsule membranes, encapsulation of cells for producing multicellular spheroids and investigating the mechanics of tumor progression in vitro with three-dimensional environments, and functionalization of Ca-Alg capsule membranes by addition of functional materials with thermo and pH-responsive switching functions are highlighted. This review provides guidance for the further design and fabrication of novel capsule membranes as well as their applications in enzyme catalytic reactions, immobilizations of cells and foods, and controlled release of chemicals.     

Mathematical model for ethanol production from mixed sugars by Pichia stipitis

A mathematical model for estimating the dynamic behavior of ethanol production from mixed sugars such as glucose and xylose is presented. This model was constructed by introducing the term for ethanol production into the diauxic growth model proposed previously by the authors. It was assumed that the first substrate, glucose, is metabolized by a constitutive enzyme and the second substrate, xylose, is utilized by an inducible enzyme. The synthesis of the inducible enzyme is controlled by the catabolite repression caused by glucose and with the induction caused by xylose as an inducer, and the xylose is then converted into cell mass and ethanol by the inducible enzyme. The parameters of the model were estimated from the experimental data in the medium containing glucose and xylose, singly or in combination in a batch culture. The application of the model was examined for experiments in both batch and continuous culture, with glucose and xylose as carbon sources. The calculated values, according to the model, corresponded satisfactorily with experimental data, such as cell growth, substrate consumption, and ethanol production, especially in the estimation of the lag times between the first log phase and the second log phase in cell growth and ethanol production. © 2001 Society of Chemical Industry     

Improved experimental method for measuring gas diffusivity through thin porous media

Gas diffusion through porous media is critical for the high current density operation of a polymer electrolyte membrane fuel cell, where the electrochemical reaction becomes rate limited by the diffusive flux of reactants. Precise knowledge of the diffusivity through various components in a fuel cell is necessary for accurate modeling and analysis. However, many experimental measurements of diffusivity in literature have high measurement uncertainty. In this study, an improvement to the accuracy of the Loschmidt cell method is presented for measuring the diffusivity through materials with a submillimeter thickness. The diffusivity through various gas diffusion layers (GDLs) is measured, and the relative differences between GDLs are explained using scanning electron microscopy and the method of standard porosimetry. The experimental results from this study and others in current literature are used to develop a generalized correlation for the diffusibility as a function of porosity in the through‐plane direction of GDLs. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1409–1419, 2013     

Solid‐state microcellular high temperature vulcanized (HTV) silicone rubber foam with carbon dioxide

A series of microcellular high temperature vulcanized (HTV) silicone rubber foams were prepared using CO₂ as a physical blowing agent. Rheological properties, gas diffusive behavior, and foaming parameters of silicone rubber were investigated. The results show that saturation pressure has a significant effect on the diffusivity of CO₂ in HTV silicone rubber matrix. The gas concentration and diffusivity increase from 2.45 wt % to 3.24 wt %, and from 1.62 × 10^?5 cm²/s to 7.83 × 10^?5 cm²/s as the saturation pressure increases from 2 MPa to 5 MPa, respectively. The value of the gas diffusivity in HTV silicone rubber is almost 1000 times higher than that of the gas diffusivity in polyetherimide (PEI) matrix. Additionally, microcellular HTV silicone rubber foams with the smallest cell diameter of 9.8 μm and cell density exceeding 10⁸ cells/cm³ are achieved. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44807.