Protein and cell patterning in closed polymer channels by photoimmobilizing proteins on photografted poly(ethylene glycol) diacrylate

Definable surface chemistry is essential for many applications of microfluidic polymer systems. However, small cross-section channels with a high surface to volume ratio enhance passive adsorption of molecules that depletes active molecules in solution and contaminates the channel surface. Here, we present a one-step photochemical process to coat the inner surfaces of closed microfluidic channels with a nanometer thick layer of poly(ethylene glycol) (PEG), well known to strongly reduce non-specific adsorption, using only commercially available reagents in an aqueous environment. The coating consists of PEG diacrylate (PEGDA) covalently grafted to polymer surfaces via UV light activation of the water soluble photoinitiator benzoyl benzylamine, a benzophenone derivative. The PEGDA coating was shown to efficiently limit the adsorption of antibodies and other proteins to <5% of the adsorbed amount on uncoated polymer surfaces. The coating could also efficiently suppress the adhesion of mammalian cells as demonstrated using the HT-29 cancer cell line. In a subsequent equivalent process step, protein in aqueous solution could be anchored onto the PEGDA coating in spatially defined patterns with a resolution of <15 μm using an inverted microscope as a projection lithography system. Surface patterns of the cell binding protein fibronectin were photochemically defined inside a closed microfluidic device that was initially homogeneously coated by PEGDA. The resulting fibronectin patterns were shown to greatly improve cell adhesion compared to unexposed areas. This method opens for easy surface modification of closed microfluidic systems through combining a low protein binding PEG-based coating with spatially defined protein patterns of interest.     

聚乙二醇型聚氨酯脲的热激放电电流分析

用热激放电电流技术研究了具有微相分离结构的聚乙二醇型多嵌段聚醚氨酯脲的驰豫行为，通过浇铸ＰＥＵＵ的Ｎ，Ｎ－二甲基乙酰胺溶液所得的ＰＥＵＵ薄膜，其ＴＳＤＣ谱显示４个峰发现这些峰与软段的分子运动即氧亚乙基序列的局部运动、微布朗运动引起的玻璃化转变，Ｍａｘｗｅｌｌ－Ｗａｇｎｅｒ－Ｓｉｌｌａｒｓ界面极化以及各种带电离子的迁移密切相关，这些．实验结果已经证明，ＴＳＤＣ分析是研究高分子固态离子导体的一种有价值     

Polyelectrolyte multilayer surface functionalization of poly(dimethylsiloxane) (PDMS) for reduction of yeast cell adhesion in microfluidic devices

Polyelectrolyte multilayers (PEMs) based on the combinations poly(diallyldimethylammonium chloride)∕poly(acrylic acid) (PDADMAC∕PAA) and poly(allylamine hydrochloride)∕PAA (PAH∕PAA) were adsorbed on poly(dimethylsiloxane) (PDMS) and tested for nonspecific surface attachment of hydrophobic yeast cells using a parallel plate flow chamber. A custom-made graft copolymer containing poly(ethylene glycol) (PEG) side chains (PAA-g-PEG) was additionally adsorbed on the PEMs as a terminal layer. A suitable PEM modification effectively decreased the adhesion strength of Saccharomyces cerevisiae DSM 2155 to the channel walls. However, a further decrease in initial cell attachment and adhesion strength was observed after adsorption of PAA-g-PEG copolymer onto PEMs from aqueous solution. The results demonstrate that a facile layer-by-layer surface functionalization from aqueous solutions can be successfully applied to reduce cell adhesion strength of S. cerevisiae by at least two orders of magnitude compared to bare PDMS. Therefore, this method is potentially suitable to promote planktonic growth inside capped PDMS-based microfluidic devices if the PEM deposition is completed by a dynamic flow-through process.     

Implementation of tetra-poly(ethylene glycol) hydrogel with high mechanical strength into microfluidic device technology

Hydrogels have several excellent characteristics suitable for biomedical use such as softness, biological inertness and solute permeability. Hence, integrating hydrogels into microfluidic devices is a promising approach for providing additional functions such as biocompatibility and porosity, to microfluidic devices. However, the poor mechanical strength of hydrogels has severely limited device design and fabrication. A tetra-poly(ethylene glycol) (tetra-PEG) hydrogel synthesized recently has high mechanical strength and is expected to overcome such a limitation. In this research, we have comprehensively studied the implementation of tetra-PEG gel into microfluidic device technology. First, the fabrication of tetra-PEG gel/PDMS hybrid microchannels was established by developing a simple and robust bonding technique. Second, some fundamental features of tetra-PEG gel/PDMS hybrid microchannels, particularly fluid flow and mass transfer, were studied. Finally, to demonstrate the unique application of tetra-PEG-gel-integrated microfluidic devices, the generation of patterned chemical modulation with the maximum concentration gradient: 10% per 20 μm in a hydrogel was performed. The techniques developed in this study are expected to provide fundamental and beneficial methods of developing various microfluidic devices for life science and biomedical applications.     

IT治理对企业的影响分析

本文首先分析了IT治理的背景与应用现状,提出了IT治理的概念和内容,并研究了IT治理对企业的影响机制。指出了如何通过IT治理的途径控制企业IT风险、提高信息资源利用率、实现信息技术价值交付等目标的解决办法,对推进信息化进程具有积极的指导意义。     

Stable chemical bonding of porous membranes and poly(dimethylsiloxane) devices for long-term cell culture

We have investigated the bonding stability of various silane treatments for the integration of track-etched membranes with poly(dimethylsiloxane) (PDMS) microfluidic devices. We compare various treatments using trialkoxysilanes or dipodal silanes to determine the effect of the organofunctional group, cross-link density, reaction solvent, and catalyst on the bond stability. We find that devices made using existing silane methods delaminated after one day when immersed in cell culture medium at 37 °C. In contrast, the dipodal silane, bis[3-(trimethoxysilyl)propyl]amine, is shown to yield stable and functional integration of membranes with PDMS that is suitable for long-term cell culture. To demonstrate application of the technique, we fabricated an open-surface device in which cells cultured on a track-etched membrane can be stimulated at their basal side via embedded microfluidic channels. C2C12 mouse myoblasts were differentiated into myotubes over the course of two weeks on these devices to demonstrate biocompatibility. Finally, devices were imaged during the basal-side delivery of a fluorescent stain to validate the membrane operation and long-term stability of the bonding technique.     

Surface modification on polydimethylsiloxane-based microchannels with fragmented poly(l-lactic acid) nanosheets

Surface modification is a critical issue in various applications of polydimethylsiloxane (PDMS)-based microfluidic devices. Here, we describe a novel method through which PDMS-based microchannels were successfully modified with fragmented poly(l-lactic acid) (PLLA) nanosheets through a simple patchwork technique that exploited the high level of adhesiveness of PLLA nanosheets. Compared with other surface modification methods, our method required neither complicated chemical modifications nor the use of organic solvents that tend to cause PDMS swelling. The experimental results indicated that the modified PDMS exhibited excellent capacity for preventing the adhesion and activation of platelets. This simple yet efficient method can be used to fabricate the special PDMS microfluidic devices for biological, medical, and even hematological purposes.     

论改革的成败原因(上)

当代中国改革能否成功依赖于各种内外条件的创造,通过对世界上有广泛影响的重要改革的政治条件、经济基础、主导力量、民心向背、战略策略、传导机制、文化传统、外部环境的成败原因分析,总结其经验教训,能够成为未来下一步改革的镜鉴.     

论会计政策变更对会计信息的影响

对会计政策及其变更的本质进行了论述，探讨了会计政策变更后，对会计信息的影响及会计处理、披露方法，并通过实例加以说明，旨在保证会计信息质量的提高和对会计政策变更重要意义的认识。     

物联网产业联盟监督体系结构

为了科学与有效地对物联网产业联盟进行监督与控制,在系统阐述物联网产业联盟协同监督原则的基础上,构建物联网产业联盟监督体系结构.分析组成物联网产业联盟监督系统各要素之间关系,提出以体系结构为基础的协同监督思想,从而提高对物联网产业联盟的监督效能,降低监督成本,为物联网产业联盟监督机制的建立打下良好的基础.     

Simple surface modification of poly(dimethylsiloxane) for DNA hybridization

Here, we present a simple chemical modification of poly(dimethylsiloxane) (PDMS) by curing a mixture of 2 wt% undecylenic acid (UDA) in PDMS prepolymer on a gold-coated glass slide. This gold slide had been previously pretreated with a self-assembled hydrophilic monolayer of 3-mercaptopropionic acid (MPA). During curing of the UDA∕PDMS prepolymer, the hydrophilic UDA carboxyl moieties diffuses toward the hydrophilic MPA carboxyl moieties on the gold surface. This diffusion of the UDA within the PDMS prepolymer to the surface is a direct result of surface energy minimization. Once completely cured, the PDMS is peeled off the gold substrate, thereby exposing the interfacial carboxyl groups. These groups are then available for subsequent attachment of 5(')-amino terminated DNA oligonucleotides via amide linkages. Our results show that the covalently tethered oligonucleotides can successfully capture fluorescein-labeled complementary oligonucleotides via hybridization, which are visualized using fluorescence microscopy.