Patterned cell culture inside microfluidic devices

This paper describes a simple plasma-based dry etching method that enables patterned cell culture inside microfluidic devices by allowing patterning, fluidic bonding and sterilization steps to be carried out in a single step. This plasma-based dry etching method was used to pattern cell-adhesive and non-adhesive areas on the glass and polystyrene substrates. The patterned substrate was used for selective attachment and growth of human umbilical vein endothelial cells, MDA-MB-231 human breast cancer cells, NIH 3T3 mouse fibroblasts, and primary rat cortical neurons. Finally, we have successfully combined the dry-patterned substrate with a microfluidic device. Patterned primary rat neurons were maintained for up to 6 days inside the microfluidic devices and the neurons' somas and processes were confined to the cell-adhesive region. The method developed in this work offers a convenient way of micropatterning biomaterials for selective attachment of cells on the substrates, and enables culturing of patterned cells inside microfluidic devices for a number of biological research applications where cells need to be exposed to well-controlled fluidic microenvironment.     

Nanoelectrochemical analysis inside a single living cell

This critical opinion reviews the methods to construct and apply electrodes for analysis inside single cells and of single organelles. Nanoelectrochemical methodology, with an emphasis on nanoelectrode construction and analysis of metabolites, neurotransmitters, reactive oxygen and nitrogen species, glucose, oxygen, hydrogen peroxide, and ions in cells are discussed for measurements from cytoplasm to single organelles.     

Low surface energy polymers and surface-active block polymers. III. Adamantyl-containing polymers

Two adamantyl-containing oxazoline monomers. 2-(1-adamantyl)-2-oxazoline, A , and 2-(1-adamantylmethyl)-2-oxazoline, B , were synthesized, and polymerized in 1,2-dichlorobenzene to give polymers PA and PB respectively. Both polymers are highly crystalline and showed very high T_m's (269°C for PA and 320°C for PB ) and little solubility in common organic solvents. Annealed PA showed a critical surface tension of 23.6 dyne/cm. PB was not soluble in the many organic solvents tested at room temperature. Due to its high T_m and insolubility, contact angle measurements on PB were impossible. Diblock copolymers based on different weight ratios of A and 2-ethyl-2-oxazoline, E , showed relatively narrow molecular weight distribution (MWD) when methyl p-nitrobenzenesulfonate, I , was used as initiator. After annealing, diblock polymers with B/I = 7, 10, or 12 showed T_m's (200–281°C); after quenching the same samples showed T_c's (160–171°C), which were lower than that of pure PB , 215°C. The quenched diblocks showed single T_g's (63–82°C) which implies that these short blocks are compatible. Diblock polymer with B/I = 5 and E/I = 20 was amorphous and displayed inverse emulsifying ability in styrene + water emulsion polymerization. BEB type triblock polymers prepared using ethylene glycol dinosylate as initiator had broader MWD and higher T_m's compared to their diblock counterparts with the same B/E wt% and B/I ratios. These triblock polymers were not completely soluble in styrene and/or water and therefore could not be used as emulsifying agents.     

Folding of the Tau Protein on Microtubules

Microtubules are regulated by microtubule‐associated proteins. However, little is known about the structure of microtubule‐associated proteins in complex with microtubules. Herein we show that the microtubule‐associated protein Tau, which is intrinsically disordered in solution, locally folds into a stable structure upon binding to microtubules. While Tau is highly flexible in solution and adopts a β‐sheet structure in amyloid fibrils, in complex with microtubules the conserved hexapeptides at the beginning of the Tau repeats two and three convert into a hairpin conformation. Thus, binding to microtubules stabilizes a unique conformation in Tau.     

钡铁氧体微管的制备及镧掺杂对其性能的影响

以Ba(NO₃)₂和Fe(NO₃)₃为原料与不同比例的柠檬酸在水溶液中形成溶胶,把溶胶滴于脱脂棉模板上,水分挥发后在脱脂棉表面形成凝胶,于马弗炉中850 ℃煅烧2 h后制得了BaFe₁₂O₁₉微管,并在最佳柠檬酸用量时对BaFe₁₂O₁₉微管进行掺杂制得了BaLa_xFe_12-xO₁₉(x=0～0.3)微管。利用X射线衍射(XRD)﹑扫描电子显微镜(SEM)﹑透射电子显微镜(TEM)对样品的物相﹑形貌和粒径进行表征,并利用振荡样品磁强计(VSM)对样品进行磁性能研究。结果表明：借助脱脂棉模板,采用溶胶凝胶法制备了外径在8～13 μm之间,壁厚在0.5～2 μm之间的BaFe₁₂O₁₉微管,柠檬酸的加入使得微管出现破裂,随着柠檬酸用量的增加,BaFe₁₂O₁₉微管的矫顽力和饱和磁化强度先提高后下降,随着La掺入量的增加BaFe₁₂O₁₉微管的矫顽力、饱和磁化强度以及剩余磁化强度都先增加后减小,但饱和磁化强度和剩余磁化强度的最大值滞后于矫顽力的最大值,当柠檬酸与金属离子的物质的量之比为1∶1,x为0.05时850 ℃煅烧后制得了矫顽力、饱和磁化强度和剩余磁化强度分别为6 153.6 Oe,61.1和36.1 emu·g^-1的BaLa_xFe_12-xO₁₉微管。并就柠檬酸和La掺杂对微管的形成和磁性能的影响原理做了系统的研究。     

Studies on coordination polymers : Part II. Coordination polymers of 1,6-dihydroxyphenazine

Coordination polymers of 1, 6-dihydroxyphenazine (I) with Cu(II), Zn(II), Ni (II), Co(II) and Hg(II) were prepared and studied. All the polymers formed were dark blue to black powders, very insoluble in the common solvents, apparently of low molecular weight, and decomposed at temperatures ranging from 200 to 280°. The zinc polymer was the most stable, mercury the least. Infrared studies confirmed the proposed chelation reaction between the metal ion and (I). The polymers of Co and Hg were amorphous, whereas those of Cu, Zn, and Ni were crystalline. When used as a spot test reagent, (I) gave instant color reactions with 15 common ions but neither the sensitivity nor selectivity of the reagent is impressive.     

Folding of ubiquitin: a simple model describes the strange kinetics

The ubiquitin mutant UbG folding experiments of Sabelko et al., in which "strange kinetics" were observed, are interpreted in terms of a simple kinetic model. A minimal set of states consisting of a semicompact globule, two off-pathway traps, and the native state are included; the fully unfolded state is not considered because folding to the semicompact globule is fast. Both the low- and the high-temperature experiments of Sabelko et al. are fitted by a system of kinetic equations determining the transitions between these states. It is possible that cold- and heat-denaturated states of UbG are the basis of the off-pathway traps. The fits of the kinetic model to the experimental results provides an estimate of the rate constants for the various reaction channels and show how their contributions vary with temperature. Introduction of an on-pathway intermediate instead of one of the off-pathway traps does not lead to agreement with the experiments.     

Organometallic polymers. III. Organometallic modifications of diene polymers

A process for the chemical modification of polybutadienes and natural rubber by various metallocene compounds is described. Soluble products of up to 43% ferrocene content were obtained. The effect of substrate, metallocene, and reaction conditions on the course and extent of substitution was investigated. The glass transition temperature T_g was found to increase considerably with the degree of substitution, e.g., cis-polybutadiene substituted with ferrocene (18 mole-%) has a T_g of 30°C, as compared with ?91°C for the unsubstituted polymer.     

Low surface energy polymers and surface active block polymers. I. t-butylphenyl containing polymers

Two new monomers in the 2-oxazoline series were synthesized and polymerized. These were 2-[4-(t-butyl)phenyl]-2-oxazoline ( I ) and 2-[(3-(3,5-di-t-butyl)phenoxy)propyl]-2-oxazoline ( II ). The polymer from I crystallized readily during bulk polymerization and showed T_m at 592 K (319°C). After annealing, the polymer showed a critical surface tension of 23.2 dyn/cm. Polymer from II was amorphous; hence, annealing showed little effect on contact angles. Block polymers were made with I (Xn = 10) and ethyl oxazoline (Xn = 6,20,60). Very sharp molecular weight distributions were obtained. All samples crystallized when annealed. The block polymer was an effective emulsifier for emulsion polymerization of butyl acrylate at 0.1%.     

Organometallic polymers. IV. Organometallic modifications of halogen-containing polymers

The synthesis of ferrocene-containing polymers by chemical modification of chlorinated polyethylenes, polyvinyl chloride (PVC), and other halogenated polymers, under Friedel-Crafts conditions, is described. The effect of reaction conditions on the structure and composition of the products obtained with various substrates was investigated. Soluble polymers of up to 62% ferrocene content were obtained. In most cases, substitution was accompanied by dehydrohalogenation. The ferrocene-to-vinylene ratio was higher in the reaction products of chlorinated polyethylenes than in those of PVC.     

Thermotropic liquid crystalline polymers. I. Cholesterol-containing polymers and copolymers

An approach to the creation of thermotropic cholesterol-containing liquid crystalline polymers by the chemical binding of cholesterol molecules with side chains of comblike polymers is presented. This type of structure permits a decrease in the steric hindrances provided by the backbone chains for the purpose of realizing the liquid crystalline state. A number of new cholesteric esters of poly(N-methacryloyl-ω-aminocarbonic acid)s (PChMAA-n) with different side-chain lengths (n = 2–11) as well as a series of copolymers of ChMA-n with n-alkylacrylates and n-alkylmethacrylates have been synthesized. The experimental evidence of liquid crystalline structure formation in these polymers in glass, viscoelastic, and fluid states is discussed. Molecular and supermolecular structures of cholesterol-containing comblike polymers have been studied and the model of macromolecular packing in the liquid crystalline state is proposed. It is shown that the existence of a layered order of side methylene groups together with ordering of cholesterol groups is necessary to the production of the liquid crystalline state in these polymers.     

Electron-transfer polymers. XXXIX. Redox polymers based on duroquinonyl glycol

Redox polyurethanes, polyesters, and alternate copolyurethanes and copolycarbonates from two kinds of benzoquinonyl glycol were prepared based on 2-(duroquinonyl)-propan-1,3-diol. The oxidized polymer is stable. When the fully reduced polymer in solution is exposed to air the durohydroquinonyl residues are oxidized to the quinone form while the less substituted hydroquinonyl glycol residues remain stable in the reduced form. There is thus prepared polymer with oxidized and reduced groups alternating along the chain.     

Microcirculation within grooved substrates regulates cell positioning and cell docking inside microfluidic channels

Immobilization of cells inside microfluidic devices is a promising approach for enabling studies related to drug screening and cell biology. Despite extensive studies in using grooved substrates for immobilizing cells inside channels, a systematic study of the effects of various parameters that influence cell docking and retention within grooved substrates has not been performed. We demonstrate using computational simulations that the fluid dynamic environment within microgrooves significantly varies with groove width, generating microcirculation areas in smaller microgrooves. Wall shear stress simulation predicted that shear stresses were in the opposite direction in smaller grooves (25 and 50 microm wide) in comparison to those in wider grooves (75 and 100 microm wide). To validate the simulations, cells were seeded within microfluidic devices, where microgrooves of different widths were aligned perpendicularly to the direction of the flow. Experimental results showed that, as predicted, the inversion of the local direction of shear stress within the smaller grooves resulted in alignment of cells on two opposite sides of the grooves under the same flow conditions. Also, the amplitude of shear stress within microgrooved channels significantly influenced cell retainment in the channels. Therefore, our studies suggest that microscale shear stresses greatly influence cellular docking, immobilization, and retention in fluidic systems and should be considered for the design of cell-based microdevices.     

Sulfur-containing polymers. XVIII. Preparation and properties of thiuram polysulfide polymers

Thiuram polysulfide polymers have been prepared from alkali metal bisdithiocarbamates either by oxidation with ammonium persulfate or by polycondensation with sulfur chlorides. In some cases, isothiocyanate formation and/or thiourea formation were noticed. The polymer properties were significantly affected by the diamines used. Polymers derived from p-phenylenediamine decomposed gradually at room temperature with the liberation of elemental sulfur. Polymers based on aliphatic primary diamines were more stable. Piperazine gave the most stable polymer.     

Functional monomers and polymers. LXI. Photochemical reactions on the synthetic polymers containing thymine bases

Photodimerization of N-2-isobutyloxyethyl thymine (T-M), bis[2-(5-methyl-1-primidinyl)-ethyl] glutarate (T-T), poly(N-2-methacryloyloxyethyl thymine) (polyMAOT), and poly(N-2-acryloyloxyethyl thymine) (poly AOT) was studied in dimethylformamide solution. The rate of intramolecular photodimerization of polyMAOT and polyAOT was 5.7 and 7.2 times faster, respectively, than that of T-T. In T-M, however, intermolecular photodimerization did not occur under the reaction condition used. Quenching studies with isoprene suggest that the photodimerization of T-T occurs predominantly in an excited triplet state, whereas that of polyMAOT and polyAOT occur in singlet and triplet states. It was concluded that the photodimers of T-T, polyMAOT, and polyAOT are two syn-fused cyclobutane-type dimers (cis-syn and trans-syn). Quantum efficiencies of thymine base disappearance were determined by ultraviolet (UV) analysis to be 0.0012 for T-T, 0.0084 for polyMAOT, and 0.010 for polyAOT.     

Functional polymers. XXI

Several 2(2-hydroxyphenyl)2H-benzotriazoles with more than one benzotriazole group substituted on di- and trihydroxybenzenes were synthesized by azo coupling ofo-nitrobenzenediazonium chloride with resorcinol or phloroglucinol followed by reductive cyclization with zinc powder and sodium hydroxide. By careful diazonium coupling witho-nitrobenzenediazonium chloride, the monobenzotriazyl compound, 4(2H-benzotriazole-2-yl)1,3-dihydroxybenzene [2(2,4-dihydroxyphenyl)2H-benzotriazole] was obtained. All compounds have unusual spectral characteristics with high extinction coefficients, cut off of the absorption below 400 nm and are excellent candidates for ultraviolet stabilizers.     

Coordination polymers. IX

Poly-(butanediol-1,4-adipate) and poly-(diethyleneglycol-succinate) polyesters and their ionized derivatives, containing Mg²⁺ and Zn²⁺ ions with different stoichiometric ratios to the chain-end COOH groups of the polyesters have been investigated by derivatograph.The thermal decompositions of the metal-containing polyesters differ significantly from those of the unionized polyesters. These differences are connected with the chemical repeating unit of the polyesters and the chemical nature of the metal ions, and proportional to the amount of the latter.An explanation is given of the catalytic effect of metal ions on the process of decomposition of the polyesters.

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Zusammenfassung Poly-(butandiol-1,4-adipat) und Poly-(diethylenglycolsuccinat) polyester und ihre «ionisierten» Derivate — mit Mg²⁺ — und Zn²⁺-Ionengehalt in verschiedenen stöchiometrischen Verhältnissen zu den endständigen COOH-Gruppen der Polyester — wurden im Derivatographen untersucht.Die thermische Zersetzung der metallhaltigen Polyester unterscheidet sich wesentlich von nicht-ionisierten Polyestern. Diese Unterschiede sind mit den sich wiederholenden chemischen Einheiten der Polyester und der chemischen Beschaffenheit der Metallionen verbunden, und proportional dem Anteil derselben.Es wird eine Erklärung des katalytischen Effekts der Metallionen auf den Zersetzungsvorgang der Polyester gegeben.

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-1,4 «» , Mg²⁺ Zn²⁺ . , «» . . .

     

Halato-telechelic polymers. XV. Ionic cross-interactions of immiscible telechelic polymers: A reversible pathway to block copolymer-type materials

Phase separation of two immiscible polymer blends can be controlled by ionic cross-interactions of the end-groups as promoted by proton transfer from acid end-groups of polymer PA to aliphatic tert-amine end-groups of PB. IR spectroscopy supports the occurrence of proton transfer with formation of ammonium carboxylate ion pairs that influences the solution behavior of the blends. Optical microscopy illustrates the opportunity to get finely dispersed blends at a scale of ca. 0.2 μm depending on nature, molecular weight, and functionality of the immiscible polymers and strength of the ion pairs. T_g measurements are in agreement with the general pattern reported for multiphase block polymers, and give consistency to an analogy between finely phase separated blends of acid and tert-amine telechelic polymers and related block polymers.     

Organosilane polymers: Formable polymers containing methylsilylene units

Organosilane polymers containing methylsilylene units were prepared by sodium condensation of MeHSiCl₂ alone or with R¹R²SiCl₂ (R¹ and R² = alkyl, aryl, or aralkyl) in a blend of toluene and dioxane followed by fast filtration under N₂. These polymers are readily soluble in common solvents and can be drawn into fibers or formed into films by molding, casting, or potting. They can be crosslinked by oxidation, irradiation, or hydrosilylation of vinylsilane in the presence of platinum complexes. The effect of the quantity of MeHSiCl₂ on molecular weights of copolymers was also discussed.