Circular‐shaped microfluidic device to study the effect of shear stress on cellular orientation

Understanding the effects of shear stress on mammalian cells is a crucial factor for understanding a number of biological processes and diseases. Here, we show the development of a circular‐shaped microfluidic device for the facile generation of shear stress gradients. With this microfluidic device, the effect of shear stress on orientation of human umbilical vein endothelial cells was studied. This microfluidic device, which enables to control the alignment of human umbilical vein endothelial cells within a microchannel, can be a valuable tool to mimic blood vessels.     

Copper‐Free Huisgen Cycloaddition for the 14‐3‐3‐Templated Synthesis of Fusicoccin‐Peptide Conjugates

Mid‐sized molecules have emerged as an attractive chemical space and potentially provide a robust basis for the development of synthetic agents to control intracellular protein interactions. However, the limited cell permeability and chemical tractability of such agents remain to be addressed. We envisioned that target‐templated synthesis of such mid‐sized molecules might provide a solution. Here, we exploited a copper‐free Huisgen cycloaddition for template synthesis using a peptide fragment containing a 4,8‐diazacyclononyne (DACN) moiety and an azide‐containing fusicoccin derivative in the presence or absence of recombinant 14‐3‐3ζ protein in vitro. Time‐course changes in the yield of products demonstrated that the reaction was accelerated in the presence of 14‐3‐3 and one of the regioisomers was generated predominantly, supporting the template effect.     

Synthesis and Anti‐HIV Activity of Triazolo‐Fused,Medium‐Sized Cyclic Nucleoside Analogs Prepared by an Intramolecular Huisgen 1,3‐Dipolar Cycloaddition

Medium‐sized cyclic nucleosides containing a fused triazole ring were synthesized via intramolecular Huisgen 1,3‐dipolar cycloadditon reaction. 2′,3′‐seco‐Uridine was employed as the key intermediate for the introduction of azido and alkynyl moieties in the defined positions of the reaction precursors. The cycloaddition reactions were achieved in high yields by heating the precursor in refluxing toluene. The uracil base in these target compounds was successfully transformed to the corresponding cytosine. The synthesized compounds were evaluated in a MAGI assay for their anti‐HIV activities, and in a H9 T lymphocytes assay for their cell toxicities.     

Synthesis and Anti‐HIV Activity of Triazolo‐Fused 3′,5′‐Cyclic Nucleoside Analogues Derived from an Intramolecular Huisgen 1,3‐Dipolar Cycloaddition

Triazolo‐fused 3′,5′‐cyclic nucleoside analogues were synthesized by an intramolecular 1,3‐dipolar cycloaddition of nucleoside‐derived azido‐alkynes in a regio‐ and stereospecific manner. The thymine nucleoside base in these target compounds was transformed successfully into the corresponding 5‐methylcytosine component. The synthesized compounds were examined in a MAGI assay for exploring the anti‐HIV activity and in a H9 T lymphocytes assay for measuring the cell toxicity.     

Immobilization of copper ions onto α‐amidotriazole‐functionalized magnetic nanoparticles and their application in the synthesis of triazole derivatives in water

A new heterogeneous copper catalyst was synthesized by immobilization of copper ions onto magnetic nanoparticles with a new ligand based on triazole. The catalyst was characterized using scanning and transmission electron microscopies, atomic absorption and Fourier transform infrared spectroscopies, and thermogravimetric, elemental and energy‐dispersive X‐ray analyses. The results confirmed that a good level of organic groups was immobilized on the magnetic nanoparticles. Huisgen cycloaddition reaction was chosen as a model reaction for the investigation of catalyst activity under green conditions. Phenylacetylene and benzyl bromide derivatives were used for the synthesis of triazoles. The reaction proceeded with good to excellent yields for various alkynes and alkyl halides. To investigate catalyst activity for inactive alkynes, aliphatic alkynes were used in the model reaction. The corresponding triazoles were obtained in good to excellent yields and a high regioselectivity for products was obtained. The catalyst was easily separated using an external magnetic field and subsequently reused in ten reaction cycles without any loss of catalytic activity. Copyright © 2016 John Wiley & Sons, Ltd.     

Simple,low‐cost fabrication of semi‐circular channel using the surface tension of solder paste and its application to microfluidic valves

This work presents a simple, low‐cost method to fabricate semi‐circular channels using solder paste, which can amalgamate the cooper surface to form a half‐cylinder mold using the surface tension of Sn–Pd alloy (the main component in solder paste). This technique enables semi‐circular channels to be manufactured with different dimensions. These semi‐circular channels will then be integrated with a polymethylmethacrylate frame and machine screws to create miniaturized, portable microfluidic valves for sequential liquid delivery and particle synthesis. This approach avoids complicated fabrication processes and expensive facilities and thus has the potential to be a useful tool for lab‐on‐a‐chip applications.     

Ultrathin gradient films using thiol‐ene polymerizations

The application of surface‐attached, thiol‐ene polymer films for controlling material properties in a gradient fashion across a surface was investigated. Thiol‐ene films were attached to the surface by first depositing a thiol‐terminated self‐assembled monolayer and performing a thiol‐ene photopolymerization reaction on the surface. Property gradients were created either by creating and modifying a gradient in the surface thiol density in the SAM or by changing the polymerization conditions or both. Film thickness was modified across the substrate by changing either the density of the anchoring thiol functional groups or by changing the reaction conditions such as exposure time. Thicker films (1–11 nm) were obtained by polymerizing acrylate polymer brushes from the surface with varying exposure time (0–60 s). The two factors, that is, the surface thiol density and the exposure time, were combined in orthogonal directions to obtain thiol‐ene films with a two‐dimensional thickness gradient with the maximum thickness being 4 nm. Finally, a thiol‐acrylate Michael type addition reaction was used to modify the surface thiol density gradient with the cell‐adhesive ligand, Arg‐Gly‐Asp‐Ser (RGDS), which subsequently yielded a gradient in osteoblast density on the surface. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 7027–7039, 2006     

Hypervalent iodine‐mediated direct azidation of polystyrene and consecutive click‐type functionalization

Polystyrene was directly azidated in 1,2‐dichloroethane or chlorobenzene using a combination of trimethylsilyl azide and a hypervalent iodine (III) compound, (diacetoxyiodo)benzene. 2D NMR HMBC experiments indicated that the azide groups were attached to the polymer backbone and also possibly to the aromatic pendant groups. The amount of introduced azide groups was estimated by semi‐quantitative IR spectroscopy and elemental analysis. Approximately 1 in every 11 styrene units could be modified by using a ratio of hypervalent iodine compound to trimethylsilyl azide to styrene units of 1:2.1:1 at 0 °C for 4 h followed by heating to 50 °C for 2 h in chlorobenzene. The azidated polymers were further used as backbone precursors in the synthesis of polymeric brushes with hydrophilic side chains via a copper‐catalyzed click grafting‐onto reaction with poly(ethylene oxide) monomethyl ether 4‐pentynoate. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 966–974, 2010     

Versatile ω‐end group functionalization of RAFT polymers using functional methane thiosulfonates

Five different polymers, poly[methyl methacrylate] (PMMA), poly[lauryl methacrylate] (PLMA), poly[diethylene glycol methacrylate] (PDEGMA), poly[N‐isopropylacrylamide] (PNIPA), and poly[styrene] (PS) prepared by the RAFT process and thus terminated with dithioesters were aminolyzed in the presence of S‐3‐butynyl methane thiosulfonate (MTS), which was synthesized in two steps. Analysis of the polymers by 2D NMR, UV–vis absorbance, and gel permeation chromatography revealed them to quantitatively carry acetylene end groups connected with disulfide bridges, indicating that functional MTS reagents can be employed for end group functionalization of RAFT polymers. This versatile method is of advantage compared with conjugations with functional maleimides, where isolation of terminal thiols is often required but inexpedient for poly[(meth)acrylates] because their terminal thiols may undergo backbiting and thus avoid conjugation. The acetylene‐terminated polymers were bound to an azide functionalized glass surface in a Cu(I) catalyzed cycloaddition. The modified surfaces exhibited water contact angles corresponding to the polarity of the attached polymers. In the case of the stimulus responsive polymers PNIPA and PDEGMA, the surfaces showed temperature‐dependent contact angles. The disulfide bond connecting the polymers to the surface could be selectively cleaved and resulted in all surfaces having the same contact angle, independent of the nature of the polymer prior attached to the surface. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3118–3130, 2009     

High‐throughput microfluidic device for single cell analysis using multiple integrated soft lithographic pumps

The ability to accurately control fluid transport in microfluidic devices is key for developing high‐throughput methods for single cell analysis. Making small, reproducible changes to flow rates, however, to optimize lysis and injection using pumps external to the microfluidic device are challenging and time‐consuming. To improve the throughput and increase the number of cells analyzed, we have integrated previously reported micropumps into a microfluidic device that can increase the cell analysis rate to ∼1000 cells/h and operate for over an hour continuously. In order to increase the flow rates sufficiently to handle cells at a higher throughput, three sets of pumps were multiplexed. These pumps are simple, low‐cost, durable, easy to fabricate, and biocompatible. They provide precise control of the flow rate up to 9.2 nL/s. These devices were used to automatically transport, lyse, and electrophoretically separate T‐Lymphocyte cells loaded with Oregon green and 6‐carboxyfluorescein. Peak overlap statistics predicted the number of fully resolved single‐cell electropherograms seen. In addition, there was no change in the average fluorescent dye peak areas indicating that the cells remained intact and the dyes did not leak out of the cells over the 1 h analysis time. The cell lysate peak area distribution followed that expected of an asynchronous steady‐state population of immortalized cells.     

End‐group functionalization and postpolymerization modification of helical poly(isocyanide)s

This contribution presents the synthesis of helical alkyne‐terminated polymers using a functionalized Nickel complex to initiate the polymerization of menthylphenyl isocyanides. The resulting polymers display low dispersities and controlled molecular weights. Copper‐catalyzed azide/alkyne cycloadditions (CuAAC) are performed to attach various azide‐containing compounds to the polymer termini. After azido‐phosphonate moiety attachment the polymer displays a signal at 25.4 ppm in the ³¹P NMR spectrum demonstrating successful end‐group functionalization. End‐group functionalization of a fluorescent dye allows to determine the functionalization yield as 89% (±8). Successful ligation of an azide‐functionalized peptide sequence (M_KLA = 1547 g/mol) increases the M_n from 5100 for the parent polymer to 6700 for the bioconjugate as visualized by GPC chromatography. Analysis by CD spectroscopy confirms that the helical conformation of the poly(isocyanide) block in the peptide–polymer conjugate is maintained after postpolymerization modification. These results demonstrate an easy, generalizable, and versatile strategy toward mono‐telechelic helical polymers. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2766–2773     

Recyclable Porous Polymer‐Supported Copper Catalysts for Glaser and Huisgen 1,3‐Diolar Cycloaddition Reactions

A family of polymer‐attached phenanthrolines was prepared from solvothermal copolymerization of divinylbenzene with N‐(1,10‐phenanthroline‐5‐yl)acrylamide in different ratios. The polymer‐supported copper catalysts were obtained through typical impregnation with copper(II) salts. The polymers and supported copper catalysts have been characterized by N₂ adsortion, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermogravimetric analysis (TG); they exhibit a high surface area, hierarchical porosity, large pore volume, and high thermal and chemical stabilities. The copper catalyst has proved to be highly active for Glaser homocoupling of alkynes and Huisgen 1,3‐diolar cycloaddition of alkynes with benzyl azide under mild conditions at low catalyst loading. The heterogeneous copper catalyst is more active than commonly used homogeneous and nonporous polystyrene‐supported copper catalysts. In particular, the catalyst is easily recovered and can be recycled at least ten times without any obvious loss in catalytic activity. Metal leaching was prevented due to the strong binding ability of phenanthroline and products were not contaminated with copper, as determined by ICP analysis.     

Polycaprolactone solution–based ink for designing microfluidic channels on paper via 3D printing platform for biosensing application

This work reports a novel fabrication technique for development of channels on paper‐based microfluidic devices using the syringe module of a 3D printing syringe–based system. In this study, printing using polycaprolactone (PCL)‐based ink (Mw 70 000‐90 000) was employed for the generation of functional hydrophobic barriers on Whatman qualitative filter paper grade 1 (approximate thickness of 180 μm and pore diameter of 11 μm), which would effectively channelize fluid flow to multiple assay zones dedicated for different analyte detection on a microfluidic paper‐based analytical device (μPAD). The standardization studies reveal that a functional hydrophilic channel for sample conduction fabricated using the reported technique can be as narrow as 460.7 ± 20 μm and a functional hydrophobic barrier can be of any width with a lower limit of about 982.2 ± 142.75 μm when a minimum number of two layers of the ink is extruded onto paper. A comparison with the hydrodynamic model established for writing with ink is used to explain the width of the line printed by this system. A fluid flow analysis through a single channel system was also carried out to establish its conformity with the Washburn model, which governs the fluid flow in two‐dimensional μPAD. The presented fabrication technique proves to be a robust strategy that effectively taps the advantages of this 3D printing technique in the production of μPADs with enhanced speed and reproducibility.     

Logic digital fluidic in miniaturized functional devices: Perspective to the next generation of microfluidic lab‐on‐chips

Microfluidics has emerged following the quest for scale reduction inherent to micro‐ and nanotechnologies. By definition, microfluidics manipulates fluids in small channels with dimensions of tens to hundreds of micrometers. Recently, microfluidics has been greatly developed and its influence extends not only the domains of chemical synthesis, bioanalysis, and medical researches but also optics and information technology. In this review article, we will shortly discuss an enlightening analogy between electrons transport in electronics and fluids transport in microfluidic channels. This analogy helps to master transport and sorting. We will present some complex microfluidic devices showing that the analogy is going a long way off toward more complex components with impressive similarities between electronics and microfluidics. We will in particular explore the vast manifold of fluidic operations with passive and active fluidic components, respectively, as well as the associated mechanisms and corresponding applications. Finally, some relevant applications and an outlook will be cited and presented.     

Click functionalization of methacrylate‐based hydrogels and their cellular response

Methacrylate‐based hydrogels, such as homo‐ and copolymers of 2‐hydroxyethyl methacrylate (HEMA), have demonstrated significant potential for use in biomedical applications. However, many of these hydrogels tend to resist cell attachment and growth at their surfaces, which can be detrimental for certain applications. In this article, glycidyl methacrylate (GMA) was copolymerized with HEMA to generate gels functionalized with epoxide groups. The epoxides were then functionalized by two sequential click reactions, namely, nucleophilic ring opening of epoxides with sodium azide and then coupling of small molecules and peptides via Huisgen's copper catalyzed 1,3‐dipolar cycloaddition of azides with alkynes. Using this strategy it was possible to control the degree of functionalization by controlling the feed ratio of monomers during polymerization. In vitro cell culture of human retinal pigment epithelial cell line (ARPE‐19) with the hydrogels showed improved cell adhesion, growth and proliferation for hydrogels that were functionalized with a peptide containing the RGD sequence. In addition, the cell attachment progressively decreased with increasing densities of the RGD containing peptide. In summary, a facile methodology has been presented that gives rise to hydrogels with controlled degrees of functionality, such that the cell response is directly related to the levels and nature of that functionality. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1781–1789     

Fabrication of microfluidic chip using micro‐hot embossing with micro electrical discharge machining mold

This study develops an improved method for generating aluminum mold inserts used in the replication of polymer‐based microfluidic chip. Since molding masters that are suitable for microfluidic chip replication must have features whose dimensions are of the order of tens to hundreds of microns, micro electrical discharge machining is employed herein to fabricate an aluminum mold insert of a microfluidic chip. The width and depth of the aluminum mold insert for the microfluidic chip are 61.50 and 49.61 µm, respectively. The surface roughness values of the microchannel and the sample reservoir in aluminum mold insert for the microfluidic chip are 53.9 and 34.3 nm, respectively. PMMA material is adopted as the molded microfluidic chip that is produced by micro‐hot embossing molding. The PMMA material can replicate the microchannel and sample reservoir very well when the aluminum mold insert is used in micro‐hot embossing molding. The results indicate that the most important parameter in the replication of molded microfluidic chip is the embossing pressure, which is also the most important parameter in determining the surface roughness of the molded microfluidic chip. Copyright © 2010 John Wiley & Sons, Ltd.     

Staudinger–Vilarassa reaction versus Huisgen reaction for the control of surface hydrophobicity and water adhesion

Surface modifications are keys for a great number of applications. In order to perfectly control the surface properties, it is important to control the modification pathways. Two general pathways can be described in order to introduce modification on surfaces: the post‐strategies and the ante‐strategies. In this work, we focus on the comparison between the Huisgen and the Staudinger–Vilarrasa reaction for both post‐surface and ante‐surface modifications. Here, we focused on the possibility to use both two reactions to obtain superhydrophobic and oleophobic properties. This work includes monomer synthesis, surface modifications with alkyl, aryl or perfluoroalkyl chain. Copyright © 2016 John Wiley & Sons, Ltd.     

Oligonucleotides Containing 7‐Deaza‐2′‐deoxyinosine as Universal Nucleoside: Synthesis of 7‐Halogenated and 7‐Alkynylated Derivatives,Ambiguous Base Pairing,and Dye Functionalization by the Alkyne–Azide ‘Click’ Reaction

Oligonucleotides containing 7‐deaza‐2′‐deoxyinosine derivatives bearing 7‐halogen substituents or 7‐alkynyl groups were prepared. For this, the phosphoramidites 2b – 2g containing 7‐substituted 7‐deaza‐2′‐deoxyinosine analogues 1b – 1g were synthesized (Scheme 2). Hybridization experiments with modified oligonucleotides demonstrate that all 2′‐deoxyinosine derivatives show ambiguous base pairing, as 2′‐deoxyinosine does. The duplex stability decreases in the order C_d>A_d>T_d>G_d when 2b – 2g pair with these canonical nucleosides (Table 6). The self‐complementary duplexes 5′‐d(F⁷c⁷I‐C)₆, d(Br⁷c⁷I‐C)₆, and d(I⁷c⁷I‐C)₆ are more stable than the parent duplex d(c⁷I‐C)₆ (Table 7). An oligonucleotide containing the octa‐1,7‐diyn‐1‐yl derivative 1g , i.e., 27 , was functionalized with the nonfluorescent 3‐azido‐7‐hydroxycoumarin ( 28 ) by the Huisgen–Sharpless–Meldal cycloaddition ‘click’ reaction to afford the highly fluorescent oligonucleotide conjugate 29 (Scheme 3). Consequently, oligonucleotides incorporating the derivative 1g bearing a terminal C?C bond show a number of favorable properties: i) it is possible to activate them by labeling with reporter molecules employing the ‘click’ chemistry. ii) Space demanding residues introduced in the 7‐position of the 7‐deazapurine base does not interfere with duplex structure and stability (Table 8). iii) The ambiguous pairing character of the nucleobase makes them universal probes for numerous applications in oligonucleotide chemistry, molecular biology, and nanobiotechnology.     

Synthesis of Polystyrene and Poly(4‐vinylpyridine) Mixed Grafted Silica Nanoparticles via a Combination of ATRP and CuI‐Catalyzed Azide‐Alkyne Click Chemistry

Binary polystyrene and poly(4‐vinylpyridine) mixed grafted silica nanoparticles (PSt/P4VP‐g‐SNPs) are fabricated using Cu^I‐catalyzed azide‐alkyne Huisgen cycloaddition (CuAAC) via grafting‐to method. Azide‐terminated PSt and P4VP are synthesized via post‐ and pre‐atom transfer radical polymerization modification, respectively. Then, the polymers are simultaneously anchored onto alkyne‐modified SNPs by CuAAC yielding mixed brushes as shown by Raman spectroscopy, dynamic light scattering, and thermogravimetric analysis. To the best of our knowledge, this is the first report of simultaneously grafting two distinct polymer chains to synthesize mixed grafted silica nanoparticles using CuAAC technique via grafting‐to method.

     

Quantitative amine functionalization of polymeric organolithium compounds with 3‐dimethylaminopropyl chloride in the presence of lithium chloride

The addition of lithium chloride promoted the coupling reaction of hydrocarbon solutions of poly(styryl)lithium (PSLi) and poly(isoprenyl)lithium (PILi) with 3‐dimethylaminopropyl chloride to form the corresponding ω‐dimethylamino‐functionalized polymers. Quantitative amine functionalization was achieved for PSLi and PILi in the presence of 1 and 10 equivalents, respectively, of LiCl in benzene; the functionalization efficiency was only 67% for PSLi and 85% for PILi in the absence of LiCl. The polymer products were characterized by size exclusion chromatography, thin‐layer chromatography, and amine end‐group titration. The pure amine‐functionalized polymers were isolated by silica gel column chromatography. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 145–151, 2000