Amit Asthana

Facile single step fabrication of microchannels with varying size

In this report, we present a non-lithographic embedded template method for rapid and cost-effective fabrication of a monolithic microfluidic device with channels of various sizes. The procedure presented here enables the preparation of microchannels with varying dimensions in a single device without using any sophisticated micromachining instrumentation. In addition, this non-lithographic technique has also been used to fabricate a multilayer-multilevel biopolymer microdevice in a single step. To demonstrate the versatility of the presented method, we have fabricated microfluidic devices with four different materials under different curing/cross linking conditions. We have also demonstrated the application of the fabricated device to generate structured copper alginate microbeads, in vitro protein synthesis in three phase flow, and alternate plugs with liquid spacers.

Bromo-oxidation reaction in enzyme-entrapped alginate hollow microfibers

In this article, the authors present the fabrication of an enzyme-entrapped alginate hollow fiber using a microfluidic device. Further use of enzyme-entrapped alginate hollow fibers as a biocatalytic microchemical reactor for chemical synthesis is also deliberated in this article. To ensure that there is no enzyme leaching from the fiber, fiber surfaces were coated with chitosan. To confine the mobility of reactants and products within the porous hollow fibers the entire fibers were embedded into a transparent polydimethylsiloxane (PDMS) matrix which also works as a support matrix. A vanadium-containing bromoperoxidase enzyme isolated from Corallina confusa was used as a model enzyme to demonstrate the use of these alginate hollow-fiber reactors in bromo-oxidation of phenol red to bromophenol blue at different dye flow rates. Stability of the entrapped enzyme at different temperatures and the effect of the chitosan coating on the reaction conversion were also studied. It was observed that molecules as big as 27 kDa can be retained in the matrix after coating with chitosan while molecules with molecular-weight of around 378 Da can still diffuse in and out of the matrix. The kinetic conversion rate in this microfluidic bioreactor was more than 41-fold faster when compared with the standard test-tube procedure.

DNA mutation analysis based on capillary electrochromatography using colloidal poly(N-isopropylacrylamide) particles as pseudostationary phase

Poly(N-isopropylacrylamide) (PNIPAM) is an interesting class of temperature sensitive, water soluble polymer that has a lower critical solution temperature (LCST) of 32 degrees C. Above the LCST, PNIPAM gets phase-separated and precipitates out from water. The fascinating temperature-sensitive property of PNIPAM has led to a growing interest in diverse fields of applications. Recently, capillary electrochromatography (CEC) has gained attention due to the wide range of applications based on the use of open tubular capillaries. In this paper, the use of phase-separated PNIPAM as a pseudostationary phase for CEC is demonstrated for the detection of single nucleotide polymorphisms (SNPs). Owing to the dynamic coating, the phase-separated PNIPAM particles did not require any immobilization technique and could exist as a mobile stationary phase in the open tubular capillary. The heteroduplex analyses of mutation samples could be successfully performed based on the phase-separated PNIPAM particles in the constructed CEC system. The CEC system, based on PNIPAM particles capable of having a narrow size distribution, shows great potential as an alternative to conventional DNA mutation systems.

Droplet-based microfluidics.

Droplet-based microfluidics or digital microfluidics is a subclass of microfluidic devices, wherein droplets are generated using active or passive methods. The active method for generation of droplets involves the use of an external factor such as an electric field for droplet generation. Two techniques that fall in this category are dielectrophoresis (DEP) and electrowetting on dielectric (EWOD). In passive methods, the droplet generation depends on the geometry and dimensions of the device. T-junction and flow focusing methods are examples of passive methods used for generation of droplets. In this chapter the methods used for droplet generation, mixing of contents of droplets, and the manipulation of droplets are described in brief. A review of the applications of digital microfluidics with emphasis on the last decade is presented.

Rapid and cost-effective fabrication of selectively permeable calcium-alginate microfluidic device using "modified" embedded template method.

In this paper, we have presented a non-lithographic embedded template method for rapid and cost-effective fabrication of a selectively permeable calcium-alginate (Ca-alginate) based microfluidic device with long serpentine delay channel. To demonstrate the versatility of the presented method, we have demonstrated two different strategies to fabricate serpentine long delay channels without using any sophisticated microfabrication techniques, in formal lab atmosphere. The procedure presented here, also, enables the preparation of a multilayered microfluidic device with channels of varying dimensions, in a single device without using any sophisticated micromachining instrumentation. In addition, we have also qualitatively studied the diffusion of small and large molecules from a Ca-alginate based microfluidic device and proposed a method to effectively control the out-flow of macro biomolecules from the crosslinked Ca-alginate matrix to create a selectively permeable matrix required for various biological and biomimetic applications, as mentioned in the Introduction section of this work.

Enhancement of the high-Tc phase in Bi-Ca-Sr-Cu-O by ceramic processing methods

Abstract Materials in the Bi-Ca-Sr-Cu-O superconductor system were prepared by melt-quenching. Results were obtained for materials doped with small amounts of Pb and Sb. A substantial increase in the yield of the high- T c (2223) phase, with a corresponding improvement in superconducting properties, was noted for specimens heat-treated at 848°C in an atmosphere of 10% O 2 and 90% Ar. The best specimens exhibited a T c (zero resistance) near 105 K and a large (∼ 90%) 2223 content. Experimental results are discussed in the context of phase and microstructure development, and the evolution of superconducting properties with heat-treatment.

Modulation of stem cell differentiation by the influence of nanobiomaterials/carriers.

Stem cells, either neural [NSCs] or mesenchymal [MSCs], possess tremendous untapped potential for cell therapy. Unlike the NSCs, MSCs are multi-potent and they have high self-renewal capability and broad tissue distribution. Since they do not produce significant immune rejection on post-transplantation; they are better suited for cell-based therapies. However, several critical issues need to be addressed to maximize stem cell-derived therapeutic effects. The key factor affecting the therapeutic application of stem cells is exposure to hostile conditions in vivo such as oxidative stress, which results in considerably low survival rate of these cells at transplanted sites, thereby reducing the therapeutic efficiency. Such limitation has led scientists to design clinically relevant, innovative and multifaceted solutions including the use of nanobiomaterials. Use of cytocompatible nanobiomaterials holds great promise and has gained attention of researchers, worldwide. Various nanobiomaterials are being explored to increase the survival efficiency and direct differentiation of stem cells to generate tissue-specific cells for biomedical research and futuristic therapies. These materials have superior cytocompatability, mechanical, electrical, optical, catalytic and magnetic properties. Non-invasive visualization of the biological system has been developed using magnetic nanoparticles and magnetic resonance imaging [MRI] approaches. Apart from viral vectors, non-viral carriers such as DNA nano carriers, single stranded RNA nanoparticles, liposomes and carbon nanotubes/wires are being exploited for gene delivery into stem cells. This article reviews potential application of various biocompatible nanomaterials in stem cell research and development.

Fabrication of porous SiC-based ceramic microchannels via pyrolysis of templated preceramic polymers

This article reports conversion chemistry of preceramic polymer to ceramic phase during the fabrication of high-temperature stable silicon carbide and silicon carbonitride monolithic porous microchannels. The micromolding in capillaries method is used to fabricate porous channels by the initial infiltration of a solution of 1.5-µm diameter silica spheres or 1-µm diameter polystyrene spheres into polydimethylsiloxane channels followed by filling the void space among the spheres by using viscous commercial polymeric precursors. Subsequently, the polymer-sphere composite channel was cured and pyrolysed at 1200 °C under inert atmosphere, and final wet etching step of silica spheres with 10% hydrofluoric acid solution developed the pore structures by removing the silica spheres, whereas polystyrene sphere decomposes at the early stage of pyrolysis.

Growth twins in Bi 2 Ca 1 Sr 2 Cu 2 O 8 superconductor single crystals

Large-scale twin structures in single crystal Bi{sub 2}Ca{sub 1}Sr{sub 2}Cu{sub 2}O{sub 8}(2122) are reported for the first time. Symmetrical 90{degree} (i.e., {ital a}-{ital b}) twins with a (110) type twin boundary were observed. A characteristic layer-growth morphology and jagged twin walls suggests that twin formation occurred layer by layer during crystal growth, i.e., the twins were growth twins. Hot-stage optical microscopy, x-ray diffraction, and electron microscopy results are discussed with reference to twin morphology.

A microfluidic device approach to generate hollow alginate microfibers with controlled wall thickness and inner diameter

Alginate is a natural polymer with inherent biocompatibility. A simple polydimethylsiloxane (PDMS) microfluidic device based self-assembled fabrication of alginate hollow microfibers is presented. The inner diameter as well as wall thickness of the microfibers were controlled effortlessly, by altering core and sheath flow rates in the microfluidic channels. The gelation/cross-linking occured while the solutions were ejected. The microfibers were generated spontaneously, extruding out of the outlet microchannel. It was observed that the outer diameter was independent of the flow rates, while the internal diameter and wall thickness of the hollow fibers were found to be functions of the core and sheath flow rates. At a constant sheath flow, with increasing core flow rates, the internal diameters increased and the wall thicknesses decreased. At a fixed core flow, when sheath flow rate increased, the internal diameters decreased and the wall thickness increased. The immobilization of enzymes in such hollow mi...