Surface tension assisted lithography (STAL): a novel microfabrication techniques for microfluidics

Many fundamental fields of research have highly advanced in the last three decades due to the unprecedented precision and complexity enabled by the microfabrication technology. Fabrication of 3D microstructures such as simple spherical and cylindrical shapes is highly desired to accurately mimic the natural phenomena in a research environment. Surprisingly, 3D microstructures are commonly avoided if devices are to be realised using typical, planar microfabrication methods due to the limited capabilities of producing 3D structures. In fact, photolithography, the traditional and the most common method for mass-production of microfabricated systems, allows definition of almost arbitrarily complex shapes on planar surfaces, but has limited capability of producing 3D structures. Several other non-planar microfabrication techniques have been reported such as direct laser writing, inclined UV lithography, and the surface wrinkling. However, none can be considered as a true contender to the photolithography, due to the fact that each of them is subject to some combination of the following problems: costly infrastructure, long write times, poor feature addressing, poor resolution, and lack of control. This thesis explores the potential of utilising surface tension driven techniques for 3D microfabrications. The surface tension driven techniques appear promising, due to the key advantages namely, exceptionally smooth surface, cost effectiveness, and self alignment properties. Until now, little attention has been given to the surface tension driven techniques. The major contributions of this thesis include introducing, characterising, and implementing of the novel Surface Tension Assisted Lithography (STAL) technique for 3D microfabrication technique. STAL consists of a sequence of the following steps: soft lithography physically patterns the polymer, then UV exposure defines the reflow container, then a thermal treatment solidifies the container and reflows the unexposed region of the polymer, and finally an exposure ensures that the reflowed structures retain their shape. It is shown that STAL provides independent control over the height and diameter of the semi-spherical structures. There are many possible applications for 3D structures, even in the form of simple spherical caps. One of the applications of semi-spherical structures is demonstrated by fabricating novel semi-spherical microelectrodes for dielectrophoretic manipulation cells. Advantages of semi-spherical microelectrodes over 2D configurations are demonstrated through a series of experiments and numerical simulations. The potential of STAL to produce more complicated systems such as hybrid structures with planar posts integrated into STAL structures is also explored. A simplified model has been developed to predict the defection of the posts under surface tension. In the closing chapter of this thesis, the opportunities to extend STAL for producing more complex 3D structures are identified. Fabrication of convex 3D features with complex containers in the scale of conventional microfluidic structures is investigated. And also, the concept of patterning STAL structures photolithographically is explored. This combination can offer an opportunity to produce structures such as suction cups for hydrodynamic cell trapping

Microengineered structures for rapid automatic loading of optical fibre segments

We present a technique to rapidly and automatically produce sections of optical fibre and load them into arrays such that they can be nano-imprinted in parallel. The technique makes use of automated fibre feeding, cutting and alignment with microfabricated groove arrays. The system is analyzed and optimized and it is found that the geometry of the arrays themselves is a critical factor. Three types of array are investigated-simple grooves, grooves with lateral funnels at the input, and bulk silicon machined V-groove arrays with funnels in both lateral and vertical dimensions. It is found that the incorporation of funnels significantly increases the accuracy of loading, overcoming the need for precise alignment, such that a throughput nearing 1000 fibre segments an hour can be achieved. This system forms part of a sequence of novel processes for the production of nano-photonic sensors

Elastomer-based pneumatic switch for radio frequency microdevices

This paper reports the realization and characterization of a pneumatic microswitch integrated with a high-frequency radio frequency (RF) transmission line on an elastomer substrate. A process for the fabrication of low-loss RF coplanar transmission lines on flexible elastomeric polydimethylsiloxane (PDMS) substrates was developed, and devices realized using this process were used to determine the characteristics of PDMS as an RF substrate with uniform low loss and low dielectric constant being measure

Mixing characterisation for a serpentine microchannel equipped with embedded barriers

This paper describes the design, simulation, fabrication and experimental analysis of a passive micromixer for the mixing of biological solvents. The mixer consists of a T-junction, followed by a serpentine microchannel. the serpentine has three arcs, each equipped with circular barriers that are patterned as two opposing triangles. >The barriers are engineered to induce periodic perturbations in the flow field and enhance the mixing. CFD (Computational Fluid Dynamics) method is applied to optimise the geometric variables of the mixer before fabrication. The mixer is made from PDMS (Polydimethylsiloxane) using photo- and soft-lithography techniques. Experimental measurements are performed using yellow and blue food dyes as the mixing fluids. The mixing is measured by analysing the composition of the flow\u27s colour across the outlet channel. The performance of the mixer is examined in a wide range of flow rates from 0.5 to 10 µl/min. Mixing efficiencies of higher than 99.4% are obtained in the experiments confirming the results of numerical simulations. The proposed mixer can be employed as a part of lab-on-a-chip for biomedical applications

Mechanically tolerant fluidic split ring resonators

Flexible resonators are crucial elements for non-planar, conformal and curved or movable surfaces in flexible high frequency electronic environments. Here, we demonstrate a stretchable, bendable, twistable and reversibly deformable split ring resonator (SRR) operating at ∼3 GHz. The mechanical and electrical performance of the SRR was achieved by encapsulating liquid metal (galinstan) in a microfluidic channel of highly elastic polydimethylsiloxane. Applying mechanical deformation (bending, stretching and twisting) to the SRR results in minimal deviation of the transmission response. This offers a stable and predictable response for flexible electronic applications where mechanical deformation or conformity is inherent

Antioxidant,anti-acetylcholinesterase, and anticancer activities of four Polygonum species from Istanbul

© 2021,International Food Research Journal.All Rights ReservedPolygonum species are used in traditional medicine in many countries; some are also consumed as vegetables in Turkey. The ethanolic, methanolic, and chloroform extracts of four Polygonum species growing in Istanbul, namely P. aviculare, P. patulum subsp. pulchellum, P. lapathifolium, and the only endemic species P. istanbulicum were evaluated for their antioxidant, anti-acetylcholinesterase (AChE), and anticancer potentials. The total phenolic and flavonoid contents of the extracts were determined by Folin-Ciocalteu and aluminium chloride methods, respectively. The antioxidant capacities of the extracts were determined using 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging and ferric-reducing antioxidant power (FRAP) assays. The AChE inhibitory activities of the extracts were determined using the Ellman method. Each extract was screened for cytotoxic activity against NRK-52E and HeLa cervical cancer cell lines using the MTT assay. Among the extracts screened, ethanolic extract of P. istanbulicum showed the highest total phenolic (207.03 ± 14.12 mg GAE/g extract) and total flavonoid (124.95 ± 7.84 mg CE/g extract) contents, and antioxidant activity (DPPH EC50, 8.09 ± 0.50 mg/mL). The chloroform extract of P. lapathifolium exhibited the lowest total phenolic (22.33 ± 3.05 mg GAE/g extract) and total flavonoid (11.66 ± 0.36 mg CE/g extract) contents, and antioxidant activity (DPPH EC50, 218.44 ± 24.46 mg/mL). The extracts exhibited AChE inhibitory activity in a dose-dependent manner, particularly the ethanolic extract of P. istanbulicum which displayed strongest inhibition against AChE (88.2 ± 3.44%). AChE inhibition was minimal (32.19 ± 2.09 to 48.34 ± 3.41%) in the chloroform extracts. All ethanolic extracts revealed cytotoxic activity toward HeLa cells, while they were not cytotoxic toward NRK-52E cells. The ethanolic extract of P. lapathifolium showed the most potent cytotoxicity against HeLa cells (IC50, 8.70 ± 1.35 µg/mL). Results suggested that ethanol was the best solvent for extracting the phenolic, antioxidant, and anti-AChE compounds, and P. istanbulicum may be a potential source of these compounds. Further investigations are nevertheless required to identify the bioactive compounds present in Polygonum specie

A novel Surface Tension Assisted Lithography (STAL) technique for microfabrication of 3D structures

Abstract not availabl

Design, characterization and application of a novel mono-layer pin-microvalve for microfluidic devices

Valves are one of the key components in microfluidic devices to control the fluid flow. In this paper we introduce a novel manual pin-valve which can operate in both analogue (partially close) and digital (on/off) states. We also demonstrate implementation of this pin-valve in a hydrodynamic flow focusing (HFF) device

Dielectrophoresis with 3D microelectrodes fabricated by surface tension assisted lithography

This paper demonstrates the utilization of 3D semispherical shaped microelectrodes for dielectrophoretic manipulation of yeast cells. The semispherical microelectrodes are capable of producing strong electric field gradients, and in turn dielectrophoretic forces across a large area of channel cross-section. The semispherical shape of microelectrodes avoids the formation of undesired sharp electric fields along the structure and also minimizes the disturbance of the streamlines of nearby passing fluid. The advantage of semispherical microelectrodes over the planar microelectrodes is demonstrated in a series of numerical simulations and proof-of-concept experiments aimed toward immobilization of viable yeast cells

Characterization of high fluid strain micro contractions to study the stress on biological fluids

Microfluidics has the potential to enhance the understanding of the biological fluids under strain, due to the laminar nature of the fluid and the possibility to mimic the real conditions. We present advances on charaterization of a microfluidic platform to study high strain rate flows in the transport of biological fluids. These advances are improvements on the reproduction of a  constant extensional strain rate using micro contractions and development of 3D numerical models. The micro geometries have been fabricated in polydimethyl siloxame (PDMS) using standard soft-lithography techniques with a photolithographically patterned mold. A comparison of some microcontractions with different funnel characteristics is presented. The Micro Particle Image Velocimetry technique has been applied to validate the numerical simulations. We demonstrate the use of microfluidics in the reproduction of a large range of controllable extensional strains that can be used in the study of the effect of flow on biological fluids