Papers by Keyword: Soft Lithography

Abstract: Investigating the electrowetting behavior of droplets on structured surfaces provides insight in developing electric-driven microfluidic substrates and membranes. Microstructures and patterns inspired by nature could result in interestingly unique wettability and electrowetting phenomenon. In this work, the electrowetting of water droplets on a superhydrophobic leaf of desmodium (Desmodium spp) and its elastomeric replica were explored. An open electrowetting system consisted of an optical camera, platinum wire, and DC power supply with water microdroplets as test liquid was used to investigate the electrowetting behavior on the leaf. Soft lithography using elastomer was used to produce replica of the leaves. Natural cell-like patterns, including central protrusions and microhairs, contribute to the leaf's superhydrophobic properties (contact angle > 150°). The negative copy of the natural patterns generated via soft lithography produced a microstructured elastomeric film, showing a static contact angle of ~128°. Optical microscope images of the elastomeric copy revealed the successful duplication of the leaf’s surface features. Subsequent electrowetting experiments demonstrated a contact angle reduction of up to 15° and 9.5° for the natural leaf and its elastomeric replica, respectively. A pronounced electrowetting-driven droplet motion was observed on the leaf while droplet pinning was noted in the elastomer. These results offer new insights into the electrowetting phenomenon of microstructured surfaces for potential self-cleaning and water-trapping applications.

Abstract: Fabrication of patterns on silicon and gold via Dip-Pen Nanolithography (DPN) using silica sol as ink and the combination of DPN, soft lithography, and silica sol-gel to transfer patterns from silicon and gold to stainless steel were assessed. In addition, a comparison in terms of throughput and resolution of both protocols was performed. Optical, scanning electron and atomic force microscopy were used to characterize the patterns. Silica sol showed high resolution but low throughput when used to pattern directly on gold and silicon using DPN. The combination of DPN, silica sol-gel and soft lithography showed high throughput and resolution. The present experimental methodology was useful to create patterns on a surface and transfer them to another surface of interest, which may serve as a biomaterial surface modification model.

Abstract: Sub-wavelength antireflective structures are fabricated by using a soft roll-to-plate nanoimprinting lithography. The proposed methodology employs a modified polyurethane acrylate as a flexible mold due to its high resolution, chemical inertness, polymerization characteristics, and its non-wetting, very low surface energy. Large-format (750mm x 750mm) plastic film with the recombined double-sided sub-wavelength structures is obtained, which has fascinating broadband antireflective effect. The roll-to-plate ultra-voilet nanoimprinting provides the capability of patterning sub-100nm structures, a short period of process time and allows the fabrication of sub-wavelength structure on a large number of flexible or rigid substrates in an economic fashion.

Abstract: A simple design of a microchamber for use in reacting assays with limited sample availability has been proposed, analyzed using COMSOL 3.5 Multiphysics simulation and fabricated using soft-lithography technique . The design is based on differential pressure drop flow using capillary effect concept which has facilitated a number of interesting flow phenomena in micro-domains. For an average pressure drop of about 100/m in the setup, flow rates of bout 0.5 to 0.8 μl/s were obtained. The component a microchamber, three designs were tested (50, 70, 90 microns in width) to give a continuous open circuit flow. The system was designed and fabricated for continuous flow across sensing element where there is a requirement for low residence time due to fast reaction/diffusion rates.Also in this paper, is a sensitive and selective, also rapid, reliable, cost-effective, and suitable for in situ analysis polymer biosensor for new bio molecular approach for cancer and cancer related diseases detection at the early stage is demonstrated.

Abstract: A new straightforward approach for the rapid prototyping and low cost development of diffraction gratings for remote chemical gas sensing is presented. Sol gel matrices incorporating various salts, as well as specially designed polymers are employed and investigated for sensors' implementation for the detection of chemical agents under a remote point sensing scheme. The interaction between the hybrid materials and the measurands results in a reversible change of their optical characteristics that consequently modifies the gratings diffraction efficiency, resulting in an enhanced sensing ability and a stable operation.

Abstract: In this paper, we improved the design of a membrane peristaltic micropump. The pump was driven by a rotating motor with magnetically attracted steel balls on top. The size of the micropump was significantly reduced to realize small flow rate and high pressure, to serve for precision delivering applications. Testing results showed that the pump can realize small flow rate from 0.93 to 12.73 μL/min, with very high linearity. The back pressure could reach more than 83 kPa until the PDMS (polydimethylsiloxane) channel structure was destroyed under high pressure. The pulsation problem of the peristaltic pump was also mentioned, as well as the possible solution to deliver a certain amount of small sample volume.

Abstract: Traditional cell-based assays such as cell immunoassay that utilizes plastic (chamber slides, dishes, microtiter plates), Magnetic bead, enzyme-linked immunsorbent assays (ELISA) [1], FACS cell sorting is labor intensive, time consuming, and requires a large numbers of cells or reagents. In this report, a microfluidic device integrated with cell culture, washing, fixation, and antigen-antibody reaction is presented for high-throughput immunoassay. Using this microfluidic device, each assay can be performed on a small number of cells and nanolitre or picolitre of reagents, this is particularly beneficial for rare or expensive cell types such as stem cells, or flow sorted cell populations. The capability of the microfluidic device was demonstrated for seeding human umbilical cord blood mesenchymal stem cells (UC-MSCs) in chambers and detecting the expression of surface markers (CD34, CD44, CD45, CD73, CD105, HLA-DR) by immunofluorescence assay.

Abstract: Metal deposition on self-assembled monolayers (SAMs) with different terminal organic functional groups is a growing area of research and the metal-organic interface has been extensively studied in the past two decades. Apart from impacting existing technologies, it may have a profound impact on the emerging future technologies such as molecular electronics. The morphology of the deposited metals is strongly influenced by the nature of the chemical interactions occurring at the interface of the organic functional group (OFG) of the SAM and the deposited metal. Our interest for such studies stems from different perspective, as we are interested in determining the impact of the interface on the morphology and hence the magnetic properties of the deposited magnetic materials. We have sputtered a magnetic material, permalloy (Ni79Fe21), on self-assembled monolayers of polar and nonpolar molecules, and have observed contrasting magnetic behaviors of permalloy on these surfaces. We have observed the formation of uniform film on polar regions and cluster are formed on nonpolar regions. Further investigations reveal that the cluster formation gives rise to superparamagnetism, while the uniform film shows a usual ferromagnetic behavior. The observed contrast in morphology and magnetism of Py is attributed to different growth mechanisms arising from difference in polarity of the SAM surfaces.

Abstract: A liquid tunable diffractive/refractive hybrid lens which combines the use of high precision diamond turning and soft lithography is developed in this work. This diffractive/refractive hybrid lens comprises a Fresnel lens and a tunable refractive lens automatically aligned during the fabrication process. Multiple PDMS hybrid lens devices can be fabricated from the diamond-turned master mould and AFM results show that the surface quality of the PDMS lenses meets the requirements for optical purposes. The hybrid lens is tested with a green laser (λ = 532nm) and experimental results demonstrate a tunability of more than 20mm.

Abstract: Regular arrays of micro-pillars and nano-grooves structures on the silicon wafer are fabricated by using soft lithography, and the three dimension morphology of textured surface is observed by using scanning electron microscopy (SEM) and atomic force microscope (AFM). The static water contact angles are measured by using contact angle meter to characterize the wettabilities of these surfaces. To investigate how the presence of topography and the variations of wettability affect the haemocompatibility of textured surface contacted with blood, different patterned surfaces are designed and fabricated, and blood platelet adhesion test is carried out on these surfaces. The adhesion and coagulation of platelets are inspected by scanning electron microscopy (SEM). Experimental data presented in this paper indicate that different surface roughness and wettability are the important factors for blood platelet adhesion. The amount of adsorbed blood platelet is low on textured surfaces, compared with that on the flat surface. Especially, there is no coagulation and activation on the surface with nanometer grooves. That is to say, the superhydrophobic surface is apt to decrease blood platelet adhesion. The study suggests that surface with suitable wettabililty and textured structures exhibits superior blood compatibility.