Natural and bioinspired nanostructured bactericidal surfaces

Bacterial antibiotic resistance is becoming more widespread due to excessive use of antibiotics in healthcare and agriculture. At the same time the development of new antibiotics has effectively ground to a hold. Chemical modifications of material surfaces have poor long-term performance in preventing bacterial build-up and hence approaches for realising bactericidal action through physical surface topography have become increasingly important in recent years. The complex nature of the bacteria cell wall interactions with nanostructured surfaces represents many challenges while the design of nanostructured bactericidal surfaces is considered. Here we present a brief overview of the bactericidal behaviour of naturally occurring and bio-inspired nanostructured surfaces against different bacteria through the physico-mechanical rupture of the cell wall. Many parameters affect this process including the size, shape, density, rigidity/flexibility and surface chemistry of the surface nanotextures as well as factors such as bacteria specificity (e.g. gram positive and gram negative) and motility. Different fabrication methods for such bactericidal nanostructured surfaces are summarised. (C) 2017 The Authors. Published by Elsevier B.V

On-Chip Magnetic Bead and Nanoparticle Separation in Compound Droplet EWOD

A novel technique to manipulate, transport and separate magnetic beads and super-paramagnetic nanoparticles in compound droplets on open chip digital microfluidic platform using electrowetting on dielectric has been presented. Magnetic particles added in water-oil based compound droplet are used. The magnetic properties of particles and electrowetting forces are utilized to cause particle separation using magnetic and electric fields. This paper demonstrates magnetic particle concentration and separation in an open digital microfluidic platform using compound droplets. It provides a new paradigm to enhance liquid manipulation using compound droplets on lab-on-chip platforms

Effect of electrowetting induced capillary oscillations on coalescence of compound droplets

Hypothesis: Coalescence time depends on the drainage rate of the fluid-bridge separating the droplets. Drainage rate is determined by external forcing and properties of the surrounding fluid. Modulating external forcing using electrowetting induced interface motion should allow control of the drainage rate, thereby affecting the coalescence time. Hence, quick coalescence or prolonged non-coalescence can be obtained for compound droplets on the microfluidic lab-on-chip systems. Experiments: Using high-speed imaging, we have investigated the effect of electrowetting induced capillary oscillations on the coalescence of compound droplets consisting of water core encapsulated in an oil shell. A systematic study was performed by varying the shell viscosity and actuation parameters (i.e. amplitude, frequency and waveform). Findings: For actuated interface, we observed specific regimes of coalescence or non-coalescence, whereas in absence of actuation, coalescence was observed in finite time. Non-coalescence was attributed to the continuous modulation of the oil-bridge width, which was caused by the interface motion. Oil-bridge width modulation was seen to be dependent on the amplitude and shape of the excited capillary modes (axisymmetric and non-axisymmetric). These modes were tuned by the actuation parameters. This is the first report of controlling coalescence dynamics by using electrowetting induced interface motion. (C) 2018 Elsevier Inc. All rights reserved

A Novel Method for Fabricating Graphene Sensors in Channel for Biomedical Applications

Graphene is a 2D material possessing extraordinary electrical, mechanical and optical properties which paves way for biomedical applications. A well-known method to fabricate graphene-based devices is depositing graphene using chemical vapor deposition and transferring it to any substrate using polymer support like PMMA (Polymethyl methacrylate) or PDMS (Polydimethylsiloxane). In this process multiple wetting and drying steps are required which compromises the quality of graphene. Also, PMMA leaves residues that are difficult to remove. Here, we report a novel method to fabricate graphene sensors inside PDMS channels. In this method graphene/copper stack is bonded on a PDMS surface using mechanical pressure and temperature. This PDMS layer is then bonded to another PDMS substrate containing microchannel. Etchant is flown through the microchannel to etch the copper and obtain graphene on PDMS. The graphene obtained on PDMS is characterized using optical images, scanning electron microscopy and Raman spectroscopy. This is an easy, simple to use and scalable method to obtain graphene sensors inside microchannels for biomedical applications

Open‐Chip Droplet Splitting in Electrowetting

Electrowetting-on-dielectric (EWOD) has emerged as a powerful technique to perform on-chip droplet operations like transportation, dispensing, splitting, and mixing in sandwiched droplets. In contrast, open-chip droplet manipulation using electrowetting enables micro-total-analysis systems with multiple sensor integration and re-routing capabilities. Droplet splitting has been the bottleneck in developing open-chip platforms. Droplet splitting on an open-chip platform using electrowetting-on-dielectric is presented. An energy-based simulation model has been developed. It shows that splitting a sessile water droplet is impossible on an open-chip configuration because of the low pad contact angle requirement. Low contact angles cannot be achieved due to contact angle saturation in electrowetting. It is experimentally shown that splitting is possible if the droplet is engulfed in an oil shell (i.e., in compound droplets). The planar electrode configurations and regime of electrowetting numbers for which splitting can be achieved are identified. It is observed that larger gaps and higher electrowetting numbers favor symmetrical splitting because the electrostatic force driving the actuation is significantly higher than the retarding interfacial forces. Conversely, asymmetrical splitting has been obtained when the actuation force is barely sufficient. Further the splitting of surfactant-loaded single-phase sessile droplets is demonstrated and a preferential surface charging phenomenon is explained

3D Die Level Packaging for Hybrid Systems

The aim of this work is to develop and optimize processing technologies required for 3-D die level packaging of hybrid systems including MEMS and MOS components. In this paper we report the process development for stacking of ultra-thin silicon dies (as low as 10 mu m) and a basic 5 mu m thick MEMS device (Cantilever). SU-8 has been used as the patternable dielectric filler between the device layers

Multi-droplets non-coalescence on open-chip electrowetting platform

The droplet non-coalescence is an interesting phenomenon that is observed in nature. This phenomenon of non-coalescence is slightly counter-intuitive as we expect liquid interfaces of the same surface tension to merge when they come in contact. However, with the help of modulating oil film in between the liquid interface, non-coalescence is observed for long durations. In this work, we have achieved the non-coalescence of multiple compound droplets on a coplanar EWOD device. The effect of droplet volume on the non-coalescence phenomenon has been studied in two-droplet systems. We have obtained the non-coalescence regime map for different operating parameters of applied voltage and frequency. We have also explored three-droplet systems and obtained a non-coalescence regime. This open-chip coplanar EWOD device configuration can be used to scale up this phenomenon to multiple droplets

Ice area export from Laptev Sea Feb - May, 1992 - 2014

Manipulating droplets of biological fluids in an electrowetting on dielectric (EWOD)-based digital microfluidic platform is a significant challenge because of biofouling and surface contamination. This problem is often addressed by operating in an oil environment. We study an alternate configuration of sessile compound droplets having an aqueous core surrounded by a smaller oil shell. In contrast to the conventional EWOD platform, an open digital microfluidic platform enabled by the core–shell configuration will allow electrical, mechanical, or optical probes to get unrestricted access to the droplet, thus enabling highly flexible and dynamically reconfigurable lab-on-chip systems. Understanding droplet oscillations is essential as they are known to enhance mixing. To our knowledge, this is the first study of axisymmetric and nonaxisymmetric oscillations of compound droplets actuated using EWOD platforms. Mode shapes for both axisymmetric and nonaxisymmetric oscillations were studied and explained. Enhancement in the axisymmetric oscillation of the core by decreasing the shell volume was obtained experimentally and modeled theoretically. Smaller shell volumes reduce the damping losses, allowing the appearance of nonaxisymmetric modes over a larger range of operating parameters. The oscillation frequency regime for obtaining prominent nonaxisymmetric oscillations for different shell volumes was identified. Compound droplets provide a mechanism to reduce biofouling, sample contamination, and evaporation. We demonstrate axisymmetric and nonaxisymmetric oscillations of compound droplets with the biological core of red blood cells, providing crucial first steps for promoting applications such as rapid efficient assays, mixing of biological fluids, and fluidic photonics on hysteresis-free surfaces