An Inexpensive Microfluidic PDMS Chip for Visual Detection of Biofilm-forming Bacteria

Aims: Design and assembly of an inexpensive microfluidic PDMS chip for visual detection of cell adhesion and biofilm formation. Study Design: Three different styles of microchannels (2.6, 5.0, and 11.5 μl volumes) were designed, fabricated and tested for adhesion and biofilm formation in a microfluidic system. The pressure drop measurements system includes a bio-Ferrograph connected to the PDMS microchannel via a syringe and a pressure transducer. Methodology: Microfluidic chips were fabricated using Polydimethylsiloxane (PDMS) by means of soft lithography. Different cell densities of E.coli K12 cells were introduced to investigate adhesion and biofilm formation at different time intervals. Stabilization time and hydraulic resistance were obtained via a Bio-Ferrograph connected to a pressure transducer. Results: PDMS microfluidic volume (2.6 μl) failed to generate noticeable biofilm, while slight and greatest yield occurred with PDMS microchannels (5.0, and 11.5 μl), respectively, and could detect as low as 26 cells in 11.5 μl microchannel. As incubation time and/or initial cell density increases, cell adhesion increased, illustrated by crystal violet color intensity. High stabilization time (3 h) didn’t allow for bacterial attachment and cultivation inside the microchannel (2.6 μl) while lower stabilization time (10 min) yielded the highest capacity of cell adhesion in microchannel (11.5 μl). Conclusions: We developed a microfluidic chip with low stabilization time and hydraulic resistance, thus offering more volume for adhesion of bacterial cells and biofilm formation. It allowed bacterial cultivation without any addition of nutrients. The microfluidic chip provides a platform to monitor biofilm growth and can be integrated in situ investigations for biological systems, food biotechnology and other industrial biotechnology applications. This would allow a non-destructive and non-invasive monitoring of the biofilm-forming bacteria inside the PDMS microfluidic chip. This work opens opportunities for further investigations of pressure drop phenomena in microchannels that would otherwise go unnoticed in macro scale measurements

Partnership for International Research and Education in Microfluidic Technology with Applications in Point of Care Diagnostic

This poster summarizes the research highlights of a project conducted as part of an National Science Foundation (NSF) partnership for research and education. The objective of this multidisciplinary, international project was to conduct research on microfluidic technology and applications. The project team is comprised of participants from the University of Rhode Island and the Technical University of Braunschweig in Germany. The research focuses on the following four tasks: Task 1 – Discovery of disease biomarkers; Task 2 –Streaming based microfluidic platform for pumping, mixing, separation and detection; Task 3 – Development of rapid, quantitative and sensitive microfluidic fluorescence immunosensors for point-of-care diagnostics; and Task 4 – Microfluidic ocean based applications. The following elements are examined in Task 3: Enzyme-linked Immunosorbent Assay (ELISA) by manipulation of magnetic beads in microfluidic channel network; development of charged coupled device (CCD) contact imaging system for lab-on-a-chip biosensors for detection of disease biomarkers; a portable and hand-held lab-on-a-chip system for detection of disease biomarkers; on-chip valveless sequential sample loading, mixing, and micro-pneumatic valves; and numerical simulation of microfluidics using dissipative particle dynamics

Experiments of contact melting under vibration within rectangular enclosure

The results of contact melting experiments in rectangular enclosures with phase change materials (PCM) of n-octadecane are reported with and without vibration. Isothermal wall condition is maintained on the top, bottom and two side walls of the test cells, while the remaining front and back walls are well insulated by double-layer Plexiglas. The cross sections of test cells are 52.2 mm x 130.5 mm, 82.5 mm × 82.5 mm, and 130.5 mm × 52.2 mm, respectively. The solid-liquid interface contour is videotaped to obtain the melted volume fraction. It is shown that melting rates are increased under vibrating conditions and melting enhancement is increased with the acceleration of vibration. Compared to the stationary experiments, the maximum melting rate enhancement of 95 percent is observed. Aspect ratio is an important parameter for contact melting with and without vibration. Preliminary experiments also show that the horizontal vibration increases the melting rate more than the vertical vibration

Experimental study of effect of vibration on ice contact melting within rectangular enclosures

Experiments on ice contact melting within a rectangular enclosure under vibrating conditions are performed. Isothermal wall condition is maintained on the test cells with aspect ratios of 0.4, 1.0. and 2.5, respectively. It is shown that melting rates are increased under vibrating conditions and melting enhancement is proportional to the acceleration of vibration. Compared to the stationary experiments, the maximum melting rate enhancement of 170 % is observed. Aspect ratio plays an important role in melting process and the lowest melting rates occur in both stationary and vibrating conditions for aspect ratio of 1.0. The relative melting enhancement by vibration for both high and low aspect ratios are significant. The increase in melting due to vibration is more pronounced for the low Stefan numbers. Preliminary experiments show that horizontal vibration can be more effective than vertical vibration to enhance the melting rate

A streaming flow based Lab-on-chip platform technology

Numerous studies on microfluidics diagnostic devices have been published in the last decade. Although the first generation of Lab-on-chip (LOC) devices was functional in 1999, some of the promises of microfluidics (integration of all functions on a chip and the commercialization of truly handheld microfluidic instruments) have yet to be fulfilled. The major challenges of LOC technology include costeffective pumping, function integration, multiple detection, and system miniaturization. In this paper, we propose a novel and simple streaming-based LOC technology that may have potential to directly address these challenges. The phenomenon of the flow streaming is found in zero-mean velocity oscillating flows in a wide range of channel geometries. Although there is no net flow (zero-mean velocity) across the channel, a discrepancy in velocity profiles between the forward flow and backward flow causes fluid particles near the walls to drift toward one end, while fluid particles near the centerline drift to the other end. We hypothesize that the unique characteristics of flow streaming could be used: 1) to transport, mix and separate particles/molecules/ bacterium/cells entrained in flows; 2) to perform multi-channel/generation micro-array sample distributions; and 3) to achieve function integrations and biomarker detections. Mechanisms of using flow streaming to achieve the various LOC functions are described. Preliminary results are presented to demonstrate the potential of this technology for LOC applications. Copyright © 2008 by ASME

A concept of pumpless convective micro/micro channel cooling technology

The sustained drive for faster and smaller micro electronic devices has led to a considerable increase in power density. The ability to effectively pump and enhance heat transfer in micro/mini channels is of immense technological importance. The micro channel heat exchanger has great advantages for high heat flux applications due to their high surface-to-volume ratio. Unfortunately, the small dimension of the micro channel leads to a large pressure drop and low Reynolds flow, which is usually associated with the low heat transfer coefficient. Therefore, forced convection micro heat exchangers require advanced micro pumping and heat transfer enhancement technologies. Using oscillatory flow to enhance the convective heat transfer coefficients in micro/mini channels is one of many new concepts and methodologies that have been proposed. In this paper, we propose a novel and simple streamingbased micro/mini channel cooling technology. The phenomenon of the flow streaming are found in zero-mean velocity oscillating flows in a wide range of channel geometries. Although there is no mass flow (zero-mean velocity) passing through the channel, the discrepancy in velocity profiles between the forward flow and backward flow causes fluid particles near the walls to drift toward one end while fluid particles near the centerline drift to the other end. We hypothesize that the unique characteristics of flow streaming could be used to achieve the convective cooling. The advantages of the streaming based convective cooling technique includes enhanced heat transfer coefficient, pumpless, and cost-effective. Preliminary results of scaling analysis and computer simulations are presented to demonstrate the potential of the stream based technology for micro cooling applications. Copyright © 2008 by ASME

Suspended particle streaming in an oscillatory mini/micro bifurcation network flow

Using of oscillatory flow and phase change material (PCM) microcapsules to enhance heat transport efficiency in micro-/minichannels are among many new methodologies that have been proposed. In this paper, we propose a novel and simple heat spreader concept that integrates the technologies of oscillating flow streaming and PCM microcapsules. Phenomena of the flow streaming can be found in oscillating, zero-mean-velocity flows in many channel configurations. The pumpless flow can be generated by simple heating or by channel wall vibration. Discrepancy in velocity profiles between the forward and backward flows causes fluid and particles suspended in fluids near the walls to drift toward one end while particles near the centerline drift to the other end. Preliminary work of computer simulations on fluid and suspended particle streaming in multichannel mini-bifurcation networks flows has been conducted and verified by visualization experiments. Results show that flow streaming with PCM microcapsules entrainment has the potential to be used as a cost-effective technology in a heat spreader

Streaming and phase-change material microcapsules-based mini/microheat spreader

Use of oscillatory flow and phase-change material (PCM) microcapsules to enhance heat transport efficiency in micro/minichannels is among many new concepts and methodologies that have been proposed. In this paper, we propose a novel and simple heat spreader design concept that integrates the technologies of oscillating flow streaming and PCM microcapsules. Phenomenon of the flow streaming can be found in oscillating, zeromean- velocity flows in many channel configurations. The pumpless bidirectional streaming flow can be generated by heating instability oscillation or by displacement of a lead zirconate titanate diaphragm. Discrepancy in velocity profiles between the forward and backward flows causes fluid and PCM microcapsules, suspended in the fluid near the walls, to drift toward one end while particles near the centerline move toward the other end. Flow streaming is a common mechanism in many biological systems but an innovative feature for heat transfer devices. We conducted preliminary work on scale analysis and computer simulations of suspended PCM microcapsules streaming in mini/microbifurcation networks. Computer simulated microcapsules distribution patterns are verified by visualization experiments reported in the literature. This work demonstrates that flow streaming with PCM microcapsule entrainment has the potential to be used as a costeffective technology for a heat spreader design