Microchannel fluid behavior using micropolar fluid theory

Journal ArticleIn this paper, we describe microchannel fluid behavior using a numerical model based on micropolar fluid theory and experimentally verify the model using micromachined channels. The micropolar fluid theory augments the laws of classical continuum mechanics by incorporating the effects of fluid molecules on the continuum. The behavior of fluids was studied using surface micromachined rectangular metallic pipette arrays. A downstream port for static pressure measurement was used to eliminate entrance effects. The numerical model of the micropolar fluid theory compares favorably with the experimental data

Integrated Lithographic Molding for Microneedle-Based Devices

This paper presents a new fabrication method consisting of lithographically defining multiple layers of high aspect-ratio photoresist onto preprocessed silicon substrates and release of the polymer by the lost mold or sacrificial layer technique, coined by us as lithographic molding. The process methodology was demonstrated fabricating out-of-plane polymeric hollow microneedles. First, the fabrication of needle tips was demonstrated for polymeric microneedles with an outer diameter of 250 mum, through-hole capillaries of 75-mum diameter and a needle shaft length of 430 mum by lithographic processing of SU-8 onto simple v-grooves. Second, the technique was extended to gain more freedom in tip shape design, needle shaft length and use of filling materials. A novel combination of silicon dry and wet etching is introduced that allows highly accurate and repetitive lithographic molding of a complex shape. Both techniques consent to the lithographic integration of microfluidic back plates forming a patch-type device. These microneedle-integrated patches offer a feasible solution for medical applications that demand an easy to use point-of-care sample collector, for example, in blood diagnostics for lithium therapy. Although microchip capillary electrophoresis glass devices were addressed earlier, here, we show for the first time the complete diagnostic method based on microneedles made from SU-8

Monitoring single heart cell biology using lab-on-a- chip technologies

Abstract There has been considerable interest in developing microsensors integrated within lab-on-a-chip structures for the analysis of single cells; however, substantially less work has focused on developing "active" assays, where the cell‘s metabolic and physiological function is itself controlled on-chip. The heart attack is considered the largest cause of mortality and morbidity in the western world. Dynamic information during metabolism from a single heart cell is difficult to obtain. There is a demand for the development of a robust and sensitive analytical system that will enable us to study dynamic metabolism at single-cell level to provide intracellular information on a single-cell scale in different metabolic conditions (such as healthy or simulated unhealthy conditions). The system would also provide medics and clinicians with a better understanding of heart disease, and even help to find new therapeutic compounds. Towards this objective, we have developed a novel platform based on five individually addressable microelectrodes, fully integrated within a microfluidic system, where the cell is electrically stimulated at pre-determined rates and real-time ionic and metabolic fluxes from active, beating single heart cells are measured. The device is comprised of one pair of pacing microelectrodes, used for field-stimulation of the cell, and three other microelectrodes, configured as an enzyme-modified lactate microbiosensor, used to measure the amounts of lactate produced by the heart cell. The device also enables simultaneous in-situ microscopy, allowing optical measurements of single-cell contractility and fluorescence measurements of extracellular pH and cellular Ca2+ from the single beating heart cell at the same time, providing details of its electrical and metabolic state. Further, we have developed a robust microfluidic array, wherein a sensor array is integrated within an array of polydimethylsiloxane (PDMS) chambers, enabling the efficient manipulation of single heart cells and real-time analysis without the need to regenerate either working electrodes or reference electrodes fouled by any extracellular constituents. This sensor array also enables simultaneous electrochemical and optical measurements of single heart cells by integrating an enzyme-immobilized microsensor. Using this device, the fluorescence measurements of intracellular pH were obtained from a single beating heart cell whose electrical and metabolic states were controlled. The mechanism of released intracellular [H+] was investigated to examine extracellular pH change during contraction. In an attempt to measure lactate released from the electrically stimulated contracting cell, the cause of intracellular pH change is discussed. The preliminary investigation was made on the underlying relationship between intracellular pH and lactate from single heart cells in controlled metabolic states

Protein Impregnated Polymer (PIP) Film Infrared Sensor Using Suspended Microelectromechanical Systems (MEMS) Pixels

The Air Force Research Laboratory Materials and Manufacturing Directorate have developed a novel protein impregnated polymer (PIP) suspension that changes resistivity as a function of absorbed infrared radiation. Due to this property, the PIP is a potential material for use as an uncooled bolometer, or thermal sensor. In this research, a thermally-isolated pixel design, sensor characterization methods, and sensor fabrication and processing steps were developed. To create a microbolometer, the PIP was applied to two prototype micro-electro-mechanical systems (MEMS) surface micro-machined structures. The first is a raised cantilever pixel array that uses residual stress polysilicon and metal film arms to bend the pixels away from their substrate. The second is a suspended membrane pixel array in which the backside silicon wafer substrate is removed. The thermal sensor\u27s figures of merit responsivity, detectivity, noise equivalent power, noise equivalent temperature difference, and thermal time constant, were modeled. An attempt was made to evaluate the performance of the fabricated microbolometer pixels by comparing measured data to model predictions. This research shows the PIP material can be used to make a practical thermal sensor

COMMUNICATION: Multi-site incorporation of bioactive matrices into MEMS-based neural probes

Methods are presented to incorporate polymer-based bioactive matrices into micro-fabricated implantable microelectrode arrays. Using simple techniques, hydrogels infused with bioactive molecules are deposited within wells in the substrate of the device. This method allows local drug delivery without increasing the footprint of the device. In addition, each well can be loaded individually, allowing spatial and temporal control over diffusion gradients in the microenvironment of the implanted neural interface probe. In vivo testing verified the following: diffusion of the bioactive molecules, integration of the bioactive molecules with the intended neural target and concurrent extracellular recording using nearby electrodes. These results support the feasibility of using polymer gels to deliver bioactive molecules to the region close to microelectrode shanks. This technique for microdrug delivery may serve as a means to intervene with the initial phases of the neuroinflammatory tissue response to permanently implanted microelectrode arrays.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/49187/2/jne5_4_l03.pd

An Electrochemical Sensing Platform Based on Liquid-Liquid Microinterface Arrays Formed in Laser-Ablated Glass Membranes

Arrays of microscale interfaces between two immiscible electrolyte solutions (µITIES) were formed using glass membranes perforated with microscale pores by laser ablation. Square arrays of 100 micropores in 130 µm thick borosilicate glass coverslips were functionalized with trichloro(1H,1H,2H,2H-perfluorooctyl)silane on one side, to render the surface hydrophobic and support the formation of aqueous-organic liquid-liquid microinterfaces. The pores show a conical shape, with larger radii at the laser entry side (26.5 µm) than at the laser exit side (11.5 µm). The modified surfaces were characterized by contact angle measurements and X-ray photoelectron spectroscopy. The organic phase was placed on the hydrophobic side of the membrane, enabling the array of µITIES to be located at either the wider or narrower pore mouth. The electrochemical behavior of the µITIES arrays were investigated by tetrapropylammonium ion transfer across water-1,6-dichlorohexane interfaces together with finite element computational simulations. The data suggest that the smallest microinterfaces (formed on the laser exit side) were located at the mouth of the pore in hemispherical geometry, while the larger microinterfaces (formed on the laser entry side) were flatter in shape but exhibited more instability due to the significant roughness of the glass around the pore mouths. The glass membrane-supported µITIES arrays presented here provide a new platform for chemical and biochemical sensing systems. © 2016 American Chemical Society

The use of high aspect ratio photoresist (SU-8) for super-hydrophobic pattern prototyping

In this work we present a reliable technique for the production of large areas of high aspect-ratio patterns and describe their use as model super-hydrophobic systems. The high thickness and straight sidewalls possible with SU-8 were used to generate dense patterns of small pillars. These photoresist patterns could be used directly, without the need for micromoulding. A method is given allowing resist thickness to be varied over a wide range and a bottom antireflective layer was used to simplify patterning on reflective substrates. This patterning technique allows rapid testing of wetting theories, as pattern size and depth can be varied simply and samples can be produced in sufficient numbers for laboratory use. We show how the static contact angle of water varies with pattern height for one sample-pattern and how static and dynamic contact angles vary with dimension using high aspect-ratio patterns

Alternative Post-Processing on a CMOS Chip to Fabricate a Planar Microelectrode Array

We present an alternative post-processing on a CMOS chip to release a planar microelectrode array (pMEA) integrated with its signal readout circuit, which can be used for monitoring the neuronal activity of vestibular ganglion neurons in newborn Wistar strain rats. This chip is fabricated through a 0.6 μm CMOS standard process and it has 12 pMEA through a 4 × 3 electrodes matrix. The alternative CMOS post-process includes the development of masks to protect the readout circuit and the power supply pads. A wet etching process eliminates the aluminum located on the surface of the p+-type silicon. This silicon is used as transducer for recording the neuronal activity and as interface between the readout circuit and neurons. The readout circuit is composed of an amplifier and tunable bandpass filter, which is placed on a 0.015 mm2 silicon area. The tunable bandpass filter has a bandwidth of 98 kHz and a common mode rejection ratio (CMRR) of 87 dB. These characteristics of the readout circuit are appropriate for neuronal recording applications