A. Bruno Frazier

Laminar fluid behavior in microchannels using micropolar fluid theory

Abstract In 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. Each array consisted of 5 or 7 pipettes with widths varying from 50 to 600 μm and heights ranging from 20 to 30 μm. A downstream port for static pressure measurement was used to eliminate entrance effects. A controllable syringe pump was used to provide flow while a differential pressure transducer was used to record pressure drop. The experimental data obtained for water showed an increase in the Darcy friction factor when compared to traditional macroscale theory, especially at the lower Reynolds number flows. The numerical model of the micropolar fluid theory predicted experimental data better than the classical Navier–Stokes theory and the model compares favorably with the currently available experimental data.

Hollow Metallic Micromachined Needle Arrays

In this paper, fluid coupled metallic micromachined needle arrays are designed, fabricated, packaged, and characterized. The described hollow metallic needle arrays include design features such as dual structural supports and needle coupling channels. The supports and needle walls are formed by micro-electroformed metal to provide increased structural integrity. The needle coupling channels are used to fluidically interconnect the needles and allow pressure equalization and balance of fluid flow between needles. In addition, the needle coupling channels minimize the effects of restricted needle passages by providing a redistribution point for fluid flow between them. The optimum design for the needle coupling channels is investigated using an ANSYS finite element numerical model. The significance of this work includes the development of hollow, metallic micromachined needle arrays for biomedical applications, as well as, a discussion of structural, fluidic, and biological design considerations

Electrical conductivity particle detector for use in biological and chemical micro-analysis systems

This work introduces an integrated electrical detector for use as a conductivity or impedance based detection system for miniaturized biochemical analysis systems such as liquid chromatography or field flow-fractionation systems. Motivation for use of an on-chip conductivity detector is given. The design, fabrication, and characterization of the detector in the conductivity-based detection mode are described. Critical parameters of the conductivity detector, such as time constants, detection limits, and the effects of flow rate and applied voltage on detector response, are measured. In addition, the on-chip detector is compared to a conventional off-chip, UV-based detection system. The conductivity detector was fabricated by creating low impedance electrodes on the top and bottom surface at the end of a typical separation channel. The detector was shown to easily detect particles in the working concentration range of a typical separation system at low applied voltages. The measured time constants averaged approximately 2 seconds and changed slightly with flow rate through the detector. This time constant is acceptable for typical separations that take minutes to complete. The detector was also shown to dramatically improve resolution and reduce peak broadening for the system when compared to an off-chip detector.

Fluid-coupled hollow metallic micromachined needle arrays

In this paper, fluid coupled metallic micromachined needle arrays are designed, fabricated, and characterized. The described hollow metallic needle arrays include design features such as dual structural supports and needle coupling channels. The supports and needle walls are formed by micro-electroformed metal to provide increased structural integrity. The needle coupling channels are used to fluidically interconnect the needles and allow pressure equalization and balance of fluid flow between needles. In addition, the needle coupling channels minimize the effects of restricted needle passages by providing a redistribution point for fluid flow between them. The optimum design for the needle coupling channels is investigated using an ANSYS finite element numerical model. The significance of this work includes the development of hollow, metallic micromachined needle arrays for biomedical applications, as well as, a discussion of structural, fluidic, and biological design considerations.

Micromachined electrical field-flow fractionation (/spl mu/-EFFF) system

In this work, micromachining technologies are used in the development of the next generation of precision /spl mu/-EFFF separation systems. Current macromachining techniques are the limiting factor in the development of more effective Electrical Field-Flow Fractionation (EFFF) separation systems. EFFF systems are used to separate particles in colloids such as cells or proteins. In this paper, EFFF systems are compared to other separation systems and a review of past micromachining efforts in the area of separation systems is made. The theory behind the operation and resolution of an EFFF system is surveyed and the advantages to be gained from application of micromachining technologies are discussed. A method of fabrication that relies on micromachining technologies for /spl mu/-EFFF system construction is described. The /spl mu/-EFFF system setup is described, devices are tested, compared to the current macro EFFF systems, and the results reported.

Parallel sample manipulation using micromachined pipette arrays

One of the challenges of future miniaturized biochemical analysis laboratories is manipulation of sub-(mu) L samples on a macro-scale in a parallel fashion. Todays commercially available sample handling systems for biochemical analysis are limited to wide center-to-center spacing (3.0 mm) and cannot handle sample volumes less than approximately 0.5 (mu) L. In addition, these systems are able to dispense only 6 to 12 pipettes at one time. The technique presented in this work addresses these problems by using micromachined pipette arrays for sample manipulation.

Microfabricated electric impedance chamber for the electrical characterization of single cells

Micromachining technologies were applied to fabricate metal- electrode-instrumented microchannels with cross-sectional dimensions similar in size to blood cells. The instruments enable electric impedance measurement of femptoliter quantities of materials and solutions. The completed micro- electric impedance devices were characterized with varying concentrations of phosphate buffered saline solutions, DI water, and air in the recording zone. With the microdevices on the stage of an inverted light microscope, individual living cells were positioned tightly between metal electrodes using mechanical suction. Impedance spectra form 100 Hz to 2 MHz measured in isolated toadfish red blood cells (RBCs) and human neutrophils were distinct and demonstrated the ability to permeate the cell membrane at high frequency. The cell/shunt path cut-off frequency were approximately 400 kHz at -3dB indicating that non- invasive electric impedance characterization of the cytoplasm may be feasible for his configuration. In addition, the area specific membrane capacitance was estimated for both cell types by fitting the data to a simple RC circuit model.

Characterization of a Polymer-Based Microfluidic System for Electrophysiological Studies

This paper presents the characterization of a polymer-based microfluidic system for whole-cell analysis manufactured using low-cost fabrication techniques. The multi-layer, laminate polyimide device contains features defined by a combination of laser ablation and microstenciling. This process requires minimal infrastructure and allows for a faster design-to- prototype cycle while providing the ability to integrate complex arrangements of multi-layer electrical functionality. The features include an array of analysis sites, a fluidic microchannel, and integrated electrodes for electrophysiological studies. Validation of the system for whole-cell analysis was first performed with impedance spectroscopy measurements collected on air, DI water, phosphate buffered saline (PBS), and clusters of human cancer cells. This was followed by testing the ability to use the device to control the movement and position of 10 µm diameter microbeads and dissociated cells.