John D. Brazzle

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.

A low-temperature IC-compatible process for fabricating surface-micromachined metallic microchannels

In this paper, a low-temperature integrated-circuit (IC)-compatible process for fabricating metallic microchannels is described. Arrays of 1-100 metallic microchannels have been fabricated on silicon and glass substrates. The process can be extended to many planar substrate materials including polymers and ceramics. The microchannels are formed using microelectro-formed metals. The microchannels demonstrated in this paper use nickel as the structural material and gold as the surface coating on the inside walls of the microchannels. The inner dimensions of the individual microchannels fabricated to date range from 30 /spl mu/m to 1.5 mm in width, 0.5 mm to several centimeters in length, and 5-100 /spl mu/m in thickness. The wall thickness ranges from 5 to 50 /spl mu/m. The microchannel fabrication technology enables the fabrication of surface microchannels with a relatively large cross-sectional area. The metallic microchannels can be fabricated to extend from the substrate edge. Interfacing schemes are given for attaching external pressure feeds.

Micromachined needle arrays for drug delivery or fluid extraction

Micromachined needle arrays have been designed, fabricated, and characterized. The design includes arrays of 25 needles with fluid coupling channels and dual structural supports. Numerical modeling of fluid flow characteristics was performed, demonstrating that the needle coupling channels redistribute flow when the input or output ports are fully restricted. Micromachining technologies have been used to batch fabricate hollow metallic fluid coupled needle arrays. The significance of this work includes the development of the hollow metallic micromachined needle arrays for biomedical applications, as well as a discussion of structural, fluidic, and biological design considerations. The micromachined needle array has many advantages, including (a) reduced trauma at penetration site (small size), (b) greater freedom of patient movement (minimal penetration), (c) a practically pain-free drug delivery device (distribution of force), (d) precise control of penetration depth (needle extension length), and (e) they can be stacked and packaged into a 3-D device for fluid transfer.

Micromachined pipette arrays

The design and characterization of batch fabricated metallic micromachined pipette arrays is described. The process used to fabricate the micromachined pipette arrays (MPA) includes p/sup +/ etch-stop membrane technology anisotropic etching of silicon in potassium hydroxide, sacrificial thick photoresist micromolding technology, and electrodeposition. Arrays of one to ten pipettes have been fabricated using nickel as the structural material and palladium as the biocompatible coating of inside walls. The inner dimensions of the individual pipettes fabricated to date range from 30 /spl mu/m to 1.5 mm in width, 0.5 mm to several cm in length, and 550 /spl mu/m in thickness. The center-to-center spacing of these pipettes varies from 100 /spl mu/m to several centimeters. The MPA have a number of advantages when compared to the current micropipette technology, including the ability to transfer precise volumes of samples in the submicroliter range; the ability to manipulate samples, reagents, or buffers in a highly-parallel fashion by operating hundreds of individual pipettes simultaneously; and the compatibility with the submillimeter center-to-center dimensions of the microscale biochemical analysis systems. The application of the MPA to high lane density slab gel electrophoresis is explored. Sample wells are formed in agarose gels by using micromachined combs (solid MPA) at center-to-center spacing ranging from 250 /spl mu/m to 1.9 mm. The samples are loaded using the MPA. The results of the micro-gel separations compare favorably with the standard mini-gel separations and show a twofold increase in the number of theoretical plates as well as a sixfold increase in lane density.

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

Hollow metallic micromachined needles with multiple output ports

In this paper, hollow metallic micromachined needles with multiple output ports are designed, fabricated, characterized, and packaged. The hollow metallic needles include design features such as tapered needle tips and multiple output ports on the bottom and top of each needle. The needle tip and shaft are formed by microelectroformed metal. The flow characteristics of the needles are currently being experimentally investigated and modeled using a finite element numerical model. The experimental results and theoretical models will be presented as part of this paper. The micromachined needles can be fabricated on a variety of substrates and can use micro-electroformed palladium as the structural material. The use of palladium as a structural material provides high mechanical strength and durability, as well as, biocompatibility for use in biomedical applications. The cross-sectional dimensions of individual needle tips begin at less than 10 micrometers in width and 15 micrometers in height and then taper to 200 micrometers in width and 60 micrometers in height. The significance of this work includes the development of hollow metallic micromachined needles for biomedical applications, as well as, a discussion of structural, fluidic, and packaging design considerations.

Micromachined pipette arrays (MPA)

The design and biocompatibility testing of batch fabricated micromachined pipette arrays is described. The process used to fabricate the metallic micromachined pipette arrays (MPA) includes p/sup +/ etch-stop membrane technology, anisotropic etching of silicon in potassium hydroxide, sacrificial thick photoresist micromolding technology, and micro electroforming technology. Arrays of one to ten pipettes have been fabricated using nickel as the structural material and gold as the biocompatible coating of inside walls. The inner dimensions of the individual pipettes fabricated to date range from 30 /spl mu/m to 1.5 mm in width, 0.5 mm to several cm in length, and 5 /spl mu/m to 50 /spl mu/m in thickness. The micromachined pipettes have many advantages over current micro pipette technology, including: (a) highly parallel manipulation of samples/reagents, (b) the capability to precisely define the pipette dimensions allowing for small volumes (in pL to /spl mu/L range), and (c) a wide range of pipette center-to-center spacings (from centimeters to approximately 20 /spl mu/m).

Microchannel fluid behavior using micropolar fluid theory

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. 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.

Fluid coupled metallic micromachined needle arrays

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. The authors also discuss structural, fluidic, and biological design considerations.

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.