We are developing a variety of microsystems for the separation and detection of biological samples. At the heart of these systems, inexpensive polymer microfluidic chips carry out sample preparation and analysis. Fabrication of polymer microfluidic chips involves the creation of a master in etched silicon or glass; plating of the master to produce a nickel stamp; large lot chip replication by injection molding; precision chip sealing; and chemical modification of channel surfaces. Separation chips rely on insulator-based dielectrophoresis for the separation of biological particles. Detection chips carry out capillary electrophoresis to detect fluorescent tags that identify specific biological samples. Since the performance and reliability of these microfluidic chips are very sensitive to fluidic impedance, electromagnetic flux, and zeta potential, the microchannel dimensions, shape, and surface chemistry have to be tightly controlled during chip fabrication and use. This paper will present an overview of chip design, fabrication, and testing. Dimensional metrology data, surface chemistry characterization, and chip performance data will be discussed in detail.
Sandia and Lawrence Livermore National Laboratories are developing a briefcase-sized, broad-spectrum bioagent detection system. This autonomous instrument, the BioBriefcase, will monitor the environment and warn against bacterium, virus, and toxin based biological attacks. At the heart of this device, inexpensive polymer microfluidic chips will carry out sample preparation and analysis. Fabrication of polymer microfluidic chips involves the creation of a master in etched glass; plating of the master to produce a nickel stamp; large lot chip replication by injection molding; and thermal chip sealing. Since the performance and reliability of microfluidic chips are very sensitive to fluidic impedance and to electromagnetic fluxes, the microchannel dimensions and shape have to be tightly controlled during chip fabrication. In this talk, we will present an overview of chip design and fabrication. Metrology data collected at different fabrication steps and the dimensional deviations of the polymer chip from the original design will be discussed.
A process for the rapid replication of electroforming plastic micromolds has been developed at Sandia National Laboratories, Livermore, CA. The process is based on injection molding of plastic replicates with integral metallic screens to produce sacrificial electroforming molds in which the metallic screen acts as the
conducting base and the plastic features provide insulating sidewalls. The process consists of injecting molten PMMA via a center-gate into a disk-shaped mold cavity in which a sandwich of a flow channel plate, porous Nickel foam, and metallic microscreen are placed on top of the LIGA-fabricated tooling. A numerical model
for the coupled heat transfer and fluid flow phenomena is used to investigate the effects of various process parameters on the mold-filling behavior. The results from the parametric studies are presented and discussed.
A new replication technology that produces, high aspect ratio ceramic or metal microparts by micromolding and sintering nanoparticle preforms is presented. In this LIGA replication technique, an epoxy based nanoparticle slurry is cast into sacrificial plastic micromolds produced by injection molding. The epoxy is allowed to cure and, if desired, excess epoxy is polished off to produce individual micropart preforms. The micromold is then dissolved in methylene chloride and the micropart preforms are sintered in either air (oxide ceramics) or 4% hydrogen in argon (nickel). This presentation will discuss the effects of the epoxy formulation, the microcasting procedure, and the sintering schedule on the materials properties of the final sintered microparts. It will be shown that this replication technique produces ceramic or metal microparts with micron size features and mechanical properties comparable to those of macroscopic materials.
A novel process for the rapid replication of electroforming plastic micromolds has been developed and is now being used to produce plated nickel test specimens. The process combines hot embossing or injection molding with metallic microscreens to produce sacrificial electroforming molds with conducting bases and insulating sidewalls. The replicated micromolds differ from standard LIGA molds in that the holes in the microscreen act as insulating defects in the electroforming base. The effects of such defects on the materials properties of electroformed microparts will be discussed and it will be shown that when the surface irregularities corresponding to the microscreen holes are removed, mechanical properties are experimentally indistinguishable from those found in conventionally processed LIGA specimens.
Alfredo Morales, Georg Aigeldinger, Michelle Bankert, Linda Domeier, John Hachman, Cheryl Hauck, Patrick Keifer, Karen Krafcik, Dorrance McLean, Peter Yang
The use of silver filled PMMA as a sacrificial layer for the fabrication of multilevel LIGA microparts is presented. In this technique, a bottom level of standard electroformed LIGA parts is first produced on a metallized substrate such as a silicon wafer. A methyl methacrylate formulation mixed with silver particles is then cast and polymerized around the bottom level of metal parts to produce a conducting sacrificial layer. A second level of PMMA x-ray resist is adhered to the bottom level of metal parts and conducting PMMA and patterned to form another level of electroformed features. This presentation will discuss some the requirements for the successful fabrication of multilevel, cantilevered LIGA microparts. It will be shown that by using a silver filled PMMA, a sacrificial layer can be quickly applied around LIGA components; cantilevered microparts can be electroformed; and the final parts can be quickly released by dissolving the sacrificial layer in acetone.
LIGA, an acronym from the German words for Lithography, Electroforming, and Molding, is being evaluated worldwide as a method to produce microparts from engineering materials. Much of the work to date in LIGA has focused on producing metal microparts, with nickel as the most common material of choice. There is a growing interest in producing plastic parts replicated from LIGA metal masters due largely to microanalytical instrumentation and medical applications. These plastic replicates are generally made by either hot embossing or injection molding. Ceramic replication, of particular interest for high temperature applications or to produce piezoelectric or magnetic microparts, is also emerging as an area of interest. In this paper, a model of the LIGA exposure and development processes is presented along with the result of numerical optimization of mask design and process cost. The baseline processes for a cost- effective method to produce metal microparts are discussed, along with replication methods and result for plastics and ceramics.
To determine the relative strengths of various biologic adhesives at several timepoints, we compared thrombin-activated SD (solvent-detergent treated) cryoprecipitate with laser- activated SD cryoprecipitate and a laser-activated, albumin-based glue. Male Sprague-Dawley rats (n equals 79) received four, 3-cm, dorsal skin incisions which were closed with either laser- activated cryoprecipitate, laser-activated albumin solder, thrombin-activated cryoprecipitate, or standard skin staples. The cryoprecipitate was derived from pooled human plasma and was treated with a solvent-detergent process, rendering it free of envelope-coated viruses (i.e., HBV, HIV). An 808-nm diode laser was used to activate each solder with an average duration of exposure of 75 seconds per incision. Animals were sacrificed for evaluation of wound tensile strength and histology at 0 hours, 2 hours, 4 hours, and 4 days. At all timepoints tested, laser-activated solders were significantly stronger than thrombin-activated cryoprecipitate (p < 0.03) and control wounds (p < 0.003). There was no significant difference in tensile strength between the two types of laser-activated solder at any timepoint.
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