Michael C. Murphy
Professor of Mechanical Engineering
Held the Roy O. Martin Lumber Company Professor of Engineering
3250G Patrick F. Taylor Hall
Department of Mechanical & Industrial Engineering
Louisiana State University
Baton Rouge, LA 70803
- Post Doctoral Fellowship, Mechanical Engineering, Massachusetts Institute of Technology, 1990 - 1992
- Ph.D., Mechanical Engineering, Massachusetts Institute of Technology, 1990
- M.S., Aeronautics, California Institute of Technology, 1978
- B.S., Mechanical Engineering, Cornell University, 1977
The goal of the our research is the development of a polymer microfluidic processor to extract rare target cells from whole blood and serve as a front-end for molecular profiling. Since 1995 my group has worked closely with the co-investigators on the design and fabrication polymer microfluidic systems for rapid, low cost sample preparation and mutation detection for a variety of applications. We have made advances in fabrication, assembly, and function of polymer modules and demonstrated a variety of individual devices and high throughput parallel arrays. Our prior work provides the necessary foundation to enable the research in the current proposal.
Repeatable, Precise Assembly of Polymer, Multi-Scale Fluidic Devices and Systems
Background: To achieve penetration of clinical practice modular diagnostic instruments will need to be made on low-cost, polymer platforms. Realization of complex modular systems requires the development of repeatable, reliable assembly techniques for polymer modules. The assembly problem can be broken into three parts: (1) Alignment of the modules; (2) Incorporating fluid seals that permit the transfer of analyte between modules; and (3) Bonding the components without introducing contaminants.
Central findings: We have demonstrated solutions to each step in the modular assembly problem. Passive kinematic alignment structures and exact constraint design are used widely in precision machine design and optical alignment. We applied them to polymer modules (1-2) and showed that lateral variation of less than 15 mm is possible with pin-in-v groove alignment structures in injection molded or hot embossed microstructures. Pin-in-slot structures were also incorporated in fluidic interconnects in a vertically stacked system. The transfer of rare targets, including cells and nucleic acids, between devices requires a fluidic seal to prevent leakage or loss of the analyte. We demonstrated a near zero dead volume, gasketless seal based on capillary forces induced by superhydrophobic coatings on the facing surfaces.(3) The rupture pressures and required gaps were suitable for those encountered in typical modular devices. The final step is the bonding of the substrates and cover sheets or multi-layer devices. Thermal fusion bonding (TFB) is a direct approach that is attractive due to the absence of additional contaminants or specialized structures to realize bonding. Conventional TFB uses a wide variety of heat sources and is highly variable. We have shown that immersing stacks of parts in boiling water results in excellent bonding in a short time – typically 15 min.(4) Vapor pressure can be adjusted to achieve different boiling temperatures to accommodate a variety of thermoplastics.
Impact: This work addresses the key issues in the assembly of polymer modular systems, enabling precise, repeatable assembly and minimal dead volume transfer of analyte between modules.
Role: The assembly techniques have been developed in my laboratory at LSU with collaboration of Dr. Soper (Kansas University).
Thermal Management of Polymer, Modular Microfluidic Systems
Background: Most biochemical reactions are temperature sensitive and exposure to temperatures that are too high or too low may compromise performance. To incorporate assays with thermally-driven reactions, such as polymerase chain reaction (PCR) and ligase detection reaction (LDR), on modular, polymer platforms careful design must be used to isolate temperatures to their proper zones in order to maximize yield from each assay step, particularly when rare targets such as circulating tumor cells are being characterized.
Central findings: We initially evaluated the thermal performance of our spiral continuous flow PCR, in which temperature zones were defined by fixing resistance heaters to the polycarbonate cover sheet, using an infrared camera.(1) The temperature zones were poorly defined with significant heat leakage from high temperature zones to adjacent regions. Three steps improved the definition of the temperature zones: (1) The thickness of the substrate was reduced to reduce the thermal capacitance; (2) Grooves machined in the substrate between temperature zones increased the thermal resistance; and (3) The heaters were placed on copper blocks attached to the cover sheet, generating a constant temperature boundary condition. We extended these ideas micro-titer plate formatted PCR devices (2) and stacked PCR and LDR modules. (3) For the micro-titer plate system similar thermal management techniques were applied to continuous flow reactors confined to a 9 mm X 9 mm area in a standard 96-well format. In the stacked system, thermofluidic standoffs were used to separate polymer PCR and LDR reactors. We showed that fast micro-resistance heaters could be used to generate temperature gradients in nickel gas chromatographs or applied to polymer fluidic systems.(4)
Impact: The most significant finding was that reducing thermal conduction between temperature zones increased the yield of the PCR by more than 300% to a level 72% of a block thermal cycler processing the same cocktail more slowly. In order to obtain optimal biochemical performance in thermally-driven reactions in micro- and nanofluidic systems must account for thermal isolation and management of heat transfer.
Role: This work was a multi-institutional collaboration with the University of Kansas (Dr. Soper), Cornell Medical School (Dr. Barany), and LSU (Drs. Murphy, Nikitopoulos, and Overton).
Development of Polymer, Modular Microfluidic Components and Instruments for Different Applications
Background: Development of modular systems requires the demonstration of different functional modules and the integration of multiple modules into instruments for addressing clinical or research needs for specific diseases or targets cells.
Central findings: We have demonstrated polymer modules to perform a broad spectrum of functions necessary to build a toolkit that will enable development of modular instruments to attack a variety of conditions. The set of modules includes continuous flow PCR, continuous flow LDR, circulating tumor cell capture (1), high flow rate CTC capture, and optical detection modules with parallel channels (2). A PCR/LDR stack (3) was demonstrated for the identification of mutations in the K-ras gene in colorectal cancer that incorporated fluidic/thermal standoffs to separate the PCR and LDR modules from each other, a purification step, and mixers to add the LDR reagents to the purified PCR output. Module substrates and coversheets and the standoffs all included passive kinematic alignment structures to facilitate assembly. Full modular systems have been demonstrated for tuberculosis (4) and stroke identification.
Impact: Proofs-of-concept for module and instrument development are essential to the advancement of this technology to clinical and research use.
Role: My research group has contributed both modules and the assembly technology to these advances. This work was enabled by a series of multi-institutional collaborations with University of Kansas (Dr. Soper), Cornell Medical School (Dr. Barany), SUNY Downstate Medical School (Dr. Baird) and LSU (Drs. McCarley, Murphy and Nikitopoulos).
LIGA and UV-LIGA Microfabrication
Background: The LIGA (X-ray Lithography, Electrodeposition, Molding) and UV-LIGA (Same sequence with UV lithography as the initial step) open a broad range of metal alloys, ceramics, and polymers to microsystem designers. Structures over 1 mm tall with features less than 5 mm are realizable.
Central findings: We have actively worked to extend and reduce the cost of high aspect ratio microfabrication and apply it to different fields. Techniques for the assembly of hybrid metal devices, combining off-the-shelf components and microfabricated parts, have the potential to increase the functional capability of minimally-invasive surgical tools.(1) As part of that work we investigated low cost transfer mask approaches to making X-ray masks for LIGA structures.(2) High aspect ratio nickel columns for gas chromatography were evaluated.(3) More recently we have demonstrated a UV-LIGA process for developing large area nickel mold inserts (LAMIs) for the fabrication of polymer micro-titer plate devices.(4) We have also demonstrated electrodeposition of various alloys into high aspect ratio patterns and injection molding of ceramics.
Impact: The low-cost transfer mask technology for X-ray masks is now a standard process for anyone working in high aspect ratio microfabrication. The LAMI process was used to demonstrate 96-well micro-titer plate formatted arrays for nucleic acid purification and thermal reactions (PCR). The gas chromatography work is ongoing.
Role: These developments were the product of several multi-institutional collaborations with University of Kansas (Dr. Soper), Northeastern University (Dr. Podlaha-Murphy), Institute for Microsystem Technology in Karlsruhe, Germany (IMT-FzK) (Dr. Aigeldinger) and LSU (Drs. Goettert, Murphy and Park). My research group contributed the microfabrication efforts on each of these projects.
Measurement and Characterization of Knee Joint Kinematics
Background: The ability to accurately measure and compare the 3-D skeletal kinematics of joints, such as knees, as part of standard clinical practice is limited by the ability to track bone motion and methods used to compare the measurements from different experiments or laboratories, which are coordinate system dependent.
Central findings: Direct comparison of skeletal kinematics measured with infrared LED markers mounted on the skin and in arrays on skeletal pins showed significant task dependent variation in skin marker motion relative to the bones even near bony landmarks.(1) We have continued to investigate other sensors as alternative to displacement markers.(2) We have also applied the techniques of parallel robotics to characterize joint kinematics by mapping total (variable orientation displacement), reachable (fixed orientation displacement), and velocity workspaces.(3,4)
Impact: The precise measurement of soft tissue motion and subsequent characterization of 3-D skeletal motion in a coordinate invariant manner are critical to the development of motion measurement for clinical use.
Role: This work has been developed in collaboration with University of Minnesota (Dr. Brown), MIT (Dr. Mann), and LSU (Drs. Lopez and Murphy). My research group developed algorithms, designed sensors and testbeds, and evaluated the methods.
Title: Micro-milling Machine for Micro-molding Research and Capstone Support
- This grant supports purchase of a 5-axis micro-milling machine for microfabrication of mold inserts.
Title: Biotechnology Resource Center of Biomodular Multi-scale Systems for Precision Molecular Diagnostics.
- This grant will develop a universal molecular processing system for molecular processing and sensing and disseminate the developed technology to the biotechnology and clinical communities.
Title: Point-of-Care System for Molecular Diagnosis of Stroke
- The project is to apply a panel of biomarkers developed by co-I, Alison Baird (SUNY-Stony Brook) to diagnose whether a stroke is hemorrhagic or ischemic in a modular microfluidic system. This will enable more timely decision-making at the point-of-care and allow earlier administration of the appropriate therapeutics. No direct overlap with the proposed grant, but the modular thermoplastic platform and cell sampling are similar to what we are proposing in the current proposal.
Title: Rapid Processor for Methicillin-resistant Staphylococcus aureus (MRSA) Identification in the Operating Room
- The goal is to use a cell sampling unit to selectively capture and identify bacteria in synovial fluid. The device configuration is an inversion of the current system architecture with the capture beds downstream of the narrow ports, so white blood cells and other large cells in the synovial fluid are size excluded.
You, B.-H., Park, D.S., Rani, S., and Murphy, M.C. (2015) “Assembly of Articles polymer microfluidic components and modules: Validating models of passive alignment accuracy,” JMEMS, 24(3):634-650.
Kim, N., Murphy, M.C., Soper, S. A. , and Nikitopoulos, D.E., (2014) “Liquid-Liquid Segmented Flows in Polycarbonate Microchannels with Cross-Sectional Expansions,” Int’l. J. Multiphase Flow, 58(1):83-96.
Park, T., Song, I.-H., Park, D.S., You, B.-H., and Murphy, M.C. (2012) “Thermoplastic fusion bonding using a pressure-assisted boiling point control system,” Lab-on-a-Chip, 12(16):2799-2802.
Kim, H., Murphy, M.C., and Podlaha-Murphy, E.J., (2012) “Electrodeposition of High Aspect Ratio Super Invar Microstructures Electrochemical/Electroless Deposition,” J. Electrochemical Society, 159(9):D549-D554.
Wang, H., Chen, H.-W., Hupert, M., Murphy, M.C., Soper, S.A., Williams, D., and Barany, F. (2012) “Fully integrated thermoplastic genosensor for the highly sensitive detection and identification of multi-drug resistant tuberculosis (MDR-TB),”Angewandte Chemie Int’l , 51(18):4349-4353.
Han, K., Lee, T.Y., Nikitopoulos, D.E., Soper, S.A., and Murphy, M.C. (2011) “A vertically-stacked, polymer, microfluidic point mutation analyzer: Rapid, high accuracy detection of low-abundance K-ras mutations,” Analytical Biochemistry, 417(2):211-219.