Robin H. Liu

University of Illinois, Urbana-Champaign, Urbana, Illinois, United States

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Publications (6)19.3 Total impact

  • Robin H. Liu · Qing Yu · David J. Beebe ·
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    ABSTRACT: Several microvalves utilizing stimuli-responsive hydrogel materials have been developed. The hydrogel components are fabricated inside microchannels using a liquid phase polymerization process. In-channel processing greatly simplifies device construction, assembly, and operation since the functional components are fabricated in situ and can perform both sensing and actuation functions. Two in situ photopolymerization techniques, "laminar stream mode" and "mask mode," have been explored. Three two-dimensional (2-D) valves were fabricated and tested (response time, pressure drop, maximum differential pressure). In addition, a hydrogel/PDMS three-dimensional (3-D) hybrid valve that physically separates the sensing and regulated streams was demonstrated. Analytical modeling was performed on the 3-D valve. Hydrogel-based microvalves have a number of advantages over conventional microvalves, including relatively simple fabrication, no external power requirement, no integrated electronics, large displacement (185 μm), and large force generation (22 mN)
    Journal of Microelectromechanical Systems 03/2002; 11(1-11):45 - 53. DOI:10.1109/84.982862 · 1.75 Impact Factor
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    ABSTRACT: In this paper we present an organic feedback scheme that merges microfluidics and responsive materials to address several limitations of current microfluidic systems. By using in situ fabrication and by taking advantage of microscale phenomena (e.g., laminar flow, short diffusion times), we have demonstrated feedback control of the output pH in a completely organic system. The system autonomously regulates an output stream at pH 7 under a range of input flow conditions. A single responsive hydrogel component performs the functionality of traditional feedback system components. Vertically stacked laminar flow is used to improve the time response of the hydrogel actuator. A star shaped orifice is utilized to improve the flow characteristics of the membrane/orifice valve. By changing the chemistry of the hydrogel component, the system can be altered to regulate flow based on hydrogels sensitive to temperature, light, biological/molecular, and others.
    Lab on a Chip 01/2002; 1(2):96-9. DOI:10.1039/b108078d · 6.12 Impact Factor
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    ABSTRACT: A microfluidic platform for the construction of microscale components and autonomous systems is presented. The platform combines liquid-phase photopolymerization, lithography, and laminar flow to allow the creation of complex and autonomous microfluidic systems. The fabrication of channels, actuators, valves, sensors, and systems is demonstrated. Construction times can be as short as 10 min, providing ultrarapid prototyping of microfluidic systems.
    Proceedings of the National Academy of Sciences 01/2001; 97(25). DOI:10.1073/pnas.250273097 · 9.67 Impact Factor

  • Micro Total Analysis Systems 2000, 01/2000: pages 45-48; , ISBN: 978-90-481-5496-8
  • Robin H. Liu · Michael J. Vasile · David J. Beebe ·
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    ABSTRACT: This paper presents a new application of spin-on glass to fabricate nonplanar dielectric structures (channel plate microstructures) with aspect ratios (i.e., ratio of channel length to channel width) of 20:1. A variety of microchannel geometries have been fabricated. The LIGA process is used to make nickel molds up to 150 μm in height with mechanically planarized surfaces. Spin-on glass (SOG) is applied to obtain glass structures in nickel molds. A multiple dispensing/drying/curing process was developed resulting in crack-free SOG structures. Reverse electroplating is used to remove the nickel mold and release the glass structures. The resulting freestanding glass microchannel plates (>100 μm in height) demonstrated good electrical properties (400-V/μm breakdown voltage) and good spatial definition
    Journal of Microelectromechanical Systems 07/1999; 8(2-8):146 - 151. DOI:10.1109/84.767110 · 1.75 Impact Factor
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    ABSTRACT: This paper describes the development of microchannel plate prototypes with aspect ratios of 20:1 and a variety of microchannel geometries. The LIGA process is utilized to fabricate nickel molds up to 150 μm in height with planarized surfaces. A novel application of spin-on glass is developed to obtain glass structures in Ni molds. A reverse electroplating is used to remove the Ni mold and release the glass structures with height of more than 100 μm
    Solid State Sensors and Actuators, 1997. TRANSDUCERS '97 Chicago., 1997 International Conference on; 07/1997