L.S.L. Cheung

The University of Arizona, Tucson, AZ, United States

Are you L.S.L. Cheung?

Claim your profile

Publications (13)10.71 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Dynamic states of cancer cells moving under shear flow in an antibody-functionalized microchannel are investigated experimentally and theoretically. A simplified physical model was adopted to analyze the cell motion; it features a rigid sphere, with receptors on its surface, moving above a solid surface with distributed ligands. The cell motion is described by the Langevin equation where the hydrodynamic interactions, gravitational drift force, receptor-ligand binding force, and thermal fluctuations are all taken into account. The receptor-ligand bonds are modeled as Hookean springs. In this study, three dynamic states of cell motion have been identified: (i) free motion, (ii) rolling adhesion, and (iii) firm adhesion depending on the flow shear rate. The numerical simulations allow exploring effects of numerous parameters such as cell-receptor and surface-ligand density.
    Micro Electro Mechanical Systems (MEMS), 2011 IEEE 24th International Conference on; 02/2011
  • [Show abstract] [Hide abstract]
    ABSTRACT: The lifetime of microfluidic devices depends on their ability to maintain flow without interruption. Certain applications require microdevices for transport of liquids containing particles. However, microchannels are susceptible to blockage by solid particles. Therefore, in this study, the phenomenon of interest is the formation and growth of clusters on a microchannel surface in the flow of a dilute suspension of hard spheres. Based on the present experiments, aggregation of clusters was observed for particle-laden flows in microchannels with particle void fraction as low as 0.001 and particle diameter to channel height ratio as low as 0.1. The incipience and growth of a single cluster is discussed, and the spatial distribution and time evolution of clusters along the microchannel are presented. Although the cluster size seems to be independent of location, more clusters are found at the inlet/outlet regions than in the microchannel center. Similarly as for an individual cluster, as long as particle–cluster interaction is the dominant mode, the total cluster area in the microchannel grows almost linearly in time. The effects of flow rate, particle size, and concentration are also reported. KeywordsMicrochannel suspension flow–Particle aggregation–Cluster formation and growth
    Microfluidics and Nanofluidics 01/2011; 10(3):661-669. · 3.22 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The attachment and detachment of target cancer cells from homogeneous and binary mixtures in antibody-functionalized microchannels have been studied experimentally. Under the same intermediate flow rate, the attachment rate was found to be higher, and detachment flow rate was lower, for cell lines expressing the target receptor at a higher level. For cells that do not express the target receptor, the attachment rate was much lower but did not diminish, due to non-specific binding, and the detachment rate was much higher. The bio-functional microfluidic system performance in selectively isolating target cells from binary mixtures is quantitatively characterized. While the system sensitivity is typically very high, almost 100%, the specificity is lower than 90%. Applying a unique flow scheme of a slow flow rate, for maximum capture of target cells, followed by a faster flow rate, for maximum removal of non-target cells, the specificity is enhanced to levels above 95%, even for mixtures with target cells present at 1:1,000 relative concentration ratio.
    01/2011;
  • [Show abstract] [Hide abstract]
    ABSTRACT: The system performance of an antibody-functionalized microchamber array, developed for selectively binding target cancer cells, is quantitatively characterized. The devices are designed to allow accurate counting of loaded and captured cells from heterogeneous suspensions. Specific interaction between cancer cell receptors and immobilized surface ligands has been demonstrated under static conditions. Performance measures such as specificity, sensitivity and accuracy are uniquely defined and experimentally evaluated. Several cell mixtures have been tested, and the quantitative system performance criteria are reported as a function of cell concentrations in the tested suspensions. These criteria provide a critical quantitative basis for a comparison among different systems aimed at selectively isolating target bio-species from complex mixtures.
    Micro Electro Mechanical Systems (MEMS), 2010 IEEE 23rd International Conference on; 02/2010
  • [Show abstract] [Hide abstract]
    ABSTRACT: Attachment, deformation and detachment of N-cadherin expressing prostate and breast cancer cell lines in a functionalized microchannel under hydrodynamic loading have been studied. N-cadherin antibodies are immobilized on the microchannel surface to capture the target cancer cells, PC3N and MDA-MB-231-N, from a homogeneous cell suspension. Although difficult, a significant fraction of moving cells can be captured under a low flow rate. More than 90% of the target cells are captured after a certain incubation time under no flow condition. The mechanical response of a captured cancer cell to hydrodynamic flow field is investigated and, in particular, the effect of flow acceleration is examined. The observed cell deformation is dramatic under low acceleration, but is negligible under high acceleration. Consequently, the detachment of captured cells depends on both flow rate and flow acceleration. The flow rate required for cell detachment is a random variable that can be described by a log-normal distribution. Two flow acceleration limits have been identified for proper scaling of the flow rate required to detach captured cells. A time constant for the mechanical response of a captured cell, on the order of 1 min, has been identified for scaling the flow acceleration. Based on these acceleration limits and time constant, an exponential-like empirical model is proposed to predict the flow rate required for cell detachment as a function of flow acceleration.
    Lab on a Chip 07/2009; 9(12):1721-31. · 5.70 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The effect of flow acceleration, rather than just the flow rate, on the response of an attached cancer cell is for the first time reported. Selective binding of prostate cancer cells to a surface functionalized with anti-N-cadherin antibodies utilizing a microfluidic system under flow conditions has been studied. Here, the behavior of a captured cell under a time-dependent flow field is investigated experimentally and numerically. Under slowly increasing flow rate, the cell deformation is more pronounced resulting in lower drag force on attached cells. Furthermore, the contact area between the cell and the functionalized surface is larger, potentially enhancing the cell adhesion force. Consequently, a higher flow rate is required to detach cells exposed to such a flow field. Numerical simulations have been utilized in effort to quantify the required detachment force. The results confirm that to obtain a similar shear stress, a higher flow rate is needed for attached cells under lower flow acceleration.
    Micro Electro Mechanical Systems, 2009. MEMS 2009. IEEE 22nd International Conference on; 03/2009
  • [Show abstract] [Hide abstract]
    ABSTRACT: Cluster dynamics in microchannels due to flow of dilute suspensions of polystyrene spherical particles has been studied experimentally. Cluster-cluster interaction as well as the functional dependence of cluster growth rate on several control parameters has been studied. Destructive, e.g. cluster collision, and constructive modes, e.g. cluster merging, of cluster-cluster interaction have been observed. Cluster growth rate with time is found to increase with either particle concentration or shear strain rate, and decrease with channel-height to particle-diameter ratio.
    Micro Electro Mechanical Systems, 2009. MEMS 2009. IEEE 22nd International Conference on; 03/2009
  • [Show abstract] [Hide abstract]
    ABSTRACT: polydimethylsiloxane (PDMS) based microsystems have successfully been fabricated and characterized for studying protein crystals utilizing both UV-visible spectroscopy and X-ray crystallography. Transmittance tests have been conducted with PDMS and glass substrates; the measurements indicate that in PDMS, unlike glass, the emerging intensity is higher than 50% of the incident intensity as long as the total optical path is shorter than 100 mum. Indeed, both the UV-visible spectrum and X-ray diffraction of a protein crystal enclosed in a PDMS device are almost identical to those of the crystal alone. Hence, PDMS is suitable as substrate material in device fabrication to study protein crystals. In glass, however, the UV-visible spectrum is significantly distorted and the X-ray diffraction pattern is rather weak resulting in poor signal to noise ratio. Furthermore, microsystems integrated with micro- channels allowing continuous exchange of buffer solution around the protein crystals have been tested; this would greatly enhance the potential to induce, trap and characterize functional states in proteins.
    Micro Electro Mechanical Systems, 2007. MEMS. IEEE 20th International Conference on; 01/2007
  • Man Lee, L. S. L. Cheung, Yi-Kuen Lee, Y. Zohar
    [Show abstract] [Hide abstract]
    ABSTRACT: A thermal microsystem, integrated with pressure and temperature microsensors, is fabricated to study convective boiling under nearly uniform heat flux boundary condition. The temperature and pressure distribution along the microchannel is measured correspondingly. The pressure increases with input power when two phase flow develops. A pressure peak appears at the location of liquid-vapor interface region. The transient temperature and pressure fluctuation is also measured. The dominant frequencies of the temperature and pressure fluctuation are the same values at the liquid-vapor interface region and this dominant frequencies increase with input power. Simultaneously, the qualitative visualizations of the evolving flow patterns have been correlated with the quantitative temperature and pressure measurements.
    01/2006;
  • Source
    Man Lee, Luthur Siu Lun Cheung, Yi-Kuen Lee, Yitshak Zohar
    [Show abstract] [Hide abstract]
    ABSTRACT: Forced convection boiling in microchannels is studied experimentally under the uniform heat flux boundary condition. Several microchannel heat sinks with integrated temperature sensors, spanning two orders of magnitude in height 5–500 µm, have been fabricated with designed nucleation sites on the bottom surfaces. The microchannels are capped by a glass wafer to monitor bubble activity using video microscopy. Distributed micro heater elements on the device backside are used as the heat source, while the working liquid flow rate is adjusted using a syringe pump. The boiling curves of the device temperature as a function of the input power have been measured for various flow rates. The curves for increasing and decreasing heat flux exhibit a hysteresis loop, while the conditions corresponding to the onset of nucleate boiling and critical heat flux (CHF) are clearly distinguishable. The activity of nucleation sites as well as the ensuing bubble dynamics, from incipience to departure, is found to depend on the channel height. The critical size above which a nucleation site is active, along with three aspects of bubble dynamics, namely growth rate, departure size and release frequency, have been characterized experimentally and proper control parameters have been identified.
    Journal of Micromechanics and Microengineering 10/2005; 15(11):2121. · 1.79 Impact Factor
  • Man Lee, L. Siu Lun Cheung, Yi-Kuen Lee, Man Wong, Y. Zohar
    [Show abstract] [Hide abstract]
    ABSTRACT: A thermal microsystem, integrated with pressure and temperature microsensors, is fabricated to study convective boiling under uniform heat flux boundary condition. Utilizing a wafer bond and etch back technology, the heat source, temperature and pressure sensors are separated from the fluid flow by a membrane only 1.5μm in thickness; thus, allowing experimentally good control of the thermal boundary conditions. Temperature distributions for various input power levels have been measured to obtain the boiling curves. The conditions corresponding to the onset of two phase flow, with boiling plateau, and the critical heat flux (CHF) are clearly distinguishable. Simultaneously, time-dependent pressure signals have also been recorded. In single liquid phase flow, the pressure is constant with time. However, in two phase flow, strong pressure fluctuations occur with certain frequencies. The qualitative visualizations of the evolving flow patterns have been correlated with the quantitative temperature and pressure measurements.
    Micro Electro Mechanical Systems, 2005. MEMS 2005. 18th IEEE International Conference on; 03/2005
  • L. Siu Lun Cheung, Man Lee, Yi-Kuen Lee, Man Wong, Y. Zohar
    [Show abstract] [Hide abstract]
    ABSTRACT: The height effect on bubble dynamics in a microchannel is experimentally studied. We reported that the critical size for a nucleation site to be active increases linearly with the channel height. However, once a bubble is formed, its evolution from incipience to departure can also be channel-size dependent. Thus, various microchannel heat sinks have been fabricated, about 5-10 μm in height, with integrated temperature sensors utilizing Si-to-glass anodic bonding technology. Nucleation sites have been formed on the microchannels bottom silicon surface in order to ensure regular bubble formation, while the sensors allow continuous monitoring of the wall temperature. The microchannels are capped by a glass wafer; hence, it is possible to record the bubble activity using video equipment. The three aspects of bubble dynamics: growth rate, departure size and release frequency have been characterized experimentally, and proper control parameters have been identified.
    Proceedings of the IEEE International Conference on Micro Electro Mechanical Systems (MEMS) 01/2005;
  • Man Lee, Luthur Siu Lun Cheung, Yi-Kuen Lee, Man Wong, Y. Zohar
    [Show abstract] [Hide abstract]
    ABSTRACT: Forced convection boiling in microchannels is studied experimentally under uniform heat flux boundary condition. Several microchannel heat sinks, ranging in height between 5 and 20 μm, have been fabricated using standard micromachining techniques with nucleation sites varying in size etched at the channels bottom surface. The heat flux was provided by a heater integrated at the device back side, while constant water flow rate was supplied by a syringe pump. Boiling curves of device temperature as a function of the input power have been measured for a variety of conditions. The points corresponding to the onset of nucleate boiling and critical heat flux (CHF) are clearly distinguishable. Furthermore, the boiling curves for increasing and decreasing heat flux exhibit a hysteresis loop. The activity of the nucleation sites is found to depend on the channel height. The critical size, above which nucleation sites are active, increases exponentially with the microchannel height, asymptotically approaching a theoretical value.
    Micro Electro Mechanical Systems, 2004. 17th IEEE International Conference on. (MEMS); 02/2004