Cheng-Hsin Chuang

Elastic moduli and plastic collapse strength of hexagonal honeycombs with plateau borders

The theoretical analysis for the elastic moduli and plastic collapse strength of hexagonal honeycombs with Plateau borders is proposed and presented here. The variation of cell edge thickness in real honeycombs is taken into account in deriving their elastic moduli and plastic collapse strengths. A repeating element, composed of three cell edges connected at a vertex with Plateau borders of constant radius of curvature and width, is employed to calculate the elastic moduli and plastic collapse strength of hexagonal honeycombs. Results suggest that both the elastic moduli and plastic collapse strength of hexagonal honeycombs with Plateau borders depend on their relative density and the volume fraction of solid contained in the Plateau border region. Meanwhile, effects of solid distribution on the elastic moduli and plastic collapse strength of hexagonal honeycombs are investigated, providing a guideline for the optimal microstructure design of honeycombs.

Effects of solid distribution on the elastic buckling of honeycombs

The elastic buckling strengths of honeycombs depend on their relative density, cell geometry and the elastic modulus of solid cell edges. In this study, we consider the effect of the distribution of solid between three cell edges and a vertex on elastic buckling using a semi-analytical integral-equation approach. At first, the geometry of three cell edges connected at a vertex with Plateau borders is analyzed and then employed to represent a repeating element for regular hexagonal honeycombs. The bending moments, rotational angle and the stiffness of a rotational spring corresponding to the constraint from inclined adjacent cell edges are derived for the vertical cell edge within the repeating element. Consequently, the elastic buckling strength of regular hexagonal honeycombs can be numerically obtained. Moreover, the effects of the distribution of the solid on the elastic buckling strengths of regular hexagonal honeycombs are presented and evaluated.

System-Level Biochip for Impedance Sensing and Programmable Manipulation of Bladder Cancer Cells

This paper develops a dielectrophoretic (DEP) chip with multi-layer electrodes and a micro-cavity array for programmable manipulations of cells and impedance measurement. The DEP chip consists of an ITO top electrode, flow chamber, middle electrode on an SU-8 surface, micro-cavity arrays of SU-8 and distributed electrodes at the bottom of the micro-cavity. Impedance sensing of single cells could be performed as follows: firstly, cells were trapped in a micro-cavity array by negative DEP force provided by top and middle electrodes; then, the impedance measurement for discrimination of different stage of bladder cancer cells was accomplished by the middle and bottom electrodes. After impedance sensing, the individual releasing of trapped cells was achieved by negative DEP force using the top and bottom electrodes in order to collect the identified cells once more. Both cell manipulations and impedance measurement had been integrated within a system controlled by a PC-based LabVIEW program. In the experiments, two different stages of bladder cancer cell lines (grade III: T24 and grade II: TSGH8301) were utilized for the demonstration of programmable manipulation and impedance sensing; as the results show, the lower-grade bladder cancer cells (TSGH8301) possess higher impedance than the higher-grade ones (T24). In general, the multi-step manipulations of cells can be easily programmed by controlling the electrical signal in our design, which provides an excellent platform technology for lab-on-a-chip (LOC) or a micro-total-analysis-system (Micro TAS).

Immunosensor for the ultrasensitive and quantitative detection of bladder cancer in point of care testing.

An ultrasensitive and real-time impedance based immunosensor has been fabricated for the quantitative detection of Galectin-1 (Gal-1) protein, a biomarker for the onset of multiple oncological conditions, especially bladder cancer. The chip consists of a gold annular interdigitated microelectrode array (3×3 format with a sensing area of 200µm) patterned using standard microfabrication processes, with the ability to electrically address each electrode individually. To improve sensitivity and immobilization efficiency, we have utilized nanoprobes (Gal-1 antibodies conjugated to alumina nanoparticles through silane modification) that are trapped on the microelectrode surface using programmable dielectrophoretic manipulations. The limit of detection of the immunosensor for Gal-1 protein is 0.0078mg/ml of T24 (Grade III) cell lysate in phosphate buffered saline, artificial urine and human urine samples. The normalized impedance variations show a linear dependence on the concentration of cell lysate present while specificity is demonstrated by comparing the immunosensor response for two different grades of bladder cancer cell lysates. We have also designed a portable impedance analyzing device to connect the immunosensor for regular checkup in point of care testing with the ability to transfer data over the internet using a personal computer. We believe that this diagnostic system would allow for improved public health monitoring and aid in early cancer diagnosis.

Dielectrophoretic chip with multilayer electrodes and microcavity arrays for trapping and programmable releasing of single cells

Cell characterization analysis usually involves a sequence of steps such as culture, separation, trapping, examination and recollection. In general, it is difficult to recover the identified cells and achieve a multi-run examination on a single chip for clinical samples. In the present study, a dielectrophoresis (DEP) micro-device was developed for multi-step manipulations of cells at the single-cell level. The structure of the DEP chip consisted of an indium tin oxide (ITO) top electrode, a flow chamber, a middle electrode on an SU-8 surface, a micro-cavity array of SU-8 and distributed electrodes at the bottom of the micro-cavities. The purpose of the three-layer-electrode design was threefold. First, cells could be trapped into the micro-cavities by negative DEP between the top and middle electrodes. After cells were trapped, cell analysis at the single-cell level could potentially be performed. This could include, for example, drug treatment or biomedical sensing on the chip without applying voltage. Once identified, the target cells could be individually released by controlling the bottom distributed electrodes. Finally, the rest of the trapped cells could be pulled out by a positive DEP force between the top and middle electrodes and flushed away for the next run of cell analysis. The multi-step manipulations of human bladder cancer cells (TSGH8301) were successfully demonstrated and discussed, providing an excellent platform technology for a lab-on-a-chip (LOC).

Algorithm optimization in molecular dynamics simulation

Abstract Establishing the neighbor list to efficiently calculate the inter-atomic forces consumes the majority of computation time in molecular dynamics (MD) simulation. Several algorithms have been proposed to improve the computation efficiency for short-range interaction in recent years, although an optimized numerical algorithm has not been provided. Based on a rigorous definition of Verlet radius with respect to temperature and list-updating interval in MD simulation, this paper has successfully developed an estimation formula of the computation time for each MD algorithm calculation so as to find an optimized performance for each algorithm. With the formula proposed here, the best algorithm can be chosen based on different total number of atoms, system average density and system average temperature for the MD simulation. It has been shown that the Verlet Cell-linked List (VCL) algorithm is better than other algorithms for a system with a large number of atoms. Furthermore, a generalized VCL algorithm optimized with a list-updating interval and cell-dividing number is analyzed and has been verified to reduce the computation time by 30 ∼ 60 % in a MD simulation for a two-dimensional lattice system. Due to similarity, the analysis in this study can be extended to other many-particle systems.

Theoretical expressions for describing the stiffness and strength of regular hexagonal honeycombs with Plateau borders

Abstract The effects of non-uniform cell-edge cross-section on the theoretical expressions for describing the stiffness and strength of regular hexagonal honeycombs are evaluated here. The non-uniform cross-section is taken to be a Plateau border. The microstructure coefficients and exponent constants in the theoretical expressions for describing the Youngs modulus, shear modulus, plastic collapse strength and elastic buckling strength of regular hexagonal honeycombs are modified to account for the effect of solid distribution in cell edges. Consequently, the design maps of regular hexagonal honeycombs with Plateau borders for any prescribed stiffness and strength are generated. Meanwhile, the optimal value of Φ 2 , characterizing the solid distribution in cell edges, is obtained and found to be dependent on the relative density we specified.

Flexible piezoelectric tactile sensor with structural electrodes array for shape recognition system

This study provides an efficient and feasible solution to enhance the sensitivity of traditional piezoelectric tactile sensor based on introducing structural electrode upon the sensing material. A sandwich structure for flexible tactile sensor consists of top and bottom soft substrates made of Polystyrene, and in between of two soft substrates a piezoelectric thin film, PVDF, and a PDMS microstructures array are utilized as sensing material and microstructures, respectively. The experimental results showed the output voltage was linear with contact force from 10N to 0.5 N and good reliability within low frequency range 1 ~ 100 Hz. In addition, the shape recognition also can be achieved as the objective contacted with the 4 by 4 electrodes array. The effects of structural electrode on the enhancement of sensitivity were also numerically simulated by finite element method (FEM) and verified experimentally by dynamic measurement system, respectively. In general, the flexible tactile sensor developed in this study is not only applied for detecting contact force but also for the human physiology monitoring system, such as pulsation, heart rate and blood pressure, etc.

Enhancing of intensity of fluorescence by DEP manipulations of polyaniline-coated Al2O3 nanoparticles for immunosensing

A novel modification of low-cost Al₂O₃ nanoparticles (Al₂O₃ NPs) for antibody-protein immunosensing is proposed. The modified NPs are utilized to enhance the intensity of fluorescence in a dielectrophoretic (DEP) chip with a microelectrode array. The surface of the Al₂O₃ NPs is modified by ionic polyaniline (PANDB) rather than the conventional silane (3-aminopropyltrimethoxysilane) to conjugate the antibody on the outer shell. After the PANDB-Al₂O₃ NPs is functionalized to form probes, a DEP chip with a vertical non-uniform electric field that is produced by top and bottom electrodes condenses and immobilizes the nanoprobes on the surface of the electrodes by positive DEP force for immunosensing of the fluorescent protein. Additionally, each microelectrode array can be individually controlled with/without DEP manipulation using a computer program. Experimental results indicate that PANDB-based nanoprobes provide more rapid and sensitive immunosensing than those having undergone conventional silane modification. During immunosensing, fluorescence intensity can be doubled by the application of extra DEP force. The individual control of NPs on the microelectrode array has great potential for applications in multi-antibody arrays in a single chip for immunosensing.

Impedance sensing of bladder cancer cells based on a single-cell-based DEP microchip

Differentiation of normal human bladder cell (SVHUC) between two different-grade bladder cancer cell lines (TSGH8301, grade II and TCCSUP, grade IV) was successful developed based on a dielectrophoresis (DEP) microchip with microcavity array and multilayer electrodes. Single cell could be firstly trapped in the microcavity by negative DEP force between top and middle electrodes without overlapping problem; then, the trapped cells were sensed its impedance by sweeping AC signal in between middle and bottom electrodes. As the experimental results, the impedance of higher-grade bladder cancer cells was smaller than the value of lower-grade bladder cancer cells, i.e., TCCSUP (grade IV) ≫ TSGH8301 (grade II), and the impedance of normal bladder cell was much higher than the values of both cancer cell lines. Basically, the impedances of all kinds of cell lines were decreased with the delay time measured when cells were taken out of the incubator. The largest difference of impedance between normal cells and cancer cells occurred as the delay time reached 1 hour, furthermore, the ratio of impedance between cancer cells and normal cells measured at 1 KHz and 0.2 V were 54% and 22% for TSGH8301 and TCCSUP, respectively. Consequently, the possibility of impedance measurement for evaluation of cancer cells was first proposed and investigated; moreover, the microchip provides the potential of electrical sensing for in vitro diagnosis under single cell resolution.