Dynamic simulation of a peristaltic micropump considering coupled fluid flow and structural motion

This paper presents lumped-parameter simulation of dynamic characteristics of peristaltic micropumps. The pump consists of three pumping cells connected in series, each of which is equipped with a compliant diaphragm that is electrostatically actuated in a peristaltic sequence to mobilize the fluid. Diaphragm motion in each pumping cell is first represented by an effective spring subjected to hydrodynamic and electrostatic forces. These cell representations are then used to construct a system-level model for the entire pump, which accounts for both cell- and pump-level interactions of fluid flow and diaphragm vibration. As the model is based on first principles, it can be evaluated directly from the device's geometry, material properties and operating parameters without using any experimentally identified parameters. Applied to an existing pump, the model correctly predicts trends observed in experiments. The model is then used to perform a systematic analysis of the impact of geometry, materials and pump loading on device performance, demonstrating its utility as an efficient tool for peristaltic micropump design

Complete gradient-LC-ESI system on a chip for protein analysis

This paper presents the first fully integrated gradient-elution liquid chromatography-electrospray ionization (LC-ESI) system on a chip. This chip integrates a pair of high-pressure gradient pumps, a sample injection pump, a passive mixer, a packed separation column, and an ESI nozzle. We also present the successful on-chip separation of protein digests by reverse phase (RP)-LC coupled with on-line mass spectrometer (MS) analysis

Surface micromachined electrostatically actuated micro peristaltic pump

An electrostatically actuated micro peristaltic pump is reported. The micro pump is entirely surface micromachined using a multilayer parylene technology. Taking advantage of the multilayer technology, the micro pump design enables the pumped fluid to be isolated from the electric field. Electrostatic actuation of the parylene membrane using both DC and AC voltages was demonstrated and applied to fluid pumping based on a 3-phase peristaltic sequence. A maximum flow rate of 1.7 nL min^–1 and an estimated pumping pressure of 1.6 kPa were achieved at 20 Hz phase frequency. A dynamic analysis was also performed with a lumped-parameter model for the peristaltic pump. The analysis results allow a quantitative understanding of the peristaltic pumping operation, and correctly predict the trends exhibited by the experimental data. The small footprint of the micro pump is well suited for large-scale integration of microfluidics. Moreover, because the same platform technology has also been used to fabricate other devices (e.g. valves, electrospray ionization nozzles, filters and flow sensors), the integration of these different devices can potentially lead to versatile and functional micro total analysis systems (µTAS)

Induced Stem Cells as a Novel Multiple Sclerosis Therapy.

Stem cell replacement is providing hope for many degenerative diseases that lack effective therapeutic methods including multiple sclerosis (MS), an inflammatory demyelinating disease of the central nervous system. Transplantation of neural stem cells or mesenchymal stem cells is a potential therapy for MS thanks to their capacity for cell repopulation as well as for their immunomodulatory and neurotrophic properties. Induced pluripotent stem cell (iPSC), an emerging cell source in regenerative medicine, is also being tested for the treatment of MS. Remarkable improvement in mobility and robust remyelination have been observed after transplantation of iPSC-derived neural cells into demyelinated models. Direct reprogramming of somatic cells into induced neural cells, such as induced neural stem cells (iNSCs) and induced oligodendrocyte progenitor cells (iOPCs), without passing through the pluripotency stage, is an alternative for transplantation that has been proved effective in the congenital hypomyelination model. iPSC technology is rapidly progressing as efforts are being made to increase the efficiency of iPSC therapy and reduce its potential side effects. In this review, we discuss the recent advances in application of stem cells, with particular focus on induced stem/progenitor cells (iPSCs, iNSC, iOPCs), which are promising in the treatment of MS

Superconductivity in the Nb-Ru-Ge σ\sigma-Phase

We show that the previously unreported ternary $\sigma$-phase material Nb$_{20.4}$Ru$_{5.7}$Ge$_{3.9}$ is a superconductor with a critical temperature of 2.2 K. Temperature-dependent magnetic susceptibility, resistance, and specific heat measurements were used to characterize the superconducting transition. The Sommerfeld constant $\gamma$ for Nb$_{20.4}$Ru$_{5.7}$Ge$_{3.9}$ is 91 mJ mol-f.u.$^{-1}$K$^{-2}$ and the specific heat anomaly at the superconducting transition, $\Delta$C/$\gamma$T$_c$, is approximately 1.38. The zero-temperature upper critical field ($\mu_0$H$_{c2}$(0)) was estimated to be 2 T by resistance data. Field-dependent magnetization data analysis estimated $\mu_0$H$_{c1}$(0) to be 5.5 mT. Thus, the characterization shows Nb$_{20.4}$Ru$_{5.7}$Ge$_{3.9}$ to be a type II BCS superconductor. This material appears to be the first reported ternary phase in the Nb-Ru-Ge system, and the fact that there are no previously reported binary Nb-Ru, Nb-Ge, or Ru-Ge $\sigma$-phases shows that all three elements are necessary to stabilize the material. A $\sigma$-phase in the Ta-Ru-Ge system was synthesized but did not display superconductivity above 1.7 K, which suggests that electron count cannot govern the superconductivity observed. Preliminary characterization of a possible superconducting $\sigma$-phase in the Nb-Ru-Ga system is also reported.Comment: 7 pages, 8 figures, 3 table

Integrated surface-micromachined mass flow controller

An integrated surface-micromachined mass flow controller (MFC) that consists of an electrostatically actuated microvalve and a thermal flow sensor is presented here. With a unique design and utilizing a multilayer Parylene process, the active microvalve and the flow sensor are integrated onto a single chip to perform closed-loop flow control. Sensitivity of the flow sensor is 55 μV/(μ/L/min) for airflow and 12.2 μV/(nL/min) for water. The valve is actuated with a 10 kHz AC signal and an applied pressure of 21 kPa can be sealed with an actuation voltage of 200 V_peak (±200 V). For flow control, both Pulse Width Modulation (PWM) and actuation voltage adjustment are demonstrated. PWM shows better performance in terms of controllability and linearity

Surface micromachined and integrated capacitive sensors for microfluidic applications

We have demonstrated an entire series of capacitive sensors using a multi-layer parylene/photoresist surface micromachining technology. The developed sensors are designed for total integration into parylene-based microfluidic systems for real-time system monitoring. Sensors have been demonstrated for the following applications: in-line pressure sensing (range: 0-35 kPa, resolution: 0.03 kPa); liquid front position and/or volumetric measurements (range: 0->50 pL, resolution: <5 pL); and dielectric measurements, which can be used to deduce fluid properties such as liquid composition. The reported sensor technology demonstrates versatility, high sensitivity, small footprints, and easy integration

A Sensitive Film Structure Improvement of Reduced Graphene Oxide Based Resistive Gas Sensors

This study was focused on how to improve the gas sensing properties of resistive gas sensors based on reduced graphene oxide. Sol-airbrush technology was utilized to prepare reduced graphene oxide films using porous zinc oxide films as supporting materials mainly for carbon dioxide sensing applications. The proposed film structure improved the sensitivity and the response/recovery speed of the sensors compared to those of the conventional ones and alleviated the restrictions of sensors\u27 performance to the film thickness. In addition, the fabrication technology is relatively simple and has potential for mass production in industry. The improvement in the sensitivity and the response/recovery speed is helpful for fast detection of toxic gases or vapors in environmental and industrial applications

Surface micromachined leakage proof Parylene check valve

We report here a surface micromachined leakage proof Parylene MEMS check valve that has nearly ideal performance. This new check valve has a unique design that its valve membrane has a sealing ring directly deposited on, and hence in direct contact with, the gold-coated valve seat. The adhesion between Parylene and gold is studied along with the reduction of adhesion of the sealing ring to the valve seat when self-assembled monolayer (SAM) coatings are used on gold. Testing results clearly demonstrate the effectiveness of SAM coating. Experiments show that the valves have no observable leakage in the reverse flow direction up to 30 psi and a cracking pressure less than 1 psi in the forward flow direction. Integration of this valve with microchannels in a microfluidic system is also demonstrated. Testing shows the in-channel check valve also has nearly ideal performance under both forward and reverse flow

Electrolysis-based on-chip dispensing system for ESI-MS

We report here an integrated on-chip sample dispensing system for Electrospray Ionization-Mass Spectrometry (ESI-MS) applications. The stand-alone chip includes an electrolysis-based micropump, a passive micro mixer and an ESI nozzle. Operation of the chip doesn't require any external fluidic coupling because the chip is designed to have samples filled, sealed and stored in reservoirs inside the chip before testing. Demonstrated here is a chip with two sample reservoirs and dispensing of the samples is electrically controlled individually. Experimentally, on-chip co-dispensing of two different samples is successfully achieved with a dispensing flow rate about 50 nl/min and a continuous spray for 2 minutes