B. Le Pioufle

Positioning living cells on a high-density electrode array by negative dielectrophoresis

We present in this paper a large-scale microelectrode array, which allows a dielectrophoretic positioning of cells in a matrix form. The electrode structure was chosen to produce regularly spaced field minima, toward which particles are directed and concentrated, under conditions of negative DEP. The need to power thousands of electrodes at the same time guided the choice of a multilayer structure. Cells can also be directed toward small wells formed in silicon, where they remain when the field is removed.

COMPARISON OF SPEED NONLINEAR CONTROL STRATEGIES FOR THE SYNCHRONOUS SERVOMOTOR

ABSTRACT In this paper, several strategies to improve robustness and performances of speed nonlinear control of the synchronous servomotor are proposed and compared. The followed procedure consists in imposing the maximum acceptable motor torque during any speed transient, for any load torque, (the response time becoming then optimum), by means of saturation of the current in the quadrature axis, or by means of a real time speed asymptotic trajectory computation. The latter strategy permits to eliminate the influence of an highly perturbed load torque on the regulated speed. Every controller presented here includes a load torque estimator, and a constraint on the motor currents. Simulations and experimental results are performed in order to confirm theoretical ones.

Living cells captured on a bio-microsystem devoted to DNA injection

Abstract This paper deals with the realization of a microsystem for living cell manipulation. The aim of this research is to make a high-efficiency DNA injection microsystem, thus providing a powerful tool for genetic therapy. Our microsystem is multifunctional: it is expected to catch ill cells, range them as an array, insert the therapeutic DNA as well as a control gene, detect nontransfected cells for their lysis, and liberate transfected cells for their culture and reinsertion into the body of the patient. For the cell trapping specificity, we use antibodies. For the spatial selectivity of the cell trapping (the cell has to be localized precisely on specified areas of the microsystem), two methods are presented in the paper to pattern the surfaces covered with antibodies. To make such a microsystem, we have to integrate two types of technologies: the technology of micromachining to realize the mechanical part of the microsystem (for instance, microcapillaries to lead the gene up to the cell), and the technology that is more related to biochemistry and biology for the cells linking part.

A technique to design complex 3D lab on a chip involving multilayered fluidics, embedded thick electrodes and hard packaging—application to dielectrophoresis and electroporation of cells

Nowadays, lab on chips (LOCs) require the development of new technologies in order to integrate complex fluidics, sensors, actuators, etc. Such integration requires overcoming both technological bottlenecks and an increase in production cost. We propose a technique to manufacture reusable and complex LOCs made up of SU-8 resist for the fluidic structure and of glass for the hard packaging, and are compatible with the integration of thick electrodes. The method is based on the combination of two bonding technologies, both based on a wafer bonder. The first one consists of the bonding of a thin photosensitive SU-8 dry film, which is similar to lamination. The second one is the standard bonding technique which uses a hard substrate covered by an SU-8 layer. The LOCs that can be obtained by combining these two methods are transparent, and include 3D microfluidic structures and thick electrodes. Moreover, these LOCs are reusable, packaged and ready to use. In order to validate the concept, we designed an LOC devoted to cell arraying, using dielectrophoresis, as well as to cell electroporation.

COMPARISON OF CONTROL STRATEGIES TO MINIMIZE THE TORQUE RIPPLE OF A SWITCHED RELUCTANCE MACHINE

ABSTRACT The Switched Reluctance Machine (SRM) presents simple structure with passive rotor without windings nor any magnets. That enables applications in mass production (low production and material costs) or in harsh environments (high temperature...). Unfortunately, its polyphase torque is naturally pulsed because of the highly nonlinear electromagnetic characteristics and because the phases have to be successively commutated in order to maintain a continuous rotation. A torque control associated with an appropriate strategy for the phase commutation is thus sought in order to reduce the torque ripple. Initially, the limits of the classical linear control (Proportional Integral controller) are determined. Then, the performances of the PI controller are improved by means of electromotive forces compensation. Nevertheless, the torque ripple remains significant. In order to compensate for SRM nonlinearities, we propose a nonlinear torque control associated with a suitable commutation strategy. This contro...

A microfluidic device with removable packaging for the real time visualisation of intracellular effects of nanosecond electrical pulses on adherent cells

The biological mechanisms induced by the application of nanosecond pulsed electric fields (nsPEFs: high electrical field amplitude during very short duration) on cells remain partly misunderstood. In this context, there is an increasing need for tools that allow the delivering of such pulses with the possibility to monitor their effects in real-time. Thanks to miniaturization and technology capabilities, microtechnologies offer great potential to address this issue. We report here the design and fabrication of a microfluidic device optimized for the delivery of ultra short (10 ns) and intense (up to 280 kV cm(-1)) electrical pulses on adherent cells, and the real time monitoring of their intracellular effects. Ultra short electric field pulses (nsPEFs or nanopulses) affect both the cell membrane and the intracellular organelles of the cells. In particular, intracellular release of calcium from the endoplasmic reticulum was detected in real time using the device, after exposure of adherent cells to these nsPEFs. The high intensity and spatial homogeneity of the electric field could be achieved in the device thanks to the miniaturization and the use of thick (25 μm) electroplated electrodes, disposed on a quartz substrate whose transparency allowed real time monitoring of the nsPEFs effects. The proposed biochip is compatible with cell culture glass slides that can be placed on the chip after separate culture of several days prior to exposure. This device allows the easy exposure of almost any kind of attached cells and the monitoring in real time while exposed to nsPEFs, opening large possibilities for potential use of the developed biochips.

Vacuum Casting to Manufacture a Plastic Biochip for Highly Parallel Cell Transfection

A novel polymer microarray fabrication technique is presented and applied to the realization of a biochip for highly parallelized cell transfection. The proposed microfabrication technique is derived from a macroscale rapid prototyping technique called vacuum casting. It was optimized to reduce production cost, in order to produce small series (100-10 000 chip series) of chips to meet demand in todays market of cellulomics. Microfabrication technologies and rapid prototyping technologies are combined to shape the master part, which can thus involve microsized features. The corresponding female structure is moulded in a flexible silicone material. The duplicated polymer chips are obtained by casting a thermosetting plastic under vacuum. The dimensional replication accuracy between the master part and the duplicated parts is uniform over the duplicated parts and better than 1%. Advantages of the proposed technique over existing plastic microfabrication techniques are discussed in the paper. Using this microfabrication technique, we produced a plastic biochip for highly parallelized transfection of arrays of living cells. The feasibility of parallel lipofection was demonstrated: two different plasmids encoding, respectively, eGFP and DsRED2 were inserted into HEK293T cells. The transfection was monitored through fluorescence observation after 72 h showing successful expression of both genes.

Effect of the sampling and of the phase commutation in nonlinear position control of a switched reluctance motor-analysis and compensation

In order to maximize the torque/current ratio, the phase currents of the switched reluctance motor (SRM) are controlled with regard to the rotor position. Unfortunately, during the commutation of the currents from one supply phase to another, torque ripples are naturally created. The authors show that the two combined effects of the phase commutation and of the sampling spoil the dynamic performances of the nonlinear position control. Nevertheless, with regard to todays technology, the sampling period cannot be reduced. Thus, a new phase current commutation strategy is proposed in order to reduce the torque ripple and to improve the dynamic performances of the nonlinear position control.<<ETX>>

A precise analysis of the phase commutation for the torque nonlinear control of a switched reluctance motor - torque ripples minimization

Because of its geometric and electromagnetic structure, the switched reluctance motor (SRM) naturally creates torque ripples during the commutation of the currents from one supply phase to another. We show in the paper that classical linear controllers cannot eliminate these torque pulsations. Thus, we propose a method to remove the torque ripples by applying a torque nonlinear control associated with a suitable phase commutation strategy. Indeed, a precise analysis of the phase commutation, permitted us to present a solution taking into account the currents gradient limitation due to the motor-converter set as well as the sampling effect. Finally, the effect of the modeling errors on the robustness of this control has been verified.<<ETX>>

The Electrorotation as a Tool to Monitor the Dielectric Properties of Spheroid During the Permeabilization

This paper proposes to monitor the spheroid’s permeabilization within a dedicated microfluidic device using electrorotation analyses. The combination of two electric solicitations, the negative dielectrophoresis force (nDEP) for the spheroid trapping and the electrorotation torque for its dielectric characterization, is used. An estimation of the spheroid dielectric parameters is obtained through the analysis of the rotational velocity curve versus the electric field frequency before and after the PEF application. An observation set-up includes a fast camera that allows time controlled image sequence acquisition. Frames are then digitalized and from the analysis of the rotational velocity of the spheroid, its complex permittivity is determined. Different models, involving the variation of the dielectric properties of the concentric shells that constitute the spheroid, as well as the heterogeneity of cells within each shell, are proposed and used to determine its dielectric properties.