Elisabeth Dufour-Gergam

Université Paris-Sud 11, Orsay, Île-de-France, France

Are you Elisabeth Dufour-Gergam?

Claim your profile

Publications (65)71.47 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Cells submitted to an electric field gradient experience dielectrophoresis. Such a force is useful for pairing cells prior to electrofusion. The latter event is induced by the application of electric field pulses leading to membrane fusion while cells are in physical contact. Nevertheless, the efficiency of dielectrophoretic pairing and electrofusion of cells are highly dependent on medium properties (osmolarity and conductivity). In this paper, we examine the effect of medium osmolarity on volume, viability and electrical properties of cells. Then we characterize in real time the impact of electropermeabilization of cells on their dielectrophoretic response. To do so, a microfluidic device, inducing particular field topologies is used. These real time observations are correlated to numerical analysis of the Clausius-Mossotti factor. Taking into account the identified changes, an electrofusion protocol adequate to the optimal medium (100 mOsm, 0.03 S/m) is defined. Up to 75 % simultaneous binuclear rapid electrofusions were achieved and monitored with average membrane fusion duration lower than 12 s.
    Bioelectrochemistry 12/2014; · 3.87 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: In this paper, we describe and characterize a novel method, based on silanization, for strong bonding of SU8 microchannels to poly(dimethyl)siloxane (PDMS) flexible covers. First, the SU8 surface treatment process (silanization) is characterized through atomic force microscopy and contact angle measurements. The aging study proves grafting stability during more than two days. Silanized SU8 patterns and PDMS cover are finally bonded to seal the microchannel network. Such assembled microdevices can be used without leakage at flow rates above 2.4 mL/min, corresponding to 1.2 MPa if the PDMS deformation is neglected. The bonding tensile pressure exceeds 1.5 MPa, proving the packaging strength. Furthermore, SU8-PDMS composite devices display stable bonding after several weeks of storage. This rapid low cost and low temperature bonding technique is finally successfully employed to fabricate a fully packaged biochip for electric and fluidic handling of biological cells. [2014-0116]
    Journal of Microelectromechanical Systems 10/2014; 23(5):1015-1024. · 1.92 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: In this paper, the design, the fabrication and the electromechanical characterization of polymer-based flexible pressure sensor are presented. This kind of sensors is developed for the non-invasive monitoring of pressure/force distributions that is required in many medical applications such as the monitoring of plantar pressures or chronic venous disorder treatments. The sensors considered in this paper are of a capacitive type. They are composed of two millimetric copper electrodes, separated by polydimethylsiloxane (PDMS) dielectric layers and deposited on a Kapton substrate. A study of the deformation of PDMS thin films under normal stress is carried out by finite element computations as well as experiments. This study points out a sensor design optimization parameter, the form ratio of the indented PDMS layer, which is used to design and fabricate capacitive micro-sensors samples. Preliminary electromechanical characterizations of realized sensor samples validate the approach. Under a 10 N normal stress, the sensitivity of 9 square mm sensors varies from 3% up to 17% in capacitive change, according to the chosen form ratio of the used PDMS layer.
    2014 IEEE International Symposium on Medical Measurements and Applications (MeMeA); 06/2014
  • [Show abstract] [Hide abstract]
    ABSTRACT: The aim of this work is to develop a sensitive and specific immune-sensing platform dedicated to the detection of potential biomarkers of Alzheimer disease (AD) in biological fluids. Accordingly, a controlled and adaptive surface functionalization of a silicon wafer with 7-octenyltrichlorosilane has been performed. The surface has extensively been characterized by AFM (morphology) and XPS (chemical composition) and contact angle measurements. The wettability of the grafted chemical groups demonstrated the gradual trend from hydrophilic to hydrophobic surface during functionalization. XPS evidenced the presence of silanes on the surface after silanization, and even carboxylic groups as products from the oxidation step of the functionalization process. The characterization results permitted us to define an optimal protocol to reach a high-quality grafting yield. The issue of the quality of controlled chemical preparation on bio-receiving surfaces was also investigated by the recognition of one Alzheimer disease (AD) biomarker, the Amyloïd peptide Aβ 1-42. We have therefore evaluated the biological activity of the grafted anti Aβ antibodies onto this silanized surface by fluorescent microscopy. In conclusion, we have shown, both qualitatively and quantitatively, the uniformity of the optimized functionalization on slightly oxidized silicon surfaces, providing reliable and chemically stable procedure to determine specific biomarkers of Alzheimer disease. This work opens the route to the integration of controlled immune-sensing applications on lab-on-chip systems.
    Langmuir 03/2014; · 4.38 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Cell fusion consists of inducing the formation of a hybridoma cell containing the genetic properties of the progenitor cells. Such an operation is usually performed chemically or electrically. The latter method, named electrofusion, is considered as having a strong potential, due to its efficiency and non-toxicity, but deserves further investigations prior to being applicable for key applications like antibody production and cancer immunotherapy. Indeed, to envision such applications, a high amount of hybrid cells is needed. In this context, we present in this paper a device for massive cell pairing and electrofusion, using a microarray of non-connected conductive pads. The electrofusion chamber––or channel––exposes cells to an inhomogeneous electric field, caused by the pads array, enabling the trapping and pairing of cells with dielectrophoresis (DEP) forces prior to electrofusion. Compared to a mechanical trapping, such electric trapping is fully reversible (on/off handling). The DEP force is contactless and thus eases the release of the produced hybridoma. Moreover, the absence of wire connections on the pads permits the high density trapping and electrofusion of cells. In this paper, the electric field mapping, the effect of metallic pads thickness, and the transmembrane potential of cells are studied based on a numerical model to optimize the device. Electric calculations and experiments were conducted to evaluate the trapping force. The structure was finally validated for cell pairing and electrofusion of arrays of cells. We believe that our approach of fully electric trapping with a simple structure is a promising method for massive production of electrofused hybridoma.
    Biomicrofluidics. 07/2013; 7:044101.
  • [Show abstract] [Hide abstract]
    ABSTRACT: In this paper, we investigate the different parameters that affect the distribution of the transmembrane potential of cells brought into contact before electrofusion in a miniaturized fluidic device. In particular, we discuss the deviation of the effective transmembrane voltage compared to the one predicted by Schwan’s law. The application of electric field pulses to biological cells induces a transmembrane potential which leads to cell permeabilization. Electrofusion occurs when several cells are brought into contact while they are electropermeabilized. Nevertheless, we show that in this case, the mutual presence of cells interferes on Schwan’s equation. Consequently, the transmembrane voltage at the cell contacting point is drastically reduced, which is not favorable for an electrofusion in smooth conditions, as the applied voltage needs to be increased to compensate this phenomenon. We show that the introduction of polymer obstacles reverses this trend, as the high electric field region is focused on the fusion zone. To confirm the theory we developed, quantitative biological experiments are presented in which murine melanoma cells were paired and fused in both conditions (with and without obstacles).
    The European Physical Journal Applied Physics 04/2013; 62(1):11202. · 0.79 Impact Factor
  • BiodevicesBiodevices; 01/2013
  • T.H.N. Dinh, P.-Y. Joubert, E. Martincic, E. Dufour-Gergam
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper presents an efficient and reproducible fabrication process of flexible-substrate-based pressure sensor arrays, using a technology of film transfer which has been recently developed in our laboratory [1]. The sensors are composed of two millimetric copper electrodes, separated by a polydimethylsiloxane (PDMS) dielectric layer, the operation of which is based on a capacitance change induced by an applied force. Sensor arrays were fabricated on two types of substrate: a rigid substrate (glass) used for the validation of the fabrication process, and a flexible substrate (Kapton) used to realize the wanted flexible sensors. Regarding the flexible arrays, a very small curvature radius is possible without any damage to the sensors. Six three-by-three sensor arrays were fabricated. They feature capacitances ranging from 3.45 pF to 14.40 pF, according to their dimensions. The discrepancy between the capacitances within each array is quite low (standard deviation is less than 7 % of the mean value). The sensitivity of the considered on-glass samples is around 80 pF/mN under 2N loading conditions.
    Sensors, 2013 IEEE; 01/2013
  • [Show abstract] [Hide abstract]
    ABSTRACT: Combined with high-field MRI scanners, small implanted coils allow for high resolution imaging with locally improved SNR, as compared to external coils. Small flexible implantable coils dedicated to in vivo MRI of the rat brain at 7T were developed. Based on the Multi-turn Transmission Line Resonator design, they were fabricated with a Teflon substrate using copper micromolding process and a specific metal-polymer adhesion treatment. The implanted coils were made biocompatible by PolyDimethylSiloxane (PDMS) encapsulation. The use of low loss tangent material achieves low dielectric losses within the substrate and the use of the PDMS layer reduces the parasitic coupling with the surrounding media. An implanted coil was implemented in a 7T MRI system using inductive coupling and a dedicated external pick-up coil for signal transmission. In vivo images of the rat brain acquired with in plane resolution of (150μm)(2) thanks to the implanted coil revealed high SNR near the coil, allowing for the visualization of fine cerebral structures.
    Journal of Magnetic Resonance 09/2012; 224:61-70. · 2.30 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We propose a concept of very specific immune-sensing platform dedicated to the quantification of biomarkers of Alzheimer disease (AD) in biological fluids. High sensitivity is required for the earliness of AD diagnostic, mainly based on clinical evaluation at present time. Accordingly, a controlled and adaptative surface functionalization of a silicon wafer with carboxylated alkyltrichlorosilane has been developed. The surface has extensively been characterized by AFM and X-ray Photoemissive Spectroscopy. The surface modification has been chemically assessed by XPS at each functionalization step. The survey spectra of silicon surface, after, 1, 3, 6 and 24h of silanisation, highlight a significant enhancement of the functionalization efficiency upon time. The oxidation reaction has also been investigated by XPS and showed components related to the carboxylic group. AFM measurements pointed out a morphological modification consistent with a homogenous development of the carboxylic group and an almost protein monolayer on the surface. Moreover, we evaluated the biological activity of the grafted antibodies involved in (AD) biomarker detection onto this silanized surface by fluorescent microscopy. A sandwich immunoassay dedicated to the sensitive detection of one biomarker of Alzheimer disease (AD), the amyloid peptide 1-42 (Aβ 1-42), was carried out. The results demonstrated that the controlled silanized surface provides a novel and viable way to detect biomarkers with high specificity and open the route to an original development of immune-sensing applications on such surfaces.
    Biosensors & Bioelectronics 08/2012; · 6.45 Impact Factor
  • M Deterre, E Lefeuvre, E Dufour-Gergam
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper presents an energy harvesting technique to power autonomous systems and more particularly active implantable medical devices. We employ a piezoelectric diaphragm placed in a fluidic environment such as blood subjected to very low frequency (2 Hz) pressure variations that is deflected in a quasi-static manner and transduces mechanical energy into electrical energy. In order to maximize energy generation and to get the most out of a given piezoelectric device, we propose to apply an optimized method to extract the piezoelectrically generated charge through the application of a controlled voltage. We believe that this method could be one of the improvement levers to achieve self-powered miniaturized implants. An analytical model is presented and shows that within its validity domain, the extracted energy is proportional to the desired applied voltage. Taking power electronics losses into account can yield a theoretical increase in the extracted energy of several thousand per cent. Experimental measurements in a pressure chamber have been carried out whose results corroborate the proposed model. For the tested setup, the application of a 10 V peak amplitude square-wave voltage increased the extracted energy by a factor of nine compared to a classical rectifier-based energy harvesting method.
    Smart Materials and Structures 08/2012; 21(8). · 2.45 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: In this paper, we present the development of ultra-flexible micro-antennas dedicated to MRI on small rodents. Their design is wireless and based on transmission lines into a dielectric material i.e. PDMS. To overcome the weak adhesion of metal to this polymer surface, we have developed a new fabrication process using transfer technology. This process avoids contact of PDMS with chemicals to preserve the bulk properties. An accurate alignment of conductor lines and a high transfer yield are obtained. The electromagnetic characterization of the antennas validates the reliability of the process. Bending the structures up to a radius of 2 mm does not mechanically alter the copper lines. In these conditions, only a small decrease of f0 (less than 1%) and no change in Q factor are observed. MRI micro-antennas are just an example of application for the developed process which can be used for fabrication of various metallic structures on PDMS.
    Symposium on Design, Test, Integration & Packaging of MEMS/MOEMS (DTIP); 04/2012
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In this paper, we detail how microantennae dedicated to Magnetic Resonance Imaging (MRI) can benefit from the advantages offered by polymer substrates, especially flexibility and dielectric properties. We present a monolithic and wireless design based on the transmission lines between conductor windings on both sides of a dielectric substrate and its fabrication process. This last one requires specific plasma treatments to improve polymer/metal adhesion. We have led a comparative study on the effects of the ageing time on the wettability and the metal adhesion to Kapton and Teflon surfaces. Correlation between wettability (water contact angle) and adhesion (tensile strength) has been established. Then, the use of PolyDiMethylSiloxane (PDMS) as biocompatible packaging material and the optimization of its thickness allows us to conserve suitable f0 and Q values in a conducting environment such as the biological tissues. These studies allow us to perform 7 Tesla in vivo MRI of the rat brain with a high spatial resolution of 100 x 100 x 200 µm3 and a Signal to Noise Ratio of 80.
    Polymers 02/2012; 4(1):656-673. · 2.51 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: In this paper, we present the development of implantable microcoils specifically dedicated to 7Tesla MRI of the rat brain for the diagnosis and monitoring of tumors and neurodegenerative diseases. These coils are flexible and wireless, with an easy batch fabrication. We also present for the first time a study of the packaging effects on the characteristics of the coil, F0 and Q factor. The optimization of the packaging with PDMS allows us to realize the first in vivo image of the rat brain using an implanted flexible microantenna.
    IEEE Topical Conference on Biomedical Wireless Technologies, Networks, and Sensing Systems (BioWireleSS); 01/2012
  • [Show abstract] [Hide abstract]
    ABSTRACT: Despite the large use of this material in the microsystem field, fabrication of metallic patterns on polydimethylsiloxane (PDMS) still remains a challenge. In this Letter, we present a new process based on the transfer principle and report its application to MRI microcoils. These double-side structures are well aligned and the transfer yield is higher than 90%. The limit of the working range for these flexible coils is a bending radius of 2%mm, similar to the radius of the coil. The developed process opens a wide range of further applications for flexible devices.
    Micro & Nano Letters 01/2012; 7(6):519-522. · 0.80 Impact Factor
  • Journal of The Electrochemical Society 01/2012; 159(10):D592-D596. · 2.86 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The novelty of this paper is the proof of func- tional microdevice fabrication using a recently developed low- temperature transfer process. The process is based on adhesion control of molded Ni microstructures on a donor wafer by using plasma-deposited fluorocarbon films. Low-temperature adhesive bonding of the microstructures on the target wafer using benzo- cyclobutene sealing enables mechanical tearing off from the donor wafer. Interest of this process for manufacturing microsensors is demonstrated here in the case of microbeams used as pressure sensors based on the Pirani principle. A simple analytical model is used to estimate the electrothermal behavior of the suspended microwires as a function of the ambient gas pressure. Estimations are compared to experimental measurements performed on Ni electroplated microwires of 550-1200-μm length, 10-μm width, and 0.7-7-μm thickness characterized into a vacuum chamber. These microsensors present a maximum of sensitivity in the range of 0.1-100 mbar, which is in line with standard performances of Pirani gauges. The presented results thus demonstrate the interest of a simple film transfer process for the elaboration of 3-D functional microstructures. (2011-0070)
    Journal of Microelectromechanical Systems 10/2011; 20(5):1184-1191. · 1.92 Impact Factor
  • Source
    MMBMMB; 01/2011
  • Source
    F Hamdi, O Francais, E Dufour-Gergam, B Le Pioufle
    NanobiotechNanobiotech; 01/2011
  • [Show abstract] [Hide abstract]
    ABSTRACT: The miniaturization process in active medical implantable devices is driving the development of novel energy sources such as small volume, high longevity energy harvesting systems. In this study, we present an approach for the design of an inertial energy scavenger powering cardiac implants from heart generated vibrational energy. The heart acceleration spectrum has been measured and analyzed. Achievable power level and design parameters are determined from a spectral analysis to about 100µW before electronics efficiencies for a 0.5 cm3 volume.
    01/2011;