Gaelle OFFRANC-PIRET

En résumé

Entreprises

• Inserm - Chercheur

  PARIS 13 2014 - maintenant

• Division of Solid State Physics & Biomedecine laboratory, Lund University - Chercheur

  2011 - 2013 During this post-doc, I investigated the effects of surface topography and chemistry on cell growth in order to develop highly biocompatible neural implants. Various surface topographies can be designed using either bottom-up or top-down approaches.
  
  Neural implants are already used for retinal prosthesis applications, to temper the symptoms of Parkinson's disease, or help locked-in patients to communicate, and are expected to play an increasingly important role in disease management in the future. Most of the electrodes currently used for these applications have a smooth surface and elicit a tissue response, which leads to the formation of an isolating layer around the electrodes, composed mostly of glial cells. Recently, it was shown that nanostructured surfaces can lower the tissue response to the implant. In order to understand and manipulate the way nanostructures or nanodevices interact with neural cells, we must study both the biostability and the biocompatibility of these materials.
  We report here an in vitro model where retinal cells, which comprise glial cells and neuronal cells, are cultured on different nanowire (NW) surfaces. Using this system, we have analyzed the attachment and survival of the different retinal cell types over time, as well as the degree of neurite extension of retinal cells cultured on gallium phosphide (GaP) NWs of different densities, lengths and diameters, and on (Si) NWs of different topographies and surface chemistries.
  On GaP NWs, photoreceptors, ganglion cells and bipolar cells survive on the substrates for at least 18 days in vitro (DIV). Neurons extend numerous long and branched neurites that express the synaptic vesicle marker synaptophysin. We found also a direct correlation between nanowire length and cell attachment as well as neurite elongation and our analysis suggests that neurons sense the vertical dimension of the NW and/or the biomolecules adsorbed on the nanowires. Glial cells survive until at least 18 DIV as well, but are few in number and present a different morphology than that observed on flat control substrates, suggesting that they may be less proliferative or less mature. (Piret et al, Biomaterials, 2013)
  By choosing the position of the NWs on the substrate, it is possible, in addition, to guide ganglion cell axonal growth and to confine glial cells in specific areas.
  When cultured on Si NWs, however, retinal cells do not exhibit neurite outgrowth and glial cells do not show any cytoplasmic extension. Only a few retinal cell markers are expressed or weakly expressed at 3DIV or 18 DIV. This decreased survival may be due to the degradation of the silicon nanowires over time and/or to the presence of chemical residues from the nanowire fabrication.
  
  
  

• Laboratoire LPMC, Ecole Polytechnique, Palaiseau - CDD, Post-Doctorante

  2010 - 2011 * 1st project
  Guided excitation is an attractive strategy for in situ real time use of fluorescence biochips. This post-doctoral work dealt with the deposition of an amorphous silicon carbon nanofilm on a fluorescent biochip based on this guided excitation. This nanofilm allows for a well controlled surface functionalization with limited increase of waveguide losses.
  The biochip works with a secondary excitation using Eu(TTA)3(H20)3 to absorb UV and emit at the excitation wavelength. The last one is guided thanks to the TiO2 planar waveguide which promotes the excitation and the detection of interactions at the surface of the biochip. During a real time acquisition, the fluorescence noise of the targets solution is then limited as compared to classical biochip.
  The deposition of an amorphous silicon carbon nanofilm by Plasma Enhanced Chemical Vapor Deposition is realized onto the TiO2 biochip surface. The nanofilm has to be optimized in order to keep good waveguide properties. This nanofilm allows the binding of biomolecules (DNA, proteins) through well controlled surface functionalization processes. The quality of the surface biochemistry and the quality of the waveguide will give access to additional valuable quantities on biological interaction mechanisms during fluorescent real-time measurements, and allow new diagnostic applications.
  
  *2nd project
  Nanowires made of crystalline silicon, demonstrate a high potential for applications (biosensors, batteries, solar cells, labs on chip,...). We reported, for the first time, the elaboration of similar nanostructures from amorphous silicon and silicon-carbon alloys.
  We studied the formation of hydrogenated amorphous silicon-carbon alloy (a-Si1-xCx:H) nanowires for different carbon concentrations (0 – 7 %) by using Ag-assisted electroless etching of the thin a-Si1-xCx:H films deposited by plasma-enhanced chemical vapour deposition from silane/methane gas mixtures. The nanowires morphologies (length, density, ...), studied by scanning electron microscopy, strongly depend on the concentration of the etchant (aqueous solution of hydrofluoric acide and silver nitrate), the etching time, and the carbon concentration of the deposited layer.
  Since these alloys are inexpensive and can be deposited in large area on a variety of substrates (glass, plastics, metals or semiconductors), this opens the way to the integration of such nanostructures in different devices for a variety of applications.

• Institut de Recherche Interdisciplinaire - CDD, Doctorante

  2006 - 2009 PhD "Matrix-free laser desorption/ionization mass spectrometry on silicon nanowires and applications " - IRI (Institut de Recherche Interdisciplinaire), collaboration with IEMN (Institut d'Electronique, de Microelectronique et de Nanotechnologie), IBL (Institut de Biologie de Lille), INRA (Institut National de Recherche Agronomique) and UGSF (Unité de Glycobiologie Structurale et Fonctionnelle).
  
  My PhD work dealt with the fabrication of an inorganic silicon nanowires substrate dedicated to the sensitive detection of biomolecules by laser desorption/ionisation mass spectrometry (LDI-MS).
  
  I varied the morphology, composition and surface chemistry of silicon nanowires. For this, two different synthesis of silicon nanowires have been used: the Vapor Liquid Solid one and the silicon electroless chemical etching one. The parameters of synthesis have been changed in order to lead to various types of homogeneous silicon nanowires arrays, that have been observed by Scanning Electron Microscopy. The surface chemistry of silicon nanowires has been modified by photochemical grafting of alcene or acid on silicon and has been investigated by X-ray photoelectron spectroscopy.
  
  I looked at the importance of optical and thermal properties, wetting properties and accessibility of analytes to the laser beam on the performance of silicon nanowires for LDI-MS. The optimized nanowire substrate exhibits a high sensitivity for the detection of low mass molecules (50 times higher than classical MALDI) and of peptides mixtures resulting from digestion of proteins. The silicon nanowires substrate was successfully used in a biochip format to immobilize peptides and to follow the course of the methylation reaction of those peptides. Furthermore, the silicon nanowires substrate integration in a lab on chip was investigated: a 1 µL droplet of a peptide mixture (50.10-15M) was displaced by digital microfluidics electrowetting on dielectric (EWOD) and successfully analyzed by LDI-MS.
  
  I finally developed an original method combining the chemistry and topography of silicon nanowire surface, using optical lithography and chemical plasma etching technique. This method leads to areas with different liquid/solid surface tensions and enable localized adhesion of proteins, cells and bacteria. In complement to this last work and in accordance with a future development of a cell on chip, I studied the behavior of fibroplast cells in contact with silicon nanowires: viability, shape and behavior of cells have been investigated by fluorescence microscopy, Scanning Electron Microscopy and Transmission Electron Microscopy.

Formations

• Université Lille 1 Sciences Et Technologies

  Villeneuve D'Ascq 2006 - 2010 Doctorat, spécialité Micro Nanotechnologies

• Université Paris 11 Paris Sud

  Orsay 2003 - 2006 Master en Micro Nanotechnologies, Université Lille1

• Lycée Henri Wallon

  Valenciennes 2001 - 2003 PC

Réseau

• Benoit MAUX

• Danjou PIERRE-EDOUARD

• Elisabeth GALOPIN

• Estelle MAIRIAUX

• Florian LE CADRE

• Geraldine DANTELLE

• Jean RINGOT

• Nathalie FABRE

• Olivier OFFRANC

• Toufik ABACHE