Viscoelasticity of model interphase chromosomes

We investigated the viscoelastic response of model interphase chromosomes by tracking the three-dimensional motion of hundreds of dispersed Brownian particles of sizes ranging from the thickness of the chromatin fiber up to slightly above the mesh size of the chromatin solution. In agreement with previous computational studies on polymer solutions and melts, we found that the large-time behaviour of the diffusion coefficient and the experienced viscosity of moving particles as functions of particle size deviate from the traditional Stokes-Einstein relation and agree with a recent scaling theory of diffusion of non-sticky particles in polymer solutions. Interestingly, we found that at short times large particles are temporarily "caged" by chromatin spatial constraints, which thus form effective domains whose sizes match remarkably well with recent experimental results for micro-tracers inside interphase nuclei. Finally, by employing a known mathematical relation between the time mean-square displacement of tracked particles and the complex shear modulus of the surrounding solution, we calculated the elastic and viscous moduli of interphase chromosomes. \ua9 2014 AIP Publishing LLC

Novel graphene electrode for retinal implants : an in vivo biocompatibility study

Altres ajuts: this work has made use of the Spanish ICTS Network MICRONANOFABS partially supported by MICINN and the ICTS 'NANBIOSIS'.Evaluating biocompatibility is a core essential step to introducing a new material as a candidate for brain-machine interfaces. Foreign body reactions often result in glial scars that can impede the performance of the interface. Having a high conductivity and large electrochemical window, graphene is a candidate material for electrical stimulation with retinal prosthesis. In this study, non-functional devices consisting of chemical vapor deposition (CVD) graphene embedded onto polyimide/SU-8 substrates were fabricated for a biocompatibility study. The devices were implanted beneath the retina of blind P23H rats. Implants were monitored by optical coherence tomography (OCT) and eye fundus which indicated a high stability in vivo up to 3 months before histology studies were done. Microglial reconstruction through confocal imaging illustrates that the presence of graphene on polyimide reduced the number of microglial cells in the retina compared to polyimide alone, thereby indicating a high biocompatibility. This study highlights an interesting approach to assess material biocompatibility in a tissue model of central nervous system, the retina, which is easily accessed optically and surgically

Novel Graphene Electrode for Retinal Implants: An in vivo Biocompatibility Study

Evaluating biocompatibility is a core essential step to introducing a new material as a candidate for brain-machine interfaces. Foreign body reactions often result in glial scars that can impede the performance of the interface. Having a high conductivity and large electrochemical window, graphene is a candidate material for electrical stimulation with retinal prosthesis. In this study, non-functional devices consisting of chemical vapor deposition (CVD) graphene embedded onto polyimide/SU-8 substrates were fabricated for a biocompatibility study. The devices were implanted beneath the retina of blind P23H rats. Implants were monitored by optical coherence tomography (OCT) and eye fundus which indicated a high stability in vivo up to 3 months before histology studies were done. Microglial reconstruction through confocal imaging illustrates that the presence of graphene on polyimide reduced the number of microglial cells in the retina compared to polyimide alone, thereby indicating a high biocompatibility. This study highlights an interesting approach to assess material biocompatibility in a tissue model of central nervous system, the retina, which is easily accessed optically and surgically.This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 785219 (GrapheneCore2) and No. 881603 (GrapheneCore3). DN has received funding from the doctoral school of Cerveau, cognition, comportement (3C) of Sorbonne Université. SP was also supported by the French state funds managed by the Agence Nationale de la Recherche within the Programme Investissements d’Avenir, LABEX LIFESENSES (ANR-10-LABX-65) and IHU FOReSIGHT (ANR-18-IAHU-0001). This work has made use of the Spanish ICTS Network MICRONANOFABS partially supported by MICINN and the ICTS ‘NANBIOSIS,’ more specifically by the Micro-NanoTechnology Unit of the CIBER in Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN) at the IMB-CNM

Propriétés de transport dans des tissus biomimétiques

Dans ce travail nous développons un modèle expérimental biomimétique de la communication cellule-cellule. Il s'agit de réseaux de gouttelettes aqueuses baignant dans l'huile et reliées par des bicouches lipidiques ornées de canaux ioniques. Pour produire ces réseaux de gouttelettes, nous développons d'abord une méthode d'impression originale basée sur l'extraction périodique à travers une interface huile/air d'un capillaire dans lequel la phase aqueuse est injectée. Nous incorporons ensuite aux bicouches un canal ionique – l’hémolysine - pour étudier la diffusion d'une sonde fluorescente dans des réseaux nanoporeux 1D par microscopie d’épifluorescence. Nous établissons que le temps de diffusion caractéristique dépend de façon non linéaire de la concentration introduite en nanopores. Nous montrons que nos résultats peuvent être compris par le biais d’une description théorique basée sur les temps de premier passage, dans laquelle les nanopores sont regroupés dans la membrane plutôt qu'isolés. Dans la dernière partie, nous utilisons des réactions cell-free pour exprimer directement dans les gouttelettes l'hémolysine précédemment utilisée ou le canal ionique mécanosensible MscL. Nous avons démontré dans ce cadre l'insertion et la fonctionnalité de l'hémolysine ainsi synthétisée par microscopie confocale et mesures électrophysiologiques. Ces résultats permettront d’entreprendre l'étude des propriétés de transport diffusives dans les réseaux mécanosensibles sous contrainte mécanique.In this thesis work, we develop an experimental model biomimetic of cell-cell communication. It consists in networks of aqueous droplets bathing in oil and connected by lipid bilayers decorated with ion channels. To produce these droplet networks, we first develop an original printing method based on the periodic extraction through an oil/air interface of a capillary in which the aqueous phase is injected. When the bilayers are decorated with the ion channel hemolysin, we then study the diffusion of a fluorescent probe in 1D nanoporous networks, using epifluorescence microscopy. We establish that the characteristic diffusion time depends non-linearly on the nanopores concentration. We show that our results are well captured within a first passage time theoretical description, in which nanopores are clustered rather than being independent. In the last part, we use cell-free reactions to express directly within the droplets the previously used hemolysin or the mechanosensitive ion channel MscL. We successfully demonstrate the insertion and functionality of synthesized hemolysin using both confocal microscopy and electrophysiological measurements. These results pave the way to the study of diffusive transport properties in mechanosensitive networks under mechanical stress

Characterization of Retinal Pigmented Epithelium Cells Density on a MicroElectrode Array Using Impedance Spectroscopy

International audienceThis work is aiming at using impedance measurements on MicroElectrode Array (MEA) in order to evaluate the cellular density at its surface. As the context of these measurements is retinal implants, the retinal pigmented epithelium cells (RPE) are used as cellular model. We measured the impedance changes at 4 different locations of the MEA during 13 days (approximately one measure every two days) and the cell density by manually counting them by microscope imaging taken just after the impedance measurement. A correlation between the cell density and the impedance measurement's change can be observed. The electrode interfaces and the biological cells are associated with an electrical model taking into account the ionic conduction (resistance) and polarization effects (capacitance)

Impedance spectroscopy on cell cultured microelectrode arrays as an in-vitro tool for retinal implant monitoring

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Impedance spectroscopy on cell cultured microelectrode arrays as an in-vitro tool for retinal implant monitoring

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A detailed in-vitro study of Retinal pigment epithelium’s growth as seen from the perspective of impedance spectroscopy analysis

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Impedance spectroscopy study of the retinal pigment epithelium: Application to the monitoring of blue light exposure effect on A2E-loaded in-vitro cell cultures

International audienceIn age-related macular degeneration, the retinal pigment epithelium can be damaged by light acting on photosensitizers like N-retinylidene-N-retinylethanolamine (A2E). In this paper, the underlying cellular mechanism of lesion at the cell layer scale is analyzed by impedance spectroscopy. Retinal pigment epithelium (RPE) cells are cultured on top of custom-made electrodes capable of taking impedance measurements, with the help of a custom-made electronic setup but without the use of any chemical markers. An incubator is used to house the cells growing on the electrodes. An electrical model circuit is presented and linked to the constituents of the cell layer in which various electrical elements have been defined including a constant phase element (CPE) associated to the interface between the cell layer and the electrolyte. Their values are extracted from the fitted model of the measured impedance spectra. In this paper, we first investigate which parameters of the model can be analyzed independently. In that way, the parameter's evolution is examined with respect to two different targeted changes of the epithelium: 1. degradation of tight junctions between cells by extracellular calcium sequestration with Ethylenediaminetetraacetic acid (EDTA); 2. application of high amplitude short length electric field pulses. Based on the results obtained showing a clear relation between the model and the physiological state of the cell layer, the same procedure is applied to blue light exposure experiment. When A2E-loaded cells are exposed to blue light, the model parameters indicate, as expected, a clear degradation of the cell layer opposed to a relative stability of the not loaded ones

Protuberant Electrode Structures for Subretinal Electrical Stimulation: Modeling, Fabrication and in vivo Evaluation

International audienceMany neural interfaces used for therapeutic applications are based on extracellular electrical stimulation to control cell polarization and thus functional activity. Amongst them, retinal implants have been designed to restore visual perception in blind patients affected by photoreceptor degeneration diseases, such as age-related macular degeneration (AMD) or retinitis pigmentosa (RP). While designing such a neural interface, several aspects must be taken into account, like the stimulation efficiency related to the current distribution within the tissue, the bio-interface optimization to improve resolution and tissue integration, and the material biocompatibility associated with long-term aging. In this study, we investigate the use of original microelectrode geometries for subretinal stimulation. The proposed structures combine the use of 3D wells with protuberant mushroom shaped electrode structures in the bottom, implemented on a flexible substrate that allows the in vivo implantation of the devices. These 3D microelectrode structures were first modeled using finite element analysis. Then, a specific microfabrication process compatible with flexible implants was developed to create the 3D microelectrode structures. These structures were tested in vivo to check the adaptation of the retinal tissue to them. Finally, preliminary in vivo stimulation experiments were performed