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ABSTRACT: We report a process for the realization of polyimide films with custom-designed microporosity based on the heat-induced depolymerization of polyimide-embedded polypropylene carbonate microstructures. The foam-like microstructures are up to 40 µm thick and incorporate air cavities with a width ranging from 20 to 200 µm, a length up to 5 mm and a height of 20 µm. We model the mechanical stress–strain properties of the microcavities using both analytical and numerical methods. The simulation data are in good agreement with the results of nanoindentation and microcompression experiments, which show the reduction of the effective Young's modulus from 5.77 ± 0.06 GPa for bulk polyimide to 2.51 ± 0.03 GPa for a foam-like layer.
Journal of Micromechanics and Microengineering 09/2011; 21(10):105016. · 2.11 Impact Factor
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ABSTRACT: A new type of scintillation detector is being developed with standard microfabrication techniques. It consists of a dense array of scintillating waveguides obtained by coupling microfluidic channels filled with a liquid scintillator to photodetectors. Easy manipulation of liquid scintillators inside microfluidic devices allow their flushing, renewal, and exchange making the active medium intrinsically radiation hard. Prototype detectors have been fabricated by photostructuration of a radiation hard epoxy resin (SU-8) deposited on silicon wafers and coupled to a multi-anode photomultiplier tube (MAPMT) to read-out the scintillation light. They have been characterized by exciting the liquid scintillator in the 200 micrometers thick microchannels with electrons from a <sup>90</sup>Sr yielding approximately 1 photoelectron per impinging Minimum Ionizing Particle (MIP). These promising results demonstrate the concept of microfluidic scintillating detection and are very encouraging for future developments.
IEEE Transactions on Nuclear Science 07/2011; · 1.45 Impact Factor
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ABSTRACT: The goal of this experiment was to determine the electrical properties of the tissue reaction to implanted microelectrode arrays. We describe a new method of analyzing electrical impedance spectroscopy data to determine the complex impedance of the tissue reaction as a function of postimplantation time. A model is used to extract electrical model parameters of the electrode-tissue interface, and is used to isolate the impedance of the tissue immediately surrounding the microelectrode. The microelectrode arrays consist of microfabricated polyimide probes, incorporating four 50-mum-diameter platinum microelectrodes. The devices were implanted in the primary motor cortex of adult rats, and measurements were performed for 12 weeks. Histology was performed on implants at three time points in one month. Results demonstrate that the tissue reaction causes a rapid increase in bioimpedance over the first 20 days, and then stabilizes. This result is supported by histological data.
IEEE Transactions on Biomedical Engineering 08/2009; · 2.28 Impact Factor
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ABSTRACT: A new type of scintillation detector is being developed with standard microfabrication techniques. It consists of a dense array of scintillating waveguides obtained by coupling microfluidic channels filled with liquid scintillator to photodetectors. Easy manipulation of liquid scintillators inside microfluidic devices allow their flushing, renewal and exchange making the active medium intrinsically radiation hard. The detectors have been fabricated by photostructuration of a radiation hard epoxy resin (SU-8) deposited on silicon wafers and coupled to a multi-anode photomultiplier tube (MAPMT) to read out the scintillation light. They have been characterized by exciting the liquid scintillator in the 200 micrometers thick microchannels with electrons from a <sup>90</sup>Sr yielding approximately 1 photoelectron per impinging Minimum Ionizing Particle (MIP). These promising results demonstrate the concept of microfluidic scintillating detection and are very encouraging for future developments.
Advancements in Nuclear Instrumentation Measurement Methods and their Applications (ANIMMA), 2009 First International Conference on; 07/2009
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ABSTRACT: The goal of this experiment was to determine the electrical properties of the tissue reaction to implanted microelectrode arrays. We describe a new method of analyzing electrical impedance spectroscopy data to determine the complex impedance of the tissue reaction as a function of postimplantation time. A model is used to extract electrical model parameters of the electrode-tissue interface, and is used to isolate the impedance of the tissue immediately surrounding the microelectrode. The microelectrode arrays consist of microfabricated polyimide probes, incorporating four 50- mum-diameter platinum microelectrodes. The devices were implanted in the primary motor cortex of adult rats, and measurements were performed for 12 weeks. Histology was performed on implants at three time points in one month. Results demonstrate that the tissue reaction causes a rapid increase in bioimpedance over the first 20 days, and then stabilizes. This result is supported by histological data.
IEEE transactions on bio-medical engineering 05/2009; 56(7):1909-18. · 2.15 Impact Factor
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J. Salzmann,
J.L. Guyomard,
O.P. Linderholm,
B. Kolomiets,
H. Kasi,
M. Paques,
M. Simonutti,
E. Dubus,
S. Rosolen,
J. Sahel, P. Renaud,
A.B. Safran,
S. Picaud
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ABSTRACT: The retina contains a mosaic of photoreceptors coupled to a intelligent neural network extracting important information on object edges, movements. This visual information is then transferred to the brain through the optic nerve. In pathologies like age macular degeneration or retinitis pigmentosa, photoreceptor degeneration leaves the retinal neuronal network unstimulated. Retinal prostheses propose to stimulate electrically this neuronal network to restore a useful vision for locomotion and reading. We are testing prototypes of subretinal prostheses on the retina of dystrophic rats with photoreceptor degeneration. Our experiments have enabled us to introduce reproducibly these prototypes into the subretinal space, to observe regularly the implant in vivo and measure longitudinally the electrode impedance. These in vivo measurements can then be correlated with the histological examination of the retinal tissue. In parallel, techniques were implemented to record retinal ganglion cell activity on the isolated retina to test different stimulation protocols. Classic retinal ganglion cell responses can be recorded with these techniques and allow to measure ganglion cell response to electrical stimulation. These studies should therefore contribute to improving the selectivity in the electrode retinal stimulation by retinal prostheses.
Circuit Theory and Design, 2007. ECCTD 2007. 18th European Conference on; 09/2007
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ABSTRACT: In the framework of the EU-supported research project Healthy Aims, we developed a range of novel electrode arrays and related technologies for use in hearing prosthesis. This paper summarizes our ongoing research activities on alternative electrode manufacturing routes, functional electrode interfaces and smart intra-cochlear and intra- modiolus electrode arrays.
Engineering in Medicine and Biology Society, 2007. EMBS 2007. 29th Annual International Conference of the IEEE; 09/2007
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ABSTRACT: We present the development, characterization and in vivo validation of a novel drug eluting coating that has been applied to flexible neural probes. The coating consists of drug eluting nanoparticles loaded with an anti-inflammatory drug embedded in a biodegradable polymer. The drug eluting coating is applied to flexible polymer neural probes with platinum electrodes. The drug eluting device is implanted in one hemisphere of a rat, while a control device is implanted in the opposite hemisphere. Impedance measurements are performed to determine the effect of the drug eluting coating on the tissue reaction surrounding the probe and the electrical characteristics of the devices. Probes that are coated with drug eluting coatings show better long term impedance characteristics over control probes. These coatings can be used to increase the reliability and long term success of neural prostheses.
Engineering in Medicine and Biology Society, 2007. EMBS 2007. 29th Annual International Conference of the IEEE; 09/2007
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ABSTRACT: This study describes how drug eluting coatings affect the signal quality of implantable microelectrodes. Polyimide-Platinum neural probes were micro fabricated and coated with a biodegradable polymer loaded with drug eluting nanoparticles. Electrical impedance spectroscopy was used to study how the coating affects electrical recording and stimulation characteristics. The measurements were performed in vitro and it was found that the biodegradable film slightly modified the measured impedance phase by +3deg at 10 kHz but not the magnitude. This change in impedance is permanent but does not adversely affect the recording and stimulation characteristics of the device. This result demonstrates the compatibility of controlled release drug coatings with neural probes.
Solid-State Sensors, Actuators and Microsystems Conference, 2007. TRANSDUCERS 2007. International; 07/2007
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ABSTRACT: Microcantilevers on polysilicon were manufactured and living cardiomyocytes cells from neonatal rat hearts were cultured on top of them. The cells self-organize and start to contract after three days incubation. Moving the beams on which they are attached allows the measurement of the contractile force exerted by the cardiomyocytes. With this simple setup, the evaluation of the mechanical response of the cells due to changes in medium composition or temperature can be performed.
Solid-State Sensors, Actuators and Microsystems Conference, 2007. TRANSDUCERS 2007. International; 07/2007
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ABSTRACT: We present the fabrication, characterization, use in cortical recording and histological results of a flexible implantable neural probe. The device is microfabricated in polyimide and platinum, allowing for greater flexibility. It incorporates two layers of platinum electrodes, which greatly reduces the size of neural probes and limits the insertion damage. In recording experiments, acute in-vivo measurements were performed in the mouse cortex. Local field potential, single- and multi-neuron activity were simultaneously recorded. We demonstrate using immunohistochemistry techniques reduced inflammation at the implantation site for microfabricated polyimide neural probes. We therefore show that the major advantage of using polymer probes over silicon probes is the reduced damage due to insertion and probe-brain compliance mismatch.
Micro Electro Mechanical Systems, 2007. MEMS. IEEE 20th International Conference on; 02/2007
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ABSTRACT: In the framework of the EU-supported research project Healthy Aims, we developed a range of novel electrode arrays and related technologies for use in hearing prosthesis. This paper summarizes our ongoing research activities on alternative electrode manufacturing routes, functional electrode interfaces and smart intra-cochlear and intra-modiolus electrode arrays.
Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 02/2007; 2007:515-8.
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J Salzmann,
O P Linderholm,
J-L Guyomard,
M Paques,
M Simonutti,
M Lecchi,
J Sommerhalder,
E Dubus,
M Pelizzone,
D Bertrand,
J Sahel, P Renaud,
A B Safran,
S Picaud
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ABSTRACT: In age related macular degeneration and inherited dystrophies, preservation of retinal ganglion cells has been demonstrated. This finding has led to the development of various models of subretinal or epiretinal implant in order to restore vision. This study addresses the development of a polyimide subretinal electrode platform in the dystrophic P23H rat in vivo.
A technique was developed for implanting a subretinal electrode into the subretinal space and stabilising the distal extremity of the cabling on the rat cranium in order to allow future electrical stimulations of the retina.
In vivo imaging of the retina with the scanning laser ophthalmoscope demonstrated reabsorption of the surgically induced retinal detachment and the absence of major tissue reactions. These in vivo observations were confirmed by retinal histology. The extraocular fixation system on the rat cranium was effective in stabilising the distal connector for in vivo stimulation.
This study demonstrates that a retinal implant can be introduced into the subretinal space of a dystrophic rat with a stable external connection for repeatable electrical measurements and stimulation. This in vivo model should therefore allow us to evaluate the safety and efficacy of electrical stimulations on dystrophic retina.
British Journal of Ophthalmology 10/2006; 90(9):1183-7. · 2.90 Impact Factor
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ABSTRACT: A novel contact lens with embedded sensors is being developed for continuous monitoring of the intraocular pressure in glaucoma patients. Its mode of operation and capabilities are described.
Medical device technology 07/2006; 17(5):19-21.
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ABSTRACT: An analytical solution is presented for the electric field between two facing strip electrodes situated in a microchannel, as frequently used in impedance cytometry applications. The measured change in resistance as induced by a 5 μm bead moving through the microchannel is in good agreement with the model. It is also demonstrated that the centre sensitivity is maximal for an electrode width equal to ∼56% of the channel height.
Electronics Letters 03/2006; · 0.96 Impact Factor
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ABSTRACT: Partial visual capabilities for some kind of blindness are still possible through direct electrical stimulation of retinal tissue. In this work, tunable implantable silicon CMOS pixel are presented and experimentally validated. Pulse width, stimulating output current and light sensibility may be regulated by external voltages, making this solution suitable for an auto-adapting artificial retina. Power consumption due to light detection and conversion is absolutely negligible compared to dissipation required for stimulating photoreceptors. The pixel pitch of around 70mum makes it among the smallest reported to-date
Sensors, 2005 IEEE; 12/2005
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ABSTRACT: The applications of bio-microelectromechanical systems (bioMEMS) in medicine can be classified as diagnostic or therapeutic systems. In the laboratory, microfluidic systems for cell analysis and characterization contribute to the development of diagnostic systems. Implantable biomedical microdevices can benefit many patients with neurological conditions or spinal cord injury, and flexible polymer-based microelectrode arrays are key technology in future neuroprosthetic devices. Advances in both lab-on-a-chip diagnostic systems and implantable biomedical microdevices have the potential to advance new therapies and solutions to improve our well-being.
Solid-State Device Research Conference, 2005. ESSDERC 2005. Proceedings of 35th European; 10/2005
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ABSTRACT: The large majority of microelectromechanical systems (MEMS) are fabricated on silicon, glass or Pyrex substrates by manufacturing techniques, which originated from the semiconductors industry. However, their final application often requires removal of the fabrication substrate or at least a partial release of some section of the device. This paper describes a technique based on anodic dissolution of sacrificial metal layers for the complete or partial detachment of microstructures. As an example, a thin-film of sacrificial aluminum is selectively removed in a neutral sodium chloride solution by applying a small positive potential to the aluminum. The method is evaluated theoretically and experimentally in a defined geometry and compared to diffusion-limited, chemical etching. It is shown experimentally that the process is significantly faster than conventional wet chemical etching and the method has been used to release planar and nonplanar thin-film devices made from polymers and metals. The method is applicable for a wide range of metals as sacrificial materials and is very versatile with respect to electrolyte composition and applied voltages. Ease of sacrificial material deposition (sputtering or evaporation) and structuring and the possibility of high process temperature and the nondestructive chemical environment (also environmentally friendly) during detachment make the process technology an interesting alternative to conventional chemical etching.
Journal of Microelectromechanical Systems 05/2005; · 2.10 Impact Factor
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ABSTRACT: This work reports on the design, fabrication, and characterization of CMOS pixels for subretinal implants, which seems to be an effective way to recover visual capabilities in some types of blindness. Two possible approaches are presented for CMOS pixel implementation: 1) an approach based on a light-controlled oscillator (LICOS) using a ring oscillator with an odd number of inverters and 2) an approach based on distributing a square signal at each pixel that filters out a number of pulses depending of the light intensity wave across the chip (WATCH). Both types of pixels fabricated in 0.35-μm CMOS demonstrate good mimic of the electrical behavior of human retina, with low-power consumption (typically 1 mW for a 14×14 matrix of pixels) and having small dimensions (75×78.5 μm<sup>2</sup> for LICOS and 70×50 μm<sup>2</sup> for WATCH), which make them suitable for practical implants. Experimental validation is reported on physiological solutions. Because of its characteristic, the proposed matrix of pixels could be considered as one of the first stand-alone highly integrated solutions for subretinal implant chips.
IEEE Sensors Journal 03/2005; · 1.52 Impact Factor
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Advanced Engineering Materials 09/2004; 6(9):719 - 724. · 1.18 Impact Factor
