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A. Vankov, P. Huie, M. Blumenkranz, D. Palanker; Electroadhesive Attachment of the Retinal Implants . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3172.
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Placement of the retinal implant that provides close proximity of the stimulating electrodes to the target cells remains one of the critical issues, especially for epiretinal prostheses. A retinal tack is one method currently used to attach epiretinal prosthetic devices to the retina. Achievement of a uniform proximity to the retina along the whole array having only one point of attachment may be difficult. We developed a simple and rapid technique that allows for attachment of the implant to the tissue surface in multiple locations.
Electrically induced adhesion was demonstrated in several model tissues: porcine retina and cornea in–vitro, and chicken chorioallantoic membrane in–vivo. Gold and tungsten wires and gold–coated plastic rods were used as adhesive pads. After a partial vitrectomy, adhesive pads were placed on the epiretinal surface. Electric pulses were applied to each adhesive pad while touching it with a 50 micrometer wire electrode protruding from a 20 Gauge needle that also served as a return electrode. The adhesion force was measured with a micro–dynamometer, and the width of collateral damage zone was assessed histologically.
Adhesion force of 7.5mN/cm between the chorioallantoic membrane and a 50 micrometer wire electrode was achieved using single bursts of biphasic pulses at frequency of 2 MHz with an envelop duration of 100 microseconds and amplitude of 100 V. This force exceeds the strength of the retinal attachment in rabbits by a factor of 3. Attachment of a 25 micrometer pad produced a collateral damage zone of 6 micrometers in acellular tissue (cornea), and a single layer of cells in cellular tissue (epithelium). Application of additional pulses (up to 5) increased adhesion by 70% without significant increase of the damage zone. Bond density was assessed by TEM imaging of the metal nanoparticles attached to the collagen fibrils. Strength of the individual bonds estimated from these measurements was on the order of 100 pN, corresponding to the electrostatic hydrogen bonds. Electroadhesive pad could be detached from the tissue by applying a stronger pulse, which produces a thin transient vapor cavity separating the pad from the tissue.
Electrically–induced adhesion allows for strong attachment of conductive materials to tissue using short (0.1 ms) electrical pulses. Attachment pads can be placed in several locations on the retinal implant assuring its proximity to the retinal surface along the whole area of the stimulation array. Chronic implantations are currently in progress to assess stability of the attachment over time.
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