Alfred Stett

Subretinal electronic chips allow blind patients to read letters and combine them to words

A light-sensitive, externally powered microchip was surgically implanted subretinally near the macular region of volunteers blind from hereditary retinal dystrophy. The implant contains an array of 1500 active microphotodiodes (‘chip’), each with its own amplifier and local stimulation electrode. At the implants tip, another array of 16 wire-connected electrodes allows light-independent direct stimulation and testing of the neuron–electrode interface. Visual scenes are projected naturally through the eyes lens onto the chip under the transparent retina. The chip generates a corresponding pattern of 38 × 40 pixels, each releasing light-intensity-dependent electric stimulation pulses. Subsequently, three previously blind persons could locate bright objects on a dark table, two of whom could discern grating patterns. One of these patients was able to correctly describe and name objects like a fork or knife on a table, geometric patterns, different kinds of fruit and discern shades of grey with only 15 per cent contrast. Without a training period, the regained visual functions enabled him to localize and approach persons in a room freely and to read large letters as complete words after several years of blindness. These results demonstrate for the first time that subretinal micro-electrode arrays with 1500 photodiodes can create detailed meaningful visual perception in previously blind individuals.

Can subretinal microphotodiodes successfully replace degenerated photoreceptors

The idea of implanting microphotodiode arrays as visual prostheses has aroused controversy on its feasibility from the moment it appeared in print. We now present results which basically support the concept of replacing damaged photoreceptors with subretinally implanted stimulation devices. Network activity in degenerated rat retinae could be modulated through local electrical stimulation in vitro. We also investigated the long term stability and biocompatibility of the subretinal implants and their impact on retinal physiology in rats. Ganzfeld electroretinograms and histology showed no significant side effect of subretinal implants on retinal function or the architecture of the inner retina.

Electrical multisite stimulation of the isolated chicken retina.

Visual prostheses such as subretinal implants are intended for electrical multisite excitation of the retinal network. To investigate relevant issues like spatial resolution and operational range, we have developed an in vitro method using microelectrode arrays to stimulate isolated retinae. Ganglion cell activity in the chicken retina evoked by distally applied spatial voltage patterns consisted of fast bursts, transient inhibition and delayed discharges, and depended on the amount, location and spatial pattern of the injected charge. The response was altered or disappeared when synaptic transmission was blocked. Our results indicate that shape perception and object location can be partially achieved with subretinal electrical multisite stimulation.

The Development of Subretinal Microphotodiodes for Replacement of Degenerated Photoreceptors

There are presently several concepts to restore vision in blind or highly visually handicapped persons by implanting electronic devices into the eye in order to partially restore vision. Here, the approach to replace retinal photoreceptors by a subretinally implanted microphotodiode array (MPDA) is summarized. A survey is given on the present state of the development of MPDAs, the possibility of in vitro and in vivo tests as well as first results on biocompatibility and histology. Additionally, electrophysiological recordings in rabbits and rats are presented which have received such subretinal implants.

Spatial Resolution and Perception of Patterns Mediated by a Subretinal 16-Electrode Array in Patients Blinded by Hereditary Retinal Dystrophies

PURPOSE The perception of 11 persons blinded by hereditary retinal degeneration elicited by a subretinally implanted 16-electrode array used for light-independent direct stimulation of the retina is described. This device is part of the Tübingen retina implant, which also employs a light-sensitive, multiphotodiode array (MPDA). The ability to reliably recognize complex spatial percepts was investigated. METHODS Eleven blind volunteers received implants and participated in standardized psychophysical tests investigating the size and shape of perceptions elicited by single-electrode activation, multiple-electrode activation, and activation of compound patterns such as simplified letters. RESULTS Visual percepts were elicited reliably in 8 of 11 patients. On single-electrode activation, percepts were generally described as round spots of light of distinguishable localization in the visual field. On activation of a pattern of electrodes, percepts matched that pattern when electrodes were activated sequentially. Patterns such as horizontal or vertical bars were identified reliably; the most recent participant was able to recognize simplified letters presented on the 16-electrode array. The smallest distance between sites of concurrent retinal stimulation still yielding discernible spots of light was assessed to be 280 μm, corresponding to a logMAR of 1.78. CONCLUSIONS Subretinal electric stimulation can yield reliable, predictable percepts. Patterned perception is feasible, enabling blind persons to recognize shapes and discriminate different letters. Stimulation paradigms must be optimized, to further increase spatial resolution, demanding a better understanding of physical and biological effects of single versus repetitive stimulation (ClinicalTrials.gov number, NCT00515814).

PEDOT-CNT Composite Microelectrodes for Recording and Electrostimulation Applications: Fabrication, Morphology, and Electrical Properties.

Composites of carbon nanotubes and poly(3,4-ethylenedioxythiophene, PEDOT) and layers of PEDOT are deposited onto microelectrodes by electropolymerization of ethylenedioxythiophene in the presence of a suspension of carbon nanotubes and polystyrene sulfonate. Analysis by FIB and SEM demonstrates that CNT–PEDOT composites exhibit a porous morphology whereas PEDOT layers are more compact. Accordingly, capacitance and charge injection capacity of the composite material exceed those of pure PEDOT layers. In vitro cell culture experiments reveal excellent biocompatibility and adhesion of both PEDOT and PEDOT–CNT electrodes. Signals recorded from heart muscle cells demonstrate the high S/N ratio achievable with these electrodes. Long-term pulsing experiments confirm stability of charge injection capacity. In conclusion, a robust fabrication procedure for composite PEDOT–CNT electrodes is demonstrated and results show that these electrodes are well suited for stimulation and recording in cardiac and neurophysiological research.

CYTOCENTERING: a novel technique enabling automated cell-by-cell patch clamping with the CYTOPATCH chip.

Automats for patch clamping suspended cells in whole-cell configuration must (1) bring isolated cells in contact with patch contacts, (2) form gigaseals, and (3) establish stable intracellular access that allows for high quality recording of ionic currents. Single openings in planar substrates seem to be intriguing simple solutions for these problems, but due to the low rate of formation of whole-cell configurations we discarded this approach. Single openings are not suited for both attracting cells to the opening by suction and forming gigaseals with subsequent membrane rupture. To settle the three tasks with a mechanical microstructure we developed the socalled CYTOCENTERING technique to apply to suspended cells the same operation sequence as in conventional patch clamping. With this method we immobilized selected cells from a flowing suspension on the tip of a patch pipette by suction with a success rate of 97% and formed gigaseals with a success rate of 68%. Subsequent whole-cell recordings and intracellular staining with Lucifer yellow proved the stable access to the cytoplasm. Currently, a chip with an embedded suction opening in glass surrounding the microstructured contact pipette is under development. The processing of this CYTOPATCH chip is compatible to large-volume production. The CYTOPATCH automat will allow for fully automated, parallel, and asynchronous whole-cell recordings.

Patch-clamping of primary cardiac cells with micro-openings in polyimide films

Patch-clamping is a powerful method for investigating the function and regulation of ionic channels. Currently, great efforts are being made to automate this method. As a step towards this goal, the feasibility of patch-clamping primary cells with a microscopic opening in a planar substrate was tested. Using standard microfabrication and ion beam technology, small-diameter openings (2 and 4 μm) were formed in polyimide films (thickness 6.5 μm). Single cells (sheep Purkinje heart cells, Chinese hamster ovary cells) in a suspension were positioned on top of the opening and sucked towards the opening to improve adhesion of the cell to the planar substrate, hence increasing the seal resistance. Voltage/current measurements yielded a median seal resistance of 1.3MΩ with 4 μm openings (n=24) and 26.0 MΩ with 2 μm openings (n=75), respectively. With 2 μm openings, successful loose-patch recordings of TTX-sensitive inward currents and action potentials in sheep Purkinje heart cells (n=18) were made. In rare cases, gigaseals (n=4) were also measured, and a whole-cell configuration (n=1) could be established. It was concluded that the simple planar patch approach is suitable for automated loosepatch recordings from cells in suspension but will hardly be suitable for highthroughput whole-cell patch-clamping with high-resistance seals.

Neuroprotective effect of transretinal electrical stimulation on neurons in the inner nuclear layer of the degenerated retina

Electrical stimulation has been shown to have neuroprotective effects on ganglion cells and photoreceptors in axotomized and dystrophic retinas from Royal College of Surgeons (RCS) rats. This study determined whether electrical stimulation also has a neuroprotective effect on cells in the inner nuclear layer (INL) of retinas. We cultivated retinas from adult RCS rats on microelectrode arrays and stimulated them continuously with 20 Hz for up to 5 days. Afterwards, we subjected them to quantitative immunohistochemical analysis. Using TUNEL assay we found that transretinal electrical stimulation (TRES) with charge densities within the range of 100-500 microC/cm2 reduced apoptosis of neurons in the INL of degenerated retinas from RCS -/- rats by 20% after 1 day of continuous stimulation. Antibody staining (OX-42, ED1) revealed a reduced activation of migroglial cells in RCS -/- and congenic control (RCS +/+) rat retinas by up to 50% after 1 day of stimulation. The effect of electrical stimulation on apoptosis and reduced activation of microglial cells was closely correlated with the strength and duration of the stimulation. The neuroprotective effect of TRES on neuronal cells in the INL of degenerated RCS rat retinas supports the idea that electrical stimulation may be a therapeutic option to delay the progression of retinal degeneration in patients suffering from retinitis pigmentosa.

Subretinales Mikrophotodioden-Array als Ersatz für degenerierte Photorezeptoren?

ZusammenfassungEs wird eine Übersicht über den Stand der Entwicklungen eines subretinalen, elektronischen Mikrophotodioden-Arrays gegeben, mit dem degenerierte Photorezeptoren ersetzt werden können. Verschiedene Prototypen wurden entwickelt, getestet und bei verschiedenen Versuchstieren bis zur Dauer von 18 Monaten implantiert. Die Tatsache, dass mit subretinalen Elektroden elektrische Antworten vom visuellen Kortex von Schweinen abgeleitet werden können und Antworten auch in vitro in Netzhäuten von Ratten mit Netzhautdegenerationen nachweisbar sind, zeigt die Sinnhaftigkeit dieses Ansatzes. Allerdings sind noch wichtige Fragen der Biokompatibilität, der Langzeitstabilität und der Art des vermittelbaren Bildeindrucks zu bearbeiten, bevor an einen Einsatz beim Menschen zu denken ist.AbstractA survey is given on the status of developments, concerning a subretinal electronic microphotodiode array that aims at replacing degenerated photoreceptors. Various prototypes have been developed, tested, and implanted in various experimental animals up to 18 months. The fact that electrical responses were recorded from the visual cortex of pigs after electrical stimulation by subretinal electrodes and the fact that responses are also recorded in-vitro in degenerated rat retinae, shows the feasibility of this approach. However, there are a number of open questions concerning the biocompatibility, the long-time stability, and the type of transmitted image to be solved before application in patients can be considered.