Utilising differential amplifiers for the adaptation of subretinal implants allows sufficient spatial resolution at varying ambient light surroundings in a grid of 70 /spl mu/m, as defined by physiological in vitro experiments. It has been shown that an implant can be created that can be positioned in the subretinal space. Electronic circuits have been imprinted underneath each pixel that receives their external energy by subretinal foil-bound wires. Biocompatibility and biostability tests as well as successful surgical procedures have prepared the ground for clinical study in blind RP patients.

Analysis of developmental mechanisms during neuroembryogenesis, evaluation of toxicological effects and testing of neuroprotheses rely to an increasing extent on in vivo-like in vitro models. We have developed a novel organotypic culture system of the chick retina. Tissue slices of embryonic retinae were immobilized on glass coverslips by a fibrin clot and permanently rotated between the gas and medium phase, resulting in regular formation and the maintenance of the retinal cytoarchitecture. Selection of embryonic stage, slice thickness and specimen processing were optimized for culturing. Scanning electron microscopy revealed degradation during increasing culture periods of the fibrin clot, which was used for initial immobilization of explants on glass coverslips. Simultaneously, retinal cells became exposed on the tissue surface. Even after several weeks in vitro, formation and maintenance of plexiform and nuclear layers was evident as revealed by two specific monoclonal antibodies. Immunocytochemistry employing two additional photoreceptor- and radial Müller-antibodies indicated differentiation of neuronal and glial cells specific for the retina. The organotypic culture system promises to facilitate developmental studies of retinal development. Quantitative evaluation of Na(+)-channel blocker mexiletine impact on the histogenesis of retinal explants proved the organotypic culture system to be a valuable tool also for neurotoxicological investigations.

Various neurodegenerative diseases of the retina lead to blindness. Since no pharmacological or gene therapy is available, the alternative concept of neuroprostheses has stimulated the development of micromachined photovoltaic devices. One strategy aims to replace degenerated photoreceptors by microphotodiode arrays (MPDA). MPDAs in the subretinal space shall transform light stimuli into electrical current for the stimulation of still unhampered retinal neurons. MPDAs were fabricated as silicon based multilayered PIN microstructures comprising titanium nitride stimulation electrodes of an area of 8 × 8 μm 2 . In an effort to develop meaningful tools to evaluate functional MPDA biocompatibility, a novel in vitro system was designed. Retinal cells were cultured on MPDAs, while current generation in MPDAs as in the eye was imitated by light emitting diodes (LED) operating at different wavelengths. For analysis epifluorescence and scannning electron microscopy was employed. MPDAs displayed increasing current delivery with increasing illumination. Surface modification of MPDAs including oxygen plasma treatment and adsorption of polyanions together with laminin were found to render the MPDA surface permissive for cell adhesion. Cell vitality tests using fluorescence markers revealed no adverse effects of optoelectric stimulation via LED/MPDAs. In addition, neurite formation and the expression of differentiation antigen 2A10 were unaffected after stimulation. Optoelectric stimulation allowed regular differentiation of various retinal cell types. In summary, the data provide the first evidence that optoelectric stimulation via MPDAs does not hamper cellular integrity under the experimental conditions chosen. The results support the concept of microphotodiodes as a retinal prosthesis.

Spatiotemporally coordinated activity of neural networks is crucial for brain functioning. To understand the basis of physiological information processing and pathological states, simultaneous multisite long-term recording is a prerequisite. In a multidisciplinary approach we developed a novel system of organotypically cultured rat hippocampal slices on a planar 60-microelectrode array (MEA). This biohybrid system allowed cultivation for 4 weeks. Methods known from semiconductor production were employed to fabricate and characterize the MEA. Simultaneous extracellular recording of local field potentials (LFPs) and spike activity at 60 sites under sterile conditions allowed the analysis of network activity with high spatiotemporal resolution. To our knowledge this is the first realization of hippocampus cultured organotypically on multi-microelectrode arrays for simultaneous recording and electrical stimulation. This biohybrid system promises to become a powerful tool for drug discovery and for the analysis of neural networks, of synaptic plasticity, and of pathophysiological conditions such as ischemia and epilepsy.

The present state of the art to record or to mimic electronically the human senses of olfaction and taste is characterized. In this part II, strategies are outlined to utilize chemical and biological structures with their different complexities which serve as sensor elements in (bio-) electronic noses. Finally a survey is given on the computer-science aspects of odor recognition based on these elements.

Field potential analysis can supplement network studies with information on graded neuronal activity in large populations and the physiological state of the tissue. In extracellular recordings with a microelectrode-array the authors investigated the structure of local field potentials (ERG) induced by visual stimulation and their temporal relation to spike activity in excised chicken retina segments. To assess the influence of tissue viability on both parameters the authors evaluated spike response characteristics and ERG after prolonged recording and spreading depression, a pathological phenomenon in neural tissue. Spike characteristics corresponded well to in vivo recordings with mainly phasic ON- and OFF-responses. ERGs consisted of four components differentially and reproducibly varying with the physiological state of the tissue.

A planar array of microelectrodes has been developed for monitoring the electrical activity of electrogenic cells in a cell culture by an extracellular recording mode. The design, the fabrication technique, and the characterization of the array by impedance measurements is described. The device is applied to monitor extracellular signals produced by cultured chicken embryo cardiac myocytes.

The use of cleaning instruments on titanium implants may cause undesired surface alterations. In a qualitative and quantitative assessment of these alterations, 5 titanium implant abutments were treated with a steel curet, a prototype pure titanium curet, an air abrasive polishing system, and an ultrasonic system. Custom-made polymer templates, used to secure the curet to a vertical guide bar and a spring scale to maintain a constant instrument pressure, guaranteed a standardized procedure and reproducible results. The ultrasonic and the air abrasive polishing method were also standardized. Evaluation by scanning electron microscopy (SEM) revealed surface alterations for all instruments and systems except the plastic curet, which did not roughen the surface at all. The confocal laser-scanning microscope allows a 3-dimensional reproduction of these surface alterations and their direct measurement. The profilometric tracing was not sensitive enough to register the minor effects caused by the titanium curet and the air abrasive polishing system. Dimensions of the resulting surface microstructure could be determined with the laser-scanning microscope. Since the influence of such surface defects on the peri-implant tissue reaction is unpredictable, the titanium curet and the air abrasive system can only be recommended with restrictions. The steel curet and the ultrasonic system proved to be totally unsuitable for cleaning titanium implants.

The physico-chemical properties of a biomaterial and its surface-texture greatly influence the type of tissue reaction. Grooved substrata provoke cellular orientation which is known as contact guidance. Using gingival fibroblasts it has been demonstrated that microstructured hydrophilic (by glow discharge treatment) silicone also induces cellular alignment. Further analysis of the cell contacts by laser scanning microscopy has revealed that the focal adhesion sites were also oriented along the substratum microstructures. This phenomenon supports earlier hypotheses regarding cellular alignment and may be responsible for the orientation of the whole cell.

A photolithographically produced array of 60 substrate-integrated microelectrodes was used for extracellular recording. Neuronal electrical activity was recorded from chicken retinal ganglion cells with or without stimulation by diffuse light. The retina was removed from chicken embryos of embryonic day 14-18. Only cells recorded from day 18 retina would react to photostimulation, increasing their activity when stimulated, corresponding to the developmental time course of photoreceptor differentiation.

Monoclonal antibodies to different triazines have been generated. These antibodies were used in enzyme immunoassays for detecting concentrations of propazine and hydroxyatrazine as low as 0.02 μg/l and 0.03 μg/l, respectively.

A planar array of microelectrodes has been developed for monitoring the electrical activity of neurons in cell culture. The microelectrode array was tested and characterized using impedance measurements and SEM. To verify the spatial sensitivity of the microelectrodes we used a specially developed simulation device.