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Freiburg, Germany

Schuettler M.,Laboratory for Biomedical Microtechnology | Schuettler M.,Cortec | Stieglitz T.,Laboratory for Biomedical Microtechnology | Stieglitz T.,Cortec | Stieglitz T.,Bernstein Center Freiburg
Biomedizinische Technik | Year: 2012

All today's active implantable medical devices utilize wireless telemetry, serving at least one of the two purposes: Power transmission and/or communication with an extra corporal unit. For implant powering, three strategies are widely used: 1. Primary (non-rechargeable) batteries, that require the presence of a system providing information on battery condition, warning the user/practitioner of an upcoming battery exhaustion. Usually, the implementation of such a system employs a telemetric data link. 2. Inductive coupling, using an extra corporal transmitter coil generating an alternating magnetic field, which couples through the skin into an implanted receiver coil that converts the magnetic flux into an electrical supply voltage. 3. Secondary batteries that are periodically recharged using an inductive link. Here, a power monitoring system is mandatory, commonly implemented by a telemetric link. Besides the telemetric links associated with power supply and its monitoring, implants communicate with extra-corporal units in order to transmit recorded physiological data, to report implant malfunction or critical conditions, to be re-programmed (e.g. adaptation of stimulation intensity in pacemakers), or in future applications, to communicate with other implants within a bodyinternal wireless network. © 2012 by Walter de Gruyter Berlin Boston.

Somerlik-Fuchs K.H.,Albert Ludwigs University of Freiburg | Somerlik-Fuchs K.H.,University Hospital Freiburg | Somerlik-Fuchs K.H.,Bernstein Center Freiburg | Hofmann U.G.,University Hospital Freiburg | And 4 more authors.
International IEEE/EMBS Conference on Neural Engineering, NER | Year: 2015

For most people suffering from epilepsy the unpredictability of their spontaneous seizures considerably contributes to the burden of their disease. Therefore active and passive seizure prediction methods have been investigated since the 1970s. Among them, the relative phase clustering index (rPCI) has been reported to be a promising stimulation based technique that offers the possibility to localize the seizure onset zone as well as the likelihood for a seizure occurrence within different time ranges. The adaptation of this measurement to animal models of epilepsy would not only offer the possibility to realize and test closed-loop setups based on identification of a preictal period; it would also provide the possibility to test therapeutic paradigms in a much faster and more efficient way. We investigated the transferability of the concept of the rPCI to the epilepsy model of the rat. Adaptation of stimulation parameters, especially the current amplitude, will be necessary for the application in animals, due to different electrodes as well as different anatomical sizes. Therefore, the influence of the stimulation parameters on the results of this active probing are analyzed in this study. While the amplitude and the pulse width (PWD) seem to affect the determined phase clustering index, no correlation with the frequency of test stimulus application could be proven. In the range between 1-5 μA the rPCI increased with increasing the current amplitude. Above that, it stabilized until the stimulation artifact resulted in the saturation of the amplifiers, which made the determination of the rPCI impossible. In addition, stimulation with a longer PWD resulted in higher rPCI values. © 2015 IEEE.

Hassler C.,Albert Ludwigs University of Freiburg | Hassler C.,Bernstein Center Freiburg | Boretius T.,Albert Ludwigs University of Freiburg | Stieglitz T.,Albert Ludwigs University of Freiburg | Stieglitz T.,Bernstein Center Freiburg
Journal of Polymer Science, Part B: Polymer Physics | Year: 2011

Neural implants are technical systems that restore sensory or motor functions after injury and modulate neural behavior in neuronal diseases. Neural interfaces or prostheses have lead to new therapeutic options and rehabilitation approaches in the last 40 years. The interface between the nervous tissue and the technical material is the place that determines success or failure of the neural implant. Recording of nerve signals and stimulation of nerve cells take place at this neuro-technical interface. Polymers are the most common material class for substrate and insulation materials in combination with metals for interconnection wires and electrode sites. This work focuses on the neuro-technical interface and summarizes its fundamental specifications first. The most common polymer materials are presented and described in detail. We conclude with an overview of the different applications and their specific designs with the accompanying manufacturing processes from precision mechanics, laser structuring and micromachining that are introduced in either the peripheral or central nervous system. © 2010 Wiley Periodicals, Inc.

Gierthmuehlen M.,Albert Ludwigs University of Freiburg | Wang X.,Albert Ludwigs University of Freiburg | Wang X.,Laboratory for Biomedical Microtechnology | Gkogkidis A.,Albert Ludwigs University of Freiburg | And 21 more authors.
Journal of Comparative Neurology | Year: 2014

Microelectrocorticography (μECoG) provides insights into the cortical organization with high temporal and spatial resolution desirable for better understanding of neural information processing. Here we evaluated the use of μECoG for detailed cortical recording of somatosensory evoked potentials (SEPs) in an ovine model. The approach to the cortex was planned using an MRI-based 3D model of the sheep's brain. We describe a minimally extended surgical procedure allowing placement of two different μECoG grids on the somatosensory cortex. With this small craniotomy, the frontal sinus was kept intact, thus keeping the surgical site sterile and making this approach suitable for chronic implantations. We evaluated the procedure for chronic implantation of an encapsulated μECoG recording system. During acute and chronic recordings, significant SEP responses in the triangle between the ansate, diagonal, and coronal sulcus were identified in all animals. Stimulation of the nose, upper lip, lower lip, and chin caused a somatotopic lateral-to-medial, ipsilateral response pattern. With repetitive recordings of SEPs, this somatotopic pattern was reliably recorded for up to 16 weeks. The findings of this study confirm the previously postulated ipsilateral, somatotopic organization of the sheep's sensory cortex. High gamma band activity was spatially most specific in the comparison of different frequency components of the somatosensory evoked response. This study provides a basis for further acute and chronic investigations of the sheep's sensory cortex by characterizing its exact position, its functional properties, and the surgical approach with respect to macroanatomical landmarks. J. Comp. Neurol. 522:3590-3608, 2014. © 2014 Wiley Periodicals, Inc.

Fiedler E.,Albert Ludwigs University of Freiburg | Fiedler E.,Bernstein Center Freiburg | Porto Cruz M.F.,Albert Ludwigs University of Freiburg | Cota Monjaras O.F.,Albert Ludwigs University of Freiburg | And 2 more authors.
International IEEE/EMBS Conference on Neural Engineering, NER | Year: 2015

In situ monitoring of tissue temperature during in vivo experiments can be of great advantage. It could allow the detection of inflammation development and possible infections caused by the implanted devices, the prevention of overheating due to electrical or optogenetical stimulation and the recording of effected vasodilation and increased metabolism. In this work, we present the characterization of platinum temperature sensors integrated in thin-film polyimide substrates. Three different sensor types were fabricated, with the intent to match a Pt 100, a Pt 1000 and a Pt 5000, all of them showing the typical characteristic curve of platinum for the electrical resistance as a function of temperature. Sensitivities of 0.2 ω/°C, 1.7 ω/°C and 8.8 ω/°C were determined for the different sensor types. With the Pt 5000 samples temperature changes of less than 0.5 °C could be detected reliably, independent of the ambiance being air or water. Good in vivo behavior of the platinum sensors is assumed as the fabrication process was not altered compared to established polyimide-based electrode arrays. © 2015 IEEE.

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