Biomedical subjects

T Stieglitz

Publications and source records attributed to T Stieglitz.

18 recordsLinked to original sources

PubMed2002

A biohybrid system to interface peripheral nerves after traumatic lesions: design of a high channel sieve electrode.

Peripheral nerve lesions lead to nerve degeneration and flaccid paralysis. The first objective in functional rehabilitation of these diseases should be the preservation of the neuro-muscular junction by biological means and following functional electrical stimulation (FES) may restore some function of the paralyzed limb. The combination of biological cells and technical microdevices to biohybrid systems might become a new approach in neural prosthetics research to preserve skeletal muscle function. In this paper, a microdevice for a biohybrid system to interface peripheral nerves after traumatic lesions is presented. The development of the microprobe design and the fabrication technology is described and first experimental results are given and afterwards discussed. The technical microprobe is designed in a way that meets the most important technical requirements: adaptation to the distal nerve stump, suitability to combine the microstructure with a containment for cells, and integrated microelectrodes as information transducers for cell stimulation and monitoring. Micromachining technologies were applied to fabricate a polyimide-based sieve-like microprobe with 19 substrate-integrated ring electrodes and a distributed counter electrode. Monolithic integration of fixation flaps and a three-dimensional shaping technology led to a device that might be adapted to nerve stumps with neurosurgical sutures in the epineurium. First experimental results of the durability of the shaping technology and electrochemical electrode properties were investigated. The three-dimensional shape remained quite stable after sterilization in an autoclave and chronic implantation. Electrode impedance was below 200 kOmega at 1 kHz which ought to permit recording of signals from nerves sprouting through the sieve holes.

Animals↗

PubMed2002

Considerations on noise of electrodes in combination with amplifiers for bioelectrical signal recording.

Detection of weak bioelectrical signals needs a recording system with a very low system noise. In this paper, the noise of electrodes as well as the influence of different combinations of electrodes and amplifiers on the system noise was investigated. As a first result the electrodes noise is similar to the noise of a passive electronic part with the same impedance. For smaller electrodes a reduction of the electrode impedance will reduce the system noise, also for larger electrodes the electrode itself is not the dominant noise source, so that an improvement of the amplifier is the way to get a better system. A special amplifier was tested with iridium and platinum black electrodes of different sizes.

Amplifiers, Electronic↗

PubMed2002

[Initial chronic results of flexible sieve electrodes as interface to nerve stumps].

Since more than 20 years, nerve stumps have been interfaced with sieve-like microsystems with integrated electrodes in experimental studies. In most cases, silicone tubes have been assembled on the microsystems to adapt the nerve and deliver a guidance structure for regeneration. Flexible, polyimide-based sieve electrodes with integrated fixation aids have been implanted chronically in an animal model. They have been adapted between the transsected ends of the sciatic nerve of rats and on the proximal stump in an amputation model. First electrophysiological experiments proved the functional reinnervation. Combining embryonic motor neurons with the sieve electrode, we propose a biohybrid system that is under investigation to functionally interface the distal part of a transsected peripheral nerve.

Animals↗

PubMed2002

Selective stimulation of pig radial nerve: comparison of 12-polar and 18-polar cuff electrodes.

Aiming at the development of an implantable neuroprosthesis for restoration of hand function in tetraplegic patients (C5/C6), we examined and compared the stimulation performance of two different neural electrode designs. Our studies on the radial nerve of adult pigs proved the feasibility of selective control of different forearm muscles by using only one multichannel nerve cuff electrode. The results gained by applying a 12-polar cuff electrode design were poor, while the potential of an 18-polar design was very encouraging.

Animals↗

PubMed2002

[Coating material of parlene C as encapsulation material for biomedical micro-implants].

Biomedical microsystems attain to contact with environments like blood, ephitHelium and saline solutions therefore they need an encapsulation. Parylene seems to be a suitable polymer to cover the implants and protect them against moisture and aggressive environment. This paper describes the characterisation of Parylene C coatings and its possibilities to protect implants. Beside the encapsulation of biomedical microsystems the manufacturing of fexible electrodes and the cytotoxicity behavior of RIE etched Parylene layers was investigated.

Animals↗

PubMed2001

Perforated microelectrode arrays implanted in the regenerating adult central nervous system.

Adult mammalian optic nerve axons are able to regenerate, when provided with the permissive environment of an autologous peripheral nerve graft, which is usually the sciatic nerve. This study demonstrates the ability of adult rat optic nerve axons to regenerate through the preformed perforations of a polyimide electrode carrier implanted at the interface between the proximal stump of the cut optic nerve and the stump of the peripheral nerve piece used for grafting. Evidence that retinal ganglion cells regenerated their axons through the perforated electrode carrier was obtained by retrograde labeling with a fluorescent dye deposited into the sciatic nerve graft beyond the nerve-carrier-nerve junction. The number of regenerating cells could be enhanced by injecting neuroprotective drugs like aurintricarboxylic acid and cortisol intravitreally. A second line of evidence was obtained by immunohistochemical staining with antibodies to neurofilament. Third, electrical activity of the regenerating nerves was recorded after stimulating the retina with a flash of light. The results suggest that a regenerating central nerve tract may serve as an experimental model to implant artificial microdevices to monitor the physiological and topographical properties of neurites passing through the device or to stimulate them, thus interfering with their potential to grow. This study reports for the first time that the optic nerve has unique properties, which aids in the realization of these goals.

Animals↗

PubMed2001

Immunohistochemical characterization of axonal sprouting and reactive tissue changes after long-term implantation of a polyimide sieve electrode to the transected adult rat sciatic nerve.

The development of artificial microstructures suited for interfacing of peripheral nerves is not only relevant for basic neurophysiological research but also for future prosthetic approaches. Aim of the present study was to provide a detailed analysis of axonal sprouting and reactive tissue changes after implantation of a flexible sieve electrode to the proximal stump of the adult rat sciatic nerve. We report here that massive neurite growth after implantation, steadily increasing over a period of 11 months, was observed. Parallel to this increase was the expression of myelin markers like Po, whereas non-myelin-forming Schwann cells did not change. Compared to five weeks post-implantation. where both Schwann-cell phenotypes were intermingled with each other, non-myelin-forming Schwann cells occupied a peripheral position in each microfascicle after 11 months. After an initial increase, hematogenous macrophages were down-regulated in number but maintained close contact with the implant. However, at no time were signs of its degradation observed. It is concluded that the introduced flexible polyimide electrode is suitable for contacting peripheral nerves since it permits substantial neurite growth and offers excellent long-term stability.

Animals↗

PubMed2001

Selective fascicular stimulation of the rat sciatic nerve with multipolar polyimide cuff electrodes.

PURPOSE: To assess a new flexible, multicontact spiral-cuff electrode made of polyimide with integrated platinum contacts for selective stimulation of nerve fascicles. METHODS: Polyimide cuff electrodes with 12 Pt sites in the spiral cuff were acutely implanted around the sciatic nerve of rats. Stimulation was applied through each one of the four tripoles of the cuff as single pulses of 10 microsec duration of increasing intensity. The motor responses were monitored from EMG recordings of gastrocnemius medialis (GM; innervated by the tibial nerve) and tibialis anterior (TA; innervated by the peroneal nerve) muscles. The torque developed in tbc ankle was simultaneously measured by means of a purposely designed apparatus. Recruitment curves were constructed for the CMAP of the GM and TA muscles and for the torque. RESULTS: In all nerves evaluated stimulation through one or two of the tripoles initially evoked a dorsiflexion with parallel recruitment of the TA muscle at low stimulation intensity; at higher stimulation amplitude activation of the tibial innervated muscles prevailed and led to predominant plantarflexion. On the other hand, stimulating through the other two or three tripoles evoked plantarflexion from the beginning, with increasing force from low to high stimulus intensity. The effectiveness of selective stimulation was mildly increased by applying a simultaneous transverse steering current. The threshold for torque dorsiflexion decreased and the dynamic range of stimulation that resulted in a net dorsiflexion expanded. The effects of steering currents were more noticeable with pulses of 80% than 40% of threshold value, and when applied from an opposite than from an adjacent anode. CONCLUSIONS: Despite the relative small size of the rat sciatic nerve and the close apposition of tibial and peroneal fascicles, we proved the feasibility of using multipolar polyimide cuff electrodes to produce selective fascicular nerve stimulation.

Animals↗

PubMed2000

Polyimide cuff electrodes for peripheral nerve stimulation.

This paper describes a new tripolar spiral cuff electrode, composed of a thin (10 microm) and flexible polyimide insulating carrier and three circumneural platinum electrodes, suitable for stimulation of peripheral nerves. The cuffs were implanted around the sciatic nerve of two groups of ten rats each, one in which the polyimide ribbon was attached to a plastic connector to characterize the in vivo stimulating properties of the electrode, and one without a connector for testing possible mechanical nerve damage by means of functional and histological methods. The polyimide cuff electrodes induced only a very mild foreign body reaction and did not change the nerve shape over a 2-6 month implantation period. There were no changes in the motor and sensory nerve conduction tests, nociceptive responses and walking track pattern over follow-up, and no morphological evidence of axonal loss or demyelination, except in one case with partial demyelination of some large fibers after 6 months. By delivering single electrical pulses through the cuff electrodes graded recruitment curves of alpha-motor nerve fibers were obtained. Recruitment of all motor units was achieved with a mean charge density lower than 4 microC/cm(2) for a pulse width of 50 micros at the time of implantation as well as 45 days thereafter. These data indicate that the polyimide cuff electrode is a stable stimulating device, with physical properties and dimensions that avoid nerve compression or activity-induced axonal damage.

Animals↗

PubMed1998

Stimulation and recording from regenerated peripheral nerves through polyimide sieve electrodes.

This paper describes the use of a new polyimide sieve electrode as a chronic neural interface to stimulate and record signals from regenerated peripheral nerves. Flexible thin polyimide electrodes were placed in silicone chambers and implanted between the severed ends of the sciatic nerve in rats. The sieve part of the interface has 281 round via holes of 40 microns diameter, with seven integrated recording-stimulating electrodes arranged around via holes. Axonal regeneration through the via holes was demonstrated by histological and physiological methods over a two to six month post-implantation period in all the rats. The regenerated nerves were organized in fascicles corresponding to the grid pattern of the via holes. Longitudinal sections showed myelinated fibers, with normal appearance and well developed myelin sheath, crossing the via holes. Stimulation of the regenerated nerve through the polyimide electrode evoked distal muscle and nerve responses similar in amplitude to those evoked by nerve stimulation with hook metal electrodes. The polyimide electrodes were useful for recording nerve action potentials in response to electrical stimulation of the distal regenerated nerve, and in response to functional sensory stimulation of several modalities.

Animals↗

PubMed1997

Characterization and optimization of microelectrode arrays for in vivo nerve signal recording and stimulation.

Revealing the complex signal-processing mechanisms and interconnection patterns of the nervous system has long been an intriguing puzzle. As a contribution to its understanding the optimization of the impedance behavior of implantable electrode arrays with via holes is discussed here. Peripheral axons will regenerate through these holes allowing for simultaneous nerve stimulation and signal recording. This approach is part of the ESPRIT project INTER and may eventually lead to devices driving sensory motor prosthesis with closed loop control. In the first set of experiments, micromachined platinum electrode arrays were prepared, characterized and optimized for nerve signal recording. The results of these studies are based on impedance spectroscopy and microscopic techniques. Equivalent circuits were modeled describing formally the electrical response behavior with ohmic resistances between 500 omega and 10 k omega. To attain low impedances for all electrodes on the INTER device, platinum from H2PtCl6 was electrodeposited, and sputter technology as well as electrochemical deposition from H2IrCl6 solution were used to produce thin iridium films. For the former, a lift-off process was established at one of the institutes to generate electrode structures with a line width of 5 microns. As a result in all three cases the electrodes showed almost constant impedances over the entire frequency range (10 Hz-1 kHz), which is relevant for nerve signal recording. In the second set of experiments, electrodes were optimized to allow for nerve stimulation. For this purpose, the charge delivery capacity (CDC) had to be increased and the impedance had to be decreased. Iridium oxide is the material of choice, because its CDC is much higher than the CDC of platinum at 75 microC/cm2 (Ziaie et al., 1991, IEEE Sensors & Actuators Transducers, 6, 124-127). A significant increase of the electrochemically active surface of the electrode structures could be observed by measuring the surface roughness. In first experiments, an activated iridium oxide film was formed with cyclic voltammetry and was evaluated using scanning force microscopy and impedance spectroscopy. The evaluation of the cyclic voltammograms showed a CDC up to 400 mC/cm2 for sputter deposited and oxidatively treated iridium films. Further investigations are directed towards increasing the stability of the iridium oxide electrodes with regard to long-term implants. Parallel experiments aim at the controlled axon adhesion without changing the impedance behavior of the described electrodes.

Electric Impedance↗

PubMed1997