On the Reliability of Chronically Implanted Thin-Film Electrodes in Human Arm Nerves for Neuroprosthetic Applications

Abstract

Direct stimulation of peripheral nerves can successfully provide sensory feedback to amputees while using hand prostheses. Recent clinical studies have addressed this important limitation of current prostheses solutions using different implantable electrode concepts. Longevity of the electrodes is key to success. We have improved the long-term stability of the polyimide-based transverse intrafascicular multichannel electrode (TIME) that showed promising performance in clinical trials by integration of silicon carbide adhesion layers. The TIMEs were implanted in the median and ulnar nerves of three trans-radial amputees for up to six months. Here, we present the characterization of the electrical properties of the thin-film metallization as well as material status post explantationem for the first time. The TIMEs showed reliable performance in terms of eliciting sensation and stayed within the electrochemical safe limits maintaining a good working range with respect to amplitude modulation. After termination of the trials and explantation of the probes, no signs of corrosion or morphological change to the thin-film metallization was observed by means of electrochemical and optical analysis. Damage to the metallization was assigned exclusively to mechanical impacts during explantation and handling. The results indicate that thin-film metallization on polymer substrates is applicable in permanent implant system.

Multifaceted understanding of human nerve implants to design optimized electrodes for bioelectronics

“…Details concerning design and fabrication can be found in Refs. [14,22]. S2 and S3 received also another TIME implant in the peroneal nerve.…”

“…The potential resulted from the average of four pulses (the first one of a five-pulse train was removed) with a current amplitude of 20 μA and a pulse width of 300 μs, repeated at a frequency of 1 Hz. While a safety margin has been applied in functional assessment in the patients [8], this paper uses 150 kΩ as maximum impedance for the definition of electrically functional stimulation contact sites which corresponds to 3 V as the maximum output voltage swing of the stimulator [22] including a safety margin. Preimplant ultrasound image of the nerve of interest in S1 is shown.…”

“…Five categories of stimulation contact site status were defined in order to obtain an objective classification (Fig. 5a) [22]. Category 1 represents a contact which can be compared to a pristine one, meaning from a material (not electrical) point of view, fully intact, with perfect adhesion and perfect surface integrity.…”

Interfaces with the peripheral nervous system for the control of a neuroprosthetic limb: a review

“…There was no necrosis, the formation of fibrotic capsule was limited, and all the electrodes were stable [189]. More recent studies with transradial amputees have shown the feasibility of TIME implantation in the median and ulnar nerves for 6 months [104,177]. The electrodes used in this study were polyimide-based and had silicon carbide adhesion layers which contributed to their stability.…”

Peripheral neurostimulation for encoding artificial somatosensations

“…This mapping procedure is mostly performed by an expert (e.g., clinician or bioengineer), and because it depends also by the number of ASs of the implanted electrode, it can have a long duration. For example, the implant of intraneural electrodes (e.g., TIME; Čvančara et al, 2019) requires four TIMEs for a total of 56 ASs available for the direct nerve stimulation (Petrini, Valle, Bumbasirevic, et al, 2019; Petrini, Valle, Strauss, et al, 2019). Each AS must be tested individually, and the stimulation parameters are unknown a priori.…”