Aritra Kundu

Stimulation Selectivity of the “Thin-Film Longitudinal Intrafascicular Electrode” (tfLIFE) and the “Transverse Intrafascicular Multi-Channel Electrode” (TIME) in the Large Nerve Animal Model

Neural prostheses are limited by the availability of peripheral neural electrodes to record the users intention or provide sensory feedback through functional electrical stimulation. Our objective was to compare the ability of the novel “transverse intrafascicular multi-channel electrode” (TIME) and an earlier generation “thin-film longitudinal intrafascicular electrode” (tfLIFE) to selectively stimulate nerve fascicles and activate forelimb muscles in pigs. TIME was designed to access a larger subpopulation of fascicles than tfLIFE and should therefore be able to selectively activate a larger number of muscles. Electrodes were implanted in the median nerve, and sequential electric stimulation was applied to individual contacts. The compound muscle action potentials of seven muscles were recorded to quantify muscle recruitment. As expected, TIME was able to recruit more muscles with higher selectivity than tfLIFE (significant difference when comparing the performance of an entire electrode); a similar activation current was used (no significant difference). Histological analysis revealed that electrodes were located between fascicles, which influenced the selectivity and activation current level. In conclusion, TIME is a viable neural interface for selective activation of multiple fascicles in human-sized nerves that may assist to pave the way for future neuroprosthesis applications.

Development of a neurotechnological system for relieving phantom limb pain using transverse intrafascicular electrodes (TIME)

Abstract Phantom limb pain (PLP) is a chronic condition that develops in the majority of amputees. The underlying mechanisms are not completely understood, and thus, no treatment is fully effective. Based on recent studies, we hypothesize that electrical stimulation of afferent nerves might alleviate PLP by giving sensory input to the patient if nerve fibers can be activated selectively. The critical component in this scheme is the implantable electrode structure. We present a review of a novel electrode concept to distribute highly selective electrode contacts over the complete cross section of a peripheral nerve to create a distributed activation of small nerve fiber ensembles at the fascicular level, the transverse intrafascicular multichannel nerve electrode (TIME). The acute and chronic implantations in a small animal model exhibited a good surface and structural biocompatibility as well as excellent selectivity. Implantation studies on large animal models that are closer to human nerve size and anatomical complexity have also been conducted. They proved implant stability and the ability to selectively activate nerve fascicles in a limited proximity to the implant. These encouraging results have opened the way forward for human clinical trials in amputees to investigate the effect of selective electrical stimulation on PLP.

Biosafety assessment of an intra-neural electrode (TIME) following sub-chronic implantation in the median nerve of Göttingen minipigs

Before a novel peripheral nerve interface can be applied in a neural prosthesis for human use, it is important to determine the biocompatibility of the device. The aim of the present study was to assess the biosafety of the recently developed transverse intrafascicular multi-channel electrode (TIME) in a large nerve animal model. Six TIMEs were implanted (33-38 days) into the median nerves of Göttingen minipigs, and nerve specimens were harvested for histological analysis. We analyzed samples from the area of the implant and from control regions. We found an expected layer of fibrosis around the implant and fibroblasts in both the implant and control region, however, we found no significant presence of inflammatory cells or necrosis. Our results indicated that the TIME may be an attractive, biocompatible neural interface for future neuroprosthesis applications in the clinic setting.

Subchronic stimulation performance of transverse intrafascicular multichannel electrodes in the median nerve of the Göttingen minipig.

This work evaluated the subchronic stimulation performance of an intraneural multichannel electrode (transverse intrafascicular multichannel electrode, TIME) in a large human-sized nerve. One or two TIMEs were implanted in the right median nerve above the elbow joint in four pigs for a period of 32 to 37 days (six TIMEs in total). The ability of the contact sites to recruit five muscles in the forelimb was assessed via their evoked electromyographic responses. Based on these responses, a selectivity index was defined. Four TIMEs were able to selectively recruit a subset of muscles throughout the implantation period. The required recruitment current significantly increased, while there was a tendency for the recruitment selectivity to decrease over time. Histological assessment showed that all TIMEs remained inside the nerve and that they were located between fascicles. The average thickness of the encapsulation of the electrode was estimated to be 115.4 ± 51.5 μm (mean ± SD). This study demonstrates the feasibility of keeping the TIME electrodes fixed and functional inside a large polyfascicular human-sized nerve in a subchronic setting.

Developments towards a Psychophysical Testing Platform - A Computerized Tool to Control, Deliver and Evaluate Electrical Stimulation to Relieve Phantom Limb Pain

Artificially inducing phantom hand sensations by electrical stimulation may reduce PLP. The use of implantable, multi-channel microelectrodes provides the opportunity to selectively activate sensory fibres. However, combinations of variables from a multichannel stimulation system can produce a huge number of possible stimulation paradigms. It makes the use of psychophysical evaluation of the evoked sensations an impractical and time-consuming task in the clinical setting. Our aim is to develop a computerized, automatic, psychophysical testing platform to support control, delivery and evaluation of the electrical stimulation for PLP relief.