Electrodes for the Neural Interface

An impedance model to estimate the effective active area of neuro-electrode for quality control

Numerous studies have demonstrated the effectiveness of electrical stimulation as a therapy to treat a wide range of deficits. In particular, the design of more sophisticated neuro-electrodes has led to major breakthroughs in the field. However, these new electrodes are generally manufactured in laboratories in a semi-manual, non-industrial way. As a result, there can be considerable variability in the dimensions of the electrodes manufactured, particularly in the final surface area of the electrode active sites. In this paper, we explore the use of impedance measurement as a tool for estimating the post-manufacturing effective surface area of active sites. LIFEs with variable active site sizes and electrical impedance spectroscopy were used to evaluate the approach. The relationship between impedance and active surface area was estimated by two methods: a direct method based on single frequency impedance measurement, and an indirect method based on parameter extraction from a serial R-CPE model and whole impedance spectrum. Both methods were successful in providing an accurate estimate of the active site area, with an advantage for the second method, which achieves an estimation error of less than 5%.

Imaging peripheral nerve micro-anatomy with MUSE, 2D and 3D approaches

Understanding peripheral nerve micro-anatomy can assist in the development of safe and effective neuromodulation devices. However, current approaches for imaging nerve morphology at the fiber level are either cumbersome, require substantial instrumentation, have a limited volume of view, or are limited in resolution/contrast. We present alternative methods based on MUSE (Microscopy with Ultraviolet Surface Excitation) imaging to investigate peripheral nerve morphology, both in 2D and 3D. For 2D imaging, fixed samples are imaged on a conventional MUSE system either label free (via auto-fluorescence) or after staining with fluorescent dyes. This method provides a simple and rapid technique to visualize myelinated nerve fibers at specific locations along the length of the nerve and perform measurements of fiber morphology (e.g., axon diameter and g-ratio). For 3D imaging, a whole-mount staining and MUSE block-face imaging method is developed that can be used to characterize peripheral nerve micro-anatomy and improve the accuracy of computational models in neuromodulation. Images of rat sciatic and human cadaver tibial nerves are presented, illustrating the applicability of the method in different preclinical models.

High performance conducting polymer nanofiber biosensors for detection of biomolecules

Sensitive detection and selective determination of the physiologically important chemicals involved in brain function have drawn much attention for the diagnosis and treatment of brain diseases and neurological disorders. This paper reports a novel method for fabrication of enzyme entrapped-conducting polymer nanofibers that offer higher sensitivity and increased lifetime compared to glucose sensors that are based on conducting polymer films.