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. J Polym Sci Part B: Polym Phys, 2010

https://onlinelibrary.wiley.com/doi/pdf/10.1002/polb.22169

Polymers for neural implants

Describes the design, fabrication, and testing of miniature ultraflexible ribbon cables for use with micromachined silicon microprobes capable of chronic recording and/or stimulation in the central nervous system (CNS). These interconnects are of critical importance in reliably linking these microelectrodes to the external world through a percutaneous connector. The silicon cables allow the realization of multilead, multistrand shielded local interconnects that are extremely flexible and yet strong enough to withstand normal handling and surgical manipulation. Cables 5 /spl mu/m thick, 1-5 cm long, and from 60 to 250 /spl mu/m wide have been fabricated with up to eight leads. The series lead resistance is typically 4 k/spl Omega//cm for polysilicon and 500 /spl Omega//cm for tantalum with shunt capacitance values of 5-10 pF/cm and an interlead capacitance below 10 fF/cm. Soak tests in buffered saline performed under electrical and mechanical stress have been underway for over three years and show subpicoampere leakage levels. Silicon microprobes with built-in ribbon cables have remained functional for up to one gear in the guinea pig CNS, recording driven single-unit activity and maintaining impedance levels in the 1-7 M /spl Omega/ range. >

Silicon ribbon cables for chronically implantable microelectrode arrays

Objectives and Hypothesis: This study has the specific aim of evaluating the insertion characteristics of a new cochlear implant electrode. Techniques for evaluation of fluoroscopic real time mechanical insertion dynamics, histologic electrode position and trauma results, hydraulic force, and mechanical insertion forces are presented. In addition, this study should serve to present a novel model for cochlear implant electrode insertion evaluations.

Study Design: Prospective analysis using a series of analytical techniques.

Methods: All studies are conducted in fixed cadaveric temporal bones. Real time fluoroscopic insertion evaluations, histologic evaluations for trauma and electrode position in embedded bones, hydraulic measures, and mechanical intracochlear force measurements are conducted with a current and new electrode.

Results: The Contour Advance electrode provides a more reliable and less traumatic insertion when deployed with the Advance Off Stylet technique. This is largely because of a reduction in intracochlear outer wall force generation. Fluoroscopic and histologic analysis reveal a smooth insertion without reliance on cochlear outer wall contact. No hydraulic forces were detected when measured from the superior semicircular canal ampulla.

Conclusion: The model used for this study provides valuable information to cochlear implant surgeons and design engineers. The Contour Advance electrode, inserted with the Advance Off Stylet technique, represents an improvement over the Contour electrode inserted with the standard insertion technique.

A model for cochlear implant electrode insertion and force evaluation: results with a new electrode design and insertion technique.

A multi-bipolar configured electrode array and means to uniquely position said array within the scalae of the human cochlea is described. Said array is inserted into the scala tympani, scala vestibuli or both, by a surgeon. The electrode array may be pre-formed to lightly hug the modiolar wall of a scala so as to position the electrodes in close proximity to the cochlear spiral lamina and spiral ganglia in the modiolus. Mechanical features within said array allow the surgeon to further position said array against the modiolar wall of the scala, post insertion, and to mechanically retain such positioning of said array. Such positioning is in close proximity to surviving neural sites in the spiral lamina and/or spiral ganglion cells in the modiolus to efficiently stimulate functioning auditory neural elements. The multi-bipolar electrode configuration achieves a high degree of spatial selectivity, thus improving the implantee's speech percepts.

Modiolar hugging electrode array

Biocompatibility of polyimide microelectrode array for retinal stimulation

This report describes the fabrication of a flexible multichannel electrode array suitable for use in humans. The conductors, pads, and stimulating tips are made of platinum on a polyimide substrate. Photolithographic techniques are employed in the fabrication of the electrode on a planar surface in the form of a film. The film is rolled subsequently into a cylinder of diameter 0.50 mm and the cylinder is filled with medical grade silicone rubber. The stimulation pads then form rings around the cylinder. In vitro and in vivo tests are ongoing with good results so far.

Carlos R. Pon

Papers

Cylindrical cochlear electrode array for use in humans.