Implantable neural prostheses

D. Zhou, E. Gtcsuhmm, Implantable Neural Prostheses 1-Devices and Applications (Springer,... 

D. Zhou, E. Greenbaum, Implantable Neural Prostheses 2-Techniques and Engineering Approaches (Springer, New York, 2010), p. 201 LA. Blech, J. Appl. Phys. 47(4), 1203 (1976)... 

Implanted neural prostheses must be encapsulated in order to protect their electronics against aggressive body fluids and in turn to protect the body tissue against degradation products from the electronics. The use of parylene-C as an encapsulation material... 

Implantable neural prostheses have been widely used to improve or restore main functions of nervous systems for patients with neural damage. Some common neural prostheses include cochlear implants [1-2], spinal-cord stimulators [3-6], and deep-brain stimulators [7-10], Novel neural prostheses, such as retinal prostheses [11-12] and brain-machine interfaces [13-14], with higher resolution and site specificity are being actively investigated. These devices require larger numbers of microelectrodes patterned in a very small area, more sophisticated circuit designs, and longer lifespans. 

This book. Implantable Neural Prostheses 2 Techniques and Engineering Approaches, is part two of a two-volume sequence that describes state-of-the-art advances in techniques associated with implantable neural prosthetic devices. The techniques covered include biocompatibility and biostability, hermetic packaging, electrochemical techniques for neural stimulation applications, novel electrode materials and testing, thin-film flexible microelectrode arrays, in situ characterization of microelectrode arrays, chip-size thin-film device encapsulation, microchip-embedded capacitors and microelectronics for recording, stimulation, and wireless telemetry. The design process in the development of medical devices is also discussed. 

Implantable microelectronic devices for neural prosthesis require stimulation electrodes to have minimal electrochemical damage to tissue or nerve from chronic stimulation. Since most electrochemical reactions at the stimulation electrode surface alter the hydrogen ion concentration, one can expect a stimulus-induced pH shift [17]. When translated into a biological environment, these pH shifts could potentially have detrimental effects on the surrounding neural tissue and implant function. Measuring depth and spatial profiles of pH changes is important for the development of neural prostheses and safe stimulation protocols. 

In the 1950s, a human study showing sound perception arising from electrode implantation inspired researchers across the world to investigate the possibility of a cochlear prosthesis, which, after several decades of development in academia and industry, became the hrst FDA approved neural prosthesis [17]. 

The Neural Prosthesis Program, launched in 1972 and spearheaded by F. Terry Hambrecht, MD, brought funding, focus, and coordination to the multidisciplinary effort to develop technologies to restore motor function in paralyzed individuals. The initial efforts were in electrode-tissue interaction, biomaterials and neural interface development, cochlear and visual prosthesis development and control of motor function using implanted and nonimplanted electrodes. 

Kilgore, K.L., Peckham, P.H. et al.. An implanted upper-extremity neural prosthesis follow-up of five patients, /. Bone Joint Surg. Am. 79 533-541,1997. 

A consortium of 13 technical and medical partners works on different tasks to develop a complete system for a visual prosthesis (Fig. 25). The neural pros-theses comprises a unit to record and process ambiance light, an encoder that transforms visual information into a sequence of stimulation pulses, a micro-electromechanical system that is implanted into the eye for interfacing the retina and for generating the appropriate stimuli. 

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