Insulating Biomaterials Research for Implantable Microelectronic Devices
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Insulating Biomaterials Research for Implantable Microelectronic Devices David J. Edell InnerSea Technology 1 DeAngelo Drive, Suite E Bedford, MA 01730 ABSTRACT Developments in the field of BioMEMS share many of the same issues encountered in the development of neural interface technology that has been underway for many decades. In addition to issues of function, other issues such as biocompatibility and bioresistance have also presented great challenges. The focus of this paper is on the development and testing of electrically insulating biomaterials for micro-devices that can be implanted in biological systems. A variety of accelerated degradation and accelerated detection of degradation techniques have been developed and are used to screen candidate materials. Direct tests of mechanical properties, adhesion, and chemical resistance are used for further assessment. Promising materials indicate what chemistry might be suitable for development of a Chemical Vapor Deposited (CVD) thin film coating. CVD coatings are under development that may be useful for insulation of very small, micromachined elements of an implantable device while only increasing the size of the device by a few micrometers. Materials passing in-vitro testing are then considered for in-vivo testing. Novel instrumentation for testing devices in-vivo has been developed. INTRODUCTION Micro-machined silicon technology has been under development for creation of novel, micro-implantable devices since the late 1960’s. Until relatively recently, most efforts have been directed towards development of neuroprostheses. Neuroprostheses are devices designed to interface with the nervous system for exchange of information as part of a system for restoration of a lost function such as vision, hearing, and movement [1]. Neuroprostheses are being developed for therapeutic intervention, and for rehabilitation of the deaf, blind, spinal cord injured, and amputees. Most of the future neuroprosthetic concepts require close proximity to the small (10µm nominally) and fragile cells of the nervous system. Many will be attached or embedded directly in neural tissue. Not only is neural tissue tightly packed with functional elements, but it is dynamic. Peripheral nerves stretch and relax with every motion of a limb. The spinal cord moves within the spinal canal stretching the spinal roots with every bend. The brain moves relative to the skull with every heartbeat, breath, and motion of the head. Eyes are constantly in motion creating substantial forces of acceleration on the retina. While the motions are small, they can cause significant forces which can disrupt the neural interface or cause cracking of weakened insulators. Developments in the field of BioMEMS share many of the same issues encountered in the development of neural interface technology, particularly biocompatibility and bioresistance. “Biocompatibility” refers the degree of acceptance of the implanted devices by the biological system while “bioresistance” refers to the chemical and physical stability o
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