Two implantable devices developed by American and Chinese researchers are designed to dissolve in the brain over time and may eliminate several current problems with implants.
University of Pennsylvania researchers have developed an electrode and an electrode array, both made of layers of silicon and molybdenum that can measure physiological characteristics (like neuron signals) and dissolve at a known rate (determined by the material’s thickness). The team used the device in anesthetized rats to record brain waves (EEGs) and induced epileptic spikes in intact live tissue.
Ref: Bioresorbable silicon electronics for transient spatiotemporal mapping of electrical activity from the cerebral cortex. Nature Materials (18 April 2016) | DOI: 10.1038/nmat4624
Bioresorbable silicon electronics technology offers unprecedented opportunities to deploy advanced implantable monitoring systems that eliminate risks, cost and discomfort associated with surgical extraction. Applications include postoperative monitoring and transient physiologic recording after percutaneous or minimally invasive placement of vascular, cardiac, orthopaedic, neural or other devices. We present an embodiment of these materials in both passive and actively addressed arrays of bioresorbable silicon electrodes with multiplexing capabilities, which record in vivo electrophysiological signals from the cortical surface and the subgaleal space. The devices detect normal physiologic and epileptiform activity, both in acute and chronic recordings. Comparative studies show sensor performance comparable to standard clinical systems and reduced tissue reactivity relative to conventional clinical electrocorticography (ECoG) electrodes. This technology offers general applicability in neural interfaces, with additional potential utility in treatment of disorders where transient monitoring and modulation of physiologic function, implant integrity and tissue recovery or regeneration are required.
Ref: Transient Resistive Switching Devices Made from Egg Albumen Dielectrics and Dissolvable Electrodes. ACS Applied Materials & Interfaces (7 April 2016) | DOI: 10.1021/acsami.5b10414
Egg albumen as the dielectric, and dissolvable Mg and W as the top and bottom electrodes are used to fabricate water-soluble memristors. 4 × 4 cross-bar configuration memristor devices show a bipolar resistive switching behavior with a high to low resistance ratio in the range of 1 × 102 to 1 × 104, higher than most other biomaterial-based memristors, and a retention time over 104 s without any sign of deterioration, demonstrating its high stability and reliability. Metal filaments accompanied by hopping conduction are believed to be responsible for the switching behavior of the memory devices. The Mg and W electrodes, and albumen film all can be dissolved in water within 72 h, showing their transient characteristics. This work demonstrates a new way to fabricate biocompatible and dissolvable electronic devices by using cheap, abundant, and 100% natural materials for the forthcoming bioelectronics era as well as for environmental sensors when the Internet of things takes off.