A Review: Electrode and Packaging Materials for Neurophysiology Recording Implants

Abstract

To date, a wide variety of neural tissue implants have been developed for neurophysiology recording from living tissues. An ideal neural implant should minimize the damage to the tissue and perform reliably and accurately for long periods of time. Therefore, the materials utilized to fabricate the neural recording implants become a critical factor. The materials of these devices could be classified into two broad categories: electrode materials as well as packaging and substrate materials. In this review, inorganic (metals and semiconductors), organic (conducting polymers), and carbon-based (graphene and carbon nanostructures) electrode materials are reviewed individually in terms of various neural recording devices that are reported in recent years. Properties of these materials, including electrical properties, mechanical properties, stability, biodegradability/bioresorbability, biocompatibility, and optical properties, and their critical importance to neural recording quality and device capabilities, are discussed. For the packaging and substrate materials, different material properties are desired for the chronic implantation of devices in the complex environment of the body, such as biocompatibility and moisture and gas hermeticity. This review summarizes common solid and soft packaging materials used in a variety of neural interface electrode designs, as well as their packaging performances. Besides, several biopolymers typically applied over the electrode package to reinforce the mechanical rigidity of devices during insertion, or to reduce the immune response and inflammation at the device-tissue interfaces are highlighted. Finally, a benchmark analysis of the discussed materials and an outlook of the future research trends are concluded.

Research Progress on the Flexibility of an Implantable Neural Microelectrode

“…Substrate materials with specific properties such as flexibility, biocompatibility, and stability are expected for the chronic implantation of electrodes in the complex environment of the body [15]. For all neural microelectrodes, the biocompatibility of [66]; and (c) nerve probes based on graphene, ZnO nanowires and conductive polymers [63].…”

Soft Devices for High-Resolution Neuro-Stimulation: The Interplay Between Low-Rigidity and Resolution

“…In particular, we discuss the electrode and substrate materials. For more related discussion on packaging, biocompatibility, and multi electrode array recordings we refer the interested readers to (7,(41)(42)(43)(44) and references therein.…”

“…Starting with acute inflammation, a release of reactive oxidative species (ROS), followed by possible chronic inflammation. Due to ROS attack and tissue regeneration processes, implant degradation and encapsulation, which affect long-term stability and efficacy of the device, may occur ( 41 ). Therefore, device materials must be biocompatible and withstand biological reactions.…”

“…In addition, sterilization method should be carefully chosen ( 76 ). Whichever sterilization approach is chosen (i.e., ethanol sterilization, autoclaving, UV radiation, ethylene oxide gas) should not damage the electrode mechanical or optical properties, nor accelerate corrosion, denaturation or delamination of packaging materials ( 41 , 77 ).…”

Hermetic chip-scale packaging using Au:Sn eutectic bonding for implantable devices

“…Novel implantable devices ever-expanding capabilities more often include fully wireless communication and on-node data processing, thus imposing more rigorous requirements for device packaging [3]. Nowadays, implant packages, aside from ensuring small size, reliability, and biocompatibility, may additionally require CMOS compatibility and transparency to the communication signals [4][5][6]. Until now, the majority of implants were packaged by encasing entire systems in metal or glass cases or by using thick outer coatings, mainly made of medical-grade silicones [2,6,7].…”