Barrier materials for flexible bioelectronic implants with chronic stability—Current approaches and future directions

Enming Song,John A Rogers,Jinghua Li

doi:10.1063/1.5094415

Enming Song, John A Rogers + Show 1 more

Open Access

https://doi.org/10.1063/1.5094415

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Abstract

Flexible, bio-integrated electronic systems have wide-ranging potential for use in biomedical research and clinical medicine, particularly as active implants with the ability to operate in a safe, stable fashion over extended periods of time. Here, the development of a thin, robust biofluid barriers that can simultaneously serve as long-lived sensing and/or actuating interfaces to biological systems represents a significant challenge. Requirements are for defect-free, biocompatible and impermeable materials that can be rendered in thin, flexible forms and integrated with targeted device platforms. This perspective summarizes various material strategies for this purpose, with a focus not only on properties and structures but also on their use in bioelectronic systems. The article begins with an overview of different classes of materials, including means to grow/synthesize/deposit, manipulate, and integrate them into test structures for permeability measurements and into systems for functional bio-interfaces. A comparative discussion of the most widely explored materials follows, with an emphasis on physically transferred layers of SiO2 thermally grown on silicon wafers and on their use in the most sophisticated active, bendable electronic systems for electrophysiological mapping and stimulation. These advances suggest emerging capabilities in flexible bioelectronics implants as chronic implants with diagnostic and therapeutic function across a broad scope of applications in animal model studies and human healthcare.

Highlights

The results summarized here suggest that these encapsulation strategies will create opportunities for chronic operation of many types of flexible bioelectronic implants
The resulting films are far superior to SiO2 thin films formed in other ways, including those based on sol-gel processing, chemical vapor deposition (CVD), or atomic layer deposition (ALD).45
The absence of significant changes of noise amplitude, gain, and yield within this lifetime (

Summary

Introduction

Advanced technologies that can establish long-lived, stable electronic interfaces to targeted biological systems are essential to the development of new classes of implantable devices with capabilities relevant to academic research and healthcare.1–3 Flexible, high-performance electronic/optoelectronic systems with chronic operational stability in biofluids represent recent breakthroughs in this context.4,5 Sophisticated, actively multiplexed platforms of this type are increasingly well established, with embodiments that range from thin sheets for electrophysiological mapping6,7 on cardiac tissues to penetrating pins for neural recording in the brain.8–10 These and other related systems are distinguished relative to technologies of the past by their compliant architectures and low bending stiffnesses as minimally invasive interfaces to curved, soft, and dynamic biological tissues, with electrical performance characteristics that can approach those of conventional wafer-based semiconductor devices.11–16 Applications that involve long-term, safe operation in living organisms demand perfect isolation of the backplane electronics from surrounding biofluids to avoid leakage currents scitation.org/journal/apm into adjacent tissues and degradation of underlying devices.17 The development of thin, defect-free layers of materials that can encapsulate such systems as robust biofluid barriers and, at the same time, as electrical interfaces to the surrounding biology represents a fundamental challenge, where operational timeframes may extend to the life of the patient (several decades or more).

Results

Conclusion