Wireless Battery-free and Fully Implantable Organ Interfaces

Abstract

Advances in soft materials, miniaturized electronics, sensors, stimulators, radios, and battery-free power supplies are resulting in a new generation of fully implantable organ interfaces that leverage volumetric reduction and soft mechanics by eliminating electrochemical power storage. This device class offers the ability to provide high-fidelity readouts of physiological processes, enables stimulation, and allows control over organs to realize new therapeutic and diagnostic paradigms. Driven by seamless integration with connected infrastructure, these devices enable personalized digital medicine. Key to advances are carefully designed material, electrophysical, electrochemical, and electromagnetic systems that form implantables with mechanical properties closely matched to the target organ to deliver functionality that supports high-fidelity sensors and stimulators. The elimination of electrochemical power supplies enables control over device operation, anywhere from acute, to lifetimes matching the target subject with physical dimensions that supports imperceptible operation. This review provides a comprehensive overview of the basic building blocks of battery-free organ interfaces and related topics such as implantation, delivery, sterilization, and user acceptance. State of the art examples categorized by organ system and an outlook of interconnection and advanced strategies for computation leveraging the consistent power influx to elevate functionality of this device class over current battery-powered strategies is highlighted.

Monolithically Defined Wireless Fully Implantable Nervous System Interfaces

“…The data rate of Bluetooth and other communication protocols that operate at 2.4 GHz is greater than that of the previously described options. Power consumption of BLE typically ranges from 0.5 mW to 5 mW+ depending on bandwidth demands, which limits the application to embodiments with sufficient power overhead …”

“…For the stimulation of the central nervous system, there are many examples of neuromodulation devices that are fully implanted, wireless, and battery free. These devices employ a multitude of power delivery strategies as outlined in the powering section and provide an interface through various means, through full implantation of the device and cortical mounting locations as well as subdermal locations with and without penetration of the blood–brain barrier. For this account, we will outline current methods that utilize subdermal implantation with stimulation either through transcranial means or through probes.…”

“…This enables a higher level of computation, and also, thermal management is less sensitive than the previous approaches because the electronics are located in a highly perfused area far away from the neuronal target. Temperature gradients of several degrees are subdermally nonproblematic while a temperature increase on the neural interface can very quickly result in neuromodulation with thermal effects starting from 0.2° delta Celsius having shown to induce neuromodulation . This approach is highly likely to be accepted translationally as it mirrors the implantation method of current battery-powered rigid devices, which is well-established in the field.…”

Nucleic acid-based wearable and implantable electrochemical sensors

“…These devices are designed with biocompatible housings, detection systems employing electrochemical or optical methods, and advanced communication interfaces for seamless data transmission. 79,80 Material selection plays a critical role in the development of implantable sensors, particularly when leveraging affinity probes such as nucleic acid-based recognition elements for the selective detection of neurochemical markers and circulating biomarkers. 81,82 The choice of materials is guided by the need for biocompatibility, ensuring that the sensors not only integrate seamlessly into the body's physiological environment without eliciting significant inflammatory responses but also maintain their functional integrity over time.…”

“…83 This engineering approach enables the deployment of implantable sensors that can monitor a variety of molecular targets directly within the cerebrospinal fluid (CSF) or through intravenous and subcutaneous routes for the analysis of biomarkers in blood and ISF. 11,80 By integrating nucleic acid-based recognition elements, these sensors offer the selectivity needed for the detection of specific neurotransmitters and circulating biomarkers, enhancing our ability to diagnose and monitor neurological conditions and systemic diseases.…”