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Device Technologies and Biomedical Robotics

Device Technologies and Biomedical Robotics - Poster Session E

Poster V17 - Continuous operation of battery-free implants enables advanced bone health insight

Saturday, October 26, 2024
10:00 AM - 11:00 AM EST
Location: Exhibit Hall E, F & G

Introduction:  Significant hurdles in realizing a digitally connected body with seamless high-fidelity organ interfaces and continuous operation are sourcing energy and connectivity. Continuous operation is currently limited by electrochemical power supplies that occupy large volumes. Wireless, battery-free operation is therefore paramount, requiring a system-level solution that enables seamless connection of wearable and implantable devices. Here, we present a technological framework that enables continuous operation of wireless, battery-free implants in freely moving subjects, ensuring seamless streaming of high-fidelity information from low-displacement, battery-free implants with little user interaction. This is accomplished using at-distance wirelessly recharged, wearable biosymbiotic devices for powering and communication with fully implantable NFC-enabled implants, see Fig. 1. We demonstrate this capability with osseosurface electronics that stream high-precision bone health insight, shown Fig. 2. Chronic operation of this system is shown with eleven-month-long large animal studies highlighting the ability of thin film battery-free implants to relay critical information on bone health without negative impact on the target or surrounding tissues, shown Fig. 3.

Materials and

Methods:  Biosymbiotic architecture combines 3D printed elastomer meshes with flexible electronics, batteries recharged using far-field wireless power transfer, and ultralow-power microcontrollers to enable biosignal acquisition over weeks to months. We developed a wearable biosymbiotic hub which utilizes a Near Field Communication (NFC) reader/controller and flexible coil antenna to cast power and exchange data with NFC-capable implants through tissue, see Fig. 1.
Osseosurface electronics are wireless, battery-free implantable sensors capable of high-resolution bone strain and thermography measurements. These NFC-capable devices are powered entirely by harvesting the electromagnetic field generated by the biosymbiotic hub, Fig. 1 (right).
All electronics were manufactured using polyimide-based flexPCBs, with components placed and reflowed manually. Functional characterization of the wearables and implantables included power consumption and device lifetimes, data rates and read ranges, influence of external environments, power transfer/harvesting ability, and sensing resolution vs gold standards.
Following an IACUC approved protocol, four osseosurface devices were implanted per sheep, two each onto the rear left femur and tibia, Fig. 2A. Initial placements of the biosymbiotic hub (Fig. 2A, B), were validated using x-ray images (Fig. 2C). In vivo tibial bone-strain and thermography data (Fig. 2D, 2E) was collected via the wearable, while a long-range RFID reader and coil antenna was used for the deep tissue femur implants. Bone strain was collected from sheep during gentle rocking by researchers or walking on a purpose-built treadmill for over 11 months. The biosymbiotic hub enabled the most detailed strain characterization in a freely moving large animal model to date, shown Fig. 2F.

Results, Conclusions, and Discussions: We demonstrate a wireless, wearable biosymbiotic device capable of transferring power and exchanging data with wireless, battery-free implantable devices over chronic durations. Far-field power harvesting enables seamless wireless charging of the wearable with no modification to daily routines and no interaction required from the wearer. Use of standardized RF communication protocols enables data exchange and power transfer to any NFC-capable implant. Relaying collected data using Bluetooth Low Energy maximizes compatibility with existing infrastructure.
The biosymbiotic hub presented here can power and read from devices implanted up to 50mm deep with around 600 Hz sampling rate and 16-bit fidelity. This device has a lifetime of 6.5 days without far-field power harvesting or wireless power transfer events, with full lifetime depending on how often samples are requested per day and the target read depth. Without far-field power harvesting, we expect a battery life between 66 hours (50mm deep target range) and 130 hours (20mm deep target range), obtaining nearly 36,000 bone-strain samples per 24-hour period. Using this same sample rate, a 20mm deep target range, and with far-field power harvesting, we have run the device continuously for over two weeks. Osseosurface electronics demonstrate a temperature resolution of 6 mK, a strain sensing resolution of 0.36 microstrain, and a dynamic range of 5957 microstrain.
With chronic large animal studies, high-fidelity bone strain and temperature characterization in vivo for over eleven months is demonstrated, highlighting the seamless acquisition of key markers of bone health. Mechanical testing and histological analyses show osseosurface electronics do not interfere with the wound healing process nor compromise bone integrity (Fig. 3), enabling implantation without follow-up surgeries for device removal.
This technological platform serves as an important demonstration of continuous operation of near-field enabled chronic implants that can transform postoperative monitoring to enable digitally optimized diagnostics and therapeutics.

Acknowledgements (Optional):