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Biomedical devices

Biomedical devices

Living bioelectronics capture physiological signals and deliver targeted therapy

11 Jun 2024 Tami Freeman
Jiuyun Shi holds a living bioelectronics device
The ABLE platform First author Jiuyun Shi holds a living bioelectronics device that integrates flexible electronic sensors, hydrogel and living cells to monitor and heal skin conditions. (Courtesy: Jiuyun Shi and Bozhi Tian/University of Chicago)

Electronic devices that seamlessly interface with living tissues hold potential to revolutionize disease diagnosis and treatment. But integrating electronics with the human body is a tricky task, due to mechanical incompatibilities between rigid metallic materials and soft biological tissues.

To address this challenge, Bozhi Tian and colleagues at the University of Chicago have created “living bioelectronics” designed to capture physiological signals and deliver targeted treatments. The team’s ABLE (active biointegrated living electronics) platform combines thin, flexible sensor circuitry with an ultrasoft, tissue-mimicking hydrogel made from tapioca starch and gelatin. The final ingredient is the addition of living cells into the gel, in this case Staphylococcus epidermidis, a bacterium that naturally lives on human skin and secretes compounds that regulate inflammation.

Described in Science, the ABLE platform combines three key functionalities: bioelectronics – electrical sensing to gather information from the skin and electrical stimulation to manage safety; biomechanical compatibility – a hydrogel that provides stable, conformal adherence to biological tissues, with comparable mechanical and structural properties; and the biogenic component – the bacteria themselves and biogenic polymers that enhance bacterial viability.

“By incorporating living entities into bioelectronic devices we can introduce biological functions into the electronics, such as cell-based therapeutic functions,” Tian tells Physics World. “This integration allows for more complex and responsive interactions with biological systems, enhancing the device’s capabilities and therapeutic potential.”

Detect and treat

To investigate the ABLE platform’s capabilities, Tian and colleagues, working with Simiao Niu and his team at Rutgers University, created a series of devices. First, they integrated the living hydrogel with a 15-channel mesh electronics array for surface electromyography (sEMG) intensity mapping. They attached the ABLE device to a rat’s leg and recorded the EMG signals evoked by sciatic nerve stimulation.

The device adhered conformally to the skin and recorded EMG signals with an average signal-to-noise ratio (SNR) of 26.76 dB – an improved performance compared with a gold biointerface without the hydrogel. The ABLE device could map sEMG spatial intensity over a 16 x 12.8 mm area and proved stable over 4 h, recording EMG signals without significant SNR loss.

Next, the researchers constructed an ABLE device for monitoring and treatment of psoriasis, a chronic inflammatory skin disease with no effective cure. They fabricated a mesh electronics device with a living hydrogel interface for recording heart rhythm via a six-lead surface electrocardiogram (ECG). When attached to the chest of healthy mice, the device recorded the ECG with an average SNR of 18.97 dB. In mice with psoriasis however, it recorded a significantly lower SNR of 7.96 dB, due to the thicker psoriatic skin.

When the device was applied to the animal’s skin for four days, the SNR of the recorded ECG increased. These findings demonstrate that changes in ECG signals can be used to detect skin diseases and that the living components within the ABLE system can improve psoriasis symptoms in mouse skin.

Wireless operation

To enable real-time monitoring and therapy and active circuit control, the team built a battery-free, flexible printed circuit board (FPCB) to perform wireless energy harvesting and data transfer. The resulting FPCB-based ABLE incorporates an electrical impedance circuit, and temperature and humidity sensors for real-time monitoring of disease progress, as well as delivering drug-free treatment of skin disease.

The researchers applied the FPCB-based ABLE to the skin of mice with psoriasis for four days. During this time, the device recorded a constant decrease in skin impedance, which mirrored the observed decrease in the skin’s psoriasis severity index. Humidity and temperature data provided information on the changing skin environment during this recovery process. The team note that the lightweight device did not hinder the animals’ mobility.

One challenge of employing a living hydrogel is the possibility that S. epidermidis may proliferate and lead to infections. Another issue is the safe disposal of the bacteria-laden device after use. To address these biohazard risks, the team included two disinfection electrodes in the FPCB that, upon treatment completion, deliver direct current to the living hydrogel interface for 30 min. This process effectively disinfects the bacteria within the device.

Tian notes that S. epidermidis does not cause any risks during treatment as it is a commensal, or “friendly”, bacterium that occurs naturally on skin. “As long as the concentration in the hydrogel is low, the bacteria are safe to use,” he explains. “We disinfect them at the end, given they will be trashed and leave the skin contact.”

In future work, the researchers hope to create a closed-loop system, as well as to incorporate engineered bacteria into the ABLE platform. “Our future directions also include developing implantable living bioelectronics to enhance the range and effectiveness of therapeutic applications,” says Tian.

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