Portable, wearable electronics for physiological monitoring are gaining preference over traditional tethered devices in clinical settings due to their convenience for continuous or frequent monitoring. However, they often face challenges in power supply, requiring either large batteries or frequent recharging, which may not be practical for long-term use, particularly when devices are in hard-to-reach places or are difficult to remove or reapply. In a novel development, researchers have now demonstrated that a healthcare device can be powered entirely by body heat. By integrating a pulse oximetry sensor with a flexible, stretchable, wearable thermoelectric power generator composed of liquid metal, semiconductors, and 3D-printed rubber, the novel approach offers a viable solution to battery life issues.

The team at Carnegie Mellon University’s Department of Mechanical Engineering (Pittsburgh, PA, USA) developed a new approach to extend the battery life of wearable devices by converting body heat into electrical energy using thermoelectric generators (TEGs). This innovation includes the creation of TEGsense, a health monitoring wearable that harnesses body heat for electricity to power a photonic sensing device without the need for batteries. This system utilizes high-performance TEGs made from 3D-printed elastomers blended with liquid metal epoxy polymer composites and thermoelectric semiconductors, ensuring elastic compliance and mechanical compatibility with the body.

These thermoelectric generators were tested in both energy harvesting (Seebeck) and active heating/cooling (Peltier) modes to assess their efficiency under different physical activities such as sitting, walking, and running. During tests, when worn on the forearm and engaged in outdoor walking, the TEG arrays successfully powered electronic circuitry to collect and wirelessly transmit photoplethysmography (PPG) waveform data to an external PC via Bluetooth Low Energy (BLE). The research also included testing the voltage output of these devices on the chest and wrist of participants who were at rest and in motion. Results indicated that device performance was enhanced on the wrist and during movement, benefiting from the increased airflow cooling on one side of the device while the other side was heated by the body, thus maximizing the temperature differential required for efficient energy generation.

“This is the first step toward battery-free wearable electronics,” said Mason Zadan, a graduate student and first author of the study published in Advanced Functional Materials. 

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