a) Temperature distribution image of the bioinspired thermotherapy patch affixed to the human wrist in normal, inward, and outward bending conditions. (b, c) The patch affixed to the cubital fossa area and elbow, respectively. (Image: Tampere University)

A team of researchers has developed a biodegradable, transparent, flexible, and fast-acting thermotherapy patch from plant leaves that is compatible with flexible electronic applications. Plant material was used to reduce the amount of electronic waste.

The researchers used leaves from a Bodhi tree (Ficus religiosa). The veins of the leaves have a fractal pattern that makes the surface highly flexible and shearable. Silver nanowires were attached to the leaf skeleton and the surface was encapsulated in a biodegradable, transparent tape. The fractal-based design can also be used in flexible electronic applications, as it overcomes the limitations of conventional planar designs by maximizing the surface area at the microscale, or more specifically, maximizing the surface area-to-volume ratio via simple scaling. The large surface area enables effective heat transfer, allowing a rapid response time and preventing overheating. Due to the flexibile structure and uniform heating of the patch, it can also be attached to moving joints.

In orthopedics, medical thermotherapy pads are commonly used to reduce pain, improve blood circulation, and decrease inflammation. They are also used in the treatment of arthritis, stiff joints, cervical spondylosis, and physical injuries.

Traditional thermotherapy pads are known to have caused burns, mainly among people who fall asleep with their heating pads on or among the elderly who might not be very sensitive to heat. Part of the problem is that commercial heating pads are opaque and users cannot see how their skin is reacting to the therapy.

As the thermotherapy patch is made entirely of plant-based materials, it can help reduce carbon footprint and electronic waste. All the materials used in the fabrication process are eco-friendly, economical, easily accessible, and easy to fabricate. Electronics, especially flexible electronics, are increasingly integrated into medical devices, textiles, wellness trackers, and other portable devices.

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