Flexible “smart” heater relieves joint pain caused by arthritis

Arthritis causes constant inflammation and pain in the joints, affecting the mobility and quality of life of millions of people. Although heat therapy—the application of heat to affected areas—has long been used to relieve symptoms, traditional methods such as heating pads or hot patches often do not produce the desired results. They can overheat, cause burns, or lose effectiveness over time, and rarely adapt to real-world conditions such as cold air or wet weather. In addition, many heating devices are bulky, immobile, and unable to determine when therapy is truly needed. These shortcomings highlight the urgent need for “smart” wearable devices that can monitor the body’s needs and provide safe, stable, and timely heat.

On May 13, 2025, researchers from Dalian University of Technology presented a flexible wearable thermotherapy system in the journal Microsystems & Nanoengineering. This multilayer device combines temperature and humidity sensors with a thin gold-based heater on a stretchable polyimide film. Designed for automatic, real-time use, it responds to environmental cues and body movements, providing personalized thermal treatment for joints affected by arthritis. The system represents a step forward in wearable health technology, overcoming the limitations of traditional devices and offering patients a discreet and reliable means of daily therapy and protection in a variety of settings.

At the core of the system is a kirigami-serpentine structure, an origami-like pattern that enhances flexibility and stretchability. The device, consisting of an Au temperature sensor, a poly(3,4-ethylenedioxythiophene) (PEDOT) humidity sensor, and a Joule heater, fits snugly around joints such as the knee. Using real-time data processed by a flexible circuit and Bluetooth-enabled feedback, the system can adjust heat output within 1 second, maintaining a temperature with a deviation of less than 0.1 °C at 45 °C.

This innovation supports several applications: programmable on-demand therapy with custom heating cycles; daily thermal protection that automatically activates in cold weather; and humidity control to combat moisture that impairs joint mobility. Body tests showed that the heater can increase local skin temperature even outdoors, while humidity levels steadily decrease during use. Most strikingly, the team used photoplethysmography (PPG) to measure blood flow and confirmed that thermotherapy with this system significantly enhances local perfusion — an important factor in pain relief. The design has also proven its durability over more than 1,000 cycles of use, remaining accurate during walking, warm-ups, and running. Combining high accuracy with practical applicability in real-world conditions, this soft wearable system provides clinical-grade functionality in a compact format that patients can use every day.

“Our goal was to make thermotherapy truly wearable — not just portable, but adaptive and intuitive. By integrating precise sensors and a feedback control system into a wearable form factor, we empower patients to receive real-time therapy tailored to their specific environment and condition. This technology reflects the future of personalized medicine, where treatment moves with the body and responds as needed. It’s not just engineering — it’s empathy through innovation.”

Dr. Mancy Wu, co-author of the study

In addition to alleviating arthritis, this technology sets a new direction for wearable medical devices. Its modular design, environmental responsiveness, and soft mechanics make it suitable for integration into clothing, bandages, or orthopedic undergarments. For chronic conditions sensitive to temperature and humidity, such as circulation problems, muscle injuries, or autoimmune disorders, the platform can offer personalized support. In addition, the same architecture with sensors, feedback, and heating can be adapted for wound care, smart rehabilitation, or materials that respond to the environment. As digital healthcare evolves, the union of microelectronics with human needs could change the approach to treatment—not in clinics, but directly on the body, where it is most needed.