Flexible smart heater delivers real-time thermal therapy for joint pain

Arthritis causes persistent inflammation and pain in the joints, affecting mobility and quality of life for millions. While thermotherapy—applying heat to affected areas—has long been used to ease symptoms, traditional methods like heat pads or hot patches often fall short. They can overheat, burn, or lose effectiveness over time, and they rarely adapt to real-world conditions like cold air or damp weather. Moreover, many heating devices are bulky, immobile, and unable to detect when therapy is actually needed. These shortcomings highlight the urgent demand for smart, wearable solutions that can monitor the body's needs and deliver safe, stable, and timely heat. Due to these problems, intelligent thermotherapy devices must be further explored and developed.

On May 13, 2025, researchers from Dalian University of Technology unveiled a flexible, wearable thermotherapy system (DOI: 10.1038/s41378-025-00912-8) in Microsystems & Nanoengineering. This multilayered device integrates temperature and humidity sensors with a thin gold-based heater on a stretchable polyimide film. Designed for real-time, automatic use, it responds to environmental cues and body movement, providing personalized thermal treatment for arthritic joints. The system marks a step forward in wearable health technology, addressing the limitations of conventional devices and offering patients a discreet, reliable tool for daily therapy and protection in varying conditions.

At the heart of the system is a kirigami-serpentine structure—an origami-like pattern that enhances flexibility and stretchability. Layered with an Au temperature sensor, Poly(3,4-ethylenedioxythiophene) (PEDOT)-based humidity sensor, and Joule heater, the device conforms closely to joints, such as knees, and performs reliably during movement. Using real-time data processed by a flexible circuit and Bluetooth-enabled feedback loop, the system can adjust heat output within 1 second, maintaining temperatures with less than 0.1°C variation at 45°C.

This innovation supports multiple applications: programmable on-demand therapy with customized heat cycles; daily thermal protection that automatically activates in cold weather; and moisture control to combat joint-stiffening humidity. On-body tests showed the heater could raise local skin temperature even outdoors, while humidity levels dropped steadily during use. Most strikingly, the team used photoplethysmography (PPG) to measure blood flow and confirmed that thermotherapy via this system significantly boosted local perfusion—an essential factor in pain relief. The design also proved durable through 1,000+ use cycles, remaining accurate during walking, stretching, and running. By combining high precision with real-world practicality, this soft, wearable system delivers clinical-grade function in a form factor that patients can use every day.

Our goal was to make thermal therapy truly wearable—not just portable, but adaptive and intuitive. By integrating precise sensors and closed-loop control into a stretchable format, we're giving patients the ability to receive therapy in real time, 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. Mengxi Wu, co-corresponding author of the study

Beyond arthritis relief, this technology signals a new direction for wearable health systems. Its modular design, environmental responsiveness, and soft mechanics make it well-suited for integration into clothing, bandages, or therapeutic garments. For chronic conditions sensitive to temperature and humidity—such as circulatory issues, muscle injuries, or autoimmune disorders—the platform could offer customized support. Additionally, the same sensing-feedback-heating architecture might be adapted for wound care, smart rehabilitation, or ambient-responsive materials. As digital health advances, the marriage of microscale electronics with human-scale needs could reshape how therapy is delivered—not in clinics, but directly on the body, wherever and whenever it's needed most.