Transparent Thermotherapeutic Skin Patch Based on Highly Conductive and Stretchable Copper Mesh Heater

In the present work, a stretchable transparent heater (STH) is developed consisting of a free-standing serpentine copper (Cu) mesh attached to a semipermeable polyurethane (PU) film. The as-prepared Cu mesh STH is of extremely low sheet resistance of 0.15 omega sq(-1) at an optical transmittance of 82.5%. The electrothermal and mechanical properties of the fabricated STHs are systematically studied by both experimental measurements and theoretical simulations. The Cu mesh STH proves to be highly effective. For a size of 1 cm x 2 cm skin patch, it can generate temperature up to 120 degrees C in less than 30 s at only 0.7 V supplied voltage. The average temperature drop of the Cu mesh STH is only about 10% under 50% strain at a constant voltage. In addition to the efficient heating, the Cu mesh STH demonstrates high stability during long-term repetitive heating and cooling cycles. Moreover, the STH is air permeable and highly conformable to skin. Its high transparency allows constant monitoring of skin condition during a healing process. As a proof-of-concept, a skin patch consisted of the Cu mesh STH is successfully applied to cure the epidermal tumor of lab mice, demonstrating its great potential for skin-patched thermotherapy.