Chameleon-Inspired Color-Changeable Colloidal Photonic Crystal Films Sensitive to Human Body Temperature

Article Chameleon-Inspired Color-Changeable Colloidal Photonic Crystal Films Sensitive to Human Body Temperature Toshimitsu Kanai *, Mari Sato, and Yuna Hirano Graduate School of Engineering Science, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan * Correspondence: [email protected] Received: 6 February 2025; Revised: 21 March 2025; Accepted: 24 March 2025; Published: 24 March 2025 Abstract: Artificial chameleon skins have been developed using advanced materials, such as photonic crystals, for camouflage and thermoregulation. However, to respond to subtle changes in human body temperature, the thermosensitivity, quality, and color response of these biomimetic films need to be improved. We report the development of chameleon-inspired color-changeable films with enhanced sensitivity to changes in the human body temperature. Non-close-packed colloidal photonic crystals were immobilized in a thermosensitive poly(N-isopropylacrylamide) (PNIPAM) hydrogel film and simultaneously attached to a flexible polyethylene terephthalate (PET) sheet by photopolymerization. The attachment to the PET sheet ensured high thermosensitivity and film quality besides ease of use. The film displayed full color spectrum from red to violet within a small range (~3 °C) of human body temperature without any change in the film area and film distortion. The temperature range of the full color spectrum was easily tuned by adding a poor solvent, ethylene glycol, to PNIPAM. The film attached to a human arm exhibited color changes from red to yellow, light green, and blue in response to changes in the body temperature without external heat. This study could contribute to the basic research and practical applications of artificial chameleon skins.