Mechanochromic, Low-Cost, and Structurally Colored Displays Using Biodegradable Hydroxypropyl Cellulose

Mechanochromic materials have garnered significant interest over the past decade due to their ability to change color in response to mechanical cues. While it is known that hydroxypropyl cellulose (HPC) self-assembles into biodegradable and low-cost mechanochromic materials, with a wide range of applications from edible colorants to optical strain sensors, mechanochromic HPC displays themselves are not reported. Here we address this challenge by combining thin mechanochromic HPC films with microfluidic arrays of inflatable microactuators that exert controlled forces. With these devices, the mechanochromic strain sensitivity, color resolution, response times, and operating frequencies of photonic aqueous HPC films are measured at decreasing length scales for the first time. Various pixel sizes, geometry, and input frequencies are also assessed to investigate mechanochromic HPC as a potential low-cost, biodegradable display. Potential applications range from dynamic color pixels for soft robotics to more environmentally responsible RGB display technology.