3D Printed Hydrogel-Based Sensors for Quantifying UV Exposure

Exposure to excessive ultraviolet (UV) radiation can have detrimental effects on human health. Inexpensive easy-to-use sensors for monitoring UV radiation can allow broad-scale assessment of UV exposure, but their implementation requires technology that enables rapid and affordable manufacturing of these sensors on a large scale. Herein, we report a novel three-dimensional (3D) printing procedure and printable ink composition that produce robust, flexible, and wearable UV sensors. To fabricate the sensors, a color-changing hydrogel ink was first developed from which standalone constructs were 3D printed. The ink contains alginate, gelatin, photoactive titanium dioxide nanoparticles, and dyes (methyl orange, methylene blue, and malachite green) in which the nanoparticles are used to initiate photocatalytic degradation of dyes, leading to discoloration of the dye. The sensors resemble a color-changing tattoo that loses color upon exposure to UV. The viscosity and ink composition were optimized to achieve printability and tune the mechanical properties (e.g., modulus, hardness) of the sensors. The optimized procedure enabled the one-step fabrication of mechanically stable sensors that can effectively measure outdoor sun exposure by quantifying the decrease in color, visible to the naked eye. Apart from being used as wearable sensors, these sensors have the potential to be used along with UV-based workspace sterilizing devices to ensure that surfaces have been efficiently exposed to UV. The sensors are inexpensive, stable, extremely robust, biodegradable, and easy to use. The tunability, biocompatibility, and printability of the ink offer excellent potential for developing advanced 3D printing methods that, in addition to UV sensors, can be applied more broadly to fabricate other sensing technologies for a variety of other applications.