One-pot ternary sequential reactions for photopatterned gradient multimaterials

Seamless multimaterial construction is a common motif in animal physiology. Such continuous mechanical gradients remain challenging to reproduce in engineered systems, as current resin chemistries typically result in a single fixed set of properties. As an alternative to single-property materials, we introduce a thiol-ene-epoxy-based photothermal reaction scheme that produces multimaterials by altering the polymer microstructure within a single resin. In this system, the photodosage during the first stage of processing dictates the extent of conversion for each subsequent reaction. As a result, our photochemistry can exhibit a diverse range of soft (Young's modulus, E similar to 400 kPa; elongation, dL/L-0 -300%) and stiff (E similar to 1.6 GPa; dL/L-0 similar to 3%) mechanical properties. Furthermore, we pattern photostable and mechanically robust modulus gradients (d [E-r,E- stiff/E-r,E- soft]/dx > 1,000 mm(-1)) that exceed those found in squid beaks and human knee entheses. We demonstrate the ability to build intricate multimaterial architectures including a soft, wearable braille display.