One Pot Multimaterial Photochemistries for Mechanical Gradients in Soft Wearable Tech

Seamless multimaterial construction, particularly joining soft, stretchable tissues with stiff, inextensible structures, 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 ternary sequential reaction scheme that produces multimaterials by profoundly altering the polymer microstructure from within a single resin composition. In this system, the photodosage during 3D printing sets both the shape and extent of conversion for each subsequent reaction. The different polymerization mechanisms of the subsequent stages allow our single photochemistry to exhibit a diverse range of soft (Young’s Modulus, E ~ 400 kPa; ultimate elongation, dL/L0 ~ 300%) and stiff (E ~1.6 GPa; dL/L0 ~ 3%), providing the capability to match the mechanical properties of commercial polymers and biological tissues. Further, we successfully pattern photostable and mechanically robust modulus gradients (d[Er,stiff/Er,soft]/dx > 1000 mm-1) that exceed those found in squid beaks and human knee entheses. We demonstrate the ability to 3D print intricate multimaterial architectures by fabricating a soft, wearable braille display.