Controlled Sequential Reactions for 3D Printing of Spatially Defined Multimodulus Materials

Additive manufacturing has revolutionized small scale prototype development, allowing for the rapid manufacture of previously inaccessible geometries. Stereolithography, a subset of additive manufacturing, uses 2D projections to cure thin layers of resin slowly dividing the resin vat into a solid part and liquid resin. Here we report a multicomponent system utilizing three independently controlled reactions—thiol-ene, thiol-epoxy, and epoxy-epoxy, in sequence—enabling spatially controlled stiffening while maintaining homogeneous molecular composition in the final material. Starting with an approach based on fundamental chemistry principles, material cure rates for the initial thiol-ene reaction, and exotherms of the remaining reactions to ensure independent control over the sequentially cured material. Based on these results, candidate monomers were identified from commercially available sources for formulation and material testing. The best performing formulation to date demonstrates a 30-fold difference in stiffness and around 1 mm mechanical resolution all while remaining chemically homogeneous. With the ability to dictate stiff and soft regions in the final material, in addition to the material’s stability and favorable glass transition temperature, it is envisioned that these materials, or those based on the same fundamental principles, will be used to immobilize stiff components (e.g. electronics) in an overall flexible wearable device. We present a chemically uniform band comprised of a stiff component surrounded by soft regions (>30-fold difference in modulus), patterned by 405 nm irradiation, that stretches to more than 190% its original length before failure. This demonstration serves as a signpost pointing towards the future applications of programed multimodulus materials based on the principles of one-pot orthogonal reactions.