One-pot ternary sequential reactions for photopatterned gradient multimaterials

•Thiol-ene-epoxy photochemistry for patterning diverse mechanical properties•Materials possess a stable three-orders-of-magnitude difference in Young’s modulus•Demonstration of low-cost, 3D-printed multimodulus wearable braille display Numerous research efforts seek to realize “augmented humanity,” whereby technology enhances human performance by closely interfacing engineered devices with our anatomy. A key challenge these is mismatch—electronic are composed rigid materials, but natural tissues soft. Co-depositing disparate materials at high resolution single manufacturing step often difficult implement, and abruptly joining soft-stiff leads delamination. This new thiol-ene-epoxy framework offers photopatterned control over reaction conversion and, consequently, local stiffness. Unlike previous multimaterial photopolymers that rely on “under-cured” material, this chemistry creates persistent continuous gradients spanning three orders magnitude modulus comparable animal physiology. Such capabilities enable applications, as demonstrated can be worn finger. Seamless construction common motif remain challenging reproduce systems, current resin chemistries typically result fixed set properties. As an alternative single-property we introduce thiol-ene-epoxy-based photothermal scheme produces multimaterials altering the polymer microstructure within resin. In system, photodosage during first stage processing dictates extent each subsequent reaction. result, exhibit range soft (Young’s modulus, E ∼ 400 kPa; elongation, dL/L0 300%) stiff (E 1.6 GPa; 3%) Furthermore, pattern photostable mechanically robust (d[Er, stiff/Er, soft]/dx > 1,000 mm−1) exceed those found squid beaks knee entheses. We demonstrate ability build intricate architectures including soft, display. Across length scales, biology combines structures higher functionality. prime example, load-bearing activity vertebrates relies connection bones muscle tissue.1Vogel S. 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Interfaces. 12: 17979-17987https://doi.org/10.1021/ACSAMI.0C02038Crossref Beyond poor stability, partially cured networks stretchable (ultimate 40%), which precludes their use devices. creating capable mimicking wide available commercial polymers. approach photoinitiated thiol-ene followed thiol-epoxy step-growth then elevated temperatures. unique sequence dosage determines thiol ene group (x) stage, amount created second consequently “stiff” formed third stage. applied segments part. precise yields polymers elastomers (Esoft kPa, glassy thermosets (Estiff GPa, 3%). multimaterials, always full consumption readily reacted groups processing, imparts environmental stability (Estiff/Esoft 103 after equivalent ∼1,000 h solar irradiation) final material. Not only do approximate commodity (acrylics, polyurethanes, silicones, hydrogels) anatomy (tendons, ligaments, skin, gastrointestinal tissues), photodosage-controlled, (0 ≤ d[Er,stiff/Er,soft]/dx 1,300 produced system also healthy entheses beaks. To biomimetic offer rapidly (tprint 10 min) print Designing consideration phenomenological origin polymeric ensembles macromolecular chains held together both intra- interchain interactions. At microscale, relative interactions determine how deforms load which, turn, observed macro-scale depend chain arrangements. stable, one-pot challenging: initial chemical formulation cannot change, leaving threatens proceed alter properties). Instead, leverage mechanisms yield drastically densities, viscoelastic properties, therefore, performance. Our (Figure 1A) triallyl (-ene) species, mixture (9:1 M ratio di- tetra-thiol molecules), diepoxy. 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