4D printing of photocurable shape memory resins activated via indirect heating

This work introduces a DLP-based 4D printing strategy that enables the fabrication of monolithic, electrically triggered shape-memory structures through indirect Joule heating. Two polyurethane–methacrylate-based resin blends were prepared from commercially available photopolymer resins and processed by Digital Light Processing (DLP) printing. NMR and rheological analyses confirmed the compatibility of the resin components and their suitability for vat photopolymerization processes, while FT-IR analysis demonstrated the effective crosslinking induced by UV curing. Post-curing significantly improved the mechanical properties of the printed parts, leading to elastic modulus values up to 2.9 GPa and high thermal stability. Both formulations exhibited stable shape memory behavior, with shape fixity ratio values above 93% and rapid recovery of the permanent shape upon thermal activation allowing also to lift external loads. NiCr wires have been successfully embedded during the printing process, enabling indirect activation through the Joule effect with recovery time of 20 s