Architecting nanoconfined multiphase gels as a reprocessable and multistimuli-responsive 4D printing platform

Four-dimensional (4D)-printed shape memory gels (SMGs) have shown great potential for bionic scaffolds and soft robotics. However, their practical deployment is often limited by insufficient mechanical strength and reprocessability. Here, a nanoconfined multiphase gel strategy to develop reprocessable and multistimuli-responsive 4D-printed SMGs is proposed. The developed poly(vinyl alcohol) (PVA)/chitin nanocrystals (ChNC)/paraffin wax (PW) multiphase gel (PCPG) employs zwitterionic ChNC as interfacial stabilizers to construct a nanoconfined environment through abundant interfacial interactions, including hydrophobic interactions with the paraffin (PW) microphase and hydrogen bonding with the PVA gel matrix. These synergistic interactions lead to a remarkable enhancement in tensile strength (by ~ 50%, up to ~ 1 MPa). A high loading of phase-change PW (volume fraction > 70%) imparts outstanding shape memory properties and printability, with fixation and recovery ratios both exceeding 95%, along with high responsiveness to both thermal and acoustic stimuli. Importantly, the dynamically crosslinked network combined with efficient nanoconfinement enables excellent reprocessability, and the 4D-printed PCPG retains over 85% of its original mechanical and shape memory performance after ten reprocessing cycles. This strategy successfully merges nanoconfinement design with reprocessability, providing a sustainable platform for high-performance 4D-printed bionic scaffolds.