Tuning water-cellulose interactions via copper-coordinated mercerization for hydro-actuated, shape-memory cellulosic hydroplastics

Innovative biopolymers emulating natural organisms' reversible water-induced deformations hold great potential across various domains. Here, we create a biopolymer that unifies actuation, hydrosetting, and shape-memory capabilities through copper-coordinated mercerization of nanocellulose paper. This method transforms the inherently hydrophilic, porous nanocellulose network into a compact amphiphilic membrane, distinguished by Cu2+-crosslinked hydrophobic domains acting as tough "net points," ensuring exceptional water stability and ultrahigh wet mechanical performance (94.9 MPa and 3.50 GPa). Upon hydration, the membrane swiftly establishes reversible hydrogen-bonding "switches," enabling a rapid plastic-elastic transition. The interplay between the net points and switches resolves the inherent trade-off between rapid, reversible hydrogen-bonding networks and mechanical robustness in cellulosic materials, thereby facilitating remarkable water-induced actuation, hydrosetting, and shape memory. Notably, the membrane demonstrates complex morphing and swift recovery in water, serving as a smart encrypted information carrier. Our study offers a molecular structural engineering paradigm for the rational design of advanced responsive materials.