Structural multi-colour invisible inks with submicron 4D printing of shape memory polymers

Four-dimensional (4D) printing of shape memory polymer (SMP) imparts time-responsive properties to 3D structures. This research explores submicron-scale 4D printing of an SMP, extending its applications to nanophononics. A new SMP photoresist based on Vero Clear is reported, achieving print features at ~300 nm half-pitch resolution using two-photon polymerization lithography (TPL). Size-tunable multi-color grids demonstrate shape memory effects, achieving large visual shifts through nanoscale structure deformation. Flattening renders the colors and printed information invisible, but heating above the glass transition temperature recovers the original morphology and color within seconds. This high-resolution printing and reversibility promises applications in temperature-sensitive labels, anti-counterfeiting, and tunable photonic devices.

Wang Zhang, Hao Wang, Hongtao Wang, John You En Chan, Hailong Liu, Biao Zhang, Yuan-Fang Zhang, Komal Agarwal, Xiaolong Yang, Anupama Sargur Ranganath, Hong Yee Low, Qi Ge, Joel K. W. Yang