Fully Printed Flexible Smart Hybrid Hydrogels

A printable hybrid hydrogel is fabricated by embedding poly(N-isopropy-lacrylamide) (PNIPAm) microparticles within a water-rich silica-alumina (Si/Al)-based gel matrix. The hybrid gel holds water content of up to 70 wt%, due to its unique Si/Al matrix. The hybrid hydrogel can respond to both heat and electrical stimuli, and can be directly printed layer-by-layer using a commercial 3-dimensional printer, without requiring any curing. The hybrid ink is printed onto a transparent, flexible conductive electrode composed of silver nanoparticles and sustains bending angles of up to 180 degrees, which enables patterning of various flexible devices such as smart windows and a 3D optical waveguide valve.