Dynamic borate ester bonds mediated patterned anisotropic hydrogels for information encryption

Hydrogels with oriented structures exhibit birefringence and display different interference colors between crossed polarizers, which has attracted increasing attention in the fields of information encryption. However, it remains a challenge to introduce complex anisotropic microstructures into hydrogels and enabling them to display high-resolution interference patterns with erasable and rewritable properties. In this study, we report a uniaxially oriented anisotropic polyvinyl alcohol (PVA) hydrogel mediated by dynamic borate ester bonds. Different high-resolution interference patterns can be written or transfer-printed quickly by disrupting the localized PVA-B(OH) 4 − complex structures with HCl solution. The reversible formation and dissociation of the PVA-B(OH) 4 − complex structures allow the interference pattern to be repeatedly erased and rewritten. The excellent stability of the crystalline domains of PVA confers the ability for reversible transformation between hydrogel and dry film states without compromising the accuracy and reliability of the pattern information. The created dry film with a fingerprint pattern can be used to assemble an unforgeable card, which can instantly display a fingerprint pattern in front of a cell phone screen. Double encryption of the patterned information was achieved by drying the patterned hydrogel into a curly shape and utilizing its three-dimensional structure to increase the security of the information.