Photoactive Self-shaping Hydrogels As Noncontact 3D Macro/Microscopic Photoprinting Platforms

In this study,a series of photoactive hydrogels,termed as P(AAm-co-THMMA-co-NB526)(PATN),were synthesized by white-light initiated radical copolymerization of acrylamide(AAm),N-[tris(hydroxymethyl)methyl]acrylamide(THMMA)and photocleavable crosslinker NB526,which was one of o-nitrobenzyl derivatives prepared in our lab.The physical properties of PATN hydrogels changed under 365 nm UV irradiation,for instance,equilibrium water content increased,and density,tensile strength,modulus and cross-linking density decreased.PATN hydrogels experienced spontaneous shape transformation after UV exposure,due to asymmetric photocleavage and swelling gradient generated along its thickness as light passed through the bulk.Locally irradiating could transfer 2D flat to various 3D structures such as deformations of bio-mimicking flower petals,chiral helices and Mobius Band loop.The continuum model and finite element method were used to elucidate the shape transition mechanism underlying.Furthermore,the photosensitive PATN hydrogels could be developed as photoprinting soft and wet platforms onto which specific 3D characters and images were faithfully duplicated in macro/microscale without contact by UV light irradiation under the cover of customized photomasks.Importantly,based on the photolithographic principle,a quick response(QR)code was accurately printed on the photoresponsive PATN hydrogel for the first time.Scanning QR code with a smartphone could quickly connect to a web page.This photoactive PATN hydrogel is promising to be a new printing or recording material.