4D printing of hydrogels based on poly(oxazoline) and poly(acrylamide) copolymers by stereolithography

Abstract

Programmed shape deformation of hydrogels by thermal stimulation has great potential due to the remarkable possibilities of 4D printing process in a wide domain of applications. Consequently, high requests are dedicated to the synthesis and study of smart hydrogels for additive manufacturing. This work revolves around the synthesis of two new thermo-responsive hydrogel systems based on copolymers of poly(oxazoline) and poly(acrylamide). For each system, the thermo-sensitive part corresponds to poly(2-isopropyl-2-oxazoline) (PiPrOx) or poly(N-isopropylacrylamide) (PNIPAM), while the crosslinking is carried by the poly(oxazoline) comonomer blocks. Photocrosslinked resin is obtained during the stereolithography (SLA) printing process leading to different macromolecular networks and properties. The volume transformation of the hydrogels is evaluated by the measurement of water content at different temperatures in order to estimate the sorption's kinetics and to determine the volume phase transition temperature (VPTT). The impact of the VPTT on each hydrogel system is highlighted by their mechanical properties. Finally, 3D porous structures, based on these thermo-responsive hydrogels, are manufactured by 4D SLA printing and the shrinking/expansion effects with the temperature change are illustrated.