Digital Light Processing 3D Printing of Soft Semicrystalline Acrylates with Localized Shape Memory and Stiffness Control

Multimaterial three-dimensional (3D) printing of objectswith spatiallytunable thermomechanical properties and shape-memory behavior providesan attractive approach toward programmable "smart" plasticswith applications in soft robotics and electronics. To date, digitallight processing 3D printing has emerged as one of the fastest manufacturingmethods that maintains high precision and resolution. Despite thecommon utility of semicrystalline polymers in stimuli-responsive materials,few reports exist whereby such polymers have been produced via digitallight processing (DLP) 3D printing. Herein, two commodity long-alkylchain acrylates (C-18, stearyl and C-12, lauryl)and mixtures therefrom are systematically examined as neat resin componentsfor DLP 3D printing of semicrystalline polymer networks. Tailoringthe stearyl/lauryl acrylate ratio results in a wide breadth of thermomechanicalproperties, including tensile stiffness spanning three orders of magnitudeand temperatures from below room temperature (2 & DEG;C) to abovebody temperature (50 & DEG;C). This breadth is attributed primarilyto changes in the degree of crystallinity. Favorably, the relationshipbetween resin composition and the degree of crystallinity is quadratic,making the thermomechanical properties reproducible and easily programmable.Furthermore, the shape-memory behavior of 3D-printed objects uponthermal cycling is characterized, showing good fatigue resistanceand work output. Finally, multimaterial 3D-printed structures withvertical gradation in composition are demonstrated where concomitantlocalization of thermomechanical properties enables multistage shape-memoryand strain-selective behavior. The present platform represents a promisingroute toward customizable actuators for biomedical applications.