3D printing of responsive hydrogels

Hydrogels gain much attention during recent years, due to thier outstanding properties that enable using in various applications, such as drug delivery system, tissue engineering and swimming soft robotics. Polyacrylic acid hydrogel is a responsive hydrophilic polymer that can swell or de-swell when immersed in water, reversibly. The amount of swelling can be controlled by varing the chemical compositions of the hydrogel. This hydrogel can be useful as an ink for 3D printing, enabling printing of high resolution complex objects. By understanding the impact of the printed structure on the swelling capability, the shape of obtained structures after swelling can be controlled.

In this study, we investigated the effect of composition of UV curable hydrogels on the adsorption capacity, mainly focusing on swelling control by using polyethylene glycol diacrylate (PEGDA) as a cross-linker. We demonstrate a bi-material 3D printing with two different cross-linker concentrations, that was fabricated by a Digital light processing (DLP) 3D printing. This printing technology uses a digital light source for localized curing of photo-reactive inks. The DLP 3D printer enables formation of 200-micron diameter pillars in different heights and at different densities, thus we can control the way the structure will deform and change its shape upon contact with water. By spatially varying the pillar density, we prescribe a non-flat reference geometry to the sheet. When swollen in water, the prescribed geometry is activated and the gel buckles into the desired new shape.