Micro 3D Printing of a Temperature-Responsive Hydrogel and Its Applications*

Poly(N-isopropylacrylamide) (PNIPAAm) has been extensively studied due to its unique thermo-responsive swelling behavior. However, potential of PNIPAAm has not been fully unleashed due to the limited available fabrication processes such as molding and lithographical techniques, which are often inherently 2D in nature. 3D PNIPAAm structures have been achieved employing an origami approach, but accessible 3D geometries are still limited.
Here we present micro 3D printing of PNIPAAm hydrogel using a projection micro-stereolithography (PµSL). PµSL is a lithography-based additive micro-manufacturing technique using a dynamically reconfigurable digital photomask. We investigated the effects of 3D printing parameters and resin composition on thermo-responsive swelling behavior of the printed PNIPAAm hydrogel. Utilizing the swelling characteristics of 3D printed PNIPAAm hydrogels, highly complex 3D PNIPAAm micro-structures were printed with programmed responsive deformation. 3D printing of PNIPAAm hydrogel can potentially lead to various new applications in many areas such as soft robotics, microfluidics, and drug delivery.