Abstract
We propose a method to print four-dimensional (4D) stimuli-responsive hydrogel structures with internal gaps. Our 4D structures are fabricated by printing an N-isopropylacrylamide-based stimuli-responsive pre-gel solution (NIPAM-based ink) and an acrylamide-based non-responsive pre-gel solution (AAM-based ink) in a supporting viscous liquid (carboxymethyl cellulose solution) and by polymerizing the printed structures using ultraviolet (UV) light irradiation. First, the printed ink position and width were investigated by varying various parameters. The position of the printed ink changed according to physical characteristics of the ink and supporting liquid and printing conditions including the flow rates of the ink and the nozzle diameter, position, and speed. The width of the printed ink was mainly influenced by the ink flow rate and the nozzle speed. Next, we confirmed the polymerization of the printed ink in the supporting viscous liquid, as well as its responsivity to thermal stimulation. The degree of polymerization became smaller, as the interval time was longer after printing. The polymerized ink shrunk or swelled repeatedly according to thermal stimulation. In addition, printing multi-hydrogels was demonstrated by using a nozzle attached to a Y shape connector, and the responsivity of the multi-hydrogels to thermal-stimulation was investigated. The pattern of the multi-hydrogels structure and its responsivity to thermal-stimulation were controlled by the flow ratio of the inks. Finally, various 4D structures including a rounded pattern, a spiral shape pattern, a cross point, and a multi-hydrogel pattern were fabricated, and their deformations in response to the stimuli were demonstrated.
Highlights
Accompanying the recent advances in three-dimensional (3D) printing technologies, static objects and shape-changing structures have been fabricated by 3D printers using stimuli-responsive materials
By printing internal gaps and multi-hydrogels, 4D structures can exhibit various deformations in response to external Msticirmomualcih,inaess t2h01e9r,e10i,s4s3p3 ace in which to deform. These results suggest that our proposed method12coofu1l5d enable the printing of complex 4D multi-hydrogels structures with cross points and internal gaps
We proposed a new fabrication method for 4D structures composed of stimuli-responsive hydrogels by using a viscous liquid as a supporting material during printing
Summary
Accompanying the recent advances in three-dimensional (3D) printing technologies, static objects and shape-changing structures have been fabricated by 3D printers using stimuli-responsive materials. These printed structures have been defined as four-dimensional (4D) printed structures by adding one dimension (time variation) to 3D printed structures [1,2,3,4,5]. 4D printed structures can change their shapes and functionalities in response to external stimuli such as light, heat, and pH changes. We propose a new fabrication method for 4D printing that can fabricate 3D multi-hydrogels structures with internal gaps (Figure 1). The detailed definitions of these symbols are described in each experiment section
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
