Strong Adhesion in 3D Printing of Soft Materials

(Yang et al Adv. Funct. Mater. 2019, 1901721). In our new paper, strong adhesion is achieved in integrated structures of a hydrogel and an elastomer extrusion-printed in arbitrary sequence.

Abstract:  Many recently demonstrated devices require the integration of hydrogels and hydrophobic elastomers. Extrusion print is a promising method for rapid prototyping, but existing approaches do not fulfill a basic requirement: print integrated structures of a hydrogel and an elastomer, in arbitrary sequence, with strong adhesion. This paper demonstrates an approach to fulfill this requirement. During print, the ink of each material flows through a nozzle under a pressure gradient, but retains shape against gravity and capillarity. During cure, covalent bonds form to link monomer units into polymer chains, crosslink the polymer chains into the polymer networks of the hydrogel and the elastomer, as well as interlink the two polymer networks into an integrated structure. The approach covalently interlinks the hydrogel network and the elastomer network by adding an interlink initiator in one of the inks.  Adhesion energy above 5000 Jm-2 is demonstrated. Printed morphing structures survive swelling, and printed artificial axons survive repeated hits of a hammer.  This approach opens a road to the development of soft devices for broad applications in medicine and engineering.