(356f) 3D Printing of Hydrogels with Spontaneous Formation of Solvent-Induced Patterns

Surface patterns driven by instability are commonly observed in nature. Numerous intriguing surface morphologies which provide important functions can be found in living creatures, such as folds in the human brain, wrinkles on human skins, and buckling protrusions on tumor surfaces. Numerous methods have been studied in an effort to produce controllable engineered surface patterns. Yet, majority of the work mainly focus on creating planar surface patterns with limited control on spatial distribution of patterns and not capable of fabricating 3D patterned structures, which significantly limit their applications. In this study, we used extrusion-based direct-ink-writing (DIW) using ink formulations that are able to form a wide range of solvent-induced surface instability patterns in hydrogel form. The inks are formulated from poly(hydroxyethyl methacrylate) (PHEMA) with ethylene glycol dimethacrylate (EGDMA) in the presence of a photoinitiator. We first showed the effect of ink composition and curing process on rheological properties and printability of the inks as well as pattern formation on 3D printed hydrogels. Then, by using multi-material printing we showed spatial control of pattern morphology on 2D substrates. Finally, we demonstrated fabrication of 3D scaffolds/constructs with a variety of ordered micropatterns, including hexagonal and lamellar patterns. Our approach involves three sequential steps in order to obtain optimal ink viscosity and the desired patterns. First a mixture of HEMA monomers and photoinitators were irradiated with UV light (for t₁ second) to obtain a partially polymerized poly(HEMA) prepolymer solution. The solution was then loaded in a syringe and followed by a second round of UV exposure (for t₂ second) in the presence of crosslinkers and additional photoinitiators. The printed object was subjected to UV light for t₃ second after completion of each layer. The finished print was immersed in water for 30 minutes to induced patterns. The three UV exposure times, together with the crosslinker concentrations, govern the surface morphology of the printed scaffolds, offering a novel strategy for extending the use of surface instability patterns.