Constructing 3D heterogeneous hydrogels from electrically manipulated prepolymer droplets and crosslinked microgels.

Formation of multifunctional, heterogeneous, and encoded hydrogel building blocks, or microgels, by crosslinking and assembly of microgels are two essential steps in establishing hierarchical, complicated, and three-dimensional (3D) hydrogel architectures that recapitulate natural and biological structures or originate new materials by design. However, for the variety of the hydrogel materials crosslinked differently and for the varied scales of microgels and architectures, the formation and assembly processes are usually performed separately, which increases the manufacturing complexity of designed hydrogel materials. We show the construction of hydrogel architectures through programmable formation and assembly on an electromicrofluidic platform, adopting two reciprocal electric manipulations (electrowetting and dielectrophoresis) to manipulate varied objects (i) in multiple phases, including prepolymer liquid droplets and crosslinked microgels, (ii) on a wide range of scales from micrometer functional particles or cells to millimeter-assembled hydrogel architectures, and (iii) with diverse properties, such as conductive and dielectric droplets that are photocrosslinkable, chemically crosslinkable, or thermally crosslinkable. Prepolymer droplets, particles, and dissolved molecules are electrically addressable to adjust the properties of the microgel building blocks in liquid phase that subsequently undergo crosslinking and assembly in a flexible sequence to accomplish heterogeneous and seamless hydrogel architectures. We expect the electromicrofluidic platform to become a general technique to obtain 3D complex architectures.