(494i) Self-Reinforced and 3D Printable Hydrogels Using Nanofibrous Soft Dendritic Colloids

Mechanically robust hydrogels could find applications such as biomimetic cell scaffolds, drug delivery agents, and materials for soft robotics, however, many hydrogel matrixes are too brittle or weak for such applications. One efficient approach to improve the mechanical characteristics of their matrices is to make reinforced hydrogels that incorporate inorganic or polymeric fillers such as nanofibers into the hydrogel network matrices. Here, we will report a new class of hydrogels with internal hierarchical reinforcing network from soft dendritic colloids (SDCs). The SDCs are a novel colloidal material invented in our group, which has fibrillar polymer backbone decorated by with corona of branched, self-similar fibers down to the nano-scale.^[1] The hydrogel SDCs are fabricated in a scalable process of turbulent ionic precipitation. The SDC have high excluded volume and neighboring fiber sub-contacts readily form percolated 3D networks within a medium, resulting in the efficient gelation of SDC suspensions at low volume fractions. We will first show how SDCs are fabricated and the balance of high shear and rapid precipitation govern the resulting particle morphology and properties. We will then demonstrate that alginate SDCs can be incorporated into molecular alginate hydrogel matrices to form hierarchical networks with mechanical properties resulting from synergistic combination of networks at the molecular and particle-scale. Because the reinforcing network and the hydrogel matrix are composed of the same material, these strengthened hydrogel materials are designated “homocomposites”. We show that alginate homocomposites have remarkably increased stiffness following molecular cross-linking. Furthermore, they exhibit yield stress behavior due to the SDC fiber network even prior to the slow molecular cross-linking due to the SDC microgel network. This yield stress behavior of the homocomposite pre-mixture enables 3D printing and injection of these biodegradable hydrogel materials into designed patterns and architectures with increased toughness once the secondary, ionic network reaches equilibration.

1. Roh, S., Williams, A. H., Bang, R. S., Stoyanov, S. D. & Velev, O. D. Soft dendritic microparticles with unusual adhesion and structuring properties. Nat. Mater. 18, 1315–1320 (2019).