Engineering hydrogels with homogeneous mechanical properties for controlling stem cell lineage specification.

The extracellular matrix (ECM) is mechanically inhomogeneous due to the presence of a wide spectrum of biomacromolecules and hierarchically assembled structures at the nanoscale. Mechanical inhomogeneity can be even more pronounced under pathological conditions due to injury, fibrogenesis, or tumorigenesis. Although considerable progress has been devoted to engineering synthetic hydrogels to mimic the ECM, the effect of the mechanical inhomogeneity of hydrogels has been widely overlooked. Here, we develop a method based on host-guest chemistry to control the homogeneity of maleimide-thiol cross-linked poly(ethylene glycol) hydrogels. We show that mechanical homogeneity plays an important role in controlling the differentiation or stemness maintenance of human embryonic stem cells. Inhomogeneous hydrogels disrupt actin assembly and lead to reduced YAP activation levels, while homogeneous hydrogels promote mechanotransduction. Thus, the method we developed to minimize the mechanical inhomogeneity of hydrogels may have broad applications in cell culture and tissue engineering.

Design of Self-Healing and Electrically Conductive Silk Fibroin-Based Hydrogels.

Self-healing and electrically conductive silk fibroin (SF)-based hydrogels were developed based on the dynamic assembly/disassembly nature of supramolecular complexes and the conductive nature of polypyrrole (PPy). The self-healing properties of the hydrogels were achieved through host-guest interactions between ß-cyclodextrin and amino acid side chains (tyrosine, tryptophan, phenylalanine, and histidine) on SF. PPy deposition was achieved via in situ polymerization of pyrrole using ammonium persulfate as an oxidant and laccase as a catalyst. The PPy-coated hydrogels behaved as an elastomer and displayed excellent electrical properties, with adjustable electrical conductivities ranging from 0.8 ± 0.2 to (1.0 ± 0.3) × 10-3 S·cm-1. Furthermore, possibility of potential utilization of the hydrogels in electrochemistry applications as flexible yet self-healable electrode materials was explored. This study not only shows great potential in expanding the role of silk-based devices for various applications but also provides a useful approach for designing multifunctional self-healing protein-based hydrogels.