Strain-Stiffening Hydrogels with Dynamic, Secondary Cross-Linking

Embedding Thiols into Choline Phosphate Polymer Zwitterions

The compositional scope of polymer zwitterions has grown significantly in recent years and now offers designer synthetic materials that are broadly applicable across numerous areas, including supracolloidal structures, electronic materials interfaces, and macromolecular therapeutics. Among recent developments in polymer zwitterion syntheses are those that allow insertion of reactive functionality directly into the zwitterionic moiety, yielding new monomer and polymer structures that hold potential for maximizing the impact of zwitterions on the macromolecular materials chemistry field. This manuscript describes the preparation of zwitterionic choline phosphate (CP) methacrylates containing either aromatic or aliphatic thiols embedded directly into the zwitterionic moiety. The polymerization of these functional CP methacrylates by reversible addition-fragmentation chain-transfer methodology yields polymeric zwitterionic thiols containing protected thiol functionality in the zwitterionic units. After polymerization, the protected thiols are liberated to yield thiol-rich polymer zwitterions which serve as precursors to subsequent reactions that produce polymer networks as well as polymer-protein bioconjugates.

Modeling the Maturation of the Vocal Fold Lamina Propria Using a Bioorthogonally Tunable Hydrogel Platform

Toward the goal of establishing an engineered model of the vocal fold lamina propria (LP), mesenchymal stem cells (MSCs) are encapsulated in hyaluronic acid (HA)-based hydrogels employing tetrazine ligation with strained alkenes. To mimic matrix stiffening during LP maturation, diffusion-controlled interfacial bioorthogonal crosslinking is carried out on the soft cellular construct using HA modified with a ferocious dienophile, trans-cyclooctene (TCO). Cultures are maintained in MSC growth media for 14 days to afford a model of a newborn LP that is homogeneously soft (nLP), a homogeneously stiffened construct zero (sLP0) or 7 days (sLP7) post cell encapsulation, and a mature LP model (mLP) with a stiff top layer and a soft bottom layer. Installation of additional HA crosslinks restricts cell spreading. Compared to the nLP controls, sLP7 conditions upregulate the expression of fibrous matrix proteins (Col I, DCN, and FN EDA), classic fibroblastic markers (TNC, FAP, and FSP1), and matrix remodeling enzymes (MMP2, TIMP1, and HAS3). Day 7 stiffening also upregulates the catabolic activities, enhances ECM turnover, and promotes YAP expression. Overall, in situ delayed matrix stiffening promotes a fibroblast transition from MSCs and enhances YAP-regulated mechanosensing.