Tunable Synthesis of Hydrogel Microfibers via Interfacial Tetrazine Ligation.

Crosslinked, degradable, and cell-adhesive hydrogel microfibers were synthesized via interfacial polymerization employing tetrazine ligation, an exceptionally fast bioorthogonal reaction between strained trans-cyclooctene (TCO) and s-tetrazine (Tz). A hydrophobic trisTCO crosslinker and homo-difunctional poly(ethylene glycol) (PEG)-based macromers with the tetrazine group conjugated to PEG via a stable carbamate (PEG-bisTz1) bond or a labile hydrazone (PEG-bisTz2) linkage were synthesized. After laying an ethyl acetate solution of trisTCO over an aqueous solution of bisTz macromers, mechanically robust microfibers were continuously pulled from the oil-water interface. The resultant microfibers exhibited comparable mechanical and thermal properties but different aqueous stability. Combining PEG-bisTz2 and PEG-bisTz3 with a dangling arginine-glycine-aspartic acid (RGD) peptide in the aqueous phase yielded degradable fibers that supported the attachment and growth of primary vocal fold fibroblasts. The degradable and cell-adhesive hydrogel microfibers are expected to find utility in a wide array of tissue engineering applications.

Durability of Poly(3,4-ethylenedioxythiophene) (PEDOT) films on metallic substrates for bioelectronics and the dominant role of relative shear strength.

Despite growing interest in the use of conducting polymer coatings such as poly(3,4-ethylenedioxythiophene) (PEDOT) in bioelectronics, their relatively poor mechanical durability on inorganic substrates has limited long-term and clinical applications. Efforts to enhance durability have been limited by the lack of quantifiable metrics that can be used to evaluate the polymer film integrity and associated device failure. Here we examine the hypothesis that film failure under the tribological and cyclic electrical stressing becomes substantially less likely when the interfacial shear strength (τi) exceeds the shear strength of the film (τf). In this paper, we: (1) develop a simple yet robust method to quantify the relative shear strength (τi/τf); (2) quantify the effect of substrate and surface treatment on the relative shear strength of PEDOT; (3) relate changes in relative shear strength to resistance to interface failure under cyclic electrical and tribological testing. Treating a stainless-steel substrate with an adhesion promoter increased τi/τf from 0.18 to 0.69 compared to untreated controls. On untreated gold, the τi/τf of PEDOT increased to 1.46. Whereas both cyclic electrical and tribological testing quickly and severely damaged the interface of PEDOT when τi/τf < 1, neither stimulus had any quantifiable effect on delamination when τi/τf > 1.