Brush Hydrogels with Hydrogen Bonds: A Path to Control Materials Firmness.

Biological tissues combine seemingly incompatible mechanical traits such as softness and firmness which are difficult to replicate in synthetic materials. In brush elastomers and gels, their softness and firmness are controlled by varying the length and the grafting density of side chains which result in stiffening and dilution of the stress supporting strands. However, this approach does not allow for tuning the strand's persistence length to meet a broad set of biomedical applications. We use a combination of the coarse-grained and atomistic molecular dynamics simulations and experiments to explore the effect of H-bonding between the side chains on the persistence length of the brush strands. Our simulations show that, for a given brush architecture and composition, the strand's persistence length can be varied through concentration of hydrogen bonds, temperature, and strain rate. These predictions are verified by studying viscoelastic properties of brush gels synthesized from macromonomers with secondary amine linkers between polymerizing methacrylate end groups and side chain tails.