  Gels are an increasingly important class of soft materials with applications
ranging from regenerative medicine to commodity materials. A major drawback of
gels is their relative mechanical weakness, which worsens further under strain.
We report a new class of responsive gels with latent crosslinking moieties that
exhibit strain-stiffening behavior. This property results from the lability of
disulfides, initially isolated in a protected state, then activated to
crosslink on-demand. The active thiol groups are induced to form inter-chain
crosslinks when subjected to mechanical compression, resulting in a gel that
strengthens under strain. Molecular shielding design elements regulate the
strain-sensitivity and spontaneous crosslinking tendencies of the polymer
network. These strain-responsive gels represent a rational design of new
advanced materials with on-demand stiffening properties with potential
applications in elastomers, adhesives, foams, films, and fibers.
