Taking a tip from mussels to make materials both strong and flexible

A network of loosely-linked polymers mimicking a mussel's adhesive qualities offers a way to make materials that are both strong and flexible - elements that have been widely sought but hard to produce.

The conventional approach of reinforcing polymers includes the use of fillers, and results in a trade-off between stiffness and stretchiness.

While recent techniques that distribute energy throughout a material (like interlacing networks, or employing reversible cross-links) offer enhanced results when used together, such improvements have been limited to soft and low-elastic dry networks.

Mussels have long been an inspiration for developing adhesives that work when wet, usually by including an organic compound with a chemical signature called a catechol group.

Here, Emmanouela Filippidi and colleagues produced a highly-extendable polymer-based material akin to a mussel's adhesive features (specifically, the byssal plaque and thread) by modifying several catechol groups, which they accomplished via the addition of iron molecules.

The iron molecules created a reversible and load-bearing network that was 770 times stiffer and 92 times tougher than its untreated precursor.

This result enabled the scientists to create a material that was strong, yet elastic. They say that their approach may be combined with existing polymer-hardening mechanisms, thus paving the way to other modifications and broad applications in structural, biomedical and aerospace materials.