Researchers seeking to develop self-healing hydrogels have tried to imitate the natural capability of mussels to produce sturdy, flexible threads underwater that allow the mussels to stay to rocks.
The natural process that provides these mussel threads, which are called byssal, the flexibility to break apart and re-form is purely chemical, not a biological one, MIT graduate pupil Seth Cazzell explained to the Materials Research Society fall assembly in Boston on December 5.
The critical step in the process is the chemical binding of polymer chains to a metal atom. These links are known as cross-linked metal coordination bonds. Their greatest strength happens when each metal atom binds to 3 polymer chains, and they create a network that ends in a strong hydrogel.
In a lately published PNAS paper, Cazzell and affiliate professor of materials science and engineering Niels Holten-Andersen demonstrated a way to create a self-healing hydrogel in a wider range of metallic concentrations using competition managed by the pH, or acidity and alkalinity, of the atmosphere. Cazzell is a former National Defense Science and Engineering Graduate Fellow.
In their model computational system, Cazzell confirmed that in the absence of pH-managed competition, extra metal—usually iron, aluminum, or nickel—overwhelms the flexibility of the polymer to form sturdy cross-links.
In the presence of an excessive amount of metal, the polymers will attach singly to metal atoms instead of creating cross-linked complexes, and the fabric remains a liquid.