'Chameleon' Nanomaterial Can Transform from Spring to Shock Absorber, Back Again

Researchers with the UBC Department of Chemistry have designed a 'chameleon' elastomeric protein which can be transformed from a coiled elastic spring to a stable shock absorber, and back again.

The new type of smart nanomaterial effectively combines the two extreme forms of elastic mechanical behaviour found in nature into a single protein, and has potential applications in nanomechanics and biomedical materials.

"The striking part of this finding is the sheer degree of the change in mechanical properties displayed by the protein when a molecular regulator is added" says Assistant Professor Hongbin Li, author of the study, published this week in Nature Nanotechnology. "It's also noteworthy that this change from a labile entropic spring to a mechanically stable shock absorber is fully controllable, reversible and repeatable."

Using single molecule atomic force microscopy--a powerful technique that allows researchers to manipulate proteins one molecule at a time--Li and Chemistry graduate student Yi Cao designed the new 'mutant' protein to have an elastic coil-like structure by default. However, when a molecular regulator is introduced, the protein undergoes conformational change, leading to significant mechanical stability.

"So it’s possible to engineer smart hydrogels made of this type of elastomeric protein that can change their mechanical and physical properties in response to environmental stimuli," says Li, who also holds the Canadian Research Chair in Molecular Nanoscience and Protein Engineering. Smart hydrogels can swell or shrink dramatically when they encounter small changes in temperature, pH, ionic strength, salt type, solvent, and other conditions.

Depending on their role, some naturally occurring proteins display high degrees of elasticity—for example those present in spider web silk. Elastic proteins are important structural and functional components in living cells. They serve as molecular springs in tissues to establish elastic connections and provide mechanical strength, elasticity and extensibility.