New York: Researchers at Rice University have invented an adaptive material that combines self-healing and reversible self-stiffening properties.

The researchers believe that the material called SAC (self-adaptive composite) may be a useful biocompatible material for tissue engineering or a lightweight, defect-tolerant structural component.

The scientists made SAC by mixing two polymers and a solvent that evaporates when heated, leaving a porous mass of gooey spheres. 

When cracked, the matrix quickly heals, over and over. And like a sponge, it returns to its original form after compression.

Other "self-healing" materials encapsulate liquid in solid shells that leak their healing contents when cracked. 

"Those are very cool, but we wanted to introduce more flexibility," said co-lead researcher Pei Dong, a postdoctoral researcher.

"We wanted a biomimetic material that could change itself, or its inner structure, to adapt to external stimulation and thought introducing more liquid would be a way. But we wanted the liquid to be stable instead of flowing everywhere," Dong noted.

In SAC, tiny spheres of polyvinylidene fluoride (PVDF) encapsulate much of the liquid. 

The viscous polydimethylsiloxane (PDMS) further coats the entire surface. The spheres are extremely resilient, Lou said, as their thin shells deform easily. 

Their liquid contents enhance their viscoelasticity, a measure of their ability to absorb the strain and return to their original state, while the coatings keep the spheres together, the researchers explained.

The findings appeared in the journal ACS Applied Materials and Interfaces.