The team from the Swanson School of Engineering took their inspiration from the natural world where amphibians are able to regenerate severed limbs. A paper detailing the research has been published in Nano Letters.
‘This is one of the holy grails of materials science,’ said principal investigator Anna C. Balazs, PhD. ‘While others have developed materials that can mend small defects, there is no published research regarding systems that can regenerate bulk sections of a severed material. This has a tremendous impact on sustainability because you could potentially extend the lifetime of a material by giving it the ability to regrow when damaged.’
Tissue regeneration in amphibians is guided by three sets of instructions – initiation, propagation, and termination – which Dr. Balazs described in a statement as a ‘beautiful dynamic cascade’ of biological events.
‘When we looked at the biological processes behind tissue regeneration in amphibians, we considered how we would replicate that dynamic cascade within a synthetic material,’ Dr. Balazs said. ‘We needed to develop a system that first would sense the removal of material and initiate regrowth, then propagate that growth until the material reached the desired size and then, self-terminate the process.’
‘Our biggest challenge was to address the transport issue within a synthetic material,’ Dr Balazs said. ‘Biological organisms have circulatory systems to achieve mass transport of materials like blood cells, nutrients and genetic material. Synthetic materials don’t inherently possess such a system, so we needed something that acted like a sensor to initiate and control the process.’
The team developed a hybrid material of nanorods embedded in a polymer gel, which is surrounded by a solution containing monomers and cross-linkers (molecules that link one polymer chain to another) in order to replicate the dynamic cascade.
When part of the gel is severed, the nanorods near the cut act as sensors and migrate to the new interface. The functionalised chains or ‘skirts’ on one end of these nanorods keeps them localised at the interface and the sites (or ‘initiators’) along the rod’s surface trigger a polymerization reaction with the monomer and cross-linkers in the outer solution.
Drs Xin Yong and Olga Kuksenok developed the computational models, and thereby established guidelines to control the process so that the new gel behaves and appears like the gel it replaced, and to terminate the reaction so that the material would not grow out of control.
‘The most beautiful yet challenging part was designing the nanorods to serve multiple roles,’ said Dr Yong. ‘In effect, they provide the perfect vehicle to trigger a synthetic dynamic cascade.’ The nanorods are approximately ten nanometres in thickness, about 10,000 times smaller than the diameter of a human hair.