Exceptionally tough and stretchy new hydrogels that could be used for contact lenses have been developed by US and South Korean scientists.
The gels are ten times tougher than the cartilage found in the human body and can stretch up to 20 times their original size without being permanently damaged, unlike previous types. Due to their lack of malleability, hydrogels have not been considered as structural materials, but researchers have been attempting to improve their flexibility in recent decades, enabling them to create stronger, tougher, biocompatible materials.
Harvard University's Zhigang Suo his team of scientists have now unveiled a gel with a fracture energy of around 9000Jm-2, meaning it is almost as hard to break as rubber. "The moment we put the material together, its behaviour was just spectacular – even without detailed measurement, just playing with it in your hands," he told Chemistry World. "The material property is orders of magnitude better than other reported values."
Hydrogels are already used in contact lenses, drug delivery and tissue scaffolds, so Mr Suo is sure tougher hydrogels will increase the number of applications they are used for.
The new hydrogel version incorporates two different networks of polymers, but it also makes use of two very different types of cross links. The first polymer, alginate, is cross linked by ionic bonding between calcium ions. It can 'unzip' to relieve stress and reform again afterwards - even if the gel loses some of its stiffness through stretching, the researchers can 're-zip' the alginate network with heat.
Polyacrylamide is the second polymer and is covalently cross linked, remaining intact under stress to bridge cracks. However, it is not clear precisely how the two tangled networks interact.
Vitaliy Khutoryanskiy, a materials scientist at the University of Reading said the new hydrogel is "a very elegant idea".
He explained that the research teams in the US and South Korea used "very simple chemistry" to achieve fantastic results and noted that the approach could be used elsewhere to create other more durable hydrogels.
Researchers at Kansas State University recently developed a new glue mixture that may reduce the risks after patients undergo laser eye surgery.
by Emily Tait