A supramolecular hydrogel with magnificent tensile strength
Researchers from China have accidently discovered a super strong, super stretchy hydrogel, which has the potential to be used in tissue engineering.
Originally developed in the 1950s when Otto Wichterle and Drahoslav Lim invented soft contact lenses, supramolecular hydrogels are gel-like polymers that can absorb water. Akin to natural soft tissue, their networks are held together by reversible non-covalent interactions making them attractive materials for biomedical applications.
Hydrogels have good elasticity, but their mechanical weakness lets them down. Now, a new, stronger hydrogel with ‘amazing molecular properties’ has been created by Mingyu Guo and He Huang at Soochow University. The group were making water-dispersible polyurethane adhesives and noticed that strong stretchable gels formed when the samples were left in the air for a couple of days.
The method is simple: ‘just add water’ says Guo. Water acts as an in situ chain extender to form multi-urea linkages within the hydrogel. ‘The short urea linkage formation is very important as this is what improves the elasticity and physical properties such as biocompatibility, mechanical strength and water content,’ he says. The hydrogel film can be stretched to several times its original size without fracture and a small strip can withstand 6.2kg of loading and still return to its original shape immediately after unloading. A hydrogel rod only 21.5mm thick can bear even more than 1.6tons loading without breaking.
Rodrigo Albuquerque, a supramolecular chemist from the University of São Paulo in Brazil, thinks the work opens up exciting possibilities for the rational design of a new class of hydrogel. ‘The study shows that varying the ratio between hard and soft segments of a hydrogel allows for quantitatively tuning its properties. Their hydrogel has exhibited exceptional mechanical properties, some of them being much better than those of the best hydrogels reported so far.’
‘This research will accelerate the development of new kinds of function hydrogels,’ says Tao Tu, an organic chemist from Fudan University in China. Tu was impressed by the method as well as the tunable mechanical characteristics of the hydrogel. ‘The striking issue is also the in situ chain extension strategy based on the reactions between water and –NCO groups in the polyurethane chains to form urea linkages,’ he says.
Guo believes that the water content and the strength of this hydrogel are sufficient to be used for artificial muscle and cartilage in the future.
Correction: This article was updated on 22 May to give the correct country where the work was performed.