Do you even lift? A new material is the stuff of envy for muscleheads everywhere: it bulks up and self-strengthens without ever needing to hit the gym.
Takahiro Matsuda and his colleagues at Hokkaido University in Japan have developed a “self-growing” hydrogel, which improves its size and strength after repeated mechanical force. They believe it could be used to make flexible exosuits, for people with skeletal injuries, which become stronger the more they are used.
Hydrogels are soft, flexible materials that come in a wide variety of forms: they’re used in disposable nappies and adhesive wound dressings, comprise soft contact lenses, and can even be edible – jelly is one such example. They’re formed of networks of absorbent polymer chains, and are 90 per cent water.
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The team’s self-growing hydrogel was inspired by the process human muscles undergo in response to exercise. Strength training and other activities damage muscle fibres, triggering a regeneration process that involves the growth of new tissue.
The self-growing material is composed of two intertwined networks of polymers – essentially chains of molecules: one strand is rigid, and the other soft and stretchable. When the rigid strands were broken by force – being stretched, for example – it triggered new chains and crosslinks to form, while the softer second network maintained the structure of the gel.
Developing a substance that could grow or reconstruct itself like living tissues has previously proved elusive. The self-growing hydrogel is a step up from self-healing materials, which recover to their previous state after being damaged. It’s “one of the mechanically strongest and toughest hydrogels in the world”, says Matsuda.
Just like human muscles require nutrients for growth, the hydrogel was suspended in a liquid “nutrient” solution of molecules, building blocks which it fed on to strengthen itself. By tweaking the amount and type of monomer available, as well as the applied force, the team could control the specific properties the material went on to acquire.
Beyond use in exosuits, the team also think the hydrogel could be used to create robots that can adapt to their environment, by sensing forces applied to it and increasing in toughness in areas that are stressed.
Science
