To make an artificial muscle, you need a material with both strength and flexibility. A new gel-infused wood does the trick, and could someday be used for implanted muscles or external prosthetics.
Liangbing Hu at the University of Maryland and his colleagues created this new hydrogel material, starting with a block of wood. The structure of wood, with its strong, aligned fibres, is similar to the underlying structure of muscles.
Hu and his colleagues submerged the wood in bleach to remove its lignin, the compound that makes it rigid, leaving behind only the cellulose fibres that make up the wood grain. Then, they filled in the gaps left by the lignin with hydrogel, the same water-soaked polymer that is used to make soft contact lenses. This made the material flexible and stretchy.
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The mixture was cured at 60掳C to bond the hydrogel with the cellulose skeleton of the wood, resulting in a cloudy, white gel with the strength of wood but the flexibility of gel. In the direction parallel to the wood grain, it is weaker than solid wood but about 80 times stronger than skeletal muscle. As with muscle tissue, the alignment of the fibres makes it harder to tear if you pull along the grain.
To test whether the gel was biocompatible and thus able to be implanted into the human body, they cultured embryonic kidney cells on a sample of this new material and found that the cells adhered and grew over the course of two days. They also found that liquids carrying ions like sodium and potassium could flow through the wood gel just like they flow through muscle tissue in the human body.
鈥淭his material is biocompatible and biodegradable,鈥� says Hu. 鈥淚t can be potentially used for artificial muscle, cell culture and prosthetics.鈥�
Advanced Materials
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