A bioinspired smart material that swells and contracts could be used to make optical lenses

Scientists in China have designed a biocompatible hydrogel based on the bilayer structure of plant organs. The material, which can swell and contract in response to pH changes, could be used to make optical lenses.

Plant organs like pine cones and wheat awns have inspired scientists to design smart materials that can undergo 3D shape transformations in response to external triggers, such as pH changes. However, these materials are often made from synthetic polymers, which can limit their biocompatibility.

Now, a team led by Lina Zhang at Wuhan University, China, has made a bioinspired smart hydrogel from two layers of natural polymers – chitosan (derived from shrimp shell chitin) and cellulose/carboxymethylcellulose (from plant cell walls). The two layers are held together by covalent bonds and electrostatic interactions between negatively charged carboxylate groups and positively charged ammonia groups, which make the material respond to pH changes.

The hydrogel’s bilayer structure resembles that of plant organs; by changing the material’s shape and size, the team can make different reconfigurable shapes with different movements in response to pH changes. Unlike many other smart materials, both layers are active in this hydrogel when responding to pH, so a strip of the hydrogel can bend both ways.

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