When a hydrogel disk is stretched, its area increases 100 times.
Lily Chen et al.
Hydrogels, which can stretch up to about 15 times their initial length, are among the most elastic materials known to date and could be used in robotic grippers and tendons.
Hydrogels are made of long chain polymers connected by water molecules and are well known for their stretchability, but if they are stretched too much, they often fail to return to their original shape.
lily chen Researchers at Beijing’s Tsinghua University have developed a new type of hydrogel that is highly stretchable yet retains its original shape. They modified the typical hydrogel structure by inserting what they called a pearl necklace chain, which consists of coiled polymer beads connected by chains of carbon atoms. These can expand when tension is applied and unwind when tension is released.
To create these chains, Chen and her team dried the hydrogel so that the polymer chains were pulled closer to themselves, when normally they would be pulled harder by water molecules.
They found that a 30-centimeter-long hydrogel could stretch nearly five meters and return to its original length in seconds. If you pull a 2-centimeter-wide disk of hydrogel outward in any direction, its area can increase by a factor of 100 before it returns to its original size.
The researchers also built an inflatable robotic gripper from hydrogel designed to gently handle fragile objects. These were able to grip objects such as strawberries, and were extremely damage resistant and continued to function even when a person stepped on them or punctured them with a needle.
“Usually hydrogels are stretchable but not very elastic. This gel, on the other hand, combines both properties to create a material that is both superdeformable and superelastic.” Huang Zehuan from Peking University in China was not involved in this study. “Undoubtedly, this work is a major advance in high-performance polymer materials and will spark significant interest in exploiting superelastic gels in soft robotics.”
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