A hydrogel disc that can increase 100 times in area when stretched has been developed by a team of researchers led by Lili Chen at Tsinghua University in Beijing. The hydrogel is one of the most elastic materials known, able to stretch to around 15 times its initial length. It could have applications in robotic grippers or tendons.
Hydrogels are made of polymer molecules linked by water molecules and are known for their stretchiness, but they often do not return to their original shape when overstretched. To overcome this issue, Chen and her colleagues inserted pearl-necklace chains into the hydrogel structure, made of coiled polymer beads connected by a chain of carbon atoms. These chains can unfurl under strain and rewind when the strain is released.
To create these chains, the researchers dried out the hydrogel so that the polymer chains were attracted to themselves rather than to water molecules. They found that their hydrogel could stretch to nearly 5 meters before quickly returning to its original length. A 2-centimeter-wide disc of the hydrogel could increase 100 times in area before returning to its original size.
The researchers also created inflatable robotic grippers from the hydrogel, designed to handle delicate objects like strawberries. These grippers were extremely damage resistant, able to withstand being stood on or pierced with a needle. Zehuan Huang at Peking University praised the work, stating that this hydrogel represents a major breakthrough in high-performance polymeric materials and will inspire interest in using hyper-elastic gels in soft robotics.