MIT Hydrogel is 90% Water

Transparent and viscous, a new synthetic hydrogel from Massachusetts Institute of Technology (MIT) engineers is taking cues from nature.

The new hydrogel’s toughness is comparable to the bond between tendon and cartilage on bone. It can adhere to glass, silicon, ceramics, aluminum and titanium. Additionally, more than 90% of it is composed of water.

“Basically, it’s tough bonding water,” said Hyunwoo Yuk, an MIT graduate student in mechanical engineering.

Natural hydrogels are what allow mussels and barnacles to bond to rocks, ships and whales.

“If you think about it, the human body is a hydrogel soft robot,” said Xuanhe Zhao, an associate professors with MIT’s Dept. of Mechanical Engineering, to Motherboard. “Tissue in the human body contains around 70% water; it’s basically many pieces of hydrogel together with bones, with skeletons, to form a soft robot.”

Attached to two plates of glass, MIT’s hydrogel was capable of supporting a suspended 55-lb weight. Experimenters applied the hydrogel glue to a silicon wafer, which was subsequently smashed with a hammer. Though shattered, the silicon wafer’s pieces were kept intact due to the hydrogel. Used to connect four ceramic bars, the tough hydrogel joints allowed the square to be deformed into various shapes.

In order to create a hydrogel capable of strong bonding, the researchers needed the material to exhibit two characteristics: energy dissipation and chemical anchorage. “A hydrogel that dissipates energy is essentially able to stretch significantly without retaining all the energy used to stretch it,” according to MIT. “A chemically anchored hydrogel adheres to a surface by covalently bonding its polymer network to that surface.”

The latter was achieved through a process called silanation, where the solid substrate is covered with a compound that creates a stronger bond with the hydrogel.

During a peeling test, the bond between the hydrogel and a solid substrate was so strong fibrils clung to the solid material. The researchers found the bond’s strength was 1,000 J per square meter, on par with the bond between tendon and cartilage on bone.

According to MIT, the material can be applied to underwater surfaces, potentially useful as a protective coating for boats and submarines. Additionally, it is biocompatible and may have applications in the medical field.

However, the hydrogels application to robotics and bioelectronics is most intriguing. The material’s flexibility allows for locomotion that mimics natural joints. “It can give a robot many degrees of freedom,” said Zhao.

It’s also conductive. Yuk and colleagues added salts to the hydrogel sample and stuck it between two metal plates connected by electrodes to an LED light. Switched on, the hydrogel enabled ion flow allowing the LED to light.

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