Healing hydrogel materials recover from stress

Researchers at University of Tokyo have developed biocompatible hydrogel materials can rapidly recover from mechanical stress.

Photo
A strain gauge pulls apart samples of hydrogel. (Upper) A typical gel with a notch cut into the left-hand side snapped soon after it was stretched. (Middle) The new self-reinforced gel had a notch cut into the left-hand side, and despite this it maintained integrity when stretched further than a typical hydrogel. (Lower) A diagram of the polyethylene glycol (PEG) chains and hydroxypropyl-α-cyclodextrin (HPαCD) rings stretching and relaxing.
Source: ©2021 Mayumi et al.

Hydrogels are polymer materials made mostly from water. They can be used in a wide range of medical and other applications. However, previous incarnations of the materials suffered from repeated mechanical stress and would easily become deformed. A novel crystal that can reversibly form and deform, allows hydrogels to rapidly recover from mechanical stress. This opens up the use of such biocompatible materials in the field of artificial joints and ligaments.

Many of us suffer the occasional sports injury or experience some kind of pain relating to joints and ligaments at some point in our lives. For serious injuries of this nature, there is often little that can be done to repair the damage. But a new development in the field of water-rich polymer materials known as hydrogels could find its way to the operating room in around 10 years or so. And they should stand up to the same mechanical stresses our natural joint and ligament tissues experience too. They're called self-reinforced gels.

"The problem with existing hydrogels is that they can be mechanically weak and so need strengthening," said Associate Professor Koichi Mayumi from the Institute for Solid State Physics at the University of Tokyo. "However, previous methods to toughen them up only work a limited number of times, or sometimes just once. Those gels do not recover rapidly from stresses such as impacts well at all. So we looked at other materials which do show strong recoverability, such as natural rubber. Taking inspiration from these, we created a hydrogel that exhibits rubberlike toughness and recoverability whilst maintaining flexibility."

Previous examples of toughened hydrogels use so-called sacrificial bonds which break when deformed. The destruction of the sacrificial bonds would dissipate mechanical energy giving the material strength, but the sacrificial bonds would take time, sometimes minutes, to recover. And sometimes they would not recover at all.

In contrast, Mayumi and his team introduced crystals which assemble into rigid shapes under strain, but very quickly revert back to a gel state when the strain is released. In other words, the overall hydrogel is extremely flexible at rest but firms up on impact, much like natural rubbers do. The crystalline structures are composed of polyethylene glycol (PEG) chains bound by hydroxypropyl-α-cyclodextrin (HPαCD) rings in a water-based hydrogel.

"As hydrogels are over 50% water, they are considered highly biocompatible, essential for medical applications," said Mayumi. "The next stage of research for us is to try different arrangements of molecules. If we can simplify the structures we use, then we can reduce the cost of materials which will also help accelerate adoption of them by the medical industry."

Subscribe to our newsletter

Related articles

Blood vessels grow synthetic tissue model

Blood vessels grow synthetic tissue model

Researchers have developed a cell culture system in which a functional blood vessel system is able to grow within a framework made of synthetic material.

Skeletal scaffold supports bone cells

Skeletal scaffold supports bone cells

3D models of bone formation provide a tool for tissue engineering, biomedical research and drug testing.

3D Printing living cells with unprecedented precision

3D Printing living cells with unprecedented precision

The combination of a 2Photon 3D-printer with an innovative hydrogel-based bioink allows the direct printing of 3D structures containing living cells at both the meso- and microscale.

A conductive hydrogel for medical applications

A conductive hydrogel for medical applications

Researchers have developed a method to produce graphene-enhanced hydrogels with an excellent level of electrical conductivity.

Hydrogel injection may repair heart muscle damagage

Hydrogel injection may repair heart muscle damagage

Researchers have developed an injectable hydrogel that could help repair and prevent further damage to the heart muscle after a heart attack.

Shape-changing 4D materials hold promise for bioengineering

Shape-changing 4D materials hold promise for bioengineering

New hydrogel-based materials that can change shape in response to psychological stimuli, such as water, could be the next generation of materials used to bioengineer tissues and organs.

Lasers and molecular tethers enable tissue engineering

Lasers and molecular tethers enable tissue engineering

Researchers have used lasers and molecular tethers to create perfectly patterned platforms for tissue engineering.

Bioprinting complex living tissue in seconds

Bioprinting complex living tissue in seconds

Researchers have developed an extremely fast optical method for sculpting complex shapes in stem-cell-laden hydrogels and then vascularizing the resulting tissue.

3D printing of biological tissue

3D printing of biological tissue

Scientists hope we will soon be using 3D-printed biologically functional tissue to replace irreparably damaged tissue in the body.

Popular articles

Subscribe to Newsletter