Polymers Make Strong, Stretchy Jelly

There must be a great business opportunity in building cartilage from polymers or proteins because there are many different versions of the same type of research idea.

For example, University of Pennsylvania scientists have developed a technology that uses polymers to construct a nanofibrous scaffold on which cells can colonize to repair torn tendons and ligaments. Also, researchers from Worcester Polytechnic Institute are using microthreads, built out of proteins, to help regenerate human tissue and heal wounds.

Now, Harvard University scientists have developed a hydrogel — a network of polymers that soaks up water to form a jelly-like material — that is super-strong, reports Nature. To date, the strongest hydrogels are used to make contact lenses. Researchers want to make stronger hydrogels that can be used to replace worn-out or missing cartilage, or as building blocks for growing artificial organs.

The hydrogel developed by Zhigang Suo, a materials engineer at Harvard, is made from two polymers: alginate and polyacrylamide. Alginate molecules are linked together with ionic bonds; polyacrylamide molecules are linked together by stronger covalent bonds.

When the gel is stretched or hit, the ionic bonds can break. If they do, they reform throughout the material, spreading energy over a wide area and causing fewer of the covalent bonds to be broken beyond repair. Meanwhile, the covalent bonds hold the hydrogel together so that it can return to its original shape.

Mixed together, the two polymers form a material that is stronger than its constituent parts. In fact, the energy needed to fracture the hydrogel is on par with that of natural rubber, or 9,000 joules per square meter. It can be stretched to 20 times its original length without breaking.

“You can’t even tear it apart with your hands,” Suo says.

Source: “Super-stretchy jelly can take a hit,” Nature, 9/5/12
Source: “Ball bouncing off stretching jelly,” YouTube
Image by Bpw.