Human skeletal muscle has a unique combination of properties that can be useful for a number of different materials. They're strong, soft, full of water, and resistant to fatigue. MIT researchers have found a way to give synthetic hydrogels this suite of characteristics after putting them through a vigorous workout.

The scientists mechanically trained the hydrogels by stretching them in a water bath. This aligned nanofibers inside the hydrogels to produce a strong, soft, hydrated material that resists breakdown or fatigue over thousands of repetitive movements.

The polyvinyl alcohol (PVA) hydrogels used in the experiment are well-known biomaterials for medical implants, drug coatings as well as a number of other applications. Findings were published in the Proceedings of the National Academy of Sciences.

Zhao and his colleagues describe how the hydrogels also can be 3-D-printed into a variety of shapes that can be trained to develop the suite of muscle-like properties.

“Most of the tissues in the human body contain about 70% water, so if we want to implant a biomaterial in the body, a higher water content is more desirable for many applications in the body,”  said Xuanhe Zhao, an associate professor of mechanical engineering at MIT.

In the future, the materials could be used in implants such as heart valves, cartilage replacements and spinal disks, as well as in engineering applications such as soft robots.