Hydrogels might not be known to everyone, but they’re an important and interesting innovation in bioengineering circles. The technology already has multiple applications in the medical field thanks to its strength, but it now turns out that, when given a workout, it becomes even stronger.
In a new study from the Massachusetts Institute of Technology, hydrogels were treated to a training workout to simulate the same conditions and effects of human muscle training. Made of an alcohol polyvinyl, these kinds of hydrogels are commonly used in medical implants and to transport drugs through the human body. Stretched and treated to a mechanical workout in a water bath, the became unyielding and resistant to molecular ruptures. They were able to stay structurally sound despite continuous repetitive movements.
The aim of the study was to identify a material that would be as strong as muscular tissue. One that could also account for the amount of water found within the human body. “Most of the tissues in the human body contain about 70 percent 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 MIT associate professor of mechanical engineering Xuanhe Zhao. He notes that in the future, the material could be used for a variety of medical implants. This includes “heart valves, cartilage replacements, and spinal disks, as well as in engineering applications such as soft robots.”
Hydrogels can be 3D-printed into a range of different shapes. The study initially started out as an experiment to see the fatigue point of the material, by subjecting it to rigorous handling. However after 1,000 rounds of stretching, the trained hydrogels were found to be 4,3 times stronger than the originally were. This despite some of the material having then been subjected to 30,000 stretching rounds, It remained intact, while maintaining a high water content.
“The phenomenon of strengthening in hydrogels after cyclic loading is counterintuitive to the current understanding on fatigue fracture in hydrogels, but shares the similarity with the mechanism of muscle strengthening after training,” explained Shaoting Lin, a graduate student and lead author of the study. “In an amorphous hydrogel, where the polymer chains are randomly aligned, it doesn’t take too much energy for damage to spread through the gel. But in the aligned fibers of the hydrogel, a crack perpendicular to the fibers is ‘pinned’ in place and prevented from lengthening because it takes much more energy to fracture through the aligned fibers one by one.”