Protein hydrogels combined with plastics can be injected into the human body as a vehicle to deliver drugs or cells that regenerate damaged tissue. They hold promise for treating many types of disease, including cancer. However, these injectable gels don't always maintain their solid structure once inside the body. In a breakthrough described in the journal Advanced Functional Materials, a degradable polymer-tipped network allows the gels to maintain a structure inside the body. The discovery was made by a research team at the Massachusetts Institute of Technology (Cambridge, MA) funded by the U.S. Army Research Office through the Institute for Soldier Nanotechnologies (ISN). Potential applications of these nanostructured gels include preventing blood loss, accelerating wound healing and protecting against infections and disease.

The research team was led by Bradley Olsen, an assistant professor of chemical engineering. Olsen and students worked with gels known as shear-thinning hydrogels that can switch between solid-like and liquid-like states. When exposed to mechanical stress - such as being pushed through an injection needle - these gels flow like fluid. Inside the body, the gels return to their normal solid-like state. However, shear thinning is inherently not durable because it is difficult to undergo a transition from not durable to very durable state required for a long, useful implant life. The team found a solution by creating a reinforcing network within their gels that is activated only when the gel is heated to body temperature (37 degrees Celsius). The MIT hydrogel has been designed to include a second reinforcing network, which takes shape when polymers attached to the ends of each protein bind together. They float freely in the gel at lower temperatures because they are soluble in water. When heated to body temperature, they become insoluble and separate, allowing them to join together and form a grid. The researchers found that gels with this reinforcing network were much slower to degrade when exposed to mechanical stress and were significantly stiffer. Another advantage of these gels is that they can be tuned to degrade over time, which would be useful for long-term drug release. The researchers are now working on ways to control this feature, as well as incorporating different types of biological functions into the gels.