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Polymers establish structure in drug delivery breakthrough

Protein hydrogels combined with plastics can be injected into the human body as a vehicle to deliver drugs or cells that regenerate damaged tissue. 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.

They are still vulnerable to mechanical stresses while in the human body, which can make them fall apart.

"Shear thinning is inherently not durable," says Olsen. "How do you undergo a transition from not durable, which is required to be injected, to very durable, which is required for a long, useful implant life?"

The solution is a reinforcing network within gels that is activated only when the gel is heated to body temperature.

The MIT researchers designed their hydrogel 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 gels can be tuned to degrade over time, making them useful for long-term drug release.

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