Chemical engineers at Massachusetts Institute of Technology developed a way to add structure to hydrogels injected in the body as treatments, to prevent them from liquifying. The team led by MIT engineering professor Bradley Olsen (pictured left) published its findings recently in an online issue of the journal Advanced Functional Materials; paid subscription required.
Olsen, with graduate students Matthew Glassman and Jacqueline Chan (now at Califonia Institute of Technology), addressed the problem of injectable hydrogels that can carry drugs or cells that regenerate damaged tissue that lose their semi-solid structure once inside the body. These gels, known as shear thinning gels, can convert to a liquid state when pushed through an injection needle, then revert back to a more solidified form when inside the body.
That same quality that allows the hydrogel to liquify during injection, however, can also liquify the material when submitted to mechanical stresses inside the body, thus losing the durability needed to transport cells or drugs. “How do you undergo a transition from not durable, which is required to be injected,” asks Olsen, “to very durable, which is required for a long, useful implant life?”
To address this problem, the MIT researchers created a reinforcing network property in hydrogels that is activated when the gel is heated to body temperature (98.6 F or 37 degrees C). Achieving this property is possible now with polyethylene glycol and similar polymers, but not with protein hydrogels like those used for tissue engineering functions, such as cellular adhesion and cell migration.
For this study, Olsen and colleagues adapted hydrogels with helical proteins already coiled into a ropelike structure, to which the researchers added a second network for reinforcing the original structure. The second network develops in the hydrogel when polymers attached to the ends of each protein bind together. In lower temperatures, the polymers remain water-soluble, but when heated to body temperature, they become insoluble and join together and form a sturdy grid within the gel.
The findings from lab tests show that gels with this reinforcing network are slower to degrade when exposed to mechanical stress and thus stiffer and more durable. In addition, the researchers say the gels can be tuned so they degrade over time, making the gels useful for time-released therapies. Reinforced gels could also be added to battlefield or first-responder emergency treatments to prevent blood loss, accelerate wound healing, and protect against infections.
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