The gel could be used in radiation therapy for head and neck cancers, by working to soothe the painful mouth ulcers called mucositis that often develop from exposure to the high-energy radiation.

“Mucositis is the biggest complaint from patients, and it often leads to a lowered dose of the therapy,” says Karp.

If the side effects were alleviated, more patients might safely complete their scheduled course of therapy at the higher dose, and we would expect increased survival rates.

Not only is the drug delivery targeted, but the gel also attaches more easily to the site of inflammation than to the healthy tissues around it.

“Ulcers have more of a positive charge than the other tissues, so the materials we use are more negatively charged,” says Karp.

Targeted release reduces, to one-fifth or less, the extent to which the drug can be absorbed into whole-body systems, keeping the action at the local site where it is needed. Systemic absorption is often the origin of side effects. Doses can be spaced at longer intervals, and the drug is generally more effective and less toxic. For a patient with inflammatory bowel disease, this could mean replacing a daily enema to a once-per-week regimen that targets the positively-charged surface of an inflamed colon.

Inflammation-activated gels can be used to carry and release drugs other than anti-inflammatories. The latest application for Karp’s innovation is in limb transplantation. A hind limb from a black rat transplanted to a white rat is usually rejected around 11 days later. With regular immune suppressant therapy that time is extended to 33 days. But with an injection of hydrogel loaded with the same immune suppressant drug, the leg is maintained up to 150 days later. Working with the US Army, a group in Pittsburg is taking this research further, into the pig model. Pigs are often used to test such medical procedures, because their response closely mimics the human response.

Inflammation, though widespread in human ailments, is just one possible catalyst of drug release. In a future where a medical problem can activate its own solution, our diseases may all but order their drugs for delivery.

We want to hear what you think about this article. Submit a letter to the editor or write to letters@theatlantic.com.