In the fall of 1999, a young chemical engineer named Todd Zion left his job at Eastman Kodak to enroll in the Ph.D. program at the Massachusetts Institute of Technology. While looking for a subject to research, Zion noticed a grant proposal, never funded, that another graduate student had written on the subject of drug delivery. One possibility mentioned in the proposal was the development of a kind of insulin that would automatically respond to changes in blood-sugar levels, becoming active only when needed to maintain healthy levels around the clock. If it worked, the sugar-sensitive version could transform the lives of the six million people with diabetes in the United States who use insulin. No longer would they have to test their blood-sugar levels multiple times per day and try to calculate how much insulin to take. The self-regulating insulin would curtail high sugar levels, which raise the risk of long-term complications, and eradicate, or at least reduce, the most dangerous short-term complication: hypoglycemia, when sugar levels fall so low that they can cause confusion, unconsciousness, seizures and even death.

“I thought, Wow, that is a really neat area in which to do research,” Zion told me. Other researchers had been trying for 20 years to make insulin work only when needed. The first to publish a study were the scientists Michael Brownlee and Anthony Cerami, who in 1979 embedded a sugar-encrusted form of insulin in a mesh pouch with a sugar-loving protein called lectin. The idea was that when blood-sugar levels were elevated, the lectin would bind to the sugar in the blood and allow the insulin to leak out; when sugar levels were normal, the lectin would bind to the sugar-encrusted insulin, keeping it inside the pouch. But the system was impractical, because the pouch would need to be implanted under the skin and periodically refilled. And the lectin, derived from the jack-bean plant, was toxic.

In his first three years at M.I.T., Zion used nanoscale molecular engineering to create an insulin-lectin gel that could be injected without the need for an implanted pouch, while also rejiggering the lectin to make it less toxic. “It worked great visually,” he said. When the gel was placed in a sugar solution, “you could see the outer edge getting clear and dissolving . . . almost like an ice cube melting in water.”

The problem was that, no matter how hard he tried to manipulate the gel, the insulin either leaked out too easily, even when sugar levels were low, or not easily enough, when sugar levels were high.