A drug capsule floats in the bloodstream like a tiny container. Its walls are made of a polymer that can shrink and swell with temperature. To know when the capsule will release its cargo, you need to know how strongly drug molecules cling to those walls.
Scientists figured this out on a computer, simulating the behavior of three molecules: phenol, methane, and the anticancer drug 5-fluorouracil. They placed each molecule either in pure water or in a water–pNIPAM mixture and watched where the molecule felt more at home. It turned out that phenol and the drug always prefer to stick to the polymer — at both low and high temperatures. Methane, however, behaves differently: at low temperatures it stays in water, but when heated above the critical temperature (about 32 °C for pNIPAM), it moves over to the polymer.
The researchers also found that the transfer of molecules into the polymer depends on its concentration in a simple linear way, as if the price grows in direct proportion to the amount of goods. This simplifies calculations for real microgels. Using the data, they predicted that a microgel with a radius of 50 micrometers (thinner than a human hair) would release the drug for about 2200 seconds, just over half an hour. Such calculations help design smart patches or implants that dispense medication on a schedule.
The polymer pNIPAM shrinks sharply when heated above 32 °C, expelling water — a property used in smart lenses and drug delivery systems.
In the movie Fantastic Voyage, a miniature submarine delivers a drug precisely to a diseased organ — modern microgels do something similar, minus the crew.