Soft core particles get hot under the collar

Danish and German researchers have developed a new type of particle with a hard shell and a soft core that changes depending on its temperature. Walter Richtering and Ingo Berndt of the University of Aachen, Germany, and Jan Skov Pedersen of the University of Århus, Denmark, have synthesized polymeric microspheres with a core made of poly-N-isopropylacrylamide and a shell of poly-N-isopropylmethacrylamide. The microspheres are densely packed at 70 Celsius, the temperature at which they are prepared, when they are cooled to room temperature (approx 25 Celsius, however, the core and shell have the highest water content and the lowest density and dissolved molecules can pass through the shell into the core, where they disperse. At body temperature (approx 39 Celsius), only the swelling properties of the shell are changed, which expels water, shrinks and becomes denser than the core. Substances dissolved in the core can no longer pass through the shell and are thus locked inside.