Functionally active thin film coatings find many important uses in the biomedical field as sensors and drug delivery systems. Members of IRG-II have created a new multilayer coating that can serve both functions. By creating a patterned multilayer stack comprised of alternating regions of low refractive index (nanoporous regions) and high refractive index (dense regions), the coating exhibits bright iridescent colors similar to those observed in, for example, hummingbird wings (see Figure below). In contrast to the multilayer structures evolved in nature, however, these new multilayer heterostructures have individually addressable nanoporous regions that can be selectively loaded with different drugs and therapeutic proteins. When the nanoporous regions are loaded, the refractive index changes and the color of the coating changes dramatically. Thus, independent loading of specific nanoporous regions of the multilayer makes it possible to design thin film coatings and patches with built-in self-monitoring capability for drug loading and release. With suitable design of release kinetics, the reflective color and intensity of the multilayer coating will change in a predictable manner as the contents of the different nanoporous regions are systematically released.
Figure: Patterned multilayer coatings with multiple reflective colors due to different underlying layers of high and low refractive index. Cartoon shows a side view of an area where two individually addressable nanoporous layers (green regions) overlap, producing the bright yellow color of (b). Dramatic color changes occur when the various nanoporous regions release previously loaded drugs.
