In polymer physics, the coil–globule transition is the collapse of a macromolecule from an expanded coil state through an ideal coil state to a collapsed globule state, or vice versa.  The coil–globule transition is of importance in biology due to the presence of coil-globule transitions in biological macromolecules such as proteins and DNA.  It is also analogous with the swelling behavior of a crosslinked polymer gel and is thus of interest in biomedical engineering for controlled drug delivery.  A particularly prominent example of a polymer possessing a coil-globule transition of interest in this area is that of Poly(N-isopropylacrylamide) (PNIPAAm).