Transformable core–corona nanoparticles: Simultaneous change of core morphology and corona wettability in response to temperature

We prepared transformable thermoresponsive nanoparticles with variable core softness, controlled by the nanoparticle coreʹs glass transition temperature (Tg). The nanoparticles were prepared by the dispersion copolymerization of butyl methacrylate (BMA) and/or methyl methacrylate (MMA) with a poly(N-isopropylacrylamide) (PNIPAAm) macromonomer in a polar solvent. The shape of the nanoparticle core changed with temperature. We then prepared poly(vinyl alcohol) (PVA) films with dispersed thermoresponsive nanoparticles, to elongate the nanoparticles through a uniaxial stretching of the films at 60 °C. In this manner, the nanoparticle shape changed from spherical to rod-like morphologies, depending on the degree of film extension. Additionally, the rod-shaped nanoparticles only changed back to spheres with temperature modulation. The nanoparticle coreʹs Tg value affected the rate of its physical transformation from rods to spheres at 37 °C, with a slower rate observed for increased Tg. As the nanorod shape change was relatively minor at 37 °C, we could control the shape of these transformable nanoparticles under various physiological conditions, a highly desirable feature for drug delivery applications.