Degradation and degradation-induced re-assembly of PVP-PCL micelles

The nonenzymatic and enzymatic degradation behaviors of the poly(vinyl pyrrolidone)-poly(epsilon-caprolactone) (PVP-PCL) diblock copolymers micelles in aqueous solution were investigated by dynamic light scattering (DLS), size exclusion chromatography (SEC), and high performance liquid chromatography (HPLC), and the morphology variation of these micelles in the degradation procedure were inspected by transmission electronic microscopy (TEM). It is found that the enzymatic degradation of PVP-PCL micelles is much faster and the degradation rate of PVP-PCL micelles is proportional to the enzyme concentration for a given micelles' concentration. However, in the nonenzymatic case, the degradation of PVP-PCL micelles is quite slow under neutral condition and fast in acidic or basic medium. Interestingly, morphology transformation from spheres to a necklace and rod-like nanostructure was observed during the degradation procedure under basic condition. This shape reconstruction of PVP-PCL nanoparticles in the degradation process opens a new window to fabricate hierarchical supramolecular structures.