Photo-Cross-Linking Induces Size Change and Stealth Properties of Water-Dispersible Cinnamic Acid Derivative Nanoparticles

Hydrophilic poly(ethylene glycol) (PEG) was grafted onto poly(4-cinnamic acid)-co-poly(3,4-cinnamic acid) (PCA) by Michael addition. The chemical structures of the PCA-graft-PEG (PCA-PEG) copolymers were confirmed by FT-IR and (1)H NMR measurements. The PCA-PEG nanoparticles were self-assembled by the solvent mixing method, in which additional water was dropped into a DMSO solution of the copolymer. The diameter of the PCA-PEG nanoparticles was below 100 nm, and decreased to about 30 nm upon increasing the composition ratio and molecular weight of PEG. The PCA-PEG nanoparticles showed [2 + 2] cyclobutane formation (cross-linking) following UV irradiation at λ > 280 nm. Moreover, the photo-cross-linking induced size decrement of the nanoparticles depending on the grafting degree and molecular weight of PEG. The amount of protein adsorption onto the surface of the nanoparticles was less than 30 ng/cm(2), due to the high density of PEG chains on their corona layers. Furthermore, photo-cross-linking induced a significant decrement in protein adsorption, due to an increase in PEG chain density triggered by the size decrement of the nanoparticles. These water-dispersible and photoresponsive nanoparticles would be useful as novel, functional carriers for drug delivery systems and biological diagnosis.