Temperature- and light-responsive blends of pluronic F127 and poly(N,N-dimethylacrylamide-co-methacryloyloxyazobenzene)

Photoresponsive poly(N,N-dimethylacrylamide-co-methacryloyloxyazobenzene) (DMA-MOAB) and temperature-responsive Pluronic F127 (F127) copolymers were blended to obtain systems responsive to both stimuli that are potentially useful for pharmaceutical formulations. The random DMA-MOAB copolymer undergoes a trans to cis isomerization when irradiated by 366 nm light, which modifies both the air-water interfacial behavior and the self-associative properties of the copolymer. Under dark conditions the azobenzene groups of DMA-MOAB in the trans conformation self-associate and the interactions with F127 are minimal. The cis conformation of the azobenzene groups of the DMA-MOAB copolymer is relatively more hydrophilic than the trans conformation, which causes the copolymer micelles to dissociate upon irradiation, allowing the unimers to form mixed micelles with the F127. This causes the sol-gel transition temperature of the DMA-MOAB:F127 blend to be 10 degrees C lower upon irradiation at 366 nm compared to that for the dark conditions. It has been found that F127 (10-12 wt %):DMA-MOAB (5-6 wt %) aqueous solutions have at body temperature a low viscosity when equilibrated in the dark and undergo a sol-gel transition when irradiated. Such a transition strongly alters the diffusion of solutes such as methylene blue within the solutions. This light-induced interaction between the azobenzene moieties of DMA-MOAB and F127 micelles disappears when hydroxypropyl-beta-cyclodextrin (HPbetaCD) is added to the medium. In the presence of HPbetaCD, the cis-azobenzene groups are hosted in the cyclodextrin cavities and the mixed micelles are not formed. Therefore, changes in HPbetaCD concentration could be used to modulate the response of the copolymer blends to light.