Development of light-responsive porous polycarbonate membranes for controlled caffeine delivery

For controlled caffeine release, light-responsive membranes were developed. It was possible to produce membranes that reduced their caffeine permeability resistance by about 97% when irradiated with UV-light compared to measurements at daylight. This was achieved by grafting polymers possessing photochromic units onto track-edged polycarbonate membranes. Covalently linked coatings on porous polycarbonate membranes were obtained by plasma activation of the membrane surface followed by plasma-induced graft polymerization. Copolymerization of spiro-compounds during the coating process as well as postmodification of preformed coatings with spiropyran resulted in photochromic membranes. For the copolymerization process, the synthesis of five photochromic methacrylic and acrylic spiropyrans and spirooxazines was successfully performed. Additionally, a spiropyran with carboxylic acid functionality was synthesized for the postmodification process. This enabled us to postmodify polymeric materials containing alcohol or amine groups to obtain photochromic materials. UV-irradiation of these light-responsive membranes resulted in a strong colouration of the membrane, in a reduction of surface tension, which resulted in a decreased caffeine permeability resistance. The membranes were characterized using XPS for the elemental composition of the coating, contact angle measurements for the surface tension, solid-state UV/VIS measurements for the determination of the kinetic and stability properties, and two-photon microscopy for the localisation of the photochromic substance in the porous membrane.