Encapsulation of phthalocyanines in biodegradable poly(sebacic anhydride) nanoparticles

A new series of phthalocyanine-containing biodegradable copolymers, namely poly(phthalocyanine-co-sebacic anhydride) (Pc-SA), have been synthesized. For copolymers with a low Pc content, the Pc rings exist mainly as monomeric species in chloroform, while the aggregation of these macrocycles becomes significant as the Pc content increases. Nanoparticles with an average hydrodynamic radius of 166 nm have been prepared from the copolymer Pc-SA-5, which has a Pc to sebacic acid molar ratio of 0.01, via a microphase inversion method. The collapse of polymer chains in the formation of Pe-SA-5 nanoparticles leads to aggregation of the Pc rings inside. The aggregation tendency decreases upon degradation of the nanoparticles in alkaline media, giving ultimately monomeric species. The degradation kinetics of Pc-SA-5 nanoparticles have been investigated by a combination of static and dynamic laser light scattering. It has been found that the rate of degradation increases with the pH and temperature. By using absorption and fluorescence spectroscopies, the release of Pc can be monitored, which occurs almost simultaneously with the degradation. The results suggest that this novel polymer-based colloidal system is potentially useful for the delivery and release of photosensitizers in photodynamic therapy.