Poly(3-hexylthiophene) nanoparticles as visible-light photoinitiators and photosensitizers in 3D printable acrylic hydrogels for photodynamic therapies

The design of smart photoelectrodes capable of stimulating the localized production of reactive oxygen species (ROS) on demand is of great interest for redox medicine therapies. In this work, poly(3-hexylthiophene) semiconducting polymer nanoparticles (P3HT SPNs) are used with a dual role to fabricate light-responsive hydrogels. First, P3HT SPNs act as visible-light photoinitiators to induce the photopolymerization of acrylic monomers such as acrylamide (AAm), 2-(hydroxyethyl) acrylate (HEA), and poly(ethylene glycol) diacrylate (PEGDA). This leads to the formation of acrylic hydrogels loaded with the P3HT SPNs, as demonstrated by photo-rheology and infrared spectroscopy. Furthermore, P3HT SPNs are also successfully used as photoinitiators for digital light processing (DLP) 3D printing purposes to fabricate shape-defined intelligent hydrogels. Interestingly, P3HT SPNs retain their photoelectrochemical properties when embedded within the polymer hydrogels, showing photocurrent densities that range from similar to 0.2 to similar to 1.1 mu A cm-2 depending on the intensity of the visible light-lamp (lambda = 467 nm). Second, they can be used as photosensitizers (PS) to generate reactive oxygen species (ROS), 12-15 mu M H2O2, on demand. The acrylic hydrogels containing P3HT SPNs do not exhibit cytotoxic effects under normal physiological conditions in the darkness against mouse glioma 261 (GL261) cells and S. aureus bacteria. However, they induce a similar to 50% reduction GL261 cancer cell viability and a similar to 99% S. aureus cell death in contact with them upon illumination (lambda = 467 nm) due to the localized overproduction of ROS, which makes them attractive candidates for photodynamic therapies (PDT).