In the last few decades, reactive oxygen species (ROS) have emerged as a highly powerful cell-signaling agent in disease but also in physiology. ROS effect can vary from detrimental with harmful effects on cell viability to highly beneficial in most biological processes, including cell differentiation, proliferation, and migration, up to specific functionality.^[1] The controlled production of ROS through exogenous stimuli such as light is expected to provide lower invasiveness, relying on wireless stimulation, reversibility, and high spatial selectivity. Semiconducting polymers, originally used in organic electronics, are attracting increasing attention as phototriggers of ROS due to their biocompatibility, intrinsic conductivity and optical properties. For such a purpose, semiconducting polymers are usually processed in the form of thin films and nanoparticles whose performance is influenced by the π-conjugated semiconducting polymer structure and its 3D confinement during the nanomaterial formation. All those features clearly modulate the photophysical processes and ultimately determine their biophotonic applications. However, its application is still limited by its low efficacy and the use of bare photoexcitation does not allow for the necessary fine-tuning of ROS concentration at safe regimes for photostimulation.^{[2, 3]}

To overcome these limitations, we developed porous poly(3-hexylthiophene) (P3HT) films (PSFs) and nanoparticles (PSNPs) with an enlarged surface area (S_a) that allowed to increase the optical absorption surface area, providing easier access to optical excitation for (bio-opto)electronic applications. To that aim, opto-active, electro-active, and hydrolysable graft copolymers were synthesized through chemical oxidative polymerization of P3HT and polylactic acid (PLA), P3HT-g-PLA, with different PLA percentages to tune the pore size. The morphology and pores of PNFs were characterized by Atomic Force Microscopy (AFM) and grazing incidence small angle X-ray scattering (GISAXS), whereas the PSPNs formation and distribution were analyzed by Scanning Electron Microscopy (SEM), dynamic light scattering (~100 nm), and small angle X-ray scattering (SAXS). The PLA hydrolysis was also corroborated by Nuclear Magnetic Resonance (¹H-NMR). The optical properties of the nanomaterials were determined by UV-vis absorption and fluorescence emission spectrophotometry. Finally, the photo-electrochemical properties were determined by irradiating the nanomaterials, immersed in an aqueous physiological electrolyte, with a laser diode. Porous nanomaterials gave rise to a 4-fold increase in the photocurrent properties as compared with non-porous ones, proving enhanced opto-electronic properties of our nanomaterials. The employment of these porous nanomaterials as biophotonic devices for extracellular (PNFs) and intracellular (PSNPs) stimulations of human umbilical vein endothelial cells (HUVECs) allowed us to modulate the ROS production in the beneficial physiological range, up to 6 mW/cm² (λ = 530 nm) in the case of PSNPs, to favor tissue regeneration processes.^{[4, 5]}