A NIR-responsive upconversion implant for wireless photodynamic therapy of tumors

Photosensitizer-mediated photodynamic therapy (PDT) enables wireless tumor inactivation by releasing cytotoxic reactive oxygen species (ROS). Nevertheless, the activation of conventional photosensitizers typically depends on visible light with limited tissue penetration, thereby restricting their therapeutic efficacy in deep-seated tumors. To overcome this limitation, an upconversion implant was engineered to function as a flexible internal light-emitting device by converting deeply penetrating near-infrared-I (NIR-I) light into visible light. Specifically, a composite PDT nanosystem was constructed by linking NaYF₄:Yb,Er upconversion nanoparticles with the rose bengal photosensitizer-whose emission and absorption spectra are well-matched-using polyvinylpyrrolidone (PVP) as a molecular bridge. This PDT nanosystem was subsequently incorporated into poly-L-lactic acid (PLLA) scaffolds fabricated via selective laser sintering. Under 980 nm laser irradiation, the upconversion implant was capable of wirelessly emitting upconverted visible light through more than 2 cm of an in vitro tissue model and generating abundant ROS via the photodynamic effect. In vitro cell experiments demonstrated that the system effectively eliminated tumor cells by damaging the cell membrane and cellular genetic material. These results suggest that the scaffolds possess significant potential as anti-tumor tissue implants and offer a promising avenue for the development of innovative tumor treatment strategies.