Fully Implantable and Retrievable Upconversion Waveguides for Photodynamic Therapy in Deep Tissue

The clinical administration of biophotonic approaches, such as photodynamic therapy (PDT), is impeded by the low penetration of visible light in biological tissues. The cooperation of infrared (IR) light with deeper penetration and implantable IR-to-visible upconversion materials and devices establishes an effective strategy to generate visible light in deep tissue. In this work, a wirelessly powered upconversion waveguide-based light source is reported for PDT-based in vivo cancer treatments in deep tissue. Combining microscale IR-to-visible upconversion device arrays and a biocompatible waveguide, the implant exhibits enhanced IR transmission in biological environments and generates upconverted red emission in the target region at a depth >10 mm. The red illumination activates a photosensitizer in 5-aminolevulinic acid (5-ALA)-based PDT treatment, inducing massive apoptosis (>60% cell death) of tumor cells. After implanted in tumor-bearing mice, the waveguides enable chronic operation for more than two weeks and reveal ideal anti-tumor efficacies in the PDT process. Finally, the biocompatible waveguide can be retrieved from the tissue, leaving minimal traces after treatments. Such a waveguide implant represents a prospective technique to realize optical-based biological modulations and medical treatments within the body.