Phantoms for Nanoscale Characterization of Laser-Pigment Interactions Challenge the Fragmentation Paradigm in Tattoo Removal

The global rise in tattooing practices and laser-based removal has highlighted the need for a deeper mechanistic understanding of pigment clearance. To date, tattoo removal performed using Nd:YAG picosecond lasers has been predominantly interpreted as a photothermal fragmentation process, based largely on macroscopic and histological observations. However, nanoscale characterization of pigment transformations remains limited. The study introduces a minimal and versatile platform for the nanometric investigation of laser–pigment interactions, enabling systematic analysis under controlled conditions. Two widely used tattoo pigments were selected as model systems: carbon black (CB), clinically recognized as highly responsive to laser treatment, and titanium dioxide (TiO₂), known for its resistance to removal. Pristine and laser-irradiated samples were characterized using transmission electron microscopy (TEM, HR-TEM), dynamic light scattering (DLS), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR). Contrary to the prevailing fragmentation paradigm, CB laser exposure induces aggregate coalescence, accompanied by expansion and partial graphitization of the primary structural units. In contrast, TiO₂ exhibits negligible morphological or structural modifications upon irradiation, confirming its poor laser responsiveness. These findings challenge the conventional photothermolysis-based interpretation of tattoo removal and underscore the importance of nanoscale analyses to elucidate underlying mechanisms and its health effect.