Multiscale characterization of solar radiation-induced structural degradation in Type I collagen

Collagen, the most abundant structural protein in animals, plays a crucial role in maintaining skin integrity, elasticity, and strength. Type I collagen, which predominates in the skin, is particularly vulnerable to environmental stressors, such as solar radiation. Prolonged sun exposure accelerates collagen degradation, driving skin aging and impairing tissue functionality. However, the molecular mechanisms governing these intricate processes remain unclear. In this study, we employed bovine Type I collagen as a model system to investigate the molecular alterations induced by solar radiation, focusing on changes in structure, morphology, and fibrillogenesis potential. Collagen samples were irradiated using a solar simulator that mimics the full solar spectrum to ensure standardized conditions. Structural changes at different levels, were analyzed using a multi-technique approach combining classical spectroscopies, fluorescence lifetime imaging microscopy, and scattering-type scanning near-field optical microscopy (s-SNOM). This multimodal approach enabled both sensitive detection of molecular alterations and spatial mapping of local heterogeneities within collagen fibers. Results indicate partial destabilization of the triple-helical structure and a loss of cross-links and telopeptides, consistent with molecular misalignment. FLIM imaging on samples stained with Anilinonaphthalene-1-sulfonic acid (ANS), a gold standard fluorescent dye for the study of protein conformational transition highlighted increased sample heterogeneity and a reduction in hydrophobic regions, pointing to structural disruption which could be also related to the loss of self-assembly capabilities of collagen molecules.