Abstract
Collagen, the primary structural protein in the extracellular matrix, plays a critical role in tissue architecture and mechanical integrity. This study investigates the structural and nonlinear optical properties of atelocollagen (Acol) and telocollagen (Tcol) in response to pH variations by using second harmonic scattering (SHS), polarization-resolved SHS (P-SHS), and atomic force microscopy (AFM). AFM imaging revealed distinct morphological differences, with Acol forming wavy, non-cross-linked, and randomly arranged fibers, while Tcol exhibited a more interconnected, mesh-like fibrillar network. SHS and P-SHS measurements further confirmed these differences, indicating significant variations in hyperpolarizability and depolarization ratio (DR) between Acol and Tcol. The results suggest that telopeptides play a crucial role in collagen fibrillogenesis, influencing the molecular symmetry and optical responses. The observed differences in nonlinear optical properties highlight the potential of SHS as a powerful tool for characterizing collagen self-assembly mechanisms. These findings contribute to a broader understanding of collagen organization in biological and biomaterial contexts, with implications for tissue engineering, fibrosis research, and regenerative medicine. Future work should explore how external factors, such as ionic strength and cross-linking agents, further modulate collagen fibril formation and its mechanical properties.