Human hair aging beyond graying: A case-comparative biointerface phenotype from a 104-year-old donor

Human hair graying is a visible manifestation of aging, but pigment loss may not capture the broader physicochemical state of the mature hair surface. We examined naturally aged scalp hair using a case-comparative design comprising pigmented black (B) and white-gray (W) fibers from the same approximately 50-year-old female donor and white fibers from a single 104-year-old donor (C), treated as a descriptive extreme-age case. SEM-EDS, AFM-QNM, directional one-dimensional power spectral density (1D PSD), time-resolved apparent contact angle on aligned mini-tresses, and albumin-equivalent protein release probed complementary dimensions of the hair biointerface. Formal inference was restricted to B-W. SEM peak-to-valley descriptors showed no significant B-W differences after multiplicity correction. In contrast, EDS detected a selective normalized carbon-associated difference, 1D PSD identified a change in spectral slope (β; pBH = 0.00108), and AFM-QNM Bearing Area differed for adhesion, deformation, and DMT modulus. CLR-PCA nevertheless showed substantial B-W overlap. None of the eight primary wettability/asymmetry endpoints differed significantly after correction, and protein release was also non-significant (p = 0.415). C showed a descriptive pattern of heterogeneous cuticular organization, relatively higher Na/K and lower Ca EDS responses, stronger long-wavelength topographical contributions, and broader AFM-QNM heterogeneity while retaining predominantly high apparent contact angles and protein extractability within the adult range. Overall, the results show that surface-resolved compositional, topographical, and nanomechanical contrasts can occur without corresponding shifts in macroscopic wettability or aqueous protein extractability; the single-donor C observations should not be generalized as centenarian biomarkers. Statistical summary: 7,173 words in the main text; 8 figures; 0 tables.