Equilibrium water sorption characteristics of the human nail

The physical and transport properties of keratinized tissues are closely related to their water content. This report presents water uptake and desorption isotherms for the human nail and compares them with those of wool, horn, hair, and stratum corneum. Nail absorbed a maximum of approximately 0.3 g H(2)O/g dry tissue, with the shape and magnitude of the isotherm most closely resembling horn. Hysteresis between uptake and desorption was observed, similar to that of other keratins. The shape of the isotherms was adequately described by both the D'Arcy-Watt and Guggenheim-Anderson-deBoer (GAB) models; however, small positive deviations from both models were found in the relative humidity range, 30-60%. Directionally better fits to the data were found with the D'Arcy-Watt model. This analysis suggests that most of the water in the tissue was in a strongly bound state, consistent with observations made by other techniques.