Hydration dynamics of human fingernails: an ellipsometric study.

Area of Science:

• Biophysics
• Materials Science
• Biomaterials

Background:

• Human fingernails are complex biomaterials primarily composed of keratin.
• Understanding the hydration dynamics of fingernails is crucial for various applications, including cosmetics and dermatology.
• Keratin's interaction with water influences its mechanical and structural properties.

Purpose of the Study:

• To quantitatively investigate the hydration and dehydration kinetics of human fingernails.
• To differentiate between various water binding states within the fingernail structure.
• To model the water transport mechanisms in keratin-based materials.

Main Methods:

• Spectroscopic ellipsometry was employed to measure the complex refractive index (ñ=n+ik) of human fingernails.
• The study analyzed changes in ñ during controlled hydration and dehydration cycles.
• A kinetic model was developed to interpret the observed water dynamics.

Main Results:

• Three distinct time domains with characteristic time constants (4, 150, and 3200 min) were identified during hydration/dehydration.
• A two-process model (fast and slow) accurately described the experimental data.
• The fast process was attributed to "free" water between keratin filaments, and the slow process to "bound" water within keratin complexes.

Conclusions:

• Human fingernails exhibit complex water binding behavior with distinct kinetic components.
• The findings provide insights into the microstructural organization of water within keratin.
• The developed model offers a framework for understanding water dynamics in similar proteinaceous biomaterials.