Rhodamine B diffusion in hair as a probe for structural integrity

Area of Science:

• Materials Science
• Biophysics
• Cosmetic Science

Background:

• Hair structure comprises cuticle and cortex layers.
• Chemical, photochemical, and physical treatments can damage hair.
• Understanding diffusion dynamics is key to assessing hair integrity.

Purpose of the Study:

• To investigate Rhodamine B dye diffusion in chemically, photochemically, and physically altered hair.
• To compare spectrophotometry and fluorescence microscopy for analyzing dye diffusion.
• To validate a methodology using apparent diffusion coefficient as a hair damage index.

Main Methods:

• Utilized spectrophotometry and fluorescence optical microscopy with image analysis.
• Applied the Einstein-Smoluchowski equation to determine apparent diffusion coefficients.
• Examined dye diffusion in bleached, photobleached, and abraded hair, with and without ceramide emulsion.

Main Results:

• Dye diffusion was significantly faster in the hair cuticle than in the cortex.
• Apparent diffusion coefficients decreased up to seven-fold when dye penetrated the cortex.
• Hair treatments markedly altered apparent diffusion coefficients in the cuticle.
• Rhodamine B penetration primarily occurred through an intercellular pathway.

Conclusions:

• The apparent diffusion coefficient of Rhodamine B can serve as a reliable index for quantifying hair damage.
• The validated methodology offers a novel approach for assessing hair structural integrity.
• Intercellular pathways are crucial for dye penetration into hair structures.