J. Cosmet. Sci., 69, 357–362 (September/October 2018) 357 Investigating Prevention of UV Damage to Hair Using Raman Spectroscopy CARRIE B. GRUNDMAN, Aveda, The Estée Lauder Companies, Blaine, MN 55449 Synopsis The goal of this work is to demonstrate the impact of UV and potential protective materials on hair fi ber cuticle protein structure using Raman spectroscopy. INTRODUCTION Damage is a top consumer hair care concern because it can result in a variety of undesir- able effects, including breakage, unmanageability, fl y-aways, dry-feeling hair, lack of shine, and split ends. The need for protection against hair damage follows directly from the impact of many hair-related habits and treatments, as well as environmental exposure, on hair fi ber structure. In this work, ultraviolet (UV) radiation was chosen as a model insult because of the fact that exposure is diffi cult to avoid altogether, UV tends to exacerbate the damaging effects of other treatments, and there is no standardization or analogous sun protection factor (SPF) index for hair fi bers. Although there are many facets involved in the interaction between UV and hair fi bers, this work builds on the following key facts from literature: UV has suffi cient energy to break disulfi de bonds (1), which are integral to hair fi ber structural integrity. UV also tends to damage the cu- ticle before the cortex (2–4). Kuzuhara has illustrated the utility of Raman spectroscopy for measuring hair fi ber cuticle protein structure (5–8). The goal of this work, therefore, is to demonstrate the impact of UV and potential protective materials on hair fi ber cuticle protein structure using Raman spectroscopy. This work focuses only on one measure of UV damage and protection. METHODS Whole fi bers of unpigmented hair were used in this work with and without treatment with neat solutions of six commercially available raw materials (materials A–F) advertised Address all correspondence to cgrundma@aveda.com.
JOURNAL OF COSMETIC SCIENCE 358 by the manufacturers as being UV protectants. Hair fi bers were treated with materials of interest, exposed to a controlled amount of UV, and analyzed using Raman spectroscopy. The Atlas Suntest XXL+ (Atlas Material Testing Solutions, Mount Prospect, IL) with daylight fi lters gave UV exposure from 300 to 400 nm. The irradiance was set at 62 W/m2, which gave a total energy of 5.4 MJ/m2 over the course of 24 h. This exposure level was in line with Signori’s low UV exposure level: a few hours per day over the course of about 1 mo (1). The black standard temperature, the highest temperature the sample surfaces could reach, was set at 65°C. The relative humidity was fi xed at 55%. Raman spectra were collected using a XPlora Plus spectrometer (Horiba Scientifi c, Piscataway, NJ). The use of unpigmented hair eliminated fl uorescence and required minimal sample preparation. Raman provided a direct measure of disulfi de content and good spatial resolution with a spot size of approximately 0.5 μm. At least three hair fi bers for each treatment were fi xed to aluminum foil–covered microscope slides, as shown in Figure 1. Spectra from 200 to 3,200 1/cm were taken starting at the surface of the hair fi ber and into the hair fi ber at 0.5 μm intervals to 3 μm toward the fi ber center, giving information on the protein structure of the cuticle. These spectra were averaged, and at least three hair fi bers for each treatment were analyzed. The 785-nm laser was used at full power (100 mW at the laser source) through a ×100 objective, and 1,200 g/mm with 10-s acquisition time and three accumulations gave good signal to noise. The spectra were baselined using linear chords connected to the spectra. Spectra were normalized to peaks that did not show sig- nifi cant change upon the UV exposure used in this study: Phe at 1,003 1/cm, CH2 bending at 1,448 1/cm, amide I at 1,655 1/cm, and CH signatures at approximately 2,920 1/cm. Raman data can provide quantitative information two approaches are shown in Figure 2. The double-cursor approach to extracting data is favorable because it requires the least amount of data manipulation, but this technique cannot resolve overlapping peaks. Gaussian/Lorentzian peak fi tting allows for peak deconvolution but involves the inherent uncertainty of mathematical peak fi tting routines. Prior knowledge of anticipated peak posi- tions and reasonable initial parameters prove helpful in using this approach to peak fi tting. The Raman peaks for the different conformations of the disulfi de bond appear at different wavenumbers (9). The disulfi de peak can be deconvoluted using Gaussian/Lorentzian peak fi tting. However, for simplicity in this work due to the presence of treatment materials in addition to hair fi bers, the disulfi de peak at about 505–511 1/cm was chosen as representative of the hair fi ber disulfi de content. Gaussian/Lorentzian peak fi tting was Figure 1. Example microscope slide with unpigmented hair fi bers attached and hair fi ber schematic with Raman spectrum acquisition position indicator.
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