An international team of scientists – led by Dr Vesna Stanic of the Brazilian Synchrotron Light Source – has detected new structural features of human hair.

Human hair structure has been studied extensively for more than 70 years, but a complete picture of its local structure has proven elusive.

“Human hair is primarily composed of keratin molecules arranged in hierarchical structure, where the fundamental building block is called an intermediated filament,” Dr Stanic said.

While studying materials used for hair treatments, Dr Stanic and her colleagues wondered what effect these treatments were having on the diffraction pattern of the hair.

Although diffraction patterns have been examined and reported in several publications in the past, they involved bundles of hair fibers or microdiffraction on single hair fibers; and, most significantly, the X-ray beam was always oriented perpendicular to the hair fiber axis.

So the scientists decided to take a closer look at the diffraction pattern of the hair by measuring it with an X-ray beam aimed parallel to the hair axis.

By using a sub-micron X-ray beam and transmission electron microscopy, they were able to spatially resolve the local structure of the three main regions of the human hair: the medulla, the cortex and the cuticle.

The researchers performed a full diffraction map from a 30 micron thick cross-section of hair, with the incident beam parallel to the hair axis and compared it to the diffraction map with the beam perpendicular to the hair axis.

“We found that as one moves the X-ray beam from the exterior of the hair to the medulla, the arrangement of the keratin fibrils become increasingly disordered. The combination of the sub-micron X-ray beam and the cross-section geometry enables us to detect a new structural features not previously observed,” Dr Stanic said.

They discovered that within the cuticle a key diffraction feature of the alpha keratin is absent – indicating the presence of beta keratin instead of the alpha keratin phase.

Until now, it was believed that keratin in the whole hair had only an alpha conformation.

“The study provides irrefutable experimental evidence of the hair phase variation across the three main regions of hair and is an important step toward gaining a better understanding of hierarchical ordering of the intermediate filaments of keratin,” Dr Stanic said.

“It also highlights the importance of using a submicron X-ray beam to unravel the structures of poorly ordered, multiphase systems such as hair.”

Dr Stanic and co-authors believe the cosmetics industry will benefit from their findings, which were presented on Wednesday, July 29th at the American Crystallographic Association 2015 Meeting in Philadelphia.

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Vesna Stanic et al. Sub-micron X-ray Beam Study of Human Hair. American Crystallographic Association 2015 Meeting, abstract # 4.2.4.02