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Local structure of human hair spatially resolved by sub-micron X-ray beam.

Stanić V, Bettini J, Montoro FE, Stein A, Evans-Lutterodt K - Sci Rep (2015)

Bottom Line: We also find that in the cuticle, a key diffraction feature is absent, indicating the presence of the β-keratin rather than that of the α-keratin phase.This is direct structural evidence that the cuticle contains β-keratin sheets.This work highlights the importance of using a sub-micron x-ray beam to unravel the structures of poorly ordered, multi-phase systems.

View Article: PubMed Central - PubMed

Affiliation: Brazilian Synchrotron Light Source, CNPEM, SP 13083-970, Brazil.

ABSTRACT
Human hair has three main regions, the medulla, the cortex, and the cuticle. An existing model for the cortex suggests that the α-keratin- based intermediate filaments (IFs) align with the hair's axis, but are orientationally disordered in-plane. We found that there is a new region in the cortex near the cuticle's boundary in which the IFs are aligned with the hair's axis, but additionally, they are orientationally ordered in-plane due to the presence of the cuticle/hair boundary. Further into the cortex, the IF arrangement becomes disordered, eventually losing all in-plane orientation. We also find that in the cuticle, a key diffraction feature is absent, indicating the presence of the β-keratin rather than that of the α-keratin phase. This is direct structural evidence that the cuticle contains β-keratin sheets. This work highlights the importance of using a sub-micron x-ray beam to unravel the structures of poorly ordered, multi-phase systems.

No MeSH data available.


Related in: MedlinePlus

SEM image of a human hair fiber is shown in (A) with schematic overlays on to the cut face of the hair fiber to emphasize the relative size of the hair and the main hair regions. In (B), we spatially position the SAXS diffraction patterns relative to each other, so that the locations match the position of the x-ray beam on the sample, thus generating a SAXS “map” of human hair. This map allows us to see the spatial variation of the SAXS patterns from a 30-micron- thick cross-section of hair. The incident x-ray beam is  to the hair axis. SEM zoom of selected cross section from (A) is overlapped to the SAXS map showing the real-space cross section of the cuticle and cortex. Magnified views of the characteristic SAXS patterns are shown in (C) for the medulla, (D) for the cortex, and in (N) for the cuticle. (E,F) are for the newly discovered intermediate zone. Corresponding Scanning Transmission Electron Microscopy (STEM) images shown in (G,H,J,L).
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f1: SEM image of a human hair fiber is shown in (A) with schematic overlays on to the cut face of the hair fiber to emphasize the relative size of the hair and the main hair regions. In (B), we spatially position the SAXS diffraction patterns relative to each other, so that the locations match the position of the x-ray beam on the sample, thus generating a SAXS “map” of human hair. This map allows us to see the spatial variation of the SAXS patterns from a 30-micron- thick cross-section of hair. The incident x-ray beam is to the hair axis. SEM zoom of selected cross section from (A) is overlapped to the SAXS map showing the real-space cross section of the cuticle and cortex. Magnified views of the characteristic SAXS patterns are shown in (C) for the medulla, (D) for the cortex, and in (N) for the cuticle. (E,F) are for the newly discovered intermediate zone. Corresponding Scanning Transmission Electron Microscopy (STEM) images shown in (G,H,J,L).

Mentions: While Human hair has been studied by x-ray diffraction and electron microscopy for many years123456789, a complete picture has been elusive because hair is weakly scattering, disordered, and heterogeneous. Human hair is a hierarchical structure, largely constituted of intermediate filaments (IFs) that in turn are made up of keratin molecules110. Hair has three main regions: (1) the medulla on the central axis, (2) the cortex, and, (3) the cuticle at the exterior of the hair, (Fig. 1A,B). The medulla mainly is filled with a keratin matrix partially composed of IFs that are spatially and orientationally disordered. The majority of the cortex has a dense packing of IFs aligned along the axis of the hair, but are fluid-like in two dimensions in the plane perpendicular to the hair’s axis. The cuticle is well organized in a layered 1D-ordered structure.


Local structure of human hair spatially resolved by sub-micron X-ray beam.

Stanić V, Bettini J, Montoro FE, Stein A, Evans-Lutterodt K - Sci Rep (2015)

SEM image of a human hair fiber is shown in (A) with schematic overlays on to the cut face of the hair fiber to emphasize the relative size of the hair and the main hair regions. In (B), we spatially position the SAXS diffraction patterns relative to each other, so that the locations match the position of the x-ray beam on the sample, thus generating a SAXS “map” of human hair. This map allows us to see the spatial variation of the SAXS patterns from a 30-micron- thick cross-section of hair. The incident x-ray beam is  to the hair axis. SEM zoom of selected cross section from (A) is overlapped to the SAXS map showing the real-space cross section of the cuticle and cortex. Magnified views of the characteristic SAXS patterns are shown in (C) for the medulla, (D) for the cortex, and in (N) for the cuticle. (E,F) are for the newly discovered intermediate zone. Corresponding Scanning Transmission Electron Microscopy (STEM) images shown in (G,H,J,L).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4663634&req=5

f1: SEM image of a human hair fiber is shown in (A) with schematic overlays on to the cut face of the hair fiber to emphasize the relative size of the hair and the main hair regions. In (B), we spatially position the SAXS diffraction patterns relative to each other, so that the locations match the position of the x-ray beam on the sample, thus generating a SAXS “map” of human hair. This map allows us to see the spatial variation of the SAXS patterns from a 30-micron- thick cross-section of hair. The incident x-ray beam is to the hair axis. SEM zoom of selected cross section from (A) is overlapped to the SAXS map showing the real-space cross section of the cuticle and cortex. Magnified views of the characteristic SAXS patterns are shown in (C) for the medulla, (D) for the cortex, and in (N) for the cuticle. (E,F) are for the newly discovered intermediate zone. Corresponding Scanning Transmission Electron Microscopy (STEM) images shown in (G,H,J,L).
Mentions: While Human hair has been studied by x-ray diffraction and electron microscopy for many years123456789, a complete picture has been elusive because hair is weakly scattering, disordered, and heterogeneous. Human hair is a hierarchical structure, largely constituted of intermediate filaments (IFs) that in turn are made up of keratin molecules110. Hair has three main regions: (1) the medulla on the central axis, (2) the cortex, and, (3) the cuticle at the exterior of the hair, (Fig. 1A,B). The medulla mainly is filled with a keratin matrix partially composed of IFs that are spatially and orientationally disordered. The majority of the cortex has a dense packing of IFs aligned along the axis of the hair, but are fluid-like in two dimensions in the plane perpendicular to the hair’s axis. The cuticle is well organized in a layered 1D-ordered structure.

Bottom Line: We also find that in the cuticle, a key diffraction feature is absent, indicating the presence of the β-keratin rather than that of the α-keratin phase.This is direct structural evidence that the cuticle contains β-keratin sheets.This work highlights the importance of using a sub-micron x-ray beam to unravel the structures of poorly ordered, multi-phase systems.

View Article: PubMed Central - PubMed

Affiliation: Brazilian Synchrotron Light Source, CNPEM, SP 13083-970, Brazil.

ABSTRACT
Human hair has three main regions, the medulla, the cortex, and the cuticle. An existing model for the cortex suggests that the α-keratin- based intermediate filaments (IFs) align with the hair's axis, but are orientationally disordered in-plane. We found that there is a new region in the cortex near the cuticle's boundary in which the IFs are aligned with the hair's axis, but additionally, they are orientationally ordered in-plane due to the presence of the cuticle/hair boundary. Further into the cortex, the IF arrangement becomes disordered, eventually losing all in-plane orientation. We also find that in the cuticle, a key diffraction feature is absent, indicating the presence of the β-keratin rather than that of the α-keratin phase. This is direct structural evidence that the cuticle contains β-keratin sheets. This work highlights the importance of using a sub-micron x-ray beam to unravel the structures of poorly ordered, multi-phase systems.

No MeSH data available.


Related in: MedlinePlus