Using hybrid atomic force microscopy and infrared spectroscopy (AFM‐IR) to identify chemical components of the hair medulla on the nanoscale

Abstract

Atomic force microscopy integrated with infrared spectroscopy (AFM‐IR) has been used to topographically and chemically examine the medulla of human hair fibres with nanometre scale lateral resolution. The mapping of cross‐sections of the medulla showed two distinct structural components which were subsequently characterised spectroscopically. One of these components was shown to be closely similar to cortical cell species, consistent with the fibrillar structures found in previous electron microscope (EM) investigations. The other component showed large chemical differences from cortical cells and was assigned to globular vacuole species, also confirming EM observations. Further characterisation of the two components was achieved through spectral deconvolution of the protein Amide‐I and ‐II bands. This showed that the vacuoles have a greater proportion of the most thermodynamically stable conformation, namely the antiparallel β‐sheet structures. This chimes with the observed lower cysteine concentration, indicating a lower proportion of restrictive disulphide cross‐link bonding. Furthermore, the large α‐helix presence within the vacuoles points to a loss of matrix‐like material as well as significant intermolecular stabilisation of the protein structures. By analysing the carbonyl stretching region, it was established that the fibrillar, cortical cell‐like components showed considerable stabilisation from H‐bonding interactions, similar to the cortex, involving amino acid side chains whereas, in contrast, the vacuoles were found to only be stabilised significantly by structural lipids.

Nanoindentation study of human fingernail for determining its structural elasticity

“…The Young's modulus was higher in the cuticle, cortex, and medulla layers, consistent with previous reports 24 . Medulla is an amorphous structure formed by fibrous structures derived from cortex cells, and is believed to have a lower Young's modulus than the cortex 27 …”

“…24 Medulla is an amorphous structure formed by fibrous structures derived from cortex cells, and is believed to have a lower Young's modulus than the cortex. 27 The SEB values of the hair samples were estimated from Equation (8) using the determined values of E 4 , E 5 , and E 6 . The values of α and β were assumed to be 0.925 and 0.125, respectively, from the literature.…”

Photoinduced force microscopy as a novel method for the study of microbial nanostructures

“…Some variations in the thickness of sections can be expected due to differences in physical properties between the resin and biological matter. 42,43 Transmission electron microscopy (TEM)…”

The Role of Lipids in the Process of Hair Ageing

“…They contain a mixture of nonesterified and esterified lipids, primarily saturated and carboxylate soaps, which could partially exhibit a crystalline phase. Recently, hair medulla was also found to contain globular structures assigned to the air-filled vacuoles interspersed with fibrillar ones, encompassed by a membrane, with the structural lipids providing the dominant interactions [46]. Squalene and oleic acid have also been detected [47].…”