Human hair is comprised of a highly complex biomaterial, α-keratin. Some of
the key features of keratin are its robust nature and strong mechanical stability.
These qualities originate from the molecular assembly of the proteins and are
described by a two-phase model. Highly ordered crystalline intermediate
filaments are interspersed within a less-ordered amorphous matrix. Developing a
further understanding of the internal sub-structures of hair fibres, particularly
with relation to the effect of chemical agents on these structures is imperative to
the personal care and cosmetic industries. This information could direct the
growth and expansion of new cosmetic treatments.

Nuclear magnetic resonance experiments have been utilised as a method to
measure and quantify “damage” to hair fibres caused by chemical modifications.
X-ray scattering experiments were employed to investigate the effect of chemical
agents on the sub-structures of hair. Equilibrium and time-resolved hydration
experiments were used to ascertain both the lateral and axial swelling of the
intermediate filaments and how “damage” affects this. Micro-focus x-ray
scattering techniques provided information on the scattering patterns produced
by the three principal hair structures; the cuticle, the cortex and the medulla.

Some of the key findings of this research include the use of spin-lattice
relaxation times as a robust and reproducible method for quantifying hair
damage. Time-resolved hydration experiments demonstrated that both the
magnitude and rate of swelling a fibre undergoes can be altered through chemical
agents. The distribution of intermediate filaments within the cortex was
measured for the first time by x-ray scattering, showing a clear increase in the
density towards the centre of the fibres. These findings and use of the various
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techniques begin to produce a tool-kit for measuring and quantifying the effect
of chemical treatments on human hair fibres.