Multiscale modelling of human hair
TLDR Human hair becomes weaker and stretches more easily at higher temperatures.
The study presented a multiscale modelling approach to understand the mechanics of human hair fibres. At the microscale, molecular-dynamics simulations showed that the force required to mechanically unfold a coiled coil of filament proteins was approximately 1 nN, significantly higher than the reversible force. A statistical mechanical model was developed, predicting a linear decrease in yield stress with temperature, which was experimentally confirmed by stretching hair fibres at elevated temperatures. The study also examined the correlation between unfolding units, estimating an interface energy of about 12 kJ/mol. At the nanometre scale, a particle-based model of a macrofibril was used, where mesoscale particles representing keratin protein coiled coils were assembled into filaments within a matrix. The macrofibril's thermal properties in the yield region aligned with the two-state model, as observed in non-equilibrium computer simulations.
