Biomechanics of hair fibre growth: A multi-scale modeling approach

Abstract In an actively growing scalp hair, the cells proliferating at the basal zone of the hair follicle commence a journey of approximately 4 mm in two weeks before emerging from the scalp surface as a strong rigid fiber. This maturation process of the nascent hair fiber involves many biological, biochemical and biomechanical factors. While we have a rich understanding of the regulatory elements governing biological and biochemical processes, our understanding of the role of biomechanical factors in hair fiber protrusion is virtually null. By adopting a multiscale mechanical modeling approach, here we sought to add a new dimension to the understanding of hair fiber growth. An overall mechanical model constructed to correspond to the entire follicle is complemented and informed by predictions obtained from tissue and cell-scale models. Combined, the simulations suggest that biomechanical features such as follicle geometry, hydrostatic state of tissues layers, material stiffness, keratinization-mediated hardening, and desmosome-correlated shear sliding behaviors are likely to play important roles in hair fiber protrusion. The simulation results predict fine tuning of biomechanical parameters to be a key strategy to ensure smooth hair fiber protrusion while maintaining sufficient anchoring strength against external disturbance. The in silico model of a hair follicle sets a framework for experimental validation and guides the investigation of biomechanical underpinnings of hair growth processes.