Three-dimensional architecture of macrofibrils in the human scalp hair cortex.
Human scalp hairs are comprised of a central cortex enveloped by plate-like cuticle cells. The elongate cortex cells of mature fibres are composed primarily of macrofibrils-bundles of hard-keratin intermediate filaments (IFs) chemically cross-linked within a globular protein matrix. In wool, three cell types (ortho-, meso- and paracortex) contain macrofibrils with distinctly different filament arrangements and matrix fractions, but in human hair macrofibril-cell type relationships are less clear. Here we show that hair macrofibrils all have a similar matrix fraction (∼0.4) and are typically composed of a double-twist architecture in which a central IF is surrounded by concentric rings of tangentially-angled IFs. The defining parameter is the incremental angle increase (IF-increment) between IFs of successive rings. Unlike the wool orthocortex, hair double-twist macrofibrils have considerable inter-macrofibril variation in IF increment (0.05-0.35°/nm), and macrofibril size and IF increment are negatively correlated. Correspondingly, angular difference between central and outer-most IFs is up to 40° in small macrofibrils, but only 5-10° in large macrofibrils. Single cells were observed containing mixtures of macrofibrils with different diameters. These new observations advance our understanding of the nano-level and cell-level organisation of human hair, with implications for interpretation of structure with respect the potential roles of cortex cell types in defining the mechanical properties of hair.
Food & Bio-Based Products, AgResearch Lincoln Research Centre, Lincoln, New Zealand. Electronic address: duane.harland@agresearch.co.nz.
Duane P
DP
Harland
Food & Bio-Based Products, AgResearch Lincoln Research Centre, Lincoln, New Zealand.
Richard J
RJ
Walls
Food & Bio-Based Products, AgResearch Lincoln Research Centre, Lincoln, New Zealand. Electronic address: james.vernon@agresearch.co.nz.
James A
JA
Vernon
Food & Bio-Based Products, AgResearch Lincoln Research Centre, Lincoln, New Zealand. Electronic address: jolon.dyer@agresearch.co.nz.
Jolon M
JM
Dyer
Food & Bio-Based Products, AgResearch Lincoln Research Centre, Lincoln, New Zealand. Electronic address: joy.woods@agresearch.co.nz.
Joy L
JL
Woods
Hair CTI, Unilever R&D, Port Sunlight, Bebington, UK. Electronic address: fraser.bell@unilever.com.
Fraser
F
Bell
D055032:Electron Microscope Tomography; D006197:Hair / Q000737:chemistry*; D006801:Humans; D007382:Intermediate Filaments / Q000737:chemistry / Q000648:ultrastructure; D012535:Scalp / Q000737:chemistry*
Double-twist structure; Electron tomography; Hair cell types; Hair cortex; Macrofibril