Fig. 1

（a） Diagram of single fiber strength tester device; （b） Schematic diagram of hair tensile property test"

Fig. 2

（a） Typical stress-strain curve model of hair; （b） Schematic diagram of hair fiber load-elongation and recovery curves"

Tab. 1

Notation of the variables for the elastic region （The description for each variable gives the Dia-Stron notation in square brackets and a short description on how the variable is derived）"

Tab. 2

Notation of the variables for the yield region. （FCA = fibre cross-sectional area. Parameters are normalized with respect to FCA to yield material specific variables）"

Tab. 3

Notation of the variables for the post-yield region"

Fig. 3

（a） Schematic 3D representation of one hair shaft cut: 1-hair cuticle; 2-medullary cells; 3-cell membrane complex; 4-macrofibril; 5-matrix; 6-microfibrils or intermediate fibrils; 7-protofibrils; （b） chemical bonds between hair keratin"

Fig. 4

Schematic diagram of tensile simulation in water （left） and vacuum （right） environment"

Fig. 5

（a） Typical stress-strain curves at different relative humidities; （b） representative stress-strain curves of hair under different temperatures in water; （c）Protein degradation obtained for non-irradiated and irradiated hair at 500 W/m2 during 9, 18 and 36 h （*p < 0.05）; （d） Breaking strength data for photo-oxidized （Mercury-vapor and Xenon lamps） and bleached hair sample"

Fig. 6

Fracture stress （BS） of natural （blue） and bleached （red） hair in wet （a） and dry （b） conditions as a function of heat treatment level"

Fig. 7

（a） TEM photographs of longitudinal sections of the cuticle region in healthy （left） and permed （right） hair; （b） Schematic diagram of stress/strain curves of hair fibers in water （0 To C） and reducing solution （0 To D）"

Fig. 8

Fracture load （a） and Young’s modulus （b） versus age of volunteers （“*” indicates significant difference compared to other groups）; percentage of secondary structure in hair for Asian （c） and Caucasian （d） hair at different stretching ratios"

Fig. 9

Effect of keratin and keratin-related proteins on hair properties: （a） Schematic representation of the effect of keratin extracted from wool on the properties of untreated, permed and over-bleached hair; （b） Application of K31 protein on chemically damaged hair improves the mechanical properties and thickness of the fiber"

Fig. 10

Protective effect of a peptide-based on hair keratin type Ⅱ cuticular Hb5 protein （KP） and KP-fusionproteins: （a） The KP peptide is able to improve the keratin fibers’ integrity by the formation of new disulfide bonds; （b） Application of KP-Cryst fusion proteins before high-temperature treatments protects hair fibers against degradation"