دندانه گذاری نانو از کورتکس مو
Abstract
Introduction
Experimental
Results and Discussion
Conclusion
References
Abstract
Reports related to cuticle damage and hair’s mechanical properties are of interest to dermatologists in treatment of hair disorders. Apart from tensile test, few studies were reported on mechanical properties of hair, especially nanomechanical properties of cortex and medulla regions. Inner diameter of hair fiber (8-12 µm) is considered as medulla and it exists in hair at the beginning of the anagen phase. This study is aimed for quantitative comparison of nanomechanical properties between cortex and medulla and also with respect to donor age by performing nanoindentation on fiber cross sections using two different instruments. The medulla and cortex regions revealed hardness values of 70-170 MPa and 200-312 MPa, respectively. Similarly lower values of indentation modulus were observed for medulla compared to cortex because medulla has poorer orientation of microfibrils compared to the surrounding cortex. This study also found a linear correlation between hardness and indentation modulus especially for medulla region. This could be due to the fact that organization of the microfibrils increases from the medulla center to medulla periphery. It is also found that donor age has no influence on cortex modulus and hardness. The findings of this study will be useful for dermatologists in estimating the hair disorders and for estimating dye uptake of keratin fibers in textiles.
Introduction
Human hair and wool are made up of keratin proteins. Microscopically hair is divided into three parts namely cuticle, cortex, and medulla. The outer surface of hair fiber consists of 6 to 10 layers of cuticles which are glued together by cell membrane complex (CMC). The cortex is the thicker part in hair fiber and it consists of elongated cortical cells and each cortical cell consists of macrofibrils of 0.4-0.5 μm diameter. Macrofibrils are made up of microfibrils which are embedded in a strong matrix having around 21 % cystine content (high in S-S linkages) [2]. CMC is present between the cortical cells, but macrofibrils are separated from each other by intermacrofibrillar matrix. Microfibril is the same as the intermediate filament of 7-10 nm diameter and microfibrils overall are low in cystine (6 %) content (low in S-S linkages). The medulla is a thin cylindrical layer in the center of the hair fiber with one or more loosely packed porous regions and it also made of microfibrils. Medulla can be continuous or fragmented or absent in human hair fibers, but it exists in most of the animal hair fibers [3]. Medulla occupies around 22-25 % of the whole hair fiber at the beginning of the anagen phase and slowly it disappears by the end of the anagen phase which normally lasts for 2-5 years [4]. Medulla has high lipid content and low cystine content compared to the rest of fiber. Among the hairs, beard hair has lower number of S-S linkages due to the extensive medullation compared to scalp hair [5]. Medulla’s function is not yet completely elucidated since it is difficult to isolate for further characterization. Recently, Wagner et al. [6] studied the medulla region using cryofractured samples and observed three subunits of medulla (globular structures, unorganized microfibrils, and smooth covering layer). From the TEM images, they have concluded that thin medulla has a sharp interface with cortex, whereas thick medulla shows gradual organization of the microfibrils from the medulla center to medulla periphery, i.e. interface with cortex. So it can be said that medulla region has weak nanocomposite structure on the inner side and shows progressive strengthening of the composite structure towards the outer side resembling plant fiber cross sections [7]. But no studies were carried out to quantify the weak nanocomposite structure of medulla region because of its low diameter (8-12 µm).