Keratin-based Materials

Narendra Reddy, Wenlong Zhou, Mingbo Ma

• Publisher: De Gruyter
• Year: 2020
• Print ISBN: 9781501519130
• eBook ISBN: 9781501511875
• Edition: 1
• Topic: Biological Sciences
• Subtopic: Biotechnology
• Index: Biological Sciences

The book introduces readers to the unique aspects of keratin and opportunities to develop various bioproducts and biomaterials from keratins. It discusses the structure, properties and specific applications of keratins extracted from different sources. Applications include keratins as absorbents, reinforcements or matrices for composites, hydrogels and fibres.

Chapter 1 Introduction to keratin

Keratin is one of the most common protein biopolymers found in nature. There are several sources and types of keratin but it has been suggested that keratin from human and bovine sources are similar with respect to charge, size and immunoreactivity. Based on their distinct structure and properties, keratins have been classified as soft and hard keratins. Soft keratins are those found as intermediate filaments (IFs) in the epithelia and arranged in loosely packed bundles and responsible for the mechanical resilience of the epithelial cells. Hard keratins are those found in ordered arrays in matrix of cysteine rich proteins in hairs, nails, claws and beaks and contribute to the tough structure of epidermal appendages (Rouse, 2010; Thibaut, 2003). Keratin exists in mammals, reptiles and birds and fishes as many parts of the body including hoof, horn, fur, wool, skin, quill, feathers, beaks and slime (McKittrick, 2012). Keratin broadly refers to the insoluble proteins found in the IFs which form a major portion of the cytoplasmic epithelia and epidermal appendage structures such as hair, wool, horns and nails. Few keratins are found only in the epithelial cells and are characterized by unique physiochemical properties and their primary function is to protect the epithelial cells from mechanical and nonmechanical stresses that could cause cell death (Coulombe, 2002). Additional functions of keratins include cell signaling, stress response and apoptosis. Although keratin is commonly considered to be a single substance, it is a mixture of proteins and enzymes. Other characteristics of keratin include indigestibility to pepsin or trypsin and also to dilute acids, alkalis, water and organic solvents. Keratins are also generally insoluble in salt solutions but can be made soluble in the presence of urea and other denaturing agents.

Based on their structure, keratins can also be classified as α-keratin or β-keratin. The α-keratin is fibrillar in nature and is composed of helical structure with the micofibrils embedded in an amorphous keratin matrix and aligned along the fiber axis. These amorphous regions have higher sulfur content with considerable amounts of disulfide bonds from the cysteine residues whereas the microfibrillar proteins having relatively low sulfur content are mostly made from hydrogen bonding which are responsible for determining the secondary structure of the proteins (Duer, 2003). α-Keratins can be further classified as the low sulfur containing α-keratins (40–60 kDa) (about 50%–60%) and high sulfur matrix proteins (10–25 kDa). α-Keratins in filament form provide toughness to the hair fibers whereas the α-keratins in matrix proteins provide adhesiveness to cortical cells. Unlike the α-keratins, the β-keratins are synthesized in the form of hard structures (claws and beaks) and are produced in the epidermis of skin appendages (Toni, 2007). β-Keratins have low solubility, have molecular weights between 10 and 25 kDa and are characterized by a distinct X-ray diffraction pattern. Since they form the outer layers, β-keratins have excellent chemical resistance and mechanical strength (Valle, 2010). Filaments in β-keratins have β sheet content that repeats every 3–4 nm and structurally highly resistant compared to α-keratins (Toni, 2007; Valle, 2010). However, the molecular and functional relationship between α- and β-keratins is not clearly understood.

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Table of contents

• Title Page
• Copyright
• Contents
• Chapter 1 Introduction to keratin
• Chapter 2 Extraction of keratin
• Chapter 3 Applications of keratin hydrolysates
• Chapter 4 Films/membranes from keratin and their applications
• Chapter 5 Keratin made into gels
• Chapter 6 Keratin for environmental remediation
• Chapter 7 Biocomposites
• Chapter 8 Fibers from keratin
• Chapter 9 Keratin micro/nanoparticles
• Chapter 10 Miscellaneous applications of keratin
• Index