Keratin as a Protein Biopolymer

What is keratin? And why to use the keratin? Well known that protein is a part of every cell in living organism’s body which plays many different roles to keep living things alive and healthy. The importance of protein for the growth and repair of muscles, bones, skin, tendons, ligaments, hair, eyes, and other tissues is proven since a very long time. Proteins also exist in the form of enzymes and hormones needed for metabolism, digestion, and other important processes. Natural proteins are purified from natural sources. Keratin is among the most copious proteins found associated with the body of reptiles, birds, and mammals. It is a structural constituent of nail, wool, feathers, and hoofs which offers strength to body and muscles. Nowadays, the keratin-rich waste biomass produced from poultry and meat industry imposes serious threat to environment and living beings. We need to explore various techniques and methods for the extractions and use of keratin from waste biomass. From the industrial point of view, keratin is a useful product in the medical, pharmaceutical, cosmetic, and biotechnological industries. Materials obtained from keratin may be converted into porous foam of different sponges, shapes, coatings, mats, microfibers, gels, and materials of high molecular weight. In this chapter, we briefly describe the various sources, properties, and structures of keratin.

Keratin is a global class of biological material, which represents a group of cysteine-rich filament-forming proteins. They serve as a shielding layer for the epidermal appendages like nails, claws, beak, hair, wool, horns, and feathers. These proteins are further subdivided into two different class based on their secondary structure: α-keratin and β-keratin. Keratin is insoluble in hot or cold water; this unique property helps to prevent their digestion by proteolytic enzymes. Additionally, their complex hierarchical-like filament-matrix structure at nanoscale and the polypeptide chains create a robust wall for protection against heat stress, pathogen invasions (particularly through skin), mechanical damage, etc. In this review, we are trying to attempt a linear focus in the direction of structure, function, extraction of keratin, and its industrial applications.

Keratin is a high-sulphur content protein, highly abundant in nature since it is the major component of feathers, hair, wool, horns and nails. In recent years, keratin-based materials have received great consideration due to its unique features in terms of ability to absorb heavy metals and other toxic compounds, thus resulting particularly useful for water and air purification. Moreover, due to its intrinsic efficacy in promoting cells growth, along with its ability to encapsulate both hydrophobic and hydrophilic drugs, keratin has been increasingly studied for the preparation of a wide range of bio-medical devices, especially in the field of tissue engineering and controlled drug delivery. Extraction of keratin from low-cost biomasses deriving from food industry by-products (especially slaughterhouse, dairy and poultry industry) is a challenging process hampered by the presence of a high content of disulphide bonds that bestow the protein with high resistance to chemical, enzymatic and thermal treatments. Thus, the large-scale use of keratin strongly depends on the development of cost-effective and time-efficient extraction methods. This chapter gives an overview on the availability of different keratinous biomasses and examines the various extraction methods proposed in the literature, underlining their advantages and limitations. Moreover, a detailed comparison between the chemical–physical properties of keratins obtained from different biomasses is here reported.

This chapter deals with the various ways in which keratin (extracted from different sources) can be processed to obtain different types of products. In the first section, solvents and polymers that must be employed to make this natural biopolymer usable are discussed. Sections 2–5 are mainly oriented in the transformations of keratin in processes such as spinning, electrospinning, casting, foaming, and freeze-drying. In addition, some products (fibers, nanofibers, films, coating, and sponge) and applications (filtration, adsorption, and scaffolds) corresponding to the procedures mentioned above are reported. The last section is related to the chemical treatments (e.g., crosslinking) applied to keratin to modify its properties.

Keratins are insoluble, fibrous, and structural proteins that are present in the epidermis and its appendages and these include feather, hair, wool, nail, hoof, and horns. Keratins adhere epidermal cells to one another and provide protection on the skin. They are structurally stabilized by their tightly packed peptide chains and the existence of several cross-linkages by disulphide bonds, hydrogen bonding, and hydrophobic interactions. Keratin-containing materials are generated abundantly as by-products of agro-industrial processing and constitute nuisance in the environment as a result of their recalcitrance to degradation by regular proteolytic enzymes like pepsin, trypsin, and papain. The traditional physical and chemical techniques for their treatment are expensive, energy consuming, can damage some essential amino acids, and non-environmentally benign. However, degradation by a variety of microorganisms had proven to be a viable alternative means of keratin treatment. A vast variety of bacteria, fungi, and actinomycetes have been recognized as keratin degraders. They degrade keratins mainly with their keratinases, which sometimes act synergistically with other enzymes like disulfide reductases and cysteine dioxygenase for effective degradation of keratins. The microbial keratinases hydrolyze keratins into soluble proteins, peptides, and amino acids. They are utility enzymes with very diverse biotechnological applications. Biodegradation of keratin-rich wastes by microorganisms is therefore an efficient, cheap, and eco-friendly method of waste management and production of products of high biotechnological value. The present review examines the trends in the role of microorganisms for the biotechnological treatment of keratin-rich wastes.

Keratin has recently gained a lot of limelight among various proteins. Keratin is a renewable, sustainable, biocompatible, and biodegradable bioresource, and these characteristics make it a promising candidate for diverse applications. It is a fibrous protein mainly found in feathers, hair, wool, animal claws, and fingernails. It is one of the key structural materials present in the outer layer of human skin, hence having a lot of applications in developing cosmetics. As an effective biopolymer, keratin containing a different sequence of amino acids have several functional properties and applications. One of the major applications is to be used as a biosorbent in wastewater treatment, which is attributed to expose functional groups present in the highly folded network of amino acids and their modification that improves the reactivity as adsorbent. Keratin-based nanocomposites are used in tissue engineering as it can impart characteristics like increased regeneration and hydration. Another great application in the field of biomedical engineering is drug delivery using keratin-based carriers. Thermoplastics developed from keratins can be used as films in biomedical application. This chapter will highlight the major applications of keratin proteins in detail.

Keratin is a nearly ubiquitous, filamentous protein with high amounts of sulfur molecules. The sulfur content of keratin, resulting from a high proportion of cystine residues, is significant to the form and function of keratin in naturally occurring structures and chemically synthesized biomaterials. The intrinsic physical and chemical properties of keratin have led to the development of a variety of biotechnical and materials science applications. The exploitation of the biochemical and physical properties of this abundant and naturally occurring protein has led to numerous novel uses including drug delivery, dental implants, wound dressings, and food packaging. This chapter describes the intrinsic properties of keratin, as well as the production and use of keratin-based biofilms and biofibers.

The present chapter is aimed towards giving an overview of the applications of keratin as a potential biomaterial substitute in the field of biotechnology. Keratin is a fibrous protein and considered as biomaterial due to its biocompatible and biodegradable characteristics. Its use as biopolymer has been the subject of intense investigation over the past few years. Wool, feather, horn and hooves, etc., are strong in terms of mechanical strength due to the presence of keratin. But once keratin is extracted from natural sources then, it becomes poor in mechanical properties. So, the blending of keratin with other biopolymer can improve the material properties like strength, flexibility, and water vapor permeability. The malleable nature of keratin proves its biotechnological applications such as tissue engineering scaffold, green composites, green cement, bioplastic, etc. The functional groups and chemical structures of keratin govern its properties and morphology, which gives an opportunity to control the design of desired molecular structure for various applications, and varies from industrial to the biotechnological field. Recently, the biodegradable keratin-based biopolymers have gained considerable importance in the medical field as they avoid additional surgery to remove the implants and lack of medical waste burden. Thus, much attention needs to be undertaken on the development of composite biomaterial derived from keratin.