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Keratin Materials
Cosmetics, Hair care & growth, Leather industry, Animal feed,
Tissue engineering, Controlled released & delivery, Vascular graft Wound healing, Hemostasis, Bone regeneration, Peripheral nerve repair,...

Keratin (/ˈkɛrətɪn/[1][2]) is one of a family of fibrous structural proteins. It is the key structural material making up hair, horns, claws, hooves, and the outer layer of human skin. Keratin is also the protein that protects epithelial cells from damage or stress. Keratin is extremely insoluble in water and organic solvents. Keratin monomers assemble into bundles to form intermediate filaments, which are tough and form strong unmineralized epidermal appendages found in reptiles, birds, amphibians, and mammals.[3][4] The only other biological matter known to approximate the toughness of keratinized tissue is chitin.[5][6][7].
https://en.wikipedia.org/wiki/Keratin

Keratin (/ˈkɛrətɪn/[1][2]) is one of a family of fibrous structural proteins. It is the key structural material making up hair, horns, claws, hooves, and the outer layer of human skin. Keratin is also the protein that protects epithelial cells from damage or stress. Keratin is extremely insoluble in water and organic solvents. Keratin monomers assemble into bundles to form intermediate filaments, which are tough and form strong unmineralized epidermal appendages found in reptiles, birds, amphibians, and mammals.[3][4] The only other biological matter known to approximate the toughness of keratinized tissue is chitin.[5][6][7].
https://en.wikipedia.org/wiki/Keratin

Microscopy of keratin filaments inside cells
Examples of occurrence
Keratin filaments are abundant in keratinocytes in the cornified layer of the epidermis; these are proteins which have undergone keratinization. In addition, keratin filaments are present in epithelial cells in general. For example, mouse thymic epithelial cells (TECs) are known to react with antibodies for keratin 5, keratin 8, and keratin 14. These antibodies are used as fluorescent markers to distinguish subsets of TECs in genetic studies of the thymus.     

Additionally, the baleen plates of filter-feeding whales are made of keratin.


Horns such as those of the impalaare made up of keratin covering a core of live bone.
Keratins (also described as cytokeratins) are polymers of type I and type II intermediate filaments, which have only been found in the genomes of chordates (vertebrates, Amphioxus, urochordates). Nematodes and many other non-chordate animals seem to only have type VI intermediate filaments, lamins, which have a long rod domain (vs. a short rod domain for the keratins).
 
Keratins are naturally derived proteins that can be fabricated into several biomaterials morphologies including films, sponges and hydrogels. As a physical matrix, keratin biomaterials have several advantages of both natural and synthetic materials that are useful in tissue engineering and controlled released applications. Like other naturally derived protein biomaterials, such as collagen, keratin possess amino acid sequences, similar to the ones found on extracellular matrix (ECM), that may interact with integrins showing their ability to support cellular attachment, proliferation and migration. The ability of developing biomaterials that mimic ECM has the potential to control several biological processes and this is the case for keratin which has been used in a variety of biomedical applications due to its biocompatibility and biodegradability.
https://pdfs.semanticscholar.org/ab50/ecefd0eb689b0cbd09ddb0589aa865ad1c64.pdf
 
Keratin Application Market Analysis
Cosmetics Hair care & growth Leather industry Animal feed
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Tissue engineering Controlled released & delivery Vascular graft Hemostasis & Wound healing
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Bone regeneration Peripheral nerve repair    
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Extraction of keratin from keratinaceous substrates
Keratins are removed from the cortex first by using chemicals to break the disulfide bonds that are prevalent in keratinized tissues. The alpha and gamma-keratins are converted to their non-crosslinked forms by oxidation [22, 2426] or reduction [22, 27-29], during which cystine is converted to either cysteic acid or cysteine, respectively. The free proteins extracted with denaturating solvents produce a solution that can be purified by filtration and dialysis.

Keratin-based biomaterials fabrication
 The interest of using keratin as a biomaterial in medical applications is based on several key properties that contribute to the overall physical, chemical and biological behavior of these biomaterials. Extracted keratin proteins have an intrinsic ability to self-assemble and polymerize into fibrous and porous films gels and scaffolds. The spontaneous selfassembly of keratin has been studied extensively at both microscale [35-37] and macroscale levels [38]. Furthermore, the presence of cell adhesion sequences, arginine-glycine aspartic acid (RGD) and leucine-aspartic acid-valine (LDV) on the keratin protein derived from wool and hair, makes keratin biomaterials able to support cell attachment and growth.

Keratin Films and Coatings
Keratin films can be prepared by solvent casting. This technology is becoming increasingly attractive for the production of films with extremely high quality requirements. The advantage of this technology includes uniform thickness distribution, maximum optical purity, and extremely low haze and is a technique easy to use. The ability of keratin solution to self-assemble into films was described by Yamauchi et al. [56] and, the physicochemical properties and biodegradability of the solvent-cast keratin films were evaluated. Pure keratin films presented low mechanical strength but the addition of glycerol resulted in transparent films, with increased mechanical strength, flexible and biodegradable both in vitro (trypsin) and in vivo (subcutaneous implantation in mice) [56]. Furthermore, these films proven to promote and increased cell adhesion and growth when compared to collagen and glass.    
 
Keratin 3D-Constructs
The ability of extracted keratin to self-assemble into three dimensional porous structures has led to their development as scaffolds for biomedical applications. The sponge scaffolds were fabricated by lyophilization of an aqueous keratin solution after controlled freezing. This resulted in sponges with homogeneous porous microstructures. Lyophilization or freeze-drying technique is based upon the principle of sublimation. The protein solution, of desired concentration, is frozen and solvent is removed by lyophilization under the high vacuum. Porous structures are formed from the voids left by the removal of the solvent. Thus, the frozen solvent acts as porogen to produce porous materials. The pore size can be controlled by the freezing rate and pH; a fast freezing rate produces smaller pores.

Keratin-based drug delivery systems
Drug delivery which takes into consideration the carrier, the route of administration and the target, has evolved into a strategy of processes and devices designed to enhance the efficacy of therapeutic agents through controlled release. For many drug applications controlled drug delivery has even become a prerequisite to achieve therapeutic efficacy and/or avoid adverse side effects [87, 88]. Controlled drug delivery systems are not only to protect and stabilize the incorporated drug but also help to maintain significant local levels for sustained therapeutic response at low frequency of administration. Biomaterials for controlled drug delivery systems have to meet several requirements.  
A variety of polymers have been investigated for drug delivery purposes However, there remains a need for biomaterials that can be highly controlled in terms of composition and sequence, structure and architecture, mechanical properties and function. To address these requirements, the exploration of keratin as a biomaterial for controlled drug delivery has widely expanded over the last few years. The most common and easiest way of incorporating drugs into keratin biomaterials is by dissolving or mixing them directly into the keratin solution before processing. The challenge of this method is to ensure that there is no detrimental impact of the fabrication process on the integrity and bioactivity of the drug. Keratin can be used to increase the release in highly hydrophobic and non-degradable systems. The release rate can be modulated by film composition and that the mechanism is dominated by film degradation and diffusion [92]. In this way, keratin can be used to increase the release in highly hydrophobic and non-degradable systems. The incorporation of drugs into nanoparticles is another option. It was shown that higher release rates are obtained at intracellular level (higher GSH concentration) with efficient internalization showing the promising applications of keratin-g-PEG as drug carriers for cancer therapy.    

Keratin in biomedical applications   
Keratin have a strong potential for development as clinically relevant biomaterials because they are abundant, bioactive and a realistic source of autologous proteins.

Ocular surface reconstruction:
The results suggested that keratin films could represent the replacement of the amniotic membrane in ophthalmology because keratin films are more transparent and stiffer than AM with similar levels of corneal epithelial cells attachment and proliferation.

Hemostatic agent:
Keratin hydrogels for the treatment of acute myocardial infarction, promoting angiogenesis. It was hypothesized that keratin hydrogel has the ability to adsorb fluid and bind cells to act as an effective hemostatic agent.

Nerve tissue regeneration:
The studies revealed that keratin biomaterial is neuroconductive and contain regulatory molecules capable of enhancing nerve tissue regeneration by enhancing the activity of Schwann cells.

Wound healing:
 Cross-linked keratin powder, films and hydrogels showed significant proliferation of wound healing cell lines like microvascular endothelial cells, keratinocytes and fibroblasts. Moreover, incubation of keratin materials with lymphocytes (T cells) and activated lymphocytes showed, respectively, no proliferation and normal growth, indicating that keratin materials are nonimmunogenic and that the body’s normal cell-mediated immune response is not inhibited by keratin materials.
These were also applied to wounds on animals (rats) and humans, and a faster healing of the wounds treated with keratin materials was observed and, in the human model, with reduced pain [47, 49]. It was investigated the biological mechanism underlying the observed clinical benefits of keratin-based products as wound treatments [109]. The results suggested that the beneficial effects of keratin are related to its positive effects on re-epithelialization via stimulation of keratinocyte migration and production of collagen type IV and VII.  
 
                                                   

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