The Use of Keratin As Potential Biomaterial for Bio-Dental Applications
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Mini Review Open Access Journal of Mini Review Biomedical Science ISSN: 2690-487X The Use of Keratin as Potential Biomaterial for Bio- Dental Applications Lavanya Ajay Sharma, Robert M Love and Ajay Sharma* School of Dentistry and Oral Health, Griffith University, Australia ABSTRACT For a century, keratins extracted from different sources are being used for medical, cosmetic and textile applications. The excellent bioactivity and physiochemical properties of these protein extracts have recently led to the popularity of a keratin as biomaterial. Like other naturally derived biomaterials, keratins have the potential to form a defined, three-dimensional microstructure that supports cell infiltration, proliferation, and cell-guided tissue formation. In addition, the natural abundance, intrinsic biocompatibility, and mechanical durability of keratins have shown promise in the field of biomaterials in diverse biomedical applications. This mini review summarizes the biological properties, explores in brief the extraction methods and advances of keratin as a biomaterial in KEYWORDS:various biomedical and dental applications. Keratin, Scaffold, Biomaterial, Pulp regeneration, Tissue engineering INTRODUCTION fibroin, chitosan and keratin. Of these, keratin have been promising Dental caries is one of the most common prevalent chronic polymers for developing scaffolds for tissue engineering purpose. diseases in the world. Current restorative procedures remove Advances in the extraction, purification, and characterization of the carious tissue and replace it with a dental restorative material. protein have led to fabrication of several physical forms of coatings, However, these materials have little or no ability to remineralize films, foams, sponges and hydrogels [5-7]. Accordingly, a thorough teeth and maintain a good seal, leading to high failure rates [1]. literature search was carried out using different on-line databases Data for 166 million dental restorations in the United States suggest (Ovid, Embase, PubMed, and Web of Science). Articles were selected that more than half were replacements for failed restorations based on keywords such as “keratin,” “scaffold,” “biomaterial,” [2]. Hence, current research in dental material science is focused “regeneration,” and “tissue engineering” in different combinations. on developing bioactive materials regrow lost tissues based on Original research articles and selected review reports, published the principles of tissue engineering. In addition, one of the main in the English language, were included. This was supplemented by focuses in biomaterial research has been to develop scaffolds that a manual search and by examination of the bibliographies of the mimic native tissue in structure and function. For this purpose, identified articles. Research letters to editor, abstract only articles, many investigators have explored the use of natural polymers due posters, unpublished articles and short communications were to their ability to perform very specific biochemical, mechanical and excluded but read to identify potential studies. This review aims structural roles [3]. Natural polymers mimicking the extracellular primarily to present an overview of the biological properties of matrix (ECM) offer advantages of good bioactivity, structural keratin extracts relevant to their role as a biomaterials and further, support and biodegradability over to synthetic polymers [4]. Several to discuss briefly different processing methods followed by a proteins have been investigated in relation to the development of description of both the above-mentioned biopolymer advance as a naturally derived biomaterials, including collagen, albumin, gelatin, potential biomaterial for dental applications. Quick Response Code: Address for correspondence: Ajay Sharma, School of Dentistry and Oral Health, Received: June 16, 2020 Published: August 10, 2020 Griffith University, Australia How to cite this article: . The Use of Keratin as Potential Biomaterial for Bio-Dental Applications. 2020 - 2(5) OAJBS.ID.000204. DOI: 10.38125/ OAJBS.000204 Lavanya AS, Robert ML, Ajay S C 2020 Open Access Journal of Biomedical Science 510 Open Acc J Bio Sci. August - 2(5): 510-516 Ajay Sharma Mini Review KERATIN AS A BIOMATERIAL amino acid sequences are responsible for the distinct structural difference. Most notably, hard keratins contain higher content of Keratins are a class of intermediate filament proteins (IFPs) cysteine residues in their non-helical domains that make them originally comprising the broad category of insoluble proteins that tougher and more durable than the epithelial soft keratins [12]. form the bulk of epidermal structures (i.e., hair, wool, horns, hooves For this reason, the hard keratins have been widely investigated and nails) [8]. Keratins can be also classified as ‘hard-keratin’ or for their use as biomaterials for more several years now. Their ‘soft-keratin’ according the sulphur content [9]. ‘‘Hard’ keratins structural components include outer cuticle, middle cortex and have > 3% wt sulphur content and are primarily present in hair, inner medulla (Figure 1). The bulk of keratins are in the cortex wool, feather, nails and horns [10]. Hard keratins form ordered which can be divided into: (1) low-sulphur, “alpha” keratins which arrays of intermediate filaments (IFs) embedded in a matrix of are about 50-60 % (MW 40-60 kDa), and (2) 20-30 % high-sulphur, cystine rich proteins and contribute to the tough structure of matrix proteins (MW 10-25 kDa). The abundant alpha keratins epidermal appendages. On the other hand, soft keratins (with a are the intermediate filament proteins (IFPs). Keratin IFPs are the sulphur content <3%) consist of loosely packed bundles of IFs that major structural component that imparts mechanical strength, helps in providing mechanical resilience [11]. Both these types of inertness and rigidity [13]. keratins have similar secondary structures but the differences in Figure 1. Early in 1970s the research on extracted keratin proteins was c) They have demonstrated chemotactic and cell instructive focussed on developing different physical forms like films, coatings, capabilities due to the presence of cell adhesion sequences, such as fibres and foams. The potential use of keratin as a biomaterial in glutamic acid-aspartic acid-serine (EDS), arginine–glycine–aspartic medical applications began as early as 1982 when a Japanese acid (RGD) and leucine-aspartic acid-valine (LDV) that mimic the scientist published the first study describing the use of keratin extracellular matrix (ECM) [16,17]. coated, vascular grafts to control bleeding and their proven d) Implanted keratin scaffolds display minimal inflammation, biocompatibility [14]. The main reasons for the use of keratins as a support host tissue vascularization and degrade slowly biomaterial could be listed as: Such desirable biologic properties of keratin, plus its availability a) They are a family of structural proteins with more than 70 from readily renewable natural sources, have fuelled research into homologs, giving rise to an unprecedented biocompatibility keratin as a biomaterial. Much has been done to establish various b) They have an intrinsic ability to self-assemble and suitable methods for the fabrication and characterization of polymerize into porous, fibrous scaffolds [15] keratin-based new products, such as films, coatings or gels, powder, Table 1: Keratin-based products based on films/coatings. sponges, three dimensional scaffolds and fibres (Table 1-3). Experimental Ref. Source Type of Study Application Approach * Keratin + RGDS (blends Excellent substrates for [18] Sheep wool with natural polymers) mammalian cell growth * Keratin films + silk fibronin antithrobogenic properties [19,20] Sheep wool (blends with natural and biocompatibility polymers) * Useful materials for anti- [21] Human hair and nails Keratin films allergic actions. C 2020 Open Access Journal of Biomedical Science 511 Open Acc J Bio Sci. August - 2(5): 510-516 Mini Review Mini Review Ajay Sharma Improved mechanical * Keratin + glycerol + chitosan films (blends with natural properties with [22] Sheep wool polymers); Keratin films antibacterial activity chemically cross-linked Good mechanical properties with EGDE and GDE and biocompatibility * Casting keratin Increased cell growth on [23] Human hair precipitation with TCA and nanosuspension nanosuspension * Alternative for human amniotic membrane [24] Human hair Keratin films for ocular surface * reconstruction Films by solvent Nail plate model for drug [25] Human hair Keratinevaporation + ceramides permeation * Alternative model to assay the in vitro skin [26] Sheep wool membranes to simulate permeability study of small stratum corneum * molecules. Keratin + hydroxyapatite + Cytocompatible with [27] Human hair gentamycin coating antibacterialGood corneal activity ** [28] Human hair Keratin films biocompatibility and Potential scaffolds for Keratin + PLLA transparency * [29] Sheep wool wound dressing and tissue biocomposite films engineering * Potential application [30] Human hair Keratin + minocycline films in periodontal tissue Abbreviations: * in vitro, ** in vivo, RGDS-Cell adhesion peptide Arg-Gly-Asp-Ser; EGDE - Ethylene glycolregeneration diglycidyl ether; GDE-Glycerol diglycidyl ether; TCA-Trichloroacetic acid; bFGF: Basic fibroblast growth factor. Table 2: Based on powders/ sponges / fibres. Experimental Ref. Source Type of Study Application Approach * Support long-term and [31] Sheep wool Keratin