Keratin-based Materials Research Articles

Versatile Keratin Fibrous Adsorbents with Rapid-Response Shape-Memory Features for Sustainable Water Remediation.

Biodegradable shape-memory polymers derived from protein substrates are attractive alternatives with strong potential for valorization, although their reconstruction remains a challenge due to the poor processability and inherent instability. Herein, based on Maillard reaction and immobilization, a feather keratin fibrous adsorbent featuring dual-response shape-memory is fabricated by co-spinning with pullulan, heating, and air-assisted spraying ZIF-8-NH2. Maillard reaction between the amino group of keratin and the carbonyl group of pullulan improves the mechanics and thermal performance of the adsorbent. ZIF-8-NH2 immobilization endows the adsorbent with outstanding multipollutant removal efficiency (over 90%), water stability, and photocatalytic degradation and sterilization performance. Furthermore, the adsorbent can be folded to 1/12 of its original size to save space for transportation and allow for rapid on-demand unfolding (12 s) upon exposure to water and ultraviolet irradiation to facilitate the adsorption and photocatalytic activity with a larger water contact area. This research provides new insight for further applications of keratin-based materials with rapid shape-memory features.

Wool Keratin Nanofibers for Bioinspired and Sustainable Use in Biomedical Field.

Keratin is a biocompatible and biodegradable protein as the main component of wool and animal hair fibers. Keratin-based materials support fibroblasts and osteoblasts growth. Keratin has been extracted by sulphitolysis, a green method (no harmful chemicals) with a yield of 38-45%. Keratin has been processed into nanofibers from its solutions by electrospinning. Electrospinning is a versatile and easy-to-use technique to generate nanofibers. It is an eco-friendly and economical method for the production of randomly and uniaxially oriented polymeric nanofibers. Thanks to their high specific surface area, nanofibers have great potential in the biomedical field. Keratin nanofibers have received significant attention in biomedical applications, such as tissue engineering and cell growth scaffolds, for their biocompatibility and bio-functionality. Accordingly, we propose an extensive overview of recent studies focused on the optimization of keratinbased nanofibers, emphasizing their peculiar functions for cell interactions and the role of additive phases in blends or composite systems to particularize them as a function of specific applications (i.e., antibacterial).

Lignin and Keratin-Based Materials in Transient Devices and Disposables: Recent Advances Toward Materials and Environmental Sustainability.

Rising concerns and the associated negative implications of pollution from e-waste and delayed decomposition and mineralization of component materials (e.g., plastics) are significant environmental challenges. Hence, concerted pursuit of accurate and efficient control of the life cycle of materials and subsequent dematerialization in target environments has become essential in recent times. The emerging field of transient technology will play a significant role in this regard to help overcome current environmental challenges by enabling the use of novel approaches and new materials with unique functionalities to produce devices and materials such as disposable diagnostic devices, flexible solar panels, and foldable displays that are more ecologically benign, low-cost, and sustainable. The prerequisites for materials employed in transient devices and disposables include biodegradability, biocompatibility, and the inherent ability to mineralize or dissipate in target environments (e.g., body fluids) in a short lifetime with net-zero impact. Biomaterials such as lignin and keratin are well-known to be among the most promising environmentally benign, functional, sustainable, and industrially applicable resources for transient devices and disposables. Consequently, considering the current environmental concerns, this work focuses on the advances in applying lignin and keratin-based materials in short-life electronics and single-use consumables, current limitations, future research outlook toward materials, and environmental sustainability.

Physicochemical characterisation of bio-based insulation to explain their hygrothermal behaviour

The utilisation of bio-based building materials as hygric buffers has received recent research interest due to their moisture sorption and thermal behaviours which are positive for indoor comfort. Their hygrothermal properties are known but not fully understood, especially when these bio-based materials are exposed to frequent indoor relative humidity (RH) levels. For the first time, it is identified the characteristics at a micro-level responsible for the hygrothermal performance. Bio-based samples utilised within this paper are: Saw Mill Residue (SMR), Wool 1 (W1), Wool 2(W2), Wood Pellets (WP), Straw (STW) and Wood Wool Board (WWB). Results included thermal analysis (DSC, TGA, DTG), chemical analysis (FTIR) and optical microscopy (SEM) to understand and compare how these bio-based materials behave when stabilised at 53% and 75% RH. For cellulose based samples it was demonstrated that in a dynamic hygrothermal environment SMR and WP are the most hygrothermal stable and for keratin-based materials, W1 is the most stable. For the keratin-based samples when conditioned at 75%, as per the intensity of FTIR spectra, the regularity of molecular chain, W2 has the more ordered material structure but W1 is affected more in terms of hydroxyl absorbance from the spectra. These experiments give a greater insight into the dynamic way in which RH affects the thermal stability of samples. This research paper outlines fundamental differences within materials physical properties and chemical reactions. From the 6 different materials that were used, SMR was demonstrated to be the most thermally stable sample overall.

Selective laser sintering responses of keratin-based bio-polymer composites

Keratin-based materials have unique biological and mechanical attributes due to the protein's molecular structure and organisation. The current study evaluates the possible consolidation of keratin powders by selective laser sintering (SLS), a key enabler of additive manufacturing. The laser energy input became too intense for the thermally sensitive keratin powders. However, polymer keratin composites developed by blending with polyamide and polyethylene powders were evaluated and shown to be suitable for processing by SLS. Blends were thermally characterised to establish the initial process conditions. Morphological evaluation of the initial sintered samples allowed optimisation of the energy densities. Mechanical responses of the samples produced under these conditions were evaluated. Polymer-keratin composites were established as candidate materials for SLS. Critical attributes of these material combinations require further optimisation before these materials would be competitive in the market place.

Thermal insulation design bioinspired by microstructure study of penguin feather and polar bear hair

Nature is an amazing source of inspiration for the design of thermal insulation strategies, which are key for saving energy. In nature, thermal insulation structures, such as penguin feather and polar bear hair, are well developed; enabling the animals’ survival in frigid waters. The detailed microscopy investigations conducted in this study, allowed us to perform microstructural analysis of these thermally insulating materials, including statistical measurements of keratin fiber and pore dimensions directly from high resolution Scanning Electron Microscope (SEM) images. The microscopy study revealed many similarities in both materials, and showed the importance of their hierarchically-organized porous structure. Finally, we propose the schematic configuration of a thermally-insulating structure, based on the penguin feather and polar bear hair. These optimized thermal-insulator systems indicate the road maps for future development, and new approaches in the design of material properties. Statement of significanceWe present the first detailed comparison of microstructures of penguin feather and polar bear hair for designing optimum thermal insulation properties. This unique study involves the measurement of the sizes of pores and fibers of these two keratin-based materials, including the investigation of their 3D arrangements. We revealed porosity interconnection, especially in polar bear hair, which is one of the key designs exhibited by thermal insulation materials.

Possible beneficiation of waste chicken feathers via conversion into biomedical applications

Keratin-based waste materials such as wool and waste chicken feathers are driving investigations to beneficiate them. The poultry industry in South Africa generates about 230 million kg of waste chicken feathers per annum, which makes them the abundant keratin source. most of which is disposed of by landfilling or combustion. The current disposal techniques through landfilling or combustion are not environmentally friendly. Thus, methods for beneficiation of the waste are needed. Considering that chicken feathers are comprised of mainly keratin, it is plausible that the keratin can be exploited for application in biomedical applications. However, keratin biomaterials have not found a breakthrough in clinical applications. The keratin can be recovered in the form of fibres or dissolved from feathers in suitable solvents. Regenerated keratin biomaterials can take the form of hydrogels, membranes, films, sponges, scaffolds, and nanofibres. These materials possess excellent properties that can be applied to different fields, including the health sector. Currently, there is no review paper that puts together all possible beneficiations of waste chicken feathers keratin in biomedicine. Therefore, this work exposes the chemistry and characteristics of keratin from different sources including chicken feather keratin in relation to their potential use in the biomedical applications. This review also highlights the properties of regenerated keratin and corresponding biomaterials, including electrospun regenerated keratin fibres for biomedical applications. Keratin nanofibres, also possess advanced properties for biomedical applications due to nanofibres reception in medical applications. Keratin is one biopolymer that can function as an acceptable biopolymer. The review indicates that there is a need for biopolymers as many fields rely on petroleum-based polymers which tend to have biocompatibility limits and are unsustainably resourced.

Методи екстракції кератинів із вовни та волосся і перспективи їхнього застосування в біомедицині й біоінженерії

The present article gives the overview of scientific information on the hair structure, the structural and functional properties of keratins, and methods of their extracting from the natural fibers. The article substantiates an importance of keratin extraction by breaking the disulfide bonds and converting the keratin into a soluble form while maintaining covalent bonds. Such extraction preserves the native properties of these proteins, that ensures their further use as functional biomaterials. The examples of such properties are: resistance of keratin to the effects of chemical and biological factors (due to high frequency of disulfide bonds that make a large number of chemical modifications of proteins possible) and high biocompatibility and low cytotoxicity of keratin-based preparations (due to a similarity of keratin to the extracellular matrix of biological tissues). The keratin-based materials, obtained by this way and then lyophilized, can form fibrillar structures when a particular solvent is selected. The methods of keratins extraction, as well as the efficiency and electrophoretic profiles of obtained extracts, were also analyzed. The purposeful extraction is carried out by the methods based on oxidation, reduction, and sulfitolysis reactions. The oxidation reactions of keratin are irreversible and cause the oxidation of cysteine residues to cysteic acid with the formation of keratosis. At the same time, keratin is obtained due to a reduction reactions. As a result of the reversible process of sulfitolysis, the S-sulfonate anion is formed. The paper also considers promising applications of extracted keratin in biomedicine and bioengineering. The biomedical technologies are related to the effective treatment of hair pathologies. The second area is the creation of keratin-based biomaterials with a wide range of applications, such as tissue engineering, reparative medicine, textile industry, agriculture, cosmetology, and production of cleaning equipment. The third area of keratins application is the identification of a person. Such application makes an important contribution to the anthropological research and forensic science. High resistance of hair proteins to adverse environmental conditions makes this area very promising. Keywords: hair, keratins, extraction

Synthesis and fabrication of a keratin-conjugated insulin hydrogel for the enhancement of wound healing

Accelerating and regulating collagen formation during wound healing repair is key issues for skin regeneration. Insulin can promote the healing of damaged skin by stimulating cellular migration and angiogenesis. Here, human hair keratin-conjugated insulin was synthesized to enhance full-thickness skin regeneration based on the excellent wound healing and hemostatic effects of keratin and the collagen deposition regulation ability of insulin. The insulin-conjugated keratin (Ins-K) was synthesized through the EDC/NHS reaction, which can supply a sustained release of insulin. The Ins-K hydrogel displayed similar water absorption, porosity and rheology properties to those of the keratin hydrogel. However, the Ins-K hydrogel shows a stronger hemostatic ability than the keratin hydrogel group, with a stronger wound healing effect found for the Ins-K hydrogel in the early regeneration stage (first 2 weeks) than for the keratin hydrogel treatment, resulting in smoother skin tissues at an excision section realized by regulating transforming growth factor β1 (TGF-β1) and hydroxyproline (HYP) expression. The results demonstrate that keratin promotes hemostasis and wound healing after insulin conjugation, which highlights the potential of keratin-based materials in tissue regeneration applications.

Oxidative Modification of Trichocyte Keratins.

Oxidation of keratin results in a range of deleterious effects, including discolouration and compromised physical and mechanical properties. Keratin oxidative degradation is driven by molecular-level events, with accumulation of modifications at the protein primary level resulting directly in changes to secondary, tertiary and quaternary structure, as well as eventually changes in the observable physical and chemical properties. Advances in proteomic analysis techniques provide an increasingly clearer insight into the cascade of molecular modification underpinning keratin oxidation and how this translates through to higher order changes in properties. This chapter summarises the effects of oxidation on keratin-based materials, the types of molecular modification associated with this, and advances in techniques and approaches for characterising this modification.

Quantitative Change in Disulfide Bonds and Microstructure Variation of Regenerated Wool Keratin from Various Ionic Liquids

Ionic liquids (ILs) have been employed as solvents for dissolving wool keratin which can be further regenerated and applied in high-value and biocompatible keratin-based materials. It is urgent to determine the changes in disulfide bonds and keratin microstructures in the dissolution process for designing efficient ILs. Herein, the breakage of disulfide bonds by ILs was verified for the first time using a model compound, oxidized glutathione. Furthermore, at least 65% of disulfide bonds in keratin should be cleaved in order to be dissolved in ILs. The keratin regenerated in a series of ILs, and variable conditions were also characterized by a combination of S-linked techniques. The results indicated that changing both anions and cations can lead to a dramatically different ability to cleave disulfide bonds, while the side chains of the cations have little effect on it. Also, the dissolution variables, such as temperature and time, led to different amounts of disulfide bonds remaining in the regenerated ke...

Keratose/poly (vinyl alcohol) blended nanofibers: Fabrication and biocompatibility assessment

Increasing interest in using keratin-based materials for biomedical application has prompted the development of keratin/PVA nanofibers. To date, several kinds of keratins (including wool, feather, and human hair reductive keratins)/PVA blended nanofibers have been fabricated but limited to the in vitro studies. However, few studies focused on the in vivo biocompatibility test of keratin/PVA nanofibers. Herein, the keratose (oxidative keratin)/PVA nanofiber, a novel type of keratin/PVA nanofiber, was fabricated with an electrospinning technique. The obtained nanofibers possess uniform fibrous structure, suitable hydrophilicity and mechanical properties, which could be affected by the mass ratio of keratose to PVA. Furthermore, the biocompatibility tests of keratose/PVA nanofibers have been performed by subcutaneous implantation into SD rats. H&E staining and Masson's trichrome staining revealed that the implants were highly compatible with body tissue, and no acute toxic effects as well as no tissue damage were observed. The implants were fully degraded within four weeks. Beyond this, the analysis of proinflammatory cytokines in rat serum indicated that the implants induced normal immune response and had no immunogenicity. These results demonstrate that keratose/PVA nanofibers have the potential for biomedical applications due to the favorable biocompatibility and biodegradability.

Culturing fibroblasts in 3D human hair keratin hydrogels.

Human hair keratins are readily available, easy to extract, and eco-friendly materials with natural bioactivities. Keratin-based materials have been studied for applications such as cell culture substrates, internal hemostats for liver injury, and conduits for peripheral nerve repair. However, there are limited reports of using keratin-based 3D scaffolds for cell culture in vitro. Here, we describe the development of a 3D hair keratin hydrogel, which allows for living cell encapsulation under near physiological conditions. The convenience of making the hydrogels from keratin solutions in a simple and controllable manner is demonstrated, giving rise to constructs with tunable physical properties. This keratin hydrogel is comparable to collagen hydrogels in supporting the viability and proliferation of L929 murine fibroblasts. Notably, the keratin hydrogels contract less significantly as compared to the collagen hydrogels, over a 16-day culture period. In addition, preliminary in vivo studies in immunocompetent animals show mild acute host tissue response. These results collectively demonstrate the potential of cell-loaded keratin hydrogels as 3D cell culture systems, which may be developed for clinically relevant applications.

Dissolution and regeneration of wool via controlled disintegration and disentanglement of highly crosslinked keratin

For the first time, pure protein fibers with good mechanical properties were obtained from waste wool after effective de-crosslinking and disentanglement of the highly crosslinked keratin. Every year, more than 1.6 billion pounds of wool keratin-based materials were discarded. Effort has been devoted to convert the keratin resources into high value-added products, especially fibers. In 1940s, pure keratin fibers had been developed from feathers. However, after trying the method, we found the results were not repeatable and did not find any other successful repetition. So far, no effective dissolution and spinning methods have been developed to obtain pure keratin fibers with potential for real applications. In this research, keratin with preserved backbones after de-crosslinking was obtained. Subsequently, surfactant endowed the keratin with satisfactory stretchability for fiber spinning. Fibers of 20 μm with good tensile strength were successfully developed. The technology could be applied onto other highly crosslinked proteins, including feather keratin from poultry industry, sorghum protein and soy protein in bioenergy co-products for production of various industrial products.

Blend films of human hair and cellulose prepared from an ionic liquid

Human hair keratin/cellulose blend films were prepared in 1-butyl-3-methylimidazoles chloride ([BMIM]Cl) ionic liquid (IL), by the combination of human hair keratin and cotton fibers in different mass proportion, and these films were formed subsequently from the coagulated solutions. The hair/cellulose blend films were prepared by taking different weight ratios of hair and cellulose in ILs, dissolving them individually and mixing them with each other. For example, 90/10 hair /cellulose blends were prepared by mixing hair solution (9 g of 8wt% hair/[BMIM]Cl) and cellulose solution (1 g of 8wt% cellulose/[BMIM]Cl) together to get a mixture solution, and stirring them at 80℃ for 1 h in order to ensure complete intermixing. Then hair/cellulose blend films were obtained. The tests indicated that there was a good compatibility between human hair and cellulose in the regenerated human hair/cellulose blends as determined by Fourier transform infrared spectroscopy and transmission of light. The crystallization behavior and scanning electron microscope photograph showed that human hair and cellulose are miscible. The films were analyzed by thermogravimetric and differential scanning calorimetry; the results showed that the blend films exhibited an increasing trend of the mechanical property and thermal stability with increase in cellulose content in the blends. This could be used for the development of keratin-based materials with improved mechanical properties.

Progresses in treatment of collagen and keratin-based materials with silver nanoparticles

Abstract The treatment of chromium tanned sheepskins with poly(hydroxyl urethane) and dispersion of chemically synthesized nanosilver showed the best resistance to fungi and bacterial exposure tests. These collagen-based materials containing different amounts of nanosilver were investigated by Atomic Absorption Spectroscopy, Atomic Force Microscopy and Scanning Electron Microscopy coupled with Energy Dispersive X-Ray Spectroscopy. The influence of sheepskins treated with silver nanoparticles on the wound healing process was assessed and the nanoparticles concentration seems to have a positive effect up to 370 ppm and does not influence the inflammatory process above this concentration.

Keratin-based antimicrobial textiles, films, and nanofibers.

The combination of appealing structural properties, biocompatibility, and the availability of renewable and inexpensive raw materials, make keratin-based materials attractive for a variety of applications. In this paper, we report on the antimicrobial functionalization of keratin-based materials, including wool cloth and regenerated cellulose/keratin composite films and nanofibers. The functionalization of these materials was accomplished utilizing a facile chlorination reaction that converts the nitrogen-bearing moieties of keratin into halamine compounds. Halamine-charged wool cloth exhibited rapid and potent bactericidal activity against several species of bacteria and induced up to a 5.3 log (i.e., 99.9995%) reduction in the colony forming units of Bacillus thuringiensis spores within 10 min. Keratin-containing composites were prepared by the spin coating and coaxial electrospinning of extracted/oxidized alpha-keratin and cellulose acetate (CA) solubilized in formic acid, followed by CA deacetylation. Regenerated cellulose/keratin materials chlorinated to display halamines were also effective in killing Escherichia coli and Staphylococcus aureus bacteria. Electrospun core/shell nanofibers engineered to maximize keratin-Cl surface area displayed higher activity against S. aureus than films composed of the same materials. The halamine-based antimicrobial functionalization methods demonstrated for keratin-based materials in this paper are anticipated to translate to other protein biopolymers of interest to the biomaterials community.

The Structure, Functions, and Mechanical Properties of Keratin

Keratin is one of the most important structural proteins in nature and is widely found in the integument in vertebrates. It is classified into two types: α-helices and β-pleated sheets. Keratinized materials can be considered as fiber-reinforced composites consisting of crystalline intermediate filaments embedded in an amorphous protein matrix. They have a wide variety of morphologies and properties depending on different functions. Here, we review selected keratin-based materials, such as skin, hair, wool, quill, horn, hoof, feather, and beak, focusing on the structure–mechanical property-function relationships and finally give some insights on bioinspired composite design based on keratinized materials.

Keratin–hydroxyapatite composites: Biocompatibility, osseointegration, and physical properties in an ovine model

Reconstituted keratin has shown promise as an orthopaedic biomaterial. This in vivo study investigates the biological response of composite materials prepared from reconstituted keratin containing a high content of hydroxyapatite (HA) (40 wt % HA), implanted for up to 18 weeks in the long bones of sheep. Keratin-HA composites were compared with a commercially available polylactic acid (PLA) HA composite (BIO RCI HA®, Smith and Nephew). Porous keratin-HA materials displayed excellent biocompatibility and osseointegration, with full integration into bone by 12 weeks. Dense keratin-HA materials also showed excellent biocompatibility, with a more limited osseointegration, involving the penetration of new bone into the periphery of the implant after eight weeks. In contrast, the PLA-HA implant did not integrate with surrounding tissue. Microindentation showed that porous keratin-HA implants were initially soft, but became stiffer as new bone penetrated the implant from four weeks onwards. In contrast, although the initial rigidity of dense keratin-HA composites was maintained for at least two weeks, the implant material weakened after four weeks. The PLA-HA implant maintained its physical properties throughout the course of the trial. This study demonstrates the increased osseointegration/osteoconduction capacity of keratin-HA composites and provides further evidence supporting the suitability of keratin-based materials, such as bone graft substitutes and soft tissue fixation devices.