Human hair keratin and its-based biomaterials for biomedical applications

Harnessing the potential of microbial keratinases for bioconversion of keratin waste

The increasing global consumption of poultry meat has led to the generation of a vast quantity of feather keratin waste daily, posing significant environmental challenges due to improper disposal methods. A growing focus is on utilizing keratinous polymeric waste, amounting to millions of tons annually. Keratins are biochemically rigid, fibrous, recalcitrant, physiologically insoluble, and resistant to most common proteolytic enzymes. Microbial biodegradation of feather keratin provides a viable solution for augmenting feather waste's nutritional value while mitigating environmental contamination. This approach offers an alternative to traditional physical and chemical treatments. This review focuses on the recent findings and work trends in the field of keratin degradation by microorganisms (bacteria, actinomycetes, and fungi) via keratinolytic and proteolytic enzymes, as well as the limitations and challenges encountered due to the low thermal stability of keratinase, and degradation in the complex environmental conditions. Therefore, recent biotechnological interventions such as designing novel keratinase with high keratinolytic activity, thermostability, and binding affinity have been elaborated here. Enhancing protein structural rigidity through critical engineering approaches, such as rational design, has shown promise in improving the thermal stability of proteins. Concurrently, metagenomic annotation offers insights into the genetic foundations of keratin breakdown, primarily predicting metabolic potential and identifying probable keratinases. This may extend the understanding of microbial keratinolytic mechanisms in a complex community, recognizing the significance of synergistic interactions, which could be further utilized in optimizing industrial keratin degradation processes.

Advanced Triboelectric Applications of Biomass-Derived Materials: A Comprehensive Review

The utilization of triboelectric materials has gained considerable attention in recent years, offering a sustainable approach to energy harvesting and sensing technologies. Biomass-derived materials, owing to their abundance, renewability, and biocompatibility, offer promising avenues for enhancing the performance and versatility of triboelectric devices. This paper explores the synthesis and characterization of biomass-derived materials, their integration into triboelectric nanogenerators (TENGs), and their applications in energy harvesting, self-powered sensors, and environmental monitoring. This review presents an overview of the emerging field of advanced triboelectric applications that utilize the unique properties of biomass-derived materials. Additionally, it addresses the challenges and opportunities in employing biomass-derived materials for triboelectric applications, emphasizing the potential for sustainable and eco-friendly energy solutions.

Keratin as an effective coating material for in vitro stem cell culture, induced differentiation and wound healing assays

The utilization of stem cells in tissue engineering holds great promise as efficient tools for tissue regeneration and in treating numerous musculoskeletal diseases. However, several limiting factors, such as precise delivery and control of differentiation of these stem cells as well as mimicking the microenvironment required to modulate stem cell behaviour in-vivo, have given rise to an urgent need for the development of new biomaterials which could be tailored to enhance cell renewal and/or direct cell fates. Keratin-rich biological materials offer several advantages, such as biocompatibility, tailorable mechanical properties, huge bioavailability, non-toxicity, non-immunogenic, and intrinsic tissue repair and/or regeneration capabilities, which makes them highly valued. In the present work, we report the preparation of keratin-based bio-materials from goat hair waste and its effectiveness as a coating material for in vitro culture and induced differentiation of mesenchymal stem cells (MSC's) and primary goat fibroblast cells. Since no known keratinase enzymes are expressed as such in human and/or animal systems, these keratin biomaterials could be used to slow the rate of degradation and deliver keratin-loaded stem cell scaffolds to induce their directed differentiation in vivo. The generated keratin materials have been characterized for surface morphology, protein structures, size and other properties using SDS-PAGE, LC/MS-MS, SEM, FTIR etc. Also, in vitro cell culture assays such as cell adhesion, viability using MTT, live dead assays, differentiation assays and in vitro scratch/wound healing assays were performed. Our results provide important data supporting tissue engineering applications of these keratinous biomaterials by combining the unique biological characteristics of goat hair-derived keratin material with the regenerative power of stem cells and their combinatorial use in applications such as disease treatment and injury repair as well as their use in the preparation of wound healing products, such as dressings and bandages, for management of clinical care in animals.

Endothelium-Mimicking Bilayer Vascular Grafts with Dual-Releasing of NO/H2S for Anti-Inflammation and Anticalcification

Vascular complications caused by diabetes impair the activities of endothelial nitric oxide synthase (eNOS) and cystathionine γ-lyase (CSE), resulting in decreased physiological levels of nitric oxide (NO) and hydrogen sulfide (H2S). The low bioavailability of NO and H2S hinders the endothelialization of vascular grafts. In this study, endothelium-mimicking bilayer vascular grafts were designed with spatiotemporally controlled dual releases of NO and H2S for in situ endothelialization and angiogenesis. Keratin-based H2S donor was synthesized and electrospun with poly(l-lactide-co-ε-caprolactone) (PLCL) as the outer layer of the graft to release H2S. Hyaluronic acid, one of the major glycosaminoglycans in endothelial glycocalyx, was complexed with Cu ions as the inner layer to mimic glutathione peroxidase (GPx) and maintain long-term physiological NO flux. The synergistic effects of NO and H2S of bilayer grafts selectively promoted the regeneration and migration of human umbilical vascular endothelial cells (HUVECs), while inhibiting the overproliferation of human umbilical artery smooth muscle cells (HUASMCs). Bilayer grafts could effectively prevent vascular calcification, reduce inflammation, and alleviate endothelial dysfunction. The in vivo study in a rat abdominal aorta replacement model for 1 month showed that the graft had a good patency rate and had potential for vascular remodeling in situ.

Recent advances in keratin for biomedical applications

The development of keratin-based biomaterials provides an approach to addressing related environmental pollutants and turns waste into wealth. Keratin possesses various merits, such as biocompatibility, biodegradability, hemostasis, non-immunogenicity, antibacterial activity, antioxidation, multi-responsiveness, and abundance in nature. Additionally, keratin biomaterials have been extensively employed in various biomedical applications such as drug delivery, wound healing, and tissue engineering. This review focuses on the properties and biomedical applications of keratin biomaterials. It is anticipated to provide valuable insights for the research and development of keratin biomaterials.

Aligned Ice Templated Biomaterial Strategies for the Musculoskeletal System

Aligned pore structures present many advantages when conceiving biomaterial strategies for treatment of musculoskeletal disorders. Aligned ice templating (AIT) is one of the many different techniques capable of producing anisotropic porous scaffolds; its high versatility allows for the formation of structures with tunable pore sizes, as well as the use of many different materials. AIT has been found to yield improved compressive properties for bone tissue engineering (BTE), as well as higher tensile strength and optimized cellular alignment and proliferation in tendon and muscle repair applications. This review evaluates the work that has been done in the last decade toward the production of aligned pore structures by AIT with an outlook on the musculoskeletal system. This work describes the fundamentals of the AIT technique and focuses on the research carried out to optimize the biomechanical properties of scaffolds by modifying the pore structure, categorizing by material type and application. Related topics including growth factor incorporation into AIT scaffolds, drug delivery applications, and studies about immune system response will be discussed.

In Situ Synthesis of Keratin and Melanin Chromophoric Submicron Particles

In humans, melanin plays an esthetic role, dictating hair and skin color and traits, while keratin is the protein that comprises most of the epidermis layer. Eumelanin and pheomelanin are types of melanin synthesized from the same building blocks via enzymatic oxidation. Pheomelanin has an additional building block, cysteine amino acid, which affects its final structure. Keratin contains high cysteine content, and by exploiting free thiols in hydrolyzed keratin, we demonstrate the formation of keratin-melanin (KerMel) chromophoric submicron particles. Cryo-TEM analyses found KerMel particle sizes to be 100-300 nm and arranged in the form of a central keratin particle with polymerized l-dopa chains. Attenuated total reflection (ATR)-FTIR, UV-vis, and fluorescence measurements identified new chemical bonds, indicating the formation of KerMel particles. Finally, KerMel replicated natural skin tones and proved cytocompatibility for human epidermal keratinocytes at concentrations below 0.1 mg/mL. Taken together, KerMel is a novel, tunable material that has the potential to integrate into the cosmetic industry.

An in vitro analysis of the hemostatic efficacy of fibrinogen precipitation with varied keratin fraction compositions

In preclinical studies, human hair has demonstrated effective hemostatic properties, potentially attributed to keratin proteins facilitating rapid conversion of fibrinogen to fibrin during coagulation. However, the rational use of human hair keratin for hemostasis remains unclear, given its complex mixture of proteins with diverse molecular weights and structures, leading to variable hemostatic capacity. To optimize the rational utilization of human hair keratin for hemostasis, we investigated the effects of different keratin fractions on keratin-mediated fibrinogen precipitation using a fibrin generation assay. Our study focused on high molecular weight keratin intermediate filaments (KIFs) and lower molecular weight keratin-associated proteins (KAPs) combined in various ratios during the fibrin generation. Scanning electron microscope analysis of the precipitates revealed a filamentous pattern with a broad distribution of fiber diameters, likely due to the diversity of keratin mixtures involved. An equal proportion of KIFs and KAPs in the mixture yielded the most extensive precipitation of soluble fibrinogen in an in vitro study, potentially due to structure-induced exposure of active sites. However, all hair protein samples exhibited diverse catalytic behaviors compared to thrombin, highlighting the potential of utilizing specific hair fractions to develop hair protein-based hemostatic materials with optimized capacity.

Chlorhexidine-loaded polysulfobetaine/keratin hydrogels with antioxidant and antibacterial activity for infected wound healing

Multifunctional hydrogel dressings are promising for wound healing. In the study, chlorhexidine(CHX) loaded double network hydrogels were prepared by free radical polymerization of sulfobetaine and oxidative self-crosslinking of reduced keratin. The introduced keratin and CHX endowed hydrogels with cytocompatibility, antioxidant capability as well as enhanced antibacterial activity due to the antifouling property of polysulfobetaine. These hydrogels exhibited acidity, glutathione(GSH), and trypsin triple-responsive release behaviors, resulting in the accelerated release of CHX under wound microenvironments. Intriguingly, the freeze-drying hydrogels could be ground to powders and sprinkled on the irregular wound bed, followed by absorbing wound fluid to reform hydrogel in situ. These aerogel powders were more convenient for sterilization, formulation, and storage. Further, these aerogel powders could be rejected after being mixed with an appropriate amount of water. In vivo infected wound healing confirmed that the aerogel powder dressing significantly promoted collagen deposition and reduced inflammation, thereby accelerating the closure and regeneration of skin wounds. Taken together, these degradable aerogel powders have great potential applications for wound healing.

Synthesis, characterization and optimization of chicken bile-mediated silver nanoparticles: a mechanistic insight into antibacterial and antibiofilm activity

The fast-growing urbanization and slow progress in the field of waste management have led to the accumulation of large quantities of animal wastes. The present work focused on the synthesis of low-cost and eco-friendly chicken bile juice-mediated silver nanoparticles (BJ-AgNP). Results reveal that bile juices have enough potentiality towards the synthesis of almost uniform sizes (average size < 50 nm) of BJ-AgNPs which remains stable for more than 6 months. Response surface methodology (RSM) successfully demonstrated the optimised condition of BJ-AgNP synthesis. Factors like concentration of salt and bile extract and temperature are significantly responsible for nanoparticle synthesis. The synthesis of nanoparticle was further characterized using UV-Vis, TEM, FESEM, XRD, FTIR, TGA, and EDS. The synthesised nanoparticle showed excellent bactericidal activity against both Gram positive and Gram negative bacteria with MIC and MBC of 40 and 50 μg/mL for Bacillus subtilis (MTCC-441) and 60 and 60 μg/mL for Eschecheria coli (MTCC-1687) respectively. The synthesised nanoparticle also exhibited as an antibiofilm activity against B. subtilis, with ~89% biofilm inhibition efficacy at 4 X MIC, having optimal bacterial concentration of 10⁶ CFU/mL. Therefore, the present findings clearly demonstrated that an absolute animal waste could be a valuable ingredient in the field of therapeutic nanoscience.

Novel PLCL nanofibrous/keratin hydrogel bilayer wound dressing for skin wound repair

In this study, a novel poly(L-lactate-caprolactone) copolymer (PLCL) nanofibrous/keratin hydrogel bilayer wound dressing loaded with fibroblast growth factor (FGF-2) was prepared by the low-pressure filtration-assisted method. The ability of the keratin hydrogel in the bilayer dressing to mimic the dermis and that of the nanofibrous PLCL to mimic the epidermis were discussed. Keratin hydrogel exhibited good porosity and maximum water absorption of 874.09%. Compared with that of the dressing prepared by the coating method, the interface of the bilayer dressing manufactured by the low-pressure filtration-assisted method (filtration time: 20 min) was tightly bonded, and its bilayer dressing interface could not be easily peeled off. The elastic modulus of hydrogel was about 44 kPa, which was similar to the elastic modulus of the dermis (2-80 kPa). Additionally, PLCL nanofibers had certain toughness and flexibility suitable for simulating the epidermal structures. In vitro studies showed that the bilayer dressing was biocompatible and biodegradable. In vivo studies indicated that PLCL/keratin-FGF-2 bilayer dressing could promote re-epithelialization, collagen deposition, skin appendages (hair follicles) regeneration, microangiogenesis construction, and adipose-derived stem cells (ADSCs) recruitment. The introduction of FGF-2 resulted in a better repair effect. The bilayer dressing also solved the problems of poor interface adhesion of hydrogel/electrospinning nanofibers. This paper also explored the preliminary role and mechanism of bilayer dressing in promoting skin healing, showing that its potential applications as a biomedical wound dressing in the field of skin tissue engineering.

Tannic Acid-Assisted Immobilization of Copper(II), Carboxybetaine, and Argatroban on Poly(ethylene terephthalate) Mats for Synergistic Improvement of Blood Compatibility and Endothelialization

Due to thrombosis and intimal hyperplasia, small-diameter vascular grafts have poor long-term patency. A combination strategy based on nitric oxide (NO) and anticoagulants has the potential to address those issues. In this study, poly(ethylene terephthalate) (PET) mats were prepared by electrospinning and coated with tannic acid (TA)/copper ion complexes. The chelated copper ions endowed the mats with sustained NO generation by catalytic decomposition of endogenous S-nitrosothiol. Subsequently, zwitterionic carboxybetaine acrylate (CBA) and argatroban (AG) were immobilized on the mats. The introduced AG and CBA had synergistic effects on the improvement of blood compatibility, resulting in reduced platelet adhesion and prolonged blood clotting time. The biocomposite mats selectively promoted the proliferation and migration of human umbilical vein endothelial cells while inhibiting the proliferation and migration of human umbilical arterial smooth muscle cells under physiological conditions. In addition, the prepared mats exhibited antibacterial activity against Escherichia coli and Staphylococcus aureus. Collectively, the prepared mats hold great promise as artificial small-diameter vascular grafts.

Keratin-mediated hair growth and its underlying biological mechanism

Here we show that intradermal injection of keratin promotes hair growth in mice, which results from extracellular interaction of keratin with hair forming cells. Extracellular application of keratin induces condensation of dermal papilla cells and the generation of a P-cadherin-expressing cell population (hair germ) from outer root sheath cells via keratin-mediated microenvironmental changes. Exogenous keratin-mediated hair growth is reflected by the finding that keratin exposure from transforming growth factor beta 2 (TGFβ2)-induced apoptotic outer root sheath cells appears to be critical for dermal papilla cell condensation and P-cadherin-expressing hair germ formation. Immunodepletion or downregulation of keratin released from or expressed in TGFβ2-induced apoptotic outer root sheath cells negatively influences dermal papilla cell condensation and hair germ formation. Our pilot study provides an evidence on initiating hair regeneration and insight into the biological function of keratin exposed from apoptotic epithelial cells in tissue regeneration and development.

Biocompatibility and antioxidant activity of a novel carrageenan based injectable hydrogel scaffold incorporated with Cissus quadrangularis: an in vitro study

Background

Over the past years, polysaccharide-based scaffolds have emerged as the most promising material for tissue engineering. In the present study, carrageenan, an injectable scaffold has been used owing to its advantage and superior property. Cissus quadrangularis, a natural agent was incorporated into the carrageenan scaffold. Therefore, the present study aimed to assess the antioxidant activity and biocompatibility of this novel material.

Methods

The present in vitro study comprised of four study groups each constituting a sample of 15 with a total sample size of sixty (n = 60). The carrageenan hydrogel devoid of Cissus quadrangularis acted as the control group (Group-I). Based on the concentration of aqueous extract of Cissus quadrangularis (10% w/v, 20% w/v and 30% w/v) in carrageenan hydrogel, respective study groups namely II, III and IV were considered. Antioxidant activity was assessed using a 1,1-diphenyl-2-picrylhydrazyl radical scavenging assay, whereas the biocompatibility test was performed using a brine shrimp lethality assay. The microstructure and surface morphology of the hydrogel samples containing different concentrations of Cissus quadrangularis aqueous extract was investigated using SEM. One-way ANOVA with the post hoc tukey test was performed using SPSS software v22.

Results

A significant difference (P < 0.05) in the antioxidant activity was observed among the study groups. Group III reported the highest activity, whereas the control group showed the least antioxidant activity. Additionally, a significant (P < 0.01) drop in the antioxidant activity was observed in group IV when compared with group III. While assessing the biocompatibility, a significant (P < 0.001) dose-dependent increase in biocompatibility was observed with the increasing concentration of aqueous extract of Cissus quadrangularis. SEM analysis in group III showed even distribution throughout the hydrogel although the particles are close and densely arranged. Reduced antioxidant activity in group IV was probably due to clumping of the particles, thus reducing the active surface area.

Conclusion

Keeping the limitations of in vitro study, it can be assumed that a carrageenan based injectable hydrogel scaffold incorporated with 20% w/v Cissus quadrangularis can provide a favourable micro-environment as it is biocompatible and possess better antioxidant property.

Division of force among layers constituting human hair during bending and tension

Human hair is a three-layered structure comprising the inner medulla, middle cortex, and outer cuticle layer. When a hair is subjected to bending or tensile load, each of these layers absorbs a certain amount of the force applied. However, the magnitude of the force absorbed by each layer is not easy to estimate. This is because, in addition to Young's modulus of each layer, the absorption depends on the area of each layer as seen in the cross-section. This study used a strategic way of combining experiment and theory and found that Young's modulus of the cuticle layer changes in the face of bending and tension. Considering this, the ratio of force sharing inside a human hair was estimated. Bending and tensile tests were conducted on single human hairs to determine the structural elasticity for both deformations which expresses the deformability of the hair independent of its external dimensions. Moreover, Young's modulus of each layer was determined by nanoindentation of hair cross-section. By comparing the structural elasticity determined experimentally with that determined theoretically, Young's modulus of the cuticle layer against tension was found to be 25% of that against bending. Based on this finding, it was found that the cuticle layer bears 35% of the force endured during bending, and the cortex bears the rest; when subjected to tension, the cortex bears more than 90% of the force.

Valorization of Human Hair and Its Derivatives in Tissue Engineering: A Review

Human hair is a potential biomaterial for biomedical applications. Improper disposal of human hair may pose various adverse effects on the environment and human health. Therefore, proper management of human hair waste is pivotal. Human hair fiber and its derivatives offer various advantages as biomaterials such as biocompatibility, biodegradability, low toxicity, radical scavenging, electroconductivity, and intrinsic biological activity. Therefore, the favorable characteristics of human hair have rendered its usage in tissue engineering (TE) applications including skin, cardiac, nerve, bone, ocular, and periodontal. Moreover, the strategies by utilizing human hair as a biomaterial for TE applications may reduce the accumulation of human hair. Thus, it also improves human hair waste management while promoting natural, environmental-friendly, and nontoxic materials. Furthermore, promoting sustainable materials production will benefit human health and well-being. Hence, this article reviews and discusses human hair characteristics as sustainable biomaterials and their recent application in TE applications. Impact Statement This review article highlights the sustainability aspects of human hair as raw biomaterials and various elements of human hair that could potentially be used in tissue engineering (TE) applications. Furthermore, this article discusses numerous benefits of human hair, highlighting its value as biomaterials in bioscaffold development for TE applications. Moreover, this article reviews the role and effect of human hair in various TE applications, including skin, cardiac, nerve, bone, ocular, and periodontal.

Protein by-products: Composition, extraction, and biomedical applications

Significant upsurge in animal by-products such as skin, bones, wool, hides, feathers, and fats has become a global challenge and, if not properly disposed of, can spread contamination and viral diseases. Animal by-products are rich in proteins, which can be used as nutritional, pharmacologically functional ingredients, and biomedical materials. Therefore, recycling these abundant and renewable by-products and extracting high value-added components from them is a sustainable approach to reclaim animal by-products while addressing scarce landfill resources. This article appraises the most recent studies conducted in the last five years on animal-derived proteins' separation and biomedical application. The effort encompasses an introduction about the composition, an overview of the extraction and purification methods, and the broad range of biomedical applications of these ensuing proteins.

Design and Synthesis of Stem Cell-Laden Keratin/Glycol Chitosan Methacrylate Bioinks for 3D Bioprinting

With the advancements in tissue engineering and three-dimensional (3D) bioprinting, physiologically relevant three-dimensional structures with suitable mechanical and bioactive properties that mimic the biological tissue can be designed and fabricated. However, the available bioinks are less than demanded. In this research, the readily available biomass sources, keratin and glycol chitosan, were selected to develop a UV-curable hydrogel that is feasible for the 3D bioprinting process. Keratin methacrylate and glycol chitosan methacrylate were synthesized, and a hybrid bioink was created by combining this protein-polysaccharide cross-linked hydrogel. While human hair keratin could provide biological functions, the other composition, glycol chitosan, could further enhance the mechanical strength of the construct. The mechanical properties, degradation profile, swelling behavior, cell viability, and proliferation were investigated with various ratios of keratin methacrylate to glycol chitosan methacrylate. The composition of 2% (w/v) keratin methacrylate and 2% (w/v) chitosan methacrylate showed a significantly higher cell number and swelling percentage than other compositions and was designated as the bioink for 3D printing afterward. The feasibility of stem cell loading in the selected formula was examined with an extrusion-based bioprinter. The cells and spheroids can be successfully printed with the synthesized bioink into a specific shape and cultured. This work provides a potential option for bioinks and delivers insights into personalization research on stem cell-laden biofabricated hydrogels in the future.

Characterization of a Human Platelet Lysate-Loaded Keratin Hydrogel for Wound Healing Applications In Vitro

One of the promising approaches to facilitate healing and regenerative capacity includes the application of growth-factor-loaded biomaterials. Human platelet lysate (hPL) derived from platelet-rich plasma through a freeze-thaw process has been used as a growth factor rich therapeutic in many regenerative applications. To provide sustained local delivery of the hPL-derived growth factors such as epidermal growth factor (EGF), the hPL can be loaded into biomaterials that do not degrade rapidly in vivo. Keratin (KSO), a strong filamentous protein found in human hair, when formulated as a hydrogel, is shown to sustain the release of drugs and promote wound healing. In the current study, we created a KSO biomaterial that spontaneously forms a hydrogel when rehydrated with hPL that is capable of controlled and sustained release of pro-regenerative molecules. Our study demonstrates that the release of hPL is controlled by changing the KSO hydrogel and hPL-loading concentrations, with hPL loading concentrations having a greater effect in changing release profiles. In addition, the 15% KSO concentration proved to form a stable hydrogel, and supported cell proliferation over 3 days without cytotoxic effects in vitro. The hPL-loaded keratin hydrogels show promise in potential applications for wound healing with the sustained release of pro-regenerative growth factors with easy tailoring of hydrogel properties.

Bioconversion of Keratin Wastes Using Keratinolytic Microorganisms to Generate Value-Added Products

The management of keratinous wastes generated from different industries is becoming a major concern across the world. In each year, more than a billion tons of keratin waste is released into the environment. Despite some trials that have been performed and utilize this waste into valuable products, still a huge amount of keratin waste from different sources is a less explored biomaterial for making valuable products. This indicates that the huge amount of keratin waste is neither disposed properly nor converted into usable products rather thrown away to the environment that causes environmental pollution. Due to the introduction of this waste associated with different pathogenic organisms into soil and water bodies, human beings and other small and large animals are affected by different diseases. Therefore, there is a need for modern and ecofriendly approaches to dispose and convert this waste into usable products. Hence, the objective of this review is to give a concise overview regarding the degradation of keratin waste by biological approaches using keratinase producing microorganisms. The review also focuses on the practical use of keratinases and the economical importance of bioconverted products of keratinous wastes for different applications. Various researches have been studied about the source, disposal mechanisms, techniques of hydrolysis, potential use, and physical and chemical properties of keratin wastes. However, there is negligible information with regard to the use of keratin wastes as media supplements for the growth of keratinolytic microorganisms and silver retrieval from photographic and used X-ray films. Hence, this review differs from other similar reviews in the literature in that it discusses these neglected concerns.

Dexamethasone-loaded keratin films for ocular surface reconstruction

Amniotic membrane (AM) is often applied as a substitute material during ocular surface reconstruction. However, since AM has several disadvantages, alternative materials must be considered for this application. Keratin films made from human hair (KFs) have previously been presented as a promising option; they exhibited suitable characteristics and satisfactory biocompatibility in an in vivo rabbit model. Nevertheless, dexamethasone (DEX) eye drops are necessary after surgery to suppress inflammation. Since eye drops must be administered frequently, this might result in poor patient compliance, and the release of DEX at the transplant site would be clinically beneficial. Therefore, we aimed to incorporate DEX into KFs without hindering the positive film characteristics. Drug-loaded KFs were generated either by suspension technique or by the addition of solubilizing agents. The resulting specimens were analyzed regarding appearance, loading capacity, transparency, mechanical characteristics, swelling behavior and in vitro release. Furthermore, biocompatibility was assessed in vitro by determining the cell viability, seeding efficiency and growth behavior of corneal epithelial cells. The amount of incorporated DEX influenced the transparency and biomechanical properties of the films, but even highly loaded films showed properties similar to those of AM. The suspension technique was identified as the best incorporation approach regarding chemical stability and prolonged DEX release. Moreover, suspended DEX in the films did not negatively impact cell seeding efficiencies, and the cell-growth behaviors on the specimens with moderate DEX loads were satisfactory. This suggest that these films could comprise a suitable alternative material with additional anti-inflammatory activity for ocular surface reconstruction. Graphical abstract.

Hydrogen Sulfide Releasing Hydrogel for Alleviating Cardiac Inflammation and Protecting Against Myocardial Ischemia-Reperfusion Injury

Myocardial infarction is one of the leading causes of death worldwide. Thus, protection against myocardial ischemia-reperfusion injury is particularly important to improve the prognosis of myocardial infarction. Recently, hydrogen sulfide...

Nitric oxide-releasing poly(ε-caprolactone)/S-nitrosylated keratin biocomposite scaffolds for potential small-diameter vascular grafts

Rapid endothelialization and regulation of smooth muscle cell proliferation are crucial for small-diameter vascular grafts to address poor compliance, thromboembolism, and intimal hyperplasia, and achieve revascularization. As a gaseous signaling molecule, nitric oxide (NO) regulates cardiovascular homeostasis, inhibits blood clotting and intimal hyperplasia, and promotes the growth of endothelial cells. Due to the instability and burst release of small molecular NO donors, a novel biomacromolecular donor has generated increasing interest. In the study, a low toxic NO donor of S-nitrosated keratin (KSNO) was first synthesized and then coelectrospun with poly(ε-caprolactone) to afford NO-releasing small-diameter vascular graft. PCL/KSNO graft was capable to generate NO under the catalysis of ascorbic acid (Asc), so the graft selectively elevated adhesion and growth of human umbilical vein endothelial cells (HUVECs), while inhibited the proliferation of human aortic smooth muscle cells (HASMCs) in the presence of Asc. In addition, the graft displayed significant antibacterial properties and good blood compatibility. Animal experiments showed that the biocomposite graft could inhibit thrombus formation and preserve normal blood flow via single rabbit carotid artery replacement for 1 month. More importantly, a complete endothelium was observed on the lumen surface. Taken together, PCL/KSNO small-diameter vascular graft has potential applications in vascular tissue engineering with rapid endothelialization and vascular remolding.

Biocompatible and photocrosslinkable poly(ethylene glycol)/keratin biocomposite hydrogels

A biocompatible hydrogel is ideal for tissue engineering and regeneration. In this study, methacrylated keratin (KerMA) was synthesized for the first time and then blended with poly(ethylene glycol dimethacrylate) (PEGDMA) to form hydrogel through photocrosslinking. The chemical structure, gelation time, swelling behavior, hydrophilicity, cytotoxicity, and 3D printability of PEGDMA/KerMA hydrogels were characterized and exploited. The PEGDMA/KerMA hydrogels performed good cytocompatibility, providing potential applications for tissue engineering and regenerative medicine.

Closing the Loop with Keratin-Rich Fibrous Materials

One of the agro-industry's side streams that is widely met is the-keratin rich fibrous material that is becoming a waste product without valorization. Its management as a waste is costly, as the incineration of this type of waste constitutes high environmental concern. Considering these facts, the keratin-rich waste can be considered as a treasure for the producers interested in the valorization of such slowly-biodegradable by-products. As keratin is a protein that needs harsh conditions for its degradation, and that in most of the cases its constitutive amino acids are destroyed, we review new extraction methods that are eco-friendly and cost-effective. The chemical and enzymatic extractions of keratin are compared and the optimization of the extraction conditions at the lab scale is considered. In this study, there are also considered the potential applications of the extracted keratin as well as the reuse of the by-products obtained during the extraction processes.

Raman and photoluminescence spectroscopy analysis of gamma irradiated human hair

Preliminary study has been made of black human hair, carbon concentration of some 53%, a model in examining the potential of hair of the human head in retrospective and emergency biodosimetry applications, also offering effective atomic number near to that of water. The hair samples were exposed to \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^{60}$$\end{document}60Co gamma rays, delivering doses from 0 to 200 Gy. Structural alterations were observed, use being made of Raman and photoluminescence (PL) spectroscopy. Most prominent among the features observed in the first-order Raman spectra are the D and G peaks, appearing at 1370 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\pm }} 18\,{\hbox {cm}}^{-1}$$\end{document}±18cm-1 and 1589 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\pm }} 11\,{\hbox {cm}}^{-1}$$\end{document}±11cm-1 respectively, the intensity ratio \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{{I}}}_{{{D}}}{{/}}{{{I}}}_{{{G}}}$$\end{document}ID/IG indicating dose-dependent defects generation and annealing of structural alterations. The wavelengths of the PL absorption and emission peaks are found to be centred at \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$592.3 \pm 12.5$$\end{document}592.3±12.5 nm and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$1077.4 \pm 7.3$$\end{document}1077.4±7.3 nm, respectively. The hair samples mean band gap energy (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{{E}}}_{{{g}}}$$\end{document}Eg) post-irradiation was found to be \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$2.10 \pm 0.04$$\end{document}2.10±0.04 eV, of the order of a semiconductor and approximately two times the \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{{E}}}_{{{g}}}$$\end{document}Eg of other carbon-rich materials reported via the same methodology.

Keratin-tannic acid complex nanoparticles as pH/GSH dual responsive drug carriers for doxorubicin

Drug-loaded nanoparticles have been widely used in the field of tumor treatment due to their low side effects and reduced frequency of administration. In this study, pH and glutathione (GSH) dual-responsive keratin-tannic acid (TA) complex nanoparticles were established to trigger drug release under tumor microenvironments. Reductive keratin was first extracted using a reduction method. Then, keratin-TA complex nanoparticles (KNPs) were self-assembled via non-covalent interaction and further stabilized by self-crosslinking of thiols. This method was facile and green without chemicals during the whole procedure. KNPs exhibited pH and GSH dual responsiveness as well as charge reversibility in the simulated tumor microenvironment. The anticancer drug of doxorubicin (DOX) was loaded on KNPs by hydrophobicity and hydrogen bonds. Drug-loaded KNPs accelerated drug release under mimicked tumor microenvironments, performing high toxic against A549 cells while low toxic on normal cells. Besides, drug-loaded nanoparticles could be endocytosed by tumor cells. Based on these results, KNPs may serve as drug carriers for therapeutic delivery.

Fabrication of PCL/keratin composite scaffolds for vascular tissue engineering with catalytic generation of nitric oxide potential

Tissue-engineered vascular grafts (TEVGs) have been proposed as a promising approach to fulfill the need for small-diameter blood vessel substitutes. However, common failure caused by thrombosis and neointimal proliferation after implantation has restricted their use in the clinic. Herein, a NO-generating scaffold for vascular tissue engineering was developed by coelectrospinning poly(ε-caprolactone) (PCL) with keratin. The morphology and surface chemical composition were characterized via SEM, ATR-FTIR spectroscopy and XPS. The biocomposite scaffold selectively enhanced the adhesion and growth of endothelial cells (ECs) while suppressing the proliferation of smooth muscle cells (SMCs) in the presence of GSH and GSNO due to the catalytic generation of NO. In addition, these mats displayed excellent blood compatibility by prolonging the blood-clotting time. In summary, these NO-generating PCL/keratin scaffolds have potential applications in vascular tissue engineering with rapid endothelialization and reduced SMC proliferation.

Structure of Keratin

Keratins, as a group of insoluble and filament-forming proteins, mainly exist in certain epithelial cells of vertebrates. Keratinous materials are made up of cells filled with keratins, while they are the toughest biological materials such as the human hair, wool and horns of mammals and feathers, claws, and beaks of birds and reptiles which usually used for protection, defense, hunting and as armor. They generally exhibit a sophisticated hierarchical structure ranging from nanoscale to centimeter-scale: polypeptide chain structures, intermediated filaments/matrix structures, and lamellar structures. Therefore, more and more attention has been paid to the investigation of the relationship between structure and properties of keratins, and a series of biomimetic materials based on keratin came into being. In this chapter, we mainly introduce the hierarchical structure, the secondary structure, and the molecular structure of keratins, including α- and β-keratin, to promote the development of novel keratin-based biomimetic materials designs.

Collagen/kerateine multi-protein hydrogels as a thermally stable extracellular matrix for 3D in vitro models

Objective: To determine whether the addition of kerateine (reduced keratin) in rat tail collagen type I hydrogels increases thermal stability and changes material properties and supports cell growth for use in cellular hyperthermia studies for tumor treatment.Methods: Collagen type I extracted from rat tail tendon was combined with kerateine extracted from human hair fibers. Thermal, mechanical, and biocompatibility properties and cell behavior was assessed and compared to 100% collagen type I hydrogels to demonstrate their utility as a tissue model for 3D in vitro testing.Results: A combination (i.e., containing both collagen 'C/KNT') hydrogel was more thermally stable than pure collagen hydrogels and resisted thermal degradation when incubated at a hyperthermic temperature of 47°C for heating durations up to 60 min with a higher melting temperature measured by DSC. An increase in the storage modulus was only observed with an increased collagen concentration rather than an increased KTN concentration; however, a change in ECM structure was observed with greater fiber alignment and width with an increase in KTN concentration. The C/KTN hydrogels, specifically 50/50 C/KTN hydrogels, also supported the growth and of fibroblasts and MDA-MB-231 breast cancer cells similar to those seeded in 100% collagen hydrogels.Conclusion: This multi-protein C/KTN hydrogel shows promise for future studies involving thermal stress studies without compromising the 3D ECM environment or cell growth.

Fundamentals and Current Strategies for Peripheral Nerve Repair and Regeneration

A body of evidence indicates that peripheral nerves have an extraordinary yet limited capacity to regenerate after an injury. Peripheral nerve injuries have confounded professionals in this field, from neuroscientists to neurologists, plastic surgeons, and the scientific community. Despite all the efforts, full functional recovery is still seldom. The inadequate results attained with the "gold standard" autograft procedure still encourage a dynamic and energetic research around the world for establishing good performing tissue-engineered alternative grafts. Resourcing to nerve guidance conduits, a variety of methods have been experimentally used to bridge peripheral nerve gaps of limited size, up to 30-40 mm in length, in humans. Herein, we aim to summarize the fundamentals related to peripheral nerve anatomy and overview the challenges and scientific evidences related to peripheral nerve injury and repair mechanisms. The most relevant reports dealing with the use of both synthetic and natural-based biomaterials used in tissue engineering strategies when treatment of nerve injuries is envisioned are also discussed in depth, along with the state-of-the-art approaches in this field.

Hydrogels and Dentin-Pulp Complex Regeneration: From the Benchtop to Clinical Translation

Dentin-pulp complex is a term which refers to the dental pulp (DP) surrounded by dentin along its peripheries. Dentin and dental pulp are highly specialized tissues, which can be affected by various insults, primarily by dental caries. Regeneration of the dentin-pulp complex is of paramount importance to regain tooth vitality. The regenerative endodontic procedure (REP) is a relatively current approach, which aims to regenerate the dentin-pulp complex through stimulating the differentiation of resident or transplanted stem/progenitor cells. Hydrogel-based scaffolds are a unique category of three dimensional polymeric networks with high water content. They are hydrophilic, biocompatible, with tunable degradation patterns and mechanical properties, in addition to the ability to be loaded with various bioactive molecules. Furthermore, hydrogels have a considerable degree of flexibility and elasticity, mimicking the cell extracellular matrix (ECM), particularly that of the DP. The current review presents how for dentin-pulp complex regeneration, the application of injectable hydrogels combined with stem/progenitor cells could represent a promising approach. According to the source of the polymeric chain forming the hydrogel, they can be classified into natural, synthetic or hybrid hydrogels, combining natural and synthetic ones. Natural polymers are bioactive, highly biocompatible, and biodegradable by naturally occurring enzymes or via hydrolysis. On the other hand, synthetic polymers offer tunable mechanical properties, thermostability and durability as compared to natural hydrogels. Hybrid hydrogels combine the benefits of synthetic and natural polymers. Hydrogels can be biofunctionalized with cell-binding sequences as arginine-glycine-aspartic acid (RGD), can be used for local delivery of bioactive molecules and cellularized with stem cells for dentin-pulp regeneration. Formulating a hydrogel scaffold material fulfilling the required criteria in regenerative endodontics is still an area of active research, which shows promising potential for replacing conventional endodontic treatments in the near future.

Strategies for improved hair binding: Keratin fractions and the impact of cationic substructures

Keratin extracts and hydrolysates from varying sources, their chemical modifications and compositions thereof have shown potential in the restoration of hair properties. Within this study on reactivity of thiol groups and the shielding effect of anionic charges the binding of keratin-associated proteins (KAP) and α-keratins (Ker) extracted from human hair to natural and permed hair fibers was evaluated. Selectively extracted KAP and Ker were preactivated with 6-mercaptonicotinamide in a quantity of 194 ± 21 μmol/g for KAP and 169 ± 27 μmol/g for Ker resulting in 1.9- and 1.4-fold enhanced binding to natural hair, respectively. The amount of accumulated Ker on hair fibers was furthermore increased by 1.7-fold in presence of 25 mM L-arginine. Perming of hair impaired binding characteristics of Ker with negligible effects for preactivation, whereas unmodified and preactivated KAP showed results comparable to natural hair. Strongly enhanced penetrability after perming was reflected by the mean penetration depth for fluorescein of 25 μm compared to 5 μm for natural fibers.

Keratin-dopamine conjugate nanoparticles as pH/GSH dual responsive drug carriers

Drug-loaded nanoparticles have been widely used in the field of tumor treatment due to their low side effects and reduced frequency of administration. In this study, keratin-dopamine conjugate was first synthesized by amidation reaction and then formed nanoparticles by self-polymerization of dopamine segment. Keratin-dopamine conjugate nanoparticles (KNPs) exhibited pH and glutathione (GSH) dual responsiveness in the simulated tumor environment. These nanoparticles were able to load anti-cancer drug doxorubicin (DOX) through electrostatic interactions and hydrogen bonds. These drug-loaded KNPs (DKNPs) exhibited controlled drug release in a tumor simulation environment. Meanwhile, DKNPs performed a stronger inhibitory effect on tumor cells compared with human normal tissue cells. Based on the above results, keratin-dopamine conjugate based drug carriers had a broad prospect in the field of cancer treatment.

Self-crosslinked keratin nanoparticles for pH and GSH dual responsive drug carriers

Nano-drug delivery system (NDDS) has attracted widespread attention for their controlled drug release. In this work, keratin nanoparticles (KNPs) were prepared by self-crosslinking. No toxic chemical crosslinkers were added in the whole procedure. The morphology and size of KNPs were tested by transmission electron microscopy (TEM) and dynamic light scattering (DLS), respectively. The KNPs exhibited GSH and pH dual responsiveness as well as charge conversion, which were beneficial to tumor therapy. In addition, the anticancer drug of doxorubicin (DOX) could be loaded on KNPs by hydrophobicity and hydrogen bonds. The drug-loaded keratin nanoparticles (KDNPs) accelerated drug release under mimicked tumor microenvironments. In addition, KDNPs could effectively inhibit tumor cell growth while performing low toxicity on normal cells. Moreover, KDNPs could be uptaken by tumor cells through endocytosis. Based on the results, keratin-based nanoparticles were suitable candidates for drug microcarriers.

Protein-Polysaccharide Composite Materials: Fabrication and Applications

Protein-polysaccharide composites have been known to show a wide range of applications in biomedical and green chemical fields. These composites have been fabricated into a variety of forms, such as films, fibers, particles, and gels, dependent upon their specific applications. Post treatments of these composites, such as enhancing chemical and physical changes, have been shown to favorably alter their structure and properties, allowing for specificity of medical treatments. Protein-polysaccharide composite materials introduce many opportunities to improve biological functions and contemporary technological functions. Current applications involving the replication of artificial tissues in tissue regeneration, wound therapy, effective drug delivery systems, and food colloids have benefited from protein-polysaccharide composite materials. Although there is limited research on the development of protein-polysaccharide composites, studies have proven their effectiveness and advantages amongst multiple fields. This review aims to provide insight on the elements of protein-polysaccharide complexes, how they are formed, and how they can be applied in modern material science and engineering.

Keratinous materials: Structures and functions in biomedical applications

Keratins are a family of fibrous proteins anticipated to possess wide-ranging biomedical applications due to their abundance, physicochemical properties and intrinsic biological activity. This review mainly focuses on the biomaterials derived from three major sources of keratins; namely human hair, wool and feather, that have effective applications in tissue engineering, wound healing and drug delivery. This article offers five viewpoints regarding keratin i) an introduction to keratin protein extraction and keratin-based scaffold fabrication methods ii) applications in nerve and bone tissue engineering iii) a review on the keratin dressings applied to different types of wounds to facilitate wound healing and thereby repair the skin iv) the utilization of keratinous materials as a carrier system for therapeutics with a controlled manner v) a discussion regarding the main challenges for using keratin in biomedical applications as well as its future prospects.

Keratin Associations with Synthetic, Biosynthetic and Natural Polymers: An Extensive Review

Among the biopolymers from animal sources, keratin is one the most abundant, with a major contribution from side stream products from cattle, ovine and poultry industry, offering many opportunities to produce cost-effective and sustainable advanced materials. Although many reviews have discussed the application of keratin in polymer-based biomaterials, little attention has been paid to its potential in association with other polymer matrices. Thus, herein, we present an extensive literature review summarizing keratin's compatibility with other synthetic, biosynthetic and natural polymers, and its effect on the materials' final properties in a myriad of applications. First, we revise the historical context of keratin use, describe its structure, chemical toolset and methods of extraction, overview and differentiate keratins obtained from different sources, highlight the main areas where keratin associations have been applied, and describe the possibilities offered by its chemical toolset. Finally, we contextualize keratin's potential for addressing current issues in materials sciences, focusing on the effect of keratin when associated to other polymers' matrices from biomedical to engineering applications, and beyond.

Carboxymethyl cellulose-human hair keratin hydrogel with controlled clindamycin release as antibacterial wound dressing

This study offers a new antibacterial wound dressing from carboxymethyl cellulose (CMC)-human hair keratin with topical clindamycin delivery. Keratin was successfully extracted from human hair. Different sponges fabricated by changing CMC to keratin ratio were characterized and compared. Halloysite nanotubes were used as carriers to control the clindamycin release. Various characterization techniques were used to determine the effects of keratin addition on the structure, morphology, physical properties, drug release, antibacterial activity, and cellular behavior of CMC hydrogels. As proved by SEM and EDS, porous structure with interconnected pores was successfully formed and clindamycin-loaded HNTs were uniformly dispersed within the porous structures. Increasing the keratin in CMC hydrogel not only lowered its water vapor transmission rate to a suitable range for wound healing but also improved the water stability of CMC hydrogel. The in vitro release study indicated that clindamycin was released slower in samples containing higher keratin and the Fickian diffusion mechanism controlled their release profile. The fabricated dressing effectively inhibits S. aureus bacterial colonies growth after 24 h. Fibroblast culturing on the fabricated sponges indicated that cellular attachment, proliferation, and spreading were significantly enhanced with increasing the keratin amount.

Human hair keratins promote the regeneration of peripheral nerves in a rat sciatic nerve crush model

Axon regeneration and functional recovery after peripheral nerve injury remains a clinical challenge. Injury leads to axonal disintegration after which Schwann cells (SCs) and macrophages re-engage in the process of regeneration. At present, biomaterials are regarded as the most promising way to repair peripheral nerve damage. As a natural material, keratin has a wide range of sources and has good biocompatibility and biodegradability. Here, a keratin was extracted from human hair by reducing method and a keratin sponge with porous structure was obtained by further processing. The results suggested that keratin can promote cell adhesion, proliferation, migration as well as the secretion of neurotrophic factors by SCs and the regulation of the expression of macrophage inflammatory cytokines in vitro. We report for the first time that human hair keratin can promote the extension of axon in DRG neurons. The motor deficits caused by a sciatic nerve crush injury were alleviated by keratin sponge dressing in vivo. Thus, keratin has been identified as a valuable biomaterial that can enhance peripheral nerve regeneration.

Recombinant Human Hair Keratin Nanoparticles Accelerate Dermal Wound Healing

In recent years, favorable enhanced wound-healing properties and excellent biocompatibility of keratin derived from human hair have attracted considerable attention. Recombinant keratin proteins can be produced by recombinant DNA technology and have higher purity than extracted keratin. However, the wound-healing properties of recombinant keratin proteins remain unclear. Herein, two recombinant trichocyte keratins including human type I hair keratin 37 and human type II hair keratin 81 were expressed using a bacterial expression system, and recombinant keratin nanoparticles (RKNPs) were prepared via an ultrasonic dispersion method. The molecular weight, purity, and physicochemical properties of the recombinant keratin proteins and nanoparticles were assessed using gel electrophoresis, circular dichroism, mass spectrometry, and scanning electron microscope analyses. The RKNPs significantly enhanced cell proliferation and migration in vitro, and the treatment of dermal wounds in vivo with RKNPs resulted in improved wound healing associated with improved epithelialization, vascularization, and collagen deposition and remodeling. In addition, the in vivo biocompatibility test revealed no systemic toxicity. Overall, this work demonstrates that RKNPs are a promising candidate for enhanced wound healing, and this study opens up new prospects for the development of keratin biomaterials.

Thermal Conductivity of Protein-Based Materials: A Review

Fibrous proteins such as silks have been used as textile and biomedical materials for decades due to their natural abundance, high flexibility, biocompatibility, and excellent mechanical properties. In addition, they also can avoid many problems related to traditional materials such as toxic chemical residues or brittleness. With the fast development of cutting-edge flexible materials and bioelectronics processing technologies, the market for biocompatible materials with extremely high or low thermal conductivity is growing rapidly. The thermal conductivity of protein films, which is usually on the order of 0.1 W/m·K, can be rather tunable as the value for stretched protein fibers can be substantially larger, outperforming that of many synthetic polymer materials. These findings indicate that the thermal conductivity and the heat transfer direction of protein-based materials can be finely controlled by manipulating their nano-scale structures. This review will focus on the structure of different fibrous proteins, such as silks, collagen and keratin, summarizing factors that can influence the thermal conductivity of protein-based materials and the different experimental methods used to measure their heat transfer properties.

Bio- and Fossil-Based Polymeric Blends and Nanocomposites for Packaging: Structure⁻Property Relationship

In the present review, the possibilities for blending of commodities and bio-based and/or biodegradable polymers for packaging purposes has been considered, limiting the analysis to this class of materials without considering blends where both components have a bio-based composition or origin. The production of blends with synthetic polymeric materials is among the strategies to modulate the main characteristics of biodegradable polymeric materials, altering disintegrability rates and decreasing the final cost of different products. Special emphasis has been given to blends functional behavior in the frame of packaging application (compostability, gas/water/light barrier properties, migration, antioxidant performance). In addition, to better analyze the presence of nanosized ingredients on the overall behavior of a nanocomposite system composed of synthetic polymers, combined with biodegradable and/or bio-based plastics, the nature and effect of the inclusion of bio-based nanofillers has been investigated.

Keratin nanoparticles-coating electrospun PVA nanofibers for potential neural tissue applications

Keratin has the potential to improve biocompatibility and bioactivity of polymeric nanofibers. However, the addition of keratin into the blend nanofiber would decrease the mechanical properties of nanofibers due to the poor spinnability of keratin, and caused inhomogeneous distribution of keratin inside the nanofibers. Therefore, polymeric nanofibers surface-modified with keratin nanoparticles would improve the hydrophility and mechanical property. In this study, keratose (oxidative keratin, KOS) nanoparticles-coating PVA nanofibers (KNPs/PVA) were fabricated by electrospray deposition after electrospinning and acted on neural cells. The chemical conformation, mechanical properties and wettability of KNPs/PVA nanofibers were characterized. The KNPs/PVA nanofibers provided better wettability and stronger mechanical properties compared to KOS/PVA blend nanofibers at the same mass ratio of KOS to PVA. Furthermore, KNPs/PVA nanofibers displayed better cyto-biocompatibility in terms of cell morphology, adhesion and proliferation compared with PVA nanofibers and KOS/PVA blend nanofibers. These results suggested that polymeric nanofibers surface-modified with KOS nanoparticles can provide superior wettability, mechanical properties and biocompatibility by comparison with the blend nanofibers.