Culturing fibroblasts in 3D human hair keratin hydrogels

A facile method to fabricate versatile keratin cryogels for tissue engineering applications

Human hair keratin (HHK) has been extensively explored as a biomaterial for soft tissue regeneration due to their excellent bioactivity and biocompatibility. The possibility to fabricate HHK into three-dimensional (3D) hydrogels with physical properties resembling soft tissues has been well demonstrated. However, conventional keratin hydrogels often exhibit a dense architecture that could hinder cell filtration. In the present study, HHK-based cryogels were fabricated using a freeze-thaw (FT) method, where oxidized dopamine (ODA) was employed to covalently crosslink thiol/amine rich-keratin molecules at sub-zero temperatures. The obtained HHK-ODA cryogels have micron-sized pores ranging between 100 and 200 μm and mechanical properties that can be tuned by varying the crosslinking density between ODA and HHK. Through optimization of the weight content of ODA and the number of FT cycles, the compressive strengths and stiffnesses of these cryogels achieved 15-fold increments from ∼1.5 kPa to ∼22 kPa and ∼300 Pa to ∼5000 Pa, respectively. The HHK-ODA cryogels competently supported human dermal fibroblast spreading and proliferation. Overall, this study exhibited a facile method to fabricate mechanically superior keratin-based cryogels with cell compatible microarchitecture, circumventing the need for complicated chemical modifications and the use of cytotoxic crosslinkers.

Recent omics advances in hair aging biology and hair biomarkers analysis

Aging is a complex natural process that leads to a decline in physiological functions, which is visible in signs such as hair graying, thinning, and loss. Although hair graying is characterized by a loss of pigment in the hair shaft, the underlying mechanism of age-associated hair graying is not fully understood. Hair graying and loss can have a significant impact on an individual's self-esteem and self-confidence, potentially leading to mental health problems such as depression and anxiety. Omics technologies, which have applications beyond clinical medicine, have led to the discovery of candidate hair biomarkers and may provide insight into the complex biology of hair aging and identify targets for effective therapies. This review provides an up-to-date overview of recent omics discoveries, including age-associated alterations of proteins and metabolites in the hair shaft and follicle, and highlights the significance of hair aging and graying biomarker discoveries. The decline in hair follicle stem cell activity with aging decreased the regeneration capacity of hair follicles. Cellular senescence, oxidative damage and altered extracellular matrix of hair follicle constituents characterized hair follicle and hair shaft aging and graying. The review attempts to correlate the impact of endogenous and exogenous factors on hair aging. We close by discussing the main challenges and limitations of the field, defining major open questions and offering an outlook for future research.

Protein-modified nanomaterials: emerging trends in skin wound healing

Prolonged inflammation can impede wound healing, which is regulated by several proteins and cytokines, including IL-4, IL-10, IL-13, and TGF-β. Concentration-dependent effects of these molecules at the target site have been investigated by researchers to develop them as wound-healing agents by regulating signaling strength. Nanotechnology has provided a promising approach to achieve tissue-targeted delivery and increased effective concentration by developing protein-functionalized nanoparticles with growth factors (EGF, IGF, FGF, PDGF, TGF-β, TNF-α, and VEGF), antidiabetic wound-healing agents (insulin), and extracellular proteins (keratin, heparin, and silk fibroin). These molecules play critical roles in promoting cell proliferation, migration, ECM production, angiogenesis, and inflammation regulation. Therefore, protein-functionalized nanoparticles have emerged as a potential strategy for improving wound healing in delayed or impaired healing cases. This review summarizes the preparation and applications of these nanoparticles for normal or diabetic wound healing and highlights their potential to enhance wound healing.

Human Hair Keratin-Based Hydrogels in Regenerative Medicine: Current Status and Future Directions

Regenerative medicine (RM) is a multidisciplinary field that utilizes the inherent regenerative potential of human cells to generate functionally and physiologically acceptable human cells, tissues, and organs in vivo or ex vivo. An appropriate biomaterial scaffold with desired physicochemical properties constitutes an important component of a successful RM approach. Among various forms of biomaterials explored until the present day, hydrogels have emerged as a versatile candidate for tissue engineering and regenerative medicine (TERM) applications such as scaffolds for spatial patterning and delivering therapeutic agents, or substrates to enhance cell growth, differentiation, and migration. Although hydrogels can be prepared from a variety of synthetic polymers as well as biopolymers, the latter are preferred for their inherent biocompatibility. Specifically, keratins are fibrous proteins that have been recently explored for constructing hydrogels useful for RM purposes. The present review discusses the suitability of keratin-based biomaterials in RM, with a particular focus on human hair keratin hydrogels and their use in various RM applications.

Protein-Based Hydrogels and Their Biomedical Applications

Hydrogels made from proteins are attractive materials for diverse medical applications, as they are biocompatible, biodegradable, and amenable to chemical and biological modifications. Recent advances in protein engineering, synthetic biology, and material science have enabled the fine-tuning of protein sequences, hydrogel structures, and hydrogel mechanical properties, allowing for a broad range of biomedical applications using protein hydrogels. This article reviews recent progresses on protein hydrogels with special focus on those made of microbially produced proteins. We discuss different hydrogel formation strategies and their associated hydrogel properties. We also review various biomedical applications, categorized by the origin of protein sequences. Lastly, current challenges and future opportunities in engineering protein-based hydrogels are discussed. We hope this review will inspire new ideas in material innovation, leading to advanced protein hydrogels with desirable properties for a wide range of biomedical applications.

Bioinspired Robust Keratin Hydrogels for Biomedical Applications

Although keratins are robust in nature, hydrogels producing their extracts exhibit poor mechanical properties due to the complicated composition and ineffective self-assembly. Here we report a bioinspired strategy to fabricate robust keratin hydrogels based on mechanism study through recombinant proteins. Homotypic and heterotypic self-assembly of selected type I and type II keratins in different combinations was conducted to identify crucial domain structures for the process, their kinetics, and relationship with the mechanical strength of hydrogels. Segments with best performance were isolated and used to construct novel assembling units. The new design outperformed combinations of native proteins in mechanical properties and in biomedical applications such as controlled drug release and skin regeneration. Our approach not only elucidated the critical structural domains and underlying mechanisms for keratin self-assembly but also opens an avenue toward the rational design of robust keratin hydrogels for biomedical applications.

Tissues and organ printing: An evolution of technology and materials

Since its beginnings, three-dimensional printing (3DP) technology has been successful because of ongoing advances in operating principles, the range of materials and cost-saving measures. However, the 3DP technological progressions in the biomedical sector have majorly taken place in the last decade after the evolution of novel 3DP systems, generally categorised as bioprinters and biomaterials to provide a replacement, transplantation or regeneration of the damaged organs and tissue constructs of the human body. There is now substantial scientific literature accessible to support the benefits of digital healthcare procedures with the help of bioprinters. It is of the highest significance to know the fundamental principles of the available printers and the compatibility of biomaterials as their feedstock, notwithstanding the huge potential of bioprinting systems to manufacture organs and other human body components. This paper provides a precise and helpful reading of the different categories of bioprinters, suitable biomaterials, numerical simulations and modelling and examples of much acknowledged clinical practices. The paper will also cite the prominent issues that still have not received desired solutions. Overall, the article will be of great use for all the professionals, scholars and engineers concerned with the 3DP, bioprinting and biomaterials.

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.

Sustainable Applications of Animal Waste Proteins

Currently, the growth of the global population leads to an increase in demand for agricultural products. Expanding the obtaining and consumption of food products results in a scale up in the amount of by-products formed, the development of processing methods for which is becoming an urgent task of modern science. Collagen and keratin make up a significant part of the animal origin protein waste, and the potential for their biotechnological application is almost inexhaustible. The specific fibrillar structure allows collagen and keratin to be in demand in bioengineering in various forms and formats, as a basis for obtaining hydrogels, nanoparticles and scaffolds for regenerative medicine and targeted drug delivery, films for the development of biodegradable packaging materials, etc. This review describes the variety of sustainable sources of collagen and keratin and the beneficial application multiformity of these proteins.

Design and Fabrication of Polymeric Hydrogel Carrier for Nerve Repair

Nerve regeneration and repair still remain a huge challenge for both central nervous and peripheral nervous system. Although some therapeutic substances, including neuroprotective agents, clinical drugs and stem cells, as well as various growth factors, are found to be effective to promote nerve repair, a carrier system that possesses a sustainable release behavior, in order to ensure high on-site concentration during the whole repair and regeneration process, and high bioavailability is still highly desirable. Hydrogel, as an ideal delivery system, has an excellent loading capacity and sustainable release behavior, as well as tunable physical and chemical properties to adapt to various biomedical scenarios; thus, it is thought to be a suitable carrier system for nerve repair. This paper reviews the structure and classification of hydrogels and summarizes the fabrication and processing methods that can prepare a suitable hydrogel carrier with specific physical and chemical properties. Furthermore, the modulation of the physical and chemical properties of hydrogels is also discussed in detail in order to obtain a better therapeutic effect to promote nerve repair. Finally, the future perspectives of hydrogel microsphere carriers for stroke rehabilitation are highlighted.

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.

Molecular interaction and partitioning in α-keratin using 1H NMR spin-lattice (T1) relaxation times

The interactions between small molecules and keratins are poorly understood. In this paper, a nuclear magnetic resonance method is presented to measure changes in the ¹H T₁ relaxation times of small molecules in human hair keratin to quantify their interaction with the fibre. Two populations of small-molecule compounds were identified with distinct relaxation times, demonstrating the partitioning of the compounds into different keratin environments. The changes in relaxation time for solvent in hair compared with bulk solvent were shown to be related to the molecular weight (MW) and the partition coefficient, LogP, of the solvent investigated. Compounds with low MWs and high hydrophilicities had greater reductions in their T₁ relaxation times and therefore experienced increased interactions with the hair fibre. The relative population sizes were also calculated. This is a significant step towards modelling the behaviour of small molecules in keratinous materials and other large insoluble fibrous proteins.

Keratin-Alginate Sponges Support Healing of Partial-Thickness Burns

Deep partial-thickness burns damage most of the dermis and can cause severe pain, scarring, and mortality if left untreated. This study serves to evaluate the effectiveness of crosslinked keratin–alginate composite sponges as dermal substitutes for deep partial-thickness burns. Crosslinked keratin–alginate sponges were tested for the ability to support human dermal fibroblasts in vitro and to support the closure and healing of partial-thickness burn wounds in Sus scrofa pigs. Keratin–alginate composite sponges supported the enhanced proliferation of human dermal fibroblasts compared to alginate-only sponges and exhibited decreased contraction in vitro when compared to keratin only sponges. As dermal substitutes in vivo, the sponges supported the expression of keratin 14, alpha-smooth muscle actin, and collagen IV within wound sites, comparable to collagen sponges. Keratin–alginate composite sponges supported the regeneration of basement membranes in the wounds more than in collagen-treated wounds and non-grafted controls, suggesting the subsequent development of pathological scar tissues may be minimized. Results from this study indicate that crosslinked keratin–alginate sponges are suitable alternative dermal substitutes for clinical applications in wound healing and skin regeneration.

Anisotropic hair keratin-dopamine composite scaffolds exhibit strain-stiffening properties

Human hair keratin (HHK) has been successfully explored as raw materials for three-dimensional scaffolds for soft tissue regeneration due to its excellent biocompatibility and bioactivity. However, none of the reported HHK based scaffolds is able to replicate the strain-stiffening capacity of living tissues when responding to large deformations. In the present study, strain-stiffening property was achieved in scaffolds fabricated from HHK via a synergistic effect of well-defined, aligned microstructure and chemical crosslinking. Directed ice-templating method was used to fabricate HHK-based scaffolds with highly aligned (anisotropic) microstructure while oxidized dopamine (ODA) was used to crosslink covalently to HHKs. The resultant HHK-ODA scaffolds exhibited strain-stiffening behavior characterized by the increased gradient of the stress-strain curve after the yield point. Both ultimate tensile strength and the elongation at break were enhanced significantly (~700 kPa, ~170%) in comparison to that of HHK scaffolds lacking of aligned microstructure or ODA crosslinking. In vitro cell culture studies indicated that HHK-ODA scaffolds successfully supported human dermal fibroblasts (HDFs) adhesion, spreading and proliferation. Moreover, anisotropic HHK-ODA scaffolds guided cell growth in alignment with the defined microstructure as shown by the highly organized cytoskeletal networks and nuclei distribution. The findings suggest that HHK-ODA scaffolds, with strain-stiffening properties, biocompatibility and bioactivity, have the potential to be applied as biomimetic matrices for soft tissue regeneration.

Keratose hydrogel for tissue regeneration and drug delivery

Keratin (KRT), a natural fibrous structural protein, can be classified into two categories: "soft" cytosolic KRT that is primarily found in the epithelia tissues (e.g., skin, the inner lining of digestive tract) and "hard" KRT that is mainly found in the protective tissues (e.g., hair, horn). The latter is the predominant form of KRT widely used in biomedical research. The oxidized form of extracted KRT is exclusively denoted as keratose (KOS) while the reduced form of KRT is termed as kerateine (KRTN). KOS can be processed into various forms (e.g., hydrogel, films, fibers, and coatings) for different biomedical applications. KRT/KOS offers numerous advantages over other types of biomaterials, such as bioactivity, biocompatibility, degradability, immune/inflammatory privileges, mechanical resilience, chemical manipulability, and easy accessibility. As a result, KRT/KOS has attracted considerable attention and led to a large number of publications associated with this biomaterial over the past few decades; however, most (if not all) of the published review articles focus on KRT regarding its molecular structure, biochemical/biophysical properties, bioactivity, biocompatibility, drug/cell delivery, and in vivo transplantation, as well as its applications in biotechnical products and medical devices. Current progress that is directly associated with KOS applications in tissue regeneration and drug delivery appears an important topic that merits a commentary. To this end, the present review aims to summarize the current progress of KOS-associated biomedical applications, especially focusing on the in vitro and in vivo effects of KOS hydrogel on cultured cells and tissue regeneration following skin injury, skeletal muscle loss, peripheral nerve injury, and cardiac infarction.

Preparation of dynamic covalently crosslinking keratin hydrogels based on thiol/disulfide bonds exchange strategy

Dynamic covalently crosslinking (DCC) hydrogels can mimic extracellular matrix and have the functions such as self-healing, self-adapting, and shape memory. The DCC keratin hydrogels based on thiol group-disulfide bonds exchange strategy have no reports so far as we know. Herein, inspired by the rich content of the intramolecular disulfide bonds and free thiol groups in the keratins extracted by reducing agents, we report a simple thiol-disulfide bonds exchange strategy for preparing the DCC keratin hydrogels. While the pH value of the keratin solution extracted by reducing agents was adjusted to 9.5-10.0, the keratin hydrogels showed the characteristic with injectability, self-healing, self-adapting, biocompatibility, and redox-responsive capacity. The extracted type II neutral/alkali keratin plays a critical role in imparting the keratin hydrogels with the reversibility behaviors due to that the keratins could build dynamic covalent bonds through thiol oxidation and disulfide exchange reactions in alkali conditions. This strategy provides an inspiration for forming DCC keratin hydrogel by avoiding the extra introduction of chemical crosslinking agents.

Glucose-triggered in situ forming keratin hydrogel for the treatment of diabetic wounds

The development of protein-based in situ forming hydrogel remains a big challenge due to the limited chemical groups in proteins. Keratins are a group of cysteine-rich structural protein found abundant in skin and skin appendant. Recently, our lab has established a disulfide shuffling strategy to prepare keratin hydrogels via oxygen (O₂) oxidation. However, such hydrogel still needed to be molded in advance. In this work, inspired by the fact that glucose commonly exists in body fluids, a glucose-triggered in situ forming keratin hydrogel was developed based on the disulfide shuffling strategy via a higher oxidation force of hydrogen peroxide (H₂O₂). The hydrogel precursor solution consisted of keratin, cysteine and glucose oxidase (GOD), which could generate H₂O₂ in an indirect and mild way via GOD-catalyzed oxidation of glucose in body fluids. Our findings demonstrated that the GOD-catalyzed oxidation method not only shortened the gelation time but improved the mechanical strength of the hydrogel by comparison with O₂ oxidation and direct addition of H₂O₂ solution methods, and realized in situ gelation within 3 min on a full-thickness wound bed in normal mice. Moreover, the in situ forming keratin hydrogel was applied as a drug depot for wound repair, and the deferoxamine-loaded one accelerated healing in the full-thickness wounds of streptozotocin-induced diabetic rats, notably by promoting angiogenesis and neovascularization in wounds. STATEMENT OF SIGNIFICANCE: Studies show that keratin hydrogels possess tissue regeneration capacity, especially in skin wound repair. However, most of the reported keratin hydrogels needed to be molded in advance and cannot fit irregular wound shape. This work describes a glucose-triggered in situ forming keratin hydrogel via a disulfide shuffling strategy under the oxidation of hydrogen peroxide. Of note, the hydrogen peroxide was supplied indirectly by glucose oxidase-catalyzed oxidation of glucose in wound fluids, and this method needed no additional crosslinking agents or chemical modifications on keratins. Our findings showed that this hydrogel realized in situ gelation within 3 min on a full-thickness wound bed and enabled an injectable mode with good filling ability toward irregular wounds. Moreover, this hydrogel could be applied as a drug depot for the treatment of diabetic wounds.

Study on the Structure and Properties of Biofunctional Keratin from Rabbit Hair

Keratin is widely recognized as a high-quality renewable protein resource for biomedical applications. A large amount of rabbit hair waste is produced in textile industries, because it has high medullary layer content, but poor spinnability. Therefore, it is of great significance to extract keratin from waste rabbit hair for recycling. In this research, an ultrasonic-assisted reducing agent-based extraction method was developed and applied to extract keratin from rabbit hair. The results showed that the ultrasonic treatment had a certain destructive effect on the structure of the fiber, and when combined with reducing agent, it could effectively promote the dissolution of rabbit hair, and extract keratin with high molecular weight between 31 and 94 kDa. The structure and properties of keratin were studied. Compared to the rabbit hair, the cystine content of keratin was significantly reduced, and the secondary structure changed from α-helix to β-sheet. The keratin products show excellent biocompatibility and antioxidant capacity. In addition, large keratin particles can be formed by assembly with a balance between intermolecular hydrophobic attraction as the concentration of urea in keratin solution decreased during dialysis.

Self-Assembly of Solubilized Human Hair Keratins

Human hair keratins have proven to be a viable biomaterial for diverse regenerative applications. However, the most significant characteristic of this material, the ability to self-assemble into nanoscale intermediate filaments, has not been exploited. Herein, we successfully demonstrated the induction of hair-extracted keratin self-assembly in vitro to form dense, homogeneous, and continuous nanofibrous networks. These networks remain hydrolytically stable in vitro for up to 5 days in complete cell culture media and are compatible with primary human dermal fibroblasts and keratinocytes. These results enhance the versatility of human hair keratins for applications where structured assembly is of benefit.

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.

Characterization of Anisotropic Human Hair Keratin Scaffolds Fabricated via Directed Ice Templating

Human hair keratin (HHK) is successfully exploited as raw materials for 3D scaffolds for soft tissue regeneration owing to its excellent biocompatibility and bioactivity. However, most HHK scaffolds are not able to achieve the anisotropic mechanical properties of soft tissues such as tendons and ligaments due to lack of tunable, well-defined microstructures. In this study, directed ice templating method is used to fabricate anisotropic HHK scaffolds that are characterized by aligned pores (channels) in between keratin layers in the longitudinal plane. In contrast, pores in the transverse plane maintain a homogenous rounded morphology. Channel widths throughout the scaffolds range from ≈5 to ≈15 µm and are tunable by varying the freezing temperature. In comparison with HHK scaffolds with random, isotropic pore structures, the tensile strength of anisotropic HHK scaffolds is enhanced significantly by up to fourfolds (≈200 to ≈800 kPa) when the tensile load is applied in the direction parallel to the aligned pores. In vitro results demonstrate that the anisotropic HHK scaffolds are able to support human dermal fibroblast adhesion, spreading, and proliferation. The findings suggest that HHK scaffolds with well-defined, aligned microstructure hold promise as templates for soft tissues regeneration by mimicking their anisotropic properties.

Peptide-protein coassembling matrices as a biomimetic 3D model of ovarian cancer

Bioengineered three-dimensional (3D) matrices expand our experimental repertoire to study tumor growth and progression in a biologically relevant, yet controlled, manner. Here, we used peptide amphiphiles (PAs) to coassemble with and organize extracellular matrix (ECM) proteins producing tunable 3D models of the tumor microenvironment. The matrix was designed to mimic physical and biomolecular features of tumors present in patients. We included specific epitopes, PA nanofibers, and ECM macromolecules for the 3D culture of human ovarian cancer, endothelial, and mesenchymal stem cells. The multicellular constructs supported the formation of tumor spheroids with extensive F-actin networks surrounding the spheroids, enabling cell-cell communication, and comparative cell-matrix interactions and encapsulation response to those observed in Matrigel. We conducted a proof-of-concept study with clinically used chemotherapeutics to validate the functionality of the multicellular constructs. Our study demonstrates that peptide-protein coassembling matrices serve as a defined model of the multicellular tumor microenvironment of primary ovarian tumors.

Keratin - Based materials for biomedical applications

Keratin constitutes the major component of the feather, hair, hooves, horns, and wool represents a group of biological material having high cysteine content (7-13%) as compared to other structural proteins. Keratin -based biomaterials have been investigated extensively over the past few decades due to their intrinsic biological properties and excellent biocompatibility. Unlike other natural polymers such as starch, collagen, chitosan, the complex three-dimensional structure of keratin requires the use of harsh chemical conditions for their dissolution and extraction. The most commonly used methods for keratin extraction are oxidation, reduction, steam explosion, microbial method, microwave irradiation and use of ionic liquids. Keratin -based materials have been used extensively for various biomedical applications such as drug delivery, wound healing, tissue engineering. This review covers the structure, properties, history of keratin research, methods of extraction and some recent advancements related to the use of keratin derived biomaterials in the form of a 3-D scaffold, films, fibers, and hydrogels.

Sustained delivery of alendronate by engineered collagen scaffold for the repair of osteoporotic bone defects and resistance to bone loss

Researches of biomaterials for osteoporotic bone defects focus on the improvement of its anti-osteoporosis ability, due to osteoporosis is a kind of systemic and long-range bone metabolism disorder. Nevertheless, how to steadily deliver anti-osteoporosis drugs in osteoporotic bone defects is rarely studied. Reported evidences have shown that alendronate (Aln) is known to not only restrain osteoclasts from mediating bone resorption but also stimulate osteoblasts to regenerate bone tissue. Here, we developed an engineered implantable scaffold that could sustainably release Aln for osteoporotic bone defects. Briefly, Aln was added into 2% collagen (Col) solution to form a 5 mg/ml mixture. Then the mixture was filled into pre-designed round models (diameter: 5 mm, height: 2 mm) and crosslinked to obtain engineered Col-Aln scaffolds. The release kinetics showed that Aln was released at an average rate of 2.99 μg/d in the initial 8 days and could sustainably release for 1 month. To detect the repair effects of the Col-Aln scaffolds for osteoporotic defects, the Col and Col-Aln scaffolds were implanted into 5 mm cranial defects in ovariectomized rats. After 3 months, the cranial defects implanted with Col-Aln scaffolds achieved more bone regeneration in defect area (11.74 ± 3.82%) than Col scaffold (5.12 ± 1.15%) (p < .05). Moreover, ovariectomized rats in Col-Aln scaffold group possessed more trabecular bone in femur metaphysis than Col scaffold group as analyzed by Micro-CT. This study demonstrated the engineered Col-Aln scaffold has the potential to repair osteoporotic bone defects and resist bone loss in osteoporosis.

Thermal responsive poly(N-isopropylacrylamide) grafted chicken feather keratin prepared via surface initiated aqueous Cu(0)-mediated RDRP: Synthesis and properties

Poultry chicken feather keratin was extracted and then modified for the fabrication of keratin-graft-PNIPAM copolymers. The keratin was well extracted from feather fiber and powdered. Subsequently, it underwent the surficial functionalization process with initiator groups. After the study conducted full disproportionation of Cu(I)Br/Me₆Tren into Cu(0) and Cu(II)Br₂ in the solvent, surface initiated aqueous Cu(0)-mediated reversible-deactivation radical polymerization (RDRP) of N-isopropylacrylamide (NIPAM) was performed in a methanol/water mixture solvent. The reaction was performed rapidly and efficiently, during which over 100% graft rate was achieved at 60 min. After 6 h reaction, 200% graft rate could be achieved. High graft rate (up to 287%) was achieved, and graft rate could be regulated by controlling the reaction time and the addition of monomer. The fabricated keratin-g-PNIPAM exhibited a rough surface. As revealed from the results of thermal analysis, the thermal stability of keratin-g-PNIPAM was enhanced noticeably compared with the original keratin. Besides, grafted PNIPAM chains exhibited a higher glass transition temperature. The grafted keratin particles displayed enhanced hydrophilicity. Keratin-g-PNIPAMs exhibit a lower LCST comparing to homopolymer and the flocculation in hot water behavior could be controlled by regulating graft rate.

Fabrication of mechanical robust keratin film by mesoscopic molecular network reconstruction and its performance for dye removal

Regenerated keratin-based adsorbents have attracted much attention in environmental pollution remediation. However, fabricating keratin-based adsorbents with excellent adsorption performance is still a challenging issue due to its weak mechanical property. In this study, mechanical robust keratin composite films were designed and engineered at mesoscopic scale by molecular network reconstruction strategy. It was found that the β-crystallites structure of silk fibroin template could induce the transformation of free unfolded molecular chains of keratin to β-sheet conformation and further resulted in the controllable manipulating of the mechanical properties of keratin films. This mechanical reinforced composite film showed high adsorption efficiency and capacity for dyes as well as ideal regeneration and recycling performance. Adsorption behavior of reactive brilliant blue KN-R by keratin composite films was comprehensively studied. The adsorption capacity (q_e) and removal efficiency for KN-R by the adsorbent could reach as high as 190.84 mg/g and 98.52%, respectively. The adsorbent exhibited excellent regeneration and recycling performance due to its mechanical robustness. The molecular network reconstruction strategy is both straightforward and effective for fabricating mechanical robust adsorbent for pollutant remediation.

Halloysite/Keratin Nanocomposite for Human Hair Photoprotection Coating

We propose a novel keratin treatment of human hair by its aqueous mixtures with natural halloysite clay nanotubes. The loaded clay nanotubes together with free keratin produce micrometer-thick protective coating on hair. First, colloidal and structural properties of halloysite/keratin dispersions and the nanotube loaded with this protein were investigated. Above the keratin isoelectric point (pH = 4), the protein adsorption into the positive halloysite lumen is favored because of the electrostatic attractions. The ζ-potential magnitude of these core-shell particles increased from -35 (in pristine form) to -43 mV allowing for an enhanced colloidal stability (15 h at pH = 6). This keratin-clay tubule nanocomposite was used for the immersion treatment of hair. Three-dimensional-measuring laser scanning microscopy demonstrated that 50-60% of the hair surface coverage can be achieved with 1 wt % suspension application. Hair samples have been exposed to UV irradiation for times up to 72 h to explore the protection capacity of this coating by monitoring the cysteine oxidation products. The nanocomposites of halloysite and keratin prevent the deterioration of human hair as evident by significant inhibition of cysteic acid. The successful hair structure protection was also visually confirmed by atomic force microscopy and dark-field hyperspectral microscopy. The proposed formulation represents a promising strategy for a sustainable medical coating on the hair, which remediates UV irradiation stress.

Delayed two steps PRP injection strategy for the improvement of fat graft survival with superior angiogenesis

Platelet-rich plasma (PRP) has been widely used to improve the fat retention rate in autologous fat transplantation since it possesses a good angiogenesis capability in vivo. However, due to the short half-life of growth factors released from PRP and its uneven distribution in injected fat tissue, the strategy of PRP in fat transplantation needs further improvement. Since the capillaries started to grow into fat grafts in 1 week and vascular growth peaks in the second week after transplantation, we hypothesized that delayed two-steps PRP injection into the interior of grafts, accompanied with the extent of neovascularization might theoretically promote microvessel growth inside transplanted adipose tissue. 24 nude mice were divided into three groups: Blank group (0.35 mL fat mixed with 0.15 mL saline, N = 8), Single step group (0.35 mL fat mixed with 0.15 mLPRP, N = 8), and Two steps group (0.35 mL fat (day 0) + 0.075 mL PRP (day 7) + 0.075 mL PRP (day 14), N = 8). At 6 and 14 weeks post-transplantation, grafts were dissected, weighted, and assessed for histology, angiogenesis, fat regeneration and inflammation level. The weight and volume of the fat samples revealed no statistical difference among the three groups at 6 weeks after fat transplantation. The weight and volume of the Two steps group fat samples showed significantly higher compared to that in Blank and Single step groups at 14 weeks after fat transplantation (weight: 137.25 ± 5.60 mg versus 87.5 ± 3.90 mg,106.75 ± 2.94 mg, respectively; volume: 0.13 ± 0.01 mL versus 0.08 ± 0.01 mL, 0.09 ± 0.01 mL, respectively). Histological assessments indicated that delayed two-steps PRP injection strategy helps to improve adipose tissue content and reduce the composition of fibrous connective tissue at 14 weeks after fat transplantation. At 6 weeks and 14 weeks after transplantation, CD31 immunofluorescence indicated that delayed two-steps PRP injection strategy helps to improve angiogenesis and significantly higher compared to that in Blank and Single step groups (6 weeks: 28.75 ± 4.54 versus 10.50 ± 2.06, 21.75 ± 1.85; 14 weeks: 21.75 ± 2.86 versus 9.87 ± 2.08, 11.75 ± 1.47, respectively). Preadipocyte count indicated delayed two-steps PRP injection strategy might promote fat regeneration and significantly higher compared to that in Blank and Single step groups at 14 weeks (129.75 ± 6.57 versus 13.50 ± 3.50, 17.12 ± 6.23, respectively). In this study, we demonstrated that the novel delayed two-steps PRP injection strategy remarkably enhanced the long-term fat retention rate and improved the neovascularization extent in the interior of the fat graft. Platelet-rich plasma, Delayed two-steps injection, Angiogenesis, Fat transplantation.

Hair keratin promotes wound healing in rats with combined radiation-wound injury

Keratins derived from human hair have been suggested to be particularly effective in general surgical wound healing. However, the healing of a combined radiation-wound injury is a multifaceted regenerative process. Here, hydrogels fabricated with human hair keratins were used to test the wound healing effects on rats suffering from combined radiation-wound injuries. Briefly, the keratin extracts were verified by dodecyl sulfate polyacrylamide gel electrophoresis analysis and amino acid analysis, and the keratin hydrogels were then characterized by morphological observation, Fourier transform infrared spectroscopy analysis and rheology analyses. The results of the cell viability assay indicated that the keratin hydrogels could enhance cell growth after radiation exposure. Furthermore, keratin hydrogels could accelerate wound repair and improve the survival rate in vivo. The results demonstrate that keratin hydrogels possess a strong ability to accelerate the repair of a combined radiation-wound injury, which opens up new tissue regeneration applications for keratins.

In Vivo Evaluation of Three-Dimensional Printed, Keratin-Based Hydrogels in a Porcine Thermal Burn Model

Keratin is a natural material that can be derived from the cortex of human hair. Our group had previously presented a method for the printed, sequential production of three-dimensional (3D) keratin scaffolds. Using a riboflavin-sodium persulfate-hydroquinone (initiator-catalyst-inhibitor) photosensitive solution, we produced 3D keratin-based constructs through ultraviolet crosslinking in a lithography-based 3D printer. In this study, we have used this bioink to produce a keratin-based construct that is capable of delivering small molecules, providing an environment conducive to healing of dermal burn wounds in vivo, and maintaining stability in customized packaging. We characterized the effects of manufacturing steps, such as lyophilization and gamma irradiation sterilization on the properties of 3D printed keratin scaffolds prepared for in vivo testing. Keratin hydrogels are viable for the uptake and release of contracture-inhibiting Halofuginone, a collagen synthesis inhibitor that has been shown to decrease collagen synthesis in fibrosis cases. This small-molecule delivery provides a mechanism to reduce scarring of severe burn wounds in vitro. In vivo data show that the Halofuginone-laden printed keratin is noninferior to other similar approaches reported in literature. This is indicative that the use of 3D printed keratin is not inhibiting the healing processes, and the inclusion of Halofuginone induces a more organized dermal healing after a burn; in other words, this treatment is slower but improves healing. These studies are indicative of the potential of Halofuginone-laden keratin dressings in dermal wound healing. We aim to keep increasing the complexity of the 3D printed constructs toward the production of complex scaffolds for the treatment and topographical reconstruction of severe burn wounds to the face.

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.

Healing of Chronic Wounds: An Update of Recent Developments and Future Possibilities

Chronic wounds are the result of disruptions in the body's usual process of healing. They are not only a source of significant pain and discomfort but also, more importantly, an unguarded port of entry for pathogens into the body. While our current understanding of this phenomenon is far from complete, findings in physiological patterns and advancements in wound healing technologies have helped develop wound management and healing solutions to this long-standing medical challenge. This review presents an overview of known wound healing mechanics, abnormalities that lead to chronic wounds, and a summary of established and new wound healing technologies. Various approaches to heal wounds are discussed, from dermal replacements to advanced biomaterial-based treatments, from cell-, synthetic-, and composite-based approaches to preclinical approaches, which make developing such products possible. While tested breakthrough products are described, the authors focused more on recently developed innovations, which are at varying stages of maturity. The review concludes with a note on future perspectives and opinions on where the field and industry are headed and where they should be. Impact Statement Wound healing is an important area of research and clinical practice, and has captured the attention of tissue engineers since the nascent beginnings of the discipline. Tissue-engineered skin was the first FDA-approved product, achieved in 1996. Despite this success, and the passage of time, healing wounds, particularly chronic wounds, remains a vexing challenge. This comprehensive review article will provide readers with a synopsis of current issues, research approaches, animal models, technologies, and products that span the continuum from early development to clinical studies, in the hope of fueling new interests and ideas to overcome this long-standing medical challenge.

N-acetyl cysteine-loaded graphene oxide-collagen hybrid membrane for scarless wound healing

Wound dressings composed of natural polymers, such as type I collagen, possess good biocompatibility, water holding capacity, air permeability, and degradability, and can be used in wound repair. However, due to the persistent oxidative stress in the wound area, the migration and proliferation of fibroblasts might be suppressed, leading to poor healing. Thus, collagen-containing scaffolds are not suitable for accelerated wound healing. Antioxidant N-acetyl cysteine (NAC) is known to reduce the reactive oxygen species (ROS) and has been widely used in the clinic. Theoretically, the carboxyl group of NAC allows loading of graphene oxide (GO) for sustained release and may also enhance the mechanical properties of the collagen scaffold, making it a better wound-dressing material. Herein, we demonstrated an innovative approach for a potential skin-regenerating hybrid membrane using GO incorporated with collagen I and NAC (N-Col-GO) capable of continuously releasing antioxidant NAC. Methods: The mechanical stability, water holding capacity, and biocompatibility of the N-Col-GO hybrid membrane were measured in vitro. A 20 mm rat full-skin defect model was created to evaluate the repair efficiency of the N-Col-GO hybrid membrane. The vascularization and scar-related genes in the wound area were also examined. Results: Compared to the Col only scaffold, N-Col-GO hybrid membrane exhibited a better mechanical property, stronger water retention capacity, and slower NAC release ability, which likely promote fibroblast migration and proliferation. Treatment with the N-Col-GO hybrid membrane in the rat wound model showed complete healing 14 days after application which was 22% faster than the control group. HE and Masson staining confirmed faster collagen deposition and better epithelization, while CD31 staining revealed a noticeable increase of vascularization. Furthermore, Rt-PCR demonstrated decreased mRNA expression of profibrotic and overexpression of anti-fibrotic factors indicative of the anti-scar effect. Conclusion: These findings suggest that N-Col-GO drug release hybrid membrane serves as a better platform for scarless skin 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.

A Therapeutic Microneedle Patch Made from Hair-Derived Keratin for Promoting Hair Regrowth

Activating hair follicle stem cells (HFSCs) to promote hair follicle regrowth holds promise for hair loss therapy, while challenges still remain to develop a scenario that enables enhanced therapeutic efficiency and easy administration. Here we describe a detachable microneedle patch-mediated drug delivery system, mainly made from hair-derived keratin, for sustained delivery of HFSC activators. It was demonstrated that this microneedle device integrated with mesenchymal stem cell (MSC)-derived exosomes and a small molecular drug, UK5099, could enhance the treatment efficiency at a reduced dosage, leading to promoted pigmentation and hair regrowth within 6 days through two rounds of administration in a mouse model. This microneedle-based transdermal drug delivery approach shows augmented efficacy compared to the subcutaneous injection of exosomes and topical administration of UK5099.

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.

Collagen Functionalized With Graphene Oxide Enhanced Biomimetic Mineralization and in Situ Bone Defect Repair

Biomimetic mineralization using simulated body fluid (SBF) can form a bonelike apatite (Ap) on the natural polymers and enhance osteoconductivity and biocompatibility, and reduce immunological rejection. Nevertheless, the coating efficiency of the bonelike apatite layer on natural polymers still needs to be improved. Graphene oxide (GO) is rich in functional groups, such as carbonyls (-COOH) and hydroxyls (-OH), which can provide more active sites for biomimetic mineralization and improve the proliferation of the rat bone marrow stromal cells (r-BMSCs). In this study, we introduced 0%, 0.05%, 0.1%, and 0.2% w/v concentrations of GO into collagen (Col) scaffolds and immersed the fabricated scaffolds into SBF for 1, 7, and 14 days. In vitro environment scanning electron microscopy (ESEM), energy-dispersive spectrometry (EDS), thermogravimetric analysis (TGA), micro-CT, calcium quantitative analysis, and cellular analysis were used to evaluate the formation of bonelike apatite on the scaffolds. In vivo implantation of the scaffolds into the rat cranial defect was used to analyze the bone regeneration ability. The resulting GO-Col-Ap scaffolds exhibited a porous and interconnected structure coated with a homogeneous distribution of bonelike apatite on their surfaces. The Ca/P ratio of 0.1% GO-Col-Ap group was equal to that of natural bone tissue on the basis of EDS analysis. More apatites were observed in the 0.1% GO-Col-Ap group through TGA analysis, micro-CT evaluation, and calcium quantitative analysis. Furthermore, the 0.1% GO-Col-Ap group showed significantly higher r-BMSCs adhesion and proliferation in vitro and more than 2-fold higher bone formation than the Col-Ap group in vivo. Our study provides a new approach of introducing graphene oxide into bone tissue engineering scaffolds to enhance biomimetic mineralization.

Off-the-Shelf Biomimetic Graphene Oxide-Collagen Hybrid Scaffolds Wrapped with Osteoinductive Extracellular Matrix for the Repair of Cranial Defects in Rats

Hydrogels such as type I collagen (COL) have been widely studied in bone tissue repair, whereas their weak mechanical strength has limited their clinical application. By adding graphene oxide (GO) nanosheets, researchers have successfully improved the mechanical properties and biocompatibility of the hydrogels. However, for large bone defects, the osteoinductive and cell adhesion ability of the GO hybrid hydrogels need to be improved. Mesenchymal stem cell (MSC) secreted extracellular matrix (ECM), which is an intricate network, could provide a biomimetic microenvironment and functional molecules that enhance the cell proliferation and survival rate. To synergize the advantages of MSC-ECM with GO-COL hybrid implants, we developed a novel ECM scaffold construction method. First, an osteoinductive extracellular matrix (OiECM) was created by culturing osteodifferentiated bone marrow mesenchymal stem cells (BMSCs) for 21 days. Then, the GO-COL scaffold was fully wrapped with the OiECM to construct the OiECM-GO-COL composite for implantation. The morphology, physical properties, biocompatibility, and osteogenic performance of the OiECM-GO-COL implants were assessed in vitro and in vivo (5 mm rat cranial defect model). Both gene expression and cell level assessments suggested that the BMSCs cultured on OiECM-GO-COL implants had a higher proliferation rate and osteogenic ability compared to the COL or GO-COL groups. In vivo results showed that the OiECM-GO-COL implants achieved better repair effects in a rat critical cranial defect model, whereas bone formation in other groups was limited. This study provides a promising strategy, which greatly improves the osteogenic ability and biocompatibility of the GO hydrogels without the procedure of seeding and culturing MSCs on scaffolds in vitro, demonstrating its potential as an off-the-shelf method for bone tissue engineering.

Freeze-thaw cycles for biocompatible, mechanically robust scaffolds of human hair keratins

The keratin-based scaffolds are getting more and more attention in the application of tissue engineering. Though various approaches have been considered to improve the physical properties of these scaffolds, few succeeded in achieving the enhanced properties of the pure keratin scaffolds. Due to the presence of -OH, -NH₂ , >CO, and -SH on the extracted human hair keratin (HHK), the formation of hydrogen bonds and disulfide bridges could be triggered under certain conditions, leading to the self-cross-linking of HHK materials. Herein, a simple and green strategy was introduced, via freeze-thaw cycles of keratin solutions without addition of extraneous reagents, to obtain the mechanically robust HHK scaffolds. The comparative quantitation of residual -SH among the samples treated with 1, 5, and 9 cycles confirmed the oxidation in the thaw process for forming disulfide bonds. So, the equivalent thaw time was applied in this study, and three groups of the treated samples after 1, 5, and 9 cycles with an appropriate extension thaw time were prepared to solely investigate the effects of physical cross-linking networks, primarily by formation of hydrogen bonds, on the properties of the obtained scaffolds. The systematic assessments including swelling behavior, porosity, thermal analysis, compressive measurement, and microstructural observation confirmed that the repetitive freeze-thaw treatment contributed to mechanically robust scaffolds with good porous interconnectivity. The cell culturing experiments further verified that these HHK scaffolds had desirable cytocompatibility, permitting the proper proliferation, attachment, and infiltration. Accordingly, this study provided a simple and efficient method to obtain biocompatible, mechanically robust keratin scaffolds. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1452-1461, 2019.

GRGDS-functionalized chitosan nanoparticles as a potential intravenous hemostat for traumatic hemorrhage control in an animal model

Hemostats, which are used for immediate intervention during internal hemorrhage in order to reduce resulting mortality and morbidity, are relatively rare. Here, we describe novel intravenous nanoparticles (CPG-NPs-2000) with chitosan succinate (CSS) as cores, polyethylene glycol (PEG-2000) as spacers and a glycine-arginine-glycine-aspartic acid-serine (GRGDS) peptide as targeted, active hemostatic motifs. CPG-NPs-2000 displayed significant hemostatic efficacy, compared to the saline control, CSS nanoparticles, and tranexamic acid in liver trauma rat models. Further studies have demonstrated that CPG-NPs-2000 are effectively cleared from organs and blood, within 2 and 48 h, respectively. In addition, administration of CPG-NPs-2000 does not affect clotting function under normal physiological conditions, indicating their potential safety in vivo. CPG-NPs-2000 exhibit excellent thermal stability, good solubility, and redistribution ability, in addition to being low cost. These characteristics indicate that CPG-NPs-2000 may have strong potential as effective intravenous hemostats for treating severe internal bleeding.

Keratin: dissolution, extraction and biomedical application

Keratinous materials such as wool, feathers and hooves are tough unique biological co-products that usually have high sulfur and protein contents. A high cystine content (7-13%) differentiates keratins from other structural proteins, such as collagen and elastin. Dissolution and extraction of keratin is a difficult process compared to other natural polymers, such as chitosan, starch, collagen, and a large-scale use of keratin depends on employing a relatively fast, cost-effective and time efficient extraction method. Keratin has some inherent ability to facilitate cell adhesion, proliferation, and regeneration of the tissue, therefore keratin biomaterials can provide a biocompatible matrix for regrowth and regeneration of the defective tissue. Additionally, due to its amino acid constituents, keratin can be tailored and finely tuned to meet the exact requirement of degradation, drug release or incorporation of different hydrophobic or hydrophilic tails. This review discusses the various methods available for the dissolution and extraction of keratin with emphasis on their advantages and limitations. The impacts of various methods and chemicals used on the structure and the properties of keratin are discussed with the aim of highlighting options available toward commercial keratin production. This review also reports the properties of various keratin-based biomaterials and critically examines how these materials are influenced by the keratin extraction procedure, discussing the features that make them effective as biomedical applications, as well as some of the mechanisms of action and physiological roles of keratin. Particular attention is given to the practical application of keratin biomaterials, namely addressing the advantages and limitations on the use of keratin films, 3D composite scaffolds and keratin hydrogels for tissue engineering, wound healing, hemostatic and controlled drug release.