Electrospun human keratin matrices as templates for tissue regeneration

Development of keratin-based fibers fabricated by interfacial polyelectrolyte complexation for suture applications

Interfacial Polyelectrolyte Complexation (IPC) is a convenient way to produce composite, micro-scale fibers. In this paper, we report the successful development of novel keratin-based IPC fibers and also demonstrate the feasibility of using these fibers as sutures through a proof-of-concept in vivo study. Two composite fibers were produced: chitosan-keratin (CK) and keratin-keratin (KK). These fibers were evaluated for their physico-chemical, mechanical and biochemical properties. In the dry state, the CK fiber had a greater Young's modulus of about 2 GPa while the KK fiber registered a longer strain-at-break of about 100 % due to the strain-stiffening effect. Notably, the keratins were found to assemble into amyloids within the composite fibers based on Congo red staining and Wide-Angle X-Ray Scattering. Functionally, both fibers were malleable could be weaved, braided and knotted. When used as sutures to close incisional wounds in mice over 21 days, these fibers were found to elicit minimal host tissue response and were partially degraded over the duration. Interestingly, the KK fiber evoked a lower extent of immune cell response and fibrous capsule encapsulation that was comparable to commercial, non-absorbable Dafilon® sutures. This work demonstrated the possibility of producing keratin-based IPC fibers which may find practicality as medical sutures.

Investigation of human hair keratin-based nanofibrous scaffold for skin tissue engineering application

Keratin-based nanofibers were fabricated using the electrospinning technique, and their potential as scaffolds for tissue engineering was investigated. Keratin, extracted from the human hair, was blended with poly(vinyl alcohol) (PVA) in an aqueous medium. Morphological characterizations of the fabricated PVA-keratin nanofiber (PK-NF) random and aligned scaffolds performed using a scanning electron microscope (SEM) revealed the formation of uniform and randomly oriented nanofibers with an interconnected three-dimensional network structure. The mean diameter of the nanofibers ranged from 100 to 250 nm. Functional groups and structural studies were done by infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analysis. FTIR study suggested that PVA interacted with keratin by hydrogen bonding. Moreover, the in vitro cell culture study could suggest that PK-NF scaffolds were non-cytotoxic by supporting the growth of murine embryonic stem cells (ESCs), human keratinocytes (HaCaT), and dermal fibroblast (NHDF) cell lines. Further, the immunocytochemical characterization revealed the successful infiltration, adhesion, and growth of ESCs, HaCaT, and NHDF cells seeded on PK-NF scaffolds. However, there was no noteworthy difference observed concerning cell growth and viability irrespective of the random and aligned internal fibril arrangement of the PK-NF scaffolds. The infiltration and growth pattern of HaCaT and NHDF cells adjacent to each other in a 3D co-culture study mimicked that of epidermal and dermal skin cells and indeed underscored the potential of PK-NFs as a scaffold for skin tissue engineering.

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.

Human Hair Keratin Composite Scaffold: Characterisation and Biocompatibility Study on NIH 3T3 Fibroblast Cells

The aim of this study was to transform human hair keratin waste into a scaffold for soft tissue engineering to heal wounds. The keratin was extracted using the Shindai method. Keratin and polyvinyl alcohol (PVA) was cross-linked with alginate dialdehyde and converted into a scaffold by the freeze-drying method using gentamycin sulphate (GS) as a model drug. The scaffold was subjected to Fourier transform infrared spectra (FTIR), swelling index, porosity, water absorption, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), X-ray diffraction (XRD), drug release, and cell viability (MTT) analysis. The scaffold was tested for keratinocyte growth using the murine fibroblast cell line (NIH 3T3 cells). The outcome from the keratin had a molecular weight band between 52-38 kDa in SDS-PAGE (Sodium dodecylsulfate-Polyacrylamide gel electrophoresis). A porous scaffold was capable of water absorption (73.64 ± 14.29%), swelling ability (68.93 ± 1.33%), and the release of GS shown as 97.45 ± 4.57 and 93.86 ± 5.22 of 1:4 and 1:3 scaffolds at 16 h. The physicochemical evaluation revealed that the prepared scaffold exhibits the proper structural integrity: partially crystalline with a strong thermal property. The scaffold demonstrated better cell viability against the murine fibroblast cell line (NIH 3T3 cells). In conclusion, we found that the prepared composite scaffold (1:4) can be used for wound healing applications.

Development of a Multi-Layer Skin Substitute Using Human Hair Keratinic Extract-Based Hybrid 3D Printing

Large-sized or deep skin wounds require skin substitutes for proper healing without scar formation. Therefore, multi-layered skin substitutes that mimic the genuine skin anatomy of multiple layers have attracted attention as suitable skin substitutes. In this study, a novel skin substitute was developed by combining the multi-layer skin tissue reconstruction method with the combination of a human-derived keratinic extract-loaded nano- and micro-fiber using electrospinning and a support structure using 3D printing. A polycaprolactone PCL/keratin electrospun scaffold showed better cell adhesion and proliferation than the keratin-free PCL scaffold, and keratinocytes and fibroblasts showed better survival, adhesion, and proliferation in the PCL/keratin electrospun nanofiber scaffold and microfiber scaffold, respectively. In a co-culture of keratinocytes and fibroblasts using a multi-layered scaffold, the two cells formed the epidermis and dermal layer on the PCL/keratin scaffold without territorial invasion. In the animal study, the PCL/keratin scaffold caused a faster regeneration of new skin without scar formation compared to the PCL scaffold. Our study showed that PCL/keratin scaffolds co-cultured with keratinocytes and fibroblasts promoted the regeneration of the epidermal and dermal layers in deep skin defects. Such finding suggests a new possibility for artificial skin production using multiple cells.

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.

Tendon tissue engineering: Cells, growth factors, scaffolds and production techniques

Tendon injuries are a global health problem that affects millions of people annually. The properties of tendons make their natural rehabilitation a very complex and long-lasting process. Thanks to the development of the fields of biomaterials, bioengineering and cell biology, a new discipline has emerged, tissue engineering. Within this discipline, diverse approaches have been proposed. The obtained results turn out to be promising, as increasingly more complex and natural tendon-like structures are obtained. In this review, the nature of the tendon and the conventional treatments that have been applied so far are underlined. Then, a comparison between the different tendon tissue engineering approaches that have been proposed to date is made, focusing on each of the elements necessary to obtain the structures that allow adequate regeneration of the tendon: growth factors, cells, scaffolds and techniques for scaffold development. The analysis of all these aspects allows understanding, in a global way, the effect that each element used in the regeneration of the tendon has and, thus, clarify the possible future approaches by making new combinations of materials, designs, cells and bioactive molecules to achieve a personalized regeneration of a functional tendon.

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.

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.

New Nanofibers Based on Protein By-Products with Bioactive Potential for Tissue Engineering

Concentrated collagen hydrolysate (HC10CC), rabbit collagen glue (RCG), and keratin hydrolysate (KH) were investigated in terms of their extraction from mammalian by-products and processing by electrospinning. The electrospun nanofibers were characterized by scanning electron microscopy coupled with the energy dispersive X-ray spectroscopy (SEM/EDS), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), differential scanning calorimetry (DSC), and indentation tests. The cytotoxicity of the electrospun nanofibers was conducted on L929 fibroblast cells using MTT and LDH assays and cell morphology observations. The electrospun RCG and KH nanofibers morphology showed an average size of nanofibers ranging between 44 and 410 nm, while the electrospun HC10CC nanofibers exhibited higher sizes. The ATR-FTIR spectra performed both on extracted proteins and electrospun nanofibers showed that the triple helix structure of collagen is partially preserved. The results were in agreement with the circular dichroism analysis for protein extracts. Furthermore, the viscoelastic properties of electrospun KH nanofibers were superior to those of electrospun RCG nanofibers. Based on both in vitro quantitative and qualitative analysis, the electrospun nanofibers were not cytotoxic, inducing a healthy cellular response. The results of new electrospun protein-based nanofibers may be useful for further research on bioactive properties of these nanofibers for tissue engineering.

4D printing and stimuli-responsive materials in biomedical aspects

Three-dimensional (3D) printing has revolutionized the world manufacturing production. In biomedical applications, however, 3D printed constructs fell short of expectations mainly due to their inability to adequately mimic the dynamic human tissues. To date, most of the 3D printed biomedical structures are largely static and inanimate as they lack the time-dependant dimension. To adequately address the dynamic healing and regeneration process of human tissues, 4D printing emerges as an important development where "time" is incorporated into the conventional concept of 3D printing as the fourth dimension. As such, additive manufacturing (AM) evolves from 3D to 4D printing and in the process putting stimulus-responsive materials in the limelight. In this review, the state-of-the-art efforts in integrating the time-dependent behaviour of stimulus-responsive materials in 4D printing will be discussed. In addition, current literatures on the interactions between various types of stimuli (categorized under physical, chemical and biological signals) with the associated stimulus-responsive materials will be the major focus in this review. Lastly, potential usage of 4D printing in biomedical applications will also be discussed, followed by technical considerations as well as outlook for future discoveries. STATEMENT OF SIGNIFICANCE: In this Review, we have demonstrated the significance of 4D printing in biomedical applications, in which "time" has been incorporated into the conventional concept of 3D printing as the 4th dimension. As such, 4D printing differentiates and evolves from 3D printing using stimulus-responsive materials which can actively respond to external stimuli and more sophisticated "hardware"-printer which can achieve multi-printing via mathematical-predicted designs that are programmed to consider the transformation of 3D constructs over time. The emphasize will be on the interactions between various types of stimuli (categorized under physical, chemical and biological signals) with the associated stimulus-responsive materials, followed by technical considerations as well as outlook for future discoveries.

Therapeutic strategies for skin regeneration based on biomedical substitutes

Regenerative medicine and tissue engineering (TE) have experienced significant advances in the development of in vitro engineered skin substitutes, either for replacement of lost tissue in skin injuries or for the generation of in vitro human skin models to research. However, currently available skin substitutes present different limitations such as expensive costs, abnormal skin microstructure and engraftment failure. Given these limitations, new technologies, based on advanced therapies and regenerative medicine, have been applied to develop skin substitutes with several pharmaceutical applications that include injectable cell suspensions, cell-spray devices, sheets or 3Dscaffolds for skin tissue regeneration and others. Clinical practice for skin injuries has evolved to incorporate these innovative applications to facilitate wound healing, improve the barrier function of the skin, prevent infections, manage pain and even to ameliorate long-term aesthetic results. In this article, we review current commercially available skin substitutes for clinical use, as well as the latest advances in biomedical and pharmaceutical applications used to design advanced therapies and medical products for wound healing and skin regeneration. We highlight the current progress in clinical trials for wound healing as well as the new technologies that are being developed and hold the potential to generate skin substitutes such as 3D bioprinting-based strategies.

Improving Thermal, Mechanical, and Barrier Properties of Feather Keratin/Polyvinyl Alcohol/Tris(hydroxymethyl)aminomethane Nanocomposite Films by Incorporating Sodium Montmorillonite and TiO₂

In this study, feather keratin/polyvinyl alcohol/tris(hydroxymethyl)aminomethane (FK/PVA/Tris) bionanocomposite films containing two types of nanoparticles, namely one-dimensional sodium montmorillonite (MMT) clay platelets (0.5, 1, 3, and 5 wt%) and three-dimensional TiO₂ nanospheres (0.5, 1, 3, and 5 wt%), are prepared using solvent casting method. X-ray diffraction studies confirm the completely exfoliated structure of FK/PVA/Tris/MMT nanocomposites. The successful formation of new hydrogen bonds between the hydroxyl groups of the film matrix and the nanofillers is confirmed by Fourier transform infrared spectroscopy. The tensile strength, elongation at break, and initial degradation temperature of the films are enhanced after MMT and TiO₂ incorporation. The water vapor permeability, oxygen permeability, and light transmittance decrease with increase in TiO₂ and MMT contents. In summary, nanoblending is an effective method to promote the application of FK/PVA/Tris blend films in the packaging field.

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.

Improving the Water Resistance and Mechanical Properties of Feather Keratin/Polyvinyl Alcohol/Tris(Hydroxymethyl)Aminomethane Blend Films by Cross-Linking with Transglutaminase, CaCl₂, and Genipin

The high moisture sensitivity of feather keratin/polyvinyl alcohol/tris(hydroxymethyl)aminomethane (FK/PVA/Tris) blend films hinders their application in the packaging field. Thus, in order to improve the water resistance and mechanical properties of such blend films, we attempted cross-linking the blend film with cross-linking agents such as transglutaminase (TG), CaCl₂, and genipin. Obvious differences in the morphology of the blended films were observed by scanning electron microscopy before and after cross-linking, indicating that cross-linking can inhibit the phase separation of the blend film. Conformational changes in the blend films after cross-linking were detected by Fourier transform infrared spectroscopy. Importantly, from examination of the total soluble mass, contact angle measurements, and water vapor permeability tests, it was apparent that cross-linking greatly improved the water resistance of the blend films, in addition to enhancing the mechanical properties (i.e., tensile strength and elongation at break). However, cross-linking was also found to reduce the oxygen barrier properties of the blend films. Therefore, cross-linking appears to be an effective method for promoting the application of FK/PVA/Tris blend films in the packaging field.

Mesenchymal Stem Cell Secretome Improves Tendon Cell Viability In Vitro and Tendon-Bone Healing In Vivo When a Tissue Engineering Strategy Is Used in a Rat Model of Chronic Massive Rotator Cuff Tear

BACKGROUND

Massive rotator cuff tears (MRCTs) represent a major clinical concern, especially when degeneration and chronicity are involved, which highly compromise healing capacity.

PURPOSE

To study the effect of the secretome of mesenchymal stem cells (MSCs) on tendon cells (TCs) followed by the combination of these activated TCs with an electrospun keratin-based scaffold to develop a tissue engineering strategy to improve tendon-bone interface (TBi) healing in a chronic MRCT rat model.

STUDY DESIGN

Controlled laboratory study.

METHODS

Human TCs (hTCs) cultured with the human MSCs (hMSCs) secretome (as conditioned media [CM]) were combined with keratin electrospun scaffolds and further implanted in a chronic MRCT rat model. Wistar-Han rats (N = 15) were randomly assigned to 1 of 3 groups: untreated lesion (MRCT group, n = 5), lesion treated with a scaffold only (scaffold-only group, n = 5), and lesion treated with a scaffold seeded with hTCs preconditioned with hMSCs-CM (STC_hMSC_CM group, n = 5). After sacrifice, 16 weeks after surgery, the rotator cuff TBi was harvested for histological analysis and biomechanical testing.

RESULTS

The hMSCs secretome increased hTCs viability and density in vitro. In vivo, a significant improvement of the tendon maturing score was observed in the STC_hMSC_CM group (mean ± standard error of the mean, 15.6 ± 1.08) compared with the MRCT group (11.0 ± 1.38; P < .05). Biomechanical tests revealed a significant increase in the total elongation to rupture (STC_hMSC_CM, 11.99 ± 3.30 mm; scaffold-only, 9.89 ± 3.47 mm; MRCT, 5.86 ± 3.16 mm; P < .05) as well as a lower stiffness (STC_hMSC_CM, 6.25 ± 1.74 N/mm; scaffold-only, 6.72 ± 1.28 N/mm; MRCT, 11.54 ± 2.99 N/mm; P < .01).

CONCLUSION

The results demonstrated that hMSCs-CM increased hTCs viability and density in vitro. Clear benefits also were observed when these primed cells were integrated into a tissue engineering strategy with an electrospun keratin scaffold, as evidenced by improved histological and biomechanical properties for the STC_hMSC_CM group compared with the MRCT group.

CLINICAL RELEVANCE

This work supports further investigation into the use of MSC secretome for priming TCs toward a more differentiated phenotype, and it promotes the tissue engineering strategy as a promising modality to help improve treatment outcomes for chronic MRCTs.

Cellulose/keratin–catechin nanocomposite hydrogel for wound hemostasis

Rapid wound hemostatic was achieved by a composite hydrogel based on human hair keratin–catechin nanoparticles and cellulose.

Human Hair Keratin for Biocompatible Flexible and Transient Electronic Devices

Biomaterials have been attracting attention as a useful building block for biocompatible and bioresorbable electronics due to their nontoxic property and solution processability. In this work, we report the integration of biocompatible keratin from human hair as dielectric layer for organic thin-film transistors (TFTs), with high performance, flexibility, and transient property. The keratin dielectric layer exhibited a high capacitance value of above 1.27 μF/cm² at 20 Hz due to the formation of electrical double layer. Fully solution-processable TFTs based on p-channel poly[4-(4,4-dihexadecyl-4H-cyclopenta[1,2-b:5,4-b]dithiophen-2-yl)-alt[1,2,5]thiadiazolo[3,4-c]-pyridine] (PCDTPT) and keratin dielectric exhibited high electrical property with a saturation field-effect mobility of 0.35 cm²/(Vs) at a low gate bias of -2 V. We also successfully demonstrate flexible TFTs, which exhibited good mechanical flexibility and electrical stability under bending strain. An artificial electronic synaptic PCDTPT/keratin transistor was also realized and exhibited high-performance synaptic memory effects via simple operation of proton conduction in keratin. An added functionality of using keratin as a substrate was also presented, where similar PCDTPT TFTs with keratin dielectric were built on top of keratin substrate. Finally, we observed that our prepared devices can be degraded in ammonium hydroxide solution, establishing the feasibility of keratin layer as various components of transient electrical devices, including as a substrate and dielectric layer.

Functional electrospun fibers for the treatment of human skin wounds

Wounds are trauma induced defects of the human skin involving a multitude of endogenous biochemical events and cellular reactions of the immune system. The healing process is extremely complex and affected by the patient's physiological conditions, potential implications like infectious pathogens and inflammation as well as external factors. Due to increasing incidence of chronic wounds and proceeding resistance of infection pathogens, there is a strong need for effective therapeutic wound care. In this context, electrospun fibers with diameters in the nano- to micrometer range gain increasing interest. While resembling the structure of the native human extracellular matrix, such fiber mats provide physical and mechanical protection (including protection against bacterial invasion). At the same time, the fibers allow for gas exchange and prevent occlusion of the wound bed, thus facilitating wound healing. In addition, drugs can be incorporated within such fiber mats and their release can be adjusted by the material and dimensions of the individual fibers. The review gives a comprehensive overview about the current state of electrospun fibers for therapeutic application on skin wounds. Different materials as well as fabrication techniques are introduced including approaches for incorporation of drugs into or drug attachment onto the fiber surface. Against the background of wound pathophysiology and established therapy approaches, the therapeutic potential of electrospun fiber systems is discussed. A specific focus is set on interactions of fibers with skin cells/tissues as well as wound pathogens and strategies to modify and control them as key aspects for developing effective wound therapeutics. Further, advantages and limitations of controlled drug delivery from fiber mats to skin wounds are discussed and a future perspective is provided.

Antibacterial nanofibrous scaffolds with lowered cytotoxicity using keratin extracted from quail feathers

This study aims to extract keratin from quail feather wastes and incorporate it with silver nanoparticles into a synthetic biodegradable polymer in order to fabricate a nanofibrous scaffold with improved biomedical properties. Polyvinyl alcohol was used as the host polymer and spinning dopes with different amounts (0, 0.15, and 0.75 wt %) of extracted keratin and the same amount of silver nanoparticles prepared in order to fabricate scaffolds. According to the results, the scaffolds with a higher amount of extracted keratin (i.e. 0.75 wt %) provided less bead formation and more uniformity; also, they gave 99.9% and 98% of the antibacterial activity against gram negative ( Escherichia coli) and gram positive ( Staphylococcus aureus) bacteria, respectively. The analysis of the biological response of fibroblast cells cultured on the synthetic scaffolds exhibited remarkable improvement in comparison to the pristine (polyvinyl alcohol-Ag) scaffolds. This article concludes that the addition of extracted keratin into a polymeric matrix (polyvinyl alcohol) can improve both antibacterial properties and cell viability for the resultant scaffolds, and this qualifies them as potent candidates for biomedical applications.

Fabrication and Characterization of Electrospun PCL-MgO-Keratin-Based Composite Nanofibers for Biomedical Applications

Polymeric nanofibers are of great interest in biomedical applications, such as tissue engineering, drug delivery and wound healing, due to their ability to mimic and restore the function of natural extracellular matrix (ECM) found in tissues. Electrospinning has been heavily used to fabricate nanofibers because of its reliability and effectiveness. In our research, we fabricated poly(ε-caprolactone)-(PCL), magnesium oxide-(MgO) and keratin (K)-based composite nanofibers by electrospinning a blend solution of PCL, MgO and/or K. The electrospun nanofibers were analyzed by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), mechanical tensile testing and inductively-coupled plasma optical emission spectroscopy (ICP-OES). Nanofibers with diameters in the range of 0.2–2.2 µm were produced by using different ratios of PCL/MgO and PCL-K/MgO. These fibers showed a uniform morphology with suitable mechanical properties; ultimate tensile strength up to 3 MPa and Young’s modulus 10 MPa. The structural integrity of nanofiber mats was retained in aqueous and phosphate buffer saline (PBS) medium. This study provides a new composite material with structural and material properties suitable for potential application in tissue engineering.

Modulating Mesenchymal Stem Cell Behavior Using Human Hair Keratin-Coated Surfaces

Human mesenchymal stem cells (hMSCs) have shown great potential for therapeutic purposes. However, the low frequencies of hMSCs in the body and difficulties in expanding their numbers in vitro have limited their clinical use. In order to develop an alternative strategy for the expansion of hMSCs in vitro, we coated tissue culture polystyrene with keratins extracted from human hair and studied the behavior of cells from 2 donors on these surfaces. The coating resulted in a homogeneous distribution of nanosized keratin globules possessing significant hydrophilicity. Results from cell attachment assays demonstrated that keratin-coated surfaces were able to moderate donor-to-donor variability when compared with noncoated tissue culture polystyrene. STRO-1 expression was either sustained or enhanced on hMSCs cultured on keratin-coated surfaces. This translated into significant increases in the colony-forming efficiencies of both hMSC populations, when the cells were serially passaged. Human hair keratins are abundant and might constitute a feasible replacement for other biomaterials that are of animal origin. In addition, our results suggest that hair keratins may be effective in moderating the microenvironment sufficiently to enrich hMSCs with high colony-forming efficiency ex vivo, for clinical applications.

Culturing fibroblasts in 3D human hair keratin hydrogels

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

Calcium phosphate coated Keratin-PCL scaffolds for potential bone tissue regeneration

The incorporation of hydroxyapatite (HA) nanoparticles within or on the surface of electrospun polymeric scaffolds is a popular approach for bone tissue engineering. However, the fabrication of osteoconductive composite scaffolds via benign processing conditions still remains a major challenge to date. In this work, a new method was developed to achieve a uniform coating of calcium phosphate (CaP) onto electrospun keratin-polycaprolactone composites (Keratin-PCL). Keratin within PCL was crosslinked to decrease its solubility, before coating of CaP. A homogeneous coating was achieved within a short time frame (~10min) by immersing the scaffolds into Ca(2+) and (PO4)(3-) solutions separately. Results showed that the incorporation of keratin into PCL scaffolds not only provided nucleation sites for Ca(2+) adsorption and subsequent homogeneous CaP surface deposition, but also facilitated cell-matrix interactions. An improvement in the mechanical strength of the resultant composite scaffold, as compared to other conventional coating methods, was also observed. This approach of developing a biocompatible bone tissue engineering scaffold would be adopted for further in vitro osteogenic differentiation studies in the future.

Silk fibroin–keratin based 3D scaffolds as a dermal substitute for skin tissue engineering

Development of highly vascular dermal tissue-engineered skin substitutes with appropriate mechanical properties and cellular cues is in need for significant advancement in the field of dermal reconstruction.