Understanding the nano-topography changes and cellular influences resulting from the surface adsorption of human hair keratins

Curcumin-loaded keratin-chitosan hydrogels for enhanced peripheral nerve regeneration

Peripheral nerve injury often leads to symptoms of motor and sensory impairment, and slow recovery of nerves after injury and limited treatment methods will aggravate symptoms or even lead to lifelong disability. Curcumin can promote peripheral nerve regeneration, but how to accurately deliver the appropriate concentration of curcumin in the local peripheral nerve remains to be solved. In this study, we designed a human hair keratin/chitosan (C/K) hydrogel with sodium tripolyphosphate ions crosslinked to deliver curcumin topically. Chitosan improves the mechanical properties of hydrogels and keratin improves the biocompatibility of hydrogels. C/K hydrogel showed good cytocompatibility, histocompatibility and degradability. In vitro experiments showed that hydrogels can continuously release curcumin for up to 10 days. In addition, a comprehensive analysis of behavioral, electrophysiological, histology, and target organ recovery results in animal experiments showed that locally delivered curcumin can enhance nerve regeneration in addition to hydrogels. In short, we provide a new method that combines the advantages of human hair keratin, chitosan, and curcumin for nerve damage repair.

Human hair proteins as natural reactive oxygen species scavengers for in vitro applications

Human hair proteins are recognized for their intrinsically high cysteine content. They can be solubilized while preserving their highly reductive thiol groups for free radical scavenging applications. The presence of aromatic and nucleophilic amino acids such as methionine, serine, phenylalanine, and threonine further contribute to the antioxidative potential of this material. Herein, utilizing the DPPH (2,2-diphenyl-1-picrylhydrazyl) and acellular 2',7'-dichlorodihydrofluorescein diacetate (H₂ DCFDA) assays, keratins are demonstrated to possess the highest radical scavenging activity among the studied hair proteins. Consequently, protection against hydrogen peroxide-induced oxidative stress in human dermal fibroblasts (HDFs) cultured in human hair keratin supplemented media is demonstrated. Quenching of reactive oxygen species in the HDF is observed using the CellROX Green dye and the expression levels of antioxidant (HMOX1, SOD2, GPX1) and tumor suppressor (TP53) genes is analyzed using qPCR. Collectively, this study presents further evidence and demonstrates the in vitro application potential of hair proteins, especially keratins, as an antioxidizing supplement.

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.

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.

Coating biopolymer nanofibers with carbon nanotubes accelerates tissue healing and bone regeneration through orchestrated cell- and tissue-regulatory responses

Tailoring the surface of biomaterial scaffolds has been a key strategy to modulate the cellular interactions that are helpful for tissue healing process. In particular, nanotopological surfaces have been demonstrated to regulate diverse behaviors of stem cells, such as initial adhesion, spreading and lineage specification. Here, we tailor the surface of biopolymer nanofibers with carbon nanotubes (CNTs) to create a unique bi-modal nanoscale topography (500 nm nanofiber with 25 nm nanotubes) and report the performance in modulating diverse in vivo responses including inflammation, angiogenesis, and bone regeneration. When administered to a rat subcutaneous site, the CNT-coated nanofiber exhibited significantly reduced inflammatory signs (down-regulated pro-inflammatory cytokines and macrophages gathering). Moreover, the CNT-coated nanofibers showed substantially promoted angiogenic responses, with enhanced neoblood vessel formation and angiogenic marker expression. Such stimulated tissue healing events by the CNT interfacing were evidenced in a calvarium bone defect model. The in vivo bone regeneration of the CNT- coated nanofibers was significantly accelerated, with higher bone mineral density and up-regulated osteogenic signs (OPN, OCN, BMP2) of in vivo bone forming cells. The in vitro studies using MSCs could demonstrate accelerated adhesion and osteogenic differentiation and mineralization, supporting the osteo-promoting mechanism behind the in vivo bone forming event. These findings highlight that the CNTs interfacing of biopolymer nanofibers is highly effective in reducing inflammation, promoting angiogenesis, and driving adhesion and osteogenesis of MSCs, which eventually orchestrate to accelerate tissue healing and bone regeneration process. STATEMENT OF SIGNIFICANCE: Here we demonstrate that the interfacing of biopolymer nanofibers with carbon nanotubes (CNTs) could modulate multiple interactions of cells and tissues that are ultimately helpful for the tissue healing and bone regeneration process. The CNT-coated scaffolds significantly reduced the pro-inflammatory signals while stimulating the angiogenic marker expressions. Furthermore, the CNT-coated scaffolds increased the bone matrix production of bone forming cells in vivo as well as accelerated the adhesion and osteogenic differentiation of MSCs in vitro. These collective findings highlight that the CNTs coated on the biopolymer nanofibers allow the creation of a promising platform for nanoscale engineering of biomaterial surface that can favor tissue healing and bone regeneration process, through a series of orchestrated events in anti-inflammation, pro-angiogenesis, and stem cell stimulation.

Enhanced performance of chitosan/keratin membranes with potential application in peripheral nerve repair

Although surgical management of peripheral nerve injuries (PNIs) has improved over time, autografts are still the current "gold standard" treatment for PNIs, which presents numerous limitations. In an attempt to improve natural biomaterial-based nerve guidance conduits (NGCs), chitosan (CHT), a derivative of the naturally occurring biopolymer chitin, has been explored for peripheral nerve regeneration (PNR). In addition to CHT, keratin has gained enormous attention as a biomaterial and tissue engineering scaffolding. In this study, biomimetic CHT/keratin membranes were produced using a solvent casting technique. These membranes were broadly characterized in terms of their surface topography and physicochemical properties, with techniques such as Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), contact angle, weight loss and water uptake measurements, Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). Biological in vitro assays were also performed, where a preliminary cytotoxicity screening with the L929 fibroblast cell line revealed that the membranes and respective materials are suitable for cell culture. In addition, Schwann cells, fibroblasts and endothelial cells were directly seeded in the membranes. Quantitative and qualitative assays revealed that the addition of keratin enhanced cell viablity and adhesion. Based on the encouraging in vitro results, the in vivo angiogenic/antiangiogenic potential of CHT and CHT/keratin membranes was assessed, using an optimized chick embryo chorioallantoic membrane assay, where higher angiogenic responses were seen in keratin-enriched materials. Overall, the obtained results indicate the higher potential of CHT/keratin membranes for guided tissue regeneration applications in the field of PNR.

Effects of Tunable Keratin Hydrogel Erosion on Recombinant Human Bone Morphogenetic Protein 2 Release, Bioactivity, and Bone Induction

IMPACT STATEMENT

Recombinant human bone morphogenetic protein 2 (rhBMP-2) delivery from collagen sponges for bone formation is an important clinical example of growth factors in tissue engineering. Side effects from rhBMP-2 burst release and rapid collagen resorption have led to investigation of alternative carriers. Here, keratin carriers with tunable erosion rates were formulated by varying disulfide crosslinking via ratios of oxidatively (keratose) to reductively (kerateine) extracted keratin. In vitro rhBMP-2 bioactivity increased with kerateine content, reaching levels greater than with collagen. Heterotopic bone formation in a mouse model depended on the keratin formulation, highlighting the importance of the growth factor carrier.

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.

A nanofibrous electrospun patch to maintain human mesenchymal cell stemness

Mesenchymal stem cells (MSCs) have been extensively investigated in regenerative medicine because of their crucial role in tissue healing. For these properties, they are widely tested in clinical trials, usually injected in cell suspension or in combination with tridimensional scaffolds. However, scaffolds can largely affect the fates of MSCs, inducing a progressive loss of functionality overtime. The ideal scaffold must delay MSCs differentiation until paracrine signals from the host induce their change. Herein, we proposed a nanostructured electrospun gelatin patch as an appropriate environment where human MSCs (hMSCs) can adhere, proliferate, and maintain their stemness. This patch exhibited characteristics of a non-linear elastic material and withstood degradation up to 4 weeks. As compared to culture and expansion in 2D, hMSCs on the patch showed a similar degree of proliferation and better maintained their progenitor properties, as assessed by their superior differentiation capacity towards typical mesenchymal lineages (i.e. osteogenic and chondrogenic). Furthermore, immunohistochemical analysis and longitudinal non-invasive imaging of inflammatory response revealed no sign of foreign body reaction for 3 weeks. In summary, our results demonstrated that our biocompatible patch favored the maintenance of undifferentiated hMSCs for up to 21 days and is an ideal candidate for tridimensional delivery of hMSCs. The present work reports a nanostructured patch gelatin-based able to maintain in vitro hMSCs stemness features. Moreover, hMSCs were able to differentiate toward osteo- and chondrogenic lineages once induces by differentiative media, confirming the ability of this patch to support stem cells for a potential in vivo application. These attractive properties together with the low inflammatory response in vivo make this patch a promising platform in regenerative medicine.

Keratin mediated attachment of stem cells to augment cardiomyogenic lineage commitment

The objective of this work was to develop a simple surface modification technique using keratin derived from human hair for efficient cardiomyogenic lineage commitment of human mesenchymal stem cells (hMSCs). Keratin was extracted from discarded human hair containing both the acidic and basic components along with the heterodimers. The extracted keratin was adsorbed to conventional tissue culture polystyrene surfaces at different concentration. Keratin solution of 500μg/ml yielded a well coated layer of 12±1nm thickness with minimal agglomeration. The keratin coated surfaces promoted cell attachment and proliferation. Large increases in the mRNA expression of known cardiomyocyte genes such as cardiac actinin, cardiac troponin and β-myosin heavy chain were observed. Immunostaining revealed increased expression of sarcomeric α-actinin and tropomyosin whereas Western blots confirmed higher expression of tropomyosin and myocyte enhancer factor 2C in cells on the keratin coated surface than on the non-coated surface. Keratin promoted DNA demethylation of the Atp2a2 and Nkx2.5 genes thereby elucidating the importance of epigenetic changes as a possible molecular mechanism underlying the increased differentiation. A global gene expression analysis revealed a significant alteration in the expression of genes involved in pathways associated in cardiomyogenic commitment including cytokine and chemokine signaling, cell-cell and cell-matrix interactions, Wnt signaling, MAPK signaling, TGF-β signaling and FGF signaling pathways among others. Thus, adsorption of keratin offers a facile and affordable yet potent route for inducing cardiomyogenic lineage commitment of stem cells with important implications in developing xeno-free strategies in cardiovascular regenerative medicine.

Effects of chemical structures of polycarboxylic acids on molecular and performance manipulation of hair keratin

A non-toxic hair crosslinking formula containing polycarboxylic acids and featuring a high treatment performance and mechanical retention is developed.

Modulation of keratin in adhesion, proliferation, adipogenic, and osteogenic differentiation of porcine adipose-derived stem cells

Recently, keratin attracts tremendous interest because of its intrinsic ability to interact with different cells. It has the potential to serve as a controllable extracellular matrix protein that can be used to demonstrate cell mechanism and cell-matrix interaction. However, there have been relatively few studies on the effects of keratin on stem cells. In the present work, we study the effects of human keratin on porcine adipose-derived stem cells (pASCs) and a series of selective cell lines: 3T3 fibroblasts, Madin-Darby canine kidney (MDCK) cells, and MG63 osteoblasts. Relative to un-treated culture plate, our results showed that keratin coating substrates promote cell adhesion and proliferation to above cell lines. Keratin also improved pASCs adhesion, proliferation, and enhanced cell viability. Evaluation of genetic markers showed that adipogenic and osteogenic differentiations of pASCs can be successfully induced, thus demonstrating that keratin did not influence the stemness of pASCs. Furthermore, keratin improved adipogenic differentiations of pASCs in terms of up-regulations in lipoprotein lipase, peroxisome proliferator-activated receptor gamma, and CCAAT-enhancer-binding protein alpha. The osteogenic markers type I collagen, runt-related transcription factor 2, and vitamin D receptor were also upregulated when pASCs cultured on keratin substrates. Therefore, keratin can serve as a biological derived material for surface modification and scaffold fabrication for biomedical purpose. The combination of keratin with stem cells may be a potential candidate for tissue repair in the field of regenerative medicine. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 180-192, 2017.

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.

Evaluation of the osteoinductive potential of a bio-inspired scaffold mimicking the osteogenic niche for bone augmentation

Augmentation of regenerative osteogenesis represents a premier clinical need, as hundreds of thousands of patients are left with insufficient healing of bony defects related to a host of insults ranging from congenital abnormalities to traumatic injury to surgically-induced deficits. A synthetic material that closely mimics the composition and structure of the human osteogenic niche represents great potential to successfully address this high demand. In this study, a magnesium-doped hydroxyapatite/type I collagen scaffold was fabricated through a biologically-inspired mineralization process and designed to mimic human trabecular bone. The composition of the scaffold was fully characterized by XRD, FTIR, ICP and TGA, and compared to human bone. Also, the scaffold microstructure was evaluated by SEM, while its nano-structure and nano-mechanical properties were evaluated by AFM. Human bone marrow-derived mesenchymal stem cells were used to test the in vitro capability of the scaffold to promote osteogenic differentiation. The cell/scaffold constructs were cultured up to 7 days and the adhesion, organization and proliferation of the cells were evaluated. The ability of the scaffold to induce osteogenic differentiation of the cells was assessed over 3 weeks and the correlate gene expression for classic genes of osteogenesis was assessed. Finally, when tested in an ectopic model in rabbit, the scaffold produced a large volume of trabecular bone in only two weeks, that subsequently underwent maturation over time as expected, with increased mature cortical bone formation, supporting its ability to promote bone regeneration in clinically-relevant scenarios. Altogether, these results confirm a high level of structural mimicry by the scaffold to the composition and structure of human osteogenic niche that translated to faster and more efficient osteoinduction in vivo--features that suggest such a biomaterial may have great utility in future clinical applications where bone regeneration is required.

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.

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.

Potential avoidance of adverse analgesic effects using a biologically "smart" hydrogel capable of controlled bupivacaine release

Acute pain remains a tremendous clinical and economic burden, as its prevalence and common narcotic-based treatments are associated with poorer outcomes and higher costs. Multimodal analgesia portends great therapeutic promise, but rarely allows opioid sparing, and new alternatives are necessary. Microparticles (MPs) composed of biodegradable polymers [e.g., poly(lactic-co-glycolic acid) or PLGA] have been applied for controlled drug release and acute pain treatment research. However, foreign particles' presence within inflamed tissue may affect the drug release or targeting, and/or cause a secondary inflammatory reaction. We examined how small alterations in the particulate nature of MPs affect both their uptake into and subsequent activation of macrophages. MPs composed of PLGA and chitosan (PLGA-Chi) loaded with bupivacaine (BP) were engineered at different sizes and their opsonization by J774 macrophages was assessed. Uptake of PLGA-Chi by macrophages was found to be size dependent, but they were not cytotoxic or proinflammatory in effect. Moreover, encapsulation of MPs in a thermoresponsive loading gel (pluronic F-127) effectively prevented opsonization. Finally, MPs displayed sustained, tunable release of BP up to 7 days. These results demonstrate our ability to develop a drug delivery system capable of controlled release of local anesthetics to treat acute/subacute pain while concurrently avoiding enhanced inflammation.

Crucial transcription factors in tendon development and differentiation: their potential for tendon regeneration

Tendons that connect muscles to bone are often the targets of sports injuries. The currently unsatisfactory state of tendon repair is largely attributable to the limited understanding of basic tendon biology. A number of tendon lineage-related transcription factors have recently been uncovered and provide clues for the better understanding of tendon development. Scleraxis and Mohawk have been identified as critical transcription factors in tendon development and differentiation. Other transcription factors, such as Sox9 and Egr1/2, have also been recently reported to be involved in tendon development. However, the molecular mechanisms and application of these transcription factors remain largely unclear and this prohibits their use in tendon therapy. Here, we systematically review and analyze recent findings and our own data concerning tendon transcription factors and tendon regeneration. Based on these findings, we provide interaction and temporal programming maps of transcription factors, as a basis for future tendon therapy. Finally, we discuss future directions for tendon regeneration with differentiation and trans-differentiation approaches based on transcription factors.

Enhanced osteogenesis by a biomimic pseudo-periosteum-involved tissue engineering strategy

Elaborating a bone replacement using tissue-engineering strategies for bone repair seems to be a promising remedy. However, previous platforms are limited in constructing three-dimensional porous scaffolds and neglected the critical importance of periosteum (a pivotal source of osteogenic cells for bone regeneration). We report here an innovative method using the periosteum as a template to replicate its exquisite morphologies onto the surfaces of biomaterials. The precise topographic cues (grooved micropatterns) on the surface of collagen membrane inherited from the periosteum effectively directed cell alignment as the way of natural periosteum. Besides, we placed the stem-cell and endothelial-cell-laden collagen membrane (pseudo-periosteum) onto a three-dimensional porous scaffold. The pseudo-periosteum-covered scaffolds showed remarkable osteogenesis when compared with the pseudo-periosteum-free scaffolds, indicating the significant importance of pseudo-periosteum on bone regeneration. This study gives a novel concept for the construction of bone tissue engineering scaffold and may provide new insight for periosteum research.

Electrospun human keratin matrices as templates for tissue regeneration

Aim: The aim of this work was to study the feasibility of fabricating human hair keratin matrices through electrospinning and to evaluate the potential of these matrices for tissue regeneration. Materials & methods: Keratin was extracted from human hair using Na2S and blended with poly(ethylene oxide) in the weight ratio of 60:1 for electrospinning. Physical morphology and chemical properties of the matrices were characterized using scanning electron microscopy and Fourier transform infrared spectroscopy, respectively. Cell viability and morphology of murine and human fibroblasts cultured on the matrices were evaluated through the Live/Dead® assay and scanning electron microscopy. Results: Electrospun keratin matrices were successfully produced without affecting the chemical conformation of keratin. Fibroblasts cultured on keratin matrices showed healthy morphology and penetration into matrices at day 7. Conclusion: Electrospun human hair keratin matrices provide a bioinductive and structural environment for cell growth and are thus attractive as alternative templates for tissue regeneration.