Fabrication of PHBV/keratin composite nanofibrous mats for biomedical applications

The Effect of Multilayered Electrospun PLLA Nanofibers Coated with Human Amnion or Bladder ECM Proteins on Epithelialization and Smooth Muscle Regeneration in the Rabbit Bladder

Nanofibrous scaffolds have attracted much attention in bladder reconstruction approaches due to their excellent mechanical properties. In addition, their biological properties can be improved by combination with biological materials. Taking into account the advantages of nanofibrous scaffolds and decellularized extracellular matrix (dECM) in tissue engineering, scaffolds of poly-L-lactic acid (PLLA) coated with decellularized human amnion membrane (hAM) or sheep bladder (SB)-derived ECM proteins are developed (amECM-coated PLLA and sbECM-coated PLLA, respectively). The bladder regenerative potential of modified electrospun PLLA scaffolds is investigated in rabbits. The presence of ECM proteins is confirmed on the nanofibers' surface. Coating the surface of the PLLA nanofibers improves cell adhesion and proliferation. Histological and immunohistochemical evaluations show that rabbits subjected to cystoplasty with a multilayered PLLA scaffold show de novo formation and maturation of the multilayered urothelial layer. However, smooth muscle bundles (myosin heavy chain [MHC] and α-smooth muscle actin [α-SMA] positive) are detected only in ECM-coated PLLA groups. All groups show no evidence of a diverticulumor fistula in the urinary bladder. These results suggest that the biofunctionalization of electrospun PLLA nanofibers with ECM proteins can be a promising option for bladder tissue engineering. Furthermore, hAM can also replace animal-sourced ECM proteins in bladder tissue regeneration approaches.

Effect of Recombinant Spidroins Self-Assembly on Rheological Behavior of Their Dispersions and Structure of Electrospun Nanofibrous Materials

The effect of primary amino acid sequence in recombinant spidroins on their spatial organization is crucial for the fabrication of artificial fibers and fibrous materials. This study focuses on the rheological properties of aqueous and alcoholic solutions of recombinant analogs of natural spidroins (rS1/9 and rS2/12), as well as the structure of their films and nanofibrous materials. Non-Newtonian flow behavior of aqueous solutions of these proteins was observed at certain concentrations in contrast to their solutions in hexafluoroisopropanol. The secondary structure of recombinant spidroins was addressed by IR spectroscopy, whereas their self-organization in various solvents was studied by AFM and cryo-TEM. The influence of the solvent on the structure and properties of the films and nanofibrous materials produced by electrospinning has been established.

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

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

Multiresponsive Keratin-Polysulfobetaine Conjugate-Based Micelles as Drug Carriers with a Prolonged Circulation Time

A protein-polymer conjugate combines the chemical properties of a synthetic polymer chain with the biological properties of a protein. In this study, the initiator terminated with furan-protected maleimide was first synthesized through three steps. Then, a series of zwitterionic poly[3-dimethyl(methacryloyloxyethyl)ammonium propanesulfonate] (PDMAPS) was synthesized via atom transfer radical polymerization (ATRP) and optimized. Subsequently, well-controlled PDMAPS was conjugated with keratin via thiol-maleimide Michael addition. The keratin-PDMAPS conjugate (KP) could self-assemble in an aqueous solution to form micelles with low critical micelle concentration (CMC) values and good blood compatibility. The drug-loaded micelles exhibited triple responsiveness to pH, glutathione (GSH), and trypsin under tumor microenvironments. In addition, these micelles showed high toxicity against A549 cells while low toxicity on normal cells. Furthermore, these micelles performed prolonged blood circulation.

Recent Development of Polyhydroxyalkanoates (PHA)-Based Materials for Antibacterial Applications: A Review

The diseases caused by microorganisms are innumerable existing on this planet. Nevertheless, increasing antimicrobial resistance has become an urgent global challenge. Thus, in recent decades, bactericidal materials have been considered promising candidates to combat bacterial pathogens. Recently, polyhydroxyalkanoates (PHAs) have been used as green and biodegradable materials in various promising alternative applications, especially in healthcare for antiviral or antiviral purposes. However, it lacks a systematic review of the recent application of this emerging material for antibacterial applications. Therefore, the ultimate goal of this review is to provide a critical review of the state of the art recent development of PHA biopolymers in terms of cutting-edge production technologies as well as promising application fields. In addition, special attention was given to collecting scientific information on antibacterial agents that can potentially be incorporated into PHA materials for biological and durable antimicrobial protection. Furthermore, the current research gaps are declared, and future research perspectives are proposed to better understand the properties of these biopolymers as well as their possible applications.

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(3HB-co-3HV))/Bacterial Cellulose (BC) Biocomposites for Potential Use in Biomedical Applications

The aim of this study was to obtain biocomposites consisting of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), bacterial cellulose (BC) and α-tocopherol by a melt processing technique for potential use in biomedical applications. The melt processing and roughness of biocomposites were evaluated and compared to sample without BC. The degradation rate of PHBV/BC biocomposites was measured in phosphate buffer saline (PBS) by determining the mass variation and evidencing of thermal and structural changes by differential scanning calorimetry (DSC) and attenuated total reflectance-Fourier transformed infrared spectrometry (ATR-FTIR). The cell viability, cell morphology, cell cycle distribution and total collagen content were investigated on murine NCTC fibroblasts. Overall, the adding of BC to polyester matrix led to an adequate melt processing of biocomposites and increased surface roughness and cytocompatibility, allowing the cells to secrete the extracellular matrix (collagen) and stimulate cell proliferation. Results showed that the PHBV/BC biocomposites were favorable for long-term degradation and could be used for the design of medical devices with controlled degradability.

Hydrogen sulfide-releasing polyurethane/gelatin/keratin-TA conjugate mats for wound healing

Hydrogen sulfide (H₂S) has indispensable effects on wound healing promotion, such as anti-inflammatory, cell proliferation enhancement, and angiogenesis improvement. However, small-molecular donors have drawbacks of burst release and low biocompatibility. In this study, a novel bio-macromolecular donor of H₂S based on a keratin-thiobenzoic acid conjugate (KTC) was first synthesized by a thiol-disulfide exchange reaction. Then, the KTC was incorporated into polyurethane and gelatin to fabricate nanofibrous mats by electrospinning. Interestingly, both the KTC donor and biocomposite mats were capable of releasing H₂S triggered by glutathione (GSH) under physiological conditions. These mats had excellent water absorption capacity, demonstrating their great ability to absorb tissue exudate. In addition, these mats possessed a notable antioxidant ability, thereby protecting cell membranes from oxidation. Cell assays in vitro demonstrated that these mats could promote cell proliferation and migration. Furthermore, the in vivo full-thickness defect model verified that these H₂S-releasing wound dressing mats could accelerate granulation tissue formation, enhance collagen deposition, and promote angiogenesis. Based on these advantages, these wound dressing mats had great potential applications for wound healing.

Biomedical Applications of Polyhydroxyalkanoate in Tissue Engineering

Tissue engineering technology aids in the regeneration of new tissue to replace damaged or wounded tissue. Three-dimensional biodegradable and porous scaffolds are often utilized in this area to mimic the structure and function of the extracellular matrix. Scaffold material and design are significant areas of biomaterial research and the most favorable material for seeding of in vitro and in vivo cells. Polyhydroxyalkanoates (PHAs) are biopolyesters (thermoplastic) that are appropriate for this application due to their biodegradability, thermo-processability, enhanced biocompatibility, mechanical properties, non-toxicity, and environmental origin. Additionally, they offer enormous potential for modification through biological, chemical and physical alteration, including blending with various other materials. PHAs are produced by bacterial fermentation under nutrient-limiting circumstances and have been reported to offer new perspectives for devices in biological applications. The present review discusses PHAs in the applications of conventional medical devices, especially for soft tissue (sutures, wound dressings, cardiac patches and blood vessels) and hard tissue (bone and cartilage scaffolds) regeneration applications. The paper also addresses a recent advance highlighting the usage of PHAs in implantable devices, such as heart valves, stents, nerve guidance conduits and nanoparticles, including drug delivery. This review summarizes the in vivo and in vitro biodegradability of PHAs and conducts an overview of current scientific research and achievements in the development of PHAs in the biomedical sector. In the future, PHAs may replace synthetic plastics as the material of choice for medical researchers and practitioners.

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

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

Development and Advantages of Biodegradable PHA Polymers Based on Electrospun PHBV Fibers for Tissue Engineering and Other Biomedical Applications

Biodegradable polymeric biomaterials offer a significant advantage in disposable or fast-consuming products in medical applications. Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) is an example of a polyhydroxyalkanoate (PHA), i.e., one group of natural polyesters that are byproducts of reactions taking place in microorganisms in conditions with an excess carbon source. PHA polymers are a promising material for the production of everyday materials and biomedical applications. Due to the high number of monomers in the group, PHAs permit modifications enabling the production of copolymers of different compositions and with different proportions of individual monomers. In order to change and improve the properties of polymer fibers, PHAs are combined with either other natural and synthetic polymers or additives of inorganic phases. Importantly, electrospun PHBV fibers and mats showed an enormous potential in both the medical field (tissue engineering scaffolds, plasters, wound healing, drug delivery systems) and industrial applications (filter systems, food packaging). This Review summarizes the current state of the art in processing PHBV, especially by electrospinning, its degradation processes, and biocompatibility studies, starting from a general introduction to the PHA group of polymers.

One-Pot Process: Microwave-Assisted Keratin Extraction and Direct Electrospinning to Obtain Keratin-Based Bioplastic

Poultry feathers are among the most abundant and polluting keratin-rich waste biomasses. In this work, we developed a one-pot microwave-assisted process for eco-friendly keratin extraction from poultry feathers followed by a direct electrospinning (ES) of the raw extract, without further purification, to obtain keratin-based bioplastics. This microwave-assisted keratin extraction (MAE) was conducted in acetic acid 70% v/v. The effects of extraction time, solvent/feathers ratio, and heating mode (MAE vs. conventional heating) on the extraction yield were investigated. The highest keratin yield (26 ± 1% w/w with respect to initial feathers) was obtained after 5 h of MAE. Waste-derived keratin were blended with gelatin to fabricate keratin-based biodegradable and biocompatible bioplastics via ES, using 3-(Glycidyloxypropyl)trimethoxysilane (GPTMS) as a cross-linking agent. A full characterization of their thermal, mechanical, and barrier properties was performed by differential scanning calorimetry, thermogravimetric analysis, uniaxial tensile tests, and water permeability measurements. Their morphology and protein structure were investigated using scanning electron microscopy and attenuated total reflection-infrared spectroscopy. All these characterizations highlighted that the properties of the keratin-based bioplastics can be modulated by changing keratin and GPTMS concentrations. These bioplastics could be applied in areas such as bio-packaging and filtration/purification membranes.

Stepwise immobilization of keratin-dopamine conjugates and gold nanoparticles on PET sheets for potential vascular graft with the catalytic generation of nitric oxide

Gold nanoparticles(AuNPs) are capable to catalyze the nitric oxide (NO) generation from endogenous and exogenous donors, thereby promoting re-endothelialization and inhibiting intimal hyperplasia and thrombosis. Herein, keratin-dopamine conjugates were synthesized and then immobilized on the surface of the pre-aminolyzed poly(ethylene terephthalate) (PET) via self-polymerization of dopamine residue, following by the formation of AuNPs in situ without extra reductant. The modified PET sheets(PET-AuNPs) could promote the growth of HUVECs while inhibit the proliferation of HUASMCs due to their catalytic generation of NO from GSNO. In addition, these sheets exhibited antibacterial properties and good blood compatibility without hemolysis. Taken together, this strategy for designing prosthetic vascular grafts to treat cardiovascular diseases has great potential.

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.

Catalytic Generation of Nitric Oxide from Poly(ε-caprolactone)/Phosphobetainized Keratin Mats for a Vascular Tissue Engineering Scaffold

Tissue-engineered vascular graft (TEVG) is a promising alternative to meet the clinical demand of organ shortages. Herein, human hair keratin was extracted by the reduction method, followed by modification with zwitterionic 2-methacryloyloxyethyl phosphorylcholine (MPC) through thiol-Michael addition to improve blood clotting nature. Then, phosphobetainized keratin (PK) was coelectrospun with poly(ε-caprolactone) (PCL) to afford PCL/PK mats with a ratio of 7:3. The surface morphology, chemical structure, and wettability of these mats were characterized. The biocomposite mats selectively enhanced adhesion, migration, and growth of endothelial cells (ECs) while suppressed proliferation of smooth muscle cells (SMCs) in the presence of glutathione (GSH) and GSNO due to the catalytic generation of NO. In addition, these mats exhibited good blood anticoagulant activity by reducing platelet adhesion, prolonging blood clotting time, and inhibiting hemolysis. Taken together, these NO-generating PCL/PK mats have potential applications as a scaffold for vascular tissue engineering with rapid endothelialization and reduced SMC proliferation.

Keratinous materials: Structures and functions in biomedical applications

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

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

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

Poly(ε-caprolactone)/keratin/heparin/VEGF biocomposite mats for vascular tissue engineering

Vascular endothelial growth factor (VEGF) is an effective growth and angiogenic cytokine, which stimulates proliferation and survival of endothelial cells, and promotes angiogenesis and vascular permeability. Binding VEGF with heparin could protect it from rapid degradation, subsequently allowing it to be controlled release. Primarily, poly(ε-caprolactone) (PCL) and keratin were coelectrospun, followed by conjugating with heparin and subsequently binding VEGF. The loaded heparin and VEGF on these mats were quantified, respectively. The surface characteristics of mats were investigated by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The VEGF delivery results indicated these mats could sustainably release VEGF for 2 weeks. Cell viability assays suggested these mats were valid to accelerate human umbilical vein endothelial cells (HUVECs) proliferation, while inhibit human umbilical arterial smooth muscle cells (HUASMCs) growth under the combined actions of VEGF and heparin. The results tested by blood clotting times (APTT, PT, and TT), hemolysis, and platelet adhesion indicated the mats were blood compatible. To sum up, these biocomposite mats are ideal scaffolds for vascular tissue engineering.

Heparinized PCL/keratin mats for vascular tissue engineering scaffold with potential of catalytic nitric oxide generation

Heparins are capable of improving blood compatibility, enhancing HUVEC viability, while inhibiting HUASMC proliferation. Combination of biodegradable poly(ε-caprolactone) (PCL) with keratin and heparins would provide an anticoagulant and endothelialization supporting environment for vascular tissue engineering. Herein, PCL and keratin were first coelectrospun and then covalently conjugated with heparins. The resulting mats were surface-characterized by ATR-FTIR, SEM, WCA, and XPS. Cell viability data showed that the heparinized PCL/keratin mats could motivate the adhesion and growth of HUVEC, while inhibit HUASMC proliferation. In addition, these mats could prolong blood clotting time and reduce platelet adhesion as well as no erythrolysis. Interestingly, these mats could catalyze the NO donor in blood to release NO, which could enhance endothelial cell growth, while decrease smooth muscle cell proliferation and platelet adhesion. In summary, the heparinized mats would be a good candidate as a scaffold for vascular tissue engineering. This study is novel in that we prepared a type of heparinized tissue scaffold that could catalyze the NO donor to release NO to regulate endothelialization without angiogenesis and thrombus formation.

Protein-Based Fiber Materials in Medicine: A Review

Fibrous materials have garnered much interest in the field of biomedical engineering due to their high surface-area-to-volume ratio, porosity, and tunability. Specifically, in the field of tissue engineering, fiber meshes have been used to create biomimetic nanostructures that allow for cell attachment, migration, and proliferation, to promote tissue regeneration and wound healing, as well as controllable drug delivery. In addition to the properties of conventional, synthetic polymer fibers, fibers made from natural polymers, such as proteins, can exhibit enhanced biocompatibility, bioactivity, and biodegradability. Of these proteins, keratin, collagen, silk, elastin, zein, and soy are some the most common used in fiber fabrication. The specific capabilities of these materials have been shown to vary based on their physical properties, as well as their fabrication method. To date, such fabrication methods include electrospinning, wet/dry jet spinning, dry spinning, centrifugal spinning, solution blowing, self-assembly, phase separation, and drawing. This review serves to provide a basic knowledge of these commonly utilized proteins and methods, as well as the fabricated fibers’ applications in biomedical research.

Surface Modification of SPIONs in PHBV Microspheres for Biomedical Applications

Surface modification of superparamagnetic iron oxide nanoparticles (SPIONs) has been introduced with lauric acid and oleic acid via co-precipitation and thermal decomposition methods, respectively. This modification is required to increase the stability of SPIONs when incorporated in hydrophobic, biodegradable and biocompatible polymers such as poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV). In this work, the solid-in-oil-in-water (S/O/W) emulsion-solvent extraction/evaporation method was utilized to fabricate magnetic polymer microspheres incorporating SPIONs in PHBV. The prepared magnetic PHBV microspheres exhibited particle sizes <1 µm. The presence of functional groups of lauric acid, oleic acid and iron oxide in the PHBV microspheres was confirmed by Fourier Transform Infrared spectroscopy (FTIR). X-ray diffraction (XRD) analysis was performed to further confirm the success of the combination of modified SPIONs and PHBV. Thermogravimetric analysis (TGA) indicated that PHBV microspheres were incorporated with SPIONs^Lauric as compared with SPIONs^Oleic. This was also proven via magnetic susceptibility measurement as a higher value of this magnetic property was detected for PHBV/SPIONs^Lauric microspheres. It was revealed that the magnetic PHBV microspheres were non-toxic when assessed with mouse embryotic fibroblast cells (MEF) at different concentrations of microspheres. These results confirmed that the fabricated magnetic PHBV microspheres are potential candidates for use in biomedical applications.

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.

Surface modification of PHBV nanofiber mats for rapid cell cultivation and harvesting

To maintain the original function of a specific tissue for therapeutic tissue engineering, an advanced cell culture surface for repeat cell proliferation is necessary. We designed a novel cell proliferation and rapid harvesting surface by combining nonwoven nanofiber mat and a thermo-responsive polymer. Nanofibrous poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) mats were fabricated by the electrospinning technique. A poly(N-isopropylacrylamide) (PNIPAM) thermo-responsive layer was grafted on the PHBV nanofiber mat by electron beam irradiation. The average diameter of the PNIPAM-grafted PHBV nanofibers was determined by SEM. ATR-FTIR and ESCA were used to confirm the grafting of PNIPAM onto the PHBV nanofiber surface. Water contact angles on the mats were measured in response to temperature changes. Human adipose-derived stem cells (ADSCs) were cultured on the PNIPAM-grafted PHBV nanofiber mat to investigate cell proliferation, harvesting, and functionality during repeat subculture. Detached ADSCs from each surface by low temperature treatment and trypsin-EDTA were compared by a fluorescence-activated cell sorter (FACS) using expression of stem cell membrane-specific markers such as CD-13 PE, CD-29 PE, and CD-90 FITC. The mass cultivation and intact harvesting of stem cells by low temperature treatment using a thermo-responsive PHBV nanofiber mat is a promising technique for use in regenerative medicine and stem cell therapy.

Electrospun protein nanofibers in healthcare: A review

Electrospun nanofibers are being utilized for a wide range of healthcare applications. A plethora of natural and synthetic polymers are exploited for their ability to be electrospun and replace the complex habitat provided by the extracellular matrix for the cells. The fabrication of nanofibers can be tuned to act as a multicarrier system to deliver drugs, growth factors and health supplements etc. in a sustained manner. Owing to its pliability, nanofibers reached its heights in tissue engineering and drug delivery applications. This review mainly focuses on various standardized parameters and optimized blending ratios for animal and plant proteins to yield fine, continuous nanofibers for effective utilization in various healthcare applications.

Fabrication of poly(ε-caprolactone)/keratin nanofibrous mats as a potential scaffold for vascular tissue engineering

The natural abundance of cell adhesion sequences, RGD (Arg-Gly-Asp) and LDV (Leu-Asp-Val) in the keratins make them suitable as biomaterials for tissue engineering applications. Herein, keratins were coelectrospun with poly(ε-caprolactone)(PCL) at the ratio of 9/1, 8/2, and 7/3 to afford nanofibrous mats. The resulting mats were surface-characterized by ATR-FTIR, SEM, WCA, and XPS. Cell attachment data showed that NIH 3T3 cells adhered more to the PCL/keratin nanofibrous mats than the pristine PCL mats. The MTT assay revealed that the PCL/keratin mats had improved cell viability. The blood clotting time test (APTT, PT, and TT) indicated the PCL/keratin mats exerted good blood compatibility. These mats would be a good candidate as a scaffold for vascular tissue engineering.

Third generation poly(hydroxyacid) composite scaffolds for tissue engineering

Bone tissue engineering based on scaffolds is quite a complex process as a whole gamut of criteria needs to be satisfied to promote cellular attachment, proliferation and differentiation: biocompatibility, right surface properties, adequate mechanical performance, controlled bioresorbability, osteoconductivity, angiogenic cues, and vascularization. Third generation scaffolds are more of composite types to maximize biological-mechanical-chemical properties. In the present review, our focus is on the performance of micro-organism-derived polyhydroxyalkanoates (PHAs)-polyhydroxybutyrate (PHB) and polyhydroxybutyrate-co-valerate (PHBV)-composite scaffolds with ceramics and natural polymers for tissue engineering applications with emphasis on bone tissue. We particularly emphasize on how material properties of the composites affect scaffold performance. PHA-based composites have demonstrated their biocompatibility with a range of tissues and their capacity to induce osteogenesis due to their piezoelectric properties. Electrospun PHB/PHBV fiber mesh in combination with human adipose tissue-derived stem cells (hASCs) were shown to improve vascularization in engineered bone tissues. For nerve and skin tissue engineering applications, natural polymers such as collagen and chitosan remain the gold standard but there is scope for development of scaffolds combining PHAs with other natural polymers which can address some of the limitations such as brittleness, lack of bioactivity and slow degradation rate presented by the latter. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1667-1684, 2017.

Electrospun polyurethane/keratin/AgNP biocomposite mats for biocompatible and antibacterial wound dressings

Keratin based biomaterials have emerged as potential candidates for various biomedical and biotechnological applications due to their intrinsic biocompatibility, biodegradability, mechanical durability, and natural abundance.

Differences in cytocompatibility between collagen, gelatin and keratin

Keratins are cysteine-rich intermediate filament proteins found in the cytoskeleton of the epithelial cells and in the matrix of hair, feathers, wool, nails and horns. The natural abundance of cell adhesion sequences, RGD (Arg-Gly-Asp) and LDV (Leu-Asp-Val), makes them suitable for tissue engineering applications. The purpose of our study is to evaluate their cytocompatibility as compared to well-known collagen and gelatin proteins. Herein, collagen, gelatin and keratin were blended with poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) and electrospun to afford nanofibrous mats, respectively. These PHBV/protein composite mats were characterized by field emission scanning electron microscopy (FE-SEM), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), and dynamic mechanical analysis (DMA). The cytocompatibility was evaluated with cell adhesion, cell viability and cell proliferation. The data from MTT and BrDU revealed that collagen had significantly superior cytocompatibility as compared to gelatin and keratin. Gelatin showed a better cytocompatibility than keratin without statistical significance difference. Finally, we gave the reasons to account for the above conclusions.

An update on clinical applications of electrospun nanofibers for skin bioengineering

Mimicking morphological similarities of the natural extra cellular matrix (ECM), described by ultrafine continuous fibers, high surface to volume ratio, and high porosity is valuable for effective regeneration of injured skin tissue. Electrospun nanofibers, being one of the most favorable and fast developing products of technology today, display a tremendous potential in wound healing and skin tissue engineering. Under the remarkable attention being given to electrospun nanofibrous scaffolds in promoting wound healing and skin regeneration, this review focuses on the potential of the electrospinning technique as a promising tool for constructing polymeric nanofibrous scaffolds with the favorable physicochemical properties needed for skin bioengineering. In addition, current applications of electrospun nanofibrous matrices for skin bioengineering are detailed in this review.

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.

Poly-3-hydroxybutyrate-co-3-hydroxyvalerate containing scaffolds and their integration with osteoblasts as a model for bone tissue engineering

Nano/micro engineered polymeric materials offer expansive scope of biomimetic scaffolds for bone tissue engineering especially those involving electrospun biodegradable nanofibers incorporated with inorganic nanoparticles, thus mimicking the extracellular matrix of bone both structurally and chemically. For the first time, poly-3-hydroxybutyrate-co-3-hydroxyvalerate containing natural poly-(α, β)-DL-aspartic acid and inorganic hydroxyapatite nanofibers were fabricated using poly-3-hydroxybutyrate-co-3-hydroxyvalerate: poly-(α, β)-DL-aspartic acid at a ratio of 80:20 (w/w) added with 1% (w/v) of hydroxyapatite, by the process of electrospinning. The surface morphology, chemical, and mechanical properties of electrospun poly-3-hydroxybutyrate-co-3-hydroxyvalerate, poly-3-hydroxybutyrate-co-3-hydroxyvalerate/poly-(α, β)-DL-aspartic acid, and poly-3-hydroxybutyrate-co-3-hydroxyvalerate/poly-(α, β)-DL-aspartic acid/hydroxyapatite nanofibers were characterized by using field emission scanning electron microscope, Fourier transform infrared spectroscopy, and tensile tester, respectively. Human fetal osteoblasts were cultured on different nanofibrous scaffolds for evaluating the cell proliferation, alkaline phosphatase activity, and mineralization. Cells on poly-3-hydroxybutyrate-co-3-hydroxyvalerate/poly-(α, β)-DL-aspartic acid/hydroxyapatite scaffolds demonstrated higher proliferation (30.10%) and mineral deposition (37.60%) than the cells grown on pure poly-3-hydroxybutyrate-co-3-hydroxyvalerate scaffolds. Obtained results highlight the synergistic effect of poly-3-hydroxybutyrate-co-3-hydroxyvalerate, poly-(α, β)-DL-aspartic acid, and hydroxyapatite towards the enhancement of the osteoinductivity and osteoconductivity of human fetal osteoblasts, demonstrating the appropriate physicochemical and biological properties of poly-3-hydroxybutyrate-co-3-hydroxyvalerate/poly-(α, β)-DL-aspartic acid/hydroxyapatite nanofibers to function as a substrate for bone tissue regeneration.

Preparation of keratin/chlorhexidine complex nanoparticles for long-term and dual stimuli-responsive release

Nanoscale polyion complex formation via the electrostatic complexation of a polyelectrolyte and a charged drug is the most convenient method for building a drug delivery system that simultaneously realizes the carrier preparation and drug embedding.

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.

Fibrous protein nanofibers

One of the promising new techniques in the production of biomaterials is the electrospinning process, whereby fibers of uniform thickness down to the nanoscale can be produced from solutions of polymeric material in a high electric field. At the same time there has been increasing interest in the manufacture of biodegradable nanomaterials from nonfood sources and this has led to investigations into the use of proteins such as collagen, keratin, and fibroin. Explorations into the use of these proteins in the generation of mats suitable for filtration purposes or scaffolds with applications for tissue engineering form the subject of this review.

Novel wound dressing based on nanofibrous PHBV-keratin mats

Keratin is an important protein used for wound healing and tissue recovery. In this study, keratin was first extracted from raw materials and chemically modified to obtain stable keratin (m-keratin). The raw and m-keratin were examined by Raman spectroscopy. The molecular weight of the m-keratin was analysed by SDS-PAGE. The m-keratin was then blended with poly(hydroxybutylate-co-hydroxyvalerate) (PHBV) and electrospun to afford nanofibrous mats. These mats were characterized by field emission scanning electron microscopy (FE-SEM), electron spectroscopy for chemical analysis (ESCA) and atomic force microscopy (AFM). From the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) data, it was found that introduction of keratin enhanced cell proliferation. From wound-healing test and histological examination results, it was shown that the composite mats accelerated wound recovery remarkably as compared to the PHBV control. It was concluded that PHBV-keratin may be a good candidate as a wound dressing.