A smart methodology to fabricate electrospun chitosan nanofiber matrices for regenerative engineering applications

Enhancing Electrospinnability of Chitosan Membranes in Low-Humidity Environments by Sodium Chloride Addition

The electrospinning of pure chitosan nanofibers is highly sensitive to environmental humidity, which limits their production consistency and applicability. This study investigates the addition of sodium chloride (NaCl) to chitosan solutions to enhance spinnability and mitigate the effigurefects of low humidity. NaCl was incorporated into the electrospun chitosan solution, leading to increased conductivity and decreased viscosity. These modifications improved the electrospinning process. Comparative analyses between chitosan membranes (CM) and sodium-chloride-added chitosan membranes (SCM) revealed no significant differences in chemical structure, mechanical strength, or in vitro cell proliferation. This indicates that the addition of 1% (w/v) NaCl does not adversely affect the fundamental properties of the chitosan membranes. The findings demonstrate that NaCl addition is a viable strategy for producing electrospun chitosan nanofibers in low-humidity environments, maintaining their physicochemical properties while enhancing spinnability.

Design of Collagen and Gelatin-based Electrospun Fibers for Biomedical Purposes: An Overview

Collagen and gelatin are essential natural biopolymers commonly utilized in biomaterials and tissue engineering because of their excellent physicochemical and biocompatibility properties. They can be used either in combination with other biomacromolecules or particles or even exclusively for the enhancement of bone regeneration or for the development of biomimetic scaffolds. Collagen or gelatin derivatives can be transformed into nanofibrous materials with porous micro- or nanostructures and superior mechanical properties and biocompatibility using electrospinning technology. Specific attention was recently paid to electrospun mats of such biopolymers, due to their high ratio of surface area to volume, as well as their biocompatibility, biodegradability, and low immunogenicity. The fiber mats with submicro- and nanometer scale can replicate the extracellular matrix structure of human tissues and organs, making them highly suitable for use in tissue engineering due to their exceptional bioaffinity. The drawbacks may include rapid degradation and complete dissolution in aqueous media. The use of gelatin/collagen electrospun nanofibers in this form is thus greatly restricted for biomedicine. Therefore, the cross-linking of these fibers is necessary for controlling their aqueous solubility. This led to enhanced biological characteristics of the fibers, rendering them excellent options for various biomedical uses. The objective of this review is to highlight the key research related to the electrospinning of collagen and gelatin, as well as their applications in the biomedical field. The review features a detailed examination of the electrospinning fiber mats, showcasing their varying structures and performances resulting from diverse solvents, electrospinning processes, and cross-linking methods. Judiciously selected examples from literature will be presented to demonstrate major advantages of such biofibers. The current developments and difficulties in this area of research are also being addressed.

Photo-induced protonation assisted nano primary battery for highly efficient immobilization of diverse heavy metal ions

Highly-stable heavy metal ions (HMIs) appear long-term damage, while the existing remediation strategies struggle to effectively remove a variety of oppositely charged HMIs without releasing toxic substances. Here we construct an iron-copper primary battery-based nanocomposite, with photo-induced protonation effect, for effectively consolidating broad-spectrum HMIs. In FCPBN, Fe/Cu cell acts as the reaction impetus, and functional graphene oxide modified by carboxyl and UV-induced protonated 2-nitrobenzaldehyde serves as an auxiliary platform. Due to the groups and built-in electric fields under UV stimuli, FCPBN exhibits excellent affinity for ions, with a maximum adsorption rate constant of 974.26 g∙mg-1∙min-1 and facilitated electrons transfer, assisting to reduce 9 HMIs including Cr2O72-, AsO2-, Cd2+ in water from 0.03 to 3.89 ppb. The cost-efficiency, stability and collectability of the FCPBN during remediation, and the beneficial effects on polluted soil and the beings further demonstrate the splendid remediation performance without secondary pollution. This work is expected to remove multi-HMIs thoroughly and sustainably, which tackles an environmental application challenge.

Antifungal Activity of Chitosan/Poly(Ethylene Oxide) Blend Electrospun Polymeric Fiber Mat Doped with Metallic Silver Nanoparticles

In this work, the implementation of advanced functional coatings based on the combination of two compatible nanofabrication techniques such as electrospinning and dip-coating technology have been successfully obtained for the design of antifungal surfaces. In a first step, uniform and beadless electrospun nanofibers of both polyethylene oxide (PEO) and polyethylene (PEO)/chitosan (CS) blend samples have been obtained. In a second step, the dip-coating process has been gradually performed in order to ensure an adequate distribution of silver nanoparticles (AgNPs) within the electrospun polymeric matrix (PEO/CS/AgNPs) by using a chemical reduction synthetic process, denoted as in situ synthesis (ISS). Scanning electron microscopy (SEM) has been used to evaluate the surface morphology of the samples, showing an evolution in average fiber diameter from 157 ± 43 nm (PEO), 124 ± 36 nm (PEO/CS) and 330 ± 106 nm (PEO/CS/AgNPs). Atomic force microscopy (AFM) has been used to evaluate the roughness profile of the samples, indicating that the ISS process induced a smooth roughness surface because a change in the average roughness Ra from 84.5 nm (PEO/CS) up to 38.9 nm (PEO/CS/AgNPs) was observed. The presence of AgNPs within the electrospun fiber mat has been corroborated by UV-Vis spectroscopy thanks to their characteristic optical properties (orange film coloration) associated to the Localized Surface Plasmon Resonance (LSPR) phenomenon by showing an intense absorption band in the visible region at 436 nm. Energy dispersive X-ray (EDX) profile also indicates the existence of a peak located at 3 keV associated to silver. In addition, after doping the electrospun nanofibers with AgNPs, an important change in the wettability with an intrinsic hydrophobic behavior was observed by showing an evolution in the water contact angle value from 23.4° ± 1.3 (PEO/CS) up to 97.7° ± 5.3 (PEO/CS/AgNPs). The evaluation of the antifungal activity of the nanofibrous mats against Pleurotus ostreatus clearly indicates that the presence of AgNPs in the outer surface of the nanofibers produced an important enhancement in the inhibition zone during mycelium growth as well as a better antifungal efficacy after a longer exposure time. Finally, these fabricated electrospun nanofibrous membranes can offer a wide range of potential uses in fields as diverse as biomedicine (antimicrobial against human or plant pathogen fungi) or even in the design of innovative packaging materials for food preservation.

Chitosan-based organic/inorganic composite engineered for UV light-controlled smart pH-responsive pesticide through in situ photo-induced generation of acid

BACKGROUND

Confined by the volatile property, pesticides are overused and lost significantly during and after spraying, weakening the ecological microbalance among different species of lives. Acid-responsive pesticide is a type of smartly engineered pesticides that contribute to the improvement of utilization efficiency of pesticidal active ingredients in acid-controlled manner, whilst the implementation of acidic solutions may disturb the balance of microenvironment surrounding targeted plants or cause secondary pollution, underscoring the input of acid in a more precise strategy.

RESULTS

Chitosan was chemically modified with a photoacid generator (2-nitrobenzaldehyde) serving as a light-maneuvered acid self-supplier, based on which a smart pesticide was formulated by the integration of attapulgite and organophosphate insecticide chlorpyrifos. Under the irradiation of UV light (365 nm), the modified chitosan would undergo a photolytic reaction to generate an acid and pristine chitosan, which seized the labile protons and facilitated the release of chlorpyrifos based on its inherent pH-responsive flexibility. According to the pesticide release performance, the release rate of chlorpyrifos under UV light (27.2 mW/cm² ) reached 78%, significantly higher than those under sunlight (22%, 4.2 mW/cm² ) and in the dark (20%) within the same time, consistent with the pH reduction to 5.3 under UV light and no obvious pH change for the two other situations, exhibiting an attractive UV light-controlled, acid-propelled release behavior.

CONCLUSION

Compared to direct acid spray approach, the proposed in situ photo-induced generation of acid locally on the spots of applied pesticide circumvents the problem of acid contamination to nontargets, demonstrating higher efficiency and biocompatibility for the controlled delivery of acid-responsive pesticides and pest management. © 2022 Society of Chemical Industry.

New chitosan Schiff base and its nanocomposite: Removal of methyl green from aqueous solution and its antibacterial activities

New chitosan Schiff base (CS-NB) and its CS-NB-NiFe nanocomposite have been prepared and characterized by FTIR spectroscopy, XRD, SEM and DSC. FT-IR spectra and XRD patterns revealed the preparation of chitosan Schiff base CS-NB and its CS-NB-NiFe nanocomposite. DSC demonstrated the endo and exothermic correspondence the evaporation of solvent and decomposition of pyranose ring, respectively. Antibacterial activities was evaluated for the as-prepared compounds against two Gram-positive (Staphylococcus aureus and Bacillus cereus) and two Gram-negative (Escherichia coli and Pseudomonas aeruginosa) bacteria and the results shows that the antibacterial activities of the compounds are found to be stronger than that of chitosan. The order of antibacterial effect according to inhibitory zone around is as follows: S. aureus > E. coli > B. cereus > P. aeruginosa. In addition, the removal of methyl green (MG) dye using CS-NB and its CS-NB-NiFe nanocomposite were analyzed and results showed that the compounds can be effectively used to remove of MG from aqueous solution. Results show that the percentage removal of MG by nanocomposite is higher than Schiff base.

Effects of air discharge on surface charges and cell walls of Fusarium oxysporum

Air discharge showed significant inhibition on mycelial growth and spore germination of Fusarium oxysporum, one of the main spoilage fungi in post-harvest lotus roots which is an important economic aquatic vegetable in China. However, the antimicrobial mechanism of air discharge is not clear yet. In the present study, the effects of air discharge on F. oxysporum separated from post-harvest rotten lotus roots were characterized by analyzing surface charges, cell wall permeability, and changes in chitin and chitosan including surface morphology, functional groups, degree of deacetylation, crystallinity, and C/N ratio. After air discharge treatments, alkaline phosphatase leak assay revealed that cell wall permeability of F. oxysporum was magnified. What's more, zeta potentials of F. oxysporum increased and negative charges on cell surfaces decreased. The ordered and compact molecular arrangements of chitin and chitosan in cell walls of F. oxysporum were reduced. The deacetylation degree of chitin and chitosan increased, and the C/N ratios of chitin and chitosan decreased. It was concluded from these results that air discharge caused the transformation in structures of chitin and chitosan, resulting in the exposure of positively charged amino groups and decrease of negative charges on cell surfaces which brought damage to the structure and function of F. oxysporum's cell walls.

Regenerative engineering: a review of recent advances and future directions

Regenerative engineering is defined as the convergence of the disciplines of advanced material science, stem cell science, physics, developmental biology and clinical translation for the regeneration of complex tissues and organ systems. It is an expansion of tissue engineering, which was first developed as a method of repair and restoration of human tissue. In the past three decades, advances in regenerative engineering have made it possible to treat a variety of clinical challenges by utilizing cutting-edge technology currently available to harness the body's healing and regenerative abilities. The emergence of new information in developmental biology, stem cell science, advanced material science and nanotechnology have provided promising concepts and approaches to regenerate complex tissues and structures.

Fabrication of Biomedical Scaffolds Using Biodegradable Polymers

Degradable polymers are used widely in tissue engineering and regenerative medicine. Maturing capabilities in additive manufacturing coupled with advances in orthogonal chemical functionalization methodologies have enabled a rapid evolution of defect-specific form factors and strategies for designing and creating bioactive scaffolds. However, these defect-specific scaffolds, especially when utilizing degradable polymers as the base material, present processing challenges that are distinct and unique from other classes of materials. The goal of this review is to provide a guide for the fabrication of biodegradable polymer-based scaffolds that includes the complete pathway starting from selecting materials, choosing the correct fabrication method, and considering the requirements for tissue specific applications of the scaffold.

Biopolymer-nanotube nerve guidance conduit drug delivery for peripheral nerve regeneration: In vivo structural and functional assessment

Peripheral nerve injuries account for roughly 3% of all trauma patients with over 900,000 repair procedures annually in the US. Of all extremity peripheral nerve injuries, 51% require nerve repair with a transected gap. The current gold-standard treatment for peripheral nerve injuries, autograft repair, has several shortcomings. Engineered constructs are currently only suitable for short gaps or small diameter nerves. Here, we investigate novel nerve guidance conduits with aligned microchannel porosity that deliver sustained-release of neurogenic 4-aminopyridine (4-AP) for peripheral nerve regeneration in a critical-size (15 mm) rat sciatic nerve transection model. The results of functional walking track analysis, morphometric evaluations of myelin development, and histological assessments of various markers confirmed the equivalency of our drug-conduit with autograft controls. Repaired nerves showed formation of thick myelin, presence of S100 and neurofilament markers, and promising functional recovery. The conduit's aligned microchannel architecture may play a vital role in physically guiding axons for distal target reinnervation, while the sustained release of 4-AP may increase nerve conduction, and in turn synaptic neurotransmitter release and upregulation of critical Schwann cell neurotrophic factors. Overall, our nerve construct design facilitates efficient and efficacious peripheral nerve regeneration via a drug delivery system that is feasible for clinical applications.

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Nerve guidance conduit platform with tunable scaffold properties for repair and regeneration of large-gap nerve injuries.

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Sustained 4-aminopyridine release amplifies neurotrophic factor release by Schwann cells to promote axon regeneration.

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Longitudinally aligned scaffold pores and controllable physicochemical properties provide guidance for axon regeneration.

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Critical-size rat sciatic nerve defect healing both structurally and functionally resembled autograft control treatment.

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Innovative and transformative scaffold technology imbued with structural and functional features for tissue regeneration.

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Scaffold enable tailorable release profiles for small molecules proteins and electrical stimulation for tissue regeneration.

Cellulosic fabric treated with hyperbranched polyethyleneimine derivatives for improving antibacterial, dyeing, pH and thermo-responsive performance

Having cotton fabrics with multifunctional properties is of the most research focused on using either different processes or new and different materials. Improving thermo - responsive and antibacterial properties of cotton fabrics decorated with silver nanoparticles and nanogel has been investigated. During this research silver nanoparticles (AgNPs) have been in situ prepared using poly(N-isopropyl acrylamide)/polyethyleneimine microgel. Prepared particles have been characterized, visualized their morphological structure and their particle through microscopic analysis, which proved that their particle size was in range of (6-10 nm). The decorated gel with silver nanoparticles has been functionalized with silicone compounds to produce hybrid material. The produced gel has been characterized for its pH, temperature, textural, rheological, antimicrobial, cytotoxicity, and conductivity properties. The functional properties of the treated and untreated fabrics have been investigated, and the results proved that treated fabric has conductivity, antibacterial, pH and thermo-responsive properties.

Biomedical Implants for Regenerative Therapies

Regenerative therapies aim to develop novel treatments to restore tissue function. Several strategies have been investigated including the use of biomedical implants as three-dimensional artificial matrices to fill the defect side, to replace damaged tissues or for drug delivery. Bioactive implants are used to provide growth environments for tissue formation for a variety of applications including nerve, lung, skin and orthopaedic tissues. Implants can either be biodegradable or non-degradable, should be nontoxic and biocompatible, and should not trigger an immunological response. Implants can be designed to provide suitable surface area-to-volume ratios, ranges of porosities, pore interconnectivities and adequate mechanical strengths. Due to their broad range of properties, numerous biomaterials have been used for implant manufacture. To enhance an implant’s bioactivity, materials can be functionalised in several ways, including surface modification using proteins, incorporation of bioactive drugs, growth factors and/or cells. These strategies have been employed to create local bioactive microenvironments to direct cellular responses and to promote tissue regeneration and controlled drug release. This chapter provides an overview of current bioactive biomedical implants, their fabrication and applications, as well as implant materials used in drug delivery and tissue regeneration. Additionally, cell- and drug-based bioactivity, manufacturing considerations and future trends will be discussed.

Nanofiber Technology for Regenerative Engineering

Regenerative engineering is powerfully emerging as a successful strategy for the regeneration of complex tissues and biological organs using a convergent approach that integrates several fields of expertise. This innovative and disruptive approach has spurred the demands for more choice of biomaterials with distinctive biological recognition properties. An ideal biomaterial is one that closely mimics the hierarchical architecture and features of the extracellular matrices (ECM) of native tissues. Nanofabrication technology presents an excellent springboard for the development of nanofiber scaffolds that can have positive interactions in the immediate cellular environment and stimulate specific regenerative cascades at the molecular level to yield healthy tissues. This paper systematically reviews the electrospinning process technology and its utility in matrix-based regenerative engineering, focusing mainly on musculoskeletal tissues. It briefly outlines the electrospinning/three-dimensional printing system duality and concludes with a discussion on the technology outlook and future directions of nanofiber matrices.

Multi-layer dressing made of laminated electrospun nanowebs and cellulose-based adhesive for comprehensive wound care

In this work, multi-layer wound dressing was made of laminated layers of electrospun fibers supported by adhesive sheet. Graft copolymerization of methyl methacrylate (MMA) and 2-Ethyl-1-hexyl acrylate (EHA) onto carboxymethyl cellulose (CMC) was conducted to obtain an adhesive sheet with 1.52 (N/cm²) loop tack, 1.7 (N/cm) peel strength and 25 s shear strength. Diclofenac sodium, anti-inflammatory drug, was loaded to the adhesive sheet with encapsulation efficiency 73%. The contact layer to wound was made of synthesized anti-bleeding agents, chitosan iodoacetamide (CI) loaded into electrospun polyvinyl alcohol (PVA) fibers. It was fabricated from fiber diameter 300 nm by electrospinning of 5% wt/v of CI (D.S. 18.7%) mixed with 10% wt/v PVA, at 20 kV and 17 cm airgap. The second, pain-relief layer was fabricated by encapsulating up to 50% wt/wt of capsaicin into gelatin nanofibers (197 nm) crosslinked by glyoxal. The third, antimicrobial layer was fabricated from PVA electrospun fibers loaded with 2% wt/wt gentamicin. Biocompatibility test showed insignificant adverse effects of the fabricated layers on fibroblast cells. Animal test on rat showed accelerated wound healing from 21 to 7 days for the multi-layer dressing. Histopathological findings corroborated the intactness of the epidermis layer of the treated samples.

Polymeric ionically conductive composite matrices and electrical stimulation strategies for nerve regeneration: In vitro characterization

Stem cell strategies and the use of electrical stimulation (ES) represent promising new frontiers for peripheral nerve regeneration. Composite matrices were fabricated by coating electrospun polycaprolactone/cellulose acetate micro-nanofibers with chitosan and ionically conductive (IC) polymers including, sulfonated polyaniline, and lignin sulfonate. These composite matrices were characterized for surface morphology, coating uniformity, ionic conductivity, and mechanical strength to explore as scaffold materials for nerve regeneration in conjunction with ES. Composite matrices measured conductivity in the range of 0.0049-0.0068 mS/m due to the uniform coating of sulfonated polymers on the micro-nanofibers. Thin films (2D) and composite fiber matrices (3D) of IC polymers seeded with human mesenchymal stem cells (hMSCs) were electrically stimulated at 0.5 V, 20 Hz for 1 h daily for 14 days to study the changes in cell viability, morphology, and expression of the neuronal-like phenotype. In vitro ES lead to changes in hMSCs' fibroblast morphology into elongated neurite-like structures with cell bodies for ES-treated and positive control growth factor-treated groups. Immunofluorescent staining revealed the presence of neuronal markers including β3-tubulin, microtubule-associated protein 2, and nestin in response to ES. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1792-1805, 2019.

Engineered Skin Tissue Equivalents for Product Evaluation and Therapeutic Applications

The current status of skin tissue equivalents that have emerged as relevant tools in commercial and therapeutic product development applications is reviewed. Due to the rise of animal welfare concerns, numerous companies have designed skin model alternatives to assess the efficacy of pharmaceutical, skincare, and cosmetic products in an in vitro setting, decreasing the dependency on such methods. Skin models have also made an impact in determining the root causes of skin diseases. When designing a skin model, there are various chemical and physical considerations that need to be considered to produce a biomimetic design. This includes designing a structure that mimics the structural characteristics and mechanical strength needed for tribological property measurement and toxicological testing. Recently, various commercial products have made significant progress towards achieving a native skin alternative. Further research involve the development of a functional bilayered model that mimics the constituent properties of the native epidermis and dermis. In this article, the skin models are divided into three categories: in vitro epidermal skin equivalents, in vitro full-thickness skin equivalents, and clinical skin equivalents. A description of skin model characteristics, testing methods, applications, and potential improvements is presented.

A review on applications of chitosan-based Schiff bases

Biopolymers have become very attractive as they are degradable, biocompatible, non-toxic and renewable. Due to the intrinsic reactive amino groups, chitosan is vibrant in the midst of other biopolymers. Using the versatility of these amino groups, various structural modifications have been accomplished on chitosan through certain chemical reactions. Chemical modification of chitosan via imine functionalization (RR'CNR″; R: alkyl/aryl, R': H/alkyl/aryl and R″: chitosan ring) is significant as it recommends the resultant chitosan-based Schiff bases (CSBs) for the important applications in the fields like biology, catalysis, sensors, water treatment, etc. CSBs are usually synthesized by the Schiff condensation reaction between chitosan's amino groups and carbonyl compounds with the removal of water molecules. In this review, we first introduce the available synthetic approaches for the preparation of CSBs. Then, we discuss the biological applications of CSBs including antimicrobial activity, anticancer activity, drug carrier ability, antioxidant activity and tissue engineering capacity. Successively, the applications of CSBs in other fields such as catalysis, adsorption and sensors are demonstrated.

Polyaconitic acid/functional amine/azo dye composite as a novel hyper-branched polymer for cotton fabric functionalization

A new hyperbranched polymer based on aconitic acid and two different amine (triethnaol amine and diethylenetriamine) with different functional groups; hydroxyl and amine groups respectively was successfully synthesised by A2B3 polymerization technique and characterised using Fourier Transform Infrared (FT-IR), Nuclear Magnetic Resonance (NMR), rheological properties, antimicrobial and cytotoxicity activity. In addition, a new heterocyclic azo dye was synthesised and characterised using FT-IR, NMR, mass spectra and antimicrobial activity. Characterisation provides that both composites and azo dye have been well prepared. A mixture from both hyberbranched polymer and synthesised azo dye have been applied to cotton fabrics. Evaluation of treated fabrics shows that, the surface of treated fabrics has a thin film from applied composite which coated the whole fibre surface. Treated fabrics have good antimicrobial activity against gram positive, gram negative bacteria and fungi. Fastness properties, physical and mechanical properties for treated fabrics were also evaluated.

Spiral Layer-by-Layer Micro-Nanostructured Scaffolds for Bone Tissue Engineering

This Article reports the fabrication and characterization of composite micro-nanostructured spiral scaffolds functionalized with nanofibers and hydroxyapatite (HA) for bone regeneration. The spiral poly(lactic acid-co-glycolic acid) (PLGA) porous microstructure was coated with sparsely spaced PLGA nanofibers and HA to enhance surface area and bioactivity. Polyelectrolyte-based HA coating in a layer-by-layer (LBL) fashion allowed 10-70 μM Ca²⁺/mm² incorporation. These scaffolds provided a controlled release of Ca²⁺ ions up to 60 days with varied release kinetics accounting up to 10-50 μg. Spiral scaffolds supported superior adhesion, proliferation, and osteogenic differentiation of rat bone marrow stromal cells (MSCs) as compared to controls microstructures. Spiral micro-nanostructures supported homogeneous tissue ingrowth and resulted in bone-island formation in the center of the scaffold as early as 3 weeks in a rabbit ulnar bone defect model. In contrast, control cylindrical scaffolds showed tissue ingrowth only at the surface because of limitations in scaffold transport features.

Pyrazole-based compounds in chitosan liposomal emulsion for antimicrobial cotton fabrics

The chemistry of pyrazoles has gained increasing attention due to its diverse pharmacological properties such as antiviral, antagonist, antimicrobial, anticancer, anti-inflammatory, analgesic, anti-prostate cancer, herbicidal, acaricidal and insecticidal activities. 1-Phenyl pyrazole-3, 5-diamine, 4-[2-(4-methylphenyl) diazenyl] and 1H- pyrazole-3 (1), 5-diamine, 4-[2-(4-methylphenyl) diazenyl] (2) were synthesized, characterized and encapsulated into liposomal chitosan emulsions for textile finishing. The chemical modifications of cotton fabrics were demonstrated by infrared analysis. Retention of the fabric mechanical properties was investigated by reporting the tensile strength values. Synthesized pyrazole-based compounds were screened for cytotoxicity against skin fibroblast cell line and showed very limited toxicity for both compounds. Antimicrobial potentials of the treated cotton fabrics were tested against bacterial strains E. coli ATCC 8379 and Staphylococcus aureus ATCC 25923.

Electrospun Collagen Nanofibers and Their Applications in Skin Tissue Engineering

Electrospinning is a simple and versatile technique to fabricate continuous fibers with diameter ranging from micrometers to a few nanometers. To date, the number of polymers that have been electrospun has exceeded 200. In recent years, electrospinning has become one of the most popular scaffold fabrication techniques to prepare nanofiber mesh for tissue engineering applications. Collagen, the most abundant extracellular matrix protein in the human body, has been electrospun to fabricate biomimetic scaffolds that imitate the architecture of native human tissues. As collagen nanofibers are mechanically weak in nature, it is commonly cross-linked or blended with synthetic polymers to improve the mechanical strength without compromising the biological activity. Electrospun collagen nanofiber mesh has high surface area to volume ratio, tunable diameter and porosity, and excellent biological activity to regulate cell function and tissue formation. Due to these advantages, collagen nanofibers have been tested for the regeneration of a myriad of tissues and organs. In this review, we gave an overview of electrospinning, encompassing the history, the instrument settings, the spinning process and the parameters that affect fiber formation, with emphasis given to collagen nanofibers' fabrication and application, especially the use of collagen nanofibers in skin tissue engineering.

Fabrication of bi-layer scaffold of keratin nanofiber and gelatin-methacrylate hydrogel: Implications for skin graft

Bi-layer scaffold composed of human hair keratin/chitosan nanofiber mat and gelatin methacrylate (GelMA) hydrogel was fabricated by using electrospinning and photopolymerization techniques. To prepare the nanofiber layer, the blend solution of human hair keratin and chitosan (mixture ratio: 5/5) was electrospun using formic acid as a solvent in the presence of poly(ethylene glycol), followed by cross-linking with glutaraldehyde. The tensile strength of the human hair keratin/chitosan nanofiber mat was much higher than that of pure human hair keratin nanofiber mat. Meanwhile, the blend nanofiber mat was relatively more compatible with HaCaT cell proliferation and keratinocyte differentiation than the pure chitosan nanofiber mat. The bi-layer scaffold was prepared by photopolymerization of GelMA under the cross-linked nanofiber mat. To evaluate the feasibility as a skin graft, human fibroblast was encapsulated in the hydrogel layer and HaCaT cells were cultured on the nanofiber layer and they were co-cultured for 10days. As a result, the encapsulated fibroblasts proliferated in the hydrogel matrix and HaCaT cells formed a cell layer on the top of scaffold, mimicking dermis and epidermis of skin tissue.

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.

Bioactive polymeric scaffolds for tissue engineering

A variety of engineered scaffolds have been created for tissue engineering using polymers, ceramics and their composites. Biomimicry has been adopted for majority of the three-dimensional (3D) scaffold design both in terms of physicochemical properties, as well as bioactivity for superior tissue regeneration. Scaffolds fabricated via salt leaching, particle sintering, hydrogels and lithography have been successful in promoting cell growth in vitro and tissue regeneration in vivo. Scaffold systems derived from decellularization of whole organs or tissues has been popular due to their assured biocompatibility and bioactivity. Traditional scaffold fabrication techniques often failed to create intricate structures with greater resolution, not reproducible and involved multiple steps. The 3D printing technology overcome several limitations of the traditional techniques and made it easier to adopt several thermoplastics and hydrogels to create micro-nanostructured scaffolds and devices for tissue engineering and drug delivery. This review highlights scaffold fabrication methodologies with a focus on optimizing scaffold performance through the matrix pores, bioactivity and degradation rate to enable tissue regeneration. Review highlights few examples of bioactive scaffold mediated nerve, muscle, tendon/ligament and bone regeneration. Regardless of the efforts required for optimization, a shift in 3D scaffold uses from the laboratory into everyday life is expected in the near future as some of the methods discussed in this review become more streamlined.

Electrospun cellulose acetate composites containing supported metal nanoparticles for antifungal membranes

Electrospun cellulose acetate composites containing silver and copper nanoparticles supported in sepiolite and mesoporous silica were prepared and tested as fungistatic membranes against the fungus Aspergillus niger. The nanoparticles were in the 3-50nm range for sepiolite supported materials and limited by the size of mesopores (5-8nm) in the case of mesoporous silica. Sepiolite and silica were well dispersed within the fibers, with larger aggregates in the micrometer range, and allowed a controlled release of metals to create a fungistatic environment. The effect was assessed using digital image analysis to evaluate fungal growth rate and fluorescence readings using a viability stain. The results showed that silver and copper nanomaterials significantly impaired the growth of fungi when the spores were incubated either in direct contact with particles or included in cellulose acetate composite membranes. The fungistatic effect took place on germinating spores before hyphae growth conidiophore formation. After 24h the cultures were separated from fungistatic materials and showed growth impairment only due to the prior exposure. Growth reduction was important for all the particles and membranes with respect to non-exposed controls. The effect of copper and silver loaded materials was not significantly different from each other with average reductions around 70% for bare particles and 50% for membranes. Copper on sepiolite was particularly efficient with a decrease of metabolic activity of up to 80% with respect to controls. Copper materials induced rapid maturation and conidiation with fungi splitting in sets of subcolonies. Metal-loaded nanomaterials acted as reservoirs for the controlled release of metals. The amount of silver or copper released daily by composite membranes represented roughly 1% of their total load of metals. Supported nanomaterials encapsulated in nanofibers allow formulating active membranes with high antifungal performance at the same time minimizing the risk of nanoparticle release into the environment.

Preparation of Nanofibers with Renewable Polymers and Their Application in Wound Dressing

Renewable polymers have attracted considerable attentions in the last two decades, predominantly due to their environmentally friendly properties, renewability, good biocompatibility, biodegradability, bioactivity, and modifiability. The nanofibers prepared from the renewable polymers can combine the excellent properties of the renewable polymer and nanofiber, such as high specific surface area, high porosity, excellent performances in cell adhesion, migration, proliferation, differentiation, and the analogous physical properties of extracellular matrix. They have been widely used in the fields of wound dressing to promote the wound healing, hemostasis, skin regeneration, and treatment of diabetic ulcers. In the present review, the different methods to prepare the nanofibers from the renewable polymers were introduced. Then the recent progress on preparation and properties of the nanofibers from different renewable polymers or their composites were reviewed; the application of them in the fields of wound dressing was emphasized.

Nanofibers of cellulose and its derivatives fabricated using direct electrospinning

A short review with 49 references describes the electrospinninng (ES) process for polysaccharides, cellulose and chitosan, and their derivatives, including cellulose acetate and hydroxypropyl cellulose. A majority of applied studies adopted a two step-process, in which the cellulose acetate was used for the first ES process, followed by acetyl group removal to regenerate cellulose thin fibers. The electrospun nonwoven fabrics (ESNW) of regenerated cellulose can be modified by introduction of aldehyde groups by oxidative cleavage of vicinal diols using periodates, and these aldehyde groups serve as acceptors of foreign substances, with various chemical/biological functions, to be immobilized on the fiber surfaces in the ESNW matrices. Direct electrospinning of cellulose from trifluroacetic acid solution was also developed and the applied studies were summarized to conclude the current trends of interests in the ES and related technologies.