Deposition of electrospun fibers on reactive substrates for in vitro investigations

Improved cell growth on additively manufactured Ti64 substrates with varying porosity and nanofibrous coating

3T3 Swiss albino mouse cells are often used in biotechnological applications. These cells can grow adherently on suitable surfaces. In our study, they were grown on different titanium substrates, comparing commercially available titanium sheets of grade 1 and grade 2, respectively, with Ti64 which was 3D printed with different porosity in order to identify potential substitutes for common well-plates, which could - in case of 3D printed substrates - be produced in various shapes and dimensions and thus broaden the range of substrates for cell growth in biotechnology and tissue engineering. In addition, thin layers of poly(acrylonitrile) (PAN) nanofibers were electrospun on these substrates to add a nanostructure. The common titanium sheets showed lower cell cover factors than common well plates, which could not be improved by the thin nanofibrous coating. However, the Ti sheets with nanofiber mat coatings showed higher cell adhesion and proliferation than pure PAN nanofiber mats. The 3D printed Ti64 substrates prepared by laser metal fusion, on the other hand, enabled significantly higher proliferation of (66 ± 8)% cover factor after three days of cell growth than well plates which are usually applied as the gold standard for cell cultivation ((48 ± 11)% cover factor under identical conditions). Especially the Ti64 samples with higher porosity showed high cell adhesion and proliferation. Our study suggests investigating such porous Ti64 samples further as a potential future optimum for cell adhesion and proliferation.

Measuring Physical Properties of Electrospun Nanofiber Mats for Different Biomedical Applications

Electrospun nanofiber mats are nowadays often used for biotechnological and biomedical applications, such as wound healing or tissue engineering. While most studies concentrate on their chemical and biochemical properties, the physical properties are often measured without long explanations regarding the chosen methods. Here, we give an overview of typical measurements of topological features such as porosity, pore size, fiber diameter and orientation, hydrophobic/hydrophilic properties and water uptake, mechanical and electrical properties as well as water vapor and air permeability. Besides describing typically used methods with potential modifications, we suggest some low-cost methods as alternatives in cases where special equipment is not available.

Investigation of the Morphological Structure of Needle-Free Electrospun Magnetic Nanofiber Mats

Electrospun magnetic nanofibers are promising for a variety of applications in biomedicine, energy storage, filtration or spintronics. The surface morphology of nanofiber mats plays an important role for defined application areas. In addition, the distribution of magnetic particles in nanofibers exerts an influence on the final properties of nanofiber mats. A simple method for the production of magnetic nanofiber mats by the addition of magnetic nanoparticles in an electrospinning polymer solution was used in this study. In this work, magnetic nanofibers (MNFs) were prepared by needle-free electrospinning technique from poly(acrylonitrile) (PAN) in the low-toxic solvent dimethylsulfoxide (DMSO) and 20 wt% Fe3O4 at different parameter conditions such as PAN concentration, voltage and ultrasonic bath. The distribution of nanoparticles in the fiber matrix was investigated as well as the chemical and morphological properties of the resulting magnetic nanofibers. In addition, the surface morphology of magnetic nanofiber mats was studied by confocal laser scanning microscope (CLSM), scanning electron microscope (SEM), Fourier transform infrared microscope (FTIR) and ImageJ software, and distribution of Fe3O4 particles in the matrix was investigated by energy dispersive X-ray spectroscopy (EDX).

Electrospinning Nanofiber Mats with Magnetite Nanoparticles Using Various Needle-Based Techniques

Electrospinning can be used to produce nanofiber mats containing diverse nanoparticles for various purposes. Magnetic nanoparticles, such as magnetite (Fe₃O₄), can be introduced to produce magnetic nanofiber mats, e.g., for hyperthermia applications, but also for basic research of diluted magnetic systems. As the number of nanoparticles increases, however, the morphology and the mechanical properties of the nanofiber mats decrease, so that freestanding composite nanofiber mats with a high content of nanoparticles are hard to produce. Here we report on poly (acrylonitrile) (PAN) composite nanofiber mats, electrospun by a needle-based system, containing 50 wt% magnetite nanoparticles overall or in the shell of core–shell fibers, collected on a flat or a rotating collector. While the first nanofiber mats show an irregular morphology, the latter are quite regular and contain straight fibers without many beads or agglomerations. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) reveal agglomerations around the pure composite nanofibers and even, round core–shell fibers, the latter showing slightly increased fiber diameters. Energy dispersive X-ray spectroscopy (EDS) shows a regular distribution of the embedded magnetic nanoparticles. Dynamic mechanical analysis (DMA) reveals that mechanical properties are reduced as compared to nanofiber mats with smaller amounts of magnetic nanoparticles, but mats with 50 wt% magnetite are still freestanding.

Electrospinning of Chitosan for Antibacterial Applications—Current Trends

Chitosan is a natural biopolymer that can be suitable for a wide range of applications due to its biocompatibility, rigid structure, and biodegradability. Moreover, it has been proven to have an antibacterial effect against several bacteria strains by incorporating the advantages of the electrospinning technique, with which tailored nanofibrous scaffolds can be produced. A literature search is conducted in this review regarding the antibacterial effectiveness of chitosan-based nanofibers in the filtration, biomedicine, and food protection industries. The results are promising in terms of research into sustainable materials. This review focuses on the electrospinning of chitosan for antibacterial applications and shows current trends in this field. In addition, various aspects such as the parameters affecting the antibacterial properties of chitosan are presented, and the application areas of electrospun chitosan nanofibers in the fields of air and water filtration, food storage, wound treatment, and tissue engineering are discussed in more detail.

Electrospun Nanofibrous Membranes for Tissue Engineering and Cell Growth

In biotechnology, the field of cell cultivation is highly relevant. Cultivated cells can be used, for example, for the development of biopharmaceuticals and in tissue engineering. Commonly, mammalian cells are grown in bioreactors, T-flasks, well plates, etc., without a specific substrate. Nanofibrous mats, however, have been reported to promote cell growth, adhesion, and proliferation. Here, we give an overview of the different attempts at cultivating mammalian cells on electrospun nanofiber mats for biotechnological and biomedical purposes. Starting with a brief overview of the different electrospinning methods, resulting in random or defined fiber orientations in the nanofiber mats, we describe the typical materials used in cell growth applications in biotechnology and tissue engineering. The influence of using different surface morphologies and polymers or polymer blends on the possible application of such nanofiber mats for tissue engineering and other biotechnological applications is discussed. Polymer blends, in particular, can often be used to reach the required combination of mechanical and biological properties, making such nanofiber mats highly suitable for tissue engineering and other biotechnological or biomedical cell growth applications.

Application of Electrospun Nanofibers for Fabrication of Versatile and Highly Efficient Electrochemical Devices: A Review

Electrochemical devices convert chemical reactions into electrical energy or, vice versa, electricity into a chemical reaction. While batteries, fuel cells, supercapacitors, solar cells, and sensors belong to the galvanic cells based on the first reaction, electrolytic cells are based on the reversed process and used to decompose chemical compounds by electrolysis. Especially fuel cells, using an electrochemical reaction of hydrogen with an oxidizing agent to produce electricity, and electrolytic cells, e.g., used to split water into hydrogen and oxygen, are of high interest in the ongoing search for production and storage of renewable energies. This review sheds light on recent developments in the area of electrospun electrochemical devices, new materials, techniques, and applications. Starting with a brief introduction into electrospinning, recent research dealing with electrolytic cells, batteries, fuel cells, supercapacitors, electrochemical solar cells, and electrochemical sensors is presented. The paper concentrates on the advantages of electrospun nanofiber mats for these applications which are mostly based on their high specific surface area and the possibility to tailor morphology and material properties during the spinning and post-treatment processes. It is shown that several research areas dealing with electrospun parts of electrochemical devices have already reached a broad state-of-the-art, while other research areas have large space for future investigations.

Melt Electrowritten In Vitro Radial Device to Study Cell Growth and Migration

The development of in vitro assays for 3D microenvironments is essential for understanding cell migration processes. A 3D-printed in vitro competitive radial device is developed to identify preferred Matrigel concentration for glioblastoma migration. Melt electrowriting (MEW) is used to fabricate the structural device with defined and intricate radial structures that are filled with Matrigel. Controlling the printing path is necessary to account for the distance lag in the molten jet, the applied electric field, and the continuous direct-writing nature of MEW. Circular printing below a diameter threshold results in substantial inward tilting of the MEW fiber wall. An eight-chamber radial device with a diameter of 9.4 mm is printed. Four different concentrations of Matrigel are dispensed into the radial chambers. Glioblastoma cells are seeded into the center and grow into all chambers within 8 days. The cell spreading area demonstrates that 6 and 8 mg mL^-1 of Matrigel are preferred over 2 and 4 mg mL^-1 . Furthermore, topographical cues via the MEW fiber wall are observed to promote migration even further away from the cell seeding depot. Previous studies implement MEW to fabricate cell invasive scaffolds whereas here it is applied to 3D-print in vitro tools to study cell migration.

Magnetic Properties of Electrospun Magnetic Nanofiber Mats after Stabilization and Carbonization

Magnetic nanofibers are of great interest in basic research, as well as for possible applications in spintronics and neuromorphic computing. Here we report on the preparation of magnetic nanofiber mats by electrospinning polyacrylonitrile (PAN)/nanoparticle solutions, creating a network of arbitrarily oriented nanofibers with a high aspect ratio. Since PAN is a typical precursor for carbon, the magnetic nanofiber mats were stabilized and carbonized after electrospinning. The magnetic properties of nanofiber mats containing magnetite or nickel ferrite nanoparticles were found to depend on the nanoparticle diameters and the potential after-treatment, as compared with raw nanofiber mats. Micromagnetic simulations underlined the different properties of both magnetic materials. Atomic force microscopy and scanning electron microscopy images revealed nearly unchanged morphologies after stabilization without mechanical fixation, which is in strong contrast to pure PAN nanofiber mats. While carbonization at 500 °C left the morphology unaltered, as compared with the stabilized samples, stronger connections between adjacent fibers were formed during carbonization at 800 °C, which may be supportive of magnetic data transmission.

Orientation of Electrospun Magnetic Nanofibers Near Conductive Areas

Electrospinning can be used to create nanofibers from diverse polymers in which also other materials can be embedded. Inclusion of magnetic nanoparticles, for example, results in preparation of magnetic nanofibers which are usually isotropically distributed on the substrate. One method to create a preferred direction is using a spinning cylinder as the substrate, which is not always possible, especially in commercial electrospinning machines. Here, another simple technique to partly align magnetic nanofibers is investigated. Since electrospinning works in a strong electric field and the fibers thus carry charges when landing on the substrate, using partly conductive substrates leads to a current flow through the conductive parts of the substrate which, according to Ampère's right-hand grip rule, creates a magnetic field around it. We observed that this magnetic field, on the other hand, can partly align magnetic nanofibers perpendicular to the borders of the current flow conductor. We report on the first observations of electrospinning magnetic nanofibers on partly conductive substrates with some of the conductive areas additionally being grounded, resulting in partly oriented magnetic nanofibers.

Increased Mechanical Properties of Carbon Nanofiber Mats for Possible Medical Applications

Carbon fibers belong to the materials of high interest in medical application due to their good mechanical properties and because they are chemically inert at room temperature. Carbon nanofiber mats, which can be produced by electrospinning diverse precursor polymers, followed by thermal stabilization and carbonization, are under investigation as possible substrates for cell growth, especially for possible 3D cell growth applications in tissue engineering. However, such carbon nanofiber mats may be too brittle to serve as a reliable substrate. Here we report on a simple method of creating highly robust carbon nanofiber mats by using electrospun polyacrylonitrile/ZnO nanofiber mats as substrates. We show that the ZnO-blended polyacrylonitrile (PAN) nanofiber mats have significantly increased fiber diameters, resulting in enhanced mechanical properties and thus supporting tissue engineering applications.

Comparative Study of Pleurotus ostreatus Mushroom Grown on Modified PAN Nanofiber Mats

Pleurotus ostreatus is a well-known edible mushroom species which shows fast growth. The fungus can be used for medical, nutritional, filter, or packaging purposes. In this study, cultivation experiments were carried out with Pleurotus ostreatus growing on polyacrylonitrile (PAN) nanofiber mats in the presence of saccharose and Lutrol F68. The aim of this study was to find out whether modified PAN nanofiber mats are well suited for the growth of fungal mycelium, to increase growth rates and to affect mycelium fiber morphologies. Our results show that Pleurotus ostreatus mycelium grows on nanofiber mats in different morphologies, depending on the specific substrate, and can be used to produce a composite from fungal mycelium and nanofiber mats for biomedical and biotechnological applications.

Preliminary Study of Ultrasonic Welding as a Joining Process for Electrospun Nanofiber Mats

Electrospinning can be used to create nanofiber mats for diverse applications, from wound dressings and tissue engineering to filters for medical and biotechnological applications. In most of these applications, it is necessary to fix the nanofiber mat on a macroscopic textile fabric, on another nanofiber mat or within a frame to keep it at the desired position. Due to their extremely low thickness and areal mass, however, nanofiber mats are easily destroyed by sewing, and in several situations glued bonds are too thick and not flexible enough. Here we report on ultrasonic welding of polyacrylonitrile nanofiber mats, suggesting this method as a joining process without destruction of the mat morphology for thermoplastic nanofiber mats. A variety of welding patterns results in different adhesion forces between both joined nanofiber mats and different failure mechanisms, with some welding patterns enabling bonding stronger than the mats themselves. Our findings show that ultrasonic welding is a possible joining method for polyacrylonitrile nanofiber mats.

Dye-Sensitized Solar Cells with Electrospun Nanofiber Mat-Based Counter Electrodes

Textile-based dye-sensitized solar cells (DSSCs) can be created by building the necessary layers on a textile fabric or around fibers which are afterwards used to prepare a textile layer, typically by weaving. Another approach is using electrospun nanofiber mats as one or more layers. In this work, electrospun polyacrylonitrile (PAN) nanofiber mats coated by a conductive polymer poly(3,4-ethylenedioxythiopene) polystyrene sulfonate (PEDOT:PSS) were used to produce the counter electrodes for half-textile DSSCs. The obtained efficiencies were comparable with the efficiencies of pure glass-based DSSCs and significantly higher than the efficiencies of DSSCs with cotton based counter electrodes. The efficiency could be further increased by increasing the number of PEDOT:PSS layers on the counter electrode. Additionally, the effect of the post treatment of the conductive layers by HCl, acetic acid, or dimethyl sulfoxide (DMSO) on the DSSC efficiencies was investigated. Only the treatment by HCl resulted in a slight improvement of the energy-conversion efficiency.

Colonization and osteogenic differentiation of different stem cell sources on electrospun nanofiber meshes

Numerous challenges remain in the successful clinical translation of cell-based therapies for musculoskeletal tissue repair, including the identification of an appropriate cell source and a viable cell delivery system. The aim of this study was to investigate the attachment, colonization, and osteogenic differentiation of two stem cell types, human mesenchymal stem cells (hMSCs) and human amniotic fluid stem (hAFS) cells, on electrospun nanofiber meshes. We demonstrate that nanofiber meshes are able to support these cell functions robustly, with both cell types demonstrating strong osteogenic potential. Differences in the kinetics of osteogenic differentiation were observed between hMSCs and hAFS cells, with the hAFS cells displaying a delayed alkaline phosphatase peak, but elevated mineral deposition, compared to hMSCs. We also compared the cell behavior on nanofiber meshes to that on tissue culture plastic, and observed that there is delayed initial attachment and proliferation on meshes, but enhanced mineralization at a later time point. Finally, cell-seeded nanofiber meshes were found to be effective in colonizing three-dimensional scaffolds in an in vitro system. This study provides support for the use of the nanofiber mesh as a model surface for cell culture in vitro, and a cell delivery vehicle for the repair of bone defects in vivo.

A novel route for the production of chitosan/poly(lactide-co-glycolide) graft copolymers for electrospinning

Both chitosan and polylactide/polyglycolide have good biocompatibility and can be used to produce tissue engineering scaffolds for cultured cells. However the synthetic scaffolds lack groups that would facilitate their modification, whereas chitosan has extensive active amide and hydroxyl groups which would allow it to be subsequently modified for the attachment of peptides, proteins and drugs. Also chitosan is very hydrophilic, whereas PLGA is relatively hydrophobic. Accordingly there are many situations where it would be ideal to have a copolymer of both, especially one that could be electrospun to provide a versatile range of scaffolds for tissue engineering. Our aim was to develop a novel route of chitosan-g-PLGA preparation and evaluate the copolymers in terms of their chemical characterization, their performance on electrospinning and their ability to support the culture of fibroblasts as an initial biological evaluation of these scaffolds. Chitosan was first modified with trimethylsilyl chloride, and catalyzed by dimethylamino pyridine. PLGA-grafted chitosan copolymers were prepared by reaction with end-carboxyl PLGA (PLGA-COOH). FT-IR and(1)H-NMR characterized the copolymer molecular structure as being substantially different to that of the chitosan or PLGA on their own. Elemental analysis showed an average 18 pyranose unit intervals when PLGA-COOH was grafted into the chitosan molecular chain. Differential scanning calorimetry results showed that the copolymers had different thermal properties from PLGA and chitosan respectively. Contact angle measurements demonstrated that copolymers became more hydrophilic than PLGA. The chitosan-g-PLGA copolymers were electrospun to produce either nano- or microfibers as desired. A 3D fibrous scaffold of the copolymers gave good fibroblast adhesion and proliferation which did not differ significantly from the performance of the cells on the chitosan or PLGA electrospun scaffolds. In summary this work presents a methodology for making a hybrid material of natural and synthetic polymers which can be electrospun and reacts well as a substrate for cell culture.

Functionalization of electrospun poly(ε-caprolactone) fibers with the extracellular matrix-derived peptide GRGDS improves guidance of schwann cell migration and axonal growth

The best available treatment of peripheral nerve lesions involves transplantation of an autologous nerve. This approach, however, entails sensory deficits at the donor site and requires additional surgery. Such limitations have motivated the search for a bioengineering solution to design artificial implants. For this purpose we are producing orientated biodegradable microfibers of poly(ε-caprolactone) (PCL) with electrospinning. The present study describes the functionalization of these electrospun fibers with biologically active peptides to produce guidance structures for Schwann cell migration and axonal regeneration. For the chemical modification PCL was blended with star-shaped NCO-poly(ethylene glycol)-stat-poly(propylene glycol) (PCL/sPEG) as a covalent linker for the peptide GRGDS, derived from extracellular matrix proteins. To test biological functions of electrospun fibers, Schwann cell migration and axonal growth from dorsal root ganglia explants were investigated with time lapse video microscopy. Migrating Schwann cells as well as growing sensory axons closely followed the electrospun fibers with occasional leaps between adjacent fibers. Cell migration was characterized by frequent changes in velocity and direction reversals. Comparison of substrates showed that functionalized fibers caused more Schwann cells to move out of the explants, supported faster cell migration and axonal growth than the nonfunctional fibers. Using inhibitors of intracellular signaling kinases, we found that these biological effects required activation of the phosphatidyl inositol-3-kinase pathway. Since sPEG-containing fibers also showed low levels of nonspecific protein adsorption, which is desirable in the context of artificial implant design, the peptide modification of fibers appears to provide good substrates for nerve repair.

Functionalization of electrospun fibers of poly(epsilon-caprolactone) with star shaped NCO-poly(ethylene glycol)-stat-poly(propylene glycol) for neuronal cell guidance

Microfibers produced with electrospinning have recently been used in tissue engineering. In the development of artificial implants for nerve regeneration they are of particular interest as guidance structures for cell migration and axonal growth. Using electrospinning we produced parallel-orientated biocompatible fibers in the submicron range consisting of poly(epsilon-caprolactone) (PCL) and star shaped NCO-poly(ethylene glycol)-stat-poly(propylene glycol) (sPEG). Addition of the bioactive peptide sequence glycine-arginine-glycine-aspartate-serine (GRGDS) or the extracellular matrix protein fibronectin to the electrospinning solution resulted in functionalized fibers. Surface characteristics and biological properties of functionalized and non-functionalised fibers were investigated. Polymer solutions and electrospinning process parameters were varied to obtain high quality orientated fibers. A polymer mixture containing high molecular weight PCL, PCL-diol, and sPEG permitted a chemical reaction between hydroxyl groups of the diol and isocyanante groups of the sPEG. Surface analysis demonstrated that sPEG at the fiber surface minimized protein adhesion. In vitro experiments using dorsal root ganglia explants showed that the cell repellent property of pure PCL/sPEG fibers was overcome by functionalization either with GRGDS peptide or fibronectin. In this way cell migration and axonal outgrowth along fibers were significantly increased. Thus, functionalized electrospun PCL/sPEG fibers, while preventing non-specific protein adsorption, are a suitable substrate for biological and medical applications.

Nanotechnology in the design of soft tissue scaffolds: innovations in structure and function

Engineered scaffolds function to supplement or replace injured, missing, or compromised tissue or organs. The current direction in this research area is to create scaffolds that mimic the structure and function of the native extracellular matrix (ECM). It is believed that the fabrication of a scaffold that has both structural integrity and allows for normal cellular function and interaction will bring scaffolds closer to clinical relevance. Nanotechnology innovations have aided in the development of techniques for the production of nanofiber scaffolds. The three major processing techniques, self-assembly, phase separation, and electrospinning, produce fibers that rival the size of those found in the native ECM. However, the simplicity, versatility, and scalability of electrospinning make it an attractive processing method that can be used to reproduce aspects of the complexity that characterizes the native ECM. Novel electrospinning strategies include alterations of scaffold composition and architecture, along with the addition and encapsulation of cells, pharmaceuticals and growth factors within the scaffold. This article reviews the major nanofiber fabrication technologies as well as delves into recent significant contributions to the conception of a meaningful and practical electrospun scaffold.

Reclaiming a natural beauty: whole-organ engineering with natural extracellular materials

The ability to engineer whole organs as replacements for allografts and xenografts is an ongoing pursuit in regenerative medicine. While challenges remain, including systemic tissue integration with angiogenesis, lymphatiogenesis and neurogenesis, ongoing efforts are working to develop novel technologies to produce implantable engineered scaffolds and potentially engineered whole organs. Natural extracellular matrix materials, commonly utilized in vitro, are now being used as effective, natural, acellular allografts, and are being integrated into nanoscale scaffolds and matrices with programmable responsiveness. Based on the significant use of natural scaffolds for tissue regeneration and bioengineering strategies, this review focuses on recent and ongoing efforts to engineer whole organs, such as the tooth, featuring natural extracellular matrix molecules.