Optimization of fully aligned bioactive electrospun fibers for “in vitro” nerve guidance

Complex architecture of natural tissues such as nerves requires the use of multifunctional scaffolds with peculiar topological and biochemical signals able to address cell behavior towards specific events at the cellular (microscale) and macromolecular (nanoscale) level. In this context, the electrospinning technique is useful to generate fiber assemblies having peculiar fiber diameters at the nanoscale and patterned by unidirectional ways, to facilitate neurite extension via contact guidance. Following a bio-mimetic approach, fully aligned polycaprolactone fibers blended with gelatin macromolecules have been fabricated as potential bioactive substrate for nerve regeneration. Morphological and topographic aspects of electrospun fibers assessed by SEM/AFM microscopy supported by image analyses elaboration allow estimating an increase of fully aligned fibers from 5 to 39 % as collector rotating rate increases from 1,000 to 3,000 rpm. We verify that fully alignment of fibers positively influences in vitro response of hMSC and PC-12 cells in neurogenic way. Immunostaining images show that the presence of topological defects, i.e., kinks—due to more frequent fiber crossing—in the case of randomly organized fiber assembly concurs to interfere with proper neurite outgrowth. On the contrary, fully aligned fibers without kinks offer a more efficient contact guidance to direct the orientation of nerve cells along the fibers respect to randomly organized ones, promoting a high elongation of neurites at 7 days and the formation of bipolar extensions. So, this confirms that the topological cue of fully alignment of fibers elicits a favorable environment for nerve regeneration.     

Electrospinning of PCL/natural rubber blends

In this study, a thermoplastic/elastomeric binary blend of non-vulcanized natural rubber (NR) and polycaprolactone (PCL) was electrospun using polymer solutions consisting of varying proportions of PCL and NR. Specifically, an 8 % (w/v) NR/toluene solution was mixed with an 8 % (w/v) PCL/chloroform solution at proportions of 2, 15, 30, and 50 % (v/v). The morphological, thermal, and mechanical properties of the electrospun mats were investigated by scanning electron microscopy (SEM), differential scanning calorimetry, and uniaxial tensile tests. The SEM images demonstrated the production of micrometer- and sub-micrometer-sized fibers with no bead formation. Fibers with diameters ranging from 1.3 μm for samples with 0 % NR to 210 nm for samples containing 50 % NR were observed. Fibers with rough and smooth morphologies were observed, showing that the PCL/NR mats had phase-separated. The blend miscibility was evaluated by thermal analysis, which showed that blending did not improve the thermal stability of the systems. An investigation of the mechanical properties of the electrospun mats showed that adding NRL to the blend increased the tensile modulus, the ultimate elasticity, and the strain. Thus, non-vulcanized NR was successfully incorporated into electrospun mats, which exhibited useful mechanical properties that could be harnessed in biomaterials applications.     

Phosphate salts facilitate the electrospinning of hyaluronic acid fiber mats

Electrospinning is a cost effective and facile method to manufacture fiber mats appropriate for biomedical applications. Due to its high molecular weight and charged backbone, hyaluronic acid (HA) fiber mats with consistent fiber morphology have been difficult to electrospin from neutral pH solutions. Here, we present that the electrospinning of HA fibers in aqueous dimethylformamide solutions is facilitated by the addition of three phosphate salts. The salts—glycerol phosphate (GP), sodium phosphate (SP), and tripolyphosphate (TPP)—facilitated electrospinning of the solutions as characterized by conductivity measurements and fiber morphology. From tensile experiments, HA mats electrospun with SP demonstrated improved Young’s modulus (12 MPa) over HA mats spun with either GP or TPP (5 and 3 MPa, respectively). This work demonstrates that a new neutral solvent system can be employed to spin HA fibers, which offers the potential for using the fibers for biomedical applications, such as a bone biomimetic.     

Crosslinking poly(allylamine) fibers electrospun from basic and acidic solutions

Mechanically robust, non-toxic polymer fiber mats are promising materials for a range of biomedical applications; however, further research into enhancing polymer selection is needed. In this study, poly(allylamine) (PAH), an amine-containing polyelectrolyte, was successfully electrospun from aqueous solutions into continuous, cylindrical fibers with a mean diameter of 150 ± 41 nm. A one-step crosslinking method using glutaraldehyde provides insight into the chemical and morphological changes that result from altering the molar ratio of amine to aldehyde groups, whereas a two-step crosslinking method yielded chemically and mechanically robust mats. These results indicate PAH fibrous mats synthesized from aqueous solutions could potentially be applied in biomedical applications.     

Electrospun aligned PLLA/PCL/functionalised multiwalled carbon nanotube composite fibrous membranes and their bio/mechanical properties

Aligned poly(L-lactide) (PLLA)/poly(ε-caprolactone) (PCL)/functionalized multiwalled carbon nanotube (F-MWNT) composite fibrous membranes were fabricated by electrospinning. Their morphology, mechanical properties, in vitro degradation and biocompatibility were studied. With a collector rotation speed of 3000 rpm, the electrospun fibers are highly aligned and the F-MWNTs are oriented along the fiber axis, reinforcing the electrospun fibrous membranes. When the F-MWNTs are incorporated, the PLLA/PCL/F-MWNT composite fibers become thinner due to the increased electrical conductivity. However, when the F-MWNTs are increased to 3.75 wt.%, the higher viscosity and aggregation of F-MWNTs have lead to the formation of beads and a wider diameter distribution in the electrospun fibers. Also, the electrospun fibers having smaller diameter, larger porosity and lower crystallinity induced by F-MWNTs have improved the bio-degradation of the PLLA/PCL/F-MWNT fibrous membranes, which have no toxic effects on the proliferation of adipose-derived stem cells.     

Electrospinning highly oriented and crystalline poly(lactic acid) fiber mats

In recent years, there has been an increased focus on sustainable, green alternatives with similar properties to conventional petroleum-based polymers. Poly(lactic acid) (PLA) is a biodegradable biopolymer which exhibits mild piezoelectric properties and has good processability which gives it potential for use in numerous existing and novel applications. The purpose of this study was to produce highly oriented and crystalline PLA electrospun fiber mats for piezoelectric applications. In order to yield a high piezoelectric constant, high crystallinity and fiber orientation are necessary. A two parallel collector set up was used to mechanically orient the fibers in the space between two copper electrodes. Voltage and feed rate were adjusted to produce smooth, oriented fibers with average diameters ranging 0.73–1.19 μm. Crystallinity and orientation were increased via hot drawing of the fiber mats and were maximized between 40 and 50 % and greater than 50 %, respectively.     

Poly(ε-caprolactone) scaffolds of highly controlled porosity and interconnectivity derived from co-continuous polymer blends: model bead and cell infiltration behavior

Porous structures destined for tissue engineering applications should ideally show controlled and narrow pore size distributions with fully interconnected pores. This study focuses on the development of novel poly(ε-caprolactone) (PCL) structures with fully connected pores of 84, 116, 141, and 162 μm average diameter, from melt blending of PCL with poly(ethylene oxide) (PEO) at the co-continuous composition, followed by static annealing and selective extraction of PEO. Our results demonstrate a low onset concentration for PEO continuity and a broad region of phase inversion. A novel in vitro assay was used to compare scaffold infiltration by 10-μm diameter polystyrene beads intended to mimic trypsinized human bone marrow stromal cells (hBMSCs). Beads showed a linear increase in the extent of scaffold infiltration with increasing pore size, whereas BMSCs infiltrated 162 and 141 μm pores, below which the cells aggregated and adhered near the seeding area with low infiltration into the porous device. While providing a baseline for non-aggregated systems, the beads closely mimic trypsinized cells at pore sizes equal to or larger than 141 μm, where optimal retention and distribution of hBMSCs are detected. A cytotoxicity assay using L929 cells showed that these scaffolds were cytocompatible and no cell necrosis was detected. This study shows that a melt blending approach produces porous PCL scaffolds of highly controlled pore size, narrow size distribution and complete interconnectivity, while the bead model system reveals the baseline potential for a homogeneous, non-aggregated distribution of hBMSCs at all penetration depths.     

Axially aligned electrically conducting biodegradable nanofibers for neural regeneration

In this study, electrically conducting axially aligned nanofibers have developed to provide both electrical and structural cues. Poly(lactide-co-glycolide) (PLGA) with poly(3-hexylthiophene) (PHT) was electrospun into 2D random (196 ± 98 nm) and 3D axially aligned nanofibers (200 ± 80 nm). Electrospun random and aligned PLGA–PHT fibers were characterized for surface morphology, mechanical property, porosity, degradability, and electrical conductivity. The pore size of random PLGA–PHT nanofibers (6.0 ± 3.3 μm) were significantly higher than the aligned (1.9 ± 0.4 μm) (P < 0.05) and the Young’s modulus of aligned scaffold was significantly lower than the random. Aligned nanofibers showed significantly lesser degradation rate and higher electrical conductivity (0.1 × 10^?5 S/cm) than random nanofibers (P < 0.05). Results of in vitro cell studies indicate that aligned PLGA–PHT nanofibers have a significant influence on the adhesion and proliferation of Schwann cells and could be potentially used as scaffold for neural regeneration.     

Preparation and characterization of mesoporous bioactive glass/polycaprolactone nanofibrous matrix for bone tissues engineering

A polycaprolactone (PCL) nanofibrous composite matrix having mesoporous bioactive glass nanoparticles (MBG) was fabricated using the electrospinning method, and the microstructural, physical and biological properties of the composite matrix were characterized. The fiber diameters of PCL, 5?% MBG/PCL (5?M-PCL) and 10?% MBG/PCL (10?M-PCL) were 575?±?162?nm, 312?±?134?nm and 321?±?144?nm, respectively. The bioactivity of the composite matrix was evaluated by soaking the matrix in 1.5× simulated body fluid; the MBG/PCL matrix showed a better biomineralization capability than did the PCL matrix. The biological performance of the PCL and the MBG/PCL were evaluated using an in vitro culture of MG63 osteoblast-like cells. We found that the cell attachment and proliferation rates were significantly higher on the 10?M-PCL than on the PCL. Moreover, the expression of several genes, including ANX-V, type I collagen and OCN, ALP activity, the deposition of calcium, and the BSP protein, were also significantly higher on 10?M-PCL than PCL. These results indicated that MBG/PCL has the ability to support cell attachment, growth, and differentiation and can also yield high bioactivity. Therefore, MBG/PCL could be potentially applied in bone implants.     

Fabrication of hydroxyapatite-poly(<Emphasis Type="Italic">ε</Emphasis>-caprolactone) scaffolds by a combination of the extrusion and bi-axial lamination processes

Hydroxyapatite (HA)/poly(ε-caprolactone) (PCL) composite scaffolds were fabricated using a combination of the extrusion and bi-axial lamination processes. Firstly, HA/PCL composites with various HA contents (0, 50, 60, 70 wt%) were prepared by mixing the HA powders and the molten PCL at 100 °C and then extruded through an orifice with dimensions of 600 × 600 μm to produce HA/PCL composite fibers. Isobutyl methacrylate (IBMA) polymer fiber was also prepared in a similar manner for use as a fugitive material. The 3-D scaffold was then produced by the bi-axial lamination of the HA/PCL and IBMA fibers, followed by solvent leaching to remove the IBMA. It was observed that the HA/PCL composites had a superior elastic modulus and biological properties, as compared to the pure PCL. The fabricated HA/PCL scaffold showed a controlled pore structure (porosity of ∼49% and pore size of ∼512 μm) and excellent welding between the HA/PCL fibers, as well as a high compressive strength of ∼7.8 MPa.     

Fabrication of poly(lactic acid)-poly(ethylene oxide) electrospun membranes with controlled micro to nanofiber sizes

Biodegradable poly(L-lactide acid) (PLLA) nanofiber membranes were prepared by electrospinning of PLLA and poly(ethylene oxide) (PEO). The selective removal of PEO by water allows to obtain smaller fiber diameters and to increase the porosity of the membranes in comparison to PLLA membranes obtained under the same electrospinning conditions. After removal of PEO membranes with fiber sizes of 260 nm and average porosity close to 80% are obtained. Thermal and infrared results confirm the poor miscibility of PLLA and PEO, with the PEO randomly distributed along the PLLA fibers. On the other, PLLA and PEO mixing strongly affect their respective degradation temperatures. The influence of the PEO in the electrospinning process is discussed and the results are correlated to the evolution of the PLLA fiber diameter.     

Surface chemistry of electrospun cellulose nitrate nanofiber membranes

Electrospinning is a rapidly developing technology that provides a unique way to produce novel polymer nanofibers with controllable diameters. Cellulose nitrate non-woven mats of submicron-sized fibers with diameters of 100-1200 nm were prepared. The effects of processing equipment collector design void gap, and steel drum coated with polyvinylidene dichloride (PVDC) were investigated. The PVDC layer applied to the rotating drum aided in fiber harvesting. Electron microscopy (FESEM and ESEM) studies of as-spun fibers revealed that the morphology of cellulose nitrate fibers depended on the collector type and solution viscosity. When a rotating steel drum was employed a random morphology was observed, while the void gap collector produced aligned fiber mats. Increases in viscosity lead to larger diameter fibers. The fibers collected were free from all residual solvents and could undergo oxygen plasma treatment to increase the hydropholicity.     

In vitro and in vivo evaluations of phenytoin sodium-loaded electrospun PVA, PCL, and their hybrid nanofibrous mats for use as active wound dressings

In this work, polyvinyl alcohol (PVA), poly(ε-caprolactone) (PCL), and their electrospun PVA/PCL (80/20) hybrid nanofibrous mats were used for the development of active wound dressings. The biocompatibility and therapeutic effects of the developed products were studied by in vitro cell culture and in vivo experimental rat wound model. The release rate measurements by HPLC showed that the PVA nanofibrous sample containing phenytoin sodium (PHT-Na) has a higher level of the drug release compared to the hybrid PVA/PCL (80/20) and PCL nanofibrous mats. A mesenchymal stem cell was seeded on neat as well as drug-loaded PVA nanofibrous mats. The results represented that the mats provide a suitable environment for cell growth and viability. PVA nanofibers containing PHT-Na have a unique performance for fibroblasts and myofibroblasts cells formation and consequently reaching to the remodeling phase and faster healing of the wounds. Also, PHT-Na-loaded electrospun PVA nanofibrous mats showed a remarkable efficiency in wound closure compared with the treatments results from gauze, commercial wound dressing Comfeel^®Plus, and 2 % PHT-Na ointment. Histology analysis showed the formation of epidermis, the lack of necrosis, and accumulation of collagen fibers in dermis for PVA nanofibrous mats containing PHT-Na.     

Sulfonated polystyrene fiber network-induced hybrid proton exchange membranes

A novel type of hybrid membrane was fabricated by incorporating sulfonated polystyrene (S-PS) electrospun fibers into Nafion for the application in proton exchange membrane fuel cells. With the introduction of S-PS fiber mats, a large amount of sulfonic acid groups in Nafion aggregated onto the interfaces between S-PS fibers and the ionomer matrix, forming continuous pathways for facile proton transport. The resultant hybrid membranes had higher proton conductivities than that of recast Nafion, and the conductivities were controlled by selectively adjusting the fiber diameters. Consequently, hybrid membranes fabricated by ionomers, such as Nafion, incorporated with ionic-conducting nanofibers established a promising strategy for the rational design of high-performance proton exchange membranes.     

High-Temperature Superconducting Fiber

In this study, we demonstrated superconductivity in a fiber with an yttrium barium copper oxide core and fused silica cladding. The fibers were fabricated via a modified melt-draw technique and post-process annealing treatment in excess oxygen. The fibers maintained overall diameters ranging from 100–900 microns and core diameters of 50–700 microns. Superconductivity of this fiber design was validated via the traditional four-point probe test method in a bath of liquid nitrogen at temperatures on the order of 93 K. The high-temperature superconducting fiber provides a glimpse of its cross cutting potential in fields of electromagnetism, healthcare, optics, and energy and lends credence to the promise for superconductivity.     

Preparation and characterization of electrospun PCL/PLGA membranes and chitosan/gelatin hydrogels for skin bioengineering applications

In this study, two distinct systems of biomaterials were fabricated and their potential use as a bilayer scaffold (BS) for skin bioengineering applications was assessed. The initial biomaterial was a polycaprolactone/poly(lacto-co-glycolic acid) (PCL/PLGA) membrane fabricated using the electrospinning method. The PCL/PLGA membrane M-12 (12% PCL/10% PLGA, 80:20) displayed strong mechanical properties (stress/strain values of 3.01 ± 0.23 MPa/225.39 ± 7.63%) and good biocompatibility as demonstrated by adhesion of keratinocyte cells on the surface and ability to support cell proliferation. The second biomaterial was a hydrogel composed of 2% chitosan and 15% gelatin (50:50) crosslinked with 5% glutaraldehyde. The CG-3.5 hydrogel (with 3.5% glutaraldehyde (v/v)) displayed a high porosity, ≥97%, good compressive strength (2.23 ± 0.25 MPa), ability to swell more than 500% of its dry weight and was able to support fibroblast cell proliferation. A BS was fabricated by underlaying the membrane and hydrogel casting method to combine these two materials. The physical properties and biocompatibility were preliminarily investigated and the properties of the two biomaterials were shown to be complementary when combined. The upper layer membrane provided mechanical support in the scaffold and reduced the degradation rate of the hydrogel layer. Cell viability was similar to that in the hydrogel layer which suggests that addition of the membrane layer did not affect the biocompatibility.     

Tetracycline hydrochloride (TCH)-loaded drug carrier based on PLA:PCL nanofibre mats: experimental characterisation and release kinetics modelling

The experimental characterisation of electrospun poly(lactic acid) (PLA):poly(ε-caprolactone) (PCL) as drug carriers, at five blend ratios from 1:0, 3:1, 1:1, 1:3 and 0:1, was holistically investigated in terms of their morphological structures, crystallinity levels and thermal properties. A widely used antibiotic tetracycline hydrochloride (TCH) was loaded to prepared fibrous mats at TCH concentrations of 1 and 5 wt%. The additional TCH into PLA:PCL better facilitates the reduction of fibre diameter than polymer blends. Increasing the TCH concentration from 1 to 5 wt% was found to result in only a modest decrease in the crystallinity level, but a significant increase in the crystallisation temperature (T _c) for PLA within PLA:PCL blends. The infrared spectra of fibre mats confirm the successful TCH encapsulation into fibrous networks. The first order and Zeng models for drug release kinetics were in better agreement with experimental release data, indicating the release acceleration of TCH with increasing its concentration. In a typical case of PLA:PCL (1:1) loaded with 5 wt% TCH, the fibre mats apparently demonstrate more wrinkled and floppy structures and increased fibre diameters and decreased inter-fibrous spaces after 7-day in vitro fibre degradation, as opposed to those obtained after 3-h degradation.     

Fabrication and application of long silicon nanowire yarns

Long silicon nanowire yarns with length up to 12 mm were fabricated from aligned silicon nanowires with crystal silicon cores of bifurcation structures as well as entangled amorphous hairy silicon oxide, which played vital roles in the formation of the yarns, and the silicon nanowire yarns were used as a pH sensor with the sensitivity of 1,080 ± 31 nS/pH in the pH range of 2–12.     

Shape stabilization,thermal energy storage behavior and thermal conductivity enhancement of flexible paraffin/MWCNTs/PP hollow fiber membrane composite phase change materials

Flexible shape-stabilized composite phase change materials (ss-CPCMs) have a wide range of potential applications because they can be woven into desired shapes. In this work, a series of novel flexible paraffin/multi-walled carbon nanotubes (MWCNTs)/polypropylene hollow fiber membrane (PHFM) ss-CPCMs (PC-PHFM-CPCMs) with weavability were fabricated for thermal energy storage. In order to select a PHFM with optimum stretching ratio as the supporting material for the flexible ss-CPCMs, PHFMs with different stretching ratios were fabricated to encapsulate the paraffin as novel flexible ss-CPCMs (P-PHFM-CPCMs). The effects of stretching ratios on the latent heats and absorption capacity were investigated. PHFM200 (polypropylene hollow fiber stretched by 200%) showed the high porosity (65.2%) and tensile strength (119.9 MPa), and the corresponding P-PHFM-CPCM200 had the largest latent heats in the melting process and solidifying process (73.90 and 76.71 J/g) and maximum paraffin absorption capacity (52.42 wt%) compared to other candidates. Paraffin/MWCNTs mixtures with high thermal conductivity were injected into the columned cavity of P-PHFM-CPCM200 to further enhance the paraffin encapsulation capacity and significantly improve their heat transfer. Among all PC-PHFM-CPCMs, PC0-PHFM-CPCM200 exhibited the maximum paraffin encapsulation capacity of 80.97 wt%. The thermal conductivity of PC-PHFM-CPCMs was obviously enhanced with the increase in the weight ratio of MWCNTs. PC4-PHFM-CPCM200 achieved the highest thermal conductivity of 0.46 W/m K, which was obviously improved by 100%. The corresponding latent heat in the solidification process was 109.2 J/g. In addition, excellent chemical compatibility and thermal stability of PC-PHFM-CPCMs were demonstrated by the Fourier transform infrared spectroscopy and thermo-gravimetric analysis.     

Electrospun poly(ε-caprolactone)/Ca-deficient hydroxyapatite nanohybrids: Microstructure,mechanical properties and cell response by murine embryonic stem cells

Nanohybrid scaffolds mimicking extracellular matrix are promising experimental models to study stem cell behaviour, in terms of adhesion and proliferation. In the present study, the structural characterization of a novel electrospun nanohybrid and the analysis of cell response by a highly sensitive cell type, embryonic stem (ES) cells, are investigated. Ca-deficient hydroxyapatite nanocrystals (d-HAp) were synthesized by precipitation. Fibrous PCL/d-HAp nanohybrids were obtained by electrospinning, d-HAp content ranging between 2 and 55 wt.%. Electrospun mats showed a non-woven architecture, average fiber size was 1.5 ±0.5 μm, porosity 80–90%, and specific surface area 16 m² g^? 1. Up to 6.4 wt.% d-HAp content, the nanohybrids displayed comparable microstructural, mechanical and dynamo-mechanical properties. Murine ES cell response to neat PCL and to nanohybrid PCL/d-HAp (6.4 wt.%) mats was evaluated by analyzing morphological, metabolic and functional markers. Cells growing on either scaffold proliferated and maintained pluripotency markers at essentially the same rate as cells growing on standard tissue culture plates with no detectable signs of cytotoxicity, despite a lower cell adhesion at the beginning of culture. These results indicate that electrospun PCL scaffolds may provide adequate supports for murine ES cell proliferation in a pluripotent state, and that the presence of d-HAp within the mat does not interfere with their growth.