Melt Electrospinning Process Research Articles

Developing strontium-substituted bioglass and polycaprolactone composite scaffolds for bone repair via hybrid electrospinning in the direct writing mode

Event Abstract Back to Event Developing strontium-substituted bioglass and polycaprolactone composite scaffolds for bone repair via hybrid electrospinning in the direct writing mode Jiongyu Ren1, Molly M. Stevens2, Roland Steck3, Keith A. Blackwood1 and Maria A. Woodruff1 1 Queensland University of Technology, The Institute of Health and Biomedical Innovation, Australia 2 Imperial College London, Department of Materials, United Kingdom 3 Queensland University of Technology, The Medical Engineering Research Facility, Australia Introduction: Electrospinning is a versatile fibre-based technique for scaffold production with smaller fibre diameter, and thus larger surface area to volume ratio compared to melt extrusion. Recent developments in direct writing melt-electrospinning makes use of the stable and predictable fibre deposition to fabricate scaffolds in the layer-by-layer manner[1],[2]. Synthetic materials including polymers and bioactive glass (BG) are most common for bone scaffold fabrication[3],[4]. Among the synthetic polymers, polycaprolactone (PCL), which is a FDA-approved aliphatic polyester, has been become a promising candidate for bone scaffold material due to its favourable rheological and viscoelastic properties[5]. Bioactive glass (BG) is a synthetic material known to bind seamlessly to bone and promote osteogenesis. Strontium-substituted BG derived from the original 45S5 BG by substituting 0-100% of the calcium component of the 45S5 formulation for strontium[6], and have shown superior osteogenic capacity to 45S5 BG[7]. We hypothesize that melt-electrospun PCL/SrBG composite scaffolds will provide a promising bone graft substitute, which will be osteoinductive, osteoconductive, capable of osteointegration and bioresorbable in a controlled rate. The scaffolds can be manufactured with a tailored structure according to specific defect site, and can be replaced by the body’s own newly regenerated bone over time. Materials and Methods: The SrBG particles were ground down to < 6 μm prior to composite preparation with a micronizing mill to reduce the risk of needle blockage. The 50 wt% PCL/SrBG composites were prepared by incorporating fine SrBG particles into the PCL bulk using solvent precipitation technique. PCL/SrBG composite scaffolds were fabricated using a novel solvent assisted hybrid melt-electrospinning technique in the direct write mode. Light microscopy and scanning electron microscopy (SEM) were used to characterize surface topography and fibre diameter. Mechanical stiffness of PCL/SrBG fibres were assessed with atomic force microscopy. Cell attachment and morphology were assessed with confocal laser scanning microscopy and SEM . Cell proliferation and osteoblastic differentiation were assessed with PicoGreen and alkaline phosphatase assays. Results and Discussion: Our hybrid melt-electrospinning system overcame the difficulties of PCL/SrBG composite melt-electrospinning associated with viscoelastic properties of the composite material. These composite scaffolds were produced in a layer-by-layer manner with 90° cross-hatched deposition with the fibre spacing of 1 mm. Examination by scanning electron microscopy showed enhanced micro structure on the surface of PCL/SrBG fibres, while the surface of PCL only fibres were smooth. The submicron structures generated during the hybrid melt-electrospinning process largely increased the surface area of composite scaffolds and created roughness ideal for cell attachment. The in vitro results showed good cell adherence onto both the PCL/SrBG and PCL only scaffolds. However, PCL/SrBG composite scaffolds showed significantly higher osteoblast differentiation compared to PCL only scaffolds. Conclusion: We are the first to produce the composite PCL/SrBG (50 wt%) scaffolds via a novel hybrid melt-electrospinning technique. These composite scaffolds are promising bone graft substitutes, and may also lead to patient-specific and off-the-shelf solution for clinical treatment of critical-sized bone defects. Dr Henrietta Cathey (Electron microscope probe analysis); Dr Charlotte Allen, Dr Sunny Hu and Mr. Mitchell De Bruyn (Inductively coupled plasma analysis); Dr Marie-Luise Wille (micro-CT scanning and analysis); Dr Christina Theodoropoulos (Confocal microscopy); Dr Tong Li (Atomic force microscopy); ARC Linkage for funding

Melt electrospinning process optimization of polylactic acid nanofibers

Melt electrospinning is a safe and simple technique for the production of micro and nanofibers which can be an alternative to conventional solvent electrospinning. The effects of various melt-electrospinning parameters, including molecular weight, electric field strength, flow rate and temperature on the morphology, and fiber diameter of polylactic acid nanofibers were studied. An orthogonal design was used to examine process parameters. It was shown that molecular weight was the predominant factor in determining the obtainable fiber diameter of the collected fibers and is the most effective parameter on the average fiber diameter of melt electrospun PLA nanofibers. The flow rate has the less important impact. Mean fiber diameter (MFD) increased by increasing MW and flow rate, but decreased by increasing electric field strength and temperature. MFD of optimized fibers was below 100 nm and the result of statistical analysis using Design Expert software was in good agreement with the experimental condition.

Photocatalytic performance of melt-electrospun polypropylene fabric decorated with TiO2 nanoparticles

Recently, nanomaterials, especially titanium-based nanomaterials, have a great potential for decolorization of textile dye effluents. In this article, the nanofibrillar filters functionalized with titanium nanoparticle (nTi) were designed to improve dyeing wastewater decolorization. Pristine polypropylene (PP) and nTi-PP nanocomposite nonwovens were produced as a photocatalyzer by melt-electrospinning process. The average diameter of pristine PP- and nTi-PP nanocomposite melt-electrospun fibers was found average as 700 ± 0.3 and 800 ± 0.4 nm, respectively. Before functionalization with nTi, the surface of fabrics was activated by a technique using glutaraldehyde (GA) and polyethyleneimine to improve decomposition activity. Scanning electron microscopy (SEM) results revealed that titanium nanoparticles were deposited uniformly on the nanofibers. X-ray photon spectroscopy (XPS) results confirmed the presence of titanium nanoparticles and generation of amine groups after modification. Photocatalytic performance of nTi-loaded pristine and nanocomposite melt-electrospun filters was investigated by using methyl orange (MO) as a model compound. The decolorization experiments were carried out by varying initial dye concentration (10, 20, 40 mg/L), pH (2, 5, and 9), and loaded TiO2 amount (1 and 2 %). According to photocatalytic decolarization test results, nTi-loaded GA-treated pristine or nTi-PP nanocomposite fabric filter has better properties compared to GA-untreated group from point of photocatalytic efficiency, especially over 90 % decolorization efficiency at GA-treated pristine and nTi-PP composite PP fabrics. The complete decolarization of MO was observed at pH value of 5, photocatalyst concentration of 20 mg/L, and 1 % nTi-loading after 3 h. The results show that surface activated PP nonwovens, which is introduced Ti nanoparticles into and onto the structure, a good photocatalytic activity.

Using mathematical modeling to control topographical properties of poly (ε-caprolactone) melt electrospun scaffolds

Melt electrospinning creates fibrous scaffolds using direct deposition. The main challenge of melt electrospinning is controlling the topography of the scaffolds for tissue engineering applications. Mathematical modeling enables a better understanding of the parameters that determine the topography of scaffolds. The objective of this study is to build two types of mathematical models. First, we modeled the melt electrospinning process by incorporating parameters such as nozzle size, counter electrode distance and applied voltage that influence fiber diameter and scaffold porosity. Our second model describes the accumulation of the extruded microfibers on flat and round surfaces using data from the microfiber modeling. These models were validated through the use of experimentally obtained data. Scanning electron microscopy (SEM) was used to image the scaffolds and the fiber diameters were measured using Quartz-PCI Image Management Systems® in SEM to measure scaffold porosity.

Tug of war effect in melt electrospinning

Solution electrospinning (ESP) has been deeply investigated currently. However, the research of melt ESP remains silent except a few progresses in device improvements and process investigation. In order to get a deeper understanding of fiber characteristics in the melt ESP process, microscopic simulation method of dissipative particle dynamics (DPD) was used here to create ESP simulation system. Fiber dropping process and the effect of spring coefficient on Tug of war effect were successfully simulated. In addition, the theory of Tug of war effect and the effect of factors on it were simulated and studied systematically. Results showed that distance between two particles and end-to-end distance of chains had the same variation tendency. The stretching and refining theory of jet was acquired.

Fabrication of poly (ϵ-caprolactone) microfiber scaffolds with varying topography and mechanical properties for stem cell-based tissue engineering applications

Highly porous poly (ϵ-caprolactone) microfiber scaffolds can be fabricated using electrospinning for tissue engineering applications. Melt electrospinning produces such scaffolds by direct deposition of a polymer melt instead of dissolving the polymer in a solvent as performed during solution electrospinning. The objective of this study was to investigate the significant parameters associated with the melt electrospinning process that influence fiber diameter and scaffold morphology, including processing temperature, collection distance, applied, voltage and nozzle size. The mechanical properties of these microfiber scaffolds varied with microfiber diameter. Additionally, the porosity of scaffolds was determined by combining experimental data with mathematical modeling. To test the cytocompatability of these fibrous scaffolds, we seeded neural progenitors derived from murine R1 embryonic stem cell lines onto these scaffolds, where they could survive, migrate, and differentiate into neurons; demonstrating the potential of these melt electrospun scaffolds for tissue engineering applications.

Study of Preparation Metallocene Based LLDPE Extra-Fibers by Melt Electrospinning Process

In this paper, metallocene based LLDPE (mLLDPE) extra-fine fiber , which can not be processed by a common solution electrospinning method.was successfully prepared via a melt electrospinning method. First, a self-designed melt electrospinning device was manufctured and it was used to produce mLLDPE fibers . Then LLDPE extra-fine fiber was successfully prepared by addition of viscosity-reducing additive such as wax, and the resulted fiber was charctered by SEM. Last, the optimal parameters for the preparation of mLLDPE fiber was determined. The experimental results show that commercial mLLDPE can hardly be processed to fibers because of its high viscosity. The diameter and morphology of resulted mLLDPE electrospun fibers depend on the electrospinning parameters such as electric field strength and collecting distance.

Preparation and characterization of poly(ɛ-caprolactone) nonwoven mats via melt electrospinning

Laser melt electrospinning is a novel technology to produce nonwoven scaffolds for tissue engineering (TE) applications. This solvent-free process is far safer than common solution electrospinning. In this paper, we demonstrated the poly(ɛ-caprolactone) (PCL) fibers diameters could be governed from 3 to 12 μm with changing electrospinning parameters. The various diameters can meet the needs of scaffold properties such as porosity, pore size, etc. Our experiential results also showed that the fibers diameter tended to decrease as laser current increased. The degradation of PCL molecular chains often occurs in the melt electrospinning process due to mechanical scission and thermal degradation. The crystallinity of as-spun PCL fibers was approximately equal to that of the annealing fibers by X-ray diffraction (XRD) and differential scanning calorimetry (DSC). In our experiential, the collected PCL electrospun fibers often fused together to form a three-dimension network structure, which is favorable to mechanical properties.

Melt electrospinning of biodegradable polyurethane scaffolds

Electrospinning from a melt, in contrast to from a solution, is an attractive tissue engineering scaffold manufacturing process as it allows for the formation of small diameter fibers while eliminating potentially cytotoxic solvents. Despite this, there is a dearth of literature on scaffold formation via melt electrospinning. This is likely due to the technical challenges related to the need for a well-controlled high-temperature setup and the difficulty in developing an appropriate polymer. In this paper, a biodegradable and thermally stable polyurethane (PU) is described specifically for use in melt electrospinning. Polymer formulations of aliphatic PUs based on (CH 2) 4-content diisocyanates, polycaprolactone (PCL), 1,4-butanediamine and 1,4-butanediol (BD) were evaluated for utility in the melt electrospinning process. The final polymer formulation, a catalyst-purified PU based on 1,4-butane diisocyanate, PCL and BD in a 4/1/3 M ratio with a weight-average molecular weight of about 40 kDa, yielded a nontoxic polymer that could be readily electrospun from the melt. Scaffolds electrospun from this polymer contained point bonds between fibers and mechanical properties analogous to many in vivo soft tissues.

Nanofibers from gas-assisted polymer melt electrospinning

The concept of a gas-assisted polymer melt electrospinning process is presented. This technique allows for reduced quenching of the melt jet in the spinning region, and thus increasing the jet attenuation rate and resulting in production of sub-micron scale fibers. A comprehensive melt electrospinning model was used to analyze the effects of the heated air stream on the polymer jet. It was found that under the investigated conditions in electrospinning of polylactic acid (PLA) melt, air drag produced an additional 10% thinning compared to the un-assisted melt electrospinning process, and the heating provided by the air stream resulted in an additional 20-fold jet thinning.

Structure of Melt Electrospun Poly(lactic acid) Fibers

Poly(L-lactic acid) fibers were prepared by the melt electro-spinning process using CO2 laser irradiation. A grounded metallic flat plate and a grounded metallic rotating blade were used to collect the electrospun fibers. The fiber structure was investigated by polarizing optical microscopy, scanning electron microscopy and X-ray diffraction. The average fiber diameters were decreased with laser output power applied, and the fiber diameters collected on the flat collector were smaller than those collected on the rotating collector. The polarized light micrograph observation under crossed-nicol clearly showed an optical anisotropy of the as-spun fibers. The X-ray diffraction patterns of the annealed fibers showed a crystal orientation. Although the uniaxial drawing of the fibers up to x 2 enhanced the crystalline orientation, the crystal modification was unchanged.

Melt electrospinning from poly(L‐lactide) rods coated with poly(ethylene‐co‐vinyl alcohol)

AbstractRodlike poly(L‐lactide) (PLLA) samples coated with poly(ethylene‐co‐vinyl alcohol) (EVOH) were made. Fibers were produced from these rodlike samples by using a melt electrospinning system equipped with a laser irradiating device, and the effects of EVOH content and the processing parameters of the melt electrospinning on fiber diameters were investigated. We also studied the fiber formation mechanism from the rods during the laser melt electrospinning process. The following conclusions were reached: (i) coating of EVOH on PLLA rods has a remarkable effect on decreasing fiber diameter from 3 μm to around 1 μm; (ii) increases in the electric field strength and temperature of spinning space decrease the average diameter of fibers produced from pure PLLA rods, and longer collector distance leads to lager PLLA fiber diameter; and (iii) the migration of PLLA component from the core to the surface of electrospun fibers takes place during the fiber formation process. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

The Effect of Applied Voltage and Laser Power on the Molecular Orientation of Laser-Electrospun Poly(ethylene terephthalate) Fibers

Laser-electrospinning is a melt electrospinning process. We investigated the influence of the draw ratio, the laser power, and the applied voltage on the structure and properties of laser-electrospun poly(ethylene terephthalate) fibers, specifically, their birefringence, boil-off shrinkage, and mechanical properties. We found that when the draw ratio was increased, the birefringence and the boil-off shrinkage of electrospun fibers increased, while their natural draw ratio and elongation at break decreased. In addition, when either the laser power or the applied voltage was increased, the birefringence decreased, whereas the natural draw ratio and elongation at break increased. The boil-off shrinkage also decreased with an increase in the draw ratio, but the laser power and applied voltage mainly influenced for lowbirefringence region.

Ultra-Fine Fibers Produced by Laser-Electrospinning

We used a CO2 laser as a heat source to avoid thermodegradation in the melt-electrospinning process (termed “laser electrospinning” (LES)). Nylon 6, polypropylene, poly (ethylene terephthalate) and poly (L-lactide-co-e-caprolactone) fiber webs were prepared by the LES. For Nylon 6 and poly (L-lactide-co-e-caprolactone), fibers having average diameters of approximately 1 μm and a coefficient of variation (CV) of no more than 20% were obtained. The effects of the applied voltage and laser power on the diameter of the PET fibers were investigated. The average diameter of the electrospun PET fibers decreased with a decrease in the applied voltage; however, using an applied voltage that was too low caused thermodegradation. The average diameter decreased with an increase in laser power. Above a certain laser power, however, shot particles and large deviations in the fiber diameter were observed.

Modeling of non-isothermal polymer jets in melt electrospinning

We have developed a model for non-isothermal, free surface flows of electrically charged viscoelastic fluids in the stable jet region of the melt electrospinning process. The model is based on thin filament approximation applied to fully coupled momentum, continuity, and energy equations, Gauss’ law, and the non-isothermal Giesekus constitutive model. The asymptotic jet thinning relationship widely used in previous electrospinning models was found not applicable for the case of polymer melts. The underlying assumption of the balance of inertial and electrical forces in the asymptotic region does not hold for typical melts which exhibit high tensile forces throughout the spinning region, particularly under non-isothermal conditions. We have developed a new initial thinning condition for fluids with low electrical conductivity and high viscosity based on a force balance near the nozzle. The resulting system of equations is solved numerically and the simulated initial jet profiles are compared to digitized experimental images of the stable melt jet near the spinneret. In addition, the predicted effects of melt temperature, flowrate, and electric field strength on the final jet diameter are compared to the final average fiber thickness from non-isothermal experiments where the whipping motion has been suppressed by rapid cooling. The simulation results are in good quantitative agreement with the flow visualization experiments on electrospinning of polylactic acid (PLA) melt under various spinning conditions.