Electrospinning and direct writing: why polymer melts are excellent fluids for 3D printing

Abstract

Event Abstract Back to Event Electrospinning and direct writing: why polymer melts are excellent fluids for 3D printing Paul Dalton1, Tomasz Jungst1, Almoatazbellah Youssef1, Andrei Hrynevich2, Gernot Hochleitner1 and Jürgen Groll1 1 University of Würzburg, Functional Materials in Medicine and Dentistry, Germany 2 RWTH Aachen, Biomedical Engineering Science, Germany Introduction: Many different fluids have been used with nozzle-based direct writing techniques, including polyelectrolytes, colloidal inks, hydrogel inks and polymer solutions[1]. A key property of any material to be 3D printed is to maintain fidelity once delivered from the nozzle, and methods such as coagulation baths or rapid solvent evaporation are often used to preserve structural fidelity of the 3D printed object. Near field solution electrospinning has been used to direct write electrospun scaffolds[1], however the layer-by-layer accuracy of fiber placement and remains challenging. Here, the direct writing of non-conductive polymer melts[2] provides both the microscale fidelity and stacking capacity to 3D print objects. Materials and Methods: A custom-built, electrically-heated and pneumatically-driven melt electrospinning writing (MEW) device was used in combination with poly(ε-caprolactone) (PCL) (PURASORB PC12 Corbion). Instrument parameters included spinneret gauges of 22-25 G, spinneret to collector gaps of 6 mm, applied voltage of 4-6 kV, and operated at 85 °C. The speed where the fiber becomes straight, termed the “critical translation speed” (CTS), was determined for each of the samples by increasing the speed of the collector stage. No post-processing was performed. Results and Discussion: Molten PCL can be direct written readily using MEW. The fiber diameters range from 2 µm to 30 µm, depending on the instrument parameters. Figure 1 shows lines of fibers collected as speeds slower increase. The buckling due to viscoelastic forces generated patterns typical of falling fluids, and are sensitive to fluctuations in fiber diameter changes. Figure 1B-D shows very consistent fluid deposition over long time periods (hours). Figure 1: A) Schematic of the MEW jet, depicting the formation of a Taylor cone and the cooling of the melt jet during the direct writing process. B-E Increasing the stage speed shows structures typical of viscous fluids. The diameter of the fibers can also be finely controlled using stage movement. Figure 2A-B shows the electrified polymer melt above the CTS as it exits the spinneret and is drawn along the stage. Increasing the stage speed (Figure 2B), the fiber was mechanically pulled which allowed a reduction in filament diameter. A standard woodpile structure was made, and accurate stacking could be achieved up to 1mm in height, depending on the fiber spacing. Depending on the instrument parameters, suspended fibers between intersections were produced (Figure 2C), or fibers could be directly piled upon each other (Figure 2D). Figure 2: Photograph of the electrified melt electrospun jet as it exits the spinneret and is drawn onto a stage moving at A) 1000 mm/min and B) 6000 mm/min. C) A stereomicrograph of woodpile PCL structures printed under solidifying conditions while D) an SEM image shows the same structure printed where fibers “sag”. Conclusion: PCL melts were excellent fluids to direct write with using electrospinning direct writing technique. A rapid cooling of the electrified jet in combination with high viscosity and low conductivity allows the production of 3D scaffolds with microscale features. The hour-to-hour processing stability, stackability and solvent-free approach of manufacturing TE scaffolds allows MEW to be a considered an emerging additive manufacturing technique. We thank the European Research Council for funding under grant agreement no. 617989 (consolidator grant Design2Heal).