0
Research Papers

Melt Electrospinning Writing Process Guided by a “Printability Number”

[+] Author and Article Information
Filippos Tourlomousis

Department of Mechanical Engineering,
Highly Filled Materials Institute,
Stevens Institute of Technology,
Hoboken, NJ 07030
e-mail: ftourlom@stevens.edu

Houzhu Ding

Department of Mechanical Engineering,
Stevens Institute of Technology,
Hoboken, NJ 07030
e-mail: ding4@stevens.edu

Dilhan M. Kalyon

Department of Chemical Engineering
and Material Science,
Highly Filled Materials Institute,
Stevens Institute of Technology,
Hoboken, NJ 07030
e-mail: dkalyon@stevens.edu

Robert C. Chang

Department of Mechanical Engineering,
Stevens Institute of Technology,
Hoboken, NJ 07030
e-mail: rchang6@stevens.edu

1Corresponding author.

Manuscript received June 22, 2016; final manuscript received March 6, 2017; published online May 8, 2017. Assoc. Editor: Yong Huang.

J. Manuf. Sci. Eng 139(8), 081004 (May 08, 2017) (15 pages) Paper No: MANU-16-1345; doi: 10.1115/1.4036348 History: Received June 22, 2016; Revised March 06, 2017

The direct electrostatic printing of highly viscous thermoplastic polymers onto movable collectors, a process known as melt electrospinning writing (MEW), has significant potential as an additive biomanufacturing (ABM) technology. MEW has the hitherto unrealized potential of fabricating three-dimensional (3D) porous interconnected fibrous mesh-patterned scaffolds in conjunction with cellular-relevant fiber diameters and interfiber distances without the use of cytotoxic organic solvents. However, this potential cannot be readily fulfilled owing to the large number and complex interplay of the multivariate independent parameters of the melt electrospinning process. To overcome this manufacturing challenge, dimensional analysis is employed to formulate a “Printability Number” (NPR), which correlates with the dimensionless numbers arising from the nondimensionalization of the governing conservation equations of the electrospinning process and the viscoelasticity of the polymer melt. This analysis suggests that the applied voltage potential (Vp), the volumetric flow rate (Q), and the translational stage speed (UT) are the most critical parameters toward efficient printability. Experimental investigations using a poly(ε-caprolactone) (PCL) melt reveal that any perturbations arising from an imbalance between the downstream pulling forces and the upstream resistive forces can be eliminated by systematically tuning Vp and Q for prescribed thermal conditions. This, in concert with appropriate tuning of the translational stage speed, enables steady-state equilibrium conditions to be achieved for the printing of microfibrous woven meshes with precise and reproducible geometries.

FIGURES IN THIS ARTICLE
<>
Copyright © 2017 by ASME
Your Session has timed out. Please sign back in to continue.

References

Saville, D. A. , 1997, “ Electrohydrodynamics: The Taylor–Melcher Leaky Dielectric Model,” Annu. Rev. Fluid Mech., 29(1962), pp. 27–64. [CrossRef]
Zeleny, J. , 1917, “ Instability of Electrified Liquid Surfaces,” Phys. Rev., 10(1), pp. 1–6. [CrossRef]
Bhardwaj, N. , and Kundu, S. C. , 2010, “ Electrospinning: A Fascinating Fiber Fabrication Technique,” Biotechnol. Adv., 28(3), pp. 325–347. [CrossRef] [PubMed]
Larrondo, L. , and St. John Manley, R. , 1981, “ Electrostatic Fiber Spinning From Polymer Melts—I: Experimental Observations on Fiber Formation and Properties,” J. Polym. Sci., Part B: Polym. Phys., 19(6), pp. 909–920. [CrossRef]
Reneker, D. H. , Yarin, A. L. , Zussman, E. , and Xu, H. , 2007, “ Electrospinning of Nanofibers From Polymer Solutions and Melts,” Adv. Appl. Mech., 41(345–346), pp. 43–195.
Ogata, N. , Shimada, N. , Yamaguchi, S. , Nakane, K. , and Ogihara, T. , 2007, “ Melt-Electrospinning of Poly(Ethylene Terephthalate) and Polyalirate,” J. Appl. Polym. Sci., 105(3), pp. 1127–1132. [CrossRef]
Tian, S. , Ogata, N. , Shimada, N. , Nakane, K. , Ogihara, T. , and Yu, M. , 2009, “ Melt Electrospinning From Poly(L-Lactide) Rods Coated With Poly(Ethylene-Co-Vinyl Alcohol),” J. Appl. Polym. Sci., 113(2), pp. 1282–1288. [CrossRef]
Ogata, N. , Lu, G. , Iwata, T. , Yamaguchi, S. , Nakane, K. , and Ogihara, T. , 2007, “ Effects of Ethylene Content of Poly(Ethylene-Co-Vinyl Alcohol) on Diameter of Fibers Produced by Melt-Electrospinning,” J. Appl. Polym. Sci., 104(2), pp. 1368–1375. [CrossRef]
Ogata, N. , Yamaguchi, S. , Shimada, N. , Lu, G. , Iwata, T. , Nakane, K. , and Ogihara, T. , 2007, “ Poly(Lactide) Nanofibers Produced by a Melt-Electrospinning System With a Laser Melting Device,” J. Appl. Polym. Sci., 104(3), pp. 1640–1645. [CrossRef]
Yang, W. M. , and Li, H. Y. , 2014, “ Principle and Equipment of Polymer Melt Differential Electrospinning Preparing Ultrafine Fiber,” IOP Conf. Ser.: Mater. Sci. Eng., 64, p. 012013.
Li, H. , Chen, H. , Zhong, X. , Wu, W. , Ding, Y. , and Yang, W. , 2014, “ Interjet Distance in Needleless Melt Differential Electrospinning With Umbellate Nozzles,” J. Appl. Polym. Sci., 131(15), pp. 1–8.
Zhmayev, E. , Cho, D. , and Joo, Y. L. , 2010, “ Nanofibers From Gas-Assisted Polymer Melt Electrospinning,” Polymer, 51(18), pp. 4140–4144. [CrossRef]
Senturk-Ozer, S. , Ward, D. , Gevgilili, H. , and Kalyon, D. M. , 2013, “ Dynamics of Electrospinning of Poly(Caprolactone) Via a Multi-Nozzle Spinneret Connected to a Twin Screw Extruder and Properties of Electrospun Fibers,” Polym. Eng. Sci., 53(7), pp. 1463–1474. [CrossRef]
Kalyon, D. M. , Yu, X. , Wang, H. , Valdevit, A. , and Ritter, A. , 2013, “ Twin Screw Extrusion Based Technologies Offer Novelty, Versatility, Reproducibility and Industrial Scalability for Fabrication of Tissue Engineering Scaffolds,” J. Tissue Sci. Eng., 4(2), pp. 2–3. [CrossRef]
Dalton, P. D. , Vaquette, C. , Farrugia, B. L. , Dargaville, T. R. , Brown, T. D. , and Hutmacher, D. W. , 2013, “ Electrospinning and Additive Manufacturing: Converging Technologies,” Biomater. Sci., 1(2), pp. 1–27. [CrossRef]
Góra, A. , Sahay, R. , Thavasi, V. , and Ramakrishna, S. , 2011, “ Melt-Electrospun Fibers for Advances in Biomedical Engineering, Clean Energy, Filtration, and Separation,” Polym. Rev., 51(3), pp. 265–287. [CrossRef]
Brown, T. D. , Dalton, P. D. , and Hutmacher, D. W. , 2011, “ Direct Writing by Way of Melt Electrospinning,” Adv. Mater., 23(47), pp. 5651–5657. [CrossRef] [PubMed]
Zhmayev, E. , Zhou, H. , and Joo, Y. L. , 2008, “ Modeling of Non-Isothermal Polymer Jets in Melt Electrospinning,” J. Non-Newtonian Fluid Mech., 153(2–3), pp. 95–108. [CrossRef]
Hutmacher, D. W. , Schantz, T. , Zein, I. , Ng, K. W. , Teoh, S. H. , and Tan, K. C. , 2001, “ Mechanical Properties and Cell Cultural Response of Polycaprolactone Scaffolds Designed and Fabricated Via Fused Deposition Modeling,” J. Biomed. Mater. Res., 55(2), pp. 203–216. [CrossRef] [PubMed]
Snyder, J. , Rin Son, A. , Hamid, Q. , and Sun, W. , 2015, “ Fabrication of Microfluidic Manifold by Precision Extrusion Deposition and Replica Molding for Cell-Laden Device,” ASME J. Manuf. Sci. Eng., 138(4), p. 041007. [CrossRef]
Sun, D. , Chang, C. , Li, S. , and Lin, L. , 2006, “ Near-Field Electrospinning,” Nano Lett., 6(4), pp. 839–842. [CrossRef] [PubMed]
Bisht, G. B., Canton, G., Mirsepassi, A., Kulinsky, L., Oh, S., Dunn-Rankin, D., and Madou, M. J., 2011, “ Controlled Continuous Patterning of Polymeric Nanofibers on Three-Dimensional Substrates Using Low-Voltage Near-Field Electrospinning,” Nano Lett., 11(4), pp. 1831–1837.
Huang, Y. , Bu, N. , Duan, Y. , Pan, Y. , Liu, H. , Yin, Z. , and Xiong, Y. , 2013, “ Electrohydrodynamic Direct-Writing,” Nanoscale, 5(24), pp. 12007–12017. [CrossRef] [PubMed]
Brown, T. D. , Dalton, P. D. , and Hutmacher, D. W. , 2016, “ Melt Electrospinning Today: An Opportune Time for an Emerging Polymer Process,” Prog. Polym. Sci., 56, pp. 116–166. [CrossRef]
Muerza-Cascante, M. L. , Haylock, D. , Hutmacher, D. W. , and Dalton, P. D. , 2014, “ Melt Electrospinning and Its Technologization in Tissue Engineering,” Tissue Eng., Part B, 21(2), pp. 1–16.
Brown, T. D. , Edin, F. , Detta, N. , Skelton, A. D. , Hutmacher, D. W. , and Dalton, P. D. , 2014, “ Melt Electrospinning of Poly(ε-Caprolactone) Scaffolds: Phenomenological Observations Associated With Collection and Direct Writing,” Mater. Sci. Eng., C, 45, pp. 698–708. [CrossRef]
Zhmayev, E. , Cho, D. , and Lak Joo, Y. , 2011, “ Electrohydrodynamic Quenching in Polymer Melt Electrospinning,” Phys. Fluids, 23(7), p. 073102. [CrossRef]
Han, T. , Reneker, D. H. , and Yarin, A. L. , 2007, “ Buckling of Jets in Electrospinning,” Polymer, 48(20), pp. 6064–6076. [CrossRef]
Morris, S. W. , Dawes, J. H. P. , Ribe, N. M. , and Lister, J. R. , 2008, “ Meandering Instability of a Viscous Thread,” Phys. Rev. E, 77(6), p. 066218. [CrossRef]
Tourlomousis, F. , Ding, H. , Dole, A. , and Chang, R. C. , 2016, “ Towards Resolution Enhancement and Process Repeatability With a Melt Electrospinning Writing Process: Design and Protocol Considerations,” ASME Paper No. MSEC2016-8774.
Tourlomousis, F. , Babakhanov, A. , Ding, H. , and Chang, R. C. , 2015, “ A Novel Melt Electrospinning System for Studying Cell Substrate Interactions,” ASME Paper No. MSEC2015-9443.
Feng, J. J. , 2003, “ Stretching of a Straight Electrically Charged Viscoelastic Jet,” J. Non-Newtonian Fluid Mech., 116(1), pp. 55–70. [CrossRef]
Jeon, H. , Simon, C. G. , and Kim, G. , 2014, “ A Mini-Review: Cell Response to Microscale, Nanoscale, and Hierarchical Patterning of Surface Structure,” J. Biomed. Mater. Res., Part B, 102(7), pp. 1580–1594. [CrossRef]
Kumar, G. , Tison, C. K. , Chatterjee, K. , Pine, P. S. , McDaniel, J. H. , Salit, M. L. , Young, M. F. , and Simon, C. G. , 2011, “ The Determination of Stem Cell Fate by 3D Scaffold Structures Through the Control of Cell Shape,” Biomaterials, 32(35), pp. 9188–9196. [CrossRef] [PubMed]
Farooque, T. M. , Camp, C. H. , Tison, C. K. , Kumar, G. , Parekh, S. H. , and Simon, C. G. , 2014, “ Measuring Stem Cell Dimensionality in Tissue Scaffolds,” Biomaterials, 35(9), pp. 2558–2567. [CrossRef] [PubMed]
Brown, T. D. , Slotosch, A. , Thibaudeau, L. , Taubenberger, A. , Loessner, D. , Vaquette, C. , Dalton, P. D. , and Hutmacher, D. W. , 2012, “ Design and Fabrication of Tubular Scaffolds Via Direct Writing in a Melt Electrospinning Mode,” Biointerphases, 7(1–4), p. 13. [CrossRef] [PubMed]
Wei, C. , and Dong, J. , 2013, “ Direct Fabrication of High-Resolution Three-Dimensional Polymeric Scaffolds Using Electrohydrodynamic Hot Jet Plotting,” J. Micromech. Microeng., 23(2), p. 025017. [CrossRef]
Farrugia, B. L. , Brown, T. D. , Upton, Z. , Hutmacher, D. W. , Dalton, P. D. , and Dargaville, T. R. , 2013, “ Dermal Fibroblast Infiltration of Poly(ε-Caprolactone) Scaffolds Fabricated by Melt Electrospinning in a Direct Writing Mode,” Biofabrication, 5(2), p. 025001. [CrossRef] [PubMed]
Mota, C. , Puppi, D. , Gazzarri, M. , Bártolo, P. , and Chiellini, F. , 2013, “ Melt Electrospinning Writing of Three-Dimensional Star Poly(ε-Caprolactone) Scaffolds,” Polym. Int., 62(6), pp. 893–900. [CrossRef]
Ko, J. , Mohtaram, N. K. , Ahmed, F. , Montgomery, A. , Carlson, M. , Lee, P. C. D. , Willerth, S. M. , and Jun, M. B. G. , 2014, “ Fabrication of Poly (ϵ-Caprolactone) Microfiber Scaffolds With Varying Topography and Mechanical Properties for Stem Cell-Based Tissue Engineering Applications,” J. Biomater. Sci. Polym. Ed., 25(1), pp. 1–17. [CrossRef] [PubMed]
Hochleitner, G. , Hümmer, J. F. , Luxenhofer, R. , and Groll, J. , 2014, “ High Definition Fibrous Poly(2-Ethyl-2-Oxazoline) Scaffolds Through Melt Electrospinning Writing,” Polymer, 55(20), pp. 5017–5023. [CrossRef]
Thibaudeau, L. , Taubenberger, A. V. , Holzapfel, B. M. , Quent, V. M. , Fuehrmann, T. , Hesami, P. , Brown, T. D. , Dalton, P. D. , Power, C. A. , Hollier, B. G. , and Hutmacher, D. W. , 2014, “ A Tissue-Engineered Humanized Xenograft Model of Human Breast Cancer Metastasis to Bone,” Dis. Models Mech., 7(2), pp. 299–309. [CrossRef]
Visser, J. , Melchels, F. P. W. , Jeon, J. E. , van Bussel, E. M. , Kimpton, L. S. , Byrne, H. M. , Dhert, W. J. A. , Dalton, P. D. , Hutmacher, D. W. , and Malda, J. , 2015, “ Reinforcement of Hydrogels Using Three-Dimensionally Printed Microfibres,” Nat. Commun., 6, p. 6933. [CrossRef] [PubMed]
Ristovski, N. , Bock, N. , Liao, S. , Powell, S. , Ren, J. , Kirby, G. T. S. , Blackwood, K. A. , and Woodruff, M. A. , 2015, “ Improved Fabrication of Melt Electrospun Tissue Engineering Scaffolds Using Direct Writing and Advanced Electric Field Control,” Biointerphases, 10(1), p. 011006. [CrossRef] [PubMed]
Hochleitner, G. , Jüngst, T. , Brown, T. D. , Hahn, K. , Moseke, C. , Jakob, F. , Dalton, P. D. , and Groll, J. , 2015, “ Additive Manufacturing of Scaffolds With Sub-Micron Filaments Via Melt Electrospinning Writing,” Biofabrication, 7(3), p. 035002. [CrossRef] [PubMed]
Haigh, J. N. , Chuang, Y. , Farrugia, B. , Hoogenboom, R. , Dalton, P. D. , and Dargaville, T. R. , 2015, “ Hierarchically Structured Porous Poly(2-Oxazoline) Hydrogels,” Macromol. Rapid Commun., 37(1), pp. 93–99. [CrossRef]
Bas, O. , De-Juan-Pardo, E. M. , Chhaya, M. P. , Wunner, F. M. , Jeon, J. E. , Klein, T. J. , and Hutmacher, D. W. , 2015, “ Enhancing Structural Integrity of Hydrogels by Using Highly Organised Melt Electrospun Fibre Constructs,” Eur. Polym. J., 72, pp. 451–463. [CrossRef]
Chen, F. , Hochleitner, G. , Woodfield, T. , Groll, J. , Dalton, P. D. , and Amsden, B. G. , 2016, “ Additive Manufacturing of a Photo-Cross-Linkable Polymer Via Direct Melt Electrospinning Writing for Producing High Strength Structures,” Biomacromolecules, 17(1), pp. 208–214. [CrossRef] [PubMed]
Noroozi, N. , 2013, “ Rheology and Processing of Biodegradable Poly(ε-Caprolactone) Polyesters and Their Blends With Polylactides,” Ph.D. thesis, The University of British Columbia, Vancouver, BC, Canada.
Hutmacher, D. W. , and Dalton, P. D. , 2011, “ Melt Electrospinning,” Chem. - Asian J., 6(1), pp. 44–56. [CrossRef] [PubMed]
McCabe, W. L. , Smith, J. C. , and Harriot, P. , 1993, “ Dimensional Analysis,” Unit Operations of Chemical Engineering, McGraw-Hill, New York, pp. 3–18.
Lin, C. C. , and Segel, L. A. , 1988, “ Simplification, Dimensional Analysis and Scaling,” Mathematics Applied to Deterministic Problemsin the Natural Science, R. E. O'Maley , ed., SIAM, Philadelphia, PA, pp. 185–204.
Fernández de la Mora, J. , 2007, “ The Fluid Dynamics of Taylor Cones,” Annu. Rev. Fluid Mech., 39(1), pp. 217–243. [CrossRef]
Helgeson, M. E. , and Wagner, N. J. , 2007, “ A Correlation for the Diameter of Electrospun Polymer Nanofibers,” AIChE J., 53(1), pp. 51–55. [CrossRef]
Bird, R. B. , Armstrong, R. C. , and Hassanger, O. , 1987, Dynamics of Polymeric Liquids, Fluid Mechanics, Wiley-Interscience, New York.
Denn, M. M. , 2008, “ Uniaxial Extensional Flow,” Polymer Melt Processing: Foundations in Fluid Mechanics and Heat Transfer, A. Varma , ed., Cambridge University Press, New York, p. 86.
Biresaw, G. , and Carriere, C. J. , 2001, “ Correlation Between Mechanical Adhesion and Interfacial Properties of Starch/Biodegradable Polyester Blends,” J. Polym. Sci., Part B: Polym. Phys., 39(9), pp. 920–930. [CrossRef]
Aguilar, S. M. , Shea, J. D. , Al-Joumayly, M. A. , Van Veen, B. D. , Behdad, N. , and Hagness, S. C. , 2012, “ Dielectric Characterization of PCL-Based Thermoplastic Materials for Microwave Diagnostic and Therapeutic Applications,” IEEE Trans. Biomed. Eng., 59(3), pp. 627–633. [CrossRef] [PubMed]
Hochleitner, G. , Youssef, A. , Hrynevich, A. , Haigh, J. N. , Jungst, T. , Groll, J. , and Dalton, P. D. , 2016, “ Fibre Pulsing During Melt Electrospinning Writing,” BioNanoMaterials, 17(3–4), pp. 159–171.
Helgeson, M. E. , Grammatikos, K. N. , Deitzel, J. M. , and Wagner, N. J. , 2008, “ Theory and Kinematic Measurements of the Mechanics of Stable Electrospun Polymer Jets,” Polymer, 49(12), pp. 2924–2936. [CrossRef]
Hohman, M. M. , Shin, M. , Rutledge, G. , and Brenner, M. P. , 2001, “ Electrospinning and Electrically Forced Jets—I: Stability Theory,” Phys. Fluids, 13(8), pp. 2201–2220. [CrossRef]
Hohman, M. M. , Shin, M. , Rutledge, G. , and Brenner, M. P. , 2001, “ Electrospinning and Electrically Forced Jets—II: Applications,” Phys. Fluids, 13(8), pp. 2221–2236. [CrossRef]
Liu, F. , and Chen, C. H. , 2014, “ Electrohydrodynamic Cone-Jet Bridges: Stability Diagram and Operating Modes,” J. Electrostat., 72(4), pp. 330–335. [CrossRef]
Scheideler, W. J. , and Chen, C. H. , 2014, “ The Minimum Flow Rate Scaling of Taylor Cone-Jets Issued From a Nozzle,” Appl. Phys. Lett., 104(2), p. 024103. [CrossRef]
Nelaturi, S. , Kim, W. , and Kurtoglu, T. , 2015, “ Manufacturability Feedback and Model Correction for Additive Manufacturing,” ASME J. Manuf. Sci. Eng., 137(2), p. 021015. [CrossRef]
Huang, Y. , Leu, M. C. , Mazumder, J. , and Donmez, A. , 2015, “ Additive Manufacturing: Current State, Future Potential, Gaps and Needs, and Recommendations,” ASME J. Manuf. Sci. Eng., 137(1), p. 014001. [CrossRef]

Figures

Grahic Jump Location
Fig. 1

Concept graph plotting the different manufacturing methods employed in the biofabrication field for scaffold-guided tissue engineering applications as a function of their resolution

Grahic Jump Location
Fig. 2

Physics of the melt electrospinning writing process. (a) Digital photographs at different time instances showing the melt electrospinning process performed with a stationary collector and the printing evolution of conical structures under the tip. The collector plate is mounted on an x–y automated stage (translational stage speed—UT = 0 mm/s). (b) (I) Digital photograph showing the jet deposition with the melt electrospinning writing process as the collector plate is moving at the critical stage speed. (II) Digital photograph showing the jet deposition as the collector plate is moving at a slightly higher speed than the critical stage speed, resulting in trailing edge formation due to the viscoelastic nature of the material.

Grahic Jump Location
Fig. 3

Categorization of independent parameters involved in melt electrospinning writing process

Grahic Jump Location
Fig. 4

Schematic illustrating the proposed heating element and the key heat transfer mechanisms in the polymer melt supply and free-flow regime. (a) computer aided design model of the industrial heat gun mounted in the heating tunnel. (b) The hot stream air causes the simultaneous heating of the polymer melt supply regime (syringe barrel and needle tip) and the free-flow regime by forced and free convection, respectively. The surface temperature on the syringe (Ts (SI:  °C)) and the temperature profile (Tt < z < Tc (SI:  °C)) along the spinline coordinate z can be controlled with an industrial heat gun for a prescribed setting of volumetric flow rate and temperature.

Grahic Jump Location
Fig. 5

Melt electrospinning writing system configuration. (a) computer aided design model showing the three distinct process regimes. (b) The polymer supply regime is heated using a heat gun that is calibrated using a thermal FLIR camera. The temperature at the surface of the melt reservoir (Ts) is determined at the position denoted by the crosshatch. (c) A digital photograph showing the thermocouple and the indexed phantom used to measure the temperature profile along the spinline in the free-flow regime. (d) The temperature profile along the free-flow regime is measured for a heat gun setting corresponding to Ts = 77.8 °C.

Grahic Jump Location
Fig. 6

Rheological characterization of PCL at different melting temperatures (Tm: 70–80–90 °C). (a) Elastic (G″) and loss moduli (G′) as a function of angular frequency (ω (SI: rad/s)). Dynamic data and fitting using the Giesekus model. (b) Polymer viscosity as a function of angular frequency (ω (SI: rad/s)) and shear rate (γ˙ (SI: s−1)). Dynamic data, steady torsional data, and fitting using the Giesekus model.

Grahic Jump Location
Fig. 7

Correlation of the Printability Number under a stationary collector with scaled dimensionless groups arising from the governing equations. (a) Normalized Printability Number (NPR,1*  = NPR,1/NPR,1,min versus normalized melting temperature (T* = Tm/Tref), where NPR,min is given for Tref = 70 °C and Q = 50 μL/h. The arrow at T* = 1.10 indicates the melting conditions set in the present study. (b) NPR,1* versus Re number, (c) NPR,1* versus De number, (d) NPR,1* versus Ca number, and (e) NPR,1* versus Ep number. Graphs in (b)–(e) are obtained for Tm = 78 °C and three different voltage potential (Vp) values.

Grahic Jump Location
Fig. 8

Digital photographs showing the temporal evolution of the printing process initiation. (I) Starting point (t = 0 min) is considered the instance at which the polymer melt enters the free-flow regime. The following are initial values of the main process parameters: volumetric flow rate (Q = 50 μL/h), voltage potential (Vp = 12.5 kV), tip to collector distance (d = 20 mm), and experimental temperature at the surface of the melt reservoir (Ts = 78 °C). (II) At t = 12 min, the elongate shape of the jet denotes incremental electrostatic forces along with the gravity forces to overcome the resistive forces (viscous, elastic, and surface tension forces). (III) At t = 15 min, the downstream forces exceed the upstream resistive forces leading to the Taylor cone formation. (IV) Within seconds, a straight cone–jet forms between the needle tip and the collector.

Grahic Jump Location
Fig. 9

Tuning of the Printability Number under a stationary collector toward steady equilibrium conditions in the free-flow regime. (a) The normalized Printability Number (NPR,1*) versus electrostatic force parameter (Ep). (b) Digital photographs corresponding to each Ep setting and associated NPR,1* illustrate the procedural steps followed to obtain a stable melt electrospun jet. This equilibrium printing state is achieved by systematically tuning the process parameters and observing the effect on the jet shape. (I) For the following initial values of the main process parameters: Q = 50 μL/h, Vp = 12.5 kV, d = 20 mm, and excess jetted material disturbs the cone–jet formation. (II) Within minutes, the jet is reformed with elevation of the Taylor cone position. (III) The collector is set closer to the needle tip (d = 15 mm), resulting in an increment of the electrical field strength. The resultant jet shape is altered, yielding stretching of the excess material and Taylor cone formation closer to the needle tip. (IV) The volumetric flow rate is decreased (Q = 25 μl/h), resulting in decreased mass delivery rate at the needle tip and optimized cone–jet formation for the prescribed electrical field strength. However, chaotic fiber jet movement is observed close to the collector plate. (IV) In order to eliminate the instabilities observed close to the collector plate, the applied voltage potential is decreased (Vp = 11.5 kV) to yield stable cone–jet formation.

Grahic Jump Location
Fig. 10

Results of a square-wave experiment showing the effect of translational stage speed (UT (mm/s)) on fiber topography and average fiber diameter (Df (μm)). (a) Bright field microscopy images of fiber topographies printed at various stage speeds (magnification: 20× and scale bar: 50 μm). The first aligned fiber is obtained at a critical stage speed (UCR (mm/s)) equal to 83 mm/s. (b) The average fiber diameter is measured for each stage setting. (Error bars denote the standard deviation of mean Df for five distinct sections along the fiber length.)

Grahic Jump Location
Fig. 11

Results of printing studies. (a) Nonwoven mesh printed with NPR,2*  = 31.9, where UT = 25 mm/s < UCR. (b) Mesh printed with NPR,2*  = 57.63, where UT = 85 mm/s ≥ UCR and nonequilibrium conditions occur in the free-flow regime. (c) Woven mesh with 0–90 deg pore architecture. (d) Woven mesh with 0–45–135–90 deg pore architecture. Both woven meshes are printed at optimum NPR,2*  = 106, where UT = 85 mm/s ≥ UCR and steady-state equilibrium condition is reached in the free-flow regime (magnification: 20×and scale bar: 50 μm).

Grahic Jump Location
Fig. 12

Woven mesh with 0–45–135–90 deg pore architecture. The mesh is printed at optimum NPR,2* = 106, where UT = 51.5 mm/s ≥ UCR and steady-state equilibrium condition is reached in the free-flow regime with Vp = 11 kV and Q = 15 μL/h. White, solid line boxes: magnified area in the middle of the mesh. Dashed boxes: areas with disturbed pore shape from inconsistent fiber deposition owing to residual charge entrapped within the printed fibers (scale bar: 100 μm).

Tables

Errata

Discussions

Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging and repositioning the boxes below.

Related Journal Articles
Related eBook Content
Topic Collections

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In