Melt electrospinning

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A polycaprolactone scaffold produced via melt electrospinning writing 150 um boxes MEW.jpg
A polycaprolactone scaffold produced via melt electrospinning writing

Melt electrospinning is a processing technique to produce fibrous structures from polymer melts for applications that include tissue engineering, textiles and filtration. In general, electrospinning can be performed using either polymer melts or polymer solutions. However, melt electrospinning is distinct in that the collection of the fiber can very focused; combined with moving collectors, melt electrospinning writing is a way to perform 3D printing. Since volatile solvents are not used, there are benefits for some applications where solvent toxicity and accumulation during manufacturing are a concern.

Contents

History

The first description of melt electrospinning was by Charles Norton in a patent approved in 1936. After this first discovery, it wasn't until 1981 that melt electrospinning was described as part of a three-paper series. [1] A meeting abstract on melt electrospinning in a vacuum was published by Reneker and Rangkupan 20 years later in 2001. [2] Since this scientific publication in 2001, there have been regular articles on melt electrospinning, including reviews on the subject. [3] In 2011, melt electrospinning combined with a translating collector was with proposed as a new class of 3D printing. [4]

Principles

The same physics of electrostatic fiber drawing apply to melt electrospinning. What differs are the physical properties of the polymer melt, compared to a polymer solution. When comparing polymer melts and polymer solutions, the former are normally more viscous than polymer solutions, and elongated electrified jets have been reported. [5] The molten electrified jet also requires cooling to solidify, while solution electrospinning relies on evaporation. While melt electrospinning typically results in micron diameter fibers, the path of the electrified jet in melt electrospinning can be predictable. [6]

Parameters

Temperature

A minimum temperature is needed to ensure a molten polymer, all the way to the tip of the spinneret. Spinnerets have a relatively short length, compared to solution electrospinning.

Flow Rate

The most significant parameter for controlling the fiber diameter is the flow rate of the polymer to the spinneret - in general, the higher the flow rate, the larger the fiber diameter. While reported flow rates are low, all of the fluid electrospun is collected, unlike solution electrospinning where a great part of the solvent is evaporated.

Molecular Weight

The molecular weight is important as to whether the polymer can be melt electrospun. For linear homogeneous polymers, a low molecular weight (below 30,000g/mol) can result in broken and poor quality fibers. [7] For high molecular weights (above 100,000 g/mol), the polymer can be very difficult to flow through the spinneret. Many melt electrospun fibers reported use molecular weights between 40,000 and 80,000 g/mol [4] or are blends of low and high molecular weight polymers. [8]

Voltage

Modifying the voltage does not greatly effect the resulting fiber diameter, however it has been reported that an optimum voltage is needed to make high quality and consistent fibers. Voltages from as low as 0.7kV up to 60kV have been used to melt electrospin. [9] [10]

Apparatus

Different melt electrospinning machines have been built, with some mounted vertically and some horizontally. The approach to heating the polymer does vary and includes electrical heaters, heated air and circulating heaters. [3] One approach to melt electrospinning is pushing a solid polymer filament into a laser, which melts and is electrospun.

Polymers

Polymers exhibiting a melting point or glass transition temperature (Tg) are required for melt electrospinning, excluding thermosets (such as bakelite) and biologically derived polymers (such as collagen). Polymers melt electrospun so far include:

  1. Polycaprolactone [4] [11]
  2. Polylactic acid [12]
  3. Poly(lactide-co-glycolide) [13]
  4. Poly(methyl methacrylate) [14] [15]
  5. Polypropylene [1] [5]
  6. Polyethylene [10]
  7. Poly(caprolactone-block-ethylene glycol) [7]
  8. Polyurethane [16]

These polymers are examples of the most used polymers, and a more comprehensive list can be found elsewhere. [3]

Uses

Potential applications of melt electrospinning mirror that of solution electrospinning. Not using solvents to process a polymer assists in tissue engineering applications where solvents are often toxic. Additionally, some polymers such as polypropylene or polyethylene are not readily dissolved, so melt electrospinning is one approach to electrospin them into fibrous material.

Tissue Engineering

Melt electrospinning is used to process biomedical materials for tissue engineering research. Volatile solvents are often toxic so avoiding solvents has benefits in this field. Melt electrospun fibers were used as part of a "bimodal tissue scaffold", where both micron-scale and nano-scale fibers were deposited simultaneously. [13] Scaffolds made via melt electrospinning can be fully penetrated with cells, which in turn produce extracellular matrix within the scaffold. [17]

Drug Delivery

Melt electrospinning is also capable to formulate drug-loaded fibers for drug delivery. It is a promising new formulation technique in the field of pharmaceutical technology to prepare amorphous solid dispersions or solid solutions with enhanced or controlled drug dissolution because it can combine the advantages of melt extrusion (e.g. solvent-free, effective amorphization, continuous process) and solvent-based electrospinning (increased surface area). [18] [19] [20]

Melt Electrospinning Writing

The electrified molten jet created via melt electrospinning has a more predictable path, and polymer fibers can be deposited accurately onto the collector. When the collector is moved at sufficient speed (referred to as the critical translation speed), straight melt electrospun fibers can be deposited in a layer upon layer approach. This enables for the fabrication of complex, well-ordered structures. [4] In this respect melt electrospinning writing (MEW) can be considered a class of 3D printing. Melt electrospinning writing has been performed using either a translating flat surface [4] or a rotating cylinder/mandrel. [11] Most polymers that can be melt-electrospun can also be written assuming the parameters can be tuned in such a way as to produce a stable jet. Piezoelectric polymers such as polyvinylidene difluoride (PVDF) have also been shown to be processable via MEW, opening up potential applications in 3d printed sensors, soft robotics, and further applications in biofabrication. [21]

Related Research Articles

<span class="mw-page-title-main">Tissue engineering</span> Biomedical engineering discipline

Tissue engineering is a biomedical engineering discipline that uses a combination of cells, engineering, materials methods, and suitable biochemical and physicochemical factors to restore, maintain, improve, or replace different types of biological tissues. Tissue engineering often involves the use of cells placed on tissue scaffolds in the formation of new viable tissue for a medical purpose, but is not limited to applications involving cells and tissue scaffolds. While it was once categorized as a sub-field of biomaterials, having grown in scope and importance, it can is considered as a field of its own.

<span class="mw-page-title-main">Electrospinning</span> Fiber production method

Electrospinning is a fiber production method that uses electric force to draw charged threads of polymer solutions or polymer melts up to fiber diameters in the order of some hundred nanometers. Electrospinning shares characteristics of both electrospraying and conventional solution dry spinning of fibers. The process does not require the use of coagulation chemistry or high temperatures to produce solid threads from solution. This makes the process particularly suited to the production of fibers using large and complex molecules. Electrospinning from molten precursors is also practiced; this method ensures that no solvent can be carried over into the final product.

<span class="mw-page-title-main">Polyglycolide</span> Chemical compound

Polyglycolide or poly(glycolic acid) (PGA), also spelled as polyglycolic acid, is a biodegradable, thermoplastic polymer and the simplest linear, aliphatic polyester. It can be prepared starting from glycolic acid by means of polycondensation or ring-opening polymerization. PGA has been known since 1954 as a tough fiber-forming polymer. Owing to its hydrolytic instability, however, its use has initially been limited. Currently polyglycolide and its copolymers (poly(lactic-co-glycolic acid) with lactic acid, poly(glycolide-co-caprolactone) with ε-caprolactone and poly (glycolide-co-trimethylene carbonate) with trimethylene carbonate) are widely used as a material for the synthesis of absorbable sutures and are being evaluated in the biomedical field.

<span class="mw-page-title-main">Polycaprolactone</span> Chemical compound

Polycaprolactone (PCL) is a synthetic, semi-crystalline, biodegradable polyester with a melting point of about 60 °C and a glass transition temperature of about −60 °C. The most common use of polycaprolactone is in the production of speciality polyurethanes. Polycaprolactones impart good resistance to water, oil, solvent and chlorine to the polyurethane produced.

<span class="mw-page-title-main">Polylactic acid</span> Biodegradable polymer

Polylactic acid, also known as poly(lactic acid) or polylactide (PLA), is a thermoplastic polyester with backbone formula (C
3H
4O
2)
n or [–C(CH
3)HC(=O)O–]
n, formally obtained by condensation of lactic acid C(CH
3)(OH)HCOOH with loss of water. It can also be prepared by ring-opening polymerization of lactide [–C(CH
3)HC(=O)O–]
2, the cyclic dimer of the basic repeating unit.

<span class="mw-page-title-main">Nonwoven fabric</span> Sheet of fibers

Nonwoven fabric or non-woven fabric is a fabric-like material made from staple fibre (short) and long fibres, bonded together by chemical, mechanical, heat or solvent treatment. The term is used in the textile manufacturing industry to denote fabrics, such as felt, which are neither woven nor knitted. Some non-woven materials lack sufficient strength unless densified or reinforced by a backing. In recent years, non-wovens have become an alternative to polyurethane foam.

<span class="mw-page-title-main">Nanofiber</span>

Nanofibers are fibers with diameters in the nanometer range. Nanofibers can be generated from different polymers and hence have different physical properties and application potentials. Examples of natural polymers include collagen, cellulose, silk fibroin, keratin, gelatin and polysaccharides such as chitosan and alginate. Examples of synthetic polymers include poly(lactic acid) (PLA), polycaprolactone (PCL), polyurethane (PU), poly(lactic-co-glycolic acid) (PLGA), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), and poly(ethylene-co-vinylacetate) (PEVA). Polymer chains are connected via covalent bonds. The diameters of nanofibers depend on the type of polymer used and the method of production. All polymer nanofibers are unique for their large surface area-to-volume ratio, high porosity, appreciable mechanical strength, and flexibility in functionalization compared to their microfiber counterparts.

<span class="mw-page-title-main">Polydioxanone</span>

Polydioxanone or poly-p-dioxanone is a colorless, crystalline, biodegradable synthetic polymer.

<span class="mw-page-title-main">Nanofabrics</span> Textiles engineered with small particles that give ordinary materials advantageous properties

Nanofabrics are textiles engineered with small particles that give ordinary materials advantageous properties such as superhydrophobicity, odor and moisture elimination, increased elasticity and strength, and bacterial resistance. Depending on the desired property, a nanofabric is either constructed from nanoscopic fibers called nanofibers, or is formed by applying a solution containing nanoparticles to a regular fabric. Nanofabrics research is an interdisciplinary effort involving bioengineering, molecular chemistry, physics, electrical engineering, computer science, and systems engineering. Applications of nanofabrics have the potential to revolutionize textile manufacturing and areas of medicine such as drug delivery and tissue engineering.

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<span class="mw-page-title-main">Spinneret (polymers)</span> Any structure natural or artificial used to extrude polymers into fibers

A spinneret is a device used to extrude a polymer solution or polymer melt to form fibers. Streams of viscous polymer exit via the spinneret into air or liquid leading to a phase inversion which allows the polymer to solidify. The individual polymer chains tend to align in the fiber because of viscous flow. This airstream liquid-to-fiber formation process is similar to the production process for cotton candy. The fiber production process is generally referred to as "spinning". Depending on the type of spinneret used, either solid or hollow fibers can be formed. Spinnerets are also used for electrospinning and electrospraying applications. They are sometimes called coaxial needles, or coaxial emitters.

Spinning is a manufacturing process for creating polymer fibers. It is a specialized form of extrusion that uses a spinneret to form multiple continuous filaments.

Nano-scaffolding or nanoscaffolding is a medical process used to regrow tissue and bone, including limbs and organs. The nano-scaffold is a three-dimensional structure composed of polymer fibers very small that are scaled from a Nanometer scale. Developed by the American military, the medical technology uses a microscopic apparatus made of fine polymer fibers called a scaffold. Damaged cells grip to the scaffold and begin to rebuild missing bone and tissue through tiny holes in the scaffold. As tissue grows, the scaffold is absorbed into the body and disappears completely.

<span class="mw-page-title-main">Hollow fiber membrane</span> Class of artificial membranes containing a semi-permeable hollow fiber barrier

Hollow fiber membranes (HFMs) are a class of artificial membranes containing a semi-permeable barrier in the form of a hollow fiber. Originally developed in the 1960s for reverse osmosis applications, hollow fiber membranes have since become prevalent in water treatment, desalination, cell culture, medicine, and tissue engineering. Most commercial hollow fiber membranes are packed into cartridges which can be used for a variety of liquid and gaseous separations.

<span class="mw-page-title-main">Melt blowing</span> Micro- and nanofiber fabrication method

Melt blowing is a conventional fabrication method of micro- and nanofibers where a polymer melt is extruded through small nozzles surrounded by high speed blowing gas. The randomly deposited fibers form a nonwoven sheet product applicable for filtration, sorbents, apparels and drug delivery systems. The substantial benefits of melt blowing are simplicity, high specific productivity and solvent-free operation. Choosing an appropriate combination of polymers with optimized rheological and surface properties, scientists have been able to produce melt-blown fibers with an average diameter as small as 36 nm.

<span class="mw-page-title-main">Alternating current electrospinning</span>

Alternating current electrospinning is a fiber formation technique to produce micro- and nanofibers from polymer solutions under the dynamic drawing force of the electrostatic field with periodically changing polarity. The main benefit of alternating current electrospinning is that multiple times higher productivities are achievable compared to widely used direct current electrospinning setups.

<span class="mw-page-title-main">Hydrogel fiber</span>

Hydrogel fiber is a hydrogel made into a fibrous state, where its width is significantly smaller than its length. The hydrogel's specific surface area at fibrous form is larger than that of the bulk hydrogel, and its mechanical properties also changed accordingly. As a result of these changes, hydrogel fiber has a faster matter exchange rate and can be woven into different structures.

<span class="mw-page-title-main">Poly(trimethylene carbonate)</span> Polycarbonate

Poly(trimethylene carbonate) (PTMC) is an aliphatic polycarbonate synthesized from the 6-membered cyclic carbonate, trimethylene carbonate (1,3-propylene carbonate or 1,3-Dioxan-2-one). Trimethylene carbonate (TMC) is a colorless crystalline solid with melting point ranging between 45°C and 48 °C and boiling point at 255°C (at 760 mmHg). TMC is originally synthesized from 1,3-propanediol with phosgene or carbon monoxide, which are highly poisonous gases. Another route is from the transesterification of 1,3-propanediol and dialkylcarbonates. This route is considered "greener" compared to the other one, since precursors can be obtained from renewable resources and carbon dioxide.

References

  1. 1 2 L. Larrondo, R. S. J. Manley, Journal of Polymer Science Part B-Polymer Physics 1981, 19, 909.
  2. ↑ R. Rangkupan, D. H. Reneker, in New Frontiers in Fiber-Based Products, The Fiber Society, Raleigh, NC, USA, 2001.
  3. 1 2 3 Hutmacher DW & Dalton PD (2011) Melt Electrospinning. Chem Asian J, 6, 44-5.
  4. 1 2 3 4 5 Brown TD, Dalton PD, Hutmacher DW. (2011) Direct Writing by Way of Melt Electrospinning. Advanced Materials, 23, 5651-57.
  5. 1 2 Dalton PD, Grafahrend D, Klinkhammer K, Klee D, Möller M (2007) Electrospinning of polymer melts: phenomenological observations. Polymer, 48, 6823-6833.
  6. ↑ Dalton PD, Vaquette C, Farrugia B, Dargaville TR, Brown TD, Hutmacher DW. (2013) Electrospinning and Additive manufacturing: converging technologies. Biomater Sci, 1, 171.
  7. 1 2 Dalton PD, Calvet J-L, Mourran A, Klee D, Möller M (2006) Melt Electrospinning of poly(ethylene oxide-block-ε-caprolactone). Biotechnol J, 1, 998-1006.
  8. ↑ Dalton PD, Jörgensen N, Groll J, Möller M (2008) Patterning of melt electrospun substrates for tissue engineering. Biomed Mater, 3, 034139.
  9. ↑ C. S. Kong, K. J. Jo, N. K. Jo, H. S. Kim, Polymer Engineering and Science 2009, 49, 391
  10. 1 2 R. J. Deng, Y. Liu, Y. M. Ding, P. C. Xie, L. Luo, W. M. Yang, Journal of Applied Polymer Science 2009, 114, 166.
  11. 1 2 Brown TD, Slotosch A, Thibaudeau L, Taubenberger A, Loessner D, Vaquette C, Dalton PD, Hutmacher DW. (2012) Design and fabrication of tubular scaffolds by direct writing in a melt electrospinning mode. Biointerphases, 7, 13, DOI 10.1007/s13758-011-0013-7.
  12. ↑ H. J. Zhou, T. B. Green, Y. L. Joo, Polymer 2006, 47, 7497.
  13. 1 2 Kim SJ, Jang DH, Park WH, Min BM (2010) Fabrication and characterization of 3-dimensional PLGA nanofiber/microfiber composite scaffolds. Polymer, 51, 1320-7
  14. ↑ X. F. Wang, Z. M. Huang, Chinese Journal of Polymer Science 2010, 28, 45.
  15. ↑ C. P. Carroll, E. Zhmayev, V. Kalra, Y. L. Joo, Korea-Australia Rheology Journal 2008, 20, 153.
  16. ↑ Karchin A, Simonovsky FI, Ratner BD, Sanders JE. (2011) Melt electrospinning of biodegradable polyurethane scaffolds. Acta Biomater, 7, 3277-84.
  17. ↑ Farrugia B, Brown TD, Hutmacher DW, Upton Z, Dalton PD, Dargaville TR. (2013) Dermal fibroblast infiltration of poly(ε–caprolactone) scaffolds fabricated by melt electrospinning in a direct writing mode. Biofabrication 5, 025001.
  18. ↑ Nagy, Z. K., Balogh, A., Drávavölgyi, G., Ferguson, J., Pataki, H., Vajna, B. and Marosi, G. (2013). "Solvent-free melt electrospinning for preparation of fast dissolving drug delivery system and comparison with solvent-based electrospun and melt extruded systems". Journal of Pharmaceutical Sciences. 102 (2): 508–517 (www.fiberpharma.co.nf). doi:10.1002/jps.23374. PMID   23161110.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  19. ↑ Balogh, A., Drávavölgyi, G., Faragó, K., Farkas, A., Vigh, T., Sóti, P. L., Wagner, I., Madarász, J., Pataki, H., Marosi, G., Nagy, Z. K. (2014). "Plasticized drug-loaded melt electrospun polymer mats: characterization, thermal degradation, and release kinetics". Journal of Pharmaceutical Sciences. 103 (4): 1278-1287 (www.fiberpharma.co.nf). doi:10.1002/jps.23904. PMID   24549788.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  20. ↑ Balogh, A., Farkas, B., Faragó, K., Farkas, A., Wagner, I., Van Assche, I., Verreck, G., Nagy, Z. K., Marosi, G. (2015). "Melt-blown and electrospun drug-loaded polymer fiber mats for dissolution enhancement: A comparative study" (PDF). Journal of Pharmaceutical Sciences. 104 (5): 1767-1776 (www.fiberpharma.co.nf). doi:10.1002/jps.24399. PMID   25761776.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  21. ↑ Florczak, S; Lorson, T; Zheng, T; Mrlik, M; Hutmacher, D.W; Higgins, M.J; Luxenhofer, R; Dalton, P.D (2019). "Melt electrowriting of electroactive poly(vinylidene difluoride) fibers". Polymer International. 68 (4): 735–745. doi: 10.1002/pi.5759 . hdl: 10072/385769 . S2CID   104438365.
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