Patent Publication Number: US-2012034461-A1

Title: Electrospinning nozzle

Description:
TECHNICAL FIELD  
     The present invention relates to an apparatus for electrospinning, electrospraying, or electrojetting, such as for use in producing fibres, droplets, or particles. In particular, the present invention relates to producing fibres having a core-shell, or core multishell structure. 
     BACKGROUND ART  
     Electrospray is a technique for dispersing a liquid to produce an aerosol. In this technique, a liquid is supplied through a capillary and a high voltage is applied to the tip of the capillary. There is also provided a plate biased at low voltage, such as ground, spaced apart from the capillary in a direction normal to the capillary. The relatively high potential at the tip of the capillary results in the formation of a Taylor cone. A liquid jet is emitted through the apex of the cone. The jet rapidly forms into droplets as a result of Coulomb repulsion in the jet as shown in  FIG. 1 . 
       FIG. 2  shows the related technique of electrospinning. Similarly to electrospray, a voltage source is connected between the tip of a capillary  1  and a collector plate  2 . Again, as a result of Coulombic and overcoming surface tension forces a Taylor cone forms. If the liquid is a polymer or other liquid with a viscosity which is high enough (due to high molecular weight), the liquid jet emitted from the Taylor cone does not break up. The jet is further elongated by electrostatic repulsion in the polymer or liquid until a thin fibre is produced. The fibre is finally deposited on the collector  2 . Instabilities in the liquid jet and evaporation of solvent can cause the fibre not to be straight and may curl. By careful choice of polymer and solvent system combined with a high enough electric field, fibres with nanometre scale diameters can be formed. 
     The electrospinning process is a particularly versatile process for the productions of nanofibres. Materials such as polymers, composites, ceramic and metal nanofibres have been fabricated directly or through post-spinning processes. Diameters of  3 - 1000  nm have been achieved. The fibres produced can be used in a diverse range of fields, from scaffolds for clinical use, to nanofibre mats for sub-micron particulate filtration. Attempts have been made to fabricate more complex fibres, such as fibres having a core material different to an outer shell, and fibre materials incorporating drugs in the outer shell or bacteria and viruses in the inner core. However, many of the techniques are confined to the laboratory because the advances required for scaling up to manufacture have not been made. UK Patent Application No. 0813601.2 describes apparatus for use in scaling up electrospinning, and is incorporated herein in its entirety. 
     Another electrohydrodynamic process is that of electrojetting in which the jet shown in  FIG. 1  or  2 , which is emitted from the Taylor Cone, is placed in the vicinity of a substrate and the jet is used to write on the substrate. This technique is used in writing electrode patterns and structures directly onto substrates. 
     US 2004/0182818 (Advion Biosciences, Inc.) describes an electrospray nozzle and monolithic substrate. The nozzle comprises a silicon substrate with a channel running between on entrance orifice and the nozzle output. The nozzle produces an electrospray perpendicular to the nozzle surface. The resulting spray is interfaced to a mass spectrometer or liquid chromatography system. The silicon substrate based nozzle is used to controllably disperse a sample into a nanoelectrospray necessary for these analytical techniques. While the electrospray nozzle described is not used for fibre production, the development of a nozzle produced from a silicon substrate opens up a number of manufacturing techniques proven by the microchip industry which may be useful in enabling the scale up of nanofibre production using electrospinning. 
     SUMMARY OF THE INVENTION 
     The present invention provides an electrospinning, electrojetting, or electrospraying device for use in forming a fluid jet from a Taylor cone, the device having a plurality of ducts arranged for supplying a plurality of fluids for use in the formation of the fluid jet. The device may be a nozzle. The ducts are arranged such that the fluid jet comprises at least one of the fluids, and that fluid is preferably a liquid. Each duct may issue into one or more openings from which the fluids are discharged to form the cone and jet. For electrohydrodynamic processes such as electrospinning, electrojetting, or electrospraying, an electric field should be present in the vicinity of the device or nozzle. Electrospinning, electrojetting, and electrospraying are related processes that differ in the resultant product as a result of differences in the viscosities and types of fluids used, the electric field applied, the distance from the nozzle to a collection surface etc. The nozzle may form part of an electrospinning, electrojetting, or electrospraying apparatus which further comprises electric field means arranged to form the fluid cone and fluid jet. The electric field means may comprise an electric field generator and a pair of electrodes for applying the electric field between the nozzle and a collection zone spaced apart from the nozzle. The apparatus may also comprise a gathering means for gathering the generated fibres or particles. The gathering means may be located in the collection zone. For electrojetting, the apparatus may comprise a translation stage for moving a substrate relative to the nozzle. 
     The one or more openings may be arranged such that in the jet a first fluid at least partially surrounds a second fluid. This allows complex fibres or particles having a core-shell, or core-multishell structure to be formed, or allows a gas or liquid sheath to be used to produce fibres or particles formed from materials supplied in highly volatile solvents. Alternatively, the openings may be arranged such that one fluid is adjacent or enclosed by another fluid. 
     The one or more openings may be arranged such that in the jet a first fluid forms a jacket around a second fluid. That is, the second fluid is within the first fluid. The one or more openings of a first duct may be concentric to the one or more opening of a second duct. 
     The nozzle may be formed on a substrate, such as a silicon substrate, to allow well developed silicon processing tools to be used. Deep silicon etching may be used. 
     The duct or openings in the ducts may have a flow cross-section with dimensions less than 0.5 mm, such as up to hundreds of microns. Each opening may have a flow cross-section less than 1.0 mm 2  or even 0.5 mm 2 . 
     The nozzle comprises walls bounding the openings, wherein the walls may protrude from a first surface of the substrate. The ducts may extend through to a second surface of the substrate opposing said first surface. 
     A channel which meets one of the ducts may be provided in the second surface of the substrate. 
     The nozzle may further comprise a gasket for sealing the nozzle to a manifold. 
     The nozzle may comprise a third duct having one or more openings. The one or more openings of the third duct may be concentric to the one or more openings of the first duct. The third duct allows fibres or particles to be produced having up to three layers, namely, a core, an inner shell, and an outer shell. 
     The first duct may have a cylindrical opening. The second duct may have an annular opening. The cylindrical opening may include a rod of smaller diameter than the opening, extending in the same direction as the duct, and bonded to a wall of the duct. 
     The nozzle may be fabricated using micro-machining. 
     A plate may be provided against the second surface of the substrate to meet a manifold. The plate may be glass. Between the plate and the substrate may be provided a silicon-on-insulator layer. The plate, silicon-on-insulator layer, and substrate may together form a demountable source, which can be demounted from the manifold, for cleaning, maintenance, or replacement with alternative nozzles. In some embodiments, one or more of the plate, and silicon-on-insulator layer, may be omitted. 
     The surfaces of the duct may be coated with a hydrophilic material, to improve wetting. The external surfaces of the nozzle may be coated with a hydrophobic material to prevent wetting. 
     The nozzle may be formed on a first substrate with an extractor electrode spaced apart from the substrate, the electrode adapted to provide an electric field symmetric about an axis through the centre of one of the ducts. 
     A plurality of nozzles may be provided on a common substrate. The plurality of nozzles may form an array. The array may be linear or two-dimensional. 
     The present invention also provides an electrospinning, electrojetting, or electrospray apparatus arranged to form a fluid jet. The apparatus may comprise a plurality of fluid reservoirs connected to a fluid delivery system, the fluid delivery system having a manifold with fluid outlets which are arranged to supply fluid to the nozzle or nozzle array, the nozzle or nozzle array sealed to the manifold by a gasket. The nozzle or nozzle array may be adapted to be demounted from the manifold. 
     The present invention also provides a method of electrospinning, electrojetting, or electrospraying, comprising supplying a plurality of fluids from a plurality of ducts such that the plurality of fluids are used in the formation of a fluid jet from a fluid cone, the resulting jet being comprised of at least one of the fluids. By formation we mean they are at least involved in allowing the fluid cone, such as a Taylor cone, to form. Thus the fluids may be a gas and one or more liquids, or a plurality of liquids. 
     One of the plurality of fluids may form a gas sheath around the fluid jet. The fluid supplied from each duct may issue into one or more openings. The jet may comprise a first fluid at least partly surrounding a second fluid. For example, the first fluid may form a liquid jacket around a second fluid. 
     The fluid supplied from a first duct may issue through one or more openings concentric to the one or more openings of a second duct. 
     The present invention comprises a method of manufacturing fibres, particles, or droplets, wherein the fibres, particles, or droplets are formed from the fluid in the fluid jet. The fibres, particles, or droplets may have a core formed of one of the fluids and a shell or shells formed of others of the fluids. 
     The present invention also comprises fibres, particles, or droplets manufactured according to the methods described above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention, along with aspects of the prior art, will now be described with reference to the accompanying drawings, of which: 
         FIG. 1  is a schematic diagram of electrospray from a capillary tube; 
         FIG. 2  is a schematic diagram of electrospinning from a capillary tube; 
         FIG. 3   a  shows in cross-section an electrospinning nozzle according to a first embodiment of the present invention; 
         FIG. 3   b  shows a cutaway plan view of the nozzle of  FIG. 3   a;    
         FIG. 4  is a cross-sectional view of an electrospinning nozzle according to a second embodiment of the present invention; 
         FIG. 5  cross-sectional view of an electrospinning nozzle according to a second embodiment of the present invention, wherein an outer annular aperture is used to provide a vapour sheath around the electrospinning fluids; 
         FIG. 6  is a schematic diagram showing nozzle coatings and electrical connections for electrospinning; 
         FIG. 7  is a schematic diagram showing how the surface tension in the nozzle bore can be lowered; 
         FIGS. 8   a - 8   d  show schematic cross-sectional views of nozzles with various coating layers; 
         FIG. 9   a  is an electron microscope image of a substrate on which a plurality of single wall nozzles are formed; 
         FIG. 9   b  shows Taylor cones formed on an array of three nozzles; 
         FIGS. 10   a  and  10   b  are perspective views of a packaged nozzle array; 
         FIG. 11  is a cross-sectional view of an electrospinning nozzle according to a third embodiment; and 
         FIGS. 12   a - 12   d  are electron microscope images of nozzles and extractor electrodes formed in silicon. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 3   a  shows a first embodiment of an electrospinning nozzle  100  and manifold  200  in cross-section. The nozzle  100  comprises a plurality of ducts  110 ,  120  through which fluid flows. The ducts shown in  FIG. 3  comprise a cylindrical bore  110  which is surrounded by an annular aperture  120 . The bore  110  and inner edge of the annular aperture  120  are bounded by a first tubular wall  130 . The annular aperture  120  is bounded at its outer edge by a second tubular wall  140 . As shown in  FIG. 3   a  the tubular walls  130 ,  140  protrude from a substrate  150 . The space formed by the bore  110  provides a channel through which a first fluid can flow. The bore  110  is generally a circular bore, although other shapes can be used. Similarly, other shapes for the aperture  120  can be used. If other shapes are used for the bore  110  and the outer annular aperture  120 , surface tension will cause a Taylor cone formed at the end of the nozzle to have a circular cross-section. Hence, for more reliable cone formation, circular and annular apertures are generally desirable. It is also desirable if the annular aperture  120  is concentric to the inner bore  110 . 
     Other embodiments may comprise other arrangements of ducts. For example,  FIG. 3   a  shows a pair of ducts, each having a single opening: one is annular aperture  120 , the other is cylindrical bore  110 . The annular aperture  120  concentrically surrounds the bore  110 . Alternatively the annular aperture could comprise a plurality of openings arranged in a circle surrounding the bore. The bore could also comprise one or more openings. There are also other embodiments where the openings from the two ducts are not arranged such that one surrounds the other. For example, a pair of ducts may be provided adjacent to each other and having triangular openings with one side of each opening parallel to a side of the other opening. The fluid exiting these openings would combine together to form a single jet. Although the surface tensions of the fluids would have to meet certain requirements to form a stable jet, such that similar solvents may be desirable, the resulting jet could still have inclusions towards the one side of the jet which would be derived from a first duct, and inclusions towards the other side of the jet derived from the second duct. Many other possible shapes of ducts, each having one or more opening may be provided, such that a fluid jet is formed from by a plurality of fluids. Of course, the fluid jet will be comprised of at least one liquid. 
     Returning to  FIG. 3   a , to generate the fluid cone or Taylor cone from the nozzle an electric field is applied between the nozzle  100  and a collector (not shown) in a similar manner to that illustrated in  FIG. 2 . The Taylor cone is formed by the balance of electrostatic and surface tension forces in the cone. As shown in  FIGS. 3   a  and  3   b  the bore  110  will form a first Taylor cone from a first fluid flowing through the bore  110 , and the outer annular aperture  120  will form a second cone concentric to the first. The outer cone will be formed from the second fluid. The first fluid and second fluid are preferably immiscible. If miscible fluids are used the fluids will tend to mix preventing the formation of two distinct concentric cones. The fluids will often be a solution comprising a polymer in solvent, although other mixtures and solutions can be used depending on the desired characteristics and composition of the resulting fibre. At least one of the fluids will contain a liquid. 
     Solutions may be made from dissolving natural or synthetic polymers in highly volatile solvents, or may be a combination of insulating or conductive nanoparticles dispersed in high volatile polymer solution. The polymers may be made to contain growth factors e.g. for tissue, bone, or a combination of these. The produced nanofibres can be used in bandages and wound dressings to assist healing. Such fibres may also be incorporated in synthetic scaffolds for clinical use. Alternatively, the polymers may contain anti-microbial particles (such as silver nanoparticles) to keep surfaces sterile. Such polymers may be used for the outer part of the fibre and therefore are delivered to the tip of the nozzle through the annular aperture. 
     In  FIG. 3 , the resulting jet from the tip of the cone will have the second fluid forming a fluid sheath around the inner core of first fluid. As the fluid in the jet moves away from the nozzle  100  and towards the collector electrode (not shown) the fluids will dry by evaporation of the solvent. When dry the resulting fibre will have a core composition determined by the components present in the first fluid. The outer composition will be determined by the components present in the second fluid. 
       FIGS. 3   a  and  3   b  show the manifold  200  which facilitates delivery of the first and second fluids through the ducts to the nozzle bore  110  and aperture  120 . As mentioned above, the nozzle  100  protrudes from one surface of a substrate  150 . On the second surface of the substrate may be provided a channel  160  to supply the first fluid to the nozzle. In the embodiment shown in  FIGS. 3   a  and  3   b  the channel  160  cross-section is less than the cross-section of the bore  110 , but alternatively the channel cross-section may be equal to, or greater than, the cross-section of the bore. The bore  110  extends through the protruding part of the nozzle  100  into the substrate  150 . The channel  160  runs from the bore  110  along the second surface of the substrate, optionally running radially out from the centre of the bore. This section of the channel  160  is made up with boundary surfaces consisting of the second surface of the substrate  150  and the manifold  200 . The channel  160  continues through the manifold  200 , running from one side of the manifold through to the other and meets fluid inlet  220 . 
     As shown in  FIGS. 3   a  and  3   b , annular aperture  120  has a radial thickness greater than the cross-sectional size of the second channel  210 . However, the annular aperture  120  may have a radial thickness less than, or equal to, the cross-sectional size of the second channel  210 . The second channel  210  may also be tapered. The whole annulus does not extend through to the second side of the substrate, but only a part of the annulus continues through the substrate. Second channel  210  meets the part of the annular aperture that extends through the substrate i.e. the duct. The channel  210  extends laterally away from the nozzle. Alternatively, channel  210  can be in the second surface of the substrate, in a similar manner to first channel  160 . Finally, channel  210  extends through the manifold to second inlet  230 . This inlet is separate from the inlet  220  to allow different fluids to be provided to the bore  110  and annular aperture  120 . The routing of the channels  160  and  210  allows the inlets  220 ,  230  to be spaced apart more than the nozzle apertures  110  and  120 . The extra spacing allows for more convenient connection to reservoirs of the two fluids. However, in some embodiments multiple nozzles are provided on a single substrate. If these nozzles are closely packed together the fluid inlets may need to be spaced more closely together especially if each nozzle is provided with two or more inlets. In such multiple nozzle embodiments, the channels  160  and  210  may instead be arranged to supply all of the nozzles on the substrate with the same fluids from only two inlets. 
     Alternatively, two or more channels may merge for mixing in a microfluidic structure built in the surface of the substrate  150  and manifold  200 . The output from the microfluidic structure may be coupled to the bore or annular aperture of the nozzle. 
       FIG. 4  shows a second embodiment of the nozzle in which three separate ducts for supplying different fluids are provided. The three ducts comprise a central bore  110 , a first annular aperture  120  and a second annular aperture  310 . The bore, first and second apertures have a common centre located at the centre of the bore  110 . The bore  110  and first annular aperture  120  are the same as the bore and annular aperture of  FIG. 3   a  and hence like reference numerals are used. The openings at the ends of the bore and apertures are sometimes referred to as interspaces. 
     This embodiment allows even more complex nanofibres to be produced. For example, each interspace may be used to supply a different fluid and therefore the produced fibre may have a core, inner shell and outer shell, each of which is made of a different material. 
     Around some of the nozzle surfaces may be provided a hydrophobic conductive coating  320 , as shown in  FIG. 4 . This coating is provided on the underside of the substrate  150  and around the sides and ends of the nozzle such that the edges of circular walls  130 ,  140 ,  330  are coated. The outside wall of third tubular wall  330  is also coated with the hydrophobic material. This hydrophobic conductive coating  320  prevents the coated surfaces from wetting with the aqueous or organic liquids and solutions normally used as solvents. Extended wetting would result in unstable Taylor Cone formation and an unstable electrospinning process. The interspaces between the tubular walls  130 ,  140 ,  330 , are not coated as these surfaces should be fully wetted to produce an even flow of fluid through the duct. The nozzle is coated by a process of angled evaporation of organic and inorganic thin films or by angled implantation of fluorine rich precursors to form, for example, fluorine-doped Diamond-Like Carbon (F-DLC). The coating composition preferably has a low sputter yield and low chemical reactivity. 
     The embodiment of  FIG. 4  also shows in more detail how the nozzle  100  interfaces with the manifold  200 . The substrate  150  with nozzle protruding there from is preferably made of silicon. Channels  160  can be etched into the back surface or the substrate to route the fluid to the nozzle. On the back surface of the silicon substrate is attached a glass or further silicon layer  340 . The manifold  200  is attached to the glass or silicon layer  340  via a gasket  350  which seals the glass or silicon layer  340  to the manifold  200 . The gasket  350  allows the nozzle to be demounted from the manifold  200  for replacement or cleaning. 
     The arrangement of  FIG. 4  can also be used to produce two-material nanofibres more reliably and with a greater range of solvents than the embodiment of  FIG. 3   a . As in the above described embodiments, the bore aperture  110  supplies a first fluid and the first annular aperture  120  supplies a second fluid. These two fluids form the core and shell of the produced nanofibre. The above described embodiments are suitable for electrospinning and electrospray of fibres and droplets from solutions using low vapour pressure solvents. However, for solutions containing nanoparticulates and high vapour pressure solvents the solvent will evaporate too readily potentially causing solid fibre or particles to form too close to the nozzle potentially blocking the nozzle. To avoid this, the outer annular aperture  310  can provide a fluid sheath around volatile high vapour pressure solvents in the inner two fluids. The sheath can be a low vapour pressure fluid which prevents rapid evaporation of the volatile solvent until it has moved away from the nozzle, thereby preventing blockages occurring in the nozzle. 
     Alternatively, the outer interspace  310  supplies more of the high vapour pressure solvent saturating the surface of the nozzle with the solvent to prevent drying. This is shown in  FIG. 5 , where the interspace of the outer annular aperture  330  carries the saturated vapour to the rim to ensure the wall  130  always has saturated vapour. 
     Further details regarding the basic electrical arrangement and the materials and coatings that may be used for the nozzle are shown in the simplified diagram of  FIG. 6 . The nozzle  100  is manufactured from silicon substrate  390 . Some or all of the surfaces of the silicon may be oxidised to silica  410 .  FIG. 6  shows all of the surfaces of the nozzle are oxidised. The silica  410  surface prevents the electrospinning fluids  440  from attacking or reacting with the silicon. In particular, the silica layer  410  prevents buffer solutions, such as those used in biosciences, from attacking the silicon. In addition to the hydrophobic coatings that may be used to prevent outer parts of the nozzle from wetting and causing unstable Taylor cone formation, hydrophilic coatings may be used. In  FIG. 6  the hydrophobic coating  420  covers the external surfaces of the nozzle. The hydrophobic coating is deposited using a “line of sight” coating technique, such as angled thermal evaporation, as discussed above. The hydrophilic coating  430  covers the internal surfaces of the nozzle to aid wetting of the fluid  440  to the bore of the nozzle  100 . An additional aid to wetting of the fluid down the length of the nozzle is to add a sharply angled concave surface to draw the fluid down the nozzle. For example,  FIG. 7  shows a rod  450  placed in the nozzle  100 . The rod has a smaller cross-section than the bore of the nozzle. Other shapes of bore and rod may be used, but in the example of  FIG. 7 , the reduced surface tension where the convex surface of the rod meets the concave surface of the bore will draw the fluid down the nozzle. 
     In  FIG. 6  electrical contact is made to the electrospinning fluid by an electrode  400  in direct contact with the fluid  440 . The electrode can be arranged to float on the fluid such that as the fluid level changes the electrode  400  stays in contact with the fluid. Alternatively, the electrode  400  can be formed on the second surface of the substrate. The second electrode  450  is formed at the collector spaced apart from the nozzle, as also shown in  FIG. 2 . 
       FIGS. 8   a - 8   c  show alternative arrangements of electrodes and coatings for the nozzle.  FIG. 8   a  shows a nozzle similar to that of  FIG. 6 , where the surface of the silicon  390  is oxidised to silica  410  on surfaces both inside the nozzle, such as in the bore, and also on external surfaces that the electrospinning fluid will not flow over. This is to protect the integrity of the nozzle from attack by reactive chemicals, solvents, or cellular matter. The inner surfaces of the nozzle, that is, the bore and fluid holding cavity are coated with a hydrophilic coating  431 . Preferably, the hydrophilic coating  431  is electrically conductive to allow electrical contact to be made to the fluid in the nozzle and as close as possible to the exit of the nozzle. This is as an alternative or in addition to the electrode being formed on the second surface of the substrate, as mentioned above. The hydrophilic coating  431  may be a bio-chemically inert electrically conductive thin film. This may take the form of a thin film metal such as platinum or a conducting ceramic such as tantalum aluminium nitride. The hydrophilic coating must not extend over the outer surfaces of the nozzle, otherwise these outer surfaces will be wetted and the Taylor cone would not be confined, resulting in electrical short circuits etc. The external surfaces of the nozzle are coated with a hydrophobic coating  421  to prevent wetting as discussed above. 
       FIG. 8   b  shows an alternative embodiment where the silicon surfaces are not oxidised and the electrically conductive hydrophilic coating, such as platinum or tantalum aluminium nitride is adhered directly to the silicon  390  on the internal surfaces of the nozzle. A hydrophobic coating  421  is applied to the external surfaces. This embodiment provides a simpler structure for electrospinning of materials that are less reactive to the silicon and do not require the silica layer to prevent the electrospinning fluid chemically attacking the silicon. 
       FIGS. 8   c  and  8   d  show the nozzle  100  mounted to a package  460 . In the embodiments of both figures electrical contact is made to the electrospinning fluid by conductor  401 . The nozzle  100  meets the package  460  where there is a hole in the package to allow the electrospinning fluid to flow into the nozzle. The conductor  401  is coated around the edge of the hole in the package. In  FIG. 8   c  the surface of the silicon nozzle has been oxidised to silica, as in  FIG. 8   a . In  FIGS. 8   c  and  8   d  a hydrophobic coating is applied to the external surfaces of the nozzle to prevent wetting and aid stable Taylor cone formation. 
       FIG. 9   a  shows a substrate that has been etched to produce a large number of nozzles. These nozzles are single wall nozzles having a single duct and single opening. They have been produced by plasma etching. Single nozzles and linear and two-dimensional nozzle arrays of concentric or single wall nozzles are microfabricated by a combination of photolithography, deep reactive ion etching, deposition and etching of thin films. The bulk material of the nozzles is silicon to allow the use of well established deep etching tools.  FIG. 9   b  shows three nozzles with Taylor cones formed and fluid jets being discharged from the cones. 
       FIGS. 10   a  and  10   b  show more details of how the nozzles  100  may be packaged. Packaging of individual nozzles would require each nozzle to be mounted separately into a holder so that it can be handled and attached to an electrospinning system. This would be costly due to the dimensions of the nozzle. Since nozzles tend to be used in arrays and the nozzles described herein are manufactured from silicon on a silicon substrate, it is convenient to package the nozzles as arrays.  FIG. 10   a  shows an array of nozzles connected by a strip of silicon substrate. The package is injection moulded plastic in which a recess is formed such that the silicon substrate partly sits in the recess. Through holes are provided through the plastic to the nozzles for the supply of fluid. This may be using one hole for all nozzles or using a separate hole for each nozzle. In the earlier described embodiments in which the nozzles have multiple openings for the manufacture of complex and/or layered fibres, each of the openings of each nozzle is supplied through a separate hole, such as to each of the fluid inlets in  FIG. 3   a . The seal between the injection moulded package and the silicon nozzle array is preferably hermetic. Around the circumference of the array, and spaced apart from the edge of the array is provided a groove on the reverse side of the package layer to the array. This groove provides a fluid seal. 
       FIG. 10   a  shows an array of ten nozzles. These are shown in a more detailed view in  FIG. 10   b . The nozzles at the end of the array are dummy nozzles that are not used for electrospinning but provide field uniformity. That is, if the nozzles at the ends of the array were used in electrospinning they would experience a different field to the other nozzles and would result in the fibres produced from the end nozzles being different to the fibre produced from the other nozzles. To avoid this, the end nozzles include an electrode for generating an electric field in the vicinity of the nozzle, but the fluid cannot pass through the nozzle. Thus, this dummy nozzle reduces differences in produced fibres caused by different electric fields at the ends of a nozzle array. 
     These arrays of nozzles can be used to produce multiple fibres simultaneously. These fibres can be produced in parallel, and optionally can be immediately woven together. Alternatively, the fibres are produced in random orientation from the nozzle, and can be later woven into thread. 
       FIG. 11  is a schematic diagram of a nozzle similar to that of  FIGS. 4 and 5 , but includes an additional electrode known as an extractor gate. The nozzle  100  comprises three ducts: a central bore  110 , a first annular aperture  120  and a second annular aperture  310 . Each duct has a single opening. Fluid is supplied to each opening through a separate microfluidic channel  500 , similar to  FIGS. 4 and 5 . The nozzle is fabricated from silicon  150 , with the layer behind the silicon being silicon-on-insulator. Similarly to  FIGS. 4 and 5 , the next layer  340  is silica glass. The silicon-on-insulator layer  510  provides a better thermal match to the glass and the silicon than placing these two materials together without the layer  510 . The next layer is gasket  350 . The gasket allows the nozzle, including the layers  150 ,  510 , and  340  to be removed from manifold  200  for replacement or cleaning. The extractor gate  520  is spaced from the substrate  150  of the nozzle by an insulating spacer  530  such as a glass microsphere. However, other shapes and materials may be used for the spacer. The extractor gate  520  is silicon that has been oxidised to silica on its surfaces. The silica surface of the extractor gate  520  is printed or coated with conductor so as to provide a uniform electric field around the circular nozzle. The extractor electrode encircles the nozzle such that the electric field lines have a circular symmetry around an axis passing through the centre of the nozzle. The extractor electrode may be formed like a via through the substrate and coated with conducting material. The via is large enough such that the fluid passes through it without touching it. 
     The extractor electrode allows a lower potential difference between the collector electrode and the fluid to be used to produce and maintain a Taylor cone. For electrospinning using multiple nozzles in an array, the extractor electrodes could be linked such that all extractor electrodes supply the same electric field. Alternatively, each extractor electrode could be controlled independently. By controlling each independently, different nozzles having different fluids passing through them could receive different fields, thereby allowing the electrospinning of each fibre to be finely controlled. This would allow the array to electrospin different fibres allowing the spun fibre to be combined with the other fibres to form complex nanofibres and biomolecular materials. 
     The embodiment of  FIG. 11  also shows an interrogation or monitoring system that may be included. This system comprises lenses  610  and optical fibres  620 . The system may also comprise Fabry-Perot micro-pressure sensors  630 . For example, optical fibres and lenses (such as ball lenses) may be used in reflection mode to check that there is fluid present in the microfluidic channel  500 . Alternatively, the sensor  630  includes a Fabry-Perot cavity which expands and contracts slightly under the pressure of the fluid. The change in dimensions of the cavity is detected by using the optical fibre in combination with an interferometer. The interrogation and monitoring systems could be used to monitor for blockages and to check fluid flow rates. Monitoring of such parameters is important for scalable systems with multiple nozzles in an array or multiple arrays. 
       FIGS. 12   a - 12   d  show some dimensions of the nozzle  100  and extractor electrode  520 .  FIGS. 12   a  and  12   b  show a plurality of nozzles. Each nozzle comprises a plurality of ducts. These include a central bore and two concentric annular apertures. Spaced from the outer annular aperture is an extractor electrode.  FIG. 12   d  shows the extractor electrode before fitting to the nozzles. The extractor electrode is comprised of a single substrate with circular holes or vias through which the nozzles are visible. In  FIG. 12   d  a single extractor electrode is used for nineteen nozzles arranged in a hexagonal pattern. The diameter of the holes in the extractor electrode is around 1.0 mm, and the distance between hole centres is around 1.5 mm. 
       FIG. 12   c  shows the walls of a nozzle in detail. Each wall is up to 5 μm thick. The central inner bore has a diameter of around 320 μm. The first annular aperture has a diameter of around 450 μm, and the second annular aperture has a diameter of around 580 μm. Hence, the two annular apertures each have a radial thickness of around 130 μm. 
     The above dimensions are only examples, and nozzles, electrodes, ducts, and openings of other dimensions can be used. For optimised eletrospinning, the size of the ducts should be determined in accordance with the viscosity of the actual fluids used. A different nozzle should be used when using different materials for electrospinning. The radius or radial thickness of the bore or annular apertures may need to be adjusted depending on the viscosity of the fluids used to provide the correct flow rate for each layer of the nanofibre. Thus, each fibre type or mix of materials may require a different nozzle to be used. Too high a flow rate may prevent Taylor cone formation or result in the material deposited in the nanofibre being of the wrong thickness. 
     The person skilled in the art will readily appreciate that various modifications and alterations may be made to the above described nozzles and electrospinning components and system without departing from the scope of the appended claims. For example, different materials, dimensions and shapes of nozzle may be used. In addition, although the above described embodiments largely relate to electrospining, these techniques and devices may also be used for electrospraying and electrojetting.