GB2462112A

GB2462112A - Producing fibres and droplets, using an electric field and moving band

Info

Publication number: GB2462112A
Application number: GB0813601A
Authority: GB
Inventors: Robert Stevens
Original assignee: Science and Technology Facilities Council
Current assignee: Science and Technology Facilities Council
Priority date: 2008-07-24
Filing date: 2008-07-24
Publication date: 2010-01-27
Anticipated expiration: 2028-07-24
Also published as: WO2010010362A9; WO2010010362A1; GB2462112B; GB0813601D0

Abstract

The band 30 moves about a roller 20 within an immersion bath 40 and a 2nd roller 10. An electrostatic field is established between the second roller 10 and a counter electrode. The fibres are preferably removed by means of airflow. The preferred apparatus also includes means for cleaning the belt 30, and depositing biological or charged material. The apparatus can be used for electrospinning of nanofibres 50 or the production of charged droplets.

Description

AN APPARATUS A1D METHOD FOR PRODUCING FIBRES

Technical Field

The present invention relates to an apparatus and method for producing fibres. In particular, the present invention relates to producing nanofibres using an electric

field.

Background Art

Electrospray is a technique for dispersing a liquid to produce an electrically charged aerosol as shown in figure 1. 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 (not shown) biased at a lower voltage potential with respect to the tip, for example the plate may be at ground. 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 a process to minimise the surface charge density.

Figure 2 shows the related technique of electrospirining. 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 Coulornbic repulsion and surface tension forces a Taylor cone forms. If the liquid comprises polymer molecules dispersed in a suitable solvent and has appropriate dielectric, conductivity, viscosity and solvent volatility, the liquid jet emitted from the Taylor cone does not break up due to entanglements of the polymer molecules. The jet is further elongated by the process of desolvation of the solvent, this increases the localised surface charge density, which increases the electrostatic repulsion causing a rapid electrostatically driven extension of the fibre to create extremely thin fibres. 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 possibly curl. By careful choice of polymer and solvent system combined with a high enough electric field, and a suitable distance between the capillary and the collector, fibres with nanometre scale diameters can be formed.

W02005/02410l describes a method of nanofibre production from a polymer solution using electrostatic spinning in an electric field created between a charged electrode and a counter electrode. Polymer solution is supplied into the electric field using a rotating cylinder, which also acts as the charged electrode. One side of the rotating cylinder is immersed in a bath of polymer solution, while the other side is open and acts as the starting point for fibre formation. The counter electrode is formed as an arc which is concentric to the cylinder. The fibres are drawn from the cylinder towards the counter electrode by the electric field. The fibres are deposited on a substrate which follows the surface of the counter electrode. This technique overcomes the problem of blocking of the capillary by using the rotating cylinder to supply the polymer solution.

The capillary based prior art methods and apparatus are difficult to scale up to produce large quantities of material. Moreover, using these techniques it is not currently possible to create complex fibres from multiple starting constituents. For example, in prior art systems solvated solutions of high molecular weight polymers are delivered to the opening in the nozzle through a tube. Mass production would require the number of nozzles to be increased, and the electro-hydrodynamic condition of each nozzle to be similar. Furthermore, changing the molecular content of the fibre in quick succession would require a complex network of fluidic channels with valves close to each delivery point.

The technique of electrospinning can be used to produce nanofibres. Such nanofibres find uses in variety of fields such as filtration, energy storage, catalysis etc.

Summary of the Invention

The present invention seeks to overcome problems of the prior art. Accordingly, the present invention provides an apparatus for producing fibres, the apparatus comprising: a band arranged around or between first and second rollers and curved around the rollers; an electric field generator

adapted to provide an electric field between an

electrospinning zone at the first roller and a counter electrode; a bath for containing liquid and arranged to wet regions of the band as it passes around the second roller, wherein the band is arranged to transport liquid from the bath to the electrospinning zone for the production of fibres in said electrospinning zone. The electric field is sufficient to draw the fibres from the liquid.

The apparatus may further comprise a drive mechanism arranged to drive the band.

Although a band tensioned between rollers is mentioned above, alternatively a band may be provided around two slide surfaces. The slide surfaces are curved thereby replacing the rollers. The band may thus be driven by a separate propulsion system.

In another alternative, more than two rollers may be used in some configurations.

The tension on the band may be provided by tensioning means other than the rollers or slide surfaces.

The fibres may be nanofibres. By nanofibres we mean fibres having a diameter between 0.5 nm and 1000 nm. But preferably, the fibres have a diameter between lOnm and nm.

The spacing of the wetting zone and electrospinning zone allows additional functionality to be provided between the two rollers, such as additional deposition devices. In addition, these deposition devices allow the composition of the fibres to be changed without time delay.

The above apparatus is described for the electrospinning of fibres, but is equally applicable to the electrospray of droplets, for example on to a surface.

The electric field generator may be arranged to provide an electric field between the surface of the band curved around the first roller and a counter electrode.

The band may be a continuous band formed of a belt, an array of belts, or an array of wires. The band may be patterned with any combination of grooves, spikes, ridges or recesses.

The apparatus may further comprise extractor electrodes arranged parallel to the first roller and spaced apart from the first roller.

The apparatus may further comprise air assist ducts located at the sides of the electrospinning zone and arranged to provide an air flow to direct the produced fibre away from the first roller.

The apparatus may further comprise a release head provided adjacent to the surface of the band, the release head arranged to atomise material or to deposit material on the belt. Optionally, the release head may be arranged adjacent to a flat surface of the band.

The apparatus may further comprise a cleaning head provided adjacent to a surface of the band, and arranged to remove material deposited on the band. The apparatus may further comprise a surface conditioning head provided adjacent to a surface of the band, and arranged to condition the surface of the band. Optionally, the cleaning head or surface conditioning head may be arranged adjacent to a flat surface of the band.

The present invention further provides an apparatus for producing fibres or droplets, comprising a surface translatable between a wetting zone and an electrospinning zone, the wetting zone including a means for releasing liquid onto the surface, and the electrospinning zone arranged to be provided with an electric field by an electric field generator. Between the wetting zone and electrospinning zone may be provided a material supply head for depositing material on the wetted translatable surface or for atomising material. The means for releasing liquid onto the translatable surface may be an immersion bath for containing liquid or a release head.

The present invention further provides an apparatus for electrospray deposition of droplets onto a surface, comprising: a band tensioned between first and second rollers and curved around the rollers; an electric field generator adapted to provide an electric field between an electrospray zone at the first roller and a counter electrode; a bath for containing liquid and arranged to wet the band as it passes around the second roller, wherein the band is arranged to transport liquid from the bath to the electrospray zone where the electric field causes jets of droplets to be released from the band and deposited on said surface. In some embodiments the deposition surface may act as the counter electrode.

A release head can be used to deposit polymer solutions on to the band for electrospray.

The present invention further provides a method of producing fibres, comprising: wetting a band with fluid, the band tensioned between first and second rollers; providing an electric field at an electrospinning zone at the first roller; driving the band to cycle the band from the first roller to the second roller, wherein the electric field at the electrospinning zone is arranged to draw fibres from the fluid on the band towards a counter electrode.

The present invention further provides a method of depositing droplets on a surface, comprising: wetting a band with a fluid, the band tensioned between first and second rollers providing an electric field between a counter electrode and an electrospray zone at the first roller; driving the band to cycle the band from the first roller to the second roller; providing a deposition surface between the first roller and the counter electrode, wherein the electric field is arranged to draw droplets from the fluid on the band to be deposited on the deposition surface.

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: Figure 1 illustrates the formation of a jet of droplet from a Taylor cone; Figure 2 illustrates the electrospinning of a fibre from a capillary; Figure 3 shows the apparatus for electrospinning or electrospray according to an embodiment of the invention; Figure 4 shows the apparatus of figure 3 with additional functional complexity added; Figures 5a and Sb show schematically the lines of force produced by an electric field applied to a roller and extractor electrodes; and Figure 6 shows an array, consisting of a plurality of the apparatus of figure 4.

Detailed Description of the Preferred Embodiments

Figure 3 shows a first embodiment comprising a band 30, such as a belt, tensioned between a pairs of rollers 10, 20.

The band 30 may either be conductive or non-conductive, or a mixture of laminated conductive and non-conductive layers.

The band 30 is continuous and takes the form of a conveyor belt extending from the first roller 10 to the second roller and back around to the first roller 10. The rollers 10, may be solid or hollow cylinders, the belt or band 30 being in contact with each roller for around half of its surface. The rollers 10, 20 are arranged parallel to each other but spaced apart. The rollers 10, 20 rotate about central axes through the cylinder and may be supported on bearings to allow the rollers to rotate with ease.

An immersion bath 40 is provided in the region of the second roller 20. The immersion bath is filled with a liquid such as a polymer solution or molten polymer 55. The roller can be partly or fully immersed in the solution, but should be sufficiently immersed that part of the band 30 passing around the second roller is immersed in the bath wetting it with liquid in the bath. This region may be known as the wetting zone.

The immersion bath may include a system to wet selected regions of the band. One embodiment could be a rotating roller which lifts solution from the bath and coats it onto the band.

In the embodiment shown in figure 3 the two rollers 10, are arranged such that the first roller 10 is vertically above the second roller 20. Other arrangements of rollers are possible. The separation of the two rollers 10, 20 is arranged such that the belt 30 is tensioned. A mount holding one of the rollers may be biased to urge the roller away from the other roller to thereby set the tension of the band.

A drive mechanism is provided to rotate the band 30 and rollers 10, 20. For example, a motor may be used to drive one of the rollers directly. Alternatively, as shown in figure 3, the first roller 10 may be driven by a drive belt from a motor 60 mounted a short distance away from the roller. The position of the motor 60 and drive belt 65 is not limited to being between the two surface of the band 30, as shown in figure 3, but may provided elsewhere with the drive belt driving either the first roller 10 or second roller 20.

The band 30, rollers 101 20, immersion bath 40 and drive mechanism are supported by a framework. The framework may be engineered to be easily dismantled for cleaning. The framework holding the second roller 20, and bath are arranged to provide control of the depth of immersion of the band 30 into the fluid in the bath 40.

Production of fibres by electrospinning requires an electric field. In one embodiment, the electric field is provided by applying a voltage between the first roller 10 and a counter electrode (not shown) provided above and spaced apart from the first roller 10. The counter electrode is normally at ground voltage. In an alternative arrangement, the band may itself be conductive and the voltage may be applied directly between the band and counter electrode. The region in which production of fibres occurs may be called the electrospinning zone. At the centre of the electrospinning zone, at the midpoint at which the band is on contact with the first roller, the force provided by the electric field will be substantially radial to the roller.

Approximately, the potential difference between the counter electrode and roller or band will be 30kv, and the separation between the two will be approximately 0.2m. Of course, the potential difference and separation may be varied together without significantly changing the magnitude of the electric field. The rollers 10, 20 and bearings are manufactured to a high accuracy to allow the gap between the surface of the band 30 and the counter electrode to be kept constant to provide a uniform field as the rollers rotate, thereby providing uniformity of electrospun fibre or electrospray coated product.

The surface of the band or belt 30 may be textured in such a way as to control fluid transport from the wetting -10 -zone to the electrospinning zone. The belt may also have high aspect ratio features on a large pitch to enhance the electric field on the surface of the belt 30 while in the electrospray zone. This will enhance Taylor cone formation and the generation of electrospray jets necessary for nanofibre formation.

The belt or band 30 may be a polished metal belt (for example, stainless steel); a patterned metal belt with grooves, spikes, ridges, or recesses and may be produced by photolithography and acid etching; a fabric or textile belt (for example, felt); a woven wire belt (for example, chain mail); an array of multicore twisted wire belts positioned side-by--side; a polymer foam or sponge-like belt; an array of wires side-by-side; or a patterned conductive or insulating polymer belt. For the cases of an array of multicore twisted wire belts or wires positioned side-by-side, the rollers may be grooved to keep the wire or wire belts spaced at the desired distance. For the non wire belts, these may be patterned with various coatings and structures to control fluid dynamics and the electric field in the electrospray zone.

The ability of the surface to be wet by the fluid is controlled by the choice of material used for the belt.

Patterning of the band may allow the band to consist of wettable and non-wettable regions.

The method of operation of the apparatus will now be described. A solvent containing polymer molecules (i.e. a solvated polymer solution) is added to the immersion bath 40. Alternatively, molten solvent may be used in conjunction with heating the bath and the band. The polymer molecules should preferably be long chain molecules with a high molecular weight. The immersion bath 40 can be temperature -11 -controlled. Heating allows higher melting point polymers to be maintained in liquid form. Cooling allows the evaporation rate of the solvent to be reduced. Additionally, some solutions or liquids may have their viscosity adjusted by changing the temperature of the immersion bath.

The band 30 is driven by the drive mechanism to pass around the second roller 20 through the immersion bath to wet the surface of the band with the liquid or solution contained in the bath 40.

The drive mechanism should be arranged to control the band speed accurately. By changing the band speed the exposure time of the band between the wetting zone and electrospinning zone may be controlled.

As the band 30 wet with liquid or solution 55 passes into the electrospinning zone, the electric field in the zone combined with any ripples in the surface of the liquid or features on the band will cause the liquid or solution to form into Taylor cones. As the band 30 moves further into the electrospinning zone, the cone will be increased in size until a jet forms. Surface charges on the jet will cause the surface area to increase thereby causing the jet to become thinner as the distance from the band or belt 30 increases.

This is known as self-extension. If the polymer molecules are of long enough chains, and any solvent evaporates then the jet will form a thin fibre. When the fibres reach a certain length they will break from the roller, partly due to the rotation of the roller. The fibres will be drawn towards the counter electrode where they will be collected.

This region may be known as the collection zone.

Although the above embodiment has been described with reference to electrospinning, the apparatus and method may also be used to deposit nanometre sized charged droplets or -12 -charged molecules by electrospray. In such a technique, the jet from the Taylor cone breaks up into charged droplets.

These droplets can be collected on a surface of a substrate located in front of the counter electrode. Similarly other embodiments described below may also be used for either electrospinning or electrospray.

Figure 4 shows a second embodiment which is based on the embodiment of figure 3, but includes additional functionality and features. The embodiment of figure 4 additionally includes an enclosure 100 which provides two main effects. Firstly, the enclosure 100 prevents solvent vapours from escaping into the local environment. Secondly, the immediate local solvent environment surrounding the band 30, rollers 10, 20, and bath 40 can be controlled. An additional effect is that the enclosure 100 also serves to protect the band and roller internal components.

The enclosure may be made from electrically insulating material or a material with a high sheet or bulk resistivity to prevent electrical charges building up on the material.

The enclosure has electrical, fluid, and fibre optic feedthroughs and at least one aperture 105 positioned above the first roller 10. The electrosprayed droplets and/or electrospun fibres emerge through this aperture 105 during production.

The control of the local solvent environment inside the enclosure 100 allows the desolvation of solutions deposited on the belt to be controlled. In turn, this allows the viscosity of the fluid on the belt to be held within suitable tolerances for electrospinning. Optionally, a solvent release mechanism or solvent extraction system may be included within the enclosure 100 to increase the precision of the amount of solvent in solution. This would -13 -allow the solution viscosity to be controlled more accurately for improved electrospinning. Such a solvent release or solvent extraction mechanism would require sensory feedback to achieve such accurate control.

Inside the enclosure 100 is also provided AC-DC or DC-DC electrical converters to generate the high voltages needed. A control system within the enclosure also provides control of the potential applied to the band 30, rollers 10, 20, and extractor electrodes 110. The control system also controls the speed of the band, and any additional modules (which will be described in more detail below) . Sensors provide feedback to the control system. The sensors may provide feedback on solution viscosity, conductivity, dielectric constant, fluid levels, temperature, humidity, partial pressures, wear of the band etc. The control system may also control the level of fluid in the immersion bath 40, the tension of the rollers 10, 20, and the depth to which the band 30 is immersed in the solution in the immersion bath 40. It may also provide to the user video information from inside the enclosure 100.

Figure 4 shows an optional heater 140 for heating the belt or band 30 (and solution on the surface of the belt) to control the temperature and viscosity at the electrospinning zone. Alternatively, heaters may be used to dry the belt 30 after the electrospinning zone. The heater may be located in the space enclosed by belt 30, or may be placed on one side or both sides of the belt. Heaters may use radiant, convection, and/or conduction heating. Radiant heating is preferred because this allows the heat source to be isolated from the high electrical potential in the region of electrospinning zone. Pyrometers or other thermal sensors -14 -could be used to monitor the temperature uniformity of the belt 30.

Also shown in figure 4 are extractor electrodes 110 located in close proximity to the electrospinning zone.

These electrodes 110 enable the electrostatic potential for Taylor cone formation to be reduced and longer fibres to be produced without requiring the potential to be increased excessively. The effect of the extractor electrodes 110 is to modify the lines of force between the band 30 and the first roller 10 to concentrate and focus the lines of force in the direction from band 30 to counter electrode.

Additionally, the extractors act to reduce the overall potential required between the band and the collector. This allows the separation between band and collector (drift region) to be increased without requiring large potentials.

The increased drift region assists in the production of dry fibres at a low electrical potential The extractor electrodes 110 consist of a pair of shaped electrodes spaced apart from the first roller. In one embodiment the electrodes may be cylindrical in the form of a wire or of a larger diameter. They are arranged parallel to the first roller as shown in figure 5a. Preferably, the extractor electrodes 110 are in a plane approximately in line with the top of the first roller, as shown in figure 5b. The electrostatic potential on each of the extractor electrodes will be at an intermediate voltage which falls between the voltage of the first roller 10 (or belt 30) and the voltage of the collector. Figures 5a and 5b show the lines of force in the electrospinriing region as a result of the combined potentials of the extractor electrodes 110 and first roller 10. The voltage difference applied between the extractor electrodes and the band depends on the geometrical -15 -configuration, the surface profile of the band, and the nature of the polymer solution.

The extractor electrodes 110 also localise the field established on the first roller to prevent it affecting the surroundings. Another benefit is that the more focussed electrical field provided by the extractor electrodes 110 results in the 11in-flight" distance between the source and the counter electrode to be increased for the same potential between the band and the collector. Hence, a greater time and distance for the self-extension of the charged fibres is achieved. Therefore, dry finer fibres having a smaller cross-section can be achieved than without the extractor electrodes.

Optionally, electrostatic lensing electrodes could be added running parallel to the axis of the roller and extractor electrodes. These lensing electrodes control the angular spread of the nanofibre and nanospray beam emitted from the surface of the belt.

Figure 4 also shows air assist ducts 120. The air assist ducts 120 help to guide the desolvating fibres away from the band 30. By guiding the fibres away from the band, the emission aperture 105 in the enclosure can be kept clean and free from fibrous material. As well as helping fibre production, this also prevents arcing. The additional air flow provided by the air assist ducts 120 also promotes desolvation of the fibres from solution. For extremely volatile solvents, the air could be dosed with solvent vapours to enhance the time before the jet dries to form the fibre. This would result in longer and finer fibres.

Additionally, the air from the air assist ducts could be dosed with molecules and particles to be deposited on the -16 -surface of the fibre to provide an outer coating to the fibre.

An advantage of the belt and roller system over the prior art single cylinder system is that the belt allows space for additional functionality to be added. For example, figure 4 shows additional dosing modules 152, 154, 156 and 158 arranged along the outside of the band for dosing the surface of the band 30 already covered with solution from the immersion bath 40. These additional dosing modules are provided for dosing the wetted belt with particulates, molecules, cells, bacteria, viruses, or engineered micro and nano structures or particles, which add features to the spun fibre or electrosprayed coating. For example, controlled amounts of silver nanoparticulates may be added to the fibre for use in SERS (Surface-enhanced Raman scattering) sensors.

In another embodiment, antibiotics may be added to the surface of the fibre for use in wound dressings.

In the embodiment of figure 4, four dosing modules 150 are shown. The first of these, furthest from the first roller 10, is a cell, virus, or bacteria deposition head 152. Secondly, there is an inkjet head 154, which could be use to deposit liquids and liquid dispersions. Thirdly, is a nebuliser or atomiser 156 which may be used for emitting a drug in a fine mist over the belt for inclusion in the fibre. Fourthly, and nearest to the first roller, is an electrospray head 158 for the deposition of biolmolecules such as proteins. The order and specific modules used in any particular application will vary and will not necessarily be that described here. Embodiments may comprise any of the modules 150 and does not require all modules to be included.

On the opposite side of the band, on the side along which the band returns to the immersion bath 40, a cleaning -17 -station 160 may be included for cleaning of the band. The cleaning may remove fibres and any remaining solvent or solution. If the surface of the band is not returned to a stable state prior to wetting, the fibre production will be inconsistent. On entry to the cleaning station 160 the band condition and levels of contamination may vary. On exit from the cleaning station 160 the band will be substantially free of organic and inorganic contaminants. Production of some fibres will require the band to be cleaner than for other types of fibre and thus depends on the type of fibre being synthesised. For materials that require extremely low levels of contamination additional cleaning stations 160 could be added. In the exemplary embodiment shown in figure 4, the cleaning station comprises four units. In the order in which the belt approaches them, they are: a mechanical or liquid cleaning unit 152, an infra-red lamp dryer 154, an air knife 156, and finally a ETJV or TJV lamp or laser 158. The mechanical or liquid cleaning unit 152 mechanical, abrasively or using liquid removes the majority of contaminants on the surface of the band 30. The infra-red lamp dryer 154 performs an initial dry of the band. The air knife 156 finishes drying the band and may also remove any remaining lose material that is adhered to the band. The EUV or TJV lamp or laser can be used to modify the surface of the band 30, for example to improve wetting of the band with polymer solution.

Alternatively, surface conditioning of the band 30 may be achieved by electron, ion, or electromagnetic radiation sources emitting radiation at the surface of the band 30.

Linear arrays or scanning sources can be mounted adjacent to the band to irradiate the band. Optionally, this irradiation can occur whilst the belt is exposed to a gas to assist -18 -modification of the band surface. Surface conditioning could be sterilisation or modification of the contact angle of the surface or its wettability. It may also increase the surface charge on the wetted surface to enable attraction of charged particles as the belt moves under a dosing module 150, for example, and electrospray or charged particulate source.

Examples of suitable radiation sources are EIJV Excimer lamps, TJV LED arrays, Corona discharge lamps, linear ion sources.

Optionally, a gas jet or gas envelope may be provided at the end of the cleaning station to perform a final surface conditioning of the band before wetting. It will be apparent to the skilled person that any one, some, or all of the above units 162, 164, 166, 168 may be incorporated into the cleaning station 160.

The above embodiments show a single electrospinning unit 99 with a single wetting zone and consequently a single electrospinning or electrospray zone. The width of the electrospinning or electrospray zone can be increased by increasing the width of the band 30, rollers 10, 20 and immersion bath 40. Alternatively, multiple electrospinning units 99 may be placed in a line with the rollers 10, 20 effectively end-on-end to cover a larger surface area. The design of the electrospinning units 99 means the units can be stacked close together with minimal space between adjacent units. As well as being able to stack the units end-on-end, lines of units can be stacked behind one another, as shown in figure 6. The two dimensional stacking arrangement shown in figure 6 allows either large volumes of the same material to be deposited, or different layers or mixtures to be laminated together.

-19 -As shown in figure 6, planar material 260 may be suspended or tensioned a short distance from a counter electrode 270. The counter electrode 270 is held at 0 Volts and acts as counter electrode for all of the electrospinning units 99. The planar material 260 is translated along a linear path to be subjected to deposition of droplets or fibres in the electrospinning zone of the electrospinning units 99. Figure 6 shows a four by four array of units 99.

Each unit can be used for depositing the same material, or each row could be used to deposit a different material to build up laminated layers on the planar material 260.

The person skilled in the art will readily appreciate that various modifications and alterations may be made to the above described apparatus and methods without departing from the scope of the appended claims. For example, although the apparatus and method has largely been described with reference to electrospinning of fibre, the above apparatus and method may readily be modified for electrospray deposition, such as the deposition of droplets on a substrate or planar material. Furthermore, variations in the materials used for the band or belt and the composition of the fibre may also be made without diverging from the general scope of the present invention.

Claims

-20 -CLAIMS: 1. Apparatus for electrospinning fibres, comprising: a band tensioned between first and second rollers and curved around the rollers;an electric field generator adapted to provide anelectric field between an electrospinning zone at the first roller and a counter electrode; a bath for containing liquid and arranged to wet the band or regions of the band as it passes around the second roller, wherein the band is arranged to transport liquid from the bath to the electrospinning zone for the production of fibres in said electrospinning zone.
2. The apparatus of claim 1, wherein the electric field generator is arranged to provide an electric field between the surface of the band curved around the first roller and a counter electrode.
3. The apparatus of any preceding claim, wherein the fibres are nanofibres.
4. The apparatus of any preceding claim, wherein the band is a belt, an array of belts, a wire or an array of wires.
5. The apparatus of claim 4, wherein the band is made of metal, fabric, textile, woven wire, an array of multicore twisted wire belts, polymer, polymer foam, or rubber.
6. The apparatus of any preceding claim, wherein the band is patterned with grooves, spikes, ridges, or recesses.
7. The apparatus of any preceding claim, further comprising a pair of extractor electrodes arranged parallel to the first roller and spaced apart symmetrically from the first roller.
8. The apparatus of claim 7, wherein the extractor electrodes are spaced from the first roller and arranged so as to increase the electric field in the electrospinning zone.
9. The apparatus of any preceding claim, further comprising air assist ducts located at the sides of the electrospinning zone and arranged to provide an airflow to direct produced fibre away from the first roller.
10. The apparatus of any preceding claim, further comprising a release head provided adjacent to a flat surface of the band, the release head arranged to atomise material or to deposit material on the belt.
11. The apparatus of any preceding claim, further comprising a release head provided adjacent to a curved surface of the band, the release head arranged to atomise material or to deposit material on the belt.
12. The apparatus of claim 10 or 11, wherein the release head is an electrospray head, a nebuliser, an atomiser, or an ink jet head.

-22 -
13. The apparatus of claim 10, 11 or claim 12, wherein the release head is arranged to release cells, virus particles, or bacteria.
14. The apparatus of any preceding claim, further comprising a cleaning head provided adjacent to a surface of the band, and arranged to remove material deposited on the band.
15. The apparatus of any preceding claim, further comprising a surface conditioning head provided adjacent to a surface of the band, and arranged to condition the surface of the band.
16. The apparatus of claim 15, wherein the surface conditioning head is adapted to use electrons, ions, or electromagnetic radiation incident on the band.
17. The apparatus of claim 14 or claim 15, wherein the cleaning head or surface conditioning head is adapted to sterilise the surface of the band.
18. The apparatus of any preceding claim, further comprising a housing enclosing the apparatus, the housing having an aperture for the electrospinning zone.
19. The apparatus of any preceding claim, further comprising a drive mechanism arranged to drive the band.
20. Apparatus for producing fibres or droplets, comprising a surface translatable between a wetting zone and an electrospinning zone, the wetting zone including an -23 -immersion bath for containing liquid, and the electrospinning zone arranged to be provided with an electric field by an electric field generator, wherein between the wetting zone and electrospinnirig zone is a material supply head for depositing material on the wetted translatable surface or for atomising material.
21. An apparatus for electrospinning of fibre comprising an array of the apparatus as claimed in any of claims 1-20.
22. Apparatus for electrospray deposition of droplets on to a surface, comprising: a band tensioned between first and second rollers and curved around the rollers;an electric field generator adapted to provide anelectric field between an electrospray zone at the first roller and a counter electrode; a bath for containing liquid and arranged to wet the band as it passes around the second roller, wherein the band is arranged to transport liquid from the bath to the electrospray zone where the electric field causes jets of droplets to be released from the band and deposited on said surface.
23. A method of producing fibres, comprising: wetting a band with fluid, the band tensioned between first and second rollers; providing an electric field at an electrospinning zone at the first roller; driving the band to cycle the band from the first roller to the second roller, -24 -wherein the electric field at the electrospinning zone is arranged to draw fibres from the fluid on the band towards a counter electrode.
24. The method of claim 23, wherein the electric field is provided at the surface of the band curved around the first roller.
25. The method of claim 23 or 24, wherein the band is wet by passing through a bath of liquid.
26. The method of any of claims 23 to 25, wherein the electric field in the electrospinning zone is increased by applying a potential to a pair of extractor electrodes.
27. The method of any of claims 23 to 26, further comprising providing a planar material in front of the counter electrode, the fibres being deposited on to the planar material.
28. The method of claim 27, further comprising moving the planar material with respect to the electrospinning zone to deposit fibres over the planar material.
29 The method of any of claims 23 to 28, further comprising forcing air through air assist ducts to direct the fibres away from the first roller.
30. The method of any of claims 23 to 29, further comprising releasing additional material on to the wet surface of the band for incorporation into the fibres.

-25 -
31. The method of any of claims 22 to 30, further comprising atomising material adjacent to the band.
32. The method of any of claims 22 to 31, further comprising cleaning or surface conditioning the band prior to wetting.
33. A method of depositing droplets on a surface, comprising: wetting a band with a fluid, the band tensioned between first and second rollers; providing an electric field between a counter electrode and an electrospray zone at the first roller; driving the band to cycle the band from the first roller to the second roller; providing a deposition surface between the first roller and the counter electrode, wherein the electric field is arranged to draw droplets from the fluid on the band to be deposited on the deposition surface.
34. Apparatus for electrospinnning of fibres substantially as herein described with reference to figures 3 to 6 of the accompanying drawings.
35. Apparatus for electrospraying of droplets onto a surface substantially as described herein with reference to figures 3 to 6 of the accompanying drawings.
36. A method of electrospinnning of fibres substantially as herein described with reference to figures 3 to 6 of the accompanying drawings.-26 -
37. A method of electrospraying of droplets onto a surface, the method substantially as described herein with reference to figures 3 to 6 of the accompanying drawings.