ELECTROSPINNING PRINTING DEVICE AND METHOD

Abstract

An electrospinning printing device and method thereof are disclosed. The device may comprise: a printing head arrangement configured to replaceably hold at least one printing head for discharging a fibrous material, and a collector arrangement configured to electrostatically attract material from the printing head, in which the collector arrangement may comprise an at least partially electrically insulated collector that is arranged to be connected to an electric power supply, and the at least one printing head is electrically grounded when held by the printing head arrangement.

Claims

1. An electrospinning printing device, comprising: a printing head arrangement configured to replaceably hold at least one printing head for discharging a fibrous material; and a collector arrangement configured to electrostatically attract material from the printing head, wherein the collector arrangement comprises an at least partially electrically insulated collector that is arranged to be connected to an electric power supply, and the at least one printing head is electrically grounded when held by the printing head arrangement.

2.-14. (canceled)

15. A method for manufacturing a biocompatible body or tissue substitute, by electrospinning, the method comprising: providing an electrically grounded printing head and an at least partly electrically insulated collector that is connected to an electric power supply, such that an electrostatic field is established between the printing head and the collector; and simultaneously and/or alternatingly drawing material out of the printing head via the electrostatic field and moving the printing head and the collector relative to each other.

16. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0058] The herein described invention will be more fully understood from the detailed description given herein below and the accompanying drawings which should not be considered limiting to the invention described in the appended claims. The drawings are showing:

[0059] FIG. 1 is a schematic diagram of an electrospinning printing device comprising an electrically grounded printing head arrangement and a collector arrangement,

[0060] FIG. 2 is a simplified perspective image of a collector arrangement wherein the edge of a collector is covered with a ring-shaped dielectric,

[0061] FIG. 3 is a simplified perspective image of a collector arrangement wherein the surface of the collector facing the printing head is fully covered with a dielectric plate,

[0062] FIGS. 4a to 4b schematic diagrams of different spinnerets,

[0063] FIG. 5 is a schematic diagram of a printing head arrangement comprising a plurality of printing heads movable in x-y-z directions and a collector arrangement movable in x-y-z directions

[0064] FIG. 6 shows a printed mesh consisting of alternating layers of an electrospun polymer melt fibre and microextruded meander-like bio-ink fibre

[0065] FIG. 7 shows a magnified section of a hybrid product produced by the present electrospinning printing device

DESCRIPTION OF THE EMBODIMENTS

[0066] Reference will now be made in detail to certain embodiments, examples of which are illustrated in the accompanying drawings, in which some, but not all features are shown. Indeed, embodiments disclosed herein may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Whenever possible, like reference numbers will be used to refer to like components or parts.

[0067] FIG. 1 schematically shows an electrospinning printing device 1 comprising a printing head arrangement 2 and a collector arrangement 3, wherein the collector arrangement 3 comprises a collector 300 connected to a regulated power supply V.sub.1 provided by a power supply unit which preferably is grounded GND. The electrical connection between the collector 300 and the power supply V.sub.1 can optionally be enabled or disabled by operating a switch SW provided in an electrical circuit of which the collector and the power supply are components. Specifically, the switch SW may take the form of an on/off switch. Alternatively, the switch SW may constitute a disconnection means such as a fuse or circuit breaker for protecting the collector and associated parts of the collector arrangement and the printing head arrangement against overvoltage.

[0068] The printing head arrangement 2 comprises a reservoir 220 containing a material suitable for electrospinning and a printing head 200 comprising a spinneret 210 along with connection means 201 in the form of a fluid opening connecting the two (shown schematically with a dotted line). The printing head 200 and the reservoir 220 are shown joined together as a reservoir-printing head unit in the form of a cartridge. It is to be understood, however, that they can be provided as separate units, for example in the form of cartridges, and that they can be joined together or held at a distance from one another in the printing head arrangement. The material in the reservoir can be a fluid comprising a polymer, such as a polymer melt. The spinneret 210 of the printing head 200 comprises a generally electrically conductive tubular housing 211 and one end comprising an opening 201 configured to receive the material from the reservoir 220 and another end comprising an exit hole 213 which is pointed at the collector arrangement 3 and from which the material being electrospun is discharged. The spinneret 210 includes a hollow needle 212 for discharging the fluid from the exit hole 213 which generally corresponds to the exit hole 213 of the printing head 200. The hollow needle 212 section and in particular the exit hole 213 have a diameter typically between 60 m and 2 mm, preferably between 100 and 500 m. The spinneret contacts the electrical ground GND via its housing 211 and/or the hollow needle 212. Instead of comprising a single opening 201 or a single exit hole 213, however, spinnerets comprising multiple openings 201 and/or multiple exit holes 213 as shown in FIG. 4 can be used.

[0069] Controlling or tempering the fluid to a desired temperature for electrospinning is achieved by an optional temperature control device, here shown to be a heating device arranged in or on the printing head. Specifically, the heating device comprises a heating coil 230 wrapped around a part of the spinneret 210 of the printing head through which the fluid flows. The heating coil is shown to be wrapped around the housing 211 of the spinneret but it may also be wrapped around the hollow needle section 212 of the spinneret. It is to be understood that the temperature control element does not necessarily have to contact the spinneret. It may instead contact another part of the printing head as long as the temperature of the material to be discharged can be controlled. Indeed, the temperature control device may contact the reservoir 220, for example a housing of the reservoir. The heating coil 230 is a resistor element with resistance that provided in a circuit having a regulated power supply V.sub.2. This circuit is preferably separate from the circuit comprising the collector 300, i.e. it is electrically decoupled from the circuit of the collector 300, which can be accomplished by electrically insulating the heating coil from the circuitry of the printing head 2 leading to the ground GND. Although a heating coil 230 is described here as a heating device for heating the fluid, another heating device can be used, such as a Pelletier element, a thermofluid circuit, a heating jacket, sleeve or patch wrapped around the housing 211 and/or the hollow needle section 212 of the spinneret 210.

[0070] Depending on the material to be discharged, the temperature control device has a cooling function. To this end, a Pelletier element and/or a thermofluid circuit can be applied to the spinneret 211.

[0071] The reservoir 220, which can be provided as a cartridge, comprises a pressure exertion device 202 for pressuring the material with a pressure P to exit the reservoir and enter the spinneret 210. The material contained in the reservoir 220 may be a fluid with a lower or higher viscosity as needed. It may also be a paste-like material. The exit end of the reservoir mated with the spinneret may comprise valve means such as a membrane that is punctured by a needle or formed at the material-receiving end of the spinneret, in particular for fluid with low viscosity such as a hydrogel. The pressure exertion device 202 may for example be carried out as a plunger or piston whose axial displacement is effected by an electric motor which may itself be part of the pressure exerting device or distinct therefrom.

[0072] In this way, the reservoir has the function of a syringe that pushes the material into the spinneret. The plunger of the reservoir is axially displaced by means of an electric motor, whereby the plunger comprises a threaded shaft that engages with a threaded rotating counter element driven by the electric motor. The reservoir 220 may optionally contain a sensor to measure its filling level and returns this information to a computer and a computer program which controls the electric motor. Alternatively, the filling level of the reservoir 220 may be determined, starting from a given initial filling level, by determining the plunger displacement directly or indirectly, for example by way of counting motor revolutions. Alternatively, the pressure exertions means 202 may include a pneumatic or hydraulic pressure device, such as an air pump that charges the plunger with a pneumatic force, or the fluid may be directly pneumatically charged and thereby pressurized.

[0073] The collector arrangement 3, of which a section is shown, comprises a collector plate 300 with a spigot 301 arranged centrally on the lower face of the collector 300. The shape and size of the collector plate 300 is chosen to match the size of the printable (working) area. Typically, it may be disc-shaped or rectangular. The material of the collector is preferably chosen to have good electrical conductivity, and to that end preferably contains steel, brass, copper or aluminium.

[0074] As an electrical insulator, a dielectric plate 320 such as a ceramic plate in the present embodiment fully covers the upper surface of the collector and has lateral dimensions greater than the collector 300 it covers. The dielectric plate 320 is fixed or glued onto the collector, for example by means of silicone or double-sided tape.

[0075] The underside of the collector arrangement 3 is covered with an epoxy resin providing it with its final mechanical stability. Instead of an epoxy resin, however, another material may be used such as a potting compound containing polyurethane or silicone. For example, a 2-K polyurethane compound may be used such as the product PUR 5620-A/5610-B of Astorit AG. As a suitable silicone material, K-silicone compounds may be used such as the product ELASTOSIL RT 428 with WACKER CATALYST T 77 2 of Wacker Chemie AG.

[0076] Viewed from the spinneret 210, the collector 300 is hidden from sight by the dielectric plate 320. Instead of a ceramic plate 320, a glass plate may be used. A transparent dielectric plate has the advantage that any cracks in the plate would be easily identified. Whichever material is used for the dielectric plate, it should not electrically charge easily and should be structurally resilient against overcurrent at breakdown voltages beyond the voltage V.sub.1, e. g. up to 30 kV, preferably of up to 120 kV, and also against physical shock such as when colliding with a hard object. The dielectric plate 320 preferably has a thickness of about 2 mm, thicker if voltages over 30 kV are applied.

[0077] Dielectric plate types with the following physical and electrical characteristics were found to be suitable:

TABLE-US-00001 Relative Thickness Dimensions Resistivity permittivity Material Type (mm) (cm cm) ( .Math. m) (.sub.r) Heraeus HOQ 300 Glass 2.14 15.70 9.80 10.sup.8 3.7 (0 to Quartz Glass Rough (400 C.) 1000 MHz, 24 C.) Thermo Fisher Glass 2.08 14.95 10.05 n/a 7.2-7.8 Electroverre-Glas Smooth Soda-Lime Glass SCHOTT Nextrema Nextrema 1.98 13.00 7.00 10.sup.8 7.8 (1 MHz, Transparent Ceramic Clear (350 C.) 25 C.) 724 - 8 SCHOTT Nextrema Nextrema 2.20 13.00 7.00 10.sup.8 6.6 (1 MHz, opaque white ceramic White (350 C.) 25 C.) 724 - 8

[0078] The collector arrangement 3 further comprises a holder 330 in the form of a tray in which the collector 300 and the dielectric plate 320 are mounted. The tray 330 is shaped as an annular disk wherein the edge of the dielectric plate 320 is mounted on the face 315 of the inner edge of the disk facing away from the printing head arrangement 2. The dielectric plate 320 may be glued onto said inner edge face. The outer edge of the tray 330 is defined by a wall 331 surrounding the inner space of the tray and extends away from the printing head arrangement 2. The space below the collector 300 enclosed by the wall 331 is filled with an epoxy resin 340 with high mechanical resilience against dielectric breakdown. Suitable exemplary epoxy resins were found to be: Araldite CW 229-3 and Aradur HW 229-1. The tray 330 can be made of plastic or aluminium or it may contain these materials as primary components. The space above surface of the dielectric plate 320 facing the printing head arrangement 2 is kept free for an uninterrupted line of sight between the exit hole 213 of the spinneret 210 and the dielectric plate 320. A high voltage cable connects the spigot 301 of the collector plate 300 to a grounded electric power supply V.sub.1 so that the collector plate can be negatively or positively charged depending on the polarity of the power supply. A switch SW is preferably provided to enable or disable electrical connection of the power supply V.sub.1 from the collector arrangement where needed.

[0079] When the power supply V.sub.1 is turned on, the collector 300 becomes positively (or negatively) charged and an electrostatic field with a potential drop of V.sub.e is created between the electrically spinneret 210 and the collector plate 300. The spinneret 210, in particular its hollow needle 212, then carries a charge opposite to that of the collector plate 300 and current flows from the tip of the hollow needle to the ground. At the same time, pressure P is applied to the fluid contained in the cartridge 220 by means of the plunger 202 according to the foregoing description and pushes the fluid through the heated section of the spinneret 210 to the exit hole 213 of the hollow needle 212 where the electrostatic field draws it out and onto the dielectric plate 320 where a printed pattern is created.

[0080] Because the spinneret 210 discharges to ground, any equipment of the printing head arrangement 2 surrounding the spinneret is a lesser source of electrical interference to the spinneret. As a result, it was found that turbulent whipping behaviour of fibrous material discharged from the spinneret could be reduced. This in turn facilitated a controlled printing process. Furthermore, because the collector 300 is connected to the power supply V.sub.1 and charged and the components of the electrospinning printing device in the immediate neighbourhood of the collector would be subject to electrical discharge emanating from the collector, protecting them against said discharge is facilitated by the dielectric plate 320 which can be mounted on the collector 300 which is easily accessible to the user.

[0081] FIG. 2 is a perspective view onto a collector arrangement 3 comprising a collector plate 300 having a charge +q and dielectric material 320 applied to the surface of the collector plate facing the printing head 2 in the edge region of the collector plate. The dielectric material creates a ring covering the edge of the collector plate 300. The upper surface of the dielectric ring 320 can be glued on to the edge region of the tray of the collector arrangement according to the foregoing description and the lower surface of the dielectric ring 320 can be glued to the edge region of the collector plate. The dielectric ring 320 prevents electric discharge from the edge region of the collector plate 300.

[0082] FIG. 3 is a perspective view onto a collector arrangement 3 comprising a collector plate 300 having a charge +q and dielectric material 320 applied to the entire surface of the collector plate facing the printing head 2 in the manner described for FIG. 1. The dielectric plate 320 not only prevents electric discharge from the edge region of the collector 300, but also from the inner surface of the collector plate facing the printing head 2 when sufficiently high voltages are reached or the dielectric material has been compromised or damaged.

[0083] The collector arrangements 3 are mounted on an x-y stage movable in the x-y plane perpendicular to the exit vector of the fibrous material from the spinneret (shown schematically in FIG. 5). Moving the x-y stage enables progressive deposition of the fibrous material ejected from the spinneret to create a desired pattern. An x-y stage controllable by a computer and a computer program and/or by a control unit can be used where an upper stage on which the collector arrangement is slidably mounted is itself slidably mounted on a lower stage, whereby the collector arrangement is displaceable at a right angle to the upper stage. The displacing movements are controlled by spindle drives. Instead of the x-y stage, and x-y-z stage may be used on which the collector arrangement 300 is mounted for positioning it in any of the 3 spatial directions. Such a positioning system may be advantageously be used in 3D printing.

[0084] FIG. 4 shows a number of possible spinneret or printing head designs for use in the presently described electrospinning printing device.

[0085] FIG. 4a schematically shows a coaxial spinneret comprising two entries or openings 214 and 215 leading into coaxial fluid channels, each fluidically connected to a different reservoir or source. One opening 214 may be provided at the upper end of the spinneret leading to the inner channel 216 whilst the other opening 215 may be provided in the side of the spinneret leading into the outer channel 217. The fluid channels merge at the bottom of the spinneret where the fluids they have channelled mix. Alternatively, the inner 216 and outer channel 217 may extend separately to the exit hole 213 so that a fibrous material exiting the spinneret 210 may consist of a core surrounded by a sheath, the core material being different than the sheath material. The coaxial spinneret 210 may alternatively receive a fluid and a gas via the openings, whereby the gas flows into the outer channel 217 of the coaxial spinneret via the side opening 215. The gas can be used for a number of purposes, including: stretching the fibrous material exiting from the inner channel, prevention of clogging, lowering its viscosity or, if a polymer solution is used, increasing the evaporation rate of the solvent. Furthermore, only the outer channel 217 need be used with a fluid if, for example, a tubular fibrous material is to be released from the spinneret.

[0086] FIG. 4b schematically shows a spinneret 210 comprising one fluid channel receiving a fluid shown by the down arrow P and plurality of exit holes 213 for simultaneously releasing a plurality of strands of fibrous material.

[0087] FIG. 5 schematically shows an embodiment on a printing head arrangement 2 comprising a plurality of printing heads 200 movably mounted on a printing head selector. The printing heads 200 may be provided separately from reservoirs or they may be joined to reservoirs (not shown) as is the case here. At least one of the printing heads 200 is configured for electrospinning and comprises a spinneret 210. Any other printing head 200 of this printing head arrangement 2 may be configured for direct writing and comprises at least one nozzle for ejecting material provided in a reservoir under pressure P. A suitable direct printing material would be a bio-ink, for example. The printing heads 200 are brought into position by a printing head selector comprising linear slides on which the printing heads are mounted, shown schematically with arrow 5, the linear slides being activated by a motor, solenoid or pneumatically. Active printing heads are in a lower position closer to the collector 300 than non-active printing heads in a higher position further away from the collector. Preferably, only one printing head is active at a time. Alternatively, as a printing head selector, a robotic printing head exchanger such as a selector wheel may be provided. Printing heads not used are preferably kept away from the working area to avoid collision and to bring them out of the exposure to the electrostatic field.

[0088] When a printing head 200 is lowered into a position for electrospinning, it engages a schematically shown electrical contact 6 provided in the printing head arrangement 2 for connecting it to the electrical ground GND. In particular, the electrical contact 6 engages with the spinneret or nozzle of the printing head 200. This ensures that every printing head 200 for electrospinning that is brought into a discharge position is electrically grounded. Alternatively, however, all printing heads 200 for electrospinning are permanently electrically grounded. Printing heads not used can be kept further away from the electrostatic field and pressure exertion means 202 (see FIGS. 1 to 3) are not activated so no material feeds into these printing heads. Because a printing head 200 for electrospinning may in some embodiments also be used for direct printing, it is to be understood that a printing head 200 for direct printing may also be brought into contact with electrical contact 6. However, printing heads 200 not configured for electrospinning, such as printing heads used for direct printing only, in particular microextrusion, can be brought into a separate printing position where no electrical grounding takes place. These printing heads 200 may be configured for direct printing and deposition of polymers or bio-inks.

[0089] The electrospinning printing device 1 further includes a control unit 8 that may be realized by a computer running a corresponding computer program, dedicated circuitry or a combination thereof. The control unit is designed to control the power supply of the electrospinning printing device. The control unit is further designed to control the pressure P for exerting a pressure on the material in the reservoir or reservoirs to be discharged from the printing head or printing heads via electrospinning and/or direct printing simultaneously and/or in an alternating manner. Although not shown in this drawing, pressure P may be exerted on the material by a pressure exertion device such as pressure exertion device 202 shown in FIGS. 1 and 3. The control unit 8 is further designed to control the movement of the collector arrangement 3 by way of a stage as described further below in a coordinated manner with the deposition of material on the substrate. If the temperature control device is present, the control unit may further be designed to control its operation.

[0090] The control unit in some embodiments is designed to coordinate the material deposition by way of electrospinning and/or applying a mechanical force, and the movement of the collector arrangement 3 such that a workpiece of defined geometry, for example a tissue substitute, is realized. The control unit may be designed to receive and/or store the workpiece geometry in form of numeric data, in particular in form of a CAD and/or CAE model.

[0091] A computer program installed on a computer controls the positioning of all printing heads 200 by controlling the printing head selector such as a selector wheel according to the desired printed product. The computer may be realised as a control unit 8 which may be integrated in the electrospinning printing device with corresponding operator interfaces or may be separated from the electrospinning printing device but connected to it via dedicated fixed-line or wireless communication channels. Part or all of the control functionality may also be realized by way of a control unit with dedicated circuitry. The control unit 8 instructs different printing heads 200 releasing different fibrous material to alternately be brought into printing positions in accordance with the desired layered structure of the product to be printed. The printing heads 220 of the printing head arrangement 2 may comprise different spinnerets or nozzles according to the foregoing description, or they may all be the same.

[0092] FIG. 5 also schematically shows and x-y-z stage 9 for positioning the collector arrangement in any of the 3 spatial directions. The constitution of the x-y-z stage 9 is described in the general part of the description of this document.

[0093] Whilst the x-y or x-y-z stage 9 and the control unit exemplarily are shown to be a part of the electrospinning printing device 1, at least one of them may alternatively be provided separately and connected to an electrospinning printing device described in this document that does not comprise positioning means for the collector arrangement and/or a control unit.

[0094] FIG. 6 shows a perspective view onto a printed product 7 produced with an electrospinning printing device 1 according to an embodiment described in this document, wherein a printing head 200 configured for electrospinning was brought into a position for electrospinning a polymer melt, resulting in the meander-like deposit of nanoscale fibrous material on a layer of the meander-like deposit of microscale fibrous material. The nanoscale fibrous material is electrospun out of a polymer melt, whereas the microscale fibrous material is microextruded out of a bio-ink. It is to be understood that not only can nanoscale and the microscale fibrous material be printed alternately in a layered structure, but that nanoscale and microscale fibrous material can also be deposited as part of one and the same layer of a layered structure or as part of single sheet. The deposited nanoscale fibrous strands have a thickness between 0.1 and 20 m whereas the deposited microscale fibrous strands have a thickness between 60 m and 1000 m. The hybrid product as depicted with this figure may comprise artificial cartilage tissue, for example.

[0095] FIG. 7 shows a section of another hybrid printed product. The magnified section 7a of the image reveals a fine-mesh substrate in the background covered with thicker strands. The fine mesh-substrate is manufactured via electrospinning and the thicker strands via direct printing, in this case via 3D printing. The thicker strands have a thickness of ca. 200 m and the fibres of the electrospun fibrous material in the background have thickness of ca 6 m. Both materials derive from polycaprolactone (PCL) that can be contained in a reservoir, moved to a printing head and discharged therefrom by electrospinning with a grounded printing head and a charged collector, followed by direct printing, in particular 3D printing, where the same or another printing head extrudes the polycaprolactone in the absence of the electrostatic field when the collector is not charged.

LIST OF DESIGNATIONS

[0096] 1 Electrospinning printing device [0097] 2 Printing head arrangement [0098] 200 Printing head [0099] 201 Connection means [0100] 202 Pressure exertion means [0101] 210 Spinneret [0102] 211 Spinneret housing [0103] 212 Spinneret nozzle/hollow needle [0104] 213 Spinneret exit hole [0105] 214 Spinneret end face opening [0106] 215 Coaxial spinneret side face opening [0107] 216 Coaxial spinneret inner channel [0108] 217 Coaxial spinneret outer channel [0109] 230 Spinneret heating device [0110] 3 Collector arrangement [0111] 300 Collector plate [0112] 301 Spigot [0113] 315 face of inner edge of disk-shaped tray 330 [0114] 320 Dielectric plate [0115] 330 Tray [0116] 331 Wall of tray [0117] 340 Potting material [0118] 4 Fibrous strand [0119] 5 Printing head selector [0120] 6 Electrical ground contact [0121] 7 Printed product [0122] 7a Magnified section of printed product [0123] 8 Control unit [0124] 9 Positioning means for collector arrangement [0125] GND Electrical ground [0126] V.sub.1 Voltage applied to collector plate [0127] V.sub.e Electrostatic potential difference between collector plate and spinneret [0128] V.sub.2 Voltage applied to heating device [0129] SW Switch [0130] P Pressure exertion