Patent Application
20140284827
The present invention relates to a method for production of two-dimensional or three-dimensional fibrous materials of microfibres or nanofibres in which at first nanofiber or microfiber is continuously drawn out of a solution, which nanofibre or microfibre is pulled to a rotary set of n electrodes by means of electrostatic field. In the process individual electrodes are arranged at regular spacing to each other and at the same distance from the set of electrodes rotation axis and parallel with it. This set of electrodes rotates and thereby the nanofibre or microfibre is wound on it. After the nanofibre or microfibre was wound the electrostatic field is disconnected and rotation of the electrode set is stopped, and a layer of microfibres or nanofibres formed in the field between two adjacent electrodes is removed. The invention also refers to an apparatus for production of the two-dimensional or three-dimensional fibrous materials of microfibres or nanofibres. This apparatus includes at least one spinning nozzle attached to a first potential and a set of electrodes facing the nozzle arranged at regular spacing to each other and attached to a second potential. Further it includes an accumulator for collecting microfibres and nanofibres settled between couples of adjacent electrodes.
Production of microfibres or nanofibres is implemented by a method of electrostatic spinning. This method is presented as “Electrospinning” in professional literature. In this method the forming of melt or solution of polymers into fibrous structures is brought about by effects of high electrostatic field. Forces of this field at first give rise to a spurt of a trickle out of the polymer solution or melt droplet and then they activate also its movement to an opposite electrode. During the movement a thinning, drawing and solidification of the polymer occur and the polymer in the solid fibres form falls on the opposite electrode, so-called collector. The whole of this fibre movement between the two electrodes is highly complicated and its trajectory is quite random. Literally chaotic movement of the flying fibre gives rise to its random depositing on the opposite electrode, where a nonwoven fibrous material with fibres having their diameter from ten nanometres to tens of micrometres is formed. This manufacturing method is known from U.S. Pat. No. 2,048,651.
Nano-fibrous or micro-fibrous materials with highly fine structure find numerous applications in many fields of advanced medicine, but also of microelectronics, optics and power engineering. Huge surface formed in relatively very small volume is one of the basic advantages of these materials, and inter-fibre spaces (pores) of these materials have very small size. Material with fine internal nano-structure or micro-structure assumes quite new properties that can be considerably different from properties of a volume sample of the same material. Additionally it is possible to control these unique properties and adapt them to requirements of particular application by a controlled production. Future applications count on a use of such materials in various fields of advanced medicine, because such material provides cells in living tissue with very favourable and natural conditions for their growth, motion and reproduction. Unfortunately the usability of such material is considerably limited just because of its internal chaotic structure. Applications of tissue engineering specify their requirements on regular 3D structures that are subsequently used as replacements of cartilages, bones, and nerve, vascular and cardiovascular transplants and the like. Just an internal axial orderliness of material considerably supports directional growth and motion of cells, tissues, and also supports regeneration of long nervous disorder. The ordered structure ensures required flexibility of the material when stressed in applications such as muscular and connective tissues replacements. Mechanical properties of the material can be quite well controlled just by choice of the internal structure axial orderliness. Need of new materials with precise internal morphology is required by numerous applications not only in the field of advanced medicine. The regular structure is quite essential also e.g. for miniature electronic or optical connections that can be provided by nanofibres or microfibres produced by the method disclosed in this invention.
Current methods and production techniques of the oriented nanofibres or microfibres are solved by means of rotating collector that is driven at high revolutions. Surface of such collector, in most cases in the shape of a cylinder or a thin rod as described in U.S. Pat. No. 4,552,707 or U.S. 20020084178, captures flying fibre and mechanically carries it in the direction of the collector own movement; the fibre is practically wrapped around the rotating cylinder. Nanofibres or microfibres are deposited directly onto the cylinder surface or are formed in a gap between two rotary rods that are positioned on one rotation axis, see U.S. 20070269481. Surface of such collector is one of the electrodes and thus it must be made of a conductive material. Unless the collector is directly connected to one of high-voltage power supply poles, see U.S. 20090108503, U.S. Pat. No. 4,689,186, or if its surface is overlapped with non-conductive substrate, significant losses of the production process efficiency arise, because practically an insulating material is inserted between two main electrodes and thus electric field is degraded and its homogeneity is disturbed. Reduced efficiency is indicated with longer deposition of fibres, because the thicker deposited layer acts also as an undesirable insulant and thus further fibres are repelled in a different direction from the collector. In the area of so far deposited fibres a charge is accumulated that has the same polarity as a charge carried by a fibre before its impact on the collector. Repulsive forces act between these charges of the same polarity, which forces influence negatively the ordering of newly deposited fibres. The negative effects of this charge are increased, when thicker fibrous layers are deposited, because fibres in upper layers are already deposited randomly and no longer respect the axial orderliness as it is with fibres deposited in lower layers. Furthermore the resulted fibrous layer has a partially limited degree of order, which is caused by capturing the flying fibre having direction different from just perpendicular to the surface of the rotating cylinder. On principal the methods mentioned above function well, however results, with regard to achieving precise orientation of the internal structure of the fibrous materials, are generally unsatisfying, because there is still high percentage of fibres in produced materials that do not respect any of preferred directions.
Subsequent manipulation with the fibrous material and its controlled taking off from the collector surface is quite essential problem that is not a part of any of contemporary technical solutions. The fibrous layer is deposited onto the collector and for its subsequent use it must be transferred usually onto quite different underlayment or into another container, etc. And so manually one by one cut out stripes of fibrous material are assembled in thicker 3D structures in examples of embodiments disclosed in patent application U.S. 20080208358A1. Such a layer is highly fine and a manipulation with the nano-fibrous or micro-fibrous material is complicated, because an irreversible damage of the layer arises very easily already when being taken off from the collector used. Any manipulation with material of a larger area is almost impossible especially with bio polymeric fibres with very low mechanical resistance. Currently there is no mechanisms solved, which would provide suitable mechanical manipulation and transfer of nano-fibrous or micro-fibrous layer onto another,, i.e. any underlayment while maintaining or even increasing of the orientation degree of the fibres in the layer.
Patent application WO2006136817A1 describes a use of a rotating collector with electrodes longitudinally arranged around an axis of rotation. Geometric dimensions of the collector are not mentioned. Authors give no method for taking off fibres from the collector carefully. No collecting mechanism for fibres deposited onto the rotating collector is solved. The described method does not solve all phases of the production process or more precisely the process is terminated by the fibres deposition. Therefore it is impossible to finish the production process without an operator intervention and manual manipulation, which results in considerable decreasing of quality and internal structure of the material.
In publication of Katta et al. (Katta P., M. Alessandro et al. NanoLetters, 4(11): 2215-2218, 2004) rotating cylinder built-up of longitudinal conductive electrodes as a collector for creating oriented fibres is used. The collector with approximately forty conductive electrodes, which are distant 10 mm from each other and create the rotating collector with diameter of 120 mm, is described in the publication. A loss of uniaxial fibres orientation during longer time deposition is demonstrated here. Optimization and description of parameters important for operational utilization are not carried out here. The authors also do not mention further steps for processing of the fibrous layer deposited onto this type of collector.
Drawbacks of state of the art mentioned above are eliminated to a considerable extent by a method of production of two-dimensional or three-dimensional fibrous materials of fibres with a diameter of microfibres or nanofibres according to the invention, in which at first nanofibre or microfibre is continuously drawn out of a solution, which nanofibre or microfibre is pulled to a rotary set of n electrodes (where n is a natural number from 1 to 200) by means of an electrostatic field. Individual electrodes of the set are arranged at regular spacing to each other and at the same distance from the set of electrodes rotation axis and parallel with it. This set of electrodes rotates and thereby the nanofibre or microfibre is wound on it. After the nanofibre or microfibre thin layer was formed the electrostatic field is disconnected and rotation of the electrode set is stopped, and a layer of microfibres or nanofibres formed in the field between two adjacent electrodes is removed. Afterwards the rotary set of electrodes turns through an angle of 360/n and the layer of microfibres or nanofibres formed between two adjacent electrodes in the field adjacent to the field, from which a layer was removed in previous step, is removed. This step is repeated n-times till layers of microfibres or nanofibres from all the fields between adjacent electrodes are removed.
In an advantageous embodiment of the method according to the invention, before the layer of microfibres or nanofibres is removed from a new field, an accumulator turns around slightly to reach a direction of microfibres or nanofibres in the removed layer that is different from the direction of microfibres or nanofibres of the preceding layer.
In another advantageous embodiment of the method according to the invention superimposed layers of microfibres or nanofibres are pressed together, whereas by pressing the layers together it is possible simultaneously to form a required three-dimensional shape of the final product. An article formed in this way can be embedded with another medium to create a composite material of required properties.
Drawbacks of the state of the art mentioned above are eliminated to a considerable extent even by an apparatus for production of two-dimensional or three-dimensional fibrous materials of microfibres or nanofibres comprising at least one spinning nozzle connected to a first potential and a set of n electrodes facing the spinning nozzle that are arranged at regular spacing and connected to a second potential, and also an accumulator for collecting microfibres or nanofibres settled between two adjacent electrodes. The set of the electrodes is pivoted in this apparatus and individual electrodes of the set of the electrodes are arranged at regular spacing to each other and at the same distance from the set of electrodes rotation axis and parallel with it. The apparatus further comprises the accumulator, which is arranged, in relation to the electrodes, movably in direction of longitudinal axes of the electrodes, for collecting microfibres or nanofibres settled between two adjacent electrodes. Furthermore this accumulator is arranged, in relation to the electrodes, movably in direction perpendicular to the longitudinal axes of the electrodes for it being brought into engagement to collect microfibres or nanofibres settled between two adjacent electrodes, and being brought out of engagement after finishing the collection of microfibres or nano fibres settled between two adjacent electrodes.
In an advantageous embodiment of the apparatus according to the invention the accumulator has a shape of parallelogram, the width of which is smaller than a distance between nearest surfaces of a couple of adjacent electrodes to enable its insertion between said adjacent electrodes.
In another advantageous embodiment of the apparatus according to the invention the accumulator is arranged rotationally around a line perpendicular to the surface of the collector and passing through the centre of the collector surface in order that the accumulator may turn around slightly to place a further layer of microfibres or nanofibres settled between two adjacent electrodes with direction of microfibres or nanofibres that is different from the direction of microfibres or nanofibres of the preceding layer.
In another advantageous embodiment of the apparatus according to the invention the accumulator has a shape of square with its side shorter than a distance between nearest surfaces of a couple of adjacent electrodes, the accumulator being arranged rotationally around a line perpendicular to the surface of the collector and passing through the centre of the collector surface in order that the accumulator may turn through an angle of 90° to place a further layer of microfibres or nanofibres settled between two adjacent electrodes with direction of microfibres or nanofibres that is perpendicular to the direction of microfibres or nanofibres of the preceding layer.
In yet another advantageous embodiment of the apparatus according to the invention the accumulator is made in the form of a dish for depositing the collected layers of nanofibres or microfibres, the apparatus being further provided with a piston for compression of the fibres into the accumulator and for compaction of individual collected layers of nanofibres or microfibres to mechanically strengthen ordered 3D structure. In such a case it is also advantageous if the accumulator is arranged rotationally around a line perpendicular to the surface of the collector and passing through the centre of the collector surface in order that the accumulator may turn around slightly to place a further layer of microfibres or nanofibres settled between two adjacent electrodes with direction of microfibres or nanofibres that is different from the direction of microfibres or nanofibres of the preceding layer.
The subject matter of the invention is described in details with reference to the accompanying drawings.
It is the aim of the present invention to accomplish the production of nano-fibrous or micro-fibrous materials with high degree of areal (2D) and volume (3D) internal ordering that can be controlled by changing process parameters for the purpose of controlling morphological and anisotropic properties of the resulting materials. Furthermore it is also the aim of the present invention to solve suitable mechanical manipulation and transfer of the new material onto any underlying or also packing material, whereas the order degree of internal structure of the material is maintained. In an advantageous embodiment of the invention a movable accumulator 7 is a suitable dish that enables easy further treatment of the fibrous material (e.g. in production of composite materials).
The subject matter of the invention is a comprehensive production process of new materials that is divided into particular process phases, the exemplary sequence of which is shown on
An exemplary embodiment of an apparatus for production of two-dimensional or three-dimensional fibrous materials composed of nanofibres or microfibres, hereinafter referred to as fibres 5, is on
a schematically depicts a cross-section of the collector 9 with four electrodes 6 and the accumulator 7. Fibres 5 are deposited by electrostatic spinning on the conductive rods of the electrodes 6 of the collector 9. Afterwards the fibres 5 are deposited on a surface of the accumulator 7 while their order is maintained. The collector 9 is equipped with four electrodes 6. The squared accumulator 7 removed a layer 8 of fibres 5 from the field between two upper electrodes. On the right the subsequent phase is depicted, where the collector 9 is turned through an angle of 90° and the accumulator removes another layer 8 of fibres 5 with the same orientation.
b schematically depicts a cross-section of the collector 9 with five electrodes 6 and the accumulator 7. Fibres 5 are deposited by electrostatic spinning onto the conductive rods of the electrodes 6 of the collector 9. Afterwards the fibres 5 are deposited on a surface of the accumulator 7 while their order is maintained. The collector 9 is equipped here with five electrodes 6. The squared accumulator 7 removed a layer 8 of fibres 5 from the field between the two upper electrodes. On the right the subsequent phase is depicted, where the collector 9 is turned through an angle of 360/5, i.e. 72° and the accumulator 7 removes another layer 8 of fibres 5 with the same orientation. There are two layers 8 of fibres 5 with the same orientation on the accumulator 7.
a schematically depicts a cross-section of the collector 9 with four electrodes 6 and the accumulator 7. Fibres 5 are deposited by electrostatic spinning on the conductive rods of the electrodes 6 of the collector 9. Afterwards the fibres 5 are deposited on the surface of the accumulator 7, while their order is maintained. The collector 9 is equipped with four electrodes 6. The squared accumulator 7 removed a layer 8 of fibres 5 from the field between the two upper electrodes. On the right the subsequent phase is depicted, where both the collector 9 and the accumulator 7 are turned through an angle of 90° and the accumulator 7 removed another layer 8 of fibres 5. Thus there are two layers 8 of fibres 5 on the accumulator 7, whereas the orientation of fibres 5 of the first layer 8 is perpendicular to the orientation of fibres 5 of the second layer 8.
b schematically depicts a cross-section of the collector 9 with five electrodes 6 and the accumulator 7. Fibres 5 are deposited by electrostatic spinning onto the conductive rods of the electrodes 6 of the collector 9. Afterwards the fibres 5 are deposited on the surface of the accumulator 7, while their order is maintained. The collector 9 is equipped here with five electrodes 6. The squared accumulator 7 removed a layer 8 of fibres 5 from the field between the two upper electrodes. On the right the subsequent phase is depicted, where the collector 9 is turned through an angle of 360/5, i.e. 72°, and the accumulator 7 is turned through an angle of 90° and removes another layer 8 of fibres 5. Thus there are two layers 8 of fibres 5 on the accumulator 7, whereas the orientation of fibres 5 of the first layer 8 is perpendicular to the orientation of fibres 5 of the second layer 8.
In operation of the apparatus for production of the two-dimensional or three-dimensional fibrous materials a prepared spinning mixture is dosed into the jet emitter 2. Afterwards a high electric voltage is connected and it causes that the solution or melt begins to escape out of the spinning nozzle 3 creating fibre 5 with diameter ranging from microfibres to nanofibres. This fibre 5 moves in the electrostatic field in the direction to the collector 9. The fibres 5 are deposited onto the rotating collector 9 in one preferred direction. After the layer 8 of the fibres 5 was formed on the collector 9, high electric voltage is disconnected and the fibre 5 quits escaping out of the spinning nozzle 3. Thereafter the accumulator 7 collects the settled fibres 5, and the layers 8 of these fibres 5 are step by step superimposed, while their degree of order is maintained. According to requirements on the resulted material, the layers 8 of the fibres 5 are superimposed so that the fibres 5 orientation may be the same in all layers, or it is possible to turn the orientation of the fibres 5 in each subsequent layer 8 through an angle, usually through 90°. After a sufficient number of the layers 8 was superimposed it is possible to compress the fibrous layers 8 and thus either a final product, that can be enfolded in a wrapping material, or a semi product intended for further processing such as an application of suitable medium so that the resulted product may be a composite material and gain required properties, comes into existence.
It is an advantage of this embodiment that the fibres 5 deposited onto the surface of the accumulator 7 have a higher degree of order than fibres 5 settled onto a surface of a rotating cylinder because further straightening of them in one direction occurs just by a movement of the accumulator 7. Thus the degree of order of the internal fibrous material structure is higher than that of the material that was formed on the surface of the rotating cylinder.
Another advantage of this embodiment, when compared with stationary segmented collector with planar electrodes, is multiple lengths of ordered nanofibres, which enables to produce materials of larger area or volume with very well ordered internal structure. At very low revs of the collector 9 first of all electrostatic forces, which act transversely between particular electrodes 6 of the collector 9, contribute to the fibre 5 orientation. On the contrary at high revs even mechanical forces, which capture flying fibre 5 and attract it to the electrodes 6 of the collector 9 namely in one direction, i.e. perpendicular to the electrodes 6, join the electrostatic forces contributing to ordered depositing of the fibres 5 onto the collector 9. That way both the important components of forces—electrostatic and mechanical—are added up and thus the resulted degree of uniaxial order of the fibres 5 is multiplied. This principal is proved by long-term experimental and theoretically supported results that demonstrate formation of very well oriented fibres 5 of a diameter ranging from microfibres to nanofibres with multiply longer length when using segmented rotating collector 9, than when using stationary segmented collector of similar geometrical parameters. In order that a very good orientation of fibres 5 may be reached, revolutions of the collector 9 described in this patent application are set to a value by several tens of percent lower, than a minimal revolutions of a cylinder with the whole of conductive surface, namely just because of the contribution of electrostatic forces. Reduction of rotating speed leads to steadier air flow, which arises around fast rotating collector 9 and which pulls flying fibres 5 in uncontrolled direction.
Yet another advantage is the possibility of implementation of all the production cycle phases in a single closed apparatus, namely in a deposition chamber, where an automatic production without an operator intervention and without being influenced by external environment is ensured, which enables to ensure the process sterility and a high quality of resulting products.
In an advantageous embodiment of this apparatus the rotating collector 9 with the set 11 of the electrodes 6 connected to the second potential comprises at least three longitudinal electrodes 6, generally N electrodes 6, and the accumulator 7 that moves successively always between two adjacent electrodes 6 in such a way, that the accumulator 7 movement direction is determined by combining a movement in direction of the common axis x of rotation of the electrodes 6 of the collector 9, and a movement in direction that forms with the axis x a specified angle β. The accumulator degree of incline is defined by an angle α. In a plane transverse to the set 11 of the electrodes 6 an angle γ is defined, which specifies an angular displacement of the accumulator and the collector 9 to each other. The next collection of the fibres 5 is performed after turning the electrodes 6 of the collector in relation to the accumulator through an angle γ=360/N.
In another exemplary embodiment of this apparatus the rotating collector 9 with electrodes 6 connected to the second potential includes at least three longitudinal electrodes 6, generally N electrodes 6, and the accumulator 7 that moves successively always between two adjacent electrodes 6 in such a way, that the next collection of fibres is performed after turning the electrodes 6 of the collector 9 in relation to the accumulator 7 through an angle γ=90+360/N. However in this case between two consecutive collections of the layers 8 of the fibres 5 the accumulator 7 turns around its axis perpendicular to the surface of the accumulator 7, which is squared in this case, through an angle of 90°. That way the fibres are deposited in individual layers, where fibres in one layer are perpendicular to fibres of preceding layer.
Yet another exemplary embodiment of the apparatus comprises the rotating collector 9 with four longitudinal electrodes 6, and the accumulator 7, which moves in a direction perpendicular to said electrodes 6 axes for enabling of an insertion of inclinable plates of the accumulator 7 between said neighbouring electrodes 6 and their release and in the lengthwise direction along the electrodes 6. The accumulator 7 is provided with four said inclinable plates capturing on their surfaces fibres 5 settled between two closest adjacent electrodes 6. After capturing of fibre layers on said inclinable plates of the accumulator 7 said inclinable plates, one after the other, are tilted 180° along the edge of the inclinable plate that is closest to the longitudinal axis of the collector 9 and the fibre layer from the inclinable plate is captured on the collecting plate that is perpendicular to the longitudinal axis of the collector 9. Thus after subsequent capturing of individual fibre layers from the subsequent inclinable plates four fibre layers laid on each other are created, the fibres 5 of each layer being perpendicular to the neighbouring layer.
Very effective drying or solidification of the fibres 5 and effective evaporation of a solvent, that is moreover not collected in vicinity of the collector 9, are also advantages of the rotating collector 9 with longitudinal electrodes 6. This has an essential influence on a diameter of the fibres 5 that are formed between electrodes 6 of the collector 9. Their diameter can be reduced by setting the parameters of the process.
In another advantageous embodiment of this apparatus the collector 9 is comprised of more than three conductive electrodes 6 that are arranged at regular spacing to each other and at the same from a common rotation axis x. The accumulator 7 has a shape of a disc and is provided with appropriate notches that enable sliding the accumulator onto the longitudinal electrodes 6 so that its movement along the rotation axis x and in the vicinity of these electrodes 6 may be enabled. During this movement, fibres 5, which were deposited in an orderly manner between adjacent electrodes 6, are placed spontaneously directly onto a surface of the accumulator 7, where stripes of new material are formed, which stripes are composed of uniaxial ordered fibres 5 with high degree of orientation.
Another advantageous embodiment comprises the cylindrical collector 9 composed of at least two longitudinal electrodes 6, generally of total number of N, where N is a natural number, parallelly arranged electrodes, the distance of which ranges from 0.1 mm to (π.d/N) mm, where d is double distance of electrodes 6 from the common rotation axis x. In the first limit case very thin conductive wires are used as the electrodes 6, in the second limit case the electrodes 6 form an integral conductive surface of the cylinder. In the first limit case fibres 5 are captured onto the very thin electrodes 6 and resulting material is composed of very well ordered fibres 5 only, the fibres having their diameter ranging from microfibres to nanofibres. In the second limit case fibres 5 are wiped off in the same way as above mentioned, whereas during the fibres 5 depositing a yarn or a filament is formed that is composed of multiple fibres 5 with a total length of π.d.
Finally in yet another advantageous embodiment of this apparatus the accumulator 7 has a shape of a dish for accumulating the collected layers 8 of fibres 5. The fibres 5 are compressed into the accumulating dish by means of a simple piston motion. Individual layers 8 are compacted in the dish and that way the ordered 3D structure is also mechanically strengthened. The dish serves for further treatment of the product, e.g. by imbedding fibres 5 with another solution, generally with another medium, a composite material of required properties is produced.
Hereinafter concrete exemplary embodiments of the apparatus according to the present invention will by described.
Fibres of 16% aqueous solution 1 of polyvinyl alcohol (PVA) were extruded from a jet emitter 2 through a spinning nozzle 3, and deposited onto a segmented collector 9 (
Fibres 5 of a diameter ranging from microfibres to nanofibres were deposited onto the rotating collector 9 with four longitudinal electrodes in the same way as mentioned in example 1. After stopping the spinning process and the rotating collector 9, the fibres 5 were wiped off by the accumulator 7 (
The present invention can be used for production of materials that are areal (2D) or voluminous (3D) from the macroscopic point of view, and which are composed of nanofibres or microfibres, whereas the internal fibrous structure of these materials is regular, ordered in one direction or in more directions.
| Number | Date | Country | Kind |
|---|---|---|---|
| PV 2011-376 | Jun 2011 | CZ | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/CZ2012/000055 | 6/22/2012 | WO | 00 | 3/19/2014 |
