Patent Grant
9745670
The present invention relates generally to the field of electrospinning. In particular, the invention relates to an electrospinning device that includes a fixture with an elongate aperture disposed between opposing elements of an electrically conductive material. These elements may include a variety of patterns and/or shapes that affect fluid flow through the aperture and electrical field across the aperture.
Electrospinning is a versatile technique for the production of small-diameter fibers of many natural and synthetic polymers. This includes biopolymers (DNA, gelatin), liquid crystalline polymers (polyaramid), textile fiber polymers (nylon) and electrically conducting polymers (polyaniline) etc. (J. of Macromolecular Science, 36(2): 169 (1997); J. of Biomedical Materials Research 72(1): 156 (20505); Nanotechnology 7(3): 216 (1996); Polymer 43(3): 775 (2002); Applied Physics Letters 83(20): 4244 (2003)). Electrospinning is a process in which ions are transferred to the gas phase by the application of a high electrical charge to a polymer solution in a liquid reservoir. Exposure of a small volume of electrically conductive liquid to an electric field causes the liquid to deform from the shape established by surface tension alone. As the voltage increases the force of the electric field approaches the surface tension of the liquid, resulting in the formation of a Taylor cone with convex sides and a rounded tip. When a threshold voltage is reached the slightly rounded tip of the cone inverts and emits a jet of liquid called a cone-jet or sheath-jet.
As the highly charged liquid jet stream travels in the air towards an electrically grounded collector it experiences bending and stretching effects due to charge repulsion and, in the process, becomes increasingly thinner. As the volatile solvent evaporates very fine polymer fibers, typically on the micro- or nano-scale, are collected on the grounded collector.
Current needle electrospinning techniques typically operate at flow rates between 1-10 mL/h, resulting in low throughput and deposition (i.e., polymer solidification). While slit-surface electrospinning offers a way to increase this output rate, this method tends to be unstable over longer periods of time and demonstrates meniscus growth. Thus, there is a need for a stable, high throughput slit-surface electrospinning process that provides longer run times and reduces meniscus formation.
In one aspect, the present invention relates to a slit-surface formed by two walls that have an S-wave pattern with matching wavelengths and amplitudes. In one embodiment, the inner and outer walls have an S-wave pattern that mirror each other. In one embodiment, the inner and outer walls have an S-wave pattern that mirror each other, and where the distance between the surfaces of the inner and outer walls is constant throughout their length.
In another aspect, the present invention relates to a slit-surface in which some, but not all, of the walls have an S-wave pattern. In one embodiment, the inner walls have an S-wave pattern while the outer walls are substantially straight. In another embodiment, outer walls have an S-wave pattern while the inner walls are substantially straight.
In another aspect, the present invention relates to a slit-surface in which the inner and outer walls have an S-wave or sinusoidal shape that are not mirror images of each other. In one embodiment, the pattern includes outer walls with an S-wave pattern having a higher frequency than the S-wave pattern of the inner walls. In one embodiment, the pattern includes inner walls with an S-wave pattern having a higher frequency that the S-wave pattern of the outer walls. In one embodiment, the inner and outer walls have and S-wave pattern that are aligned such that their wavelengths and amplitudes are matching.
In another aspect, the present invention relates to slit-surface patterns with non-curvy (i.e., non-sinusoidal) patterns. In one embodiment such patterns include, but are not limited to, hexagonal patterns, diamond patterns and the like.
In another aspect, the present invention relates to a slit-surface in which the pattern is applied to the top surface of the slit-fixture, while the inner and outer walls are substantially straight. In one embodiment, the pattern applied to the top surface is an S-wave pattern. In one embodiment, the top surface has an outwardly sloping apex. In one embodiment, the top surface has an inwardly sloping apex. In one embodiment, the top surface is concave. In one embodiment, the top surface is convex. In one embodiment, the top surface is patterned with protrusions or indentations that serve as auxiliary electrodes or enhances electric field strength.
In one aspect, the slit-surface pattern is not limited to linear shapes, but can include a closed loop such as a circle, square, triangle or the like.
In one aspect, the present invention relates to an electrospinning apparatus in which one slit-fixture (i.e., core-slit) is positioned within another slit-fixture (i.e., sheath-slit). It will be appreciated that any combination of the shapes/patterns described herein may be used for either (or both) of these fixtures.
In one aspect, the electrospinning devices for use with two or more different polymers that do not require the presence of a core-slit to generate core-sheath electrospun fibers. In one embodiment, feed tubes/needles deliver the core polymer solution directly into the emitted sheath jet. In one embodiment, feed lines/tubes deliver core polymer solution directly into the emitted sheath jet from a location underneath the sheath jet. In one embodiment, a patterned array of slit-surfaces individually feed the core polymer solution directly into each emitted sheath jet.
In one aspect, a variety of design features are available for diverting air flow away from the slit-surface, including for example the introduction of protrusions (i.e., wings) and increasing the thickness of the apex.
In one aspect, the present invention relates to a fixture (i.e., wiper) for removal of excess polymer solution that accumulates at the slit-surface due to meniscus growth and/or polymer solidification.
Non-limiting embodiments of the present invention will be described by way of example, with reference to the accompanying figures, which are schematic in nature and are not intended to be drawn to scale. In the figures, each identical or nearly identical component illustrated in typically represent by a single numeral. For purposes of clarity, not every component is labeled in every figure, nor is every component of each embodiment of the invention shown where illustration is not necessary to allow those of ordinary skill in the art to understand the invention. In the figures:
The present invention relates generally to the field of electrospinning. In particular, the invention relates to an electrospinning device that includes an electrically conductive vessel disposed between opposing elements having a variety of patterns and/or shapes that control the flow of fluids through the aperture and electrical field across the aperture.
While various aspects and embodiments of the present invention are described below, it should be understood that they are presented by way of illustration rather than limitation. The breadth and scope of the present invention is intended to cover all modifications and variations that come within the scope of the following claims are their equivalents.
The invention described herein discloses different types of patterned slit-fixtures to control the spatial and temporal emergence of electrospinning jets along a slit-surface. As used herein, the term “slit-fixture” refers to a fixture positioned on an electrospinning device through which polymer fluid exits, resulting in fiber(s). As used herein, the term “slit-surface” refers to the aperture (i.e., opening(s) or hole(s)) within a slit fixture through which the polymer fluid exits. Embodiments of the invention disclosed herein disclose a number of different designs that can be used for slit-surface electrospinning. Without being limiting to specific design features and/or methods of function, the embodiments described herein relate generally to the use of patterned fixtures to create slit-surfaces that establish (1) flow patterns or gradients and/or (2) non-uniform electric fields.
A major benefit of the patterned fixtures of the present invention is that they control the spatial and temporal emergence of electrospinning jets along the aperture surface. This provides at least two notable effects on the electrospinning process itself. First, the electrospinning jets are locally constrained, exhibiting little to no lateral movement as typically observed when using uniform straight slit-surfaces. Second, very little meniscus growth of the solution occurs along/within the aperture itself. The ability to direct (e.g., control) fluid flow while minimizing aperture occlusion due to polymer solidification (i.e., meniscus growth) provides enhanced electrospinning stability, allowing for longer continuous run times. As a result, the efficiency and productivity of slit-surface electrospinning is significantly increased.
In one embodiment of the invention, slit-fixture (10) includes a slit-surface (20) defined by inner and outer walls (30, 40) that form two wave-patterns which are mirror images of each other, as illustrated in
Slit-fixture (10) may be made of any suitable metal or conductive material known in the art and in other embodiments, may be coated with a thin layer of Teflon, lubricious polymer, or another non-stick material such as a hydrogel so as to minimize flow resistance. In other embodiments of the invention, the surface of the slit-fixture may be polished to be smooth or etched to be rough, or textured.
The relevant dimensions for the patterns and features of slit-surface (20) are shown in
In addition to the wave-like pattern described above, three other embodiments are shown in
The invention described herein is not limited to any particular shape. Aside from wave-like patterns described above, any geometric shape may be used as the replicating unit. Accordingly, it will be appreciated that inner and outer walls (30, 40) of slit-fixture (10) are not limited to wave-like or sinusoidal shapes. In other embodiments of the invention, the pattern(s) of inner and/or outer walls (30, 40) include linear features (i.e., defined by straight lines that intersect at angles relative to each other). For example, in one embodiment as shown in
In other embodiments, the wave-patterns on both the inner and outer walls (30, 40) are different. For example, as illustrated in
In yet other embodiments, the surface of slit-fixture (10) which faces the same direction as the flow of the polymer fiber being formed, hereinafter referred to as top surface (50) is patterned and may vary in shape, depth, and texture. For example, in one embodiment, as illustrated in
In other embodiments of the invention, the silt-fixture of the present invention is used to create fibers which are composed of two or more different polymers, with the core polymer concentrically contained within the other, sheath polymer. This can be achieved by placing one slit-fixture within the other, as shown in
In other embodiments, a core-slit is not needed to create polymer fibers composed of concentric, different polymers. For example, in some embodiments feed tubes or needles (80) deliver core polymer solution to the inside of an emerged electrospinning jet. This is possible due to the precise localization of electrospinning sheath jets (90), as shown in
In yet another embodiment, the slit-fixture is patterned with protrusions (100) as depicted in
In other embodiments of the invention, the patterned slit-surface (20) does not have to be linear, but can be a closed loop, such as a circle, square, triangle, etc. Similarly, slit-surfaces (20) can be branched, spiraled, or curved, as illustrated in
In other embodiments of the invention, the slit-surfaces (20) can slide or vibrate relative to each other during the electrospinning process. These mechanical movements may further assist in preventing solvent evaporation that contributes to meniscus formation. Alternatively, slit-fixtures (10) can be heated or cooled to control the temperature of the polymer solutions flowing through slit-surfaces (20).
In another embodiment, secondary element(s) having a variety of different shapes may be attached to slit-fixture (10), thus facilitating the creation of different patterns by simply removing and replacing the secondary element (
In other embodiments, design features may be included that mitigate the flow of air to the aperture of slit-surface (20) to minimize solvent evaporation. As shown in
In certain systems, electrospinning from a slit-surface results in large meniscus growth and/or the accretion of solid materials near sites of Taylor cone initiation. These in turn may compromise the morphology of the affected Taylor cones, reducing the efficiency of electrospinning. For continuous operation of such electrospinning processes, an automated fixture is used to wipe or otherwise remove the excess solution that accumulates at the slit due to the meniscus growth and/or solidification. An example of such a system is shown in
As compared to slit-surface electrospinning where the sheath-slit is not patterned, two significant effects were observed. First, there was no lateral movement of the electrospinning jets when the patterned slit was used; and second, there was no solution meniscus growth. The ability to eliminate both lateral movement and meniscus growth allows stable and continuous electrospinning to occur for greater than 10 minutes, which is equivalent to at least a five-fold increase relative to current baseline run time achieved on a straight-slit system. As shown in
While several embodiments of the present invention have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the functions and/or obtaining the results and/or advantages described herein. Each of such variations and/or modifications is deemed to be within the scope of the present invention. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials and/or configurations will depend upon the specific application or applications for which the teachings of the present invention is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, the invention may be practiced otherwise than as specifically described and claimed. The present invention is directed to each individual feature, system, article, material, kit and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits and or methods, if such features, systems, articles, materials, kits and/or methods are not mutually inconsistent, is included within the scope of the invention.
The indefinite articles “a” and “an,” as used herein, unless clearly indicated to the contrary, should be understood to mean “at least one.”
The phrase “and/or,” as used herein should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Other elements may optionally be present other than the elements specifically identified by the “and/or” clause, whether related or unrelated to those elements specifically identified unless clearly indicated to the contrary. Thus, as a non-limiting example, a reference to “A and/or B,” when used in conjunction with open-ended language such as “comprising” can refer, in one embodiment, to A without B (optionally including elements other than B); in another embodiment, to B without A (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.
As used herein, “or” should be understood to have the same meaning as “and/or” as defined above. For example, when separating items in a list, “or” or “and/or” shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, or a number or list of elements, and optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as “only one of,” or “exactly one of,” or when used in the claims, “consisting of,” will refer to the inclusion of exactly one element of a number or list of elements. In general, the term “or” as usped herein shall only be interpreted as indicating exclusive alternatives (i.e., “one or the other but not both”) when preceded by terms of exclusivity, such as “either,” “one of,” “only one of,” or “exactly one of.” “Consisting essentially of,” when used in the claims, shall have its ordinary meaning as used in the field.
As used herein, the phase “at least one,” in reference to a list or one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily indicating at least one of each and every element specifically listed within the list of elements and not excluding any combination of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase “at least one” refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, “at least one of A and B” (or, equivalently, “at least one of A or B,” or, equivalently “at least one of A and/or B”) can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc.
As used herein, the term “consists essentially of” means excluding other materials that contribute to function, unless otherwise defined herein. Nonetheless, such other materials may be present, collectively or individually, in trace amounts.
Reference throughout this specification to “one example,” “an example,” “one embodiment,” or “an embodiment,” means that a particular feature, structure, or characteristic described in connection with the example is included in at least one example of the present technology. Thus, occurrence of the phrases “in one example,” “in an example,” “one embodiment,” or “an embodiment” in various places throughout the specification are not necessarily all referring to the same example. Furthermore, the particular features, structures, routines, steps or characteristics may be combined in any suitable manner in one or more examples of the technology.
This application claims priority to and the benefit of U.S. Provisional Application Ser. No. 61/861,624, filed on Aug. 2, 2013, Titled (Patterned Slit Fixtures for High Throughput Split-Surface Electrospinning), herein incorporated by reference in its entirety.
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