Surgery: splint – brace – or bandage – Bandage structure
Reexamination Certificate
2000-05-16
2004-06-22
Lucchesi, Nicholas D. (Department: 3764)
Surgery: splint, brace, or bandage
Bandage structure
C602S042000, C602S043000, C602S045000
Reexamination Certificate
active
06753454
ABSTRACT:
TECHNICAL FIELD
This invention relates to an article of manufacture comprising electrospun fibers. More particularly, this invention relates to composite nanofibers that can be produced by electrospinning polymeric matrix material. Even more particularly, this invention relates to a non-woven nanofiber composite that possesses improved qualities regarding strength, absorbency, and pH adjustability. This invention also relates to an apparatus for electrospinning the fibers. The apparatus of the present invention allows for the application of fibers to a specific target. The apparatus also allows for the application of fibers containing a wider range of potential performance enhancing additives than was previously believed possible.
BACKGROUND OF THE INVENTION
The technique of electrospinning, also known within the fiber forming industry as electrostatic spinning, of liquids and/or solutions capable of forming fibers, is well known and has been described in a number of patents as well as in the general literature.
The process of electrospinning generally involves the creation of an electrical field at the surface of a liquid. The resulting electrical forces create a jet of liquid which carries electrical charge. Thus, the liquid jets maybe attracted to other electrically charged objects at a suitable electrical potential. As the jet of liquid elongates and travels, it will harden and dry. The hardening and drying of the elongated jet of liquid may be caused by cooling of the liquid, i.e., where the liquid is normally a solid at room temperature; evaporation of a solvent, e.g., by dehydration, (physically induced hardening); or by a curing mechanism (chemically induced hardening). The produced fibers are collected on a suitably located, oppositely charged receiver and subsequently removed from it as needed, or directly applied to an oppositely charged generalized target area.
Fibers produced by this process have been used in a wide variety of applications, and are known, from U.S. Pat. Nos. 4,043,331 and 4,878,908, to be particularly useful in forming non-woven mats suitable for use in wound dressings. One of the major advantages of using electrospun fibers in wound dressings, is that very thin fibers can be produced having diameters, usually on the order of about 50 nanometers to about 25 microns, and more preferably, on the order of about 50 nanometers to about 5 microns. These fibers can be collected and formed into non-woven mats of any desired shape and thickness. It will be appreciated that, because of the very small diameter of the fibers, a mat with very small interstices and high surface area per unit mass, two characteristics that are important in determining the porosity of the mat, can be produced.
Wound dressings formed using non-woven mats of these polymeric fibers may provide particular benefits depending upon the type of polymer or polymers used. A wettable, or hydrophilic, polymer, such as, for example, a polyurethane may be used, or a non-wetting, or at least weakly hydrophobic, polymer such as, for example, a saturated polyester, may be employed. Where the dressing is formed from a wettable polymer, blood or serum escaping from the wound tends to penetrate the dressing and the high surface area encourages clotting. Such dressings could be used as emergency dressings to halt bleeding. On the other hand, where the dressing is formed from a non-wetting polymer, and if the interstices between the fibers are sufficiently small, i.e., on the order of less than about 100 microns, tissue fluids, including blood, tend not to permeate the dressing. Consequently, the fluids are retained adjacent to the wound where clotting will occur. Subsequent removal of such a dressing is facilitated by the absence of blood clots permeating the dressing material. Still further, U.S. Pat. Nos. 4,043,331 and 4,878,908 suggest that such dressings have the advantage that they are usually sufficiently porous to allow interchange of oxygen and water vapor between the atmosphere and the surface of the wound.
Besides providing variability as to the diameter of the fibers or the shape, thickness, or porosity of any non-woven mat produced therefrom, the ability to electrospin the fibers also allows for variability in the composition of the fibers, their density of deposition and their inherent strength. The above-identified U.S. patents indicate that it is also possible to post-treat the non-woven mats with other materials to modify their properties. For example, one could increase the strength of the mat using an appropriate binder or increase water resistance by post-treating the mat with silicone or other water-resistant material.
By varying the composition of the fibers being electrospun, it will be appreciated that fibers having different physical or chemical properties may be obtained. This can be accomplished either by spinning a liquid containing a plurality of components, each of which may contribute a desired characteristic to the finished product, or by simultaneously spinning, from multiple liquid sources, fibers of different compositions that are then simultaneously deposited to form a mat. The resulting mat, of course, would consist of intimately intermingled fibers of different material. A further alternative noted in the U.S. patents is to produce a mat having a plurality of layers of different fibers of different materials (or fibers of the same material but different characteristics, e.g. diameter), as by, for example, varying the type of fibers being deposited on the receiver over time. For example, wettable and non-wetting polymers each offer additional properties that may be desirable in different applications. Wettable polymers tend to be highly absorbant but are relatively weak, while non-wetting polymers tend to be non-absorbant but relatively strong. In some applications, such as medical dressings, for example, it may be desirable to use a combination of wettable and non-wetting polymer layers in a single article. In such an application, the wettable polymer layer or layers contribute a relatively high level of absorbency to the article while the non-wetting polymer layer or layers contribute a relatively high level of strength. Use of such a laminate-type structure, however, suffers from the disadvantage that the hydrophobic layer can form a barrier to liquids and interfere with the absorption of liquid by the wettable layer. Additionally, upon absorption of liquid, the wettable polymer layer will lose its three dimensional structure, and misalignment, slipping, or even separation of the layers may occur, resulting in failure of the integrity of the article.
Thus, U.S. Pat. Nos. 4,043,331 and 4,878,908 make it clear that strong, non- woven mats comprising a plurality of fibers of organic, namely polymeric, material produced by electrostatically spinning the fibers from a liquid consisting of the material or precursor thereof is known in the art. These fibers are collected on a suitably charged receiver and subsequently removed therefrom. The mats or linings then formed on the receiver can then be transferred and used in conjunction with other previously constructed components such as, for example, mats of woven fibers and backing layers to provide a wound dressing of desired characteristics. For instance, in producing wound dressings, additional supports or reinforcement such as mats or linings of woven fibers, or backing layers are required in order to adhere the wound dressing to the skin and to provide other desirable properties to the wound dressing. As an example, a mat or lining of woven fibers may contain materials having antiseptic or wound-healing properties. Surface treatments of the already formed non-woven mats may also provide added benefits in the production of such wound dressings.
It has also been described in PCT Application No. WO 98/03267 to electrostatically spin a wound dressing in place over a wound. In such a use, the body itself is grounded and acts as a collector of the electrospun fibers. This method of synthesizing a wound dressing allows for
McManus Albert T.
Mello Charlene
Reneker Darrell H.
Schreuder-Gibson Heidi L.
Sennett Michael S.
Hamilton Lalita M
Lucchesi Nicholas D.
Roetzel & Andress
The University of Akron
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