FIBER HAVING NON-UNIFORM COMPOSITION AND METHOD FOR MAKING SAME

Abstract

A fiber having a non-uniform composition is disclosed. The fiber includes a first domain having a first composition and a second domain having a second composition different from the first composition. The fiber includes an interphase region intermediate the first and second domains that includes a blend of the first and second compositions to provide a gradual transition from the first domain composition to the second domain composition. A method for making such fibers is also disclosed.

Description

RELATED APPLICATION

This application claims priority to U.S. Provisional Application No. 61/178,649, filed May 15, 2009, which is incorporated by reference in its entirety.

FIELD

The present disclosure is generally directed to fibers and more particularly to fibers having compositional domains positioned within the fiber to provide a non-uniform composition.

BACKGROUND

Functional fibers are used for a variety of different applications across industries. In some cases the fibers are co-extruded bi-component fibers, while in many others the fibers are monofilaments subsequently overcoated by a cladding of a different material to impart or enhance functionality. Exemplary such materials include polypropylene fibers cladded with antibiotics sometimes used for internal sutures and microwires cladded with doped sheaths for use in solar energy applications.

Whether manufactured as a bi-component co-extruded device or a subsequently cladded filament, such fibers usually consist of two concentric polymer domains that oppose each other at an interface. There is, as a result, an abrupt change in composition between the domains of the two components. This in turn places limits on the functionality of the fibers and also the types of components that can be used to form such fibers.

These and other drawbacks are found in current fiber technologies.

It would be desirable to provide fibers and a method for making fibers in which multiple domains of differing compositions could be positioned adjacent one another to form a gradual transition between fiber components, thereby eliminating or ameliorating the effects of an abrupt transition between components at the interface.

It would also be desirable to provide fibers with multiple domains of differing compositions in which the number and arrangement of three or more components within the fiber can yield other advantages as a result of the spacing and positioning of the domains with respect to one another within the fiber architecture.

SUMMARY

In an embodiment of the present disclosure, a multi-component fiber is provided in which the components are arranged in at least three regions or domains. In some embodiments, the domains are arranged such that the fiber contains a radially gradient composition. In other embodiments, a multi-component fiber is provided having at least three annular domains in which the spacing and arrangement of the domains imparts a functionality to the fiber. Attributes of the embodiments may be combined with one another such that the gradient composition itself effects the functionality of the fiber.

In accordance with these embodiments, a multi-component fiber spinning process is used to produce a commingled interpenetrating placement of a plurality of components through microfluidic extrusion. The resultant commingled interpenetration defines an interphase, rather than an interface. The interphase creates a designed region that can produce gradient transition properties. The ability to create unique transitions provides the development of new architectures. In medical applications, for example, gradient transitions can be used to result in gradient erosion of the fiber.

In one embodiment, a fiber spinning apparatus having a four component spinning head is used with four different source components to provide domains having up to fifteen different compositions from the various commingling of the four source components.

An advantage is that a radially non-uniform composition can be achieved in the fiber.

Another advantage is that a gradient composition can result in transition properties not otherwise readily achievable, if at all, in fiber products.

Yet another advantage is that the compositional profile can further be varied through the introduction of three or more components into the fiber.

Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-section of a prior art bi-component fiber.

FIG. 2 shows a cross-section of a multi-component fiber having a gradient composition in accordance with an exemplary embodiment of the invention.

FIG. 3 schematically illustrates a partial cross-section of a multi-component fiber having a domain arrangement in accordance with another exemplary embodiment of the invention.

FIG. 4 shows an exemplary spinning apparatus for use in making fibers in accordance with exemplary embodiments of the invention.

FIG. 4a shows an exemplary distribution plate for use in the apparatus of FIG. 4.

FIGS. 5a and 5b schematically illustrate static mixing of fiber components in accordance with an exemplary embodiment of the invention.

FIG. 6 shows an image of a cross-section of a multi-component fiber in accordance with an exemplary embodiment having the domain arrangement illustrated in FIG. 3.

FIG. 7 shows the image of FIG. 6 under UV light.

FIGS. 8 and 9 show graphical representations of test results from the fiber shown in FIG. 6.

FIGS. 10 and 11 show graphical representations of test results from another fiber in accordance with an exemplary embodiment.

FIG. 12 shows an image of a cross-section of a multi-component fiber in accordance with an exemplary embodiment.

Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

DETAILED DESCRIPTION

FIG. 1 illustrates a cross-section of a prior art bi-component fiber 5 having a first, outer domain 100 (i.e., sheath) and a second, inner domain 200 (i.e. core) which meet at an interface 20.

FIG. 2 illustrates a cross-section of a multi-component fiber 10 in accordance with an exemplary embodiment of the invention. As illustrated, the fiber 10 has five annular domains 100, 110, 120, 130, 200, although as few as three and up to 15 or more may be provided. By “domain” is meant an identifiable region that can be distinguished from adjacent regions. Although described and illustrated herein with reference to a fiber and domains having a circular cross-sectional area, it will be appreciated that the teachings herein are not so limited and that the fiber and/or the domains contained therein may be of any desired cross-sectional geometry.

Unlike the prior art bi-component fiber 5, which has two discrete domains and a single interface resulting in an abrupt transition between the compositions of the two components that make up their respective domains, a multi-component fiber 10 of the present invention may provide a gradual compositional transition between two components to establish a gradient composition across one or more interphase regions 150. The interphase region 150 may be a series of closely spaced domains, to transition a change in composition across a radial distance, rather than an abrupt change as would be experienced at an interface. Thus, exemplary embodiments having a radially gradient composition have a composition that changes radially in a stepwise fashion across at least three domains.

In the illustrated embodiment, a core 200 and sheath 100 may each be a different component, such as those found in current bi-component fibers. A series of closely spaced intermediate domains 110, 120, 130 each comprise various combinations of the components used for the innermost and outermost domains (e.g., the core 200 and sheath 100). This allows a gradient to be established in a stepwise or smooth manner that permits a more gradual transition from the outer composition to the inner composition over a given radial distance. For example, if the inner-most domain (i.e. core) 200 has a composition of 100% of a component A and the outer-most domain (i.e. sheath) 100 has a composition of 100% of a component B, the intermediate domains may be arranged to provide, again by way of example, a domain 110 that is 67% B and 33% A, a domain 120 that is 50% B and 50% A and a domain 130 that is 33% B and 67% A (in which percentages are by weight percent). It will be appreciated that the innermost and outermost domains need not be 100% and that in certain embodiments, the domains illustrated in FIG. 2 as intermediate domain 110 and 130 could be the inner or outer most domain, respectively.

By modifying the composition gradually over a radial distance through the use of an interphase region 150, an abrupt change between the compositions of components A and B is avoided and one or more blended compositions of these components transition that change. This may permit materials to be incorporated together in a fiber that ordinarily could not be easily co-extruded with one another in a conventional bi-component fiber, such as polyethylene terephthalate and polypropylene, for example. The smoothness of the gradient may be modified by the number of intermediate domains provided within the interphase region 150 and the radial distance over which the intermediate domains 110, 120, 130 extend.

In one embodiment, each intermediate domain 110, 120, 130 of the interphase region 150 has a thickness (measured radially) in the range of about 0.25 to about 50 microns, with the interphase region 150 spanning a total radial distance in the range of about 0.25 to about 200 microns. The intermediate domains 110, 120, 130 may, independently, span a radial distance equal to or different from one another. Furthermore, the intermediate domains 110, 120, 130 typically, but do not necessarily, span a smaller radial distance than the core 200 and sheath 100.

Fibers according to certain embodiments may have a total diameter in the range as small as about 5 to about 40 microns, and in some cases may have a total diameter in the range about 10 to about 15 microns, while still achieving spatially resolvable domains. In other embodiments, the fiber may have a diameter as large as 300 microns or even up to 1000 microns depending upon the desired end use for which the fiber will be employed.

The compositions used in forming the core 200 and sheath 100, and the blends of those materials used to form the interphase region 150 can include any suitable polymeric or other extrudable material depending on the particular application for end use, including polypropylene and polyethylene, by way of example only. Further, it will be appreciated that the intermediate domains are not restricted to blends of the core and sheath components and that a third, fourth or greater number of independent components may be provided, for example, because of particular constituents which are desired to be embedded at various radial distances within the fiber.

The resultant interpenetration and commingling of components in forming the domains during fiber production may yield a fiber with final properties that are not achievable by the neat individual starting materials alone or in combination in a traditional bi-component fiber arrangement. Each component used in forming the core 200, sheath 100 and/or the intermediate domains 110, 120, 130 of the interphase region 150 may independently be a homopolymer, a co-polymer, or a blend of one or more polymers and may further include one or more additives, such as surfactants, functional additives, and/or any conventional additives used in fiber spinning that, for example, modify physical properties to aid in processing.

Surfactants may be provided as constituents in the compositions of the various components. For example, in some cases it may be desirable to further enhance the compatibility at the interface between domains of certain components, even where the compositional differences are less abrupt, which the use of surfactants can help achieve.

Functional additives which may be incorporated into various components of the fiber in accordance with exemplary embodiments may depend on the end use for which the fiber is to be employed. It will be appreciated that in certain embodiments, the distinction between various components used in forming the fiber may be in the amount and/or type of a particular additive. For example, a fiber may be formed from two components, each of which are polypropylene-based, but in which the first component is neat polypropylene having no additives and the second component includes polypropylene and a functional additive, such as a UV fluorescent with an interphase region to transition a core of the first component to a sheath of the second component and establish a transition in concentration of the fluorescent additive between these two domains.

The particular type of additive included in one or more of the fiber components and the loading of that additive in the component may depend upon the particular application for which the fiber is intended to be employed. Multi-component fibers having a gradient composition may be useful in crafting fiber architectures for many different end-use applications including, but not limited to, the controlled bioerosion of fibers in medical applications such as drug release, tissue engineering, and wound healing; smart fiber design (e.g. fibers containing materials that respond to chemistries of human activity, sensation or provide feedback response to environmental stimuli); optical waveguides; communications; applications involving the exchange of chemical and physical energy between domains such as polymeric continuous solar fiber solar collection devices, environmental sensors, geotextiles; bioremedial applications; agrochemical delivery; veterinary drug delivery and treatment; wound healing; bioengineering biomimetic tissue properties; friend or foe textiles; and food security, all by way of example only. Thus, the type of additives included with one or more components to be used within the fiber can vary widely and may include bioactive agents with chemistries such as extracellular matrix biopolymers and tissue specific growth factors; tissue specific angiogenetic factors; rational and bio-derived active pharmaceuticals; chemotherapeutic agents; antibiotics; local and/or systemic therapeutics; as well as minerals and other inorganic growth materials for tissue engineering, wound care, wound healing, and reconstructive procedures used in other types of medical practice.

The use of two distinct domains 100, 200 and an interphase region 150 as a transition can be integrated into a more complex fiber architecture having multiple different or alternating domains with multiple transition regions between them and need not be limited to a transition region between a sheath and a core. Turning to FIG. 3, an example of such an arrangement is schematically shown in which a four component fiber is formed having components A through D in a plurality of domains, in which certain domains contain a single component, with a blend of two or more components across a transition region between them.

In one embodiment, the four components are various blends of two polymeric based compositions. The components may thus be selected so that the fiber can be structured in such a way that an even smoother gradient is established between two discrete domains through an interpenetrating network of commingled fibrils during fiber formation. For example, a first component (A) could be 100% of the first composition, the second component (B) could be a 75/25 split of the first and second compositions, the third component (C) could be a 25/75 split, with the fourth component (D) being 100% by weight of the second composition. Thus, a domain provided as a blend of the first and second component (i.e., A+B) would result in a 87.5/12.5 split of the first and second compositions. In this manner, a gradient could be employed so that the amount of the second composition increases as the radial distance increases.

Alternatively, each of the components A-D may have compositions which do not include overlapping or a combination of compositions. In one embodiment, each component is a composition that contains a polymer having at least one independent property (e.g. functional, chemical or mechanical) different with respect to each of the other three. Still referring to FIG. 3, polymer A may be selected for having a pre-determined desired modulus, polymer B may be selected for having a pre-determined desired elongation, polymer C may be selected for having a pre-determined desired biological property and polymer D may be selected for having a pre-determined desired chemical activity. Through commingled placement of the four components to define a gradient (or multiple gradients as illustrated in FIG. 3) the combined properties may exceed the performance expectations of the individual materials extruded as traditional single or bi-component fibers.

It will be appreciated that in embodiments in which more than two components are provided, a gradient may still be established as a result of changes in relative weight and/or volume percentages between two or more components even if the weight percent of one or more other components does not change from one domain to the next.

The fabrication of multi-component fibers in accordance with exemplary embodiments of the invention may be performed using any suitable fiber spinning process and is preferably accomplished with a micro-extrusion fiber spinning process. In this type of process, a precision engineered die defines intended domains as nano-fiber regions (i.e., fibrils) that, when combined at the spinning head, anneal into one single fiber having any number of deliberately defined internal domains. Suitable devices and methods for co-extruding a filament of different components in a pre-determined spatial arrangement are described, for example, in U.S. Pat. Nos. 4,640,035; 5,162,074; 5,344,297; 5,466,410; 5,562,930; 5,551,588; and 6,861,142 and in WO 2007/134192, all of which are herein incorporated by reference in their entirety.

Preferably, the fiber spinning involves a high definition micro-extrusion process as described in WO 2007/134192. This process is a modification of fiber melt-flow spin extrusion adapted to produce a plurality of high definition geometric microstructures that are spatially resolved in cross-section. Spatial resolution may be obtained even in fibers having a diameter as low as about 5 to about 20 microns.

Referring to FIG. 4, a micro-extrusion apparatus 300 includes several extruder barrels 310 that intersect into a die head 320. Each barrel 310 delivers a single component for subsequent combination within the die head 320. The die head is configured such that up to four, or in some cases up to eight, different polymeric components enter a series of stacked distribution plates 330, together called a die-pack, in which the die plates have a series of predetermined openings and are oriented with respect to one another to achieve a predetermined cross-sectional architecture within the fiber. A unique die-pack may be provided for each different fiber architecture.

According to one embodiment, four barrels 310, each containing a different polymeric component, feed into the die pack. The die pack facilitates spatial resolution, in which the molten polymers traverse the die pack in a defined tortuous path through the series of distribution plates 330 that result in a combination of vertical and lateral movements of a component to position a particular component at a particular location within the cross-sectional area of the fiber to achieve a predetermined arrangement. There may be up to 64 stacked distribution plates 330 per resolved cross-section.

Each extruder barrel 310 can provide a single component to the die pack. As a result, in a four barrel extruder set up using four different components, there are 4 factorial (4!) possible static commingling combinations; however, as a result of repeat combinations a single cross-section can produce as many as 15 domains each having a different composition based on various blends of the four components.

As better seen in the underside view of a distribution plate 330 shown in FIG. 4a, each distribution plate 330 is a horizontal, lateral plane that consists of approximately 21,000 through-holes or microvias 337, which are arranged into approximately 5,250 four-hole, lateral channel-units 335. Each microvia 337 forms a corner of a single channel-unit 335, with each microvia 337 contributing one microfluidic channel to a center-point diagonal intersection of the included rectangle of the unit 335. The intersection mixing point then flows down vertically to another four-via arrangement in the next distribution plate 330 directly below. The extent of vertical downward flow may depend on the plate design.

Spatially resolved cross-sections and geometric designs are accomplished by appropriately redirecting each channel through the orientation and arrangement of the succeeding distribution plate 330. In some embodiments, the final plate in the stack, which may be referred to as a “gradient plate,” can be used to manage domain resolution.

The polymer components emerge as fibrils from the gradient plate in the commingled architecture as determined by the orientation of the distribution plates 330. The fibrils are coalesced while still molten to form a single fiber having the desired cross-sectional architecture as defined by the arrangement of the distribution plates 330 within the die pack. The formed fiber may then be wound, cut and/or spooled in accordance with well-known fiber winding techniques for subsequent use.

In some embodiments, it may be desirable to cause a further, more intimate mixing of the components after the desired architecture of the fibrils has been established through commingling, but prior to coalescing into a single fiber. In these embodiments, a series of mixing plates may be placed in a mixing stack 340 that is part of the die pack. The mixing plates may be used to statically mix two or more adjacent fibrils by splitting and recombining them multiple times. As schematically illustrated in FIG. 5a, the mixing plates combine two adjacent fibrils 510, 512 (having components 1 and 2) into a single flow channel 520, which is then split into two separate flow channels 522, 524 and recombined again. This process can be repeated several times through subsequent mixing plates to generate the desired combination of alternating components in the outgoing flow channel, as illustrated schematically in FIG. 5b after one, two and three mixes.

The ability to place fibrils of different composition next to one another provides a form of solid state mixing in which the fibrils are intermingled by their placement within the cross-sectional architecture of the fiber, and which may be further enhanced through the use of static mixing of those fibrils.

The proximity of fibrils of varying composition to one another presents the ability for the formation of interpenetrating networks, as fibrils of a first composition become commingled with fibrils of a second composition and a transition between domains is formed. Furthermore, surface energy characteristics of the various compositions of the fibrils when arranged in a commingled fashion to define the domains may result in a level of diffusion between those domains that further enhance the smoothness of the gradient across the radial distance of the fiber from one domain to the next.

In one embodiment, a fiber may be formed for medical and/or surgical applications that combines the enhanced strength found in certain medical grade fiber materials with the degradation characteristics found in biodegradable, but structurally weaker, fibers. By commingling such materials in an interpenetrating network of fibrils to form a fiber having a cross section as shown, for example, in FIG. 2 or 3, biodegradation and/or biodissolution can be managed across a gradient to achieve a high strength fiber that will biodegrade or dissolve within the body at a controlled rate.

Exemplary materials for use in such embodiments, include providing polypropylene or similar high strength material as the component for the core 200 and a degradable polymer for the sheath 100 such as polycaprolactone, poly-l-lactic acid, poly-d-lactic acid, polydioxanone, trimethylene carbonate, polyhydroxybutyrate, polyhydroxyvalerate, poly(FAD-SA), poly(CPP-SA), poly(FA-SA), poly(EAD-SA), poly glycolide, copolymers thereof, and combinations thereof. Varying combinations of the core and sheath materials may be provided as discrete intermediate domains of the interphase region 150 to form the gradient as discussed previously, for example, with respect to FIG. 2.

In another embodiment, different or additional materials and/or additives may be used to form medical fibers that can act as scaffolds for tissue engineering by, for example, incorporating medicaments and/or tissue growth promoters within certain intermediate domains. These materials are released or revealed over time as a biodegradable sheath erodes away toward those intermediate domains which contain gradually decreasing levels of biodegradable material and increasing levels of the tissue promoter. This can result in the grafting of cells to the fiber, resulting in its incorporation into surrounding tissue.

In still another embodiment, a conductive core is provided with p and n polymers commingled in alternating annular domains to form a fiber capable of collecting solar energy and converting and transferring that energy as an electrical charge. The conductive core can be used for electron/energy collection of the charge flow created between the alternating n and p domains separated by a gradient transition region in a manner similar to that of infusion of n and p type silicon used in conventional solar applications.

The conductive core can be created using conductive polymeric materials, either as neat conductive polymer or as an enhanced and/or doped conductive polymer with elements and/or molecular additives to facilitate conductivity. Exemplary organic conductive polymers include polyacetylenes, polypyroles, polythyophines, polyanalines, polythiophenes, poly p-phenylsulfide, poly(p-phenylene vinylene)s, polyindole, polypyrene, polycarbazole, polyazulene, polyazepine, polyfluorenes, and polynaphthalene. Certain undoped conjugated polymers, such as polythiophenes and polyacetylenes have a low electrical conductivity, but even at a low levels of doping (less than 1% by weight), electrical conductivity increases several orders of magnitude. In other embodiments, a conductive core can be produced by adding carbon black or metallic materials as additives to an otherwise non-conductive polymeric material, such as polyethylene.

The component used to form the n domain layer(s) can be any of the polymers used to form the conductive core containing micronized n-type dopants such as tin, germanium, silicon, phosphorous, arsenic, antimony, and elemental complexes, while the same polymer containing dopants such as boron, aluminum, or blue diamond, for example, can be used to form the component for the p domain layer(s). n-Type domains supply high levels of electron source while p-Type domains provide low electron density, such that a diffusion of electrons occurs from the region of high electron concentration (the n-type side of the junction) into the region of low electron concentration (p-type side of the junction); consequently, an n-to-p movement of electrons. The interdiffusion of the n and p domains to facilitate this movement and the generation of an electrical charge can be accomplished through the intermingling of fibrils of the n- and p-type components to form an interphase region that blends n and p type domains as previously described.

It will further be appreciated that the designs shown in FIGS. 2 and 3 are exemplary only and that any cross-sectional design in conjunction with any combination of two or more components employing an interphase transition region 150 between those two components can be used, which may depend on the particular use for which the fiber is to be employed.

EXAMPLES

The invention is further described by way of the following example, which is presented by way of illustration of the concepts described herein and is not intended to be limiting in any way.

In a first example, fibers having a cross-sectional diameter in the range of about 200 microns to about 250 microns were manufactured in accordance with the schematic cross-sectional design shown in FIG. 3 to provide gradual transitions from one phase to the next within the polymeric composition of the fiber. The fiber was comprised of four unique components designated as components A, B, C and D, each of which was fed from separate extruders into one spin head to produce a single fiber.

Component A was polypropylene that had been pre-blended with carbon black to provide a black appearance. Component B was polypropylene pre-blended with titanium dioxide and an organic UV fluorescing agent (Eastobrite OB1) to provide a white and UV responsive appearance. Component C was polypropylene pre-blended with carbon black and calcium carbonate, selected to provide a black appearance to contrast the white and UV response of component B. Component D was polypropylene pre-blended with titanium dioxide to provide a white appearance.

The sample fiber was melt spun at 230° C. using an apparatus as shown and described with respect to FIG. 4 without the using of the mixing plates in which the four components were separated into six single component domains, consistent with the schematic shown in FIG. 3. Gradual transitions were formed between each single component domains across an interphase region having three interphase domains by blending the components across the interphase domains of that separating the single component domains. The annular transitional domains of the interphase consisted of the component combinations as shown in FIG. 3. The fiber was collected and cross sectioned and examined analytically to verify the composition and determine whether the intended profile was achieved.

FIG. 6 is a magnified image of a cross-section of the sample fiber, while FIG. 7 is a magnified image of the experimental fiber taken under UV light to confirm the presence of component B. An Energy Dispersive Spectroscopy (EDS) spectrum of the fiber cross section was taken at 100× magnification on a Hitachi S-3000N SEM equipped with iXRF EDS. The sample was carbon coated in a coater supplied by Denton Vacuum to mitigate sample charging during mapping. A peak at 4.5 keV was measured, indicating the presence of titanium atoms and confirming the presence of components B & D.

FIG. 9 is an EDS map of a fiber cross section taken at 100× magnification, in which the dark spots indicate the presence of titanium. FIG. 8 represents a line scan of spectroscopic data measured horizontally across the EDS map shown in FIG. 9; the general bell shape of the spectrum is indicative of the gradient concentration of titanium.

A second example was prepared to produce a fiber in the same manner as in the previous example, except that mixing plates were incorporated into the die pack as shown in FIG. 4 to create a more intimate blend of polymers in the multi-component domains of the transition regions between the single-component domains. In the second example, the compositions of components A and B were switched (i.e., component A was polypropylene pre-blended with titanium dioxide and the organic UV fluorescing agent and component B was polypropylene that had been pre-blended with carbon black) to enhance the contrast in the studies.

This fiber was also collected and cross sectioned and examined analytically to verify the composition and determine whether the intended profile was achieved. FIGS. 10 and 11 illustrate an EDS map of the fiber cross section taken at 100× and 800× magnification, respectively. The dark spots within the map indicate the presence of the gradient distribution of titanium and confirmed that more intimate mixing was achieved. A magnified image of the cross-section of the fiber formed in the second example is shown in FIG. 12.

While the disclosure has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the essential scope thereof. Therefore, it is intended that the disclosure not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this disclosure, but that the disclosure will include all embodiments falling within the scope of the appended claims.

Claims

1. A fiber having a radially non-uniform composition comprising:

a first domain of a first composition;

a second domain of a second composition different from the first composition; and

an interphase region intermediate the first domain and the second domain, the interphase region comprising a blend of the first composition and the second composition.

2. The fiber of claim 1, wherein the first domain forms a fiber core and the second domain forms an annular sheath surrounding the core, the interphase region annularly disposed intermediate the core and the sheath.

3. The fiber of claim 1, wherein the interphase region has a thickness of about 0.25 microns to about 200 microns.

4. The fiber of claim 1, wherein the interphase region comprises a plurality of annular interphase domains in which each annular interphase domain has a weight ratio of the first composition to the second composition that is different from each domain directly adjacent thereto.

5. The fiber of claim 4, wherein each annular interphase domain has a thickness of about 0.25 microns to about 50 microns.

6. The fiber of claim 1, wherein the first composition and the second composition comprise different polymers.

7. The fiber of claim 1, wherein the first composition and the second composition comprise a same polymer.

8. The fiber of claim 1, further comprising a third composition different from each of the first and second compositions.

9. The fiber of claim 1 comprising a core forming an innermost domain, an annular sheath forming an outermost domain, a middle domain intermediate the core and the sheath, a first interphase region intermediate the core and the middle domain, and a second interphase region intermediate the middle domain and the sheath.

10. The fiber of claim 1, wherein the first or second composition comprises a material selected from the group consisting of polycaprolactone, poly-l-lactic acid, poly-d-lactic acid, polydioxanone, trimethylene carbonate, polyhydroxybutyrate, polyhydroxyvalerate, poly(FAD-SA), poly(CPP-SA), poly(FA-SA), poly(EAD-SA), poly glycolide, copolymers thereof, and combinations thereof.

11. The fiber of claim 1, wherein the first composition comprises a p-doped polymeric material and wherein the second composition comprises a n-doped polymeric material.

12. The fiber of claim 1 having a diameter in the range of between about 5 microns and about 300 microns.

13. The fiber of claim 1 having a diameter in the range of between about 5 microns and about 20 microns.

14. A fiber containing a radially gradient composition.

15. The fiber of claim 14, wherein the radially gradient composition is defined by a plurality of discrete domains in which the weight ratio of a first component to a second component in each domain increases as the radial distance increases.

16. The fiber of claim 14, wherein the radially gradient composition encompasses an interphase region of the fiber positioned intermediate a central core and a sheath of the fiber.

17. The fiber of claim 14, wherein the radially gradient composition comprises a biodegradable material selected from the group consisting of polycaprolactone, poly-l-lactic acid, poly-d-lactic acid, polydioxanone, trimethylene carbonate, polyhydroxybutyrate, polyhydroxyvalerate, poly(FAD-SA), poly(CPP-SA), poly(FA-SA), poly(EAD-SA), poly glycolide, copolymers thereof, and combinations thereof, wherein the amount of the biodegrable material in the fiber decreases along the radial distance from an outer surface to the center of the fiber.

18. A method comprising:

providing a first fiber component having a first composition and a second fiber component having a second composition different from the first composition;

extruding a plurality of fibrils from the fiber components;

commingling the fibrils in a predetermined architecture; and

coalescing the fibrils to form a fiber having a radially non-uniform composition having a first domain comprising the first component, a second domain comprising the second component, and an interphase region positioned intermediate the first and second domains and comprising a blend of the first and second components.

19. The method of claim 18, wherein the interphase region is formed having a thickness in the range of about 0.25 microns to about 50 microns.

20. The method of claim 18, wherein the interphase region comprises a plurality of annular domains.

21. The method of claim 18, further comprising after the step of commingling but before the step of coalescing, statically mixing the composition of at least two fibrils.