Processing of oriented polyethylene above its melting point.

Abstract

A method for processing expanded polyethylene (ePE), comprising: placing an ePE substrate on a heating component, wherein the ePE substrate has a first size when heated on the heating component; removing the ePE substrate from the heating component such that the ePE substrate cools and shrinks to a second size, wherein the second size is smaller than the first size; and forming the ePE substrate into an ePE article.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of Provisional Application No. 63 / 433,114, filed December 16, 2022, the entire contents of which are incorporated herein by reference for all purposes.

[0002] Field The present disclosure relates generally to apparatus, systems, and methods for processing expanded polyethylene (ePE), and more particularly, to apparatus, systems, and methods involving processing expanded polyethylene (ePE) usable in medical devices. [Background technology]

[0003] background The method used to process a material is important because it can impart certain properties to the processed material. A particular property may be necessary for the processed material to function for its intended purpose or may enable the processed material to find new uses. The selection of processing methods is important in a variety of industries, including, but not limited to, the medical device industry, particularly implantable medical devices. However, processed materials may be used in a variety of industries, and properties desirable in one industry may also be important in another.

[0004] Medical devices are often required to be adaptable to a patient's needs. For example, an implantable device made from engineered materials may need to fit within the length or diameter of a patient's lumen. However, it is costly to manufacture and store implantable devices of various sizes in small increments. Implantable devices are only offered in sizes at specific intervals determined by average sizes and may be used based on the best fit. However, the best fit does not necessarily mean the best fit. Furthermore, the diameter of a lumen may vary along the length of a patient's lumen, and therefore, it may be difficult to determine the appropriate size of an implantable device. What is needed is a material useful for providing a medical device that can provide optimal fit when implanted. Summary of the Invention

[0005] Abstract The present disclosure relates to methods for processing ePE and articles produced by such methods. For example, the methods and articles produced by such methods include exposing the ePE to temperatures above its melting point or melting temperature during processing, where the ePE exhibits desirable properties, such as diameter controllability, improved adhesion to metals, improved adhesion to other polyethylenes, length memory, expansion ability, and abrasion resistance.

[0006] According to one example ("Example 1"), a method for processing expanded (expanded, expanded, stretched, or foamed) polyethylene (ePE) includes placing an ePE substrate having a first size on a heating element, heating the ePE substrate on the heating element, removing the ePE substrate from the heating element such that the ePE substrate cools and shrinks to a second size, where the second size is smaller than the first size, and forming the ePE substrate into an ePE article.

[0007] According to another example ("Example 2"), further to Example 1, forming the ePE substrate into the ePE article includes winding the ePE substrate onto a mandrel.

[0008] According to another example ("Example 3"), further to Example 2, forming the ePE substrate into the ePE article includes melt-bonding the ePE substrate to itself along a longitudinal line.

[0009] According to another example ("Example 4"), further to Example 1, disposing the ePE substrate on the heating component includes providing the ePE substrate as a sheet of ePE.

[0010] According to another example ("Example 5"), in addition to Example 1, heating the ePE substrate on the heating element includes heating the heating element to about 110°C to 180°C.

[0011] According to another example ("Example 6"), in addition to Example 1, the method includes adhering the ePE article to metal.

[0012] According to another example ("Example 7"), in addition to Example 1, the method further includes adhering the ePE article to another polyethylene structure.

[0013] According to another example ("Example 8"), in addition to Example 1, the method further includes expanding at least a portion of the ePE article.

[0014] According to another example ("Example 9"), further to Example 8, expanding at least a portion of the ePE article includes radial expansion.

[0015] According to another example ("Example 10"), further to Example 8, expanding at least a portion of the ePE article includes longitudinal expansion.

[0016] According to one example ("Example 11"), a method for processing expanded polyethylene (ePE) includes heating an ePE substrate having a first size to a temperature above the melting temperature of the ePE, cooling the ePE substrate, wherein the ePE substrate shrinks to a second size upon cooling, the second size being smaller than the first size, and forming the ePE substrate into an ePE article.

[0017] According to another example ("Example 12"), in addition to Example 11, the ePE substrate is heated to about 110°C to 180°C.

[0018] According to another example ("Example 13"), in addition to Example 11, the method further includes expanding at least a portion of the ePE article.

[0019] According to another example ("Example 14"), in addition to Example 13, expanding at least a portion of the ePE article is performed at room temperature.

[0020] According to one example ("Example 15"), an ePE article made from expanded polyethylene (ePE) includes an ePE substrate molded into an ePE article, wherein the ePE article is formed by shrinking an ePE sheet by a method of heating and cooling, and the ePE article is expandable.

[0021] According to another example ("Example 16"), in addition to Example 15, the ePE substrate is formed into a graft.

[0022] According to another example ("Example 17"), in addition to Example 15, the ePE substrate is formed into the ePE article using a mandrel.

[0023] According to another example ("Example 18"), in addition to Example 15, the ePE article is longitudinally expandable.

[0024] According to another example ("Example 19"), further to Example 15, the ePE article is radially expandable.

[0025] According to another example ("Example 20"), in addition to Example 15, the ePE article is porous.

[0026] The above-described embodiments are merely embodiments and should not be construed as limiting or narrowing the scope of the inventive concepts otherwise provided by this disclosure. While multiple embodiments are disclosed, other embodiments will become more apparent to those skilled in the art from the following detailed description, which shows and describes illustrative embodiments. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive. [Brief explanation of the drawings]

[0027] BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings are included to provide a further understanding of the present disclosure, and are incorporated in and constitute a part of this specification, illustrating embodiments and, together with the specification, serve to explain the principles of the disclosure.

[0028] [Figure 1] FIG. 1 is a block diagram of a method for processing expanded polyethylene (ePE) including placement, removal, and molding steps according to some embodiments.

[0029] [Figure 2] FIG. 2 is a block diagram of a method for processing the expanded polyethylene (ePE) of FIG. 1, according to some embodiments, further including an expansion step.

[0030] [Figure 3] FIG. 3 is a block diagram of a method for processing expanded polyethylene (ePE) including heating, cooling, and forming steps, according to some embodiments.

[0031] [Figure 4] FIG. 4 is a block diagram of a method of processing the expanded polyethylene (ePE) of FIG. 3, according to some embodiments, further including an expansion step.

[0032] [Figure 5]FIG. 5 shows an example of a tubular article being formed from an ePE sheet, according to some embodiments.

[0033] [Figure 6] FIG. 6 shows an example of a flat article being formed from an ePE sheet, according to some embodiments.

[0034] [Figure 7] FIG. 7 illustrates an embodiment in which the tubular article of FIG. 5 is expanded to an intermediate size, according to some embodiments.

[0035] [Figure 8] FIG. 8 illustrates an embodiment in which the flat article of FIG. 6 is inflated to an intermediate size, according to some embodiments.

[0036] [Figure 9] FIG. 9A shows the microstructure of the ePE substrate of Example 1 processed above the melting temperature. [Figure 9] FIG. 9B shows the microstructure of the ePE substrate of Example 1 processed above the melting temperature.

[0037] [Figure 10] FIG. 10 shows the thickness data for the ePE substrates of Examples 1 and 2.

[0038] [Figure 11] FIG. 11 shows the bubble point data for the ePE substrates of Examples 1 and 2.

[0039] [Figure 12] FIG. 12 shows the air leakage data for the ePE substrates of Examples 1 and 2.

[0040] [Figure 13] FIG. 13 shows the peel data for the ePE substrate of Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0041] Detailed Description Definitions and Terminology The present disclosure should not be construed in a limiting sense. For example, the terms used in this application should be interpreted broadly in accordance with the meaning that one of ordinary skill in the art would assign to such terms.

[0042] With respect to terms related to imprecision, the terms "about" and "approximately" can be used interchangeably to refer to measurements that include the stated measurement and measurements that are reasonably close to the stated measurement. A measurement that is reasonably close to the stated measurement deviates from the stated measurement by a reasonably small amount, as understood and easily ascertained by one of ordinary skill in the relevant art. Such deviations can result from, for example, measurement error, differences in calibration of measuring and / or manufacturing equipment, human error in reading and / or setting measurements, slight adjustments made to optimize performance and / or structural parameters to account for variations in measurements associated with other components, specific implementation scenarios, imprecise adjustment and / or manipulation of objects by humans or machines, and / or the like. In cases where it is determined that the value of such relatively small differences would not be readily ascertained by one of ordinary skill in the relevant art, the terms "about" and "approximately" should be understood to mean plus or minus 10% of the stated value.

[0043] The term "laminate," as used herein, refers to a film, composite, or multiple layers of other materials, such as, but not limited to, polymers, such as, but not limited to, elastomers, elastomeric or non-elastomeric materials, and combinations thereof.

[0044] The term "film," as used herein, refers generically to one or more of a membrane, a composite, or a laminate.

[0045] The term "biocompatible material," as used herein, refers generally to any material that has biocompatible properties, including, but not limited to, synthetic materials such as biocompatible polymers, or biological materials such as, but not limited to, bovine pericardium. The biocompatible material can include a first film and a second film, as described herein in various embodiments.

[0046] The term "polyethylene" (PE), as used herein, includes all types of polyethylene, including but not limited to oriented polyethylene (ePE).

[0047] Description of Various Embodiments Those skilled in the art will readily appreciate that the various aspects of the present disclosure may be implemented by any number of methods and apparatus configured to perform the intended functions. It should also be noted that the accompanying drawings referred to herein are not necessarily drawn to scale and may be exaggerated to illustrate various aspects of the present disclosure, and in that regard, the drawings should not be construed as limiting.

[0048] The methods illustrated in Figures 1 and 2 are provided as examples of various features of the present methods, and while combinations of these illustrated features are clearly within the scope of the present invention, the embodiments and their illustrations are not intended to limit the inventive concepts provided herein from fewer features, additional features, or alternative features to one or more features illustrated in Figures 3 and 4. For example, in various embodiments, the process steps of Figures 1 and 2 can include process steps described with reference to Figures 3 and 4. It should also be understood that the reverse is true. One or more components illustrated in Figures 3 and 4 can be used in addition to or as a substitute for the components illustrated in Figures 1 and 2. For example, the method steps illustrated in Figures 3 and 4 can be used in conjunction with the method steps illustrated in Figures 1 and 2.

[0049] FIG. 1 is a block diagram of a method 100 for processing expanded polyethylene (ePE) according to some embodiments. Method 100 can be implemented in a variety of contexts, including medical devices, including, but not limited to, implantable medical devices. Various forms of ePE can be implemented in the method, including, but not limited to, membranes, films, tapes, tubes, etc. It is further understood that ePE can have a variety of properties, including different thicknesses, fibril and node structures, porosity, density, etc. Thus, the embodiments described herein should not be limited to any particular initial condition or morphology, but rather are broadly understood to incorporate any ePE starting material suitable for the described method.

[0050] In some embodiments, a method 100 of processing ePE includes placing 110 an ePE substrate on a heating component, removing 120 the ePE substrate from the heating component, and forming 130 the ePE substrate into an ePE article.

[0051] In some embodiments, when an ePE substrate is placed on a heating element, such as heating elements 510 and 610 shown in FIGS. 5-6, heat is transferred from the heating element to the ePE substrate, thereby heating the ePE substrate. While not limited to these embodiments, heating elements can include presses, heating pads, ovens, and the like. The heating element can be provided at a variety of temperatures, including, but not limited to, temperatures above the melting temperature of the ePE. For example, the heating element can be provided at temperatures ranging from about 110°C to about 180°C. In some embodiments, the heating element can be provided at temperatures ranging from about 110°C to about 120°C, about 120°C to about 130°C, about 130°C to about 140°C, about 140°C to about 150°C, about 150°C to about 160°C, about 160°C to about 170°C, or about 170°C to about 180°C. The heating component can be provided at any suitable temperature before placing the ePE substrate on the heating component 110, or the heating component can be heated to a suitable temperature after placing the ePE substrate on the heating component 110. In some embodiments, when the ePE substrate is placed on the heating component 110 and the heating component is at or above the melting temperature of the ePE, the ePE substrate can be heated on the heating component to a temperature above the melting temperature of the ePE. In some embodiments, the ePE substrate is heated without being constrained. In other embodiments, the ePE substrate can be constrained in the X direction (e.g., horizontally), the Y direction (e.g., longitudinally), or both the X and Y directions. In some embodiments, placing the ePE substrate on the heating component 110 can also include providing the ePE substrate as an ePE sheet. The ePE sheet has a first size when the ePE substrate is heated on the heating component. The ePE sheet can be provided as a square, rectangular, or other shape. In one embodiment, the ePE sheet is square (see FIG. 5), and the first size may be defined by a first dimension L1 (see FIG. 5).

[0052] With continued reference to FIG. 1 , the method further includes removing the ePE substrate from the heating component 120. For example, the ePE substrate is removed from the heating component after a predetermined time, after a target ePE substrate temperature has been reached, or when a desired material property has been achieved. In removing the ePE substrate from the heating component 120, the ePE substrate is removed from the heating component so that it cools. The ePE substrate can be cooled at room temperature, placed in an environment below room temperature (e.g., a freezer), or slowly cooled in an environment above room temperature. In some embodiments, the environment in which the ePE substrate is cooled can be at a steady temperature or can be at a variable temperature. In some embodiments, the variable temperature of the environment can allow the ePE substrate to cool at a controlled rate. The cooling rate of the ePE substrate can be constant or variable.

[0053] As the ePE substrate cools, it shrinks to a second size. The second size may be smaller than the first size. Continuing with embodiments in which the ePE sheet is a square sheet (e.g., as shown in FIG. 5), the second size may be defined by a second dimension L2 (see FIG. 5). The second dimension L2 (FIG. 5) may be smaller than the first dimension L1 (FIG. 5). While reference is made here to the embodiment of FIG. 5, a rectangular ePE sheet (e.g., as shown in FIG. 6) may undergo a similar process and experience similar dimensional changes upon cooling. The rectangular ePE sheet embodiment will be further described with reference to FIG. 6. It will be appreciated that when the ePE substrate is cooled so that the ePE is below a predetermined temperature, the shrinkage of the ePE substrate stops and the size of the ePE substrate stabilizes. In some embodiments, the predetermined temperature may be the melting temperature of the ePE substrate. The predetermined temperature may depend, at least in part, on the type of ePE used (e.g., oriented low molecular weight polyethylene or oriented high molecular weight polyethylene). Upon cooling, the ePE substrate can expand or swell at temperatures substantially below its melting temperature (e.g., room temperature). The ePE substrate may still be able to expand or swell at temperatures above its melting temperature.

[0054] It is understood that when the ePE substrate shrinks during the cooling process, it may be imparted with certain material properties that may be desirable in certain circumstances. For example, the cooled and shrunk ePE substrate may be capable of selective expansion or distension, better adhesion to secondary structures such as metals, PE, or other polymers, preserved length in the ePE substrate, expansion at yield, etc. Similar properties may be imparted when the ePE substrate expands or distends after cooling.

[0055] With continued reference to FIG. 1 , after removing 120 the ePE substrate from the heating element, the ePE substrate is formed into an ePE article. Forming 130 the ePE substrate into an ePE article can result in, for example, forming ePE article 540 of FIGS. 5-6 or forming ePE article 620. Forming 130 the ePE substrate into an ePE article can occur at an elevated temperature that is equal to or less than the temperature of the heating element. In some embodiments, the ePE article can be formed into a tubular article (e.g., tubular article 540 of FIG. 5 ), a flat article (e.g., flat articles 620, 630, 640, or 650 of FIG. 6 ), a film, or a laminate made from multiple layers of processed ePE. Other articles are also contemplated. In medical applications, the tubular article can be a graft, and the flat article can be a hernia patch, a cardiovascular patch, a nerve membrane, or the like.

[0056] In some embodiments, forming 130 the ePE substrate into an ePE article can further include winding the ePE substrate onto a mandrel (e.g., mandrel 530 in FIG. 5 ). This can form the ePE substrate into a tubular article (e.g., tubular article 540 in FIG. 5 ). In addition to this embodiment, forming 130 the ePE substrate into an ePE article can further include bonding or attaching the ePE substrate to itself (e.g., bonding with an adhesive, fusion bonding, or mechanically attaching with sutures). In one embodiment, the ePE substrate is bonded or attached to itself along a longitudinal line (e.g., longitudinal fusion bond line 535 in FIG. 5 ). In other embodiments, the ePE substrate is bonded or attached to itself along a horizontal line, a diagonal line, in a zone, etc. The ePE sheet can be bonded or attached to itself as the ePE is wound onto the mandrel.

[0057] In some embodiments, the method of fabricating ePE 100 can further include bonding the ePE article to a metal or metal substructure. Bonding the ePE article to a metal or metal substructure can occur simultaneously with or after forming the ePE substrate into the ePE article 130. Metal or metal substructures can include stents, occluders, shunts, valve frames, and the like.

[0058] In some embodiments, the method 100 for fabricating ePE can further include bonding the ePE article to a polyethylene or polyethylene sub-structure. Bonding the ePE article to the polyethylene or polyethylene sub-structure can occur simultaneously with or after forming the ePE substrate into the ePE article 130. The polyethylene or polyethylene sub-structure can include a graft, a valve leaflet, or the like.

[0059] Additionally, in some embodiments, the method 100 for fabricating ePE can further include adhering the ePE article to a polymer or polymer substructure. The polymer can include polytetrafluoroethylene (PTFE), including, but not limited to, expanded polytetrafluoroethylene (ePTFE). Other types of polymers are also contemplated.

[0060] 2, a block diagram of a method 200 for processing expanded polyethylene (ePE) is shown, according to some embodiments. Method 200 can be implemented in a variety of contexts, including medical devices, which can include, but are not limited to, implantable medical devices.

[0061] The method 200 for processing ePE includes placing an ePE substrate on a heating component 210, removing the ePE substrate from the heating component 220, forming the ePE substrate into an ePE article 230, and expanding at least a portion of the ePE article 240.

[0062] Method step 210 of placing the ePE substrate on a heating component can be substantially similar to placing the ePE substrate on a heating component 110 as described above with respect to Figure 1. The heating component can be, for example, heating components 510, 610 as shown in Figures 5-6. Method step 220 of removing the ePE substrate from the heating component can be substantially similar to removing the ePE substrate from the heating component 120 as described above with respect to Figure 1. Method step 230 of forming the ePE substrate into an ePE article can be substantially similar to forming the ePE substrate into an ePE article 130 as described above with respect to Figure 1. Forming the ePE substrate into an ePE article can include, for example, ePE article 540 and / or ePE article 620 of Figures 5-6.

[0063] In some embodiments, after the ePE substrate has been shrunk, heat and / or pressure can be applied to the ePE substrate to limit the amount of expansion it can undergo, allowing the ePE substrate to have a fixed or specified amount of expansion, thereby controlling the size of ePE articles formed from the ePE substrate.

[0064] When the ePE substrate is formed into an ePE article 230, the ePE article can expand. In some embodiments, the expansion 240 of at least a portion of the ePE article occurs at least at one location on the ePE article. In other embodiments, the expansion 240 of at least a portion of the ePE article can occur throughout the entire ePE article. In some embodiments, when the ePE article is in a second size, the expansion 240 of at least a portion of the ePE article can cause the ePE article to expand back to the first size. In some embodiments, when the ePE article is in a second size, the expansion 240 of at least a portion of the ePE article can cause the ePE article to expand to an intermediate size between the first and second sizes. In some embodiments, the intermediate size can include an intermediate diameter, such as the intermediate diameter DI in FIG. 7. In some embodiments, the intermediate size can also include an intermediate length, such as XI and YI in FIG. 8. In other embodiments, the intermediate size can include both an intermediate diameter and an intermediate length, such as the intermediate diameter DI and intermediate length HI in FIG. 7.

[0065] In some embodiments, expanding 240 at least a portion of the ePE article comprises radial expansion. In some embodiments, expanding 240 at least a portion of the ePE article comprises one or both of longitudinal expansion and horizontal expansion. Longitudinal expansion can be in the Y direction. Horizontal expansion can be in the X direction. In some embodiments, expanding 240 at least a portion of the ePE article comprises radial expansion and one or both of longitudinal expansion and horizontal expansion. Other embodiments are contemplated in which expansion of at least a portion of the ePE article occurs along a diagonal or other non-linear direction.

[0066] In some embodiments, inflating 240 at least a portion of the ePE article can be performed while the ePE article is at room temperature (e.g., about 25°C to 30°C). In some embodiments, inflation can be performed using a balloon (e.g., an angioplasty balloon). In some embodiments, the amount of inflation of the ePE article is limited so that balloon inflation occurs to a predetermined ePE article size. In some embodiments, inflating 240 at least a portion of the ePE article is performed by the ePE article manufacturer. In some embodiments, inflating 240 at least a portion of the ePE article can be performed by a user or a third party other than the manufacturer. In some embodiments, inflation of the ePE article 240 is performed by a physician before, during, or after a surgical procedure.

[0067] Figure 3 is a block diagram of a method 300 for processing expanded polyethylene (ePE), according to some embodiments. In some embodiments, the method of Figure 3 can be similar to the method of Figure 1. Method 300 can be implemented in a variety of contexts, including medical devices, including, but not limited to, implantable medical devices.

[0068] The method 300 of processing ePE can include heating 310 an ePE substrate to a temperature above the melting temperature of the ePE, cooling 320 the ePE substrate, and forming 330 the ePE substrate into an ePE article.

[0069] Heating the ePE substrate to a temperature above the melting temperature of the ePE (310) is accomplished using a heat source. The heat source can be similar to the heating element described above with respect to FIG. 1. The heat source can be provided at a variety of temperatures, including, but not limited to, temperatures above the melting temperature of the ePE. For example, the heat source temperature can be provided at about 110°C to about 180°C. In some embodiments, the heat source is provided at temperatures of about 110°C to about 120°C, about 120°C to about 130°C, about 130°C to about 140°C, about 140°C to about 150°C, about 150°C to about 160°C, about 160°C to about 170°C, and about 170°C to about 180°C. Heat sources can include, but are not limited to, a press, a heating pad, an oven, and the like. In some embodiments, for example, the heat source can be similar to the heating elements 510, 610 shown in FIGS. 5-6. In other embodiments, the heat source can be an indirect heat source, such as an environment set to a target temperature to heat the ePE substrate.

[0070] In some embodiments, heating the ePE substrate to a temperature above the melting temperature of the ePE 310 can be performed when the ePE substrate is unconstrained. When unconstrained, the ePE substrate may shrink or collapse upon heating. In other embodiments, the ePE substrate may be constrained in the X direction (e.g., horizontally), the Y direction (e.g., longitudinally), or both the X and Y directions. The ePE substrate may be fully or partially constrained in either the X or Y direction. When the ePE substrate is constrained, shrinkage or collapse in the constrained direction may be limited or prevented. When the ePE substrate is heated to a temperature above the melting temperature of the ePE, the ePE substrate has a first size.

[0071] With continued reference to FIG. 3 , the method 300 for processing ePE further includes cooling the ePE substrate 320. Cooling the ePE substrate can be accomplished by removing the ePE from the heat source. For example, the ePE substrate can be removed from the heat source to cool the ePE substrate after a specified time, after a target ePE substrate temperature has been reached, or after desired material properties have been achieved. The ePE substrate can be cooled at room temperature, placed in an environment below room temperature (e.g., a freezer), or slowly cooled in an environment above room temperature. In some embodiments, the environment in which the ePE substrate is cooled can be at a stable temperature or a variable temperature. In some embodiments, varying the temperature of the environment can allow the ePE substrate to cool at a controlled rate. The cooling rate of the ePE substrate can be constant or variable. Upon cooling, the ePE shrinks to a second size. The second size can be smaller than the first size. It is understood that once the ePE substrate has cooled to a predetermined temperature or below, the shrinkage of the ePE substrate stops and the size of the ePE substrate stabilizes. The predetermined temperature can be the melting temperature of the ePE substrate. It is understood that as the ePE substrate shrinks during the cooling process, it acquires certain material properties that may be desirable in certain situations. For example, the cooled, shrunken ePE substrate can have selective expansion, better adhesion to secondary structures such as metals, PE, or other polymers, a retained length in the ePE substrate, expansion at yield, and the like. In some embodiments, the predetermined temperature can be the melting temperature of the ePE substrate. The predetermined temperature can depend at least in part on the type of ePE used (e.g., low-molecular-weight stretched polyethylene or high-molecular-weight stretched polyethylene). Upon cooling, the ePE substrate can expand or swell at temperatures substantially below its melting temperature (e.g., room temperature). The ePE substrate may still be able to expand or swell at temperatures above its melting temperature.

[0072] With continued reference to FIG. 3 , after the ePE substrate is cooled, an ePE article can be formed from the ePE substrate. In some embodiments, an ePE article can be formed from the ePE substrate of a second size. Forming 330 the ePE substrate into an ePE article can be performed at an elevated temperature below the temperature of the heat source. In some embodiments, the ePE article can be formed into a tubular article (e.g., tubular article 540 of FIG. 5 ), a flat article (e.g., flat articles 620, 630, 640, or 650 of FIG. 6 ), a film, or a laminate consisting of multiple layers of processed ePE. Other articles are also contemplated. In medical applications, the tubular article can be a graft, and the flat article can be a hernia patch, a cardiovascular patch, a nerve membrane, etc.

[0073] In some embodiments, forming the ePE substrate into an ePE article 330 can further include winding the ePE substrate onto a mandrel (e.g., mandrel 530 in FIG. 5 ). This can form the ePE substrate into a tubular article (e.g., tubular article 540 in FIG. 5 ). In addition to this embodiment, forming the ePE substrate into an ePE article 130 can further include bonding or attaching the ePE substrate to itself (e.g., bonding with an adhesive, fusion bonding, or mechanically bonding with sutures). In one embodiment, the bonding or attachment of the ePE substrate to itself can occur along a longitudinal line (e.g., longitudinal fusion bond line 535 in FIG. 5 ). Other embodiments are contemplated in which the bonding or attachment of the ePE substrate to itself occurs along a horizontal line, a diagonal line, etc. The bonding or attachment of the ePE substrate to itself can occur as the ePE is wound onto the mandrel.

[0074] Referring now to Figure 4, a block diagram of a method 400 for processing expanded polyethylene (ePE) is provided, according to some embodiments. In some embodiments, the process of Figure 4 can be similar to the process of Figure 3. The method 400 for processing ePE can be implemented in a variety of contexts, including medical devices, which can include, but are not limited to, implantable medical devices.

[0075] The method 400 of processing ePE includes multiple method steps, which can include heating an ePE substrate to a temperature above the melting temperature of the ePE, cooling the ePE substrate 420, forming the ePE substrate into an ePE article 430, and expanding at least a portion of the ePE article 440.

[0076] Method step 410 of heating the ePE substrate to a temperature above the melting temperature of the ePE can be substantially similar to method step 310 of heating the ePE substrate to a temperature above the melting temperature of the ePE as described above with respect to Figure 3. The heat source can be, for example, similar to the heat source as described above with respect to Figure 3. Method step 420 of cooling the ePE substrate can be substantially similar to method step 320 of cooling the ePE substrate as described above with respect to Figure 3. Method step 430 of forming the ePE substrate into an ePE structure can be substantially similar to method step 330 of forming the ePE substrate into an ePE structure as described above with respect to Figure 3. Forming 430 the ePE substrate into an ePE structure can include, for example, forming ePE structure 540 (see Figure 5) and / or forming ePE structure 620 (see Figure 6).

[0077] In some embodiments, after the ePE substrate has been shrunk, heat and / or pressure can be applied to the ePE substrate to limit the amount of expansion that can occur, allowing the ePE substrate to have a fixed or specified amount of expansion that can be controlled, thereby controlling the size of ePE articles that can be molded from the ePE substrate.

[0078] The ePE structure is expandable. In some embodiments, expansion 440 of at least a portion of the ePE structure occurs only in a portion of the structure (e.g., at a specified longitudinal location). In some embodiments, the portion of the structure is at least one end of the ePE structure. In other embodiments, the portion of the structure is centered between both ends of the ePE structure. In other embodiments, expansion 440 of at least a portion of the ePE structure can occur over the entire structure. In some embodiments, expanding 440 at least a portion of the ePE structure can stretch the ePE structure from a second size back to a first size. In some embodiments, expanding 440 at least a portion of the ePE structure can stretch the ePE structure to an intermediate size between the first size and the second size. In some embodiments, the intermediate size can include an intermediate diameter, such as intermediate diameter DI in FIG. 7. In some embodiments, the intermediate size can also include an intermediate length, such as XI and YI in FIG. 8. In other embodiments, the intermediate size can include both an intermediate diameter and an intermediate length, such as intermediate diameter DI and intermediate length HI in FIG. 7.

[0079] In some embodiments, expanding 440 at least a portion of the ePE structure includes radial expansion. In some embodiments, expanding 440 at least a portion of the ePE structure includes one or both of longitudinal expansion and horizontal expansion. Longitudinal expansion can be in the Y direction. Horizontal expansion can be in the X direction. In some embodiments, expanding 440 at least a portion of the ePE structure includes both radial expansion and one or both of longitudinal expansion and horizontal expansion. Other embodiments are also contemplated in which expansion of at least a portion of the ePE structure occurs along a diagonal or other non-linear direction.

[0080] In some embodiments, inflation 440 of at least a portion of the ePE structure can be performed while the ePE structure is at room temperature (e.g., about 25°C to 30°C). In some embodiments, inflation can be performed using a balloon (e.g., an angioplasty balloon). In some embodiments, the amount of inflation of the ePE article is limited so that balloon inflation occurs to a predetermined ePE article size. In some embodiments, inflation 440 of at least a portion of the ePE structure is performed by the manufacturer of the ePE structure. In some embodiments, inflation 440 of at least a portion of the ePE structure can be performed by a user or a third party other than the manufacturer. In some embodiments, inflation 240 of the ePE structure is performed by a physician before, during, or after a surgical procedure.

[0081] FIG. 5 illustrates an embodiment 500 in which a tubular article 540 is formed from an ePE substrate, according to some embodiments. In some embodiments, the ePE substrate is an ePE sheet 515. The ePE sheet 515 can be similar to the ePE substrate as described above with respect to FIGS. 1-4. The ePE sheet 515 is provided as a starting material for forming the tubular article 540. In this embodiment, the tubular article 540 is an ePE structure as described above with respect to FIGS. 1-4. In some embodiments, the tubular article 540 is a graft. The method of forming the tubular article 540 can generally follow the method as described in FIGS. 1 and 2 and / or FIGS. 3 and 4.

[0082] The ePE sheet 515 is placed on a heating element 510 (e.g., a heating press). The heating element 510 is heated to a target temperature. For example, the target temperature of the heating element 510 can be provided at about 110°C to about 180°C. In some embodiments, the heat source provides a temperature of about 110°C to about 120°C, about 120°C to about 130°C, about 130°C to about 140°C, about 140°C to about 150°C, about 150°C to about 160°C, about 160°C to about 170°C, or about 170°C to about 180°C. In this embodiment, the ePE sheet 515 is unconstrained on the heating element 510. In this embodiment, the ePE sheet 515 is substantially square and defined by a first length L1.

[0083] The ePE sheet 515 is removed from the heating element 510. Once removed from the heating element 510, the ePE sheet 515 is cooled as described above with respect to removing the ePE substrate from the heating element 120, 220 and / or cooling the ePE substrate 320, 420. Upon cooling, the ePE sheet 515 shrinks into a smaller ePE sheet 520. The smaller ePE sheet 520 is defined by a second length L2. In this embodiment, the second length L2 is shorter than the first length L1. In this embodiment, the smaller ePE sheet 520 maintains the generally square shape from the ePE sheet 515; however, other configurations are contemplated in which the smaller ePE sheet 520 shrinks to a generally rectangular shape or to a non-uniform shape in the X direction (e.g., horizontally) and the Y direction (e.g., longitudinally).

[0084] The smaller ePE sheet 520 is then formed into a tubular article 540. To form the tubular article 540, the smaller ePE sheet 520 is wrapped around a mandrel 530. In this embodiment, the mandrel 530 is tubular with a diameter M1. The smaller ePE sheet 520 wrapped around the mandrel 530 is melt-bonded to itself along a longitudinal line, forming a longitudinal melt-bond line 535. Excess material 525 can be removed (e.g., trimmed) from the smaller ePE sheet 520 to form the tubular article 540. In this embodiment, the tubular article 540 has a first diameter D1. The first diameter D1 can be substantially similar to the diameter M1 of the mandrel.

[0085] The tubular article 540 can be expanded into an expanded tubular article 550. The tubular article 540 can be expandable upon cooling. In this embodiment, the tubular article 540 can be radially expanded after contracting the ePE sheet 515. The tubular article 540 can be radially expanded using a balloon. In one embodiment, the expanded tubular article 550 can have only a radially expanded portion such that the expanded tubular article 550 increases to a second diameter D2 at one end, where the second diameter D2 is greater than the first diameter D1. In another embodiment, a central portion of the tubular article 540 can be radially expanded. In other embodiments, the entire tubular article 540 can be radially expanded. In yet other embodiments, the tubular article 540 can be expanded both radially and longitudinally.

[0086] FIG. 7 illustrates an embodiment in which the tubular article 540 of FIG. 5 has been expanded to an intermediate size, according to some embodiments. FIG. 7 illustrates the tubular article 540 having a first diameter D1 and a first length H1. Generally, the first diameter D1 and the first length H1 define a first size of the tubular article 540. The tubular article 540 can be radially expanded to an expanded tubular article 550 having a second diameter D2 and expanded longitudinally to a second length H2. Generally, the second diameter D2 and the second length H2 define a second size of the tubular article 540, or the expanded tubular article 550. In some embodiments, the tubular article 540 can be expanded to an intermediate tubular article 545 having an intermediate size. The intermediate size is between the first size and the second size. In this embodiment, the tubular article 540 is expanded both radially and longitudinally. In other embodiments, the tubular article 540 can be expanded only radially or longitudinally. In this embodiment, the intermediate size is defined by an intermediate diameter DI and an intermediate length HI. In some embodiments, tubular article 540 can be expanded from a first size to an intermediate size at a first temperature to create intermediate tubular article 545. Intermediate tubular article 545 can then be expanded from the intermediate size to a second size at a second temperature to create expanded tubular article 550. In some embodiments, the first temperature is higher than the second temperature. In some instances, the second temperature is room temperature.

[0087] FIG. 6 illustrates an embodiment 600 in which a flat article 620 is formed from an ePE substrate, according to some embodiments. In this embodiment, the ePE substrate is an ePE sheet 615. The ePE sheet can be similar to the ePE substrate as described above with respect to FIGS. 1-4. The ePE sheet 615 is provided as a starting material for forming the flat article 620. In this embodiment, the flat article 620 is an ePE structure as described with respect to FIGS. 1-4. In some embodiments, the flat article 620 can be a hernia patch, a cardiovascular patch, a nerve membrane, or the like. The flat article can be a film or a multi-layer laminate. The method of forming the flat article 620 can generally follow the methods as described in FIGS. 1 and 2, and / or FIGS. 3 and 4.

[0088] The ePE sheet 615 can be placed on a heating element 610 (e.g., a T-shirt press), which can be similar to heating element 510 (FIG. 5). The heating element 610 is heated to a target temperature. For example, the target temperature of the heating element can be from about 110°C to about 180°C. In some embodiments, the heating element 610 is provided at temperatures of from about 110°C to about 120°C, from about 120°C to about 130°C, from about 130°C to about 140°C, from about 140°C to about 150°C, from about 150°C to about 160°C, from about 160°C to about 170°C, and from about 170°C to about 180°C. In this embodiment, the ePE sheet 615 is unconstrained on the heating element 610. In other embodiments, the ePE sheet 615 can be constrained in the X direction (e.g., horizontally), the Y direction (e.g., longitudinally), or both the X and Y directions. In this embodiment, the ePE sheet 615 is generally rectangular and may be defined by a first X dimension X1 and a first Y dimension Y1. Other shapes for the ePE sheet 615 are also contemplated, such as square or irregular shapes.

[0089] The ePE sheet 615 is removed from the heating element 610. The ePE sheet 615 is cooled as described above for removing the ePE substrate from the heating element 120, 220 and / or cooling the ePE substrate 320, 420. Upon removal from the heating element 610, the ePE sheet 615 shrinks to form a smaller ePE sheet 620. The smaller ePE sheet 620 is defined by a second X dimension X2 and a second Y dimension Y2. In this embodiment, the smaller ePE sheet 620 maintains a generally rectangular shape from the ePE sheet 615, although other configurations are contemplated in which the smaller ePE sheet 620 shrinks to a non-uniform shape in the X and Y directions. In one embodiment, the smaller ePE sheet 620 is a flat article 620.

[0090] The ePE substrate or flat article 620 is formed by shrinking (e.g., naturally) the ePE sheet 615 using the heating and cooling method described above with respect to Figures 1-4. The flat article 620 can expand upon cooling. The flat article 620 can expand in the longitudinal or horizontal direction after shrinking the ePE sheet 615. In one embodiment, the flat article 620 can expand in both the X direction (e.g., horizontally) and the Y direction (e.g., longitudinally) to form an XY flat article 630. The XY flat article is defined by a third X dimension X3 and a third Y dimension Y3. In some embodiments, the third X dimension X3 and the third Y dimension Y3 are greater than the second X dimension X2 and the second Y dimension Y2 of the flat article 620, respectively. In some embodiments, the third X dimension X3 and the third Y dimension Y3 are smaller than the first X dimension X1 and the first Y dimension Y1, respectively, of the ePE sheet 615. In other embodiments, the third X dimension X3 and the third Y dimension Y3 are the same as the first X dimension X1 and the first Y dimension Y1, respectively, of the ePE sheet 615.

[0091] In some embodiments, the flat article 620 can expand only in the Y direction (e.g., longitudinally) to form a Y flat article 640. This can occur when the ePE sheet 615 is partially or fully constrained in the X direction (e.g., horizontally) during the heating and cooling process. The Y flat article 640 is defined by a fourth X dimension X4 and a fourth Y dimension Y4. In some embodiments, the fourth X dimension X4 is the same as the second X dimension X2 of the flat article 620. In some embodiments, the fourth Y dimension Y4 is greater than the second Y dimension Y2 of the flat article 620. In some embodiments, the fourth Y dimension Y4 is less than the first Y dimension Y1 of the ePE sheet 615. In other embodiments, the fourth Y dimension Y4 is the same as the first Y dimension Y1 of the ePE sheet 615.

[0092] In some embodiments, the flat article 620 can expand only in the X direction (e.g., horizontally) to form the X flat article 650. This can occur when the ePE sheet 615 is partially or fully constrained in the Y direction (e.g., longitudinally) during the heating and cooling process. The X flat article 650 is defined by a fifth X dimension X5 and a fifth Y dimension Y5. In some embodiments, the fifth Y dimension Y5 is the same as the second Y dimension Y2 of the flat article 620. In some embodiments, the fifth X dimension X5 is larger than the second X dimension X2 of the flat article 620. In some embodiments, the fifth X dimension X5 is smaller than the first X dimension X1 of the ePE sheet 615. In other embodiments, the fifth X dimension X5 is the same as the first X dimension X1 of the ePE sheet 615.

[0093] FIG. 8 illustrates an embodiment in which the flat article 620 of FIG. 6 has been expanded to an intermediate size, according to some embodiments. FIG. 8 illustrates the flat article 620 having a second X dimension X2 and a second Y dimension Y2. Generally, the second X dimension X2 and the second Y dimension Y2 define a first size of the flat article 620. The flat article can be expanded horizontally and longitudinally to become an XY flat article 630 having a third X dimension X3 and a third Y dimension Y3. Generally, the third X dimension X3 and the third Y dimension Y3 define a second size of the flat article 620 for the XY flat article 630. In some embodiments, the flat article 620 can be expanded to an intermediate flat article 625 having a size intermediate between the first size and the second size. In this embodiment, the intermediate size is defined by an intermediate X dimension XI and an intermediate Y dimension YI. In some embodiments, flat article 620 can be expanded from a first size to an intermediate size at a first temperature to form intermediate flat article 625. Intermediate flat article 625 can then be expanded from the intermediate size to a second size at a second temperature to form XY flat article 630. In some embodiments, the first temperature is higher than the second temperature. In some examples, the second temperature is room temperature. While this embodiment is described above with respect to XY flat article 630, similar intermediate sizes can be formed before Y flat article 640 and X flat article 650.

[0094] An ePE substrate, as described above with reference to FIGS. 1-8, can undergo changes in its material properties during the heating-cooling process. The ePE substrate before processing can exhibit high porosity, high surface area, and high crystallinity. In some embodiments, after the ePE substrate is shrunk by the heating-cooling process, the shrunk ePE or ePE structure can have reduced porosity and reduced surface area. In some embodiments, after the ePE substrate is shrunk by the heating-cooling process, the shrunk ePE can have a similar porosity to that before the heating-cooling process, where the pore size after shrinking is smaller than before shrinking. However, the shrunk ePE may not be reduced to a fully densified state. Instead, the shrunk ePE can have pores smaller in size than the starting material, such that the ePE substrate maintains its porosity throughout processing, as shown in FIGS. 1-4. In some embodiments, the smaller pore size may not be distorted from the shape of the ePE substrate before processing. In other embodiments, the smaller pore size may be modified from the shape of the ePE substrate prior to processing. Details regarding the modification of material properties are provided in Examples 1 and 2.

[0095] Similarly, the microstructure of the ePE substrate may change upon shrinkage. The starting ePE substrate before processing may have a microstructure consisting essentially of fibrils and nodes of different lengths. In some embodiments, the fibrils may be serpentine fibrils. In some embodiments, the fibrils may be substantially all serpentine fibrils. In some embodiments, the shrunken ePE may retain a similar microstructure to the ePE substrate before processing. However, in some embodiments, shorter fibrils may be lost during processing and shrinkage of the ePE substrate. In some embodiments, upon shrinkage, the microstructure of the shrunken ePE may reform or form new connections. For example, new connections may form between fibrils, between fibrils and nodes, or between nodes. These new connections may be formed in any direction. The new connections may reduce the pore size of the shrunken ePE substrate, but the shrunken ePE substrate remains porous. When the shrunken ePE substrate is subsequently expanded, at least some of the new connections may be broken, causing the pore size to increase. In some embodiments, when laminates or other ePE articles are made with layers of ePE, new microstructural connections may form between the layers of ePE during shrinkage. Details regarding microstructural and other structural changes are described in connection with Examples 1 and 2.

[0096] The expansion rate between the precursor ePE or starting ePE material and the shrunk ePE substrate can be affected by the thermal and / or expansion history of the precursor ePE. For example, the ePE precursor can be initially stretched in a direction (e.g., X-direction, Y-direction, Z-direction, and / or radial direction, or any combination thereof) such that the ePE substrate shrinks in the same direction. This can occur due to the alignment of fibrils in the precursor ePE microstructure, and shrinkage is aligned with the fibrils. Similarly, the ePE substrate can expand in alignment with the fibrils. In this regard, the alignment of fibrils in the precursor ePE microstructure can be controlled to control the directionality of shrinkage and expansion of the ePE substrate.

[0097] In other embodiments, the presence or absence of restraint in any of the X, Y, Z, or radial directions, or any combination thereof, can affect the directionality of shrinkage and expansion of the ePE substrate. In some embodiments, the fibrils align in the X direction (e.g., horizontally) upon shrinkage, and the shrunken ePE can only shrink and expand in the X direction. This can occur when the ePE substrate is restrained in the Y direction (e.g., longitudinally) during the heating and cooling process. In other embodiments, the fibrils align in the Y direction upon shrinkage, and the shrunken ePE can only shrink and expand in the Y direction. This can occur when the ePE substrate is restrained in the X direction during the heating and cooling process. Similarly, the ePE substrate can be restrained in the Z direction (e.g., through the thickness) or radially (e.g., with a mandrel) to affect the directionality of the fibrils. Furthermore, the alignment of shrinkage and expansion can affect the direction in which new connections in the microstructure are formed upon shrinkage and the direction in which they are broken upon expansion. In this regard, the ePE substrate can be restrained to control the directionality of the shrinkage and expansion of the ePE substrate. [Example]

[0098] example Example 1 In a first example, three ePE substrates were heated above their melting temperatures: a first ePE substrate 700 was heated to approximately 127° C., a second ePE substrate 702 was heated to approximately 130° C., and a third ePE substrate 704 was heated to approximately 133° C. Each of the first, second, and third ePE substrates 700, 702, 704 comprised a first porous ePE film.

[0099] The first ePE substrate 700, the second ePE substrate 702, and the third ePE substrate 703 were each formed into a tube and then heated. A mandrel was used to apply substantially uniform heat to each of the first, second, and third ePE substrates 700, 702, and 704, although other heating sources may be used. A constant pressure was maintained without applying a vacuum while the first, second, and third ePE substrates 700, 702, and 704 were each heated. A constant low pressure of approximately 2 psi was applied using an overlap.

[0100] FIG. 9A shows a first ePE substrate 700 after being heated to 127°C and then cooled. FIG. 9B shows a second ePE substrate 702 after being heated to 130°C and then cooled. As can be seen, as the process temperature increases above the melting temperature, the ePE substrate melts, causing the material to shrink and increase in density. As shown, the second ePE substrate 702 has a reduced thickness and is denser compared to the first ePE substrate 700. The second ePE substrate 702 also appears to be compacted or densified, as if its microstructure has condensed. Furthermore, the second ePE substrate 702 has fewer visible layered structures or less void space within the ePE substrate compared to the first ePE substrate 700, further indicating a more densified, or condensed, material.

[0101] Referring to FIG. 10, the thicknesses of the first, second, and third ePE substrates 700, 702, and 704 were measured in microns (μm) after each substrate was heated. As the data shows, as the processing temperature increases, the thickness of each substrate decreases. In other words, the thickness of the third ePE substrate 704 is less than the thickness of the second ePE substrate 702, which is less than the thickness of the first ePE substrate 700. As discussed with respect to FIGS. 9A-9B, the decrease in thickness may be correlated with densification and shrinkage of the ePE substrates and / or condensation of the ePE substrate microstructure.

[0102] Referring to FIG. 11, the bubble points of the first, second, and third ePE substrates 700, 702, and 704 were measured in psi. As the data shows, the bubble point of each substrate increases as the processing temperature increases above the melting temperature. The bubble point may be correlated to the pore size present in the ePE substrate. An increase in bubble point indicates a decrease in the pore size of the substrate. In other words, the pore size of the third ePE substrate 704 is smaller than the pore size of the second ePE substrate 702, which is smaller than the pore size of the first ePE substrate 700. As discussed with respect to FIGS. 9A-9B, an increase in bubble point may also be correlated to densification and shrinkage of the ePE substrate and / or condensation of the ePE substrate's microstructure.

[0103] Furthermore, pore size may correspond to the ability of the article to selectively allow or reduce cellular infiltration, ingrowth, and / or adhesion within the structure. Smaller pore sizes may enable the respective article to reduce or limit cellular infiltration therethrough, which may be desirable in some applications, including, but not limited to, aortic devices. Larger pore sizes may allow the respective article to permit cellular infiltration therethrough. Thus, processing temperatures may be selected to increase or decrease pore size as desired, allowing or reducing cellular in-growth, respectively.

[0104] Referring to FIG. 12 , the air flow rate or air leakage through the ePE substrates was measured in liters per hour (l / hr) for the first, second, and third ePE substrates 700, 702, and 704. Air flow rate measurements were performed using an ATEQ® leak detection device. As the processing temperature increased, the air leakage for each substrate decreased. The air leakage may be correlated with the pore size present in the ePE substrate, since the larger the pore size, the more air escapes through the ePE substrate. This indicates that the pore size of each substrate decreased as the processing temperature increased. In other words, the pore size of the third ePE substrate 704 was smaller than the pore size of the second ePE substrate 702, which in turn was smaller than the pore size of the first ePE substrate 700. As illustrated in Figures 9A-9B, the reduction in air leakage may be correlated with densification and shrinkage of the ePE substrate and / or condensation of the microstructure of the ePE substrate.

[0105] Although the above examples describe tubular ePE substrates, flat ePE substrates, or ePE substrates of other shapes, can behave similarly and exhibit similar changes in material properties when heated above their melting point.

[0106] Example 2 In a second example, three ePE substrates were heated above their melting points: a fourth ePE substrate 706 was heated to approximately 127°C, a fifth ePE substrate 708 was heated to approximately 130°C, and a sixth ePE substrate 710 was heated to approximately 133°C. The fourth, fifth, and sixth ePE substrates 706, 708, and 710 each contained a second porous ePE film that was different from the first porous ePE film of Example 1.

[0107] As in Example 1, the fourth ePE substrate 706, the fifth ePE substrate 708, and the sixth ePE substrate 710 were each formed into a tube before heating. Each of the fourth, fifth, and sixth ePE substrates 706, 708, and 710 was heated substantially uniformly using a mandrel, although other heating sources could also be used. Pressure was kept constant without applying a vacuum while each of the fourth, fifth, and sixth ePE substrates 706, 708, and 710 was heated. A constant low pressure of approximately 2 psi was applied using an overlap.

[0108] As in Example 1, the thickness, bubble point, and air leakage were measured for each of the fourth, fifth, and sixth ePE substrates 706, 708, and 710. The trends in material properties were similar to those observed in Example 1. As shown in FIG. 10, as the processing temperature increased above the melting temperature, the thickness of each ePE substrate decreased. As shown in FIG. 11, as the processing temperature increased above the melting temperature, the bubble point increased. As shown in FIG. 12, as the processing temperature increased above the melting temperature, the air leakage of each substrate decreased. These results indicate that an increase in processing temperature may be correlated with densification and shrinkage of the ePE substrate, condensation of the ePE substrate's microstructure, and / or a decrease in the pore size of the ePE substrate. This also indicates that the densification, condensation of the microstructure, and decrease in pore size of each ePE substrate upon increasing processing temperature are not limited to only one type of porous ePE film, but can be observed in both the first and second porous ePE films.

[0109] Referring to FIG. 13 , peel strength was measured for each of the fourth, fifth, and sixth ePE substrates 706, 708, and 710. Peel strength was measured as the force required to peel the substrates approximately 12 mm and is reported in units of N / 12 mm. As the data shows, the peel strength of each substrate increased as the processing temperature increased above the melting temperature. In other words, the force required to pull the third ePE substrate 704 was greater than the force required to pull the second ePE substrate 702, which in turn was greater than the force required to pull the first ePE substrate 700. This increase in force may correlate with densification and compaction of the ePE substrates and / or condensation of the microstructure of the ePE substrates. The increase in force required to pull the substrates indicates that the layers or spaces within the ePE substrates decrease with increasing processing temperature, potentially resulting in the formation of new bonds within the ePE substrates.

[0110] Although the above examples are described with respect to tubular ePE substrates, flat ePE substrates or ePE substrates of other shapes can exhibit similar behavior and similar changes in material properties when heated above their melting temperature.

[0111] The invention of the present application has been described above both generally and with reference to specific embodiments. It is apparent that those skilled in the art can make various changes and modifications to the embodiments without departing from the scope of the present disclosure. Therefore, it is intended that the embodiments cover the modifications and variations of the present invention provided they fall within the scope of the appended claims and their equivalents.

Claims

1. 1. A method for processing expanded polyethylene (ePE), comprising: placing an ePE substrate on a heating component, wherein the ePE substrate has a first size; heating the ePE substrate on the heating element; removing the ePE substrate from the heated component and allowing the ePE substrate to cool and shrink to a second size, wherein the second size is smaller than the first size; and forming the ePE substrate into an ePE article; A method comprising:

2. The method of claim 1 , wherein forming the ePE substrate into the ePE article comprises wrapping the ePE substrate onto a mandrel.

3. The method of claim 2 , wherein forming the ePE substrate into the ePE article comprises melt-bonding the ePE substrate to itself along a longitudinal line.

4. The method of claim 1 , wherein placing the ePE substrate on the heating component comprises providing the ePE substrate as a sheet of ePE.

5. The method of claim 1 , wherein heating the ePE substrate comprises heating the heating component to about 110°C to 180°C.

6. The method of claim 1 further comprising adhering the ePE article to a metal.

7. The method of claim 1, further comprising adhering the ePE article to another polyethylene structure.

8. The method of claim 1, further comprising expanding at least a portion of the ePE article.

9. The method of claim 8 , wherein expanding at least a portion of the ePE article comprises radial expansion.

10. The method of claim 8 , wherein expanding at least a portion of the ePE article comprises longitudinal expansion.

11. 1. A method for processing expanded polyethylene (ePE), comprising: heating the ePE substrate to a temperature above the melting temperature of ePE, wherein the ePE substrate has a first size; cooling the ePE substrate, wherein the ePE substrate shrinks to a second size upon cooling, the second size being smaller than the first size; and forming the ePE substrate into an ePE article; A method comprising:

12. The method of claim 11, wherein the ePE substrate is heated to about 110°C to 180°C.

13. The method of claim 11 , further comprising expanding at least a portion of the ePE article.

14. The method of claim 13, wherein expanding at least a portion of the ePE article occurs at room temperature.

15. 1. An expanded polyethylene (ePE) article made from ePE, comprising: An ePE article comprising an ePE substrate formed into an ePE article, said ePE article being formed by shrinking an ePE sheet by a method of heating and cooling, said ePE article being expandable.

16. The ePE article of claim 15, wherein the ePE substrate is formed into a graft.

17. 16. The ePE article of claim 15, wherein the ePE substrate is formed into the ePE article using a mandrel.

18. The ePE article of claim 15, wherein the ePE article is longitudinally expandable.

19. The ePE article of claim 15, wherein the ePE article is radially expandable.

20. The ePE article of claim 15, wherein the ePE article is porous.

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