Multilayer heat shrink tube

Abstract

The present disclosure provides a multilayer heat shrink tubing with an outer layer including non-crosslinked PEBA; and an inner layer including maleated polyolefin. The maleated polyolefin advantageously has a melt temperature that is lower than the melt temperature of the outer layer.

Description

[0001] MULTILAYER HEAT SHRINK TUBE

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] The present application claims the benefit of U.S. Provisional Patent Application No. 63 / 649,532, filed May 20, 2024, which is incorporated herein by reference in its entirety.

[0004] FIELD OF THE INVENTION

[0005] The present application is directed to multilayer heat shrink polymeric tubing and methods for making such heat shrink polymeric tubing included as a component of a catheter assembly.

[0006] BACKGROUND OF THE INVENTION

[0007] Tubing manufactured from poly(ether-block-amide) (PEBA) copolymer resins are currently used as the outer sheath of many commercially available catheter shafts. Catheters are used to provide a shaft with intravenous channel through which medical devices or agents can be delivered into the body once the shaft has been inserted into position during a medical procedure. Catheters often include an inner channel lining comprising a lubricious material such as polytetrafluoroethylene (PTFE) to allow for easy insertion and retraction of medical devices therethrough. In many cases, a reinforcing component surrounds the lubricious inner channel of the catheter shaft to provide strength, pushability, and torque translation. This reinforcing component can be comprised of several different materials depending upon the target function and specifications of the finished catheter. Materials commonly used as a reinforcing component of catheter shafts include metallic wire braids or coils, metallic or polymeric hypodermic tubing, liquid-crystal polymer (LCP) fiber braids, and other polymeric fibers that are braided or otherwise incorporated into the composite structure of the catheter shaft. The outer sheath, also referred to herein as a catheter jacket or simply jacket, serves several functions as a component of the composite catheter shaft. The jacket provides durability by covering and protecting the outer surface of the reinforcing component. The jacket also provides a barrier that defines the outer surface of the catheter, preventing leakage of fluid, agents, devices, and other therapeutics along the length of the shaft. It is desirable for the catheter jacket to have a glossy outer surface finish to provide smooth and atraumatic transmission through vasculature while in use during a medical procedure. Catheter jackets are typically comprised of polymers such as polyamide, polyurethane, polyolefin, or poly(ether-block-amide) copolymer (PEBA). which are commercially available as medical extrusion grade resins. These resins can be converted into a tubular form via melt extrusion and subsequently used in conjunction with a process aid (also often referred to as a “fusing sleeve”) to provide an outer sheath for a catheter shaft.

[0008] Catheter shafts are typically manufactured by utilizing a fluorinated ethylene-propylene copolymer (FEP) heat shrink tubing as a process aid to form and bond the outer jacket to underlying components and finalize the catheter shaft build. Such heat shrink tubing has been produced

[0009] I commercially for several decades using various processes, for example, vacuum expansion, gas pressure forming, sequential heating / stretching and the like. Known methods for expanding heat shrink tubing are provided, for example, in the disclosures of U.S. Patent No. 2,987,767 to Edward et al.; U.S. Patent No. 3,412, 189 to Sullivan; U.S. Patent No. 7,625,194 to Yoshida et al.; U.S. Patent No. 9,296,165 to Henson; U.S. Patent No. 9,327,444 to Henson; and U.S. Patent No. 9,440,044 to Roof et al.; each of which is incorporated herein by reference.

[0010] The conventional process for catheter manufacturing is also referred to as a “reflow process” and is well known to those skilled in the art. During the reflow process, the FEP heat shrink tubing or “fusing sleeve” is placed over a set of pre-assembled catheter shaft components (i.e., a “catheter shaft pre-assembly” or “pre-assembly”) and subsequently heated to finalize the catheter shaft build. A catheter shaft pre-assembly typically comprises several components: a solid core (also referred to as a mandrel), a thin-walled lubricious liner tube, a reinforcing component, and an outer sheath tube. Preparation of the pre-assembly can involve providing a solid core that is inserted into a thin-walled lubricious tubing (also referred to herein as a “lubricious liner” or simply “liner”). The lubricious liner typically comprises an outer-surface modified thin-walled polytetrafluoroethylene (PTFE) tube (e.g., a PTFE tube with an outer surface that has been etched, e.g., sodium etched to allow for bonding with other materials). A reinforcing component can then be applied upon the outer surface of the liner (e.g., a braid, wire coil, or hypodermic tube structure can be applied over the outer surface of the liner). It is important to note that a reinforcing component is not always utilized in a catheter shaft build, particularly for catheter shafts that do not require a specific internal pressure resistance (i.e., burst resistance). After the reinforcing component is secured about the exterior (i.e., upon the outer surface) of the liner, an outer sheath tube (e.g., a medical grade PEBA tube) can be applied over the reinforcing component, providing a catheter shaft pre-assembly. The pre-assembly (i.e., the solid core, the thin-walled liner tube, the reinforcing component, and the outer sheath tube) can then be inserted into an FEP heat shrink tube and heated to melt, form, and bond the outer jacket tube to the underlying components and finalize the catheter shaft. This is an effective method for manufacturing catheter shafts because the FEP heat shrink tube has a recovery (i.e., “shrink”) temperature that is greater than the crystalline melting temperature of the outer sheath tubing. While heating the preassembly and fusing sleeve, the PEBA outer sheath tube melts and is forced by the dimensional recovery of the FEP heat shrink tube to flow radially inward and make intimate contact with the underlying components. In this way, the strong recovery force provided by the FEP heat shrink tube as it is heated (i.e., as it decreases in diameter) forces the molten PEBA tube to “reflow” within the interstices or gaps in the reinforcing material and, after cooling, a strong bond is formed between the inner surface of the outer sheath tube and the outer surface of the inner liner. Outer sheath tubes comprising polymers other than PEBA can be used in conjunction with the described reflow process. Other materials used as an outer sheath with this reflow process can comprise, for example, polyamide, polyurethane, and polyolefin. After allowing the assembly to cool, the FEP heat shrink tubing is removed and discarded. Finally, the solid core that maintains the shape of the inner lumen during reflow is removed leaving the final catheter shaft.

[0011] Many different methods of heat application are employed during the reflow process including, but not limited to, forced air ovens, hot boxes, induction heaters, heat guns, traversing laminators, lasers, and glow rings. For catheter shaft builds that utilize a coiled or braided reinforcing component, it is often specified for the outer jacket tube to flow into and fill all interstices / gaps between the underlying reinforcing material during the reflow process and bond to the outer surface of the inner liner to form a continuous composite structure. These types of designs often require a certain level of pressure (i.e., burst) resistance. If the interstices of the reinforcing material are insufficiently filled by the outer jacket tube during the reflow process, an air pocket or “bubble” remains embedded within the composite structure and is known as a void. Voids can negatively influence the durability and pressure resistance of the finished catheter shaft, in some cases. It is also important that the reflow process provides a strong bond between the PEBA outer jacket and the liner tube. In certain situations, delamination of the bond between the outer sheath tube and inner liner tube is unacceptable due to the potential for the thin-walled inner liner tube to kink or wrinkle in tortuous vascular pathways. This can hinder or ultimately prevent the transmission of a medical device or agents through the lumen.

[0012] Catheter shafts are often designed with variable flexibility along the length of the shaft to balance functionality and optimize performance at the proximal and distal ends. It is typically preferable for the distal end of a catheter to be soft and flexible to allow for maneuverability through vascular pathways. Conversely, it is desirable for the proximal portion of a catheter shaft to be stiffer (i.e., more rigid) than the distal end to provide pushability (i.e., columnar stiffness that aids in advancement and retraction) and predictable torque translation. This balance of functionality is commonly achieved by utilizing multiple outer sheath tubes of varying durometer hardness (i.e., PEBA tubes manufactured from different resin grades) along the length of the catheter shaft. Medical grade tubes that are comprised of, consist essentially of, or contain PEBA resins as a pail of a blend, can vary significantly in durometer hardness and flexibility depending on the final composition of the tubing. For example, medical grade PEBA resins manufactured by Arkema Inc., available commercially as PEBAX MED®, vary in durometer hardness from about 25 to 74 Shore D and in flexural modulus from around 12 to 700 MPa. Variable stiffness catheters are currently produced using conventional manufacturing techniques that involve FEP heat shrink tubing as a process aid. After the reinforcing component has been applied over (i.e., on the outer surface of) the inner liner, PEBA tubing across a range of durometer hardness can be sequentially slid onto and subsequently reflowed over the reinforcing component to provide the desired flexibility to each portion of the catheter shaft, forming a multi-durometer catheter shaft. This provides catheter manufacturers with the ability to alter the characteristics of the completed shaft for a specific application by varying the length and composition of the outer jacket. To finalize the multi-durometer catheter build, the prepared components are inserted into the FEP fusing sleeve and subsequently heated to melt and reflow the outer sheath tubing to provide a catheter with sections of varying flexibility (i.e., durometer hardness). It is important to note that the circumferential mechanical force provided by the FEP fusing sleeve (i.e., as it “shrinks” at a temperature above the melting point of the underlying outer sheath tubing) forces coalescence at the interface of the outer sheath tubing to provide smooth transitions between the sections.

[0013] The use of FEP heat shrink tubing adds significant material costs to the catheter manufacturing process. Development and optimization of the dimensional and recovery characteristics of the FEP fusing sleeve must be optimized for a particular catheter shaft build, most often through a third-party supplier, which can be very costly and time consuming. Some of these optimizations include adjustments to sizing, required recovery ratio, and recovery conditions that provides void elimination and a good bond between the jacket and inner liner. The labor and tooling required to remove the FEP heat shrink tubing also contributes to increased operating costs. There is also potential for the finished catheter shaft to be damaged and scrapped because of having to remove the FEP fusing sleeve after the reflow process. Moreover, the scrap FEP material generated is inconsistent with the goals of a circular economy.

[0014] SUMMARY OF THE INVENTION

[0015] The present disclosure relates to heat shrinkable polymeric tubes composed of two or more distinct layers comprising one or more polymers that are not cross-linked. In some embodiments, the disclosure relates to multilayer heat shrinkable (“heat shrink”) tubes comprising an outer layer of poly(ether-block-amide) copolymer (PEBA), wherein the PEBA is not crosslinked, and an inner layer of maleated polyethylene (PE). Typically, such multilayer heat shrink tubes are in the form of extruded and expanded tubes. It has been found that certain such extruded multilayer tubes can be expanded to form multilayer heat shrink tubes without a crosslinking step. Such multilayer heat shrink tubes can be subsequently employed during catheter shaft assembly processes as an outer jacket for catheter shafts without the need for expensive single-use manufacturing aids such as FEP heat shrink tubes. With propitious conditions of expansion, recovery ratio, and time / temperature profile for the recovery process, a satisfactory catheter shaft can be manufactured using a tube comprising noncrosslinked PEBA lined with maleated PE, which does not require removal of any single-use manufacturing aid prior to use. Several catheter shaft configurations comprising a variety of components can be assembled utilizing such a multilayer heat shrink tube as an outer jacket under conditions to be explained more fully hereafter.

[0016] The present disclosure includes, without limitation, the following embodiments.

[0017] Embodiment 1 : A multilayer heat shrink tubing comprising: an outer layer comprising noncrosslinked PEBA; and an inner layer comprising maleated polyolefin, wherein the maleated polyolefin has a melt temperature that is lower than the melt temperature of the outer layer. Embodiment 2: The multilayer heat shrink tubing Embodiment 1 wherein the heat shrink tubing has a recovery ratio (RR) greater than about 1.05: 1.

[0018] Embodiment 3: The multilayer heat shrink tubing of Embodiment 1 or 2, wherein the outer layer consists essentially of the non-crossl inked PEBA.

[0019] Embodiment 4: The multilayer heat shrink tubing of any of Embodiments 1-3, wherein the outer layer further comprises a lubricity modifier.

[0020] Embodiment 5: The multilayer heat shrink tubing of any of Embodiments 1-4, wherein the inner layer consists essentially of the maleated polyolefin.

[0021] Embodiment 6: The multilayer heat shrink tubing of any of Embodiments 1-5, wherein the maleated polyolefin comprises one or more of maleic anhydride grafted polyethylene, maleic anhydride grafted polypropylene, and maleic anhydride grafted ethylene vinyl acetate copolymer.

[0022] Embodiment 7: The multilayer heat shrink tubing of any of Embodiments 1-6, wherein the maleated polyolefin comprises maleic anhydride grafted linear low density polyethylene.

[0023] Embodiment 8: The multilayer heat shrink tubing of any of Embodiments 1-7, wherein the weight ratio of the outer layer to the inner layer is between 99: 1 and 1 :99.

[0024] Embodiment 9: The multilayer heat shrink tubing of any of Embodiments 1-8, wherein the weight ratio of the outer layer to the inner layer is between 95:5 and 5:95.

[0025] Embodiment 10: The multilayer heat shrink tubing of any of Embodiments 1-9, wherein the weight ratio of the outer layer to the inner layer is between 90: 10 and 10:90.

[0026] Embodiment 1 1 : The multilayer heat shrink tubing of any of Embodiments 1-10, wherein the weight ratio of the outer layer to the inner layer is between 75:25 and 25:75.

[0027] Embodiment 12: The multilayer heat shrink tubing of any of Embodiments 1-1 1 , wherein the RR is greater than about 1.10: 1 and / or is reducible in ID by about 9.1 %.

[0028] Embodiment 13: The multilayer heat shrink tubing of any of Embodiments 1-12, wherein the RR is greater than about 1 .2: 1 and / or reducible in ID by about 16.7%.

[0029] Embodiment 14: The multilayer heat shrink tubing of any of Embodiments 1-13, wherein the RR is greater than about 1 .3: 1 and / or reducible in ID by about 23.1%.

[0030] Embodiment 15: The multilayer heat shrink tubing of any of Embodiments 1-14, wherein the RR is greater than about 1.4: 1 and / or reducible in ID by about 28.6%.

[0031] Embodiment 16; The multilayer heat shrink tubing of any of Embodiments 1-15, wherein the RR is greater than about 1.5: 1 and / or reducible in ID by about 33.3%.

[0032] Embodiment 17: The multilayer heat shrink tubing of any of Embodiments 1-16, wherein the RR is greater than about 1 .6: 1 and / or reducible in ID by about 37.5%.

[0033] Embodiment 18: The multilayer heat shrink tubing of any of Embodiments 1-17, wherein a durometer hardness measurement of the outer layer of a flat specimen fabricated by melt pressing the heat shrink tubing in expanded form is about 20 to 80 Shore D. Embodiment 19: The multilayer heat shrink tubing of any of Embodiments 1-18, wherein the outer polymeric layer is removable after being heat shrunk.

[0034] Embodiment 20: The multilayer heat shrink tubing of any of Embodiments 1-19, wherein one or both of the inner layer and the outer layer comprises a filler.

[0035] Embodiment 21 : The multilayer heat shrink tubing of any of Embodiments 1-20, wherein one or both of the inner layer and the outer layer comprises a blend of polymers.

[0036] Embodiment 22: A recovered multilayer tube, prepared by heating the multilayer heat shrink tubing of any of Embodiments 1-20 such that the inner layer melts, forming an inner encapsulating layer and the outer layer contracts, forming an outer, contracted polymeric layer.

[0037] Embodiment 23 : The recovered multilayer tube of Embodiment 22. wherein the outer, contracted polymeric layer is removable.

[0038] Embodiment 24: An encapsulated component, comprising a component within the recovered multilayer tubing of any of Embodiments 22-23.

[0039] Embodiment 25: The encapsulated component of Embodiment 24, wherein the component is completely encapsulated by the inner encapsulating layer.

[0040] Embodiment 26: A method of encapsulating a component, comprising: applying the multilayer heat shrink tubing of any of Embodiments 1-21 around the component, heating the multilayer heat shrink tubing to recover the multilayer tube (e.g., such that the inner layer melts and the outer layer contracts), and cooling the resulting encapsulated component.

[0041] Embodiment 27: A catheter shaft pre-assembly comprising the multilayer heat shrink tubing of any of Embodiments 1-21.

[0042] Embodiment 28: The catheter shaft pre-assembly of Embodiment 28, further comprising a catheter liner in direct contact with the inner layer of the multilayer heat shrink tubing, wherein the catheter liner optionally comprises a reinforcing component (e.g., braids) on an outer surface thereof.

[0043] Embodiment 29: A catheter, prepared by heating the catheter shaft pre-assembly of Embodiment 28 such that the outer layer shrinks / recovers and the maleated polyolefin melts, e.g., where the heating is at a temperature at or greater than the melt temperature of the maleated polyolefin.

[0044] Embodiment 30: The catheter of Embodiment 29, wherein the maleated polyolefin is bonded through and at least partially encapsulates the optional reinforcing component, where present, and / or wherein the maleated polyolefin is adhered to the catheter liner.

[0045] Embodiment 31 : A catheter, comprising: a catheter liner; an optional reinforcing component (e.g., braids) on an outer surface of the catheter liner; a first layer comprising maleated polyolefin surrounding and bonded to the catheter liner, wherein the first layer is bonded through and at least partially encapsulates the optional reinforcing component, where present, and a second layer comprising recovered, non-crosslinked PEBA surrounding the first layer, wherein the maleated polyolefin has a melt temperature that is lower than the melt temperature of the second layer. Embodiment 32: The catheter of Embodiment 31 , prepared using the multilayer heat shrink tubing of any of Embodiments 1-21.

[0046] It will be apparent to those skilled in the art that other embodiments of the invention are possible and that the examples presented here are not intended to be exhaustive. These and other features, aspects, and advantages of the present disclosure will be apparent from a reading of the following detailed description together with the accompanying drawings, which are briefly described below. The present disclosure includes any combination of two, three, four, or more features or elements set forth in this disclosure or recited in any one or more of the claims, regardless of whether such features or elements are expressly combined or otherwise recited in a specific embodiment description or claim herein. This disclosure is intended to be read holistically such that any separable features or elements of the disclosure, in any of its aspects and e bodiments, should be viewed as intended to be combinable, unless the context of the disclosure clearly dictates otherwise.

[0047] BRIEF DESCRIPTION OF THE DRAWINGS

[0048] To provide an understanding of the embodiments of the invention, reference is made to the appended drawings, which are not necessarily drawn to scale, and in which reference numerals refer to components of exemplary embodiments of the invention. The drawings are exemplary only and should not be construed as limiting the invention.

[0049] FIG. 1 is a schematic of a non-limiting catheter according to certain embodiments of the present disclosure with a corresponding expanded schematic of one cross-sectional end face of the catheter;

[0050] FIG. 2 is a schematic of a non-limiting 2-layer multilayer tube according to certain embodiments of the present disclosure;

[0051] FIG. 3 is a schematic of a non-limiting 3-layer multilayer tube according to certain embodiments of the present disclosure;

[0052] FIG. 4 is a cross section image of mounted Example 2 (30x Magnification);

[0053] FIG. 5 is a cross section image of mounted Example 2 (250x Magnification); and

[0054] FIG. 6 is a cross section image of mounted Example 2 (250x Magnification).

[0055] DETAILED DESCRIPTION OF THE INVENTION

[0056] The present invention now will be described more fully hereinafter. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. As used in this specification and the claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. The present disclosure provides heat shrink tubes with unique properties and unique combinations of properties, as will be outlined further herein. Generally, a heat shrink tube is a shrinkable tubing prepared via expansion of a polymeric (“input”) tubing (e.g., an extruded tubing) to give the heat shrink tubing (also referred to herein as an “expanded” form). Upon heating, the heat shrink tubing “shrinks” to a size that is equivalent to (or close to) its original / input size, commonly referred to as its “recovered” size. The composition and overall size of a heat shrink tubing according to the present disclosure can vary widely and is not particularly limited. A heat shrink tubing can be defined, e.g., by measurable properties such as its inner diameter ("ID”) either after expansion (also referred to herein as “expanded inner diameter” (1 De)) or after recovery (also referred to herein as “recovered inner diameter” (IDr)), its length (L), its change in length upon recovery (i.e., its percent change in length upon recovery, AL), its average wall thickness, its ratio of individual average layer thicknesses (also referred to herein as “layer ratio”), its wall thickness concentricity (also referred to herein as percent concentricity or simply as concentricity), its expansion ratio (ER), its recovery ratio (RR), and its percent change in inner diameter upon recovery (AID). Such properties can be defined using the following equations:

[0057] In these equations, Leand Lrare the length of the heat shrink tubing (in expanded form) and the length of the “recovered” (i.e., heat-shrunk) tubing, respectively. ID0refers to the original internal diameter (ID) of the input tube (i.e., the tube before it is expanded and then subsequently “shrunk”); IDerefers to the internal diameter (ID) of the expanded heat shrink tubing; and IDrrefers to the internal diameter (ID) of the recovered (heat shrunk) tube. Values needed for determination of percent concentricity are the minimum wall thickness and the maximum wall thickness of the tubular walls, defined as wtmm and wtmax, respectively. wtout refers to the average thickness of the outer layer; wtin refers to the average thickness of the inner layefts); and wttotai refers to the total average wall thickness. RR, AL, and AID can be evaluated under any recovery conditions (i.e., time, temperature, and method of heat application), though the time and temperature at which an expanded tube is recovered must be specified as this can influence the observed extent of recovery (i.e., an expanded tube that is exposed to a lower temperature and / or for a shorter time may not recover to its full capability). Percent concentricity can be evaluated in the expanded or recovered state. Concentricity is a measure of wall thickness uniformity, and the concentricity value can influence performance in certain applications in both states. As used herein, the above parameters were calculated as follows.

[0058] The percent change in length (AL), also referred to herein as longitudinal change, is determined in the following manner. Prior to placing the heat shrink tubing into the oven for unrestricted recovery, the expanded tubing is cut to a length of 2.5 inches using a verified ruler. The 2.5-inch specimen length is carefully cut from the heat shrink tubing to ensure there are no burs or other deformities present, and that they are perpendicular to the longitudinal axis of the tubing. After the unrestricted recovery process at a specified temperature, the tubing length is re-measured using a verified ruler to the nearest l / 32nd of an inch to determine the amount of shrinkage or growth that has occurred during the process. For example, the expanded length is subtracted from the recovered length and divided by the expanded length, then this quantity is multiplied by 100 to give the overall percent change in length (AL) resulting from recovery. Typically, AL is measured to be in the range of about + / - 10% (i.e., the length changes by less than about 10% upon recovery).

[0059] The recovery ratio (RR), percent change in inner diameter (AID), and percent concentricity is determined in the following manner. Three 2.5-inch-long specimens are cut from the expanded tubing and their expanded ID and wall thickness is measured using verified measurement tools. Multiple wall thickness measurements must be taken to accurately determine the percent concentricity (i.e., the wall thickness uniformity) of the tubular walls. The minimum wall thickness measurement taken on the expanded tube is divided by the maximum wall thickness measurement taken on the expanded tube, and then multiplied by 100 to give the percent concentricity of the expanded tube. The specimens are then placed into an oven set at a specified temperature for approximately 10 minutes. After exposing each heat shrink tubing specimen to a specified recovery temperature for 10 minutes, it is removed from the oven and allowed to cool to ambient temperature. This subjects the expanded heat shrink tubing to an unrestricted recovery process. After cooling to ambient temperature, the recovered ID and wall thickness is measured using verified measurement tools. The expanded tubing ID is divided by the recovered tubing ID to calculate the recovery ratio (RR) of the heat shrink tube under the specified recovery conditions (i.e., recovery temperature and time). Subsequently, the percent inner diameter change of the heat shrink tubing is calculated by subtracting the recovered tubing ID from the expanded tubing ID and dividing by the expanded tubing ID, then multiplying this quantity by 100 to give the overall percent change in inner diameter (AID). The minimum wall thickness measurement taken on the recovered tube is divided by the maximum wall thickness measurement taken on the recovered tube, and then multiplied by 100 to give the percent concentricity of the recovered tube. In some embodiments, the disclosed non-crosslinked outer layer of the heat shrink tubes comprise, consist essentially of, or consist of one or more polymers such as polyamides, polyethers, polyesters, poly(ether-block-amides); or a copolymer, blend, or derivative of any two or more of the foregoing. Exemplary polymers according to the present disclosure include, but are not limited to, a poly(ether-block-amide) (PEBA) (i.e., a block copolymer comprised of a polyamide segment (e.g., polyamide 6 (PA6), or polyamide 1 1 (PAI 1), or polyamide 12 (PA 12)), a polyether segment (e.g., polyoxymethylene (POM), or polyethylene glycol (PEG), or polypropylene glycol (PPG), or polytetramethylene glycol (PTMG)), and may include a polyester segment in some grades (e.g., polyethylene adipate) (PEA))).

[0060] In certain specific embodiments, the non-crosslinked outer layer of the heat shrink tubes comprising PEBA are provided. When referring to the composition of a particular PEBA resin grade, the polyamide segment can be referred to as the “hard segment” or “hard phase”, the polyether segment can be referred to as the “soft segment” or “soft phase”, and the polyester segment (if present in low composition in particular grades of PEBA resin) acts as a chain extender. The ratio of the polyamide, polyether, and polyester segments of the PEBA in the heat shrink tube can vary greatly without departing from the present disclosure. Different composition ratios of the polyamide hard segment to polyether soft segment (in addition to a polyester chain extender in some resin grades) influences the physical properties of the supplied resin; and ultimately the final physical properties of the non-crosslinked PEBA heat shrink tubes of the present invention. Different composition ratios allow for non-crosslinked PEBA heat shrink tubes of varying flexibility (i.e., durometer hardness) to be produced.

[0061] In various embodiments, the outer layer of the heat shrink tubing disclosed herein are prepared from one or more poly(ether-block-amide) (PEBA) resins. “Resin” as used herein refers to a material consisting essentially of a given type of polymer (e.g., a copolymer) or two or more polymers / copolymers. Resins are typically provided in solid form (e.g., as solid pellets), although they are not limited thereto (with other forms including, but not limited to, powders, pastes, granules, dispersions, solutions, gels, and the like). In some embodiments, the outer layer of the heat shrink tubing disclosed herein may be prepared from a resin comprising, consisting of, or consisting essentially of a PEBA resin in one or more of the forms noted herein. In some cases, a “resin” as used herein may contain one or more additional components as additives and / or one or more additional components can be added thereto (e.g., such as a lubricant, colorant, filler, and the like). In other embodiments, one or more additional components (in granular, powder, or pellet form or in the form of a gel or liquid) can be included with the PEBA resin and extruded therewith. As such, the outer layer of the heat shrink tube ultimately produced can comprise, in some embodiments, one or more such additional component(s). In certain embodiments, the outer layer of the heat shrink tubes of the present disclosure are prepared using a PEBA resin, and thus in some embodiments, can consist of PEBA, can consist essentially of PEBA, or can comprise PEBA. Typically, PEBA resins can be provided in a variety of different forms, for example, in the forms of solid pellets, powders, granules, dispersions, solutions, gels, and the like. In certain embodiments, the outer PEBA layer of the heat shrink tubes may be prepared using medical extrusion grade PEBA resin pellets. The type of PEBA resin that is utilized in certain embodiments can vary and may include PEBA medical extrusion grade pellets of different compositions (i.e., different durometer hardness), either as a single PEBA copolymer resin grade, as a blend of two or more PEBA copolymer resin grades, or as a blend that includes a PEBA copolymer resin grade. The PEBA resins utilized in certain embodiments may also be blended or compounded with other polymeric components (e.g., such as polytetrafluoroethylene (PTFE)) to tailor the final properties of the resulting non-crosslinked outer layer of the heat shrink tube for a particular application. Exemplary medical extrusion grade PEBA resins suitable for use according to the present disclosure are commercially available as PEBAX® 7433 SA 01 MED, PEBAX® 7233 SA 01 MED, PEBAX® 7033 SA 01 MED, PEBAX® 6333 SA 01 MED, PEBAX® 5533 SA 01 MED, PEBAX® 4533 SA 01 MED, PEBAX® 4033 SA 01 MED, PEBAX® 3533 SA 01 MED, PEBAX® 2533 SA 01 MED, and PEBAX® MV 1074 SA 01 MED manufactured by Arkema, Inc, or VESTAMID® Care ME71, VESTAMID® Care ME62, VESTAMID® Care ME55, VESTAMID® Care ME47, VESTAMID® Care ME40, and VESTAMID® Care ME26 manufactured by Evonik Corporation. However, it is to be understood that the outer layer of the heat shrink tubes provided herein are not limited to PEBA resins and may be prepared using one or more of the polymeric resins described herein in addition to PEBA, or instead of PEBA.

[0062] In some embodiments, one or more additives can be incorporated within the bulk of the outer layer, and / or applied upon the outer diameter surface. In some such embodiments, the one or more additives can be distributed (e.g., substantially uniformly) throughout the outer layer thickness and length of the tubing. In some embodiments, the one or more additives may include a lubricant, e.g., such as a thermally stable extrusion process lubricant. In certain embodiments, the lubricant may be a pentaerythritol ester, such as GLYCOLUBE® from Azelis Americas, LLC, for example. In certain embodiments, the one or more additives can comprise a lubricity modifier, e.g., understood to be an additive introduced to reduce friction on material surfaces when incorporated within the material as compared to the material surface alone. Certain lubricity modifiers include, but are not limited to, any silicone oil, silicone additive or blend, or silicone-based polymer. One non-limiting example of a lubricity modifier is MOBILIZE® from Compounding Solutions LLC (a polydimethyl siloxane lubricity modifier). In some embodiments, the one or more additives may include a radiopaque filler (i.e., an inorganic radiocontrast agent) to assist in medical procedures that utilize fluoroscopy for navigation of a medical device within the body. In certain embodiments, the radiopaque filler may be barium sulfate (BaSCh), bismuth subcarbonate (Bi2O2CC>3), bismuth oxychloride (BiOCl), bismuth trioxide (BizOa), or tungsten (W), for example. In some embodiments, the one or more additives may include a pigment to provide a desired color of the final outer PEBA layer of the heat shrink tube. In some embodiments, other additives such as inert fillers, stabilizers (i.e., radiation stabilizers, antioxidants, etc.), conductive fillers, anti-tack agents and antimicrobials may be included to produce desired functionality of the final outer PEBA layer of the heat shrink tube for specific applications. The amount of additive that can be contained in the final outer PEBA layer of the heat shrink tube is not particularly limited. In some embodiments, for example, the one or more additives (e.g., lubricant, pigment, filler, etc.) may be included in an amount in the range of 0.1% to 80%, about 1% to about 30%, or about 5% to about 20% by weight based on the total weight of the outer PEBA layer of the heat shrink tube. In other embodiments, the outer PEBA layer of the heat shrink tubes may not include any additives therein.

[0063] In some embodiments, the disclosed non-crosslinked inner layers of the multilayer heat shrink tubes comprise, consist essentially of, or consist of one or more polymers such as maleated polyolefins (i.e., polyethylenes, polypropylenes, ethylene copolymers), thermoplastic polyurethanes, polyethers, polyesters, ethylene vinyl acetate copolymers, ethylene acrylic acid copolymers, ethylene ethyl acetate copolymers; or a copolymer, blend, or derivative of any two or more of the foregoing. The inner layers of the multilayer heat shrink tubes comprise, consist essentially of, or consist of one or more polymers that exhibit a melting temperature which is below the melting temperature of the outer layer polymer. Exemplary polymers according to the present disclosure include, but are not limited to, a linear low density polyethylene grafted with maleic anhydride (LLDPE-g-MA).

[0064] In various embodiments, the inner layers of the heat shrink tubing disclosed herein are prepared from one or more maleated polyolefin resins. In some embodiments, the inner layers of the heat shrink tubing disclosed herein may be prepared from a resin comprising, consisting of, or consisting essentially of a maleated polyolefin resin in one or more of the forms noted herein. In some cases, a “resin” as used herein may contain one or more additional components as additives and / or one or more additional components can be added thereto (e.g., such as a lubricant, colorant, filler, and the like). In other embodiments, one or more additional components (in granular, powder, or pellet form or in the form of a gel or liquid) can be included with the maleated polyolefin resin and extruded therewith. As such, the inner layers of the heat shrink tube ultimately produced can comprise, in some embodiments, one or more such additional component(s).

[0065] In certain embodiments, the inner layer of the heat shrink tubes of the present disclosure are prepared using a maleated polyolefin resin, and thus in some embodiments, can consist of maleated polyolefin, can consist essentially of a maleated polyolefin, or can comprise a maleated polyolefin. Typically, maleated polyolefin resins can be provided in a variety of different forms, for example, in the forms of solid pellets, powders, granules, dispersions, solutions, gels, and the like. In certain embodiments, the inner maleated polyolefin layers of the heat shrink tubes may be prepared using medical extrusion grade maleated polyolefin resin pellets. The type of maleated polyolefin resin that is utilized in certain embodiments can vary and may include maleated polyolefin medical extrusion grade pellets of different compositions (i.e., different maleic anhydride contents), either as a single maleated polyolefin resin grade, as a blend of two or more maleated polyolefin resin grades, or as a blend that includes a maleated polyolefin resin grade. The maleated polyolefin resins utilized in certain embodiments may also be blended or compounded with other polymeric components (e.g., such as polytetrafluoroethylene (PTFE)) to tailor the final properties of the resulting non-crosslinked inner layers of the heat shrink tube for a particular application. Exemplary medical extrusion grade maleated polyolefin resins suitable for use according to the present disclosure are commercially available as OREVAC® 18300M manufactured by Arkema, Inc. or REZILOK RX™ 101, manufactured by Compounding Solutions LLC. Exemplary medical extrusion grade maleic anhydride grafted linear low density polyethylene (LLDPE-g-MA) resin suitable for use according to certain embodiments of the present disclosure include, but are not limited to, resins commercially available as REZILOK® Rx-101, manufactured by Compounding Solutions LLC. However, it is to be understood that the inner layers of the heat shrink tubes provided herein are not limited to maleated polyolefin resins and may be prepared using one or more of the polymeric resins described herein in addition to maleated polyolefins, or instead of maleated polyolefins.

[0066] In some embodiments, one or more additives can be incorporated within the bulk of the inner layers, and / or applied upon the inner diameter surface. In some such embodiments, one or more additives can be distributed (e.g., substantially uniformly) throughout the inner layer thickness and length of the tubing. In some embodiments, the one or more additives may include a radiopaque filler (i.e., an inorganic radiocontrast agent) to assist in medical procedures that utilize fluoroscopy for navigation of a medical device within the body. In certain embodiments, the radiopaque filler may be barium sulfate (BaSCL), bismuth subcarbonate (BizChCOs), bismuth oxychloride (BiOCl), bismuth trioxide (BijCh), or tungsten (W), for example. In some embodiments, the one or more additives may include a pigment to provide a desired color of the final inner maleated polyolefin layers of the heat shrink tube. In some embodiments, other additives such as inert fillers, stabilizers (i.e., radiation stabilizers, antioxidants, etc.), conductive fillers, anti-tack agents and antimicrobials may be included to produce desired functionality of the final inner maleated polyolefin layers of the heat shrink tube for specific applications. The amount of additive that can be contained in the final inner maleated polyolefin layers of the heat shrink tube is not particularly limited. In some embodiments, for example, the one or more additives (e.g., lubricant, pigment, filler, etc.) may be included in an amount in the range of about 0.1% to about 80%, about 1% to about 30%, or about 5% to about 20% by weight based on the total weight of the inner maleated polyolefin layer of the heat shrink tube. In other embodiments, the inner maleated polyolefin layers of the heat shrink tubes may not include any additives therein. The sizes of multilayer heat shrink tubes within the scope of this disclosure (e.g., length, diameter (i.e., expanded inner diameter, ID), and average wall thickness) are not particularly limited. For example, the length of tubes described herein can vary from individually sized units (e.g., in some embodiments, on the order of 0.1 inches to 120 inches for catheter or medical device component manufacturing) to lengths that can readily be transported and further cut into individually sized units to large-scale production lengths (e.g., on the order of hundreds of feet and the like). The diameters of tubes described herein can vary, in particular, depending upon the application for which the tubing is intended. Certain expanded IDs of the tubes described herein, particularly for catheter and medical device uses, can range from about 0.005 inches to about 1.5 inches (e.g., about 0.01 inches to about 0.7 inches or about 0.015 inches to about 0.5 inches), although tubes having expanded IDs outside this range are also encompassed by the present disclosure, particularly in the context of applications in different fields. The layer ratios of multilayer tubes described herein can vary, in particular, depending upon the application for which the multilayer tubing is intended. Certain layer ratios of the multilayer tubes described herein, particularly for catheter and medical device uses, range from 99:1 to 1:99 inches (e.g., 95:5 to 5:95 or 75:25 to 25:75 or 50:50), although multilayer tubes having layer ratios outside this range are also encompassed by the present disclosure, particularly in the context of applications in different fields.

[0067] In general, the methods by which multilayer heat shrink tubes are prepared can vary. Generally, the desired resin or resins, such as the PEBA and maleated polyolefin resins as described herein, are converted into a multilayer tubular form via extrusion and then mechanically expanded. The means by which these steps are conducted can vary, as will be described herein.

[0068] A multilayer tube may be formed through the multilayer extrusion process. Multilayer extrusion generally comprises placing the desired resin or resins into an extruder (e.g., a single screw melt extruder) designated for a given layer or layers. Within each extruder, the resin or resins are heated, compressed, and conveyed out of the extruder and through a multilayer extrusion head (also referred to herein as a “multilayer head” or simply “head”) containing an annular die set, creating a multilayer tube. The annular die set (also referred to herein as “tooling”) consists of a circular extrusion die and a mandrel which forms the polymer melt into a tubular form as it exits the multilayer extrusion head. Within the multilayer head the polymer melts from each of the extruders are brought together with minimal mixing to allow the formation of distinct layers within the tube.

[0069] Multilayer tubes of various diameters, wall thicknesses, and lengths can be produced using the forming methods described herein. The final dimensions of the extruded multilayer tubular form can be adjusted and optimized through proper tooling selection along with other parameters in the extrusion step such as temperature, pressure, and screw rotation speed. The head is connected to a number of extruders, each of which is generally comprised of a hopper, barrel, screw, and breaker plate. The screw of each extruder is generally comprised of several sections (e.g., the feed, compression, and metering zones) that can be optimized to provide an effective and consistent extrusion process. Generally, there are multiple temperature-controlled zones throughout each extruder, each of which can be adjusted and optimized to produce tubular forms of desired dimension and quality. In some embodiments, multilayer tubing having a relatively uniform total wall thickness (i.e., high percent concentricity) is provided.

[0070] Appropriate sizing of the tooling to be used during the extrusion process is generally determined by the specified finished multilayer tubular dimensions, individual extruder specifications, the desired draw down ratio (DDR), and the draw ratio balance (DRB). The DDR and DRB are unitless quantities used by those skilled in the art to describe the relationship between the dimensions of the polymer melt as it exits the tooling to the dimensions of the final multilayer tubular form (i.e., the final extruded tube dimensions). Draw down ratio (DDR) is defined as the ratio of the cross- sectional area of the polymer melt as it exits the tooling to the cross-sectional area of the final tubular form. The molten tubular form must be “drawn down” (i.e., reduced in diameter and cross-sectional area via stretching) after exiting the tooling and before quenching (i.e., rapidly cooling in air or a chilled fluid bath) to obtain the desired final tubular dimensions. Generally, utilizing tooling that provides a high DDR with respect to the dimensions of the final tubular form enables faster line speeds (i.e., a faster production rate). It is also important to note that a tube produced with a higher DDR has a greater degree of longitudinal orientation of the polymer chains than a tube produced using a lower DDR. It is well known to those skilled in the art that imparting a particular degree of orientation on a polymeric material can influence the mechanical and physical properties of the final product. These properties (e.g., such as mechanical properties) can be optimized for a particular application (i.e., input for a secondary expansion process) by varying the degree of orientation. Draw ratio balance (DRB) is defined as the diameter ratio of the extrusion die and mandrel divided by the diameter ratio of the final tubular form. Generally, DRB characterizes the relationship between the annular shape of the polymer melt as it exits the die and the annular shape of the final tubular form. It is well known by those skilled in the art that careful tooling selection is required to achieve a stable tubular extrusion process. The dimensional relationship of the tooling used to produce a tube of a given size influences the line speed of the extrusion process (i.e., the production rate) based on the DDR. However, this dimensional relationship must be balanced because it also directly influences the overall stability of the extrusion process through the DRB. Tooling selection is an important aspect of the extrusion process to produce a tubular form of specified dimension that also has desirable mechanical characteristics.

[0071] The extruded multilayer tubular form is then typically radially expanded (e.g., by mechanical means) to provide an expanded multilayer tube, i.e., a multilayer heat shrink tube (i.e., a tubing which decreases in diameter when heated). The expansion of the input multilayer tubing (i.e., the initial extruded tubular form) can be conducted in-line with extrusion or off-line (i.e., conducted independently of and / or secondary to the extrusion process). All means for radial expansion of tubing are intended to be encompassed by the present invention. Generally, during the expansion process, the multilayer tubing is expanded radially by pressurizing the inside of the tubing, introducing stress into the tube wall. This pressurizing can be conducted by any means capable of providing a differential pressure between the inside and outside of the tubing. Such differential pressure can be created by imposing a pressure above atmospheric pressure on the inside of the tube, imposing a pressure below atmospheric pressure on the outside of the tube, or a combination of the two. The stress induced into the wall of the tube causes it to expand radially, i.e., increase in diameter. The rate of expansion can be controlled so the tube will hold the expanded state and does not recover until subjected to a further heat cycle. The extent to which a tube is expanded depends on the application for which the final heat shrink tubing is intended. The rate and extent to which a tube is expanded depends on the temperature at which the expansion process is conducted. It has been found that the expansion chamber temperature must be carefully controlled to optimize the rate and extent of expansion of the tube. In some embodiments, the tubing is expanded to an inner diameter from about 1.05 times its original (unexpanded) inner diameter to about 10 times its original (unexpanded) inner diameter.

[0072] In certain embodiments, multilayer PEBA heat shrink tubes prepared according to the present disclosure may be radially expanded using the processes described, for example, in U.S. Patent No. 9,296,165 to Henson, which is incorporated by reference herein in its entirety. For example, the Henson patent describes a process for the production of thermoplastic polymeric heat shrink tubing using a first fluid in the interior of a tube to expand it and a second fluid exterior to the tube to constrain the expansion within an expansion chamber. In other embodiments, for example, the tubing may be expanded by adjusting the flow rate of the air external to the tube, the chamber temperature, the air pressure within the tube, and the rate at which the tube moves through the expansion chamber. In certain embodiments, the heat shrink tubes of the present disclosure are expanded at elevated temperature through a die using any number of methods known to the art, and subsequently cooled at the die exit. Cooling can be accomplished using fluids such as water, oil, or air. The processing parameters that can be adjusted include, but are not limited to: die type, die diameter and length, die temperature, fluid pressure inside the tube, fluid pressure outside the tube, cooling method, cooling medium type and temperature, expansion rate, tube materials, tube ID, tube OD, and tube wall thickness.

[0073] It is noted that, although certain heat shrink PEBA tubes are known, these tubes comprise predominantly crosslinked PEBA, which provides for the heat shrink capabilities of the tubes. Generally, the PEBA heat shrink tubes provided herein are expanded under carefully controlled conditions of internal air pressure, temperature, and throughput through an expansion die prior to rapidly cooling the tube to lock in the entropically unfavorable expanded state. Examples of heat shrinkable crosslinked PEBA tubing are provided, for example, by Cobalt Polymers, TE Connectivity, and in the disclosures of U.S. Pat. No. 7,306,585 to Ross and U.S. Pat. App. Pub. No. 2008 / 0317991 to Pieslak et al. Crosslinking through chemical means or by irradiation has long been used in the production of heat shrink tubes and films in order to obtain a greater degree of elastic recovery of the expanded part upon heating (i.e., increase attainable recovery ratio and / or recovery force upon heating). Crosslinking a polymer article such as a tube or film effectively increases the molecular weight of the polymer in addition to improving its elastic response to an imposed deformation. This effective increase in molecular weight also results in a marked increase in the viscosity of the polymer (due to the increased probability of interchain entanglements), which hinders the ability of the material to flow into and fill voids (i.e., open spaces or interstices in the pattern of an underlying reinforcing component). The increased viscosity due to crosslinking also reduces the ability of the polymer to conform tightly to and bond with an underlying substrate during recovery. The increased recovery ratio attainable with crosslinked materials can also lead to unwanted deformation or damage to a sensitive underlying substrate during recovery.

[0074] Advantageously, as referenced herein, multilayer heat shrink tubes comprising an outer layer of PEBA and an inner layer of maleated polyolefin are provided, wherein a majority (e.g., the entirety) of the PEBA within the outer layer and the maleated polyolefin within the inner layer of the tube are not cross-linked. In some embodiments, the tubes provided herein comprise no cross-linked polymer, comprise less than 2% by weight of a crosslinked polymer, less than 1% by weight of a cross-linked polymer, or less than 0.5% by weight of a cross-linked polymer. The disclosed multilayer heat shrink tubes can exhibit high recovery ratios; in some embodiments, the disclosed multilayer heat shrink tubes can have recovery ratios (RRs) of greater than about 1.05: 1 , greater than about 1.10:1, greater than about 1.2:1, greater than about 1.3:1, greater than about 1.4:1, greater than about 1.5:1, or greater than about 1.6:1, e.g., about 1.05:1 to about 2:1. In some embodiments, the multilayer heat shrink tubes can be described based on the reducibility in ID (upon recovery). Examples of such values include, but are not limited to, tubes reducible in ID by at least about 4%, at least about 5%, at least about 6%, at least about 7%, at least about 8%, at least about 9%, at least about 10%, at least about 11%, at least about 12%, at least about 13%, at least about 14%, at least about 15%, at least about 20%, at least about 25%, or at least about 30%, such as about 5% to about 40%, including, e.g., about 4.8%, about 9.1%, about 16.7%, about 23.1%, about 28.6%, about 33.3%, or about 37.5%.

[0075] In some embodiments, the disclosed multilayer heat shrink tubes can be described based upon their durometer hardness measurements of the outer layer. For example, in one specific embodiment, a durometer hardness measurement of a heat shrink tubing as provided herein according to ASTM D2240 conducted on a flat specimen fabricated by melt pressing the heat shrink tubing (in expanded form) is about 20 to about 80 shore D.

[0076] The multilayer heat shrink tubes provided herein can be used in various ways. In some embodiments, they are advantageously used in catheter assembly processes, e.g., as a replacement for conventional (e.g., FEP) heat shrink tubes used as manufacturing aids to compress an underlying catheter pre-assembly during heating / reflow. Such processes can avoid the need for disposable components, e.g., the FEP heat shrink tubes typically required to produce the catheter assembly. According to the present disclosure, the provided multilayer heat shrink tubes (e.g., PEBA heat shrink tubes with an adhesive inner layer) can function both as a catheter jacket and as a processing aid / heat shrink to provide sufficient compression during heating / reflow.

[0077] As such, the disclosed multilayer heat shrink (i.e., expanded) tube enables a catheter shaft to be manufactured by heating the multilayer heat shrink tube as an outer sheath tube (“jacket”) of a catheter shaft pre-assembly, inducing dimensional recovery of the multilayer heat shrink tube and allowing for reflow of the inner layer(s) through a reinforcing component (where present) and bonding to the underlying liner without the use of a fusing sleeve (e.g., FEP). Since the polymeric material of the disclosed multilayer heat shrink tube is not crosslinked, its viscosity is such that the polymer can easily flow through and encapsulate a reinforcing component (where present) and adhere to the outer surface of the inner liner when heated under an appropriate recovery profile. The selection of an appropriate heating temperature and time (also referred to herein as “heating profile” or “recovery profile”) for a particular non-crosslinked multilayer heat shrink outer jacket tube can vary substantially depending on the underlying catheter assembly components and the composition of the non-crosslinked multilayer heat shrink tubing. In this way, expansion conditions, recovery ratio, and the recovery profile can be tailored to provide a non-crosslinked PEB A heat shrink tube with an adhesive inner layer capable of forming an outer sheath for various different types of catheter structures.

[0078] After production of the desired construct with the disclosed multilayer heat shrink tube associated therewith and during or after recovery of the multilayer heat shrink tube, if desired, the outer surface of the construct (comprising the multilayer heat shrink material) can optionally be further modified or smoothed through a secondary process. For example, in some embodiments, the construct is passed through a heated metallic die or a heated polymer-coated die during or after recovery of the multilayer heat shrink material, producing a catheter assembly comprising a modified (e.g., smoothed) outer surface. The heated die can be coated with polytetrafluoroethylene (PTFE), for example. In some embodiments, the construct is passed through a heated or polymer-coated die during or after recovery of the multilayer heat shrink material to provide a textured or engineered outer surface to modify or enhance sliding properties of the finished construct.

[0079] The use of the disclosed multilayer heat shrink tubing as an outer jacket for catheter shafts removes the need for manufacturing aids such as FEP heat shrink tubes commonly used in the production of catheter shafts. This is advantageous in many respects. Firstly, an expensive component is removed from the manufacturing process. Secondly, process scrap is reduced since the FEP heat shrink tubing must be removed and discarded after the reflow process is completed. Thirdly, the heat transfer of the recovery process is improved greatly by removing, in effect, an insulating layer (i.e., the FEP heat shrink tubing), which will improve cycle times. Finally, the potential for damaging the completed catheter shaft during manufacturing is greatly reduced if there is no need to nick, skive, or cut away an FEP heat shrink tube in order to remove it. EXAMPLES

[0080] Example 1

[0081] A commercially available poly(ether-block-amide) (PEBA) resin (Arkema, Inc, PEBAX® 5533 SA 01 MED) was obtained in pellet form and dried in a membrane dryer at 167°F overnight to ensure the resin moisture content was less than 0.15% by weight. The dried PEBA resin was placed into a resin hopper dryer to prevent re-absorption of moisture before and during extrusion. A commercially available maleic anhydride grafted linear low density polyethylene (LLDPE-g-MA) resin (Arkema, Inc, OREVAC® 183 OOM) was obtained in pellet form and placed in the resin hopper of a second single screw extruder. The dried PEBA pellets were melted and conveyed to a multilayer head by utilizing a single screw extruder having a barrel diameter of 74”, a screw rotation of 5 - 6 rpm, and barrel zone temperatures of 380 - 410°F. The LLDPE-g-MA pellets were melted and conveyed to a multilayer head by utilizing a second single screw extruder having a barrel diameter of a screw rotation of 6 - 7 rpm, and barrel zone temperatures of 380 - 410°F. The multilayer head was configured to have the PEBA as the outer layer and the LLDPE-g-MA to be the inner layer of a multilayer tube and utilized a die temperature of 390 - 405°F, and an annular die set that provided a draw down ratio (DDR) of 12 - 14. After exiting the annular die set, the multilayer input tube was passed through a chilled water bath to sufficiently quench the tubing and set the final tubular dimensions. A multilayer input tube having an average inner diameter of 0.065”, an average total wall thickness of 0.005”, and an average layer ratio of 50:50 obtained using this process.

[0082] The prepared multilayer input tube was then expanded by pressurizing the inner diameter of the tube with compressed air as the input tube resided within a stainless steel hypodermic tube (also referred to herein as a “hypodermic tube” or “hypo tube” or just “hypo”) and a forced air heating element (also referred to herein as a “thermal nozzle”) passed along the length of the hypodermic tube. The hypo tube serves as an expansion die and is used to restrict expansion of the multilayer input tube to a specified expanded diameter. The processing parameters of expansion air pressure applied to the ID of the multilayer input tubing, temperature of the pressurized expansion air applied to the ID of the multilayer input tubing, forced air heating element air temperature, forced air heating element air flowrate, forced air heating element traversal rate were all adjusted to give a noncrosslinked multilayer PEBA heat shrink tube with adhesive inner layer according to the present disclosure.

[0083] In particular, the multilayer heat shrink input tube of Example 1 was expanded using a forced air heating element air temperature of 255 - 265°F, an expansion air pressure of 35 psi, forced air heating element air flowrate of 40 liters / minute, and a forced air heating element traversal rate of 1.2 mm / s. CATHETER EXAMPLES

[0084] Example 2

[0085] A PTFE tube with a .110” average OD and a .030” average wall was inserted into the ID of an OD etched PTFE liner consisting of .115” average ID and a .0015” average wall thickness. The PTFE tube acts as a support mandrel for the OD etched PTFE liner. A Steeger USA medical catheter braider fitted with 16 carriers supporting .002” nominal OD stainless steel braid wire was used to apply full braid pattern with an average of 80 picks per inch to the outer surface of the supported OD etched PTFE liner. The multilayer heat shrink tube from Example 1 was then slid over top of the braided surface of the supported OD etched PTFE liner. This assembly (i.e., the over braided supported OD etched PTFE liner and multilayer heat shrink tube of Example 1) was suspended vertically and heated in a Beahm 815A vertical laminator equipped with a thermal nozzle set at 310°F and utilizing a thermal nozzle traverse rate of 0.2 mm / s to provide a braid reinforced catheter shaft with an outer jacket comprising non-crosslinked PEBA and maleated polyolefin layers. After cooling, the .110” OD PTFE support tube was removed from the ID of completed build. A section was cut from the completed build and cast in 2-part acrylic resin. Once the acrylic resin had cured the specimen was sectioned with an abrasive sectioning saw and then polished to yield a mounted sample of the completed build. The mounted sample was examined using a Keyence VHX-5000 digital microscope to determine if the noncrosslinked inner layer of the multilayer heat shrink tube flowed within the interstices of the braid reinforcement and made adequate contact with the outer surface of the inner liner during the heating process. Images captured during this examination are shown in FIG. 4, FIG. 5, and FIG. 6.

[0086] Example 3

[0087] A commercially available poly(ether-block-amide) (PEBA) resin (Arkema, Inc, PEBAX® 5533 SA 01 MED) was obtained in pellet form and dried in membrane dryer at 167°F overnight to ensure the resin moisture content was less than about 0.15% by weight. The dried PEBA resin was placed into a resin hopper dryer to prevent re-absorption of moisture before and during extrusion. A commercially available maleic anhydride grafted linear low density polyethylene (LLDPE-g-MA) resin (Compounding Solutions LLC, REZILOK® Rx-101) was obtained in pellet form and placed in the resin hopper of a second single screw extruder. The dried PEBA pellets were melted and conveyed to a multilayer head by utilizing a single screw extruder having a barrel diameter of3 / ”, a screw rotation of about 7.3 rpm, and barrel zone temperatures around 370°F. The LLDPE-g-MA pellets were melted and conveyed to a multilayer head by utilizing a second single screw extruder having a barrel diameter of 18mm, a screw rotation of about 5.3 rpm, and barrel zone temperatures around 400°F. The multilayer head was configured to have the PEBA as the outer layer and the LLDPE-g- MA to be the inner layer of a multilayer tube and utilized a die temperature of approximately 380°F, and an annular die set that provided a draw down ratio (DDR) around 12. After exiting the annular die set, the multilayer input tube was passed through a chilled water bath to sufficiently quench the tubing and set the final tubular dimensions. A multilayer input tube having an inner diameter of about 0.056”, an average total wall thickness of about 0.0065”, and an average layer ratio of 50:50 was obtained using this process.

[0088] The prepared multilayer input tube was then expanded using the same process as Example 1, except an expansion air pressure of 80 psi was utilized.

[0089] Example 4

[0090] A commercially available poly(ether-block-amide) (PEBA) resin (Arkema, Inc, PEBAX® 3533 SA 01 MED) compounded with a lubricity modifier (Compounding Solutions LLC, MOBILIZE®) was obtained in pellet form and dried in membrane dryer at 150°F overnight to ensure the resin moisture content was less than about 0.15% by weight. The dried PEBA compound was placed into a resin hopper dryer to prevent re-absorption of moisture before and during extrusion. A commercially available maleic anhydride grafted linear low density polyethylene (LLDPE-g-MA) resin (Compounding Solutions LLC, REZILOK® Rx-101) was obtained in pellet form and placed in the resin hopper of a second single screw extruder. The dried PEBA compound pellets were melted and conveyed to a multilayer head by utilizing a single screw extruder having a barrel diameter of3 / ?’, a screw rotation of about 8.5 rpm, and barrel zone temperatures around 370°F. The LLDPE-g-MA pellets were melted and conveyed to a multilayer head by utilizing a second single screw extruder having a barrel diameter of 18mm, a screw rotation of about 5.5 rpm, and barrel zone temperatures around 400°F. The multilayer head was configured to have the PEBA as the outer layer and the LLDPE-g-MA to be the inner layer of a multilayer tube and utilized a die temperature of approximately 380°F, and an annular die set that provided a draw down ratio (DDR) around 12. After exiting the annular die set, the multilayer input tube was passed through a chilled water bath to sufficiently quench the tubing and set the final tubular dimensions. A multilayer input tube having an inner diameter of about 0.056”, an average total wall thickness of about 0.0065”, and an average layer ratio of 50:50 was obtained using this process.

[0091] The prepared multilayer input tube was then expanded using the same process as Example 1, except a forced air heating element air temperature of 215 - 225°F, and an expansion air pressure of 27 psi was utilized.

Claims

1. CLAIMSWhat is claimed is:

1. A multilayer heat shrink tubing comprising: an outer layer comprising non-crosslinked PEBA; and an inner layer comprising maleated polyolefin, wherein the maleated polyolefin has a melt temperature that is lower than the melt temperature of the outer layer.

2. The multilayer heat shrink tubing of claim 1 wherein the heat shrink tubing has a recovery ratio (RR) greater than 1.05:1.

3. The multilayer heat shrink tubing of claim 1 or 2, wherein the outer layer consists essentially of the non-crosslinked PEBA.

4. The multilayer heat shrink tubing of claim 1 or 2, wherein the outer layer further comprises a lubricity modifier.

5. The multilayer heat shrink tubing of any of claims 1-4, wherein the inner layer consists essentially of the maleated polyolefin.

6. The multilayer heat shrink tubing of any of claims 1-5, wherein the maleated polyolefin comprises one or more of maleic anhydride grafted polyethylene, maleic anhydride grafted polypropylene, and maleic anhydride grafted ethylene vinyl acetate copolymer.

7. The multilayer heat shrink tubing of any of claims 1-5, wherein the maleated polyolefin comprises maleic anhydride grafted linear low density polyethylene.

8. The multilayer heat shrink tubing of any of claims 1-7, wherein the weight ratio of the outer layer to the inner layer is between 99:1 and 1:99.

9. The multilayer heat shrink tubing of claim 8, wherein the weight ratio of the outer layer to the inner layer is between 95:5 and 5:95.

10. The multilayer heat shrink tubing of claim 8, wherein the weight ratio of the outer layer to the inner layer is between 90:10 and 10:90.

11. The multilayer heat shrink tubing of claim 8, wherein the weight ratio of the outer layer to the inner layer is between 75:25 and 25:75.

12. The multilayer heat shrink tubing of any of claims 1-11, wherein the heat shrink tubing has a recovery ratio (RR) greater than about 1.10:1 and / or wherein the heat shrink tubing is reducible in inner diameter (ID) by about 9.1%.

13. The multilayer heat shrink tubing of claim 12, wherein the RR is greater than about 1.2: 1 and / or wherein the heat shrink tubing is reducible in ID by about 16.7%.

14. The multilayer heat shrink tubing of claim 12, wherein the RR is greater than about 1.3:1 and / or wherein the heat shrink tubing is reducible in ID by about 23.1%.

15. The multilayer heat shrink tubing of claim 12, wherein the RR is greater than about 1.4: 1 and / or wherein the heat shrink tubing is reducible in ID by about 28.6%.

16. The multilayer heat shrink tubing of claim 12, wherein the RR is greater than about 1.5:1 and / or wherein the heat shrink tubing is reducible in ID by about 33.3%.

17. The multilayer heat shrink tubing of claim 12, wherein the RR is greater than about 1.6: 1 and / or wherein the heat shrink tubing is reducible in ID by about 37.5%.

18. The multilayer heat shrink tubing of any of claims 1-17, wherein a durometer hardness measurement of the outer layer of a flat specimen fabricated by melt pressing the heat shrink tubing in expanded form is about 20 to 80 Shore D.

19. A catheter shaft pre-assembly comprising the multilayer heat shrink tubing of any of claims 1-18.

20. The catheter shaft pre-assembly of claim 19, further comprising a catheter liner in direct contact with the inner layer of the multilayer heat shrink tubing, wherein the catheter liner optionally comprises a reinforcing component (e.g., braids) on an outer surface thereof.

21. A catheter, comprising: a catheter liner; an optional reinforcing component (e.g., braids) on an outer surface of the catheter liner; a first layer comprising maleated polyolefin surrounding and bonded to the catheter liner,wherein the first layer is bonded through and at least partially encapsulates the optional reinforcing component, where present, and a second layer comprising recovered, non-crosslinked PEBA surrounding the first layer, wherein the maleated polyolefin has a melt temperature that is lower than the melt temperature of the second layer.

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