Patent Application
20160158491
The present invention is directed to dimensionally recoverable tubing. In particular, the present invention is directed to multiple wall, e.g. dual wall, dimensionally recoverable tubing for forming reinforced polymer tubing.
Single layer dimensionally recoverable tubing for a variety of applications may be formed by known processes. For example, U.S. Pat. No. 3,086,242 to Cook et al, and U.S. Pat. No. 3,370,112 to Wray, which are hereby incorporated by reference in their entirety, disclose processes and apparatus for expanding tubing by employing a pressure differential between the inside and outside of the tubing. Cook et al. and Wray describe processes for producing dimensionally recoverable tubing by crosslinking and expanding a tube of polymeric material. In both cases, the tubing is expanded by employing a pressure differential between the inside and outside of the tubing. To form the heat-recoverable tubing, the tubing is extruded or otherwise suitably formed and crosslinked. After the tubing is crosslinked, the tubing is then heated to a temperature equal to or above its crystalline melting temperature or temperature range so as to melt the crystalline structure in the material. While the tubing is at the elevated temperature, a pressure differential is imparted across the tubing wall to expand the tubing. After subjecting the tubing to this differential pressure, the tubing is then passed through a cooling zone to cool the tubing to a temperature below the crystalline melting temperature or range to form the dimensionally recoverable tubing. The pressure differential may be imparted by continuously supplying air to the interior of the tubing, while applying ambient or sub-ambient pressure outside the tubing. Upon re-heating, the tubing will recover to the configuration it had when crosslinked.
Medical devices, such as catheters, generally require reinforcing material to provide the necessary mechanical and chemical properties, including resiliency, flexibility, lubricity, and insulation, as well as resistance to the environment within the human body, useful in catheter applications. Current manufacturing methods for catheters have included a process wherein layers of uncrosslinked polymer, such as polyether block amide polymer or polyester elastomer, are disposed within an expanded fluorinated ethylene propylene (“FEP”) tube. A braid fabricated from a reinforcing material known in the art for reinforcing catheters, such as braided stainless steel fibers, is placed within the assembly. The assembly is then heated to an elevated temperature, e.g. from about 182 to about 218° C. (about 360 to about 425° F.), which results in melting of the uncrosslinked polymer as well as contraction of the FEP tubing. As the FEP tubing contracts, the FEP tubing exerts a force on the melted uncrosslinked polymer, driving the polymer onto the braid, which consolidates the assembly. After the assembly is consolidated, the FEP tubing is removed and discarded and the resulting product is suitable for use as a catheter. This method suffers from the drawback that the use of the FEP tube, or similar device, that must be removed adds complexity and cost to the process, particularly because of yield loss due to the removal of the FEP and the potential damage to the underlying layer. Further, the high temperature required to recover the FEP requires high energy costs and specialized equipment.
What is needed is a method and system for forming dimensionally recoverable tubing for use in reinforced medical devices that are easily fabricated, create less production scrap, and do not suffer from the deficiencies noted above.
One aspect of the present invention includes a multi-layered dimensionally recoverable tubing system. The system has a first layer, a second layer and a reinforcing structure. The first layer includes at least one crosslinkable polymer. The second layer is disposed adjacent to the first layer and includes a polymer. A reinforcing structure is disposed adjacent to the second layer. One or both of the first layer and second layer are dimensionally recoverable. The first layer is substantially crosslinked, and the second layer is substantially uncrosslinked. To form a reinforced medical device, the system is heated and dimensionally recovered, where the reinforcing structure becomes incorporated in the second layer.
Another aspect of the present invention includes a method for making a reinforced medical device. The method includes providing a first layer preferably having a crosslinking agent. A second layer adjacent to the first layer is provided to form a multiple layer assembly. The first layer is exposed to conditions sufficient to result in crosslinking of the first layer. The multiple layer assembly is expanded to render the multiple layer assembly dimensionally recoverable. A reinforcing structure is provided adjacent to the second layer. The multiple layer assembly is heated to a temperature sufficient to at least partially dimensionally recover the first layer and to incorporate the reinforcing structure into the second layer. The multiple layer assembly is consolidated to form a reinforced multiple layer device.
Another aspect of the present invention includes a reinforced medical device comprising a multiple layer device having at least one dimensionally recovered, polymeric first layer. In addition, the device includes at least one polymeric second layer disposed adjacent to the first layer. The device also includes a reinforcing structure incorporated into the second layer. Both the second and first layers may or may not be crosslinked.
An advantage of an embodiment of the present invention is that the dimensionally recoverable first layer provides formation and incorporation of the reinforcing structure with easier processing and reduced waste.
Another advantage of the present invention is that the process of forming the reinforced device may be performed utilizing readily available equipment with few process steps.
Another advantage of the present invention is that the first layer does not require removal after final consolidation of the reinforced device, thus minimizing the amount of production scrap.
The present invention allows a higher shrink ratio than currently available with FEP. Also, this concept can be used to connect a larger shaft to a smaller shaft with one piece.
Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.
The same reference numbers will be used throughout the drawings to refer to the same or like parts.
The present invention utilizes an assembly having at least one layer of a dimensionally recoverable material, preferably in the form of a tube or sheath, to provide a force, when heated, onto a substantially uncrosslinked material to urge the uncrosslinked material over, around and/or into a reinforcing structure, to form a reinforced structure useful as a medical device. As utilized herein “crosslinked” materials and grammatical variations thereof are defined as materials that are partially or fully crosslinked or material having high degrees of chemical (e.g., polymeric) crosslinking. As utilized herein “uncrosslinked” materials and grammatical variations thereof are defined as materials that are non-crosslinked or material having low degrees of chemical crosslinking, wherein the amount of crosslinking is sufficiently low to allow flowability. For example, uncrosslinked materials preferably have sufficient flowability to permit infiltration of a reinforcing structure into the uncrosslinked material. Further “non-crosslinkable” materials and grammatical variations thereof are defined as materials having a partial or total resistance to crosslinking when exposed to conditions sufficient to cause crosslinking in crosslinkable materials.
An embodiment of the present invention includes a multiple layer system for forming reinforced medical devices, where the multiple layer system includes at least one layer of a dimensionally recoverable material. A polymeric heat-recoverable material is a dimensionally heat unstable material frequently said to possess “elastic memory”. One form of heat-recoverable material includes tubular sheaths suitable for wrapping or encompassing elongated components. As is well-known to those skilled in the art, materials having the property of elastic memory are dimensionally heat unstable and may be caused to change shape and/or dimension by the application of heat. Elastic memory may be imparted to polymeric materials by first extruding or otherwise molding the polymer into a desired shape. The polymer is then crosslinked or given the properties of a crosslinked material by exposure to high energy radiation, e.g., a high energy electron beam, Co60 gamma irradiation, or exposure to ultra-violet irradiation, or by chemical means, e.g., incorporation of a peroxide. The crosslinked polymeric material is then heated and deformed and then locked in that deformed condition by quenching or other suitable cooling. Alternatively, for some systems, the expansion may be accomplished at room temperature by using greater force to deform the polymer. The deformed material will retain its shape almost indefinitely until exposed to an elevated temperature sufficient to cause recovery. The property of elastic memory can also be imparted without actual crosslinking to materials, such as some perfluoropolymers (e.g. polytetrafluoroethylene and FEP) and polyolefins or vinyl polymers that have a sufficiently high molecular weight to give the polymer appreciable strength at temperatures below the crystalline melting point. These materials can be expanded at temperatures between the glass transition temperature and the melting point. The expansion can be from about 120 to about 600 percent, which is often much greater than can be accomplished by simply expanding in the molten (amorphous) state.
Where a simple tubular shape is desired it may be fabricated from a flat sheet of material simply by rolling it into a tube and suitably sealing the seam. Tubing may be supplied as a sheet that is rolled into position before application of heat. Recoverable articles are frequently used to cover objects having a tubular or otherwise regular elongate configuration, to provide, for example, environmental sealing protection. Where no free end of the elongate object is available, it is common practice to use a so-called wrap-around material, that is a material, typically in the form of a sheet, that is installed by wrapping it around the object to be covered so that opposed longitudinal edges overlap. In order to hold the wrap-around material around the object, a closure means may be applied to secure together the opposed longitudinal edges; although one skilled in the art will readily appreciate that, depending on the particular application, the adhesive component may be sufficient to seal the material to the object. In an example embodiment, the tubing system is a multi-layered, heat-shrinkable tube having a substantially cylindrical shape.
For example, the tubing system may be substantially cylindrical and have a ratio of the inner diameter of the expanded tubing to the inner diameter of the recovered tubing (recovery ratio) of from about 1.2 to about 6, or much larger. The inner wall and the expanded polymeric outer jacket taken together may have a thickness of from about 0.04 mm (0.0016 inches) to about 1.25 mm (0.05 in). The inner layer may be thicker than the outer layer. Alternatively, the outer layer may be thicker than the inner layer if greater force on recovery is desired.
As shown in
The outer layer 103 further may include a crosslinking agent to promote crosslinking when irradiated with an electron beam or other suitable source of energy capable of crosslinking the material of the outer layer. Suitable crosslinking agents may include any crosslinking promoter that facilitates crosslinking within the outer layer 103 when irradiated. Suitable crosslinking promoters include, but are not limited to, triallyl cyanurate, triallyl isocyanurate, N,N′-m-phenylene-dimaleimide, and multifunctional acrylates or methacrylates. In addition or alternatively, chemical crosslinking agents, such as peroxides, may be used in place of radiation crosslinking.
The inner layer 105 preferably includes a substantially uncrosslinked elastomeric polymer. The inner layer 105 may include the polymer of the outer layer 103 or may be fabricated from a different material. The inner layer 105 is formulated with sufficient polymer and, if desired, a crosslinking inhibitor (e.g. some antioxidants), to provide resistance to crosslinking during irradiation. Crosslinking inhibitors include any materials that impart the polymer of the inner layer 105 with a resistance to crosslinking when exposed to ionizing radiation. Suitable crosslinking inhibitors include, but are not limited to, phenolic antioxidant or thioester, or aromatic disulfide. While it is preferred to substantially avoid crosslinking of the inner layer 105 for embodiments in which the inner layer must flow in contact with the reinforcing structure (not illustrated in
In an alternate embodiment, the inner layer 105 may include a flow agent, e.g., a wax. The wax preferably provides additional resistance to crosslinking, particularly when in combination with the antioxidant. Suitable wax compositions for use with the present invention may include, but are not limited to low molecular weight polyethylene or polypropylene polymers or other wax polymer compositions suitable for use in a tubing layer.
The inner layer may be crosslinked or noncrosslinked, although preferably will be uncrosslinked and may contain a crosslinking inhibitor to enhance the ability of the inner layer to flow. In an alternate embodiment, the inner layer 105 may contain an adhesive. If desired for a “reverse” embodiment such as that shown in
The inner layer 105 may include one or more of the above ingredients alone or in combination, wherein the composition may depend upon the desired properties of the resultant medical device. In addition, other additives such as color concentrates, dyes or pigments, stabilizers, fillers, crosslinking inhibitors, antioxidants, reaction promoters, lubricating agents, radiopaque fillers, or other additives may be added to the outer layer 103 and/or inner layer 105 to provide desired properties.
As discussed in greater detail above, the outer layer 103 and the inner layer 105 are formed as a dimensionally recoverable structure by known methods for rendering such polymeric materials heat-recoverable. After the outer layer 103 and inner layer 105 are formed into the multiple layer assembly 100, such as by co-extrusion into tubular geometries, the assembly is irradiated with ionizing radiation or ultraviolet radiation. Ionizing radiation may be provided by accelerated electrons, X-rays, gamma rays, alpha particles, beta particles, neutrons or other high energy radiation sources. The radiation exposure is preferably sufficient to cause crosslinking of at least the polymeric material of the outer layer 103. Radiation dosage of from 2 to 60 megarads (Mrads) may be employed to provide sufficient crosslinking to the outer layer 103. While irradiating is a preferred manner to induce crosslinking, chemical crosslinking agents may alternatively be present in the outer layer 103, wherein the crosslinking mechanism is chemical crosslinking of the polymeric material.
As discussed above, the co-extruded or otherwise formed layers are preferably crosslinked to different extents. Specifically, the outer layer 103 is preferably crosslinked to a greater extent than the inner layer 105, which is preferably non-crosslinked. As discussed above, crosslinking may be achieved by irradiating the material with a beam of high energy electrons, and the different amount of crosslinking between the outer layer 103 and the inner layer 105 is preferably provided by adding selective amounts of crosslinking promoters to the outer layer 103, antioxidants and/or crosslinking inhibitors to the inner layer 105. In another embodiment of the invention, the radiation source may be used in a manner to irradiate the outer layer 103 to a greater extent than the inner layer 105 in order to induce a greater amount of crosslinking in the outer layer 103.
In a preferred embodiment of the present invention the same polymeric material is incorporated into the outer layer 103 and the inner layer 105. The outer layer 103 is substantially fully crosslinked after irradiation and the inner layer 105 is substantially non-crosslinked. Further, while the system has been shown and described with respect to a dual layer system (i.e. an outer layer 103 and an inner layer 105) any number of layers may be provided. Furthermore, additional reinforcing structures 107 (
In order to form the medical device, the assembly 100 including the adjacent reinforcing structure 107, shown in
As shown in
The invention is not limited to the arrangement shown and described above in
In another embodiment, as shown in
While the above has been shown and described with respect to tubular structures and concentric arrangements, planar or other arrangements of dimensionally recoverable materials may be utilized, wherein the material may be joined together utilizing known bonding techniques to form reinforced devices having mechanical properties desirable for use as medical devices. In addition, the reinforced structure 400, although described as being suitable for a catheter, is also configurable into catheter components, such as balloons, or other medical devices. Further the reinforced device 400 is not limited to medical applications and may include any applications that require reinforced flexible tubing. For example, the device 400 according to embodiments of the present invention includes other medical applications, such as introducers, dilators, leaders, and physiology devices (such as ablation catheters).
One embodiment of the invention includes a dimensionally recoverable multiple layer tubing assembly for forming a reinforced medical device fabricated by coextruding an outer layer and an inner layer. When the outer layer is the crosslinked layer, it may contain 0.5-5 wt % crosslinking promoter, 2-5 wt % color concentrate, 0.5-1 wt % antioxidant and the balance substantially polymer, all weight percentages being by weight of the total composition. When the inner layer is not crosslinked, it may contain 0.5-1 wt % antioxidant, 2-5 wt % color concentrate and, optionally, 1-5 wt % crosslinking inhibitor, wherein the balance is substantially polymer, all weight percentages being by weight of the total composition. The co-extruded assembly of the outer layer and inner layer is then irradiated with an electron beam. The assembly is then expanded via conventional expansion techniques to render the assembly dimensionally recoverable. In order to form a reinforced medical device, a reinforcing structure, e.g. a braid, is disposed within the dimensionally recoverable assembly, adjacent to the inner layer. The assembly, including the braid, is heated in an oven to a temperature greater than about 120° C. (250° F.). The inner layer melts and the outer layer contracts thereby causing the inner layer to flow and incorporate the braid therein. The assembly is then permitted to cool. The resultant device includes an outer layer and a reinforced inner layer.
Another embodiment of the invention includes a dimensionally recoverable multiple layer tubing assembly for forming a reinforced medical device fabricated by coextruding an outer layer and an inner layer. The outer layer contains 0.5-5 wt % crosslinking promoter, 2-5 wt % color concentrate, 0.5-1 wt % antioxidant and the balance substantially polymer, all weight percentages being by weight of the total composition. The inner layer contains 1-5 wt % of the total composition crosslinking inhibitor, wherein the balance is substantially a polymeric material that has adhesive properties. The co-extruded assembly of the outer layer and inner layer is then irradiated with an electron beam. The assembly is then expanded via conventional expansion techniques to render the assembly dimensionally recoverable. In order to form a reinforced medical device, a reinforcing structure, e.g. stainless steel braid, is disposed within the assembly, adjacent to the inner layer. The assembly, including the braid, is heated in an oven to a temperature greater than about 120° C. (250° F.). The inner layer melts and the outer layer contracts thereby causing the inner layer to flow and incorporate the braid therein. The assembly is then permitted to cool. The resultant device includes an outer layer and a reinforced inner layer.
The principles of the invention are further illustrated by the following examples, which should not be construed as limiting.
Outer layer compositions were made on a 76.2 mm (3″) diameter, two-roll mill that was heated to 180° C. The outer layer (crosslinkable) compositions were made by mixing PEBAX™ polyether block amide polymer resins (available from Arkema Corporation) with 2.5% or 5.0% crosslinking promoter (triallyl isocyanurate). Plaques, 152 mm×152 mm×0.635 mm (6 in×6 in×0.025 in), were pressed from these blends in an electric press at 180° C. (365° F.). These plaque samples were irradiated to 10 or 20 Mrads using a 1.0 MeV electron beam and were tested for crosslink density by conducting a test for E30 at 200° C. The E30 test measured the force at 30% elongation at 200° C., using an Instron™ tester equipped with a hot box. A sample having dimensions of 6.35 mm×102 mm×0.635 mm (0.25 in×4 in×0.025 in) was placed in the Instron tester with a jaw separation of 48.3 mm (1.9 in) and pulled at a rate of 50 mm/min. This test was conducted at 200° C., i.e. at least 25° C. above the melting point of the highest melting PEBAX™ resin. (PEBAX™ 7233 had the highest melting point of 174° C.) Tubing which expands well typically has an E30 value greater than 0.34 MPa (50 psi) and preferably an E30 greater than 0.62 MPa (90 psi). The E30 data are summarized in Table 1. The melting point of each PEBAX™ resin as measured according to ASTM D-3418, and the Shore hardness (durometer), Shore D value after 15 seconds as measured by ASTM D2240, are shown in Table 1.
The inner layer (uncrosslinked) compositions were made by mixing PEBAX™ resins with 1.0-3.0% LOWINOX™ TBM6 antioxidant (a phenolic antioxidant available from Chemtura Corporation) or with a combination of 1.0-4.0% LOWINOX™ TBM6 antioxidant and 18.0% of EPOLENE™ C13 wax (available from Eastman Chemical Company). Plaques, 152 mm×152 mm×0.635 mm (6 in×6 in×0.025 in), were pressed from these blends in an electric press at 180° C. (365° F.). These plaque samples were irradiated to 10 or 20 Mrads in a 1.0 MeV electron beam and were evaluated in the Melt Flow Rate (MFR) test according to ASTM D 1238-04c test procedure, which is hereby incorporated by reference, Test Method for Flow Rates of Thermoplastics by Extrusion Plastometer, Procedure A, Condition 230/2.16 (230° C. with 2.16 kg load). Several compositions, which had MFR values equivalent or higher than the MFR of unirradiated PEBAX™ resins, were chosen for conversion into tubing prototypes. The MFR data are summarized in Table 2.
Sixteen compositions were utilized to form tubing layers. Ten compositions were for the outer layer and six compositions were for the inner layer. The outer layer compositions were modified from those of Table 1 by adding 0.5% of antioxidant (Irganox™ 1010, phenolic antioxidant available from Ciba Specialty Chemicals Corporation) and 0.5-3.0% of color concentrates (Wilson™ 50-BU-302 or Wilson™ 50-YE-308, available from PolyOne Corporation). The inner layer compositions were modified from those of Table 2 by adding 0.25% of antioxidant. Two compositions for the outer layer (15 and 16) also contained 5% of wax. These sixteen compositions represented different durometer resins.
All of the compositions listed in Table 3 were converted into dual wall tubing. Each composition was melt blended on a 31.8 mm (1.25 in) Davis Standard extruder and was pelletized. The dual wall tubing was co-extruded using a co-extrusion line to produce tubing having the layers shown in Table 4. In most of the samples both layers of each tubing prototype were made from the same resin. The outer (crosslinked) layers were extruded on a 31.8 mm (1.25 in) Davis Standard extruder at a temperature between 149° C. (300° F.) and 190° C. (374° F.). The inner (uncrosslinked) layers were extruded using a 19.1 mm (0.75 in) C. W. Brabender extruder at a temperature between 163° C. (325° F.) and 204° C. (399° F.). For example, a dual wall tubing (Example 1, Table 4) made from PEBAX™ 5533 (compositions 6 and 8, Table 3) had an extruded outside diameter (OD) of 0.89 mm) (0.035 in) and an extruded inside diameter (ID) of 0.69 mm (0.027 in), and a total average unexpanded wall thickness for the outer layer of 0.051 mm (0.002 in) and a total average unexpanded wall thickness for the inner layer of 0.051 mm (0.002 in). The tubing was irradiated to 25 Mrads using a 0.5 MeV electron beam to an E30 value at 200° C. of 0.74 MPa (107 psi) and was expanded in a pressure expander at 177° C. (350° F.) to give tubing having an expanded ID of 1.73 mm (0.068 inches) and a recovered ID of 0.686 mm (0.027 inches), an average recovered wall thickness of the outer layer of 0.076 mm (0.003 in), and an average recovered wall thickness of the inner layer of 0.064 mm (0.0025 in).
In similar manner additional dual wall tubing was made from other compositions listed in Table 3. For example, compositions 1 (outer) and 3 (inner) were combined to co-extrude dual wall tubing from PEBAX™ 7233 (Example 2, Table 4). Compositions 4 (outer) and 5 (inner) were co-extruded to a make dual wall tubing from PEBAX™ 6333 (Example 3, Table 4). Compositions 9 (outer) and 10 (inner) were co-extruded to make dual wall tubing from PEBAX™ 4033 (Example 4, Table 4). Compositions 11 (outer) and 12 (inner) were co-extruded to make dual wall tubing from PEBAX™ 3533 (Example 5, Table 4). Compositions 13 (outer) and 14 (inner) were co-extruded to make dual wall tubing from PEBAX™ 2533 (Example 6, Table 4). In addition, one tubing sample was made from two different PEBAX™ resins. The outer layer was made from PEBAX™ 3533 (composition 11) and an inner layer was made from PEBAX™ 4033 (composition 10) (Example 7, Table 4). Finally, in one tubing prototype the layers were reversed. The outer layer (uncrosslinked) was made from PEBAX™ 5333 (composition 8) and the inner layer (crosslinked) was made from PEBAX™ 5333 (composition 7) (Example 8, Table 4). All of these tubing prototypes were irradiated to 25 Mrads using a 0.5 MeV electron beam and were expanded using a pressure expander at 177° C. (350° F.).
The dimensionally recoverable multiple layer systems recited in the examples are suitable for use in the fabrication of reinforced medical devices. The assemblies 100 including the multiple layers are placed adjacent to reinforcing structure 107. The assembly including the reinforcing structure 107 is exposed to heat or is otherwise exposed to conditions to initiate dimensional recovery. As the assembly 100 recovers, the reinforcing structure 107 becomes incorporated into the recovered assembly 300.
While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
This application is a divisional application of co-pending, commonly assigned application Ser. No. 11/820,266, filed Jun. 19, 2007, the disclosure of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11820266 | Jun 2007 | US |
| Child | 15046403 | US |
