Abstract:
A process for altering the properties of extruded tubing by applying a solid particulate material to a tacky outer surface of the tubing as the tubing exists the extrusion head or die and prior to the tubing entering a cooling system of the extrusion line. The particulate material may act as a tie layer to improve the adherence of a second material to the outer surface of the extruded tubing, thus altering the tensile strength, elongation, and/or stiffness properties of the extruded tubing. In addition, the application of particulate material may be chosen to provide radiopacity to the extruded tubing. The solid particulate material may be deposited on the extruded tubing by vacuum deposition, magnetism, or pressurized means.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates generally to an extrusion process for forming medical tubing. More particularly, a melt extrusion process includes a particle deposition step that occurs downstream of the extruder die but prior to cooling of the extruder tubing. 
       BACKGROUND OF THE INVENTION 
       [0002]    Extrusion encompasses various processes that feature low tooling and labor costs, making extrusion a desirable manufacturing process especially for tubular profiles. During a melt extrusion process, a solid thermoplastic polymer material (i.e., pellets, chips, beads, power and the like) is generally fed through a transport section into a rotating screw of an extruder via a feeder or hopper. The polymer material is slowly heated as it is pressed forward toward an extrusion die, becoming a homogeneous polymeric melt that is subsequently forced through the extrusion die to form a continuous-length having a desired shape. Once cooled, the extrudate may be would onto a reel or cut into pieces of a desired length. Subsequent thermal processing steps may be used to modify or shape the extrudate into a desired configuration. 
         [0003]    Extrusion processes are often employed in producing tubing for medical applications, such as, tubing for various catheters, particularly angiography or guiding catheters, balloon angioplasty and stent delivery catheters, and medical balloons, especially high pressure dilatation and stent delivery balloons, as well as in tubing for implantation or insertion in the body for long periods of time and other applications where mechanical, physical, chemical, electrical or thermal properties are critical to the function to the finished medical device. 
         [0004]    Depending on the medical application, medical tubing used for catheters should possess a combination of desirable characteristics such as axial and torsional strength, a.k.a. pushability and torqueability, bondability, biocompatibility and/or lubricity. However, such a combination of characteristics may not be readily achievable with tubing made of only a single material. For instance, medical tubing that is to be used in making angioplasty and stent delivery catheters desirably may be formed from an inherently slippery or low-friction polymer that also may be different to effectively bond to the material of conventional balloons due to the chemical incompatibility between the materials to be bonded. Alternatively, polymer materials that demonstrate good bonding characteristics with balloons typically must be coated with a lubricant on the interior surface so that the interior surface of the catheter tubing is sufficiently low-friction for passing over a guidewire or other medical device, often necessitating an additional manufacturing step. 
         [0005]    To overcome this and other problems, it is known to provide the desired characteristics for intravascular catheters by utilizing multilayered medical tubing. In one instance, such multilayered tubing is co-extruded or overjacket extruder to have an outer layer of a bondable material, such a polyamide, polyethylene, polyurethane, or poly(ethylene terephthalate) (PET), and an inner layer of a low-friction polymer such as polytetrafluoroethylene (PTFE), fluorinated ethylene-propylene (FEP), perfluoroalkoxy polymer resin (PFA) or high density polyethylene (HDPE). In another instance, a multi-layered tubing composed of an outer layer of a bondable material, a core layer of a low-friction material, and an intermediate tie layer are co-extruded using three extruders simultaneously feeding a single die/head. 
         [0006]    Although multilayer tubing for use in medical devices may be co-extruded, maintaining the various polymers at optimum processing conditions to prevent degradation of the melts during the extrusion process is often difficult and, if unsuccessful, may result in delamination of the layers and/or a change in properties of the finished tubing, such as a decrease in tensile strength, increased brittleness, and/or insufficient flexibility. Thus a need exists in the art for medical tubing that exhibits the desired characteristics of strength, resistance to bending and torsional kinks, pushability, torqueability, bondability and/or lumen lubricity but that is made by a simpler process. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    The invention is [to be finalized after approval of claims]. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0008]    The foregoing and other features and advantages of the invention will be apparent from the following description of the invention as illustrated in the accompanying drawings. The accompanying drawings, which are incorporated herein and form a part of the specification, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention. The drawings are not to scale. 
           [0009]      FIG. 1  is a schematic representation of a conventional medical tubing extrusion line. 
           [0010]      FIG. 2  is a schematic representation of a medical tubing extrusion line in accordance with an embodiment of the present invention. 
           [0011]      FIG. 3  is a schematic representation of a portion of a medical tubing extrusion line in accordance with another embodiment of the present invention. 
           [0012]      FIG. 3A  is a cross-sectional view taken along line A-A of  FIG. 3 . 
           [0013]      FIG. 4  is a schematic representation of a portion of a medical tubing extrusion line in accordance with another embodiment of the present invention. 
           [0014]      FIG. 4A  is a cross-sectional view taken along line A-A of  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]      FIG. 1  is a schematic representation of a conventional medical tubing extrusion line  100  having a resin hopper  110 , which may also function as a resin dryer, feeding a horizontal extruder  120 . Extruder  120  includes a heated barrel and a screw that rotates within the barrel to mix, create frictional heat and feed molten resin through extrusion die or head  140 . Optionally, and as illustrated in  FIG. 1 , a melt pump  130  may be included to provide molten resin at constant pressure and flow rate to extrusion die  140 . Extrusion die  140  sits at an end of extruder  120  and is the point where the extrudate exists into air, and promptly into a cooling trough  150 . Extrusion die  140  forms the initial exterior shape of the tubing and, to form hollow tubing, typically surrounds a mandrel or pin that forms the initial interior shape of the tubing. As the hot extruded tubing or extrudate  145  exists the annular space between the pin and extrusion die  140 , its inner and outer dimensions are typically drawn down to its finished tube dimensions by action of a puller  170  positioned downstream of a cooling trough or system  150 . Controlled air pressure may also be supplied to the inside of hot extrudate  145  via an air channel through the pin. Cooling trough  150  may utilize water as the cooling medium or, alternatively, air cooling may be used. After the cooled extruder tubing product  155  exits cooling trough  150 , it may pass through a measuring gauge  160  to assure its outer diameter is within acceptable parameters. Finally, extruded tubing product  155  may be cut into lengths or wound into a spool by a cutter or winder  180 , respectively. 
         [0016]      FIG. 2  is a schematic representation of a medical tubing extrusion line  200  in accordance with an embodiment of the present invention. In addition to the apparatus discussed with reference to extrusion line  100  of  FIG. 1 , extrusion line  200  includes an inline particle deposition system  290 . Deposition system  290  is positioned on extrusion line  200  to deposit a solid particulate material on the warm, tacky outer surface of extruded tubing  145  proximate to the exit of tubing  145  from extrusion die/head  140 . In an embodiment, deposition system  290  is arranged to deposit a continuous layer of solid particulate material on the tacky outer surface of extruded tubing  145 . In various embodiments, the solid particulate material may be a metallic, polymeric or ceramic material in the form of, e.g., powder or metal filings. By “proximate to the exit of extrusion die/head  140 ,” it is meant that the deposition of solid particulate material onto the outer surface of extruded tubing  145  occurs very close in space or time, or, at or within a short distance in space or time, from extruded tubing  145  exiting extrusion die/head  140 . In turn, extruded tubing sub-product  295 , having solid particulate material on the outer surface thereof, exists particle deposition system  290  to be cooled within cooling system  150 . Accordingly, extruded tubing product  255  then exits cooling system  150  with the solid particulate material secured thereto to be subsequently wound or cut into appropriate lengths. 
         [0017]    Inline particle deposition system  290  may consist of a chamber or spray station having one or more nozzles or spray heads, such as in a pressurized spraying process. The nozzles or spray heads may be arranged to spray solid particulate material perpendicular to or at a range of angles with respect to a longitudinal axis of tacky extruded tubing  145 , to provide a continuous layer of particulate on extruded tubing  145  as it moves along extrusion line  200 . In addition, various vacuum deposition processes may be useful in inline particle deposition systems according to embodiments of the present invention. 
         [0018]    In an embodiment shown in  FIGS. 3 and 3A , inline particle deposition system  390  utilizes a magnetic process to deposit a solid particulate  303  of or including a magnetizable material, i.e., a material attracted to magnetic materials, e.g., ferrimagnetic materials such as magnetite or ferromagnetic materials such as cobalt, nickel or iron, onto the tacky outer surface of extruded tubing  345 . Extrusion die/head  340  is of the wire-covering cross head type, which includes a central passageway for feeding a core rod  301  of or including a magnetic material through extrusion die/head  340  to be covered by the polymeric material  302  forming extruded tubing  345 . In an embodiment, extruded tubing  345  enters a tumbler or other chamber  305  of inline particle deposition system  390  that hold and distributes/tumbles magnetizable solid particulate  303 , so that the solid particulate  303  may be attracted to magnetic core rod  301  within extruded tubing  345  to thereby form a deposited layer of solid particulate  303  thereon. To distribute particulate  303  around extruded tubing  345 , chamber  305  may move, e.g., vibrate or rotate, as indicated by arrows in  FIGS. 3 and 4 . In a further embodiment, solid particulate  303  may be a magnetic material and the core material may be magnetizable to achieve the same result. In turn, extruded tubing sub-product  395 , having magnetizable solid particulate material on the outer surface, thereof, exits particle deposition system  390  to be cooled within a cooling system (not shown). At some point during processing, core rod  301  is removed from extruded tubing sub-product  395  by any of the processes known to those skilled in the art, leaving a hollow passageway in the finished medical tubing product. In various embodiments, core rod  301  may be one of a filled plastic beading or metallic rod or wire that is made entirely or partially of magnetic or magnetizable materials. 
         [0019]    In an embodiment shown in  FIGS. 4 and 4A , inline particle deposition system  490  utilizes a magnetic process to deposit a magnetic or magnetizable, e.g., ferrous, solid particulate  303  onto the tacky outer surface of extruded tubing  445 . However in this embodiment, extrusion die/head  440  includes a stationary, magnetic or magnetizable core rod  401  that extends from die/head  440  into or through tumbler/chamber  305  of inline particle deposition system  490 . Stationary core rod  401  may act as a mandrel or pin to form the initial interior diameter or profile of tubing  445 , as described above. Core rod  401  extends within extruded tubing  445  as extruded tubing  445  passes through chamber  305 , so that magnetic or magnetizable solid particulate  303  may be magnetically attracted to core rod  401 . As such, a layer of solid particulate  303  is deposited on an outer surface of extruded tubing  445  as the tubing passes through chamber  305 . In turn, extruded tubing sub-product  495 , having magnetizable or magnetic solid particulate material on the outer surface thereof, exits particle deposition system  490 , eventually clearing an end  407  of stationary core rod  401 , to be cooled within a cooling system (see cooling system  150  in  FIGS. 1 and 2 ). 
         [0020]    A medical tubing made with embedded magnetizable particles, such as ferrous particles, according to embodiments of the present invention may be beneficial for viewing such tubing by magnetic resonance imaging (MRI) during use in medical procedures. 
         [0021]    Although a horizontal extruder  120  is shown in the embodiment of  FIG. 2 , it would be understood by one of ordinary skill in the art that for certain applications the use of a vertical extruder may be beneficial to avoid lateral gravitational force in assuring the production of uniformly thin-walled tubing. 
         [0022]    A process according to an embodiment of the present invention may be used to produce medical tubing having a low-friction inner surface. In such an embodiment, the selection of a solid particulate material for deposition on tacky extruded tubing  145  may be made to promote adhesion between the polymeric material of extruded low-friction tubing  145  and a second polymer, which is subsequently attached as an outer sleeve or a second extruded layer, e.g., an over-jacket extrusion, over extruded tubing  145 . Extruded tubing  145  may be made of a polyamide, such as Nylon 12, Nylon 6/6 or other nylon copolymers, as well as polyether block amides such as those commercially available under the trademark PEBAX®, a registered trademark of the Arkema Corporation. Extruded tubing  145  may then have a solid particulate material of carbon, titanium dioxide or a zeolite deposited on an outer surface thereof to form extruded tubing product  255 . Subsequently, an outer sleeve or layer of a low-friction polymer, such as high density polyethylene (HDPE), fluorinated ethylene-propylene (FEP), perfluoroalkoxy polymer resin (PFA) or polytetrafluoroethylene (PTFE), may be readily adhered to extruded tubing product  255  due to interaction between the solid particulate material and the polymeric material of the outer layer. 
         [0023]    A process according to another embodiment of the present invention may be used to produce medical tubing having a low-friction inner surface, wherein the selection of the deposited particulate material may be made to promote adhesion between the low-friction polymeric material of extruded tubing  145  and a second polymer used to form an outer sleeve or layer on extruded tubing  145 . In such an embodiment, extruded tubing  145  may be made of a low-friction polymeric material, such as FEP, HDPE, PFA or polyethylene. A solid particulate material of a thermoplastic material having a lower melt temperature than the low-friction polymeric material of extruded tubing  145 , which is also attractive for bonding to the material of the outer layer, may then be deposited on an outer surface of tubing  145  to form extruded tubing product  255 . Subsequently, an outer sleeve or layer of a second polymeric material, such as, a polyamide, Nylon 12, Nylon 6/6 or other nylon copolymer, polyether block amide or polyurethane, may be readily adhered to extruded tubing product  255  due to interaction between the deposited solid particulate material, which in this embodiment may be carbon, titanium dioxide or a zeolite or a blend of polyether block amide and low density polyethylene (LDPE), and the polymeric material of the outer layer. 
         [0024]    In an embodiment, the selection of a solid particulate material for deposition on tacky extruded tubing  145  may be made to provide radiopacity to extruded tubing  145 , as an outer layer thereof or as a radiopaque layer between extruded tubing  145  and an outer layer that may be subsequently attached. In an embodiment, a solid particulate material of bismuth subcarbonate, barium sulfate or a biocompatible metal having a high coefficient of x-ray absorption, such as precious metals or refractory metals, e.g. tungsten, tantalum, rhenium or alloys thereof may be deposited on extruded tubing  145  to form extruded tubing product  255  having enhanced radiopacity. 
         [0025]    In another embodiment, the selection of a solid particulate material for deposition on tacky extruded tubing  145  may result in improved tensile strength, elongation and stiffness properties of a final tubing product by improving adhesion of an outer jacket of a different material to extruded tubing  145 . 
         [0026]    The medical tubing produced by embodiments of the present invention may be used, for example, in medical devices suitable for percutaneous transluminal use, such as guide catheters, diagnostic catheters, stent delivery catheters or balloon angioplasty catheters. 
         [0027]    While various embodiments according to the present invention have been described above, it should be understood that they have been presented by way of illustration and example only, and not limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the appended claims and their equivalents. It will also be understood that each feature of each embodiment discussed herein, and of each reference cited herein, can be used in combination with the features of any other embodiment. All patents and publications discussed herein are incorporated by reference herein in their entirety.