WO1991007203A1

WO1991007203A1 - A catheter device

Info

Publication number: WO1991007203A1
Application number: PCT/US1990/006107
Authority: WO
Inventors: David J. Myers
Original assignee: W.L. Gore & Associates, Inc.
Priority date: 1989-11-22
Filing date: 1990-10-24
Publication date: 1991-05-30

Abstract

This invention relates to a catheter device having a tubular portion wherein said tubular portion consists essentially of porous PTFE having a density less than about 1.6 grams per cubic centimeter. A catheter device of such porous PTFE tubing is adequately rigid for use as a catheter while having good flexibility to avoid kinking during bending. It is permeable to gases but hydrophobic and resistant to cellular ingrowth. Other embodiments of this invention include a catheter device wherein the tubular portion has a tip part of either greater or lesser density than that of the remainder of the tubular portion, so that the tip part is, respectively, more rigid or more flexible than the remainder of the tubular portion. One embodiment of the present invention may be used as an infusion cannula device. A process for using the catheter device of the present invention is described.

Description

A CATHETER DEVICE

FIELD OF THE INVENTION

This invention relates to a catheter device havinα a tubular portion consisting essentially of porous polytetrafluoroethylene.

BACKGROUND

Catheters are tubular surgical devices possessinq degrees of both flexibility and rigidity, typically used for withdrawing or introducing fluids or other medical devices into various cavities of the body. Common types are blood vessel catheters including cardiac catheters and vascular access port catheters, indwelling catheters, drainage catheters, urethra catheters, peritoneal catheters and infusion cannula devices.

These catheter devices are typically inserted into tortuous vessels of the body, e.g. blood vessels, occasionally for distances in excess of 60 cm. The catheter tubing therefore must have adequate rigidity and lubricity to allow for smooth insertion to ensure its advance within the tortuous vessels of the body without risk of kinking or collapse. It should possess the ability to be rotated if necessary, also while avoiding collapse. Finally, it must also be soft and flexible so as to avoid trauma to the body vessels and to allow the catheter tube to make bends of small radius without kinkinq. The simultaneous requirements of rigidity and flexibility have heretofore resulted in catheters wherein one or the other characteristics predominates, resulting in compromised performance. Nylon, polyethylene and other relatively rigid plastics have been commonly used for conventional catheters. Composite construction techniques have been frequently used to provide catheter devices having tip parts of increased softness and flexibility. These tip parts are typically of silicone or polyurethane. Such composite constructions are of necessity more expensive and are vulnerable to separation of the interface between the different materials.

Catheters of polyethylene and nylon frequently incorporate luminal surface liners of solid, non-porous polytetrafluoroethylene (hereinafter PTFE). The use of PTFE as a liner is seen to be advantageous because PTFE is more chemically inert and bioloqically compatible than other polymeric materials. Except for infusion cannula devices of relatively short lengths, solid, non-porous PTFE tubing is rarely used by itself as a catheter material because it is excessively rigid, resulting in kinking during bending. It has only been satisfactoril employed as a thin-walled catheter liner havinq an outer surrounding jacket of supporting polyethylene, nylon or the like in order to avoid kinking.

Again, such composite constructions are necessarily difficult and expensive to manufacture. Furthermore, such composite constructions have increased wall thicknesses which limit the inside diameter available for the transport of fluids or other medical devices.

Silicone has often been used as the primary component for the tubular portions of indwelling catheters, vascular access catheters, peritoneal catheters, etc. These silicone catheters emphasize flexibility to the extent that their lack of rigidity often poses problems during insertion.

Catheter devices include infusion cannula devices. Conventional infusion cannula tubing is about 12 or 13 cm in length and has an outside diameter (O.D.) of about 1.5 mm with an inside diameter (I.D.) of about 0.8 mm. These tubes are fitted with an adapter at one end to make a complete infusion cannula device, through which a liquid medicine or other medical device may be injected into or extracted from the body cavity via the tube. In use, a metal piercing needle is inserted through the lumen of the tube, the sharp tip of the needle projecting beyond the tube. This needle with the tubing thereon is then thrust through the skin into a blood vessel, the cannula tube then being pushed forward into the blood vessel through the opening formed by the needle. The needle is then withdrawn, leaving the infusion cannula and attached adapter in position. The adapter is closed with a plug. The plug is removed when access to this blood vessel via the cannula device is needed.

In order to prevent the infusion cannula tubing from slipping out, the exposed portion must be affixed to the patient by some attaching means, commonly sutures or adhesive tape. Infusion cannula devices are typically made of relatively rigid materials such as solid, non-porous PTFE or fluorinated ethylene propylene. After being affixed, the conventional infusion cannula tubing, being rather rigid, will cause pain and discomfort should the patient move the area of the body in which the tubing is lodged. This problem is partic^arly acuτe since the insertion is usually made in a leg, arm, or thigh, thus greatly restricting the movement of that limb.

SUMMARY OF THE INVENTION

This invention relates to a catheter device having a tubular portion wherein said tubular portion consists essentially of porous PTFE having a density less than about 1.6 grams per cubic centimeter. A catheter device of such porous PTFE tubing is adequately rigid for use as a catheter while having good flexibility to avoid kinking during bending. It is permeable to gases but hydrophobic and resistant to cellular ingrowth. Other embodiments of this invention include a catheter device wherein the tubular portion has a tip part of either greater or lesser density than that of the remainder of the tubular portion, so that the tip part is, respectively, more rigid or more flexible than the remainder of the tubular portion. One- embodiment of the present invention may be used as an infusion cannula device. A process for using the catheter device of the present invention is described.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a typical catheter device having a tubular portion of porous expanded PTFE made according to one embodiment of this invention. Figure 2 shows a catheter device having a tip part of greater mean fibril length than the remainder of the tubular portion, made according to one embodiment of this invention. Figure 3 shows an infusion cannula device made according to the method of this invention. Figure 4 shows a typical metal piercing needle for use with an infusion cannula device. Figure 5 is a scanning electron microscope photomicrograph (scale: x 500) showing the outer surface of the tubular portion of a catheter device representing one embodiment of this invention, having a porous expanded PTFE microstructure of about 2.5 micron mean fibril length. Figure 6 is a scanning electron microscope photomicrograph (scale: x 500) showing the tip part of a catheter device representing one embodiment of this invention, having a porous expanded PTFE microstructure of about 10.0 micron mean fibril length.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a catheter device having a tubular portion consisting essentially of porous PTFE. It does not contain grossly measurable quantities of solid, non-oorous PTFE. Porous PTFE tubing of appropriate density is flexible and kink-resistant while still being adequately rigid for use as the tubular portion of a catheter device.

Porous PTFE is herein meant to describe PTFE that is permeable to - gases but hydroohobic (at atmospheric pressure and 23°C) and resistant to cellular ingrowth, unless stated otherwise. Cellular ingrowth into a catheter is undesirable as it would interfere with removal of the catheter. Porous PTFE has a lower density than the 2.2 g/cc value of solid, non-porous PTFE. Density is herein meant to mean the mass of a unit volume of the material including void spaces normal to the material at 23°C. The tubular portion of the catheter device of the present invention consists essentially of porous PTFE and does not contain solid, non-porous PTFE beyond the scale of the material found between the void spaces normal to the material. For example, it does not contain solid, non-porous PTFE in the manner of the device described in U.S.P. 4,280,500.

Porous PTFE can be produced by blending PTFE resin with any pore-forming agent, the ultimate density, porosity and pore size of the porous PTFE depending on the quantity and particle sizes of the pore-forming agent blended with the PTFE resin. An extrusion aid is blended with this mixture, allowing the extrusion of a tubular form. The extrusion aid and pore-forming agent are removed using a suitable technique, e.g., a solvent, leaving a tubular porous PTFE article.

Alternatively, porous expanded PTFE can be produced by the processes of extrusion, expansion and sintering described in U.S.P. 3,953,566. Porous expanded PTFE produced by the methods of U.S.?. 3,953,566 possesses a microstructure of nodes interconnected by fibrils. For use as the tubular portion of catheter devices of the present invention, the fibril length should preferably be less than about 10 microns and most preferably less than about 5 microns. \s fibril length is increased beyond about five microns the tubular portion begins to lose the rigidity necessary for use as part of a catheter device. However, longer fibril lengths, e.g., greater than five microns, can still have a useful amount of rigidity if the density is great enough. In general, rigidity and flexibility are inversely proportional characteristics with tubing of porous expanded PTFE, i.e. rigidity decreases and flexibility increases with decreasing density and increasing fibril length.

Densities of about 1.0 g/cc to about 1.6 g/cc are particularly useful for the porous PTFE tubular portions of catheter devices of the present invention.

Rigidity and flexibility are also functions of the wall thickness of the tubing. As the wall becomes thicker, the tube becomes more rigid and less flexible. Wall thickness is equal to half of the difference between the inside and outside diameters of a tube, assuming concentricity.

Fibril lengths of one to five microns are particularly useful for porous expanded PTFE tubing for catheter devices. Such devices can be practically manufactured having inside diameters of, for example, .5 mm to 5 mm and wall thicknesses of as little as .1 mm to .3 mm. The use of only PTFE provides significant advantages in terms of increased chemical inertness and biological compatibility. Surface smoothness and lubricity are also excellent, aiding in transport of fluid^'s and other medical devices and advancement and withdrawal of the catheter from body vessels.

For a given density, even shorter fibril lengths, e.g. .1 micron can be used if greater rigidity is desired.

The fibril length of expanded PTFE is determined by photographing the surfaces of the sample or the longitudinal cross sections of the wall thickness of the sample with a scanning electron microscope (SEM). The magnification level should be such that at least five complete consecutive fibrils are shown within the length of the SEM photograph. Two parallel lines are drawn 12 mm above and below the longitudinal center! ine of the photoqraDh, parallel to the direction of the fibrils. Following the top edge of the upper line and startinq from the left margin of the photograph, the distance from the left end of the first distinct fibril nearest the drawn line to the riqht end of the same fibril is measured as the first fibril length. The fibril end is the point at which the fibril contacts the node. Measurements should be made using dividers referenced to a scale that accounts for the magnification factor.

Five consecutive fibril length measurements should be made in this manner along the drawn line. The photograph should be rotated 180° and five more consecutive fibril length measurements taken from the left margin of the photograph along the top edge of the second drawn line. The mean fibril length of the sample is taken to be the mean of the ten photograph measurements. The tip part of th^'e tubular portion of the catheter device can be made to have a different density or fibril length than the non-tip part of the tubular portion if different mechanical characteristics are desired at the tip part. For example, if it is desired to have a tubular portion with a tip part of increased softness and flexibility, the tube can be made to have a lower density and/or longer fibril length at its tip than for the non-tip part of its length. A tubular portion having a one micron mean fibril length can be made to have a tip part of five micron mean fibril length, or of even ten micron fibril length. A tubular portion of 1.2 g/cc density can be made to have a tip part of 1.6 g/cc density. This is preferably done within the length of the integral tubular portion and not by adding separate extension pieces of different fibril length.

Alternatively a tip part of different density from the non-tip part of the tube may be. attached as a separate piece to the non-tip part of the tube. This may be done by thermally bonding the tip part to the non-tip part of the tube as taught by U.S.P. 4,283,448. A medical adhesive such as Dow Corning Silastic may also be used to adhere the separate pieces.

Figure 1 describes a catheter device made according to the method of this invention. 1 indicates the tubular portion of porous PTFE, 2 indicates a typical catheter connector. Figure 2 describes a second embodiment of this invention, wherein tip part 3 has been made to have a lower density or a longer fibril length than the non-tip part of the -3-

tubular portion 1, so that the tip part has increased flexibility and reduced rigidity.

Catheter devices of this invention include infusion cannula devices. Such devices made according to the methods of this invention orovide greater flexibility and patient comfort than conventional infusion cannula devices. Infusion cannula devices made of porous PTFE in such a manner as to be flexible, gas permeable, hydroohobic and resistant to cellular ingrowth, can be made to have a tin part with further increased density and rigidity for ease of insertion. Figure 3 shows an infusion cannula device of the present invention. 4 indicates a tubular portion of porous PTFE, 5 indicates the tip part of increased density for increased rigidity, and 6 shows an adapter attached by an attaching means, herein shown as a metal fastener 7. Figure 4 shows a typical piercing needle for use in inserting the infusion cannula device into the patient's body. A catheter device tube having an integral tip part of fibril length different from that of the non-tip part of. its length can be made by different processes. For example, it is possible to take a tube of porous expanded PTFE having a mean fibril length of five microns, heat only the tip part of the tube to a temperature preferably greater than its crystalline melt point, and apply a tensioning force to the tube in the direction of its length resulting in an increase in the mean fibril length of the tin part of the tube. Conversely, the tip part of the tube can be made to have a higher density during the original expansion process by keeping the tip part of the tube at a lower temperature during expansion than the non-tip part of the length of the tube. This may be done by any suitable technique, e.g. forcibly cooling the tip part while the non-tip part of the length is being heated, or by providing the tip part of the tube with a heat shield during heating of the non-tip part.

Additionally, fibril length can be reduced by heating porous expanded PTFE tubing above its crystalline melt point while the tubing is unrestrained. Thus the local application of heat to the tip part of a flexible infusion cannula tube of porous expanded PTFE can increase the density and rigidity of the tip part, leaving the non-tip part of the cannula with a high degree of flexibility.

The application of both heat and pressure or the application of pressure alone may also be used to increase the density of a porous tube. ^cor example, the ti^p part of a cannula device can De provided with a taper by reducing its outside diameter with a local application of heat and raαially-apol ied pressure. Such techniques for increasing density may be used to increase the rigidity of porous tubinq that is otherwise too flexible for use in catheter devices.

The density or fibril length through the wall thickness or cross section of the tube can be made to be non-uniform. Such a tube can be made by, for example, exposing it to a temperature differential across its wall -thickness during sintering. Such a tube can be of value as a part of a catheter device if its density is less than 1.6 g/cc or if its mean fibril length, measured at any point between the inner and outer walls, is less than about 10 microns.

It is readily apparent that one might begin with a tube of the density or fibril length desired for the tio part of the tube and modify the density or fibril length of the non-tip part to suit the requirements for the non-tip part.

It would also be possible to manufacture a catheter containing a shadow-forming agent by mixing a powdered shadow-forming agent such as barium sulfate with a fine PTFE powder and extrusion aid. A non-porous PTFE tube is extruded from this mixture and, after removal of the extrusion aid, is heated and expanded to make it porous. In this way, a catheter could be produced which would form an appropriate shadow when exposed to X-rays, etc.

Catheter devices made according to this invention may have conventional catheter connectors attached to the end opposite the tip part. They may be attached in any suitable manner, e.g., with the use of an appropriate medical adhesive such as Dow Corning "Silastic^®", by injection molding the connector directly onto the end of the tubing, or by the use of a suitable mechanical compression fitting. Catheter devices of this invention may be steam sterilized or ethylene oxide sterilized so long as the material of the connector and any associated adhesive are capable of withstanding those sterili¬ zation processes. Porous PTFE tubing is unaffected by steam and ethylene oxide.- The catheters of the present invention are used by processes which comprise inserting the catheter tip part foremost into a body vessel via an opening made into the vessel, connecting the catheter to a fluid administering device or fluid withdrawal device and administeπ^'ng or ithdrawinq fluids, and withdrawino the catheter after it is no longer needed. The catheter may also be used to introduce other medical devices such as balloon angioplasty devices into a body vessel by inserting the device through the previously introduced catheter tube.

EXAMPLES

EXAMPLE 1

A length of 4.0 mm inside diameter, 5.8 mm outside diameter porous expanded PTFE tubing was made according to the methods taught by U.S.P. 3,953,566. The extrudate was expanded at a rate of about 125% per second, from a length of 30 cm to 47 cm, resulting in a tube of 2.5 micron mean fibril length. A 20 cm length of this tube was able to be bent into a loop of about 1.0 cm inside diameter without kinking. A comparable tube of solid, non-porous PTFE was only able to be bent into a loop of about 8.0 cm inside diameter before kinking began to occur. The porous expanded PTFE tube also possessed good rigidity and crush resistance. One end of the PTFE tube was fitted over the barbed end of a standard male Luer fitting to make a complete male catheter device. A Teflon^® thread was tied circumferentially around the portion of the PTFE tube over the barbed fitting at a small diameter of the barb to secure the tubing. A 1 cm length of DuPont Teflon^® TFE (tetrafluoroethylene) heat-shrink tubing was fitted over the tied barbed fitting connection and secured with the application of heat applied by a heat gun.

EXAMPLE 2

About 1.5 cm length of one tip part of a 20 cm tube made according to Example 1 was heated by surrounding the tube end with a glow ring type device having electrical resistance heaters (made by Eraser Co., Syracuse, New York) while tension was applied to the tube parallel to the axis of the tube. The tension was released and heating was stopped after the 1.5 cm tip part length had increased to about 3.0 cm. Figure 4 shows an SEM photomicrograph of the outer surface of a sample from the non-tip part of this tube that was not heated during the application of tension. The mean fibril length is about 2.5 microns. Figure 5 shows an SEM photomicrograph of the outer surface of a sample cut from the tin part that was heated during the application of tension, the mean fibril length is shown to be about 10.0 microns.

The tin part of the tube that had been heated during the application of tension was much softer and more flexible than the non-tip part of the tube. It was also less rigid and crush resistant.

Claims

-*. ?-Cl ai m :

1. A catheter device having a tubular portion wherein said tubular portion consists essentially of oorous PTFE having a density less than about 1.6 qrams per cubic centimeter.

2. A catheter device having a tubular portion wherein said tubular portion consists essentially of porous PTFE having a density less than about 1.4 grams per cubic centimeter.

3. A catheter device having a tubular portion wherein said tubular portion consists essentially of porous PTFE having a density less than about 1.3 grams per cubic centimeter.

4. ι catheter device according to claim 1, 2 or 3 wherein said tubular portion consists essentially of porous, expanded PTFE having a mean fibril length less than about 10 microns.

5. A catheter device according to claim 1, 2 or 3 wherein said tubular portion consists essentially of porous, expanded PTFE having a mean fibril length less than about 7 microns.

6. A catheter device according to claim 1, 2 or 3 wherein said tubular portion consists essentially of porous, expanded PTFE having a mean fibril length less than about 5 microns.

7. A catheter device according to claim 1, 2 or 3 wherein said tubular portion consists essentially of porous, expanded PTFE having a mean fibril length less than about 3 microns.

8. A catheter device according to claim 1, 2 or 3 wherein said tubular portion consists essentially of porous, expanded PTFE having a mean fibril length less than about 1 micron.

9. A catheter device according to claim 1, 2 or 3 having a connector at one end.

10. A catheter device according to claim 4 having a connector at one end.

11. A catheter device according to claim 6 having a connector at one end.

12. A catheter device according to claim 1, 2 or 3 wherein said tubular portion of porous PTFE contains a shadow-forming agent.

13. A catheter device according to claim 4 wherein said tubular portion of porous expanded PTFE contains a shadow-forming agent.

14. A catheter device according to claim 6 wherein said tubular portion of porous expanded PTFE contains a shadow-forming agent.

15. A catheter device according to claim 9 wherein said tubular portion of porous PTFE contains a shadow-forming agent.

16. A catheter device according to claim 1, 2 or 3 wherein said porous PTFE tubular portion has a tip part and a non-tip part, said tip part having a different density from that of the non-tip part.

17. A catheter device according to claim 4 wherein said porous expanded PTFE tubular portion has a tip part and a non-tip part, said tip part having a different fibril length from that of the non-tip part.

18. A catheter device according to claim 6 wherein said porous expanded PTFE tubular portion has a tip part and a non-tip part, said tip part having a different fibril length from that of the non-tip part.

19. A catheter device according to claim 16 wherein said tip part has a density lower than that of said non-tip part.

20. A catheter device according to claim 17 wherein said tip part has a fibril length greater than that of said non-tip part.

21. A catheter device according to claim l'^j wherein said tip part has a density greater than that of said non-tip part.

22. A catheter device according to claim 1 having a tip part, wherein said tip part has a density less than about 2.2 grams per cubic centimeters.-

23. A catheter device according to claim 17 wherein said tip part has a fibril length less than that of said non-tip part.

24. The catheter device according to claim 1, 2 or 3 wherein said catheter device is an infusion cannula device.

25. The catheter device .according to claim 4 wherein said catheter device is an infusion cannula device.

26. The catheter device according to claim 21 wherein said catheter device is an infusion cannula device.

27. The catheter device according to claim 23 wherein said catheter device is an infusion cannula device.

28. A process of using the catheter of claim 1 having a tip part which comprises:

A. inserting said catheter tip part foremost into a body vessel via an opening made into the vessel; B. connecting said catheter to a fluid withdrawal device;

C. withdrawing fluid; and

D. withdrawing said catheter.

29. A process of using the catheter of claim 1 having a tin part which comprises:

A. inserting said catheter tip part foremost into a body vessel via an opening made into the vessel;

B. connecting said catheter to a fluid administering device;

C. administering fluid; and D. withdrawing said catheter.

30. A process of using the catheter of claim 1 having a tip part which comprises:

A. inserting a piercing needle into a body vessel;

B. inserting said catheter tip part foremost into a body vessel via the opening made by said piercing needle;

C. withdrawing said piercing needle;

D. inserting a medical device into a body vessel via said catheter; and

E. withdrawing said medical device and said catheter.