WO1997026935A1

WO1997026935A1 - Method of making small diameter catheters and the like type of reinforced tubular product

Info

Publication number: WO1997026935A1
Application number: PCT/IB1997/000138
Authority: WO
Inventors: Warren R. Burnham
Original assignee: Burnham Warren R
Priority date: 1996-01-23
Filing date: 1997-01-23
Publication date: 1997-07-31

Abstract

A small diameter reinforced catheter is produced by wrapping precoated reinforcing strands (30) on the surface of a mandrel (32) and the wrapped mandrel is introduced into a heated die (34) which compresses the wrapped strands against the mandrel (32) and at the same time heats and cures the prepolymer with both conducting and radiant heat. This allows the strands to sink into the tubing wall. Following this, the compression and the conductive heating is removed while the tubing continues to be exposed to radiant heat from the die (34). During this last stage, the tension in the strands induces the strands to assume a predetermined position between the inner and outer surfaces of the tubing.

Description

METHOD OF MAKING SMALL DIAMETER CATHETERS AND THE LIKE TYPE OF REINFORCED TUBULAR PRODUCT

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates generally to the formation of reinforced tubing and more specifically to small diameter reinforced pipe/tubing which can be used as a catheter and the like type of medical instrument. Description of the Prior Art

In the field of medical catheters, especially in the areas of small vessel therapies, there has long been a need for small diameter catheters with structural properties which cannot be attained with single substance structures. The most important property missing in small diameter catheters (5Fr and smaller for example) has always been "torqueability" and "pushability" or the ability to accurately transmit rotational and axially acting forces from the approximate proximal end to the approximate distal end for the purposes of steering during placement and for the accomplishment of therapies. In addition, there are some requirements for burst strength under pressure which exceed the properties of single substance constructions. Even multi-polymer structures in most cases do not generate composite properties at optimum levels for many uses.

In actual fact, balloon catheters have encountered thresholds which have limited the quest for ever-smaller arrangements. This is evidenced by the fact that, although high modulus reinforced catheters have been in demand, none have successfully reached the market in sizes below 4 French due to the inability to fabricate the same accurately, in volume, and at a price affordable to the medical trade.

United States Patent No. 4,764,324 which was issued on August 16, 1988 in the name of Burnham (the inventor named on the instant application) disclosed a technique for making small diameter catheter. This reference is incorporated by reference thereto.

However, in attempting to apply the technique disclosed in United States Patent No. 4,764,324 (hereinafter Burnham '324 and which is hereby incorporated by reference thereto) to the problem of manufacturing ultra small composite tubes, it was found that desired results could not be achieved. Burnham '324 discloses the steps of: preheating the polymer substrate to a controlled degree; applying reinforcement strands/electrical conductors with appropriate winding tension to cause the strands/conductors to sink below the original substrate surface to a controlled degree; and smoothing the remaining disrupted polymeric surface to reconstruct a smooth external surface. When attempting to only partially soften the walls of tiny tubes in the range of 0.008" down to 0.0005" in wall thickness, it was found that the heat transfer rate of the polymer to be softened is so high that the lineal separation of the heating area and the strand application area caused total fusion of the polymer. The cause of this problem was found to reside in the fact that a given amount of time is required for the heated polymer substrate to move from the heating area to the strand application point and that this was too long and allowed the fusion to go beyond the partial stage at even the highest speeds. This excessive fusion allowed the reinforcing strands to totally penetrate the tube wall and come into physical contact with the internal supporting mandrel. In other words the strands wound up for all intents and purposes, all the way through the wall they were meant to reinforce midway.

United States Patent No. 5,234,416 issued on August 10, 1993 to Macaulay et al . discloses a technique for forming a catheter which includes braiding a plurality of small diameter wires which have been pre-impregnated with a thermoset polymer along the whole length of a stainless steel mandrel which possibly has been pre-coated with a thin base layer of a given polymer. This intermediate product is then heated (baked) at a temperature which induces polymerization and cures the polymer. However, with this technique grinding is then necessary to smooth and round the OD. The mandrel is then removed to complete the production of the catheter. This reference also discloses the use of shrink fit plastic. The content of this reference is hereby incorporated by reference thereto.

However, this method encounters a drawbacks in that the braiding process which interlocks the reinforcing wires surprisingly reduces the "torqueability" and "pushability" of the product

United States Patent No. 4,981,478 issued on January 1, 1991 in the name of Evard et al . and United States Patent No. 5,290,230 issued on March 1, 1994 also disclose methods of producing catheters but are such as to suggest that braiding or wrapping can be used during the manufacture. Neither of these documents recognizes the drawback which is encountered with braiding. The contents of both of these documents is hereby incorporated by reference thereto.

SUMMARY OF THE INVENTION

The present invention is based on the discovery that wrapping layers of reinforcing wires (either metallic or other suitable non-metallic material) in layers which do not interwind with one another (viz., are not braided) endow greatly improved "torqueability" and "pushability" on small diameter catheters and the like.

While the preferred mode is disclosed in connection with wrapping reinforcements onto a mandrelized thermoplastic tube which is then passed through a heated die, the invention is not so limited and the techniques which are disclosed in the above mentioned patents are also envisaged as long as braiding is avoided and wrapping of layers of reinforcement is used. In the preferred embodiment, it is envisaged that a thermoplastic Nylon^® produced by Atochem will be used. BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more clearly appreciated as the disclosure of the present invention is made with reference to the accompanying drawings wherein: Fig. 1 schematically depicts the layout in which the die arrangement, which forms a vital part of the instant invention, is used when production according to a preferred embodiment of the present invention is implemented;

Fig. 2 is a sectioned perspective view showing the manner in which the reinforcing strands are wound on a mandrelized tubular substrate just as it drawn into the die shown in Fig. 1;

Figs. 3A and 3B are schematic elevation and plan views, respectively, showing details of the process depicted in Fig. 2, on an enlarged scale; and

Fig. 4 is a schematic representation showing another embodiment by which production of small diameter reinforced tubing can be achieved. DESCRIPTION OF THE PREFERRED EMBODIMENTS

Fig. 1 schematically depicts a possible layout by which the invention can be implemented. Briefly, this example is such as to include a supply of pre-mandrelized tubular product 10, means 14 for winding strands (20) of reinforcing material into individual non-woven wraps (layers) on the mandrelized tubing under a predetermined amount of tension, a heated die 16, and a large diameter pulling wheel 18 (approx 2 feet in diameter) which is used to draw the product through the die 16 at a desired rate .

It should be noted that throughout this specification, wrapping is intended to mean winding or applying reinforcing strands in a manner wherein one layer is not interwoven or interknitted with another.

Figs. 2, 3A and 3B depict the manner in which the reinforcing strands 20 are wound with a predetermined amount of tension onto the exterior of the plastic tube 22 immediately before entering the heated die 16. In this_ embodiment, the die responds to or is heated by RF energy and includes a RF guide 24 which is cast into the die proper. This arrangement allows the die to be heated to a predetermined level and accurately maintained thereat .

Alternatively, the die can be heated using a resistance heated die holder.

The process which characterizes the present invention includes three basic stages, I, II, and III

(Figs. 3A, 3B) . The first stage (I) is such that all the strands of reinforcing material 20 are wound onto the exterior of a mandrelized tubing 22 just as it enters the mouth of the die. At this stage the effects of both radiant and conducted heat start to take place.

As best seen in Figs. 3A and 3B, the inlet of the die is sized and configured such that during stage II which occurs as the just-wound strands enter the bore, the strands are subjected to a compressive force and are forced inwardly against the tubing. At this stage, physical die compression in combination with radiant and conducted heating takes place. The external portion of the tube softens and allows the compression which is being applied to the strands to induce the latter to sink into the tubing to a "flush" depth.

The final section 16a of the die bore is arranged to progressively flare out in the illustrated manner. The third stage (III) of the process occurs as the tubing passes through this flared portion. More specifically, in this third stage, the physical compression and heating by conduction stop and the effects of radiant heat and strand tension induces all of the strands to travel further radially inward to reach the required depth within the tube wall . The above process will become better appreciated as a description of a specific example is given along with comments relating to the various aspects of the process are given.

EXAMPLE In accordance with the present invention, a run was set up in a manner wherein there was no heating by the preheat oven, and heat was applied only from the wire guiding upper die. In addition to this, the die size was chosen to be the exact diameter of the polymer strand plus a thickness of wire. In this particular case, 0.044" + 0.001".

Thiε resulted in an intentional diametral interference at the die opening of 0.003", since the base structure plus 2 wire layers per side equals 0.048". This was done to cause radial compression so that heat would be transmitted to the substrate by conduction through the wire as well as radiantly within the die's cylindrical length (Stage II) with that length serving as a super small axial oven located at the wire impingement point rather than ahead of that point by a given distance. It was reasoned that if the wire and substrate heating were accomplished simultaneously, advantage could be taken of the fact that any very thin wall heats up and softens extremely rapidly.

As both the throughput rate of the substrate through the die and the wire deposition rate were variable in order to maintain the correct geometry of lay, it was possible to appropriately select the rates in combination with the amount of heat produced by the upper die, in a manner which rendered it possible to achieve a set of operating parameters which would control the wire pattern as to both geometry and depth of penetration.

This process was observed to not only produce the desired results wherein the location of the wires is exactly "midwall" at 480°F die heat, but also provided another unexpected bonus, viz., the polymer substrate has the mandrel perfectly centered therein. At the sizes contemplated in accordance with the present invention, even 0.001" eccentricity is a major error, while in an ordinary sized tube it is acceptable variation within tolerances.

However, with the present invention as physical compression, conductive heating, and radiant heating all happen simultaneously in a tiny space, the depth of wire penetration is governed by these parameters working uniformly in from the outer circumference on an essentially cold substrate which has had no opportunity to change softness/viscosity values until the instant of wire insertion. The result is absolute uniformity of depth of wire penetration regardless of random variations in wall thickness around the circumference of the structure. In addition, since all the fusion heat comes from one tightly controlled source, is applied over a structure length of 1 to 8 structure diameters, and is done in less than 0.1 seconds per wire width of axial length, the controllability of wire location and penetration borders on being essentially absolute. It should be appreciated that while the above disclosed process finds highly advantageous application with small diameter thin walled tubing, in situations wherein it is desired to achieve a mid-wall disposition of the reinforcing strands, the process is not_ι limited with respect to diameter and can be applied to larger diameter tubes which have a thin wall. Alternatively, the process can be applied to thicker walled tubing in situations wherein it is desired to set the reinforcing strands in a shallow disposition just below the surface of a relatively thick wall.

At required reinforcing depths greater than those contemplated in accordance with the present invention (deeper than 0.004" - 0.005" on any diameter structure) , pre-heating is necessary to soften the substrate deeply enough for correct strand placement while using heating rates within the tolerance range of the structure's polymer, viz., if the desired structure requires that the reinforcement/conductors be placed deeper than 0.004"/0.005" on any diameter structure, the heat required in the top die heat only mode gets to be so high as to degrade the polymer structure when run at any economical production rate. ALTERNATE EMBODIMENTS

In accordance with the invention, it is also possible to, as shown schematically in Fig. 4, to wind wraps of reinforcing wires (strands) 30 onto a mandrel 32 which can, if required, be previously coated with a base layer of polymer, either after or simultaneously being treated with "prepolymer" . In this figure, arrow "A" denotes either the pre-coating of the mandrel 32 or the application of the prepolymer to the surface of the mandrel and/or the strands 30 which are wound into wraps on the surface of the mandrel . The so called prepolymer can take the form of any of the materials disclosed in the above incorporated United States Patent No. 5,234,416. In this figure, numeral 34 denotes either an oven for heating and curing the prepolymer which has been intimately mixed with and coated over the reinforcing wraps, or heated die which can be used to both cure the polymer and smooth the OD of the product .

It is also within the scope of the present invention to add polymer after the wrapping process as indicated by arrows "B" . This post wrapping application can be made in addition to the application "A" .

Another variant resides in using element 34 as a non-heated or even cooled die to smooth the OD of the catheter as it is produced. It is also within the scope of the present invention to used either or both thermoplastic or thermosetting polymers in the manner suggested in any of the references which have been incorporated into this disclosure.

Yet another technique which can be employed is the use of shrink fit plastic. That is to say, it is possible to shrink fit a layer of plastic onto a mandrel, wrap one or more layers of reinforcing material onto the covered mandrel and then cover this with another layer of shrink fit plastic and shrink this layer into place to sandwich the wrapped layer or layers into place.

Combinations of this technique with additional polymer application is also possible in the manner indicated in United States Patent No. 5,234,416.

It will be appreciated that the present invention is by no means limited to the specific embodiments disclosed and that various changes and modifications can be made without departing from the scope of the present invention. For example, the die heating technique need not be limited to RF type heating and various other techniques could be envisaged either alone or in combination.

Claims

WHAT IS CLAIMED IS:

1. A method of forming small diameter reinforced tubing comprising the steps of: coating a mandrel with a layer of prepolymer; winding reinforcing strands under a predetermined tension onto the mandrel; and heating the prepolymer with a heated element to induce curing of the prepolymer.

2. A method as set forth in claim 1, wherein heated element comprises a die which is sized and configured to produce an interference as the strands enter a mouth of the die and thus produce a compression force which tends to force the strands radially inward into the coating of prepolymer.

3. A method as set forth in claim 2, wherein said step of applying heat includes applying both radiant and conductive heat to the first coating.

4. A method as set forth in claim 2, further comprising the step of removing the compression force and allowing radiant heat and the tension in the strands to move the strands to a predetermined position within a wall of a tubing formed by curing the prepolymer.

5. A method as set forth in claim 1, further comprising using the heated element to smooth the outside diameter of the tubing formed by curing of the prepolymer.

6. A method as set forth in claim 1, further comprising the step of adding a second coat of prepolymer to the mandrel after the reinforcing strands have been wound onto the mandrel.

7. A method as set forth in claim 6, wherein the step of heating is carried out after the addition of the second coat of prepolymer.

8. A method as set forth in claim 6, wherein the step of heating is carried out before the step of adding the second cooling of prepolymer and wherein the method further comprises a second step of heating to cure the second coating of prepolymer.

9. A method of forming small diameter reinforced tubing comprising the steps of: applying a first coating of shrink fit plastic onto a mandrel; wrapping a layer of reinforcing material onto the first coating of shrink fit plastic; applying a second coating of shrink fit plastic onto the layer of reinforcing material; and applying heat to shrink the first and second coatings of shrink fit plastic in a manner which forms a tube which encloses the layer of reinforcing material in its wall.

10. A method as set forth in claim 9, wherein said step of applying heat includes passing the mandrel through a heated die.

11. A method of forming small diameter reinforced tubing comprising the steps of: applying a first coating of one of a shrink fit plastic and a prepolymer onto a mandrel; wrapping a layer of reinforcing strands onto the first coating; applying a second coating of one of a shrink fit plastic and a prepolymer onto the layer of reinforcing strands; and applying heat to the first and second coatings.

12. A method as set forth in claim 11, wherein said step of applying heat includes : compressing the second coating and the reinforcing strands against the first coating and simultaneously applying both radiant and conductive heat to the first coating by introducing the tubing and reinforcing strands into a die which is adapted to apply heat thereto, the die being sized and configured to produce an interference as the first and second coatings and the reinforcing strands enter a mouth of the die; and removing the compressive force and allowing the radiant heat and the tension in the reinforcing strands to locate the reinforcing strands at a predetermined position within the wall tubing formed from the first and second coatings.

13. An apparatus for forming small diameter reinforced tubing comprising: means for coating a mandrel with a layer of prepolymer; means for winding reinforcing strands under a predetermined tension onto the mandrel; and means for heating the prepolymer to induce curing of the prepolymer.

14. An apparatus as set forth in claim 12, wherein the heating means comprises a die which is sized and configured to produce an interference as the strands enter a mouth of the die and thus produce a compression force which tends to force the strands radially inward into the coating of prepolymer.

15. An apparatus as set forth in claim 14, wherein the heating means applies both radiant and conductive heat to the first coating.

16. An apparatus as set forth in claim 14, wherein the heating means is arranged to remove the compressive force and allow radiant heat and the tension in the strands to move the strands to a predetermined position within a wall of tubing formed by curing the prepolymer.

17. An apparatus as set forth in claim 13, wherein the heated element is adapted to smooth the outside diameter of tubing which results from curing the prepolymer.

18. An apparatus as set forth in claim 13, further comprising means for adding a second coat of prepolymer to the mandrel after the reinforcing strands have been wound thereon.

19. An apparatus for forming small diameter reinforced tubing comprising: means for applying a first coating of shrink fit plastic onto a mandrel; means for wrapping a layer of reinforcing material onto the first coating of shrink fit plastic; means for applying a second coating of shrink fit plastic onto the layer of reinforcing material; and means for applying heat to shrink the first and second coatings of shrink fit plastic.

20. An apparatus as set forth in claim 19, wherein heat applying means comprises a heated die through which the mandrel is drawn.

21. An apparatus for forming small diameter reinforced tubing comprising: means for applying a first coating of one of a shrink fit plastic and a prepolymer onto a mandrel; means for wrapping a layer of reinforcing material onto the first coating; means for applying a second coating of one of a shrink fit plastic and a prepolymer onto the layer of reinforcing material; and means for applying heat to the first and second coatings .

22. An apparatus as set forth in claim 21, wherein the heat applying means includes : means for compressing the second coating and the reinforcing material against the first coating and simultaneously applying both radiant and conductive heat to the first and second coatings by introducing the first and second coatings and the reinforcing material into a die which is adapted to apply heat thereto, the die being sized and configured to produce an interference as the first and second coatings and the reinforcing material enter a mouth of the die; and means for removing the compressive force and allowing the radiant heat and the tension in the reinforcing material to locate the reinforcing material at a predetermined position within the wall tubing formed from the first and second coatings.

23. A reinforced tubing prepared in accordance with any one of claims 1 to 10.