Catheter having a super-elastic metallic tube body

This invention relates to a catheter, for example, a catheter to be inserted into a blood vessel such as a catheter for angiography or a catheter for dilating a blood vessel.

A catheter for angiography to be inserted into a blood vessel consisting of a main body formed of a somewhat soft thermoplastic resin and a rigidity imparting member consisting of a metallic braided wire (generally a stainless-steel wire) and disposed around the main body which is for inhibiting kinking or squash of the catheter while maintaining its high flexibility and for improving the torque transmission efficiency has conventionally been designed.

A catheter equipped with an inflatable member for dilating a stenosis portion in a blood vessel to improve the blood flow on the peripheral side of the stenosis portion which is for use in curing the stenosis portion is disclosed in EPA No. 349640 for example. This catheter comprises an inner tube made of a flexible synthetic resin, an outer tube made of a flexible synthetic resin and disposed coaxially with the inner tube and a foldable and inflatable member having a proximal end portion attached to the outer tube and a distal portion attached to the inner tube, and besides, the inner or outer tube is provided with a rigidity imparting member consisting of a metallic wire (e.g., a stainless-steel wire).

The rigidity imparting member used in the above catheter can inhibit its kinking or squash and improve its torque transmission efficiency to some extent. However, the catheter as a whole had low rigidity and particularly had a low efficiency of transmitting the pushing force given at its proximal end (pushability) and only an insufficient torque transmission efficiency.

Catheters are required to be introduced into peripheral blood vessels. Catheters which can be introduced into a more peripheral blood vessel have now become more and more desirable.

However, the above catheter, whose body portion consists of a synthetic resin tube, needs to have a certain wall thickness and therefore necessarily has a large outer diameter. Accordingly, the blood vessel into which the catheter can be introduced is restricted by its outer diameter and the catheter could only be introduced into a blood vessel sufficiently larger than the outer diameter of the catheter.

WO-A-8908473. (Boston Scientific), discloses a catheter provided with a metallic tube ending up near the distal portion of the catheter body and cooperating with a guide wire during bending of the catheter. Furthermore, the catheter comprises an helical wire coil cooperating with the metallic tube and the guide wire.

The object of the present invention is to provide a novel and improved catheter of the design that has a high efficiency of transmitting the pushing force given at its proximal end (pushability) and a high torque transmission efficiency and furthermore can be made to have a sufficiently thin wall thickness and a smaller diameter.

As claimed, the catheter of the invention comprises a body portion having a metallic tube covered with a synthetic resin tube, a distal portion and an internal lumen.

According to the invention, the metallic tube is made of a super-elastic alloy and extends from a proximal end of said body portion to a distal end of said body portion. Furthermore, the synthetic resin tube covers the entire outer surface of the super-elastic alloy tube and protrudes from the distal tip of the super-elastic alloy tube to form the distal portion of the catheter.

As also claimed, the catheter of the invention in a further embodiment comprises a body portion having a metallic tube covered with a synthetic resin layer, a distal portion and an internal lumen.

According to this embodiment of the invention, the metallic tube is made of super-elastic alloy and has a distal portion which is more flexible than another portion thereof, the more flexible portion of the super-elastic alloy tube corresponds to the distal portion of the catheter and the synthetic resin layer covers the outer surface of the entire super-elastic alloy tube.

The invention will now be described on hand of several non limitative examples illustrated on the annexed drawings.

Fig.1 is a partial longitudinal cross section of a catheter according to one preferred embodiment of the present invention.

Fig.2 is a partial longitudinal cross section of a catheter according to another preferred embodiment of the present invention.

Fig.3 is a partial longitudinal cross section of a catheter according to another preferred embodiment of the present invention.

Fig.4 is a partial longitudinal cross section of a catheter according to another preferred embodiment of the present invention.

Fig.5 is a view of a catheter according to the present invention having a hub fixed to its proximal end.

The catheter generally designated at 1 according to the present invention comprises a body portion 4a, a distal portion 4b and an internal lumen 6 at least the body portion 4a including a metallic tube 2 made of a super-elastic alloy.

Therefore, the catheter of the present invention has a high efficiency of transmitting the pushing force given at its proximal end (pushability) and a high torque transmission efficiency and can have a sufficiently thin wall thickness and a smaller diameter.

A catheter according to one preferred embodiment of the present invention shown in Fig.1 and Fig.5 will be described in the following.

The catheter 1 of this preferred embodiment is an example of use of the present invention for angiography and comprises a body portion 4a, a distal portion 4b, a lumen 6 continuous from the proximal end of the catheter 1 to its distal end, a tip end opening 5 and a hub 7 fixed to the proximal end.

The body portion 4a comprises a metallic tube 2 and a synthetic resin tube 3 covering the outer surface of the metallic tube 2, and the synthetic resin tube 3 protrudes from the distal portion of the metallic tube 2 to form the distal portion 4b of the catheter.

The metallic tube 2 is formed of super-elastic alloys, for example, Ti-Ni alloys containing 49 ∼ 58 atom% of Ni, Cu-Zn alloys containing 38.5 ∼ 41.5 % by weight of Zn, Cu-Zn-X alloys containing 1 ∼ 10 % by weight of X wherein X is selected from the group consisting of Be, Si, Sn, Al and Ga and Ni-Al alloys containing 36 ∼ 38 atom% of Al. The most preferred alloys are Ti-Ni alloys of the above composition. The super-elastic metallic tube 2 preferably has an outer diameter of 0.3 ∼ 6.0 mm, more preferably 0.4 ∼ 5.5 mm and a wall thickness of 40 ∼ 200 µm, more preferably 50 ∼ 150 µm. It preferably has a length of 500 ∼ 4,000 mm, more preferably 800 ∼ 3,000 mm, a buckling strength (yield stress under load) of 5 ∼ 200 kg/mm² at 22°C, more preferably 8 ∼ 180 kg/mm² at 22°C, and a restoring stress (yield stress upon unloading) of 3 ∼ 180 kg/mm² at 22°C, more preferably 5 ∼ 160 kg/mm² at 22°C. it is preferable that the tip of the super-elastic metallic tube 2 be tapered as shown in Fig.1 in order to prevent the tip from being separated from the synthetic resin tube 3. It is not necessary that the super-elastic metallic tube have the above outer diameter over its entire length and it is allowed to make it only partly with the above outer diameter.

As shown in Fig.1, the synthetic resin tube 3 covers the outer surface of the entire super-elastic alloy tube 2 and protrudes from the distal portion of the super-elastic alloy tube 2 to form the distal portion 4b of the curved catheter. This enables the catheter 1 of this example to have a flexible distal portion 4b. The curved portion has a shape suitable for the predetermined blood vessel into which the catheter is to be inserted.

For the synthetic resin tube 3, thermoplastic resins such as polyolefin elastomer (e.g., polyethylene elastomer, polypropylene elastomer and ethylene-propylene copolymer elastomer), polyvinyl chloride, ethylene-vinyl acetate copolymer, polyamide elastomer, polyurethane and fluorine resin and silicone rubber can be used. It is preferred to use polyamide elastomer or polyurethane. It is preferable that the synthetic resin tube 3 be sufficiently flexible to allow free kinking of the super-elastic alloy tube 2. In addition, it is preferred to incorporate a radiopaque substance into the synthetic resin to form the tube 3 because it becomes more easy to locate the catheter 1 during its introduction into the blood vessel. The radiographically sensitive substance may be a metal such as Ba, W, Bi, or a compound thereof in fine powdery form. The synthetic resin tube 3 has preferably an outer diameter of the 0.9 ∼ 7.0 mm, more preferably 1.0 ∼ 6.0 mm and a wall thickness on the outer surface of the super-elastic alloy tube 2 of 0.04 ∼ 0.3 mm, more preferably 0.06 ∼ 0.2 mm.

The outer surface of the synthetic resin tube 3 may be coated with a biocompatible especially antithrombotic resin such as polyhydroxyethyl methacrylate, or hydroxyethyl methacrylate-styrene copolymer (e.g., a HEMA-St-HEMA block copolymer). Particularly, when a material containing a radiopaque substance is used for the synthetic resin tube 3, it is preferred to perform the above coating in order to remove the roughness of the outer surface due to the radiopaque substance. Although it is preferable that the resin be a biocompatible one, a thin coating of the material used to form the synthetic resin tube 3 is also allowed.

It is preferred to apply hydrophilic treatment to the outer surface of the synthetic resin tube 3 in order to make it exhibit lubricity when contacted with blood or the like. Such hydrophilic treatments include coating with hydrophilic polymer such as poly(2-hydroxyethyl methacrylate), polyhydroxyethyl acrylate, hydroxypropyl cellulose, methylvinyl ether-maleic anhydride copolymer, polyethylene glycol, polyacrylamide or polyvinyl pyrrolidone.

It is preferable that the tip of the catheter 1 (tip of the synthetic resin tube 3) have a curved surface such as a semi- spherical surface as shown in Fig.1 in order to prevent any damage to the blood vessel wall and to improve the operability of the catheter 1.

The hub is fixed to the proximal end of the body portion 4a shown in Fig.5. The hub 7 has an opening 8 communicating with the lumen 6 and constituting an injection port for injecting X-ray contrast medium.

The hub 7 is preferably formed of thermoplastic resins, for example, polycarbonate, polyamide, polysulfine, polyallylate and methacrylate-butylene-styrene copolymer. Instead of providing such hub, an open end of the proximal end of the body portion may constitutes an injection port.

Next, a catheter according to one preferred embodiment of the present invention shown in Fig.2 will be described.

The catheter 1 of this preferred embodiment is an example of use of the present invention for angiography. This catheter comprises a body portion 4a, a distal portion 4b, a lumen 6 continuous from the proximal end of the catheter 1 to its distal tip, a tip end opening 5 and a hub (not shown). The body portion 4a and the distal portion 4b consist of a super-elastic alloy tube 2 and a synthetic resin layer 3 covering the outer surface of the tube 2.

Those materials described above can suitably be used for the super-elastic alloy tube 2. The part of the tube 2 corresponding to the body portion 4a is highly rigid and the part of the tube 2 corresponding to the distal portion 4b is more flexible than another portion of tube 2. Such a super-elastic alloy tube can be formed by separately thermally treating the body portion of the super-elastic alloy tube 2 and its distal portion under different conditions so that the body portion has a large yield stress and the distal portion has a small yield stress and is elastic.

As shown in Fig.3, the outer surface of the distal portion of the super-elastic alloy tube 2 may be provided with annular grooves in order to make the distal portion elastic. The groove shape is not restricted to annular one and it may be a spiral one. As shown in Fig. 4, the distal portion of the super-elastic alloy tube 2 may have a smaller diameter. As shown in Fig. 2, the synthetic resin layer 3 covers the outer surface of the entire super-elastic alloy tube 2. For the synthetic resin layer 3, thermoplastic resins such as polyolefin (e.g., polyethylene, polypropylene and ethylene-propylene copolymer), polyvinyl chloride, ethylene-vinyl acetate copolymer, polyamide elastomer, polyurethane, fluorine resin and silicone rubber can be used. It is preferred to use a polyolefin, a polyamide elastomer or a polyurethane.

It is preferable that the synthetic resin layer 3 be sufficiently flexible to allow free kinking of the super-elastic metallic tube 2. In addition, it is preferred to incorporate a radiopaque substance into the synthetic resin layer 3 because it becomes more easy to locate the catheter 1 during its introduction into the blood vessel. The radiographically sensitive substance may be a metal such as Ba, W, Bi or a compound thereof in find powdery form.

The synthetic resin layer 3 preferably has an outer diameter of 0.9 ∼ 7.0 mm, more preferably 1.0 ∼ 6.0 mm and a wall thickness on the outer surface of the super-elastic metallic tube 2 of 0.04 ∼ 0.3 mm, more preferably 0.06 ∼ 0.2 mm. It is preferable that the tip of the catheter (tip of the synthetic resin layer 3) has a curved surface such as a semi-spherical surface in order to prevent any damage to the blood vessel wall and to improve the operability of the catheter 1. As mentioned above, the synthetic resin layer 3 may be coated with an antithrombotic resin and hydrophilic treatment may be applied to the outer surface of the layer 3 so as to make it exhibit lubricity.

The hub is similarly shown in Fig.5 fixed to a proximal end of the body portion 4a. The hub has an opening communication with the lumen 6 and constituting an injection port for injecting X-ray contrast medium.

Since the catheter of the present invention comprises a body portion, a leading edge and an internal lumen and at least the above body portion includes a super-elastic alloy tube, the catheter of the present invention has a high efficiency of transmitting the pushing force given at its proximal end (pushability) and has a high torque transmission efficiency. Furthermore, since the body portion of the catheter includes a super-elastic alloy tube, the wall thickness of the body portion can be made sufficiently thin and a catheter with a smaller diameter can be formed.