Catheter guide wire and catheter

Abstract: A catheter guide wire which, despite its reduced diameter, exhibits improved strength and resistance to corrosion by body fluids and medicine. The catheter guide wire 10 is composed of a stainless steel core wire 11, a winding of a low carbon duplex structure steel wire 13 having a diameter smaller than 30 µm and a tensile strength higher than 300 kgf/mm², said winding covering the core wire such that the low carbon duplex structure steel wire runs obliquely to the axis of the core wire 11 and crosses each other, and a polyester resin film 15, thinner than 3 µm, covering the low carbon duplex structure steel wire 13. The catheter is composed of a resin inner tube and a low carbon duplex structure steel wire 13 covered with a polyester resin film 15, which runs around the resin inner tube obliquely to the axis and crosses each other.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention: The present invention relates to a catheter to be used for diagnosis and medical treatment and also to a guide wire to keep the catheter approximately straight. More particularly, the present invention relates to a catheter and a catheter guide wire which have improved resistance to corrosion by body fluids and drugs. 2. Description of the Prior Art: Much attention is now focused on the new method of diagnosis and medical treatment which involves the insertion of a tubular catheter into the heart, lung, stomach, or blood vessel for the extraction of body fluids or blood or for the infusion of blood or medicine. The catheter for this purpose has an L-shaped tip and is flexible so that it can be inserted into complicatedly bent blood vessels. To facilitate insertion into the body, the catheter is kept approximately straight by the aid of a guide wire inserted into it. This guide wire should have the following characteristic properties. Sufficient flexibility to permit the catheter to bend easily along the blood vessels. Sufficient strength to keep the tip of the catheter approximately straight. Small outside diameter to permit its insertion into the thin catheter. Good resistance to corrosion by body fluids and blood. The conventional guide wire-which meets these requirements is composed of a stainless steel core wire and two layers of windings of extremely thin stainless steel wire (about 30 µm in dia.) on the core wire, with the inner windings being oblique to the axis of the core wire and the outer windings crossing the inner windings. What is required of the above-mentioned catheter for diagnosis and medical treatment are: Small outside diameter and large inside diameter. Good flexibility. Good buckling resistance (which prevents the catheter from being collapsed when it is bent). Ability to transmit torque (for manipulation) to its tip. The conventional catheter to meet these requirements is made from a tube of fluoroplastic (such as Teflon). The above-mentioned catheter has recently found a new use for the remedy of obstructive jaundice induced by liver cancer. In other words, the catheter is used to inject blood or medicine (such as anticancer drug) hot directly into the affected part. The conventional method involves the heating of medicine by a warmer coil and the injection of the heated medicine through the catheter. For the effective diagnosis and medical treatment, it is necessary that the catheter be brought as close to the affected part as possible. This requires the catheter to have a smaller outside diameter and the guide wire to have a smaller diameter accordingly. A conceivable way to meet this requirement is by further reduction in the diameter of the stainless steel wire. Mere reduction in diameter, however, results in insufficient strength, making it difficult for the guide wire to keep the catheter straight, which leads to the inconvenient manipulation of the catheter. There is a limit to reducing the diameter of the stainless steel wire. One possible way of reducing the outside diameter of the conventional catheter is by the reduction of the wall thickness of the inserting part, because it is necessary to secure a certain inside diameter necessary for blood extraction or medicine injection. A problem associated with reducing the wall thickness is that the catheter is liable to collapse and to become poor in torque transmission ability. This is another factor that limits the reduction of the diameter. It is expected that the reduction in diameter of the guide wire and catheter will be achieved with the low carbon duplex structure steel wire which had previously been proposed by the present inventors. It is produced from a wire rod, 3.0-6.0 mm in diameter, composed of C: 0.01-0.50%, Si: 3.0% or less, Mn: 5.0% or less, with the remainder being Fe and inevitable impurities (by weight), by the steps of primary heat treatment, primary cold drawing, secondary heat treatment, and secondary cold drawing. The thus produced steel wire has a diameter smaller than 30 µm and a tensile strength higher than 300 kgf/mm 2 . In other words, it is stronger and tougher than stainless steel wire for the same diameter. Therefore, if the low carbon duplex structure steel wire is used as a reinforcement for the guide wire and catheter, it would be possible to reduce the diameter while meeting the above-mentioned requirements. Unfortunately, the low carbon duplex structure steel wire has a disadvantage that it immediately rusts upon direct contact with body fluids, medicine, or air because it is extremely thin. Therefore, it should be given corrosion resistance. From the EP-A-0 200 430 there is already known a guide wire according to the preamble of claim 1. This guide wire has a too large diameter. From the EP-A-0 348 573 there is already known a catheter according to the preamble of claim 3. This catheter has a too large diameter. SUMMARY OF THE INVENTION It is an object of the invention to provide a guide wire according to the preamble of claim 1 avoiding the shortcomings attached hereto. It is another object of the invention to provide a catheter according to the preamble of claim 3 avoiding the shortcomings attached hereto. According to a first aspect of the invention, the first problem is solved by the features of the characterizing part of claim 1. According to a second aspect of the invention, the second problem is solved by the features of the characterizing part of claim 3. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a diagram illustrating the catheter guide wire in a first embodiment pertaining to the first aspect of the present invention. Fig. 2 is a diagram showing a catheter, with the guide wire of the first embodiment inserted thereinto. Fig. 3 is a partially sectional view illustrating a catheter in a first embodiment pertaining to the second aspect of the invention. Fig. 4 is a perspective view showing the catheter of the first embodiment. Fig. 5 is a partially sectional side view illustrating the catheter in a second embodiment pertaining to the second aspect of the present invention. Fig. 8 is a sectional view showing the forward end of the catheter in the third embodiment. DESCRIPTION OF THE PREFERRED EMBODIMENTS The first aspect of the present invention resides in a guide wire to keep a tubular catheter approximately straight, said guide wire comprising a core wire, a winding of a low carbon duplex structure steel wire having a diameter smaller than 30 µm and a tensile strength higher than 2943 N/mm 2 (300 kgf/mm 2 ), said winding covering the core wire such that the low carbon duplex structure steel wire runs obliquely to the axis of the core wire and crosses each other, and a polyester resin film covering the low carbon duplex structure steel wire. A preferred embodiment of the present invention resides in a guide wire as defined in the first aspect, wherein the polyester resin film has a thickness smaller than 5 µm. The second aspect of the present invention resides in a catheter having an outside diameter smaller than 1 mm which is composed of a resin inner tube, a reinforcing wire running around the inner tube obliquely to the axis and crossing each other, and a polyester resin film covering the reinforcing wire, said reinforcing wire being a low carbon duplex structure steel wire having a diameter smaller than 30 µm and a tensile strength higher than 2943 N/mm 2 (300 kgf/mm 2 .) A preferred embodiment of the second aspect of the present invention resides in a catheter, wherein the polyester resin film has a thickness smaller than 5 µm. Another preferred embodiment of the second aspect of the present invention resides in a catheter, wherein the resin inner tube is covered with a plurality of the reinforcing wires arranged in belt-like form and intertwined in reticular form. The reason for using a polyester resin for the coating film is that it can be formed into a very thin film which prevents the dissolution of metal and improves the resistance to corrosion by body fluids and medicine. The polyester resin coating film should preferably be formed by repeating the application of a resin solution, so that the resulting coating film has a high density. For the effective coating of polyester resin on the low carbon duplex structure steel wire, it is desirable to form a nickel plating layer as the substrate. The nickel plating layer lowers the activity of the wire, improves the self-lubricity and corrosion resistance of the wire, and improves the adhesion to the polyester resin. Moreover, the nickel plating layer will exhibit the further improved adhesion to the polyester resin film if it is given strain hardening by plastic working. According to the first aspect of the present invention, the catheter guide wire is composed of a core wire, a winding of a low carbon duplex structure steel wire having a diameter smaller than 30 µm and a tensile strength higher than 2943 N/mm 2 (300 kgf/mm 2 ), and a polyester resin film covering the winding. The use of the low carbon duplex structure steel wire, unlike the conventional stainless steel wire, makes it possible to reduce the diameter of the guide wire, while retaining the characteristic properties required of the guide wire. Since the low carbon duplex structure steel wire is very thin, the resulting guide wire is still thinner than that of stainless steel wire even though its surface is coated with a polyester resin film. The polyester resin coating film is thin but protects the guide wire from corrosion even when it comes into direct contact with body fluids and medicine. The catheter pertaining to the second aspect of the present invention employs the low carbon duplex structure steel wire for reinforcement. This reinforcement permits the wall thickness of the inserting part to be made thinner, without any adverse effect on the buckling resistance and torque transmission ability, and also permits the outside diameter to be reduced while securing the inside diameter required. The catheter pertaining to the preferred embodiment of the present invention has improved flexibility. EXAMPLES Examples of the present invention will be described with reference to the accompanying drawings. Figs. 1 to 4 show the first embodiment of the catheter and catheter guide wire pertaining to the first and second aspects of the present invention. In Fig. 4, there is shown a catheter 1 for diagnosis and medical treatment, which is made up of a tubular inserting part 2 (1 meter long, 1 mm in outside diameter, and 0.6 mm in inside diameter), a manipulating part 3 for the blood extraction or medicine injection (fixedly connected to one end of the inserting part), and a guiding part 4 (rotatably fitted on the manipulating part). The inserting part 2 is formed slightly bent as the whole, with the forward end 2a thereof bent in "L". The forward end 2a has small holes 2b to facilitate the extraction of blood or body fluids or the injection of medicine. As Fig. 3 shows, the inserting part 2 is made up of an inner tube 5 of fluoroplastic, a layer of reinforcing wire 6, and a covering layer 7 of fluoroplastic. The reinforcing wire 6 is tightly running in two tiers around the inner tube 5 and crossing each other, oblique to the axis. The covering layer 7 is formed from a heat-shrinkable tube of fluoroplastic slipped on the layer of reinforcing wire 6. Thus there is no gap between them. Fig. 1 shows a catheter guide wire 10, which is 0.3 mm in outside diameter and approximately straight. It is inserted into the catheter 1 from the manipulating part 3 so as to keep approximately straight the inserting part 2 and forward end 2a of the catheter. The guide wire 10 is made up of a core 11 of stainless steel and a reinforcing wire 12 tightly wound double around the core. The reinforcing wire 12 runs oblique to the axis of the core 11 and crosses each other. As Fig. 1(b) shows, the reinforcing wire 6 and 12 to constitute the guide wire 10 and catheter 1 is a low carbon duplex structure steel wire 13, 10-30 µm in diameter. It has the above-mentioned composition and is produced by the above-mentioned process. It has the fine metal structure composed of fibrous cells oriented in one direction, with the size of each cell being 5-100 Å and the distance between cells being 50-1000 Å. It has a tensile strength of 2943-5886 N/mm 2 (300-600 kgf/mm 2 ). It is covered with a nickel plating layer 14, about 1 µm thick, which is free from pin-holes owing to strain hardening induced by plastic working at the time of drawing. The nickel plating layer 14 is coated with a polyester resin film 15, about 1-3 µm thick, which is formed by the repeated application of a polyester resin solution. The above-mentioned embodiment produces the following effects. When the catheter 1 is in use, the inserting part 2 is inserted into the coronary artery from the femoral artery for the administration of a radiopaque material through the small holes 2b therein. To insert the catheter 1 into the blood vessel, the guide wire 10 is inserted into the inserting part 2 so as to keep approximately straight the forward end 2a thereof, as shown in Fig. 2. When the forward end 2a reaches a bend of the blood vessel, the guide wire 10 is retracted to restore the forward end 2a to its original shape indicated by the chain line. In this way, the forward end 2a is directed to the target. The guide wire 10 is moved back and forth until the forward end 2a reaches the affected part. According to this embodiment, the guide wire 10 is composed of the reinforcing wire 12 which is the low carbon duplex structure steel wire 13, the nickel plating layer 14, and the polyester resin coating film 15. The reinforcing wire 12 itself has a high tensile strength of 2943 N/mm 2 (300 kgf/mm 2 ) and an extremely small diameter of 10-30 µm. Therefore, the guide wire can be made thin easily, unlike the conventional stainless steel wire, without any adverse effect on the retention of the catheter 1. The polyester resin thin film coating 15, which is easy to make, improves corrosion resistance and protects the guide wire from corrosion by medicine and blood. In addition, the nickel plating layer 14 improves the adhesion to the polyester resin film 15. According to this embodiment, the low carbon duplex structure steel wire 13 is used as the reinforcing wire 6 of the catheter 1. This makes it possible to reduce the wall thickness of the inserting part 2 and hence to reduce the outside diameter while maintaining the desired inside diameter. The winding of the low carbon duplex structure steel wire 13 is flexible and yet retains its shape, improving the buckling resistance and torque transmitting ability. In the first embodiment mentioned above, the reinforcing wire 6 for the catheter 1 is tightly wound double (in two tiers). However, the winding of the reinforcing wire is not limited to this structure. Fig. 5 shows the second embodiment pertaining to the preferred embodiment of the second aspect of the present invention. In this embodiment, three reinforcing wires 6 (low carbon duplex structure steel wires) are arranged parallel in belt-like form 16 and they are intertwined in reticular form on the inner tube 5 of fluoroplastic. The reinforcing belts 16 are oblique to the axis and cross each other. The catheter in the second embodiment exhibits the same characteristic properties as that in the first embodiment; moreover, it is more flexible. The low carbon duplex structure steel wire used in the first and second embodiments was tested for corrosion resistance and tensile strength. The samples for the test were three low carbon duplex structure steel wires coated with polyester resin film, each having an outside diameter of 15 , 26, and 30 µm (including the thickness of the resin coating film) and the resin coating film being 1 µm or 3 µm thick. The corrosion resistance was evaluated by measuring the area (in %) of the corrosion that occurred after the samples had been exposed to salt water spray for 2-8 hours, allowed to stand for 8 hours, and dried for 16 hours. For comparison, the same test as mentioned above was made with three samples: (1) a low carbon duplex structure steel wire, 35 µm in outside diameter, coated with a polyester film, 5 µm thick, (2) a SUS304 wire, 30 µm in diameter, and (3) a piano wire, 25,100 µm in diameter, without rust preventive treatment. The results are shown in Table 1. It is noted from Table 1 that in the case of conventional piano wire, the corroded area exceeded 50% (before breakage) 2-4 hours after salt water spray in the corrosion resistance test. By contrast, the low carbon duplex structure steel wire and SUS304 wire did not corrode at all even after drying that followed standing for 8 hours. It is also noted from Table 1 that the tensile strength of SUS304 wire is 2286 N/mm 2 (233 kgf/mm 2 ), whereas that of three samples (a), (b),and (c) of the low carbon duplex structure steel wire is 4267, 3924, and 2943 N/mm 2 (435, 400, and 300 kgf/mm 2 ), respectively, in spite of their small diameter. The tensile strength of the low carbon duplex structure steel wire having an outside diameter of 35 µm is 220 kgf/mm 2 , which is close to that of the stainless steel wire. This suggests that the resin coating film should be smaller than 3 µm in thickness. Incidentally, the tensile strength was obtained by dividing the load by the sectional area calculated from the outside diameter including the resin film thickness. [Effects of the invention] The catheter guide wire pertaining to the first aspect of the present invention, which is made up of a core wire having a diameter smaller than 30 µm, a low carbon duplex structure steel wire having a tensile strength higher than 2943 N/mm 2 (300 kgf/mm 2 ), and a polyester resin coating film having a thickness smaller than 5 µm, can be made thin easily without any adverse effect on the characteristic properties required of the guide wire. In addition, it has improved resistance to corrosion by body fluids and medicine. The catheter pertaining to the second aspect of the present invention, which is reinforced with the above-mentioned low carbon duplex structure steel wire, exhibits improved buckling resistance and torque transmitting ability even though the wall thickness of the catheter is reduced. The catheter pertaining to the fifth aspect of the present invention, in which the reinforcing wires are wound in a reticular form, has improved flexibility.

Claims: A guide wire (10) to keep a tubular catheter (1) approximately straight, said guide wire (10) comprising a core wire (11), a winding of a steel wire (12), said winding covering the core wire (11), and a plastic film covering the steel wire, characterized in that said steel wire is a low carbon duplex structure steel wire (13) having a diameter smaller than 30 µm and a tensile strength higher them 2943 N/mm 2 (300 kgf/mm 2 ), the turns of the low carbon duplex structure steel wire (13) run obliquely to the axis of the core wire (11) and cross each other, and said plastic film is a polyester resin film (15). A guide wire (10) as defined in claim 1, characterized in that the polyester resin film (15) has a thickness smaller than 5 µm. A catheter (1) which is composed of a resin inner tube (5), a reinforcing wire (6) running around the inner tube obliquely to the tube axis, and a polymeric resin film covering the reinforcing wire, said reinforcing wire being a steel wire, characterized in that the catheter (1) has an outside diameter smaller than 1 mm, said reinforcing wire is a low carbon duplex structure steel wire (13) having a diameter smaller than 30 µm and a tensile strength higher than 2943 N/mm 2 (300 kgf/mm 2 ), said polymeric resin film is a polyester resin film (15), and the turns of the low carbon duplex structure steel wire (13) cross each other. A catheter as defined in claim 3, characterized in that the polyester resin film (15) has a thickness smaller than 5 µm. A catheter as defined in claims 3 or 4, characterized in that the resin inner tube is covered with a plurality of the reinforcing wires (12) arranged in belt-like form and intertwined in reticular form.

Inventors: MIZUKAWA YOSHINOBU, UCHIMURA MASAHIKO, YUTORI TOSHIAKI, MIZUKAWA, YOSHINOBU, UCHIMURA, MASAHIKO, YUTORI, TOSHIAKI, Mizukawa, Yoshinobu, c/o Kobe Works, Uchimura, Masahiko, c/o Kobe Works, Yutori, Toshiaki, c/o Kobe Works
Applicants: KOBE STEEL LTD, KABUSHIKI KAISHA KOBE SEIKO SHO
Application year: 1992
Main classification: A61M25
IPC codes: A61M25