Plastic and nonmetallic article shaping or treating: processes – Forming continuous or indefinite length work – Layered – stratified traversely of length – or multiphase...
Reexamination Certificate
1999-12-16
2003-06-17
Eashoo, Mark (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Forming continuous or indefinite length work
Layered, stratified traversely of length, or multiphase...
C264S173160, C264S209400, C264S209500
Reexamination Certificate
active
06579484
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to tubular shafts. More particularly, the present invention involves tapering a co-extruded tubular shaft (e.g., for use in catheters).
2. Description of Related Art
In percutaneous transluminal coronary angioplasty (PTCA), catheters are inserted into the cardiovascular system via the femoral artery under local anesthesia. A pre-shaped guiding catheter is positioned in the coronary artery, and a dilatation catheter having a distensible balloon portion is advanced through the guiding catheter into the branches of the coronary artery until the balloon portion traverses or crosses a stenotic lesion. The balloon portion is then inflated with a fluid to compress the atherosclerosis in a direction generally perpendicular to the wall of the artery, thereby dilating the lumen of the artery. A standard catheter having a relatively constant diameter is difficult to use in some of the smaller arteries and in cases of more advanced stenosis where the artery is closed to such an extent that the catheter cannot be extended through the lesion. Thus, a catheter having a narrowing or a tapered shaft will be beneficial in many circumstances.
A conventional dilatation catheter
5
known in the art for use in treating angioplasty is illustrated in FIG.
1
. Typically, dilatation catheters are co-axial catheters having a cross-section such as the one illustrated in FIG.
2
.
FIG. 3
is a side cross-sectional view of catheter
5
of
FIGS. 1 and 2
. Catheter
5
has a catheter shaft having an inner member
10
extending through an outer member
12
. Typically, outer tubular member
12
is sealed to the proximal shaft of a balloon
14
, while inner tubular member
10
is sealed to the distal shaft of balloon
14
. Fluid for inflating balloon
14
coupled to the distal end of inner
10
and outer
12
members is introduced through a passageway
11
formed between the tubular members (i.e., the outer lumen). A guide wire (not shown) then passes through a central opening or lumen
13
of inner tubular member
10
.
Due to the different responsibilities of each tubular member, inner
10
and outer
12
tubular members generally have different desired material characteristics, which complicates the selection of materials for each of the various catheter components. Typically, outer member
12
is fusion bondable to another catheter component and inner member
10
has a greater lubricity than outer member
12
to allow for ease of passage by the guidewire through inner catheter shaft
13
. For example, the material of outer member
12
of the catheter shaft must be selected such that it is compatible with the polymeric material (e.g., polyethylene, terephithelate, polyamide, nylon, etc.) of the catheter component to which it is to be secured (e.g., a balloon or transition piece). Furthermore, because outer member
12
of the catheter shaft is in contact with a patient, the material must be non-traumatic to the lining of the arterial walls into which the catheter is inserted. In contrast, inner member
10
is generally selected for its lubricious properties to allow easier passage of the guide wire through inner lumen
13
. Note that the same issues as identified above exist for a catheter shaft having a single tubular member: e.g., the interior of the member should be lubricious and the exterior should be both non-traumatic to the patient and bondable to another catheter component. Thus, when dealing with a single tubular member the material selection is particularly difficult.
One solution for addressing the difficulties in material selection of the more recently developed catheters has been the production of an improved multi-layer member fabricated by a co-extrusion process. A multi-layer member may be used independently as a sheath or as a catheter having a single tubular member (i.e., a single lumen catheter), or in conjunction with a second tubular member to form a co-axial catheter. When used with a co-axial catheter, either or both of the inner and outer tubular members may be a multi-layer member.
A multi-layer member may have many layers or as few as two layers, but typically consists of two to three layers. A cross-sectional illustration of a three layer tubular member
28
is shown in FIG.
4
. An inner layer
20
is typically lubricious such that a guidewire or other device may easily be inserted through an interior lumen
26
. An outer layer
24
is fabricated from a material that may easily be bonded to another component, e.g., a balloon, and that is strong enough to resist collapse pressure. A middle layer
22
is generally an adhesive or compatibilized polymer used to enhance the integrity of member
28
.
The formation of multi-layer tubular member
28
may be achieved through a co-extrusion process using multiple extruders. Generally, the materials selected for each layer are first processed in separate extruders. Each of the selected materials is separately brought to a molten state. Then the materials are brought together to form a single hollow tubing having inner layer
20
from a first material, middle layer
22
from a second material, and outer layer
24
from a third material.
Another complicating factor in the selection of materials for the various components of catheters is the usual requirement that the proximal shaft section (
16
of
FIG. 1
) be much longer and more rigid or stiff than the distal shaft section (
18
of
FIG. 1
) such that proximal shaft section
16
provides pushability to catheter
5
. This allows the more flexible distal shaft section
18
to be readily advanced through an often tortuous anatomy. Thus, a stiff proximal shaft may often be joined to a soft distal shaft. Note that the proximal shaft may be made stiffer than the distal shaft due to a larger (i.e., thicker) diameter or through use of a stiffer proximal polymeric tubing made from polymers such as PEEK. The joint between the proximal and distal shafts, however, often makes for an undesirable, abrupt transition between shaft sections.
There are numerous methods of establishing a connection or joint between the stiff proximal shaft and the more flexible distal shaft such as laser powered fusion of polymeric materials. The abrupt transition caused by joining a larger diameter proximal shaft to a smaller diameter distal shaft not only creates a weak point on the catheter shaft at the point of joinder, but the joint region itself is typically stiff and can interfere with the overall flexibility of the catheter shaft. (See transition
30
between a proximal shaft
32
and a distal shaft
34
in FIG.
5
). Also, the fluid flow is typically retarded at a transition point
30
, which increases the deflation time. Thus, a more gradual tapering of a single catheter shaft would provide several benefits over a catheter shaft having an abrupt transition between the proximal and distal shaft sections.
One solution to providing a tapered catheter shaft has been to “neck down” a small section of a straight shaft, as illustrated in FIG.
6
. The straight shaft is submitted to post-process heating (i.e., after the shaft is formed) and then pulled in a controlled manner (i.e., necked down or stretched out). This necking process provides a necked shaft having a tapered appearance, which allows for a more flexible distal section. However, there are several limitations and problems associated with the necking down process. First, the necking down process is usually able to taper only a short section
40
of the shaft. For example, the standard length of the necked down region is approximately 2-10 cm. Thus, if a more gradual taper is desired, for example a taper of the shaft over a longer region (e.g., 1 ft.), a method other than or in addition to necking must be used to taper the shaft. Second, a relatively immediate change (i.e., 3 cm) such as transition
30
illustrated in
FIG. 5
can still result at the point of necking (i.e., where the heat is applied), resulting in a weak spot in the catheter. Such weak spots are more suscept
Chow Mina W. B.
Lee Jeong S.
Schaible Stephen G.
Tiernan Stephen J.
Advanced Cardiovascular Systems Inc.
Blakely , Sokoloff, Taylor & Zafman LLP
Eashoo Mark
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