Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Arterial prosthesis – Stent structure
Reexamination Certificate
2001-09-04
2003-03-18
Willse, David H. (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Arterial prosthesis
Stent structure
C623S001300, C623S001230
Reexamination Certificate
active
06533810
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a stent for use in a body passageway, comprising a flexible self-expandable braided tubular wall. The invention also relates to methods for manufacturing such a stent.
Use of expandable stents is known for damaged areas of body vessels such as for example food pipes, for dilatation, repair or bridging such areas. Where a patient suffers, for example, from a cancer of the esophagus while being otherwise in good status, stenting is a valuable approach to help him live. As such stents are subjected to stresses, in particular due to movements of the duct such as peristaltic movements, there is a tendency for the stent to migrate along the duct where it is placed. When the stent is used for a tumor at the end of a food pipe, for example at the junction of the esophagus and stomach, the problem of migration is further enhanced because the stent may have to protrude into the stomach. In such a case, the problem of anchoring the stent in the duct becomes particularly critical because the stent may fall into the stomach. A further problem arising with stents is that they have a tendency to close the pipe in curved areas thereof because of their deformation.
The document “Endoscopy 1992:24:416-420” describes a covered expandable metallic stent for preventing ingrowth of malignant structures. This stent is made of a steel wire bent in a zig-zag pattern and the stent legs are connected to wire skirts at each end which are intended to improve anchorage of the stent in a body passageway. In addition, 1 mm. barbs are attached to the skirts to still further enhance anchorage of the stent in the passageway. However, the document specifically outlines that migration remains a problem despite the wire skirts and barbs which were provided for anchorage purposes. Such a structure will certainly not allow safe anchoring of the stent in a condition where the stent cannot anchor at one of its ends, as in the case of a tumor at the end of the esophagus. And there are no solutions to overcome the pipe closure due to deformation of the stent in curved areas.
U.S. Pat. No. 4,655,771 discloses a stent made of a flexible tubular braided structure formed of helically wound thread elements. When the stent is deployed the stent assumes a substantially cylindrical shape as it expands and substantially conforms to the vessel wall, and the document outlines that such an expansion allows the stent to stay in place by self-fixation because of the permanent pressure of engagement against the vessel wall. Such a configuration may provide a good fixation in smooth rectilinear areas of the vessel. However, it will not provide a safe fixation in areas where a part of the stent cannot bear against the vessel wall. Nor will it solve the problem of pipe closure in curved areas of the vessel.
U.S. Pat. No. 5,064,435 shows a body implantable stent consisting of two or more generally tubular, coaxial and slidably joined stent elements each of which is of open weave construction, formed of multiple braided, helically wound strands of resilient material. The stent is thus elastically deformed to a reduced radius when deployed and it self expands radially when released after positioning in a vessel or other body cavity. To match the axial contraction of the stent upon radial expansion thereof and preserve a consistent length of the stent in spite of the axial contraction of the overlapping stent elements, the axially outward and non-overlapping portions of the stent are designed as radially outward flares to secure fixation of the stent to the vessel wall. Accordingly, axial contraction of the stent occurs as a reduction in the length of the medial region where the stent elements overlap. Other means to maintain the axial length comprise reinforcing filaments near the opposite ends of the stent elements to increase the restoring force, or fixation of hooks at the opposite ends of the stent elements, or still an elongate axially directed flexible and inextensible wire secured to the opposite ends of the stent elements. Such a configuration cannot be safely used if both the ends of the stent elements are not very strongly affixed to the vessel wall. As a matter of fact, if one of the stent elements is not firmly secured to the vessel wall, it may migrate with respect to the other stent element, for example because of peristaltic movements, whereby there may be a separation of the overlapping stent elements; where the stent is to be used at a place such as the junction of the esophagus to the stomach, the unsecured stent element will fail into the stomach. Complete separation of the stent elements will not occur in the case of use of an inextensible wire secured to opposite ends of the stent elements; however, such a wire cannot prevent part separation of the stent elements, for instance where the stent takes a relatively sharply curved configuration, which may cause serious injury to the vessel wall. And furthermore, whatever its configuration, the overlapping arrangement may still enhance the problem of pipe closure in curved areas because of the reduced flexibility resulting from the overlapping condition of the braided structure.
It is the primary object of the invention to avoid the aforesaid drawbacks. A further object of the invention is to provide a stent structure which allows safe and efficient operation in critical areas such as the end of a food pipe. Still a further object of the invention is a stent which minimizes the risk of pipe closure whatever the configuration of the body passageway. And it is also an object of the invention to provide for methods for manufacturing such a stent which are simple, efficient and economical.
SUMMARY OF THE INVENTION
Accordingly, the flexible self-expandable braided tubular wall forming the stent may comprise a first proximal segment having proximal and distal ends and a first outer diameter, a second distal segment having proximal and distal ends and a second outer diameter smaller than the said first outer diameter, and a third intermediate segment having a proximal end connected to the distal end of the first segment and a distal end connected to the proximal end of the second segment. With such a configuration the stent has a differential geometry which allows a-very strong anchor of the first proximal segment in the body passageway due to the higher radial force at that level. The third intermediate segment gives to the braiding a varying steep angle with respect to the longitudinal axis of the tubular wall which raises flexibility and/or radial force depending on the relative size of stent and vessel and on the elasticity of vessel wall; this structure also strongly limits any flattening deformation tendency whereby the deformation of the stent section remains closer to a circle. The second distal segment makes an easier and safer way through curves or at the end of a pipe. The differential geometry thus allows a higher flexibility where needed, i.e., before a curve of the body passageway, and it provides a better bend taking, a smoother way in the curve, and a better force differential to avoid migration under movements of the vessel or when the stent is placed in delicate locations such as the junction of the esophagus with the stomach.
Where the first proximal and second distal segments are cylindrical, the first proximal segment may firmly anchor in the vessel without any risk of damage to the vessel wall or to possible fistulas because of the surface repartition of the pressure of the braiding against the vessel wall, whereas the second distal segment may smoothly bear against the vessel wall, even in strongly narrowed areas.
Where the third intermediate segment is a truncated cone having a base forming the proximal end of the third intermediate segment and a top forming the distal end of the third intermediate segment, the best transitional flexibility and/or radial force repartiton is achieved between the first proximal and second distal segments. And when the third intermediate segment is formed of a plurality of c
Gianotti Marc
Hankh Susanne
Hofmann Eugen
Larkin Hoffman Daly & Lindgren Ltd.
Niebuhr Frederick W.
Phan Hien
Schneider (Europe) AG
Willse David H.
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