Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Arterial prosthesis – Stent combined with surgical delivery system
Reexamination Certificate
2001-04-27
2004-01-13
McDermott, Corrine (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Arterial prosthesis
Stent combined with surgical delivery system
C606S191000, C604S104000
Reexamination Certificate
active
06676692
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to advanced medical endoluminal devices and methods of minimally invasive treatment of blockages of the blood vessels and other tubular organs. More particularly, the present invention relates to apparatus for delivering, repositioning and/or retrieving self-expanding stents for internal reinforcing of diseased tubular structure and/or for local delivery of pharmacological or radioactive agents having a beneficial advantage of reduction of re-stenosis.
BACKGROUND OF THE INVENTION
Reference is made to a related application entitled Methods for Delivery Repositioning and/or Retrieving Self-Expanding Stents filed concurrently with this application.
A stent is a generally longitudinal cylindrical device formed of biocompatible material, such as a metal or plastic, which is used in the treatment of stenosis, strictures, or aneurysms in body blood vessels and other tubular body structures, such as the esophagus, bile ducts, urinary tract, intestines or tracheo-bronchial tree. References hereafter to “blood vessels” and “vessels” will be understood to refer to all such tubular body structures. A stent is held in a reduced diameter state during its passage through a low profile catheter until delivered to the desired location in the blood vessel, whereupon the stent radially expands to an expanded diameter state in the larger diameter vessel to hold the vessel open. As discussed below, radial expansion of the stent may be accomplished by an inflatable balloon attached to a catheter, or the stent may be of the self-expanding type that will radially expand once deployed from the end portion of a delivery catheter.
Non-diseased vessels that are stented have a tendency to develop more aggressive intimal hyperplasia than diseased vessels. Intimal hyperplasia is part of the endothelialization process by which the stent becomes incorporated into the vessel wall as a result of the vessel's reaction to a foreign body, and is characterized by deposition of cell layers covering the stent. It eventually results in formation of a neointima, which coats the stent and buries it completely in the vessel wall.
Endothelialization generally improves patency rates and the more complete the apposition of the stent to the vessel wall, the more uniform and optimal is the degree of endothelialization. Of course, a fundamental concern is that the stent be deployed in the correct desired location in the vessel as precisely as possible in the first place. This is important when delivering radiation or medication to a particular location using the stent.
Therefore, firstly, it is important that a stent be deployed in the correct desired position in the blood vessel and, secondly that the stent be as completely apposed to the vessel wall as possible.
Stents fall into one of two categories based on their mechanism of deployment and radial expansion, namely, balloon-expandable stents and self-expanding stents.
Balloon-expandable stents (BES) are mounted in their reduced diameter state on nylon or polyethylene balloons, usually by manual crimping, while others are available pre-mounted. One example of a BE is shown in U.S. Pat. No. 4,733,665 to Palmaz. BES rely solely on balloon dilation to attain the desired expanded configuration or state. This enables BES to be deployed in a relatively controlled gradual manner. BES in general have more strength than self-expanding stents and initially resist deformation as well as recoil. BES behave elastically but eventually yield and become irreversibly, i.e. plastically, deformed under external force. Most BES are less flexible than self-expanding stents and are therefore less capable of being delivered through tortuous vessels and, when a BES is deployed in a tortuous vessel, it often straightens the vessel, forcing the vessel to conform to the shape of the stent rather than vice versa. This generally results in portions of the stent not being completely apposed to the vessel wall which in turn affects endothelialization and overall patency rate.
On the other hand, BES can generally be deployed in a relatively precise manner at the correct desired location in the vessel since they can be deployed in a controlled gradual manner by gradually controlling the inflation of the balloon. This ability to gradually control the expansion of the stent, along with the fact that BES rarely change their position on the balloon during inflation, enable fine adjustments to be made by the operator in the position of the stent within the vessel prior to stent deployment.
Self-expanding stents (SES) are formed of braided stainless steel wire or shape-memory alloy such as nitinol and are generally delivered to desired locations in the body in a reduced diameter state in a low profile catheter while covered by an outer sheath which partially insulates the SES from body temperature and mechanically restrains them.
Nitinol is an alloy comprised of approximately 50% nickel and 50% titanium. Nitinol has properties of superelasticity and shape memory. Superelasticity refers to the enhanced ability of material to be deformed without irreversible change in shape. Shape memory is the ability of a material to regain its shape after deformation at a lower temperature. These physical properties of nitinol allow complex device configurations and high expansion ratios enabling percutaneous delivery through low profile access systems.
Superelasticity and shape memory are based on nitinol's ability to exist in two distinctly different, reversible crystal phases in its solid state at clinically useful temperatures. The alignment of crystals at the higher temperature is called the austenite (A) phase; the alignment of crystals at the lower temperature is called the martensite (M) phase. In between is a temperature interval of gradual transition between the A and M phases.
Under external force, the shape of a nitinol device can be greatly deformed without irreversible damage. Depending on the temperature at which this external force is applied, superelastic or shape memory effects prevail. In close vicinity to or above the temperature defining transition into the full A state, superelasticity results: as soon as the deforming force is released, the device immediately assumes it original shape. When nitinol is deformed at or below the lower temperature of the complete M transition, the shape memory effect can be exploited. The device retains its deformed shape even after the external force is removed as long as the temperature of the environment stays below the temperature of transition into A phase. Only during heating does the device resume its original shape.
While the shape memory effect is essentially a one-way type phenomena in which shape recovery occurs only upon heating the alloy to a temperature defining transition to the full A phase, by subjecting the alloy itself to a biasing force, i.e. an internal stress formed by dislocations introduced by plastic deformation in the alloy, a two-way shape memory can be imparted to the alloy so that cooling the alloy will induce a shape change.
One type of self-expanding stent is constructed of wire formed of a shape-memory alloy, such as nitinol, having a transition temperature of about body temperature, i.e. 37° C. For example, reference is made to U.S. Pat. No. 5,746,765 to Kleshinski et al. The one-way transition temperature is the temperature of transformation of a nitinol device from its collapsed state into a fully expanded configuration. The stent is preloaded on a low profile catheter by crimping the stent at room temperature (at which it can be plastically deformed) onto the catheter. An outer sheath covers the crimped stent and at least partially thermally insulates the stent as it is delivered to the desired location. Upon reaching the desired location, the sheath is withdrawn and the stent is exposed to body temperature whereupon it is naturally warmed to body temperature and expands to its expanded diameter state in supporting contact with the vessel wall. In a fully expanded sta
Morag Eyal
Perelson Ophir
Rabkin Dmitry
InTek Technology L.L.C.
McDermott Corrine
Steinberg & Raskin, P.C.
Stewart Alvin
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