Tubular restraint release approaches for electrolytic implant delivery system

Abstract

Medical devices and methods for delivery or implantation of prostheses within hollow body organs and vessels or other luminal anatomy are disclosed. The subject technologies may be used in the treatment of atherosclerosis in stenting procedures or be used in variety of other procedures. The systems may employ a self expanding stent restrained by one or more members released by an electrolytically erodable latch. Such release means do not connect directly to the implant, though one or more portions may contact it.

Description

BACKGROUND [0001] Implants such as stents and occlusive coils have been used in patients for a wide variety of reasons. One of the most common “stenting” procedures is carried out in connection with the treatment of atherosclerosis, a disease which results in a narrowing and stenosis of body lumens, such as the coronary arteries. At the site of the narrowing (i.e., the site of a lesion) a balloon is typically dilatated in an angioplasty procedure to open the vessel. A stent is set in apposition to the interior surface of the lumen in order to help maintain an open passageway. This result may be effected by means of a scaffolding support alone or by virtue of the presence of one or more drugs carried by the stent to aide in the prevention of restenosis. [0002] Various stent designs have been developed and used clinically, but self-expandable and balloon-expandable stent systems and their related deployment techniques are now predominant. Examples of self-expandable stents currently i...

AI Technical Summary

Benefits of technology

[0016] In a number of variations of the invention, the configuration of the stent or other implant employed is critical to the operation of the system. In these systems, foreshortening of the implant (i.e., decreasing length of the body, or at least a portion thereof, in transitioning from a collapsed to an expanded state) plays an important roll in stent release. In those examples of the invention where foreshortening plays a role in implant release, the implant is often adapted to be twisted and it is this twisting that assists in holding the stent at a desired diameter.

[0023] Systems employing these pass-through type of securing features may work alone by holding an implant such as a stent in a twisted state. Alternatively, they may hold such an implant in a twisted and / or axially stretched configuration with a retractable tubular sheath or restraint sleeve over the implant. In this way, the electrolytically released components can partially restrain the implant so as to reduce sleeve hold-down and / or withdrawal forces. The pinned / threaded connections are particularly space-efficient and, thus, suited for use with supplemental restraining device components while maintaining small device crossing profiles.

[0024] When employed with a retaining sleeve, as few as one location on the implant can be secured by the electrolytically released component(s). For a stent, the location may be proximal or distal. A distal location may offer improved sleeve withdrawal characteristics; a proximal location may simplify electrical conduction and or performance issues. Employing both proximal and distal electrolytic retainer attachment locations enable axial and / or torque-based implant diameter reduction techniques to reduce the force required for restraint withdrawal.

[0031] In any case, all of the above-described release members are to be actuated by electrolytic erosion through application of voltage by user action (or computer programming) with a suitable power supply. Other variations of the present invention employ a second implant retaining and release means that is tripped or actuated by action of the first release means or by the resulting configuration of the implant. In these variations of the invention, the second or subsequent means automatically completes implant release. Such action may be desired as a matter of convenience in reducing user activity, it may offer improved release speed or reliability, or it may be desirable for yet one or more other reasons.

[0032] Of these auto-release systems, a first type is one in which a floating or non-secured tubular member is set over one end of the implant. Expansion of the implant—as in the example of a stent—drives the tube off of the stent in the direction of expansion. So-displaced, the adjacent captured end of the stent is released. An interlocking key or slip-type interface may be freed-up by virtue of moving the outer sleeve. In either example, the stent may lie upon a core member along its entire length or a region under the projections may be relieved or undercut. Such relief allows for steepening of the angle that the end of the implant can assume without flexing of material. This effect offers improved mechanical advantage for moving the outer sleeve.

[0042] Another approach according to the-present invention involves system insulation in order to focus erosion, or at least maximize current density at the point of erosion. Generally, it is known that “fast acting” detachable systems can be produced by insulating or electrically isolating everything but that portion of the system where electrolytic erosion is desired. The present invention improves upon this concept in certain variations by producing system components with high-strength titanium or titanium alloy. In addition, they can be anodized to form an oxide layer insulative to DC voltage. The components are typically pre-anodized. Yet, when using higher voltages, the systems are “self-healing” such that any scratches, etc. exposing material to unintended corrosion / erosion will skin-over and maintain their integrity. Such a system is highly advantageous as it eliminates the need for polymeric insulation; further, such a system need not rely on the use of noble (or high Mendelev number) metal material selection to protect components that can be costly or cumbersome to apply, or cause failures if disturbed.

Problems solved by technology

Internal forces can be a significant issue with respect to system actuation.

Upon closer examination, each of the referenced systems has serious limitations—either in terms of clinical practicality, basic mechanical feasibility or both.

1) risk of tissue damage or vulnerable plaque dislodgement by drawing released tethers or bands past / between an open / opening stent and a vessel wall;

2) inability to employ drug elution matrix upon a stent because of direct connection of an erodable solder joint to the stent;

3) unpredictability of joint or release segment corrosion;

5) bulkiness in system design.

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