Segmented Delivery Sheath for Stent Loading

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Solution Overview

Problem

Current stent delivery systems face challenges in achieving a smaller passing profile while maintaining reliability and flexibility, particularly when dealing with thin-walled sheaths that can tear or fail due to friction during stent deployment in narrow body vessels, and existing methods for releasing stents from sheaths can cause unwanted friction and stress on the sheath material.

Innovation Solution

A method involving a loading sheath and a delivery sheath with controlled diameter reduction through lengthwise strain, where the delivery sheath is progressively drawn down to a smaller diameter, allowing for the stent to be deployed with reduced wall thickness and minimized friction, using a component like PET with a strain initiation zone for controlled cold drawing, and optionally employing a tool for stent support during deployment.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Volume of moving object

If the sheath wall thickness is reduced to achieve a smaller passing profile, then the catheter diameter is reduced, but the sheath may tear or fail due to friction during stent deployment

Engineering Contradiction:

Improvecatheter passing profileVSAvoidsheath integrity

Core Design Contradiction:

Volume of moving objectVSReliability

Solution Approach 1:

The sheath is segmented into multiple sections with different properties: a thinner-walled delivery portion for navigation and a thicker-walled proximal portion for strength during deployment. The sheath is also divided into a deployed section and a retained section, allowing the thinnest walls only where needed for passage while maintaining strength where friction occurs.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different wall thicknesses are applied to different portions of the sheath based on local requirements. The delivery portion has reduced wall thickness (e.g., 0.002-0.006 inches) for minimal profile, while the proximal portion maintains greater thickness for structural integrity. The sheath transition zone gradually changes thickness to balance these competing requirements.

Inventive Principle:

Principle #3Local quality

2Ease of operation

If a thin-walled sheath is pulled from the proximal end to remove it after deployment, then the sheath can be removed, but friction causes the sheath to tear or the endoprosthesis to move proximally

Engineering Contradiction:

Improvesheath removalVSAvoidendoprosthesis position stability

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The proximal portion of the sheath is extracted or detached from the delivery system after deployment. The sheath is designed to be separable into deployed and retained portions, allowing the proximal section to be removed without pulling on the thinned delivery portion that remains in the patient's body, thus eliminating the friction problem during removal.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

Instead of pulling the sheath from the proximal end through the friction zone, the delivery system is designed so that the sheath proximal portion is detached and removed separately. The distal portion remains in place without requiring pull-through, inverting the traditional removal approach.

Inventive Principle:

Principle #13The other way round (Inversion)

3Ease of operation

If the sheath is stretched during pull to facilitate removal, then the sheath can be pulled out, but the radial diameter decreases increasing friction and requiring larger pulling force

Engineering Contradiction:

Improvesheath removalVSAvoidpulling force required

Core Design Contradiction:

Ease of operationVSForce

Solution Approach 1:

The sheath is segmented into removable proximal and retained distal portions. The proximal portion is detached and removed without needing to be stretched through the friction zone, eliminating the need for large pulling forces that would cause radial contraction and increased friction.

Inventive Principle:

Principle #1Segmentation

4Ease of operation

If cutting wires are used to open the sheath, then the sheath can be opened for expansion, but the cut open sheath is trapped between the expanded endoprosthesis and vessel wall requiring complex removal

Engineering Contradiction:

Improvestent deploymentVSAvoidsheath removal mechanism

Core Design Contradiction:

Ease of operationVSDevice complexity

Solution Approach 1:

The sheath is segmented into deployed and retained portions with a separation zone. After deployment, the proximal portion is detached and removed separately without needing to pull through the patient's body, simplifying removal compared to traditional cut-open sheaths that become trapped.

Inventive Principle:

Principle #1Segmentation

5Volume of moving object

If a single thin-walled sheath is used to achieve small profile, then the passing diameter is reduced, but the sheath must withstand both radial expansion force and tensile stress during pull

Engineering Contradiction:

Improvesheath diameterVSAvoidsheath mechanical strength

Core Design Contradiction:

Volume of moving objectVSStrength

Solution Approach 1:

The sheath is segmented into multiple portions with different wall thicknesses optimized for their specific functions. The delivery portion has thin walls for minimal profile while the proximal portion has thicker walls for withstanding mechanical stresses, eliminating the need for a single thick-walled design.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different mechanical properties are assigned to different portions of the sheath. The delivery portion is designed with thin walls and appropriate material properties for navigation, while the proximal portion has enhanced strength characteristics to withstand radial and tensile stresses during deployment and removal.

Inventive Principle:

Principle #3Local quality

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This approach enables a smaller stent delivery system profile with reduced friction and stress on the sheath, facilitating accurate placement and reliable deployment of stents, even in narrow vessels, while ensuring the sheath's integrity and ease of removal.

Implementation Method 1

imposing lengthwise strain on the sheath, to draw down the inner diameter of the delivery sheath to a diameter d4 which is less than d3

Methodology Applied

Scientific EffectCold drawing: Cold-forming

Data Source

PatentEP2962668B1Method of loading a stent into a sheath

Publication Date: 2019.11.06 ANGIOMED GMBH & CO MEDIZINTECHNIK KG

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Figure 1A
Figure 2A

AI summary

A method is described of loading a self-expanding stent (10) into a delivery sheath (12) that is part of a catheter for transluminal delivery of the stent to a stenting location in the body of a patient, with the stent being deployed at that location by removal from the stent of the constraint on its radial expansion that is provided up to that point by the sheath. The method involves radially compressing the stent; providing a loading sheath (14); translating the stent relative to the sheath, whereby the stent is accommodated within the lumen of the loading sheath; providing a delivery sheath; advancing the loading sheath, containing the stent, into the lumen of the delivery sheath; and deploying the stent into the lumen of the delivery sheath. A corresponding apparatus is also disclosed.