Cold-Drawn Stent Sheath Loading Method

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Solution Overview

Problem

Existing stent delivery systems face challenges in achieving a smaller passing profile while maintaining reliability and flexibility, particularly when using thin-walled sheaths for small endoprostheses, as they are prone to tearing or misplacement due to friction and stretching issues during deployment.

Innovation Solution

A method and apparatus for loading a self-expanding stent into a delivery sheath with a thin-walled polymeric material that can be cold-drawn to reduce the sheath's diameter, featuring a splitting mechanism with pull elements to facilitate smooth deployment and removal, reducing friction and stress on the sheath during stent expansion and retrieval.

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 flexibility and deliverability are improved, but the sheath becomes prone to tearing and stretching during deployment

Engineering Contradiction:

Improvepassing profile diameterVSAvoidsheath integrity during deployment

Core Design Contradiction:

Volume of moving objectVSReliability

Solution Approach 1:

The sheath is pre-strained during manufacturing to induce residual compressive stresses in the radial direction. This preliminary action creates a stress state that counteracts the tensile stresses encountered during deployment, preventing the sheath from stretching or tearing even when using thin-walled constructions for reduced profile.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The manufacturing process parameters are changed to include controlled radial expansion and straining of the sheath material. This transforms the sheath's stress state from its natural condition to one with beneficial residual compressive stresses, enabling thin-walled designs to maintain reliability during deployment.

Inventive Principle:

Principle #35Parameter changes

2Ease of operation

If the sheath is pulled proximally to release the stent, then the stent deployment is achieved, but tensile stresses stretch the sheath and reduce its diameter causing friction and potential tearing

Engineering Contradiction:

Improvestent release mechanismVSAvoidsheath resistance to stretching

Core Design Contradiction:

Ease of operationVSStrength

Solution Approach 1:

The sheath is pre-conditioned during manufacturing to establish residual compressive stresses that will counteract the tensile stresses applied during proximal pulling for stent release. This preliminary stress induction ensures the sheath maintains its diameter and structural integrity throughout the deployment operation.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The tensile stresses that would normally harm the sheath by stretching and reducing its diameter are converted into a beneficial effect. The pre-induced residual compressive stresses work against these tensile forces, transforming the deployment pulling action from a potentially damaging force into a controlled release mechanism that maintains sheath integrity.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Reliability

If friction forces are reduced to enable smooth sheath removal, then complete stent deployment is achieved, but the sheath may slip or misplace during loading

Engineering Contradiction:

Improvesmooth stent deploymentVSAvoidstent positioning accuracy

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The sheath is pre-strained during manufacturing to create residual compressive stresses. This preliminary action establishes optimal friction characteristics before stent loading, providing sufficient grip to prevent slippage during loading while allowing smooth removal after deployment when the stent expands against the vessel wall.

Inventive Principle:

Principle #10Preliminary action

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

The solution enables reliable and precise placement of small endoprostheses with reduced frictional forces, minimizing the risk of sheath tearing and misplacement, allowing for thinner sheaths and more flexible stent designs, while ensuring complete removal and controlled expansion.

Implementation Method 1

cold-drawn with the stent in situ, within the lumen of the sheath

Methodology Applied

Scientific EffectCold-drawing: Cold-forming

Data Source

PatentUS9687370B2Method of loading a stent into a sheath

Publication Date: 2017.06.27 CR BARD INC

AI summary

There is disclosed herein a method of loading a self-expanding stent (10) into a delivery sheath (12) that is by itself strong enough to preserve the stent in a radially compressed pre-deployment configuration, comprising the steps of: (i) compressing the stent (10) to a relatively small diameter; (ii) providing a loading sheath (18) with an inner diameter d1; (iii) with the stent (10) exhibiting an outside diameter of d2, where d2<d1, providing relative translational movement between the stent (10) and the loading sheath (18), whereby the stent is accommodated within the lumen of the loading sheath (18); (iv) advancing the loading sheath (18), containing the stent (10), into the lumen (16) of the delivery sheath (12); and {v} deploying the stent into the lumen (16) of the delivery sheath (12), by withdrawing the loading sheath (18) while restraining the stent (10) from axial movement out of the lumen (16) of the delivery sheath (12).