MP35N Wire Electropolishing for Implantable Lead Fatigue
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Solution Overview
Problem
Existing methods for removing surface imperfections such as chevrons from MP35N wires used in implantable medical leads are either not feasible for small diameters or are slow and difficult to apply on long spools of wire.
Innovation Solution
Electropolishing MP35N wires (solid or clad) before forming them into implantable leads to remove a thin layer from the outer surface, thereby eliminating chevrons and other imperfections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If mechanical shaving is used to remove surface imperfections, then chevrons are removed from wire surface, but the method is not feasible for small diameter wires used in implantable leads
Solution Approach 1:
The patent replaces mechanical shaving with electropolishing, an electrochemical process. The wire is made the anode in an electrolytic cell, and surface imperfections are removed through controlled electrochemical dissolution rather than mechanical contact, making the process feasible for small diameter wires while effectively removing chevrons and other surface defects
Solution Approach 2:
The patent changes the fundamental mechanism from mechanical to electrochemical by adjusting process parameters such as electrolyte composition, temperature, voltage, and current density. This parameter transformation enables effective surface imperfection removal on wires with diameters as small as 0.00762 cm, which are too small for mechanical shaving
2Manufacturing precision
If plasma or sputtering is used to remove surface layer, then chevrons are removed, but the methods are slow and difficult to apply on long spools of wire
Solution Approach 1:
The electropolishing process allows continuous processing of long spools of wire through an electrolytic bath. The wire can be fed continuously through the process, with the electrochemical action occurring along the entire length of wire in the bath, enabling high productivity while effectively removing surface imperfections from extended lengths of wire
Solution Approach 2:
The patent uses an electrolytic solution (liquid medium) to facilitate the removal process. The electrolyte flows around and through the wire, enabling continuous electrochemical processing without the need for vacuum chambers or complex plasma generation equipment, thereby increasing processing speed and simplicity for long spools
3Manufacturing precision
If wire drawing is used to produce final diameter wire, then wire is formed to specification, but chevrons are created on wire surface
Solution Approach 1:
The electropolishing process is applied after wire drawing to remove the chevrons created during drawing. This preliminary surface treatment eliminates the harmful surface imperfections before the wire is formed into the final lead product, ensuring that the wire has both the correct dimensions and a smooth surface free of stress concentration points
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
Electropolishing significantly reduces or eliminates surface imperfections, enhancing the fatigue life of implantable leads by making them more resistant to stress cycles without the need for upstream process changes.
Implementation Method 1
electropolishing MP35N wires (solid or clad) before forming them into implantable leads to remove a thin layer from the outer surface, thereby eliminating chevrons and other imperfections
Data Source
Figure 1
Figure 2~2A
Figure 2B~3A
AI summary
MP35N (35%Co, 35%Ni, 20%Cr, 10% Mo) wires (solid and clad) are widely used for leads in cardiac rhythm management (CRM) and neurological electrical stimulation devices. Over the typical lifetime of a CRM device, a lead wire is subjected to stress cycling imposed by the heartbeat and is expected to survive 300 million stress cycles, or more. Premature fatigue fracture of a lead is sometimes caused by surface imperfections in the wire that has been coiled into the lead. The imperfections can result in concentration of stresses at a specific location on the wire surface. A vexing type of imperfection is a tiny surface fissure that is commonly referred to as a chevron. Wire drawing processes that are commonly used to form wires for manufacturing an implantable lead inherently produce a distribution of tiny chevrons on the wire surface. According to the present disclosure, removing chevrons and other surface imperfections using an electropolishing process helps reduce or eliminate premature fatigue failure initiated by such surface imperfection.