Nickel-Titanium Stent Surface Fatigue Resistance via HIP Transition Metal Alloying
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Solution Overview
Problem
Nickel-titanium alloy stents face durability issues due to fatigue failure caused by surface flaws and pulsatile loading, with existing electropolishing methods not effectively eliminating all surface flaws, leading to compromised structural integrity.
Innovation Solution
A surface structure for nickel-titanium components featuring a heat-treated layer with transition metals like Ta, Nb, Mo, V, Mn, Fe, Cr, Co, Ni, Cu, or Si, creating a rough outer surface with an average roughness of 0.1 to 1000 microns, which enhances fatigue resistance and bioadhesion while allowing for drug eluting capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If electropolishing is applied to nickel-titanium alloy stents to eliminate surface flaws, then fatigue life is improved, but surface flaws cannot be completely eliminated and structural integrity remains compromised
Solution Approach 1:
The patent applies hot isostatic pressing (HIP) treatment at elevated temperatures (900-1100°C) and pressures (3-10 ksi) to fundamentally alter the surface characteristics of nickel-titanium alloy stents. This thermal and pressure parameter change enables the closure of surface cracks and flaws that electropolishing cannot eliminate, thereby improving fatigue life while achieving complete surface defect remediation
Solution Approach 2:
The patent creates a composite surface structure where the base nickel-titanium alloy is combined with a heat-affected surface layer formed through HIP treatment. This composite structure features a modified surface zone with closed cracks and refined microstructure, while the bulk material retains its original properties, achieving both fatigue resistance and structural integrity
2Reliability
If smooth surfaces are maintained to improve fatigue resistance, then crack propagation is reduced, but bioadhesion and drug delivery capabilities are compromised
Solution Approach 1:
The patent divides the stent surface into two distinct functional zones: a bulk material zone with smooth characteristics for fatigue resistance, and a surface zone with controlled roughness (Ra 0.2-2.0 μm) for enhanced bioadhesion and drug delivery. This segmentation allows each zone to independently fulfill its specific function without compromising the other
Solution Approach 2:
The patent applies local quality modification by creating a surface layer with specific roughness characteristics only at the outer surface, while the bulk material and internal structure maintain smooth characteristics for fatigue resistance. The HIP treatment selectively modifies surface properties without altering the overall structural integrity, enabling simultaneous optimization of both fatigue resistance and biological functionality
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 surface structure significantly improves fatigue life and bioadhesion without compromising mechanical performance, enabling the stent to withstand physiological loads and potentially enhance drug delivery.
Implementation Method 1
a heat treated layer disposed on at least a portion of a surface of the component. The surface comprises a nickel-titanium alloy and the heat treated layer comprises a transition metal selected from the group consisting of Ta, Nb, Mo, V, Mn, Fe, Cr, Co, Ni, Cu, and Si
Implementation Method 2
a rough outer surface of the fatigue-resistant portion, where the rough outer surface has an average roughness in the range of from about 0.1 micron to about 1000 microns
Data Source
AI summary
A method of forming a surface structure of a component of a medical devices includes forming a fatigue-resistant portion, which entails forming a first layer comprising a transition metal selected from the group consisting of Ta, Nb, Mo, V, Mn, Fe, Cr, Co, Ni, Cu, and Si on at least a portion of a surface of the component, where the surface comprises a nickel-titanium alloy, and alloying the transition metal of the first layer with the nickel-titanium alloy of the surface. The method further includes forming a rough outer surface of the fatigue-resistant portion, where the rough outer surface is adapted for adhesion of a material thereto.