Ultra-Fine Stainless Steel Coiltube for Vascular Stent Delivery Systems

Product Overview

The Ultra-Fine Stainless Steel Coiltube is a precision-engineered seamless tubing solution specifically designed for vascular stent delivery systems within the interventional cardiology and peripheral vascular intervention (PVI) domains. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., this coiltube product represents the pinnacle of ultra-fine medical-grade stainless steel tubing technology, combining exceptional mechanical performance with complete MRI (Magnetic Resonance Imaging) compatibility.

Vascular stent delivery systems demand tubing that can withstand extreme push forces, compression loads, and torsional stresses during catheterization procedures while maintaining precise dimensional tolerances at the micro-scale. This coiltube product is engineered to serve as the structural backbone of stent delivery catheters, balloon-expandable stent carriers, and self-expanding stent sheaths, where the tubing must exhibit superior fatigue resistance, elastic recovery, and biocompatibility under repeated deployment cycles.

The integration of non-magnetic verification ensures that the coiltube does not interfere with MRI-guided interventional procedures, making it suitable for hybrid operating rooms where real-time magnetic resonance imaging is utilized for procedural navigation and post-deployment assessment.

Material & Properties

316LVM Stainless Steel

316LVM (Low Vanadium Medical-grade Stainless Steel) is a proprietary austenitic alloy formulation specifically optimized for medical device applications. It is an enhanced variant of the standard ASTM F138 316LVM specification, characterized by the following compositional and mechanical attributes:

Chemical Composition: 17.0–19.0% Cr, 12.0–14.0% Ni, 2.0–3.0% Mo, <0.03% C, with trace vanadium and nitrogen additions to enhance yield strength and fatigue performance
Yield Strength: 310–450 MPa (annealed condition), up to 700+ MPa (work-hardened)
Ultimate Tensile Strength: 550–700 MPa (annealed), 800–1100 MPa (cold-worked)
Non-magnetic Character: <1.0 emu/g (verified per ASTM F2613); austenitic crystal structure ensures complete non-magnetic behavior across all processing conditions
Corrosion Resistance: Superior resistance to pitting and crevice corrosion in physiological environments (0.9% NaCl, blood plasma)
Biocompatibility: Compliant with ISO 10993-1, 10993-5, and 10993-10 biological evaluation standards

L605 Stainless Steel

L605 (ASTM F138 equivalent) is a nickel-chromium-iron austenitic alloy renowned for its exceptional strength-to-weight ratio and outstanding fatigue resistance. Key properties include:

Chemical Composition: 24.0–26.0% Ni, 5.5–7.0% Cr, <0.06% C, with trace Mo and Si
Yield Strength: 400–600 MPa (annealed), 900+ MPa (work-hardened)
Ultimate Tensile Strength: 700–900 MPa (annealed), 1200–1400 MPa (cold-worked)
Non-magnetic Character: <1.0 emu/g; fully austenitic microstructure confirmed via metallographic examination
Thermal Stability: Retains mechanical properties at elevated temperatures (up to 650°C), advantageous during sterilization processes
Work-Hardening Rate: Significantly higher than 316LVM, providing enhanced fatigue life in cyclic loading applications

Specifications

Parameter	Specification	Testing Standard
Material Grade	316LVM (ASTM F138) / L605 (ASTM F138)	ASTM F138
Tube Form	Seamless Coiltube (盘管)	—
Outer Diameter (OD)	0.10 mm – 3.00 mm	ASTM A213
Wall Thickness (WT)	0.015 mm – 0.500 mm	ASTM A213
OD Tolerance	±0.005 mm (±0.0002 in)	ISO 11286
WT Tolerance	±0.003 mm (±0.0001 in)	ISO 11286
Surface Finish	Electrolytic Polishing (EP); Ra ≤ 0.10 μm	ASTM B918
Magnetic Susceptibility	< 1.0 emu/g (Non-magnetic verified)	ASTM F2613
Coil Winding	Continuous coil; minimum bend radius ≥ 5× OD	ISO 11286
Deliverable Length	Custom lengths; standard coils up to 50 m	—
Surface Passivation	Acid pickling + passivation (nitric acid or citric acid)	ASTM A967
Residual Stress	Stress-relieved post-forming; verified by XRD or magnetic Barkhausen noise (MBN)	ASTM A314
Sterilizability	Autoclave (134°C), EO, Gamma irradiation (25 kGy)	ISO 11135 / ISO 11137
Shelf Life (packaged)	≥ 5 years (desiccated, sealed packaging)	ISO 15883

Manufacturing Process

The production of ultra-fine coiltube for vascular stent delivery systems involves a multi-stage, tightly controlled manufacturing sequence designed to achieve extreme dimensional precision, surface integrity, and mechanical consistency:

Alloy Melting and Casting

316LVM or L605 alloy is melted under vacuum induction or argon oxygen decarburization (AOD) conditions to achieve ultra-low carbon and sulfur content. Billet ingots are cast and homogenized to eliminate segregation and ensure uniform microstructure.
Piercing and Hot Rolling

The ingot is heated to forging temperature and pierced to produce a seamless tube blank. Hot rolling reduces the outer diameter and wall thickness to near-final dimensions while maintaining the austenitic crystal structure.
Intermediate Annealing

Periodic solution annealing (1050–1150°C for 316LVM; 1100–1200°C for L605) in protective atmosphere or vacuum is performed between cold-work passes to restore ductility and prevent work-hardening induced cracking.
Multi-Pass Cold Drawing

The tube undergoes sequential cold-drawing through precision tungsten carbide or ceramic dies to achieve the target ultra-fine outer diameter and wall thickness. Each drawing pass is optimized for strain rate, die angle, and lubrication to minimize surface defects and maintain roundness within ±0.005 mm tolerance.
Coil Winding

The drawn tube is wound onto precision coils with controlled tension to prevent kinking, ovalization, or residual stress introduction. The minimum bend radius is maintained at ≥5× the outer diameter to preserve mechanical properties.
Final Solution Annealing

A final annealing cycle (1050–1150°C, 1–3 hours, followed by controlled cooling) is performed to relieve all cold-work-induced residual stresses, restore full austenitic structure, and achieve the target non-magnetic state.
Surface Pickling and Passivation

The coil is subjected to acid pickling (dilute nitric/hydrofluoric acid or citric acid) to remove oxide scale and surface contaminants. Subsequent passivation treatment (ASTM A967) forms a stable chromium oxide layer, enhancing corrosion resistance.
Electrolytic Polishing (EP)

Electrolytic polishing is performed in a phosphoric acid-based electrolyte at controlled temperature (40–60°C) and current density (20–40 A/dm²). This process simultaneously removes surface micro-roughness, eliminates embedded contaminants, and produces a mirror-like finish with Ra ≤ 0.10 μm. The EP process also removes any free iron from the surface, further enhancing corrosion resistance and ensuring non-magnetic surface integrity.
Non-Magnetic Verification

Each production lot undergoes rigorous magnetic susceptibility testing per ASTM F2613. Samples are measured using a vibrating sample magnetometer (VSM) or Faraday balance. Results must confirm magnetic susceptibility <1.0 emu/g. Metallographic examination confirms 100% austenitic microstructure with no ferrite or martensite phases.
Dimensional and Mechanical Testing

Comprehensive testing includes optical microscopy for OD/WT measurement (±0.001 mm resolution), hydrostatic pressure testing, tensile testing per ASTM E8/E8M, and fatigue testing per ASTM F2516. Surface roughness is verified via white light interferometry or stylus profilometry.
Biocompatibility Evaluation

Biological evaluation per ISO 10993 series: cytotoxicity (ISO 10993-5), sensitization (ISO 10993-10), irritation (ISO 10993-23), and hemocompatibility (ISO 10993-4) testing confirm suitability for prolonged blood contact in vascular applications.
Packaging and Traceability

Finished coiltube is packaged in desiccated, sealed HDPE or aluminum composite bags with full traceability documentation including heat number, lot number, material certificate (EN 10204 Type 3.1), and all test reports.

Applications

Vascular Stent Delivery Systems

This coiltube product is specifically engineered for the following interventional applications:

Stent Delivery Catheters: Serves as the outer sheath or inner pusher tube in balloon-expandable stent (BES) and self-expanding stent (SES) delivery systems. The ultra-fine wall thickness enables minimal profile designs (<0.5 mm OD) for navigating tortuous vasculature and accessing distal lesions.
Self-Expanding Stent Carriers: Functions as the compression sleeve that holds the stent in its delivery configuration. The high yield strength and elastic recovery of 316LVM/L605 ensure reliable stent deployment without carrier tube deformation.
Guidewire Lumen Tubes: Provides the central lumen through which the guidewire is advanced during stent placement, requiring extreme precision in bore diameter and surface smoothness to minimize guidewire friction.
Balloon Catheter Bodies: Used in angioplasty balloon catheters where the tubing must withstand high internal pressures (up to 20 atm / 300 psi) during balloon inflation without permanent deformation.
Peripheral Vascular Intervention (PVI) Devices: Applied in lower extremity, renal artery, and carotid artery stent delivery systems where MRI compatibility is critical for intra-procedural imaging guidance.
Hybrid OR Applications: The verified non-magnetic property (<1.0 emu/g) makes this coiltube suitable for procedures performed in MRI-compatible hybrid operating rooms, enabling real-time soft-tissue imaging without device-induced artifacts or safety hazards.

Additional Interventional Applications

Coronary intervention devices (stent grafts, drug-eluting stent delivery systems)
Peripheral balloon catheters for angioplasty
Endovascular aneurysm repair (EVAR) delivery sheaths
Neurovascular intervention catheters

Quality Certifications and Compliance

The ultra-fine coiltube for vascular stent delivery systems is manufactured and certified under the following quality frameworks and regulatory standards:

Standard / Certification	Description
ISO 13485:2016	Quality Management Systems for Medical Devices — Full compliance
ISO 9001:2015	General Quality Management System certification
ISO 14001:2015	Environmental Management System certification
ISO 10993 Series	Biological evaluation of medical devices (1, 4, 5, 10, 23)
ASTM F138	Standard Specification for 316LVM and L605 seamless tube for medical devices
ASTM F2613	Non-magnetic verification per standard test methods
ASTM B918	Electrolytic polishing of stainless steel — Process specification
ASTM A967	Acid cleaning and passivation of stainless steel parts
EN 10204 Type 3.1	Inspection certificate with test reports for each lot
CE Marking (MDR 2017/745)	EU Medical Device Regulation compliance (for finished device components)