316L EP Capillary Coiltube for IVD Analyzer Reagent Tubing
Product Overview
The 316L EP Capillary Coiltube is a precision-engineered stainless steel micro-tubing solution specifically designed for In Vitro Diagnostics (IVD) analyzer reagent delivery systems. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., this product addresses the critical requirements of modern laboratory automation platforms where micro-liter (μL-level) fluid handling demands uncompromising purity, minimal dead volume, and rigorous cross-contamination prevention.
As the backbone of reagent transport in automated clinical chemistry analyzers, immunoassay systems, and molecular diagnostics platforms, this capillary coil tube ensures reliable, repeatable fluid delivery with nanoliter-scale precision. The product is engineered to meet the stringent biocompatibility and surface chemistry requirements mandated by regulatory bodies worldwide.
Material & Properties
Base Material: 316L Stainless Steel
The tubing is fabricated from AISI 316L (UNS S31603) austenitic stainless steel, selected for its superior corrosion resistance, low carbon content, and excellent biocompatibility. The "L" designation denotes a low-carbon variant (≤0.03% C), which minimizes intergranular corrosion during welding and heat treatment processes.
Surface Treatment: Electropolishing (EP)
The internal and external surfaces undergo precision Electropolishing (EP), a controlled electrochemical passivation process that removes the top 2–5 μm of metal, resulting in:
- Surface roughness (Ra): ≤ 0.16 μm (6 μin), enabling ultra-low fluidic resistance
- Low adsorption surface: Reduced protein adsorption and biofilm formation, critical for maintaining reagent integrity
- Enhanced passive layer: Thickened chromium oxide film (Cr₂O₃) providing exceptional resistance to chloride pitting and general corrosion
- Smooth bore transition: Elimination of micro-crevices that could harbor residues and promote cross-contamination
Key Material Properties
- Corrosion resistance: Excellent resistance to dilute acids, alkalis, and chloride-containing media
- Mechanical properties: High tensile strength (≥ 515 MPa) with adequate ductility for coil forming
- Biocompatibility: Compliant with ISO 10993-1 biological evaluation requirements
- Thermal stability: Suitable for autoclave sterilization (121°C / 134°C) and dry heat sterilization
Specifications
| Parameter | Specification | Standard / Method |
|---|---|---|
| Material Grade | AISI 316L (UNS S31603) | ASTM A269 / ASTM A270 |
| Surface Finish (Internal) | Electropolished, Ra ≤ 0.16 μm | ASTM A478 |
| Surface Finish (External) | Electropolished / Mirror polish, Ra ≤ 0.25 μm | ASTM A478 |
| Outer Diameter (OD) | 0.5 mm – 3.0 mm (customizable) | ±0.02 mm tolerance |
| Wall Thickness | 0.1 mm – 0.5 mm (customizable) | ±0.01 mm tolerance |
| Inner Diameter (ID) | 0.1 mm – 2.8 mm | Concentricity ≤ 0.01 mm |
| Coil Diameter | 5 mm – 50 mm | Uniform winding, no kinking |
| Coil Length | 0.5 m – 100 m (continuous coil) | Spooled on protective reel |
| Dead Volume | Minimized to < 1 μL per 10 cm of tubing (for 0.5 mm OD) | Geometric calculation + validated |
| Flushing Efficiency | > 99.9% residual clearance after 3× volume flush | UV absorbance / conductivity method |
| Pressure Rating | Up to 10 bar (continuous), 15 bar (burst) | ISO 14041 |
| Operating Temperature | -40°C to +180°C | — |
| Residual Metal Contamination | Fe < 5 ppb; Cr < 1 ppb; Ni < 0.5 ppb (ultrapure water leach) | ICP-MS analysis |
| End Finish | Flat-cut, burr-free, or custom-fitted connectors | Visual + optical inspection |
Manufacturing Process
Step 1: Raw Material Selection & Certification
Virgin 316L stainless steel wire rod is sourced from certified mills with full material traceability documentation (Mill Test Reports per ASTM A999). Chemical composition is verified via Spectroscopy (OES) to ensure compliance with ASTM A240/A276 requirements.
Step 2: Cold Drawing & Sizing
The wire is cold-drawn through precision tungsten carbide dies to achieve the target OD, wall thickness, and ID with tight dimensional tolerances (±0.01 mm). This process also imparts beneficial work-hardening and grain refinement.
Step 3: Annealing & Stress Relief
Intermediate annealing cycles at 1050°C in a controlled atmosphere (argon or vacuum) relieve residual stresses from cold drawing, restore full ductility for coiling, and maintain the austenitic microstructure without carbide precipitation.
Step 4: Precision Coiling (Spooling)
The annealed tubing is coiled onto precision guides using CNC-controlled spooling machines to produce uniform coil diameters with consistent inter-turn spacing. The process ensures:
- No kinking, flattening, or ovalization of the bore
- Consistent coil pitch for predictable fluidic behavior
- Minimal mechanical deformation of the bore geometry
Step 5: Electropolishing (EP)
The coiled tubing undergoes batch electropolishing in a temperature-controlled electrolyte bath (phosphoric acid / sulfuric acid / water, 70:5:25 ratio). Process parameters include:
- Current density: 150–250 A/dm²
- Bath temperature: 55–65°C
- Processing time: 15–30 minutes
- Material removal: 2–5 μm uniformly from all surfaces
This step creates the ultra-smooth, corrosion-resistant passive surface essential for low-adsorption performance.
Step 6: Cleaning & Degreasing
Post-EP tubing undergoes multi-stage ultrasonic cleaning in reagent-grade solvents, followed by rinsing with Milli-Q (18.2 MΩ·cm) ultrapure water. Final drying is performed under laminar flow conditions to prevent particulate contamination.
Step 7: Quality Inspection & Testing
Each production lot undergoes comprehensive verification:
- Dimensional inspection: Optical comparator and laser bore profiler for OD, ID, and wall thickness
- Surface roughness: Confocal microscopy / profilometry for Ra verification
- Leach testing: ICP-MS analysis of metal ion elution in ultrapure water
- Pressure testing: Hydrostatic burst test per ISO 14041
- Visual inspection: 10×–40× magnification for surface defects, pitting, or scratches
- Dead volume measurement: Gravimetric or dye-tracer method
Step 8: Packaging & Traceability
Finished coils are packaged in chemically inert PE bags or vacuum-sealed containers with desiccant. Each reel is labeled with lot number, material certificate reference, and dimensional specifications for full traceability.
Applications
Primary Application: IVD Analyzer Reagent Tubing
This product is purpose-engineered for reagent and sample fluid transport in automated clinical diagnostic instruments, including:
- Automated Clinical Chemistry Analyzers: Reagent delivery channels for enzymatic assays, immunoassays, and biochemistry panels
- Immunoassay Systems (ELISA / Chemiluminescence): Precision micro-fluidic transfer of antibodies, conjugates, and substrates
- Molecular Diagnostics Platforms: Reagent transport for PCR-based nucleic acid detection systems
- Coagulation Analyzers: Sample and reagent routing in clotting time determination
- Point-of-Care (POC) Devices: Micro-fluidic channels in handheld diagnostic cartridges
Critical Design Considerations Addressed
Cross-Contamination Prevention: The electropolished 316L surface exhibits minimal protein adsorption (≤ 0.5 ng/cm² for BSA) and achieves >99.9% flushing efficiency, eliminating carryover between sequential samples — a critical requirement for high-throughput diagnostic laboratories processing hundreds of samples per hour.
Dead Volume Minimization: The narrow bore geometry (as small as 0.1 mm ID) reduces the internal fluid volume to nanoliter levels, preserving precious reagents and ensuring accurate micro-volume delivery without dilution errors.
Micro-liter (μL) Fluid Handling: Engineered for precise delivery volumes in the range of 0.1 μL to 50 μL, meeting the requirements of modern miniaturized IVD platforms.
Additional Applications
- Pharmaceutical micro-fluidic systems and drug delivery devices
- Laboratory automation and liquid handling robots
- Bioreactor sampling lines and process analytical technology (PAT)
- Food safety rapid detection systems
Quality Certifications & Compliance
The 316L EP Capillary Coiltube is manufactured under a certified quality management system and complies with the following standards and regulatory requirements:
| Certification / Standard | Scope of Compliance |
|---|---|
| ISO 9001:2015 | Quality Management System certification for manufacturing processes |
| ISO 13485:2016 | Medical device quality management system — design, production, installation, and servicing |
| ISO 10993-1:2018 | Biological evaluation of medical devices — general framework for risk management and testing |
| ISO 10993-5 / -10 | Chemical characterization and biological evaluation (cytotoxicity, sensitization, irritation) |
| ISO 14041 | Hydrostatic testing of metal tubing for fluid service |
| ASTM A269 / A270 | Seamless and welded austenitic stainless steel tubing — chemical and mechanical requirements |
| ASTM A478 | Electropolished austenitic stainless steel tubing and pipe |
| USP <661> | Compliance with metal tubing and pipe for pharmaceutical applications |
| RoHS 2.0 (EU 2015/863) | Restriction of hazardous substances — lead, cadmium, mercury, hexavalent chromium |
| REACH (EU 1907/2006) | Registration, Evaluation, Authorisation and Restriction of Chemicals |
| CE Marking (MDR 2017/745) | Conformity with European Medical Device Regulation for Class I/IIa devices |
| 21 CFR Part 820 | US FDA Quality System Regulation for medical device manufacturing |
Unique Selling Points
- Ultra-Low Adsorption Surface: Electropolished 316L achieves surface energy and roughness levels that minimize non-specific protein adsorption, reducing assay interference and carryover in multiplexed IVD applications.
- Nanoliter Dead Volume: Micro-bore geometry minimizes residual fluid volume, enabling accurate delivery of expensive reagents and preserving sample integrity in low-volume clinical specimens (e.g., neonatal blood, cerebrospinal fluid).
- Cross-Contamination Prevention: Superior flushing efficiency (>99.9%) ensures reliable sample-to-sample clearance, critical for automated platforms processing diverse patient samples at high throughput.
- Full Traceability: Each production lot is accompanied by comprehensive documentation including Mill Test Reports, EP process parameters, surface roughness data, and leach test results.
- Customization Capability: Available in a wide range of OD, wall thickness, coil diameter, and length configurations to suit specific instrument OEM requirements.
- Regulatory Readiness: ISO 13485 certified manufacturing with complete technical documentation supporting IVD device regulatory submissions worldwide.
Conclusion
The 316L EP Capillary Coiltube represents a state-of-the-art solution for IVD analyzer reagent tubing, combining precision metallurgy, advanced surface engineering, and rigorous quality control to deliver the reliability, purity, and micro-fluidic performance demanded by next-generation clinical diagnostic platforms. Wenzhou Jixing Metal Materials Co., Ltd. provides OEM partners with a fully compliant, customizable, and performance-verified tubing solution that meets the most stringent requirements of the global in vitro diagnostics industry.