Catheters & Medical Fluid Connectors Testing Guide

Common Medical Fluid Connectors that Require Mechanical Testing

Luer Fittings

Luer fittings or luer-lock fittings are intended to connect two medical devices in a liquid-leak-proof and mechanically secure manner. Applications for these male and female tapered, interlocking fittings include but are not limited to, syringes, needles, stopcocks, IV sets, and diagnostic and therapeutic catheters. Mechanical testing of luer fittings is performed to ensure they do not misconnect with other fluid connectors, and they safely and securely connect with their mating half.

Catheters and Tubing

Catheters and tubing are medical devices designed to be inserted into the body to treat diseases or perform surgical procedures. They serve various functions such as draining fluids, administering drugs, and gaining access to surgical sites. The design and mechanical properties of catheters vary based on their intended application, ranging from cardiovascular and urological to neurovascular uses. Mechanical testing is crucial to ensure their safety, durability, and efficacy, particularly because any failure could lead to significant medical complications.

Syringes

Syringes or hypodermic needles are intended for use to inject the drug substances into the bloodstream. Mechanical testing of hypodermic needle quality testing provides information on gauging, leakage, and needle insertion/penetration to ensure the end product is safe and efficacious.

Common Medical Fluid Connector Test Types & Standards:

Axial-Torsion Testing

ISO 80369-7:2021 is the current test standard to test small-bore connectors intended to be used for connections in intravascular applications or hypodermic connections in hypodermic applications of medical devices and accessories.  The standard is categorized into annexes, eight of which are applicable for mechanical testing performed to evaluate the performance requirements of the medical connectors. These annexes include:

• ISO 80369 – Annex B Small-Bore Connectors for Liquids and Gases in Healthcare Applications
  • The connector under test is assembled to an appropriate reference connector. The medium, as specified in the relevant application part of this series, is introduced into the connection and pressurized to the specified pressure.
• ISO 80369 – Annex C Small-Bore Connectors for Liquids and Gases in Healthcare Applications
  • A connector is assembled to a reference connector. Water is introduced into the connection and pressurized for the hold period.
• ISO 80369 – Annex D Small-Bore Connectors for Liquids and Gases in Healthcare Applications
  • Air leakage during aspiration in a connector assembly is tested by measuring the change in subatmospheric pressure over time after the vacuum pressure is applied to the bore of the connector.
• ISO 80369 – Annex E Small-Bore Connectors for Liquids and Gases in Healthcare Applications
  • A connector is securely assembled to an appropriate reference connector and the connection is evaluated for stress cracking by demonstrating that it properly seals utilizing the leak test.
• ISO 80369 – Annex  F Small-Bore Connectors for Liquids and Gases in Healthcare Applications
  • The security of the connection to an axial pull is determined by applying an axial separation force between the assembled connector under test and the appropriate reference connector. The connection is expected to be maintained.
• ISO 80369 – Annex G Small-Bore Connectors for Liquids and Gases in Healthcare Applications
  • The security of connection between male and female locking connectors is determined by inspecting the connection after applying specified unscrewing torque. The connection is expected to be maintained.
• ISO 80369 – Annex H Small-Bore Connectors for Liquids and Gases in Healthcare Applications
  • The resistance to overriding of male and female locking connectors is determined by observing the thread or lugs of the connector under test after applying the specified torque.
• ISO 80369 – Annex I Small-Bore Connectors for Liquids and Gases in Healthcare Applications
  • The ability to disconnect the connection using a twist of male and female connectors is determined by inspecting the connection after applying the specified torque. The connection is expected to disconnect.

Bend Testing

Bend testing provides information on the ability of catheters to bend in order to accommodate a predetermined clinically relevant radius or angle during access and delivery. Bending flexibility of a stent system may be a factor in its ability to track through the vascular anatomy, and may be a factor in vascular trauma along the delivery pathway distal to the guide catheter. Bending flexibility of a deployed stent may be one measure of its ability to flex with a vessel, or to conform to the natural curvature of a vessel. 

Bend test setup includes a universal testing machine equipped with a bend fixture where the test specimen is placed on two lower supports. The force is then applied through a loading nose. The results of bend testing provide information on a catheter’s flexural properties as well as kink resistance and rigidity.

• ASTM F2606 Standard Guide for Three-Point Bending of Balloon-Expandable Vascular Stents and Stent Systems
  • Three-point bend test method to measure the flexibility of balloon-expandable stents and stent systems
• ISO 10555-1:2013 Intravascular catheters — Sterile and single-use catheters — Part 1: General requirements
  • Requirements for intravascular catheters, supplied in the sterile condition and intended for single use, for any application
• ISO 25539‐1:2017 Cardiovascular implants – Endovascular devices – Part 1: Endovascular prostheses
  • Test method to evaluate the ability of the endovascular system to bend in order to accommodate the minimum radius or angle to be negotiated during access and delivery

Compression Testing

Radial loading, directed perpendicular to the longitudinal axis of a cylinder and applied to the outer cylindrical surface of the stent, is required to determine whether the vascular stent has adequate resistance to forces acting on it and maintain vessel patency. Depending on the type of device and the clinical concern, the resistance to these loads can be presented through multiple test outputs: radial strength, collapse pressure, or chronic outward force.

• ASTM F3067 Standard Guide for Radial Loading of Balloon-Expandable and Self-Expanding Vascular Stents
  • In vitro test methods for measuring the radial strength or collapse pressure of balloon-expandable vascular stents and chronic outward force of self-expanding vascular stents

Fatigue Testing

Fatigue tests, combined with stress/strain analysis and durability testing, simulates loads or motions that medical fluid connectors experience in the body. To avoid inducing device failure or vessel damage, balloons must withstand multiple inflations during clinical use. Fatigue test results provide an indication of device durability, longevity and reliability. Analysis from these results provide insights into lifespan, potential failure modes, and design improvements.

• • ASTM F2477 Test Methods for in-vitro Pulsatile Durability Testing of Vascular Stents
    • Test methods to evaluate the dynamic-fatigue mechanical behavior of balloon-expandable and self-expanding metallic vascular stents
  • ISO 10555-1:2013 Intravascular catheters — Sterile and single-use catheters — Part 1: General requirements
    • Requirements for intravascular catheters, supplied in the sterile condition and intended for single use, for any application
  • ISO 25539‐1:2017 Cardiovascular implants – Endovascular devices – Part 1: Endovascular prostheses
    • Test method to determine the maximum number of recommended balloon inflation cycles to the recommended inflation pressure including reliability parameters

Friction Testing

Friction testing is performed to assess the lubricity and durability of coatings applied to catheters. The most common test used for measuring surface coating friction is a pinch test, where catheters are pinched between two pads with a known normal/pinching force, while using a linear actuator to pull and push the catheter through the pads.  Cycling the catheter between the pads multiple times will result in increasing friction readings due to coating degradation.

• ISO 10555-1:2013 Intravascular catheters — Sterile and single-use catheters — Part 1: General requirements
  • Requirements for intravascular catheters, supplied in the sterile condition and intended for single use, for any application

In Vitro Testing

In vitro testing involves evaluating medical fluid connectors outside the human body, often in a controlled laboratory environment that simulates physiological conditions. This testing is crucial for understanding how devices like orthopedic implants, stents, or catheters will interact with biological tissues and fluids. It allows for thorough assessments of biocompatibility, functionality, and long-term performance.

• ASTM F2477 Test Methods for in-vitro Pulsatile Durability Testing of Vascular Stents
  • Test methods to evaluate the dynamic-fatigue mechanical behavior of balloon-expandable and self-expanding metallic vascular stents
• ASTM F3067 Standard Guide for Radial Loading of Balloon-Expandable and Self-Expanding Vascular Stents
  • In vitro test methods for measuring the radial strength or collapse pressure of balloon-expandable vascular stents and chronic outward force of self-expanding vascular stents
• ISO 25539-2:2020 Annex D Cardiovascular implants — Endovascular devices — Part 2: Vascular stents
  • In vitro test methods for the evaluation of stent systems (vascular stents and delivery systems)

Tensile Testing

Tensile testing is required to measure and report the characteristics of raw materials used in the making of a catheter as well as the mechanical properties of the end-product. In addition to the stress-strain curve generated by performing tension testing, tensile properties measured include:

• Ultimate Tensile Stress (UTS)
• Yield Strength
• Elongation
• Elastic Modulus
• Poisson’s Ratio

• • ISO 25539‐1:2017 Cardiovascular implants – Endovascular devices – Part 1: Endovascular prostheses
    • • Test method to determine the strength of the tubing used in the delivery system as appropriate to the material
  • ASTM F2516 – Nitinol Tension Testing
    • Test method to determine the strength, ductility and superelasticity under uniaxial tensile loading.

Torsion Testing

Torsion testing is performed to evaluate aspects of the long-term dimensional and structural integrity of medical fluid connectors. Torsion tests, set up to evaluate the ability of the fluid connector to provide sufficient rotation to the distal (leading) end to deliver the implant, may be conducted static only or both static and fatigue modes. Results for further analysis include the torque strength and the torsional bond strength.

• ISO 10555-1:2013 Intravascular catheters — Sterile and single-use catheters — Part 1: General requirements
  • Requirements for intravascular catheters, supplied in the sterile condition and intended for single use, for any application
• ISO 25539‐1:2017 Cardiovascular implants – Endovascular devices – Part 1: Endovascular prostheses
  • Test method to determine the torque required to break joints and/or materials in the appropriate delivery system components