The Luer connector is arguably one of the most important developments in the biomedical industry. Because it is reliable, simple to use, and economical to produce, the Luer connector has excelled in ensuring that providers all over the world can quickly and efficiently deliver treatment to patients. The recent introduction of ISO 80369 has presented new challenges for testing these connectors. This article reviews the requirements for testing to this standard and the need for equipment that can address both axial and torsional testing, as well as the complicated control methods required to perform the testing.

The Advent of the Luer Connector

While Luer connections are by far the most common in the marketplace, there has been a recent push for more specialized connectors for specific applications. (Credit: Instron)

There are two main types of Luer connection: the Luer slip and the Luer lock. The Luer slip was first created by Karl Schneider in the early 1900s and consists of a 6 percent taper fitting. The Luer lock, first developed in 1930 by the R&D team at Becton-Dickinson, utilizes a threaded connection for a more secure fit. The lock connection is further categorized into two distinct types; the standard one-piece and a two-piece rotating collar Luer lock. The Luer lock provides a more secure connection than the Luer slip and is most commonly used in situations when an injectable is kept under pressure.

In emergency situations, the need for reliable, simple, and standardized medical equipment becomes a matter of life and death. The critical need for an international standard medical connector first became apparent during an air show disaster in 1988. During the accident, which occurred at the U.S. Ramstein Air Base in Germany, miscommunication between U.S. military and German paramedics was intensified by the incompatibility of their IV catheters, which used two different types of connectors. The inability of their devices to work together slowed down treatment and ultimately led to increased casualties.

The Ramstein disaster compelled the global medical community to decisively act and move toward making the Luer connection the international standard. The larger biomedical device companies quickly began incorporating Luer connections into their devices. In the years to come, various international and national bodies would release guidelines requiring the use of the Luer design on all parenteral connections.

Testing Application-Specific Connectors

The modern-day result of this movement toward standardization is that all medical devices being released into the marketplace, whether they be vascular, enteral, respiratory, epidural, or intrathecal, must comply with ISO 80369, an international standard dictating the design requirements for Luer and application-specific connections. This standard replaces ISO 594, which was withdrawn in 2016. While Luer connections are by far the most common in the marketplace, there has been a recent push for more specialized connectors for specific applications; the purpose being to further alleviate the issue of wrongful connections. Enteral feeding connectors (ENFit®) and Neuraxial connectors (NRFit®) are both now utilizing non-Luer geometries after a significant push from within the healthcare community. These changes are intended to improve patient safety and simplify procedures for medical professionals. The testing procedures are the same as standard Luer connectors, simply requiring updated reference connectors.

The challenges of testing to ISO 80369 include the need for a testing machine with both axial and torsional capabilities. (Credit: Instron)

The challenges of testing to ISO 80369 include the need for a testing machine with both axial and torsional capabilities and software that can adequately perform the test and assess the results. Sourcing a single piece of equipment to meet these challenges is vital for companies to ensure that their products can be viable within the marketplace.

ISO 80369 Requirements

ISO 80369 outlines the mechanical tests required to properly assess a delivery device connection, and the standard also provides the performance and design requirements for specific applications. ISO 80369-20 assembles the common test methods for connectors used in all application types, and the annexes describe the testing procedure and utilize the performance requirements as referenced in the other sections. This testing includes the strength of the connection as well as the typical forces and torques required to disconnect the male and female components. The connection of interest, male or female, is matched with a reference connector, which is defined within the standard and requires precision machining to meet the specifications.

The strength of the connection is determined by applying either an axial or torsional force for a set hold period and visually evaluating whether or not the connection has failed. Failure can also be identified by an uncharacteristic drop in load or torque during the hold period. The connector’s resistance to override is also tested, which ensures that any over-torqueing will not lead to skipping of the threads or a loss of axial alignment. Aside from mechanical tests there are also evaluations of the connector’s ability to maintain constant medium (gas or liquid) pressure or withstand pressure changes. These tests require additional equipment such as pressure gauges and vacuum sources.

The mechanical testing annexes require an assembly procedure prior to testing, which consists of simultaneous axial and torsional motion. There are various ways to accomplish the assembly procedure using testing equipment. The most simplistic is an electromechanical torsion device that employs stackable deadweights and an accompanying pulley system to apply constant tensile or compressive loads. This setup does not allow for control of axial displacement or variable application of the load while under test. Such limitations prevent a user from performing all required annexes within the standard, because a separate axial-only machine would be necessary to perform the resistance to separation from axial load test (Annex H).

Biaxial Testing

The need for two machines reduces throughput and repeatability and increases testing complexity, which makes it more difficult for companies to evaluate connections. Fortunately, the functions of both machines can be combined into a single biaxial testing machine, which allows the user to have control of both axial and torsional motion, recording displacement, force, rotation, and torque. Biaxial testing machines can be either static electromechanical systems or dynamic systems. Static systems are most commonly used for this application due to their ease of use and extreme versatility. Many customers may use the same system to perform high force syringe flange breakage to ISO 11040-4 as well as low force connection disassembly testing. Dynamic systems are better suited to long-term fatigue testing and can be used to develop in-house durability tests for these connections.

Every piece of testing hardware requires associated software in order to create and run the required testing programs. Because users will interact extensively with the software, its interface needs to exhibit a balance of usability and functionality. For biaxial testing of Luer connectors, operators need to control two axes simultaneously as well as command various test parameters such as linear and angular speed, force, and torque hold criteria. For example, Annex H, the resistance to separation from an axial load, requires the assembly procedure followed by a hold at 35 N for 30 seconds. After this time, the connection is visually checked to ensure that it held.

Test systems require grips and fixtures appropriate for performing ISO 80369 testing. (Credit: Instron)

Intuitive software improves throughput and instills confidence in the test results. As an added improvement, some systems can also incorporate a camera to allow for frame-by-frame analysis of the test, making qualitative evaluation easier for the operator and lab manager.

Considerations also need to be made regarding the accuracy and resolution of the biaxial measurement devices. Depend-ing on the specific application, torque values can range between 0.018 Nm and 0.2 Nm, and force values can range from 20 N to 35 N. The device should be verifiable within the range of values being tested to, necessitating a low-capacity biaxial cell. In most cases, the accuracy of biaxial cells is lower than their uniaxial counterparts due to the effects of crosstalk. This is important to keep in mind when choosing an applicable biaxial cell.

Lastly, test systems require grips and fixtures appropriate for performing ISO 80369 testing. There are several basic options depending on the geometry of the connection being tested. An optimal grip should maintain constant contact with the Luer connector without deforming it in any way, which would invalidate the results. For smaller diameter connectors with circular cross sections, a three- or four-jaw chuck is recommended, whereas larger connectors with irregular geometries or attached to larger delivery devices like a syringe require manual side-acting grips with flat or vee profile faces. Most static and dynamic systems employ a modular design, making it easy for operators to quickly change fixtures and grips.

Choosing a Test System

The market for Luer connector devices and medical consumables as a whole is increasing, due to the substantial rise in geriatric care caused by an aging global population. Because of this surge in testing requirements, increasingly sophisticated and versatile test equipment is becoming the norm. Most standards, ISO 80369 included, will undergo changes over time, either to include new applications or to alter the test parameters: Choosing a system with an intuitive software interface enables customers to easily update their testing methods and remain in compliance with the changing standard.

When deciding on equipment for testing to ISO 80369, it is important to consider both the current and future requirements of the lab. An adaptable test system allows manufacturers to remain competitive in a crowded marketplace even as products and standards evolve over time. The Luer connection is not going away anytime soon, however, and developing the lab capabilities and knowledge base to properly test them in accordance with ISO 80369 is essential to the continued creation of reliable, easy-to-use, and economical delivery systems.

This article was written by Landon Goldfarb, Applications Engineer for Instron, Norwood, MA. For more information, visit here.