Testing Requirements of Syringes and Needle-Based Injection Systems

Interview conducted by Stuart MilneJul 12 2017

Elayne Gordonov, Market Manager - Global Bio Market at Instron, talks to AZoM about physical testing requirements of syringes, Luer connections, and needle-based injection systems in-line with ISO 80369 standards for testing medical device connections used in different clinical applications.

Could you please provide a brief overview to physical testing requirements of syringes, Luer connections, and needle-based injection systems?

Physical testing of syringes, Luer locks, and auto-injectors encompass tension, compression, and torsional tests. Generally, hypodermic syringe testing consists of determining a break-away force to push the syringe piston, and glide force to measure the frictional force required to eject the syringe’s contents. Luer lock and small bore connection testing requires several different test methods. The most common tests determine assembly force and torque of connectors, override torque, and assembly and unscrewing forces and torque. Auto-injector testing is generally the most complex and may require quantifying the dial torque when determining dosage quantity, cap removal force, activation force, glide force, and measurement of syringe ejection mass and total time of ejection. Overall, testing of syringes, Luer connectors, and auto-injectors continues to increase and become more standardized.  

You mention that there is an increasing demand for testing syringes, Luer connections, and needle based injection systems; what is driving this demand?

There are a number of macro factors that are leading to an increased use of hypodermic syringes and auto-injectors.  These factors include an aging population and a rise in type 2 diabetes in many countries including the United States, China, and India. In addition, requirements for testing Luer fittings and small bore connectors has recently changed, driven by a tragic accident when a nurse misconnected a patient's feeding tube to an intravenous line, leading to the patient's death. For decades, Luer slips (push design) and Luer locks (screw-in design) have had a universal design for manufacturers to maintain low cost and simplicity. After this accident, a team from the FDA, ISO, and AAMI collaborated to form new standardized connector designs and testing procedures within the ISO 80369 standard.

Could you summarize some of the changes in the new ISO 80369 standard?

The new ISO 80369 standard is actually not one standard, rather a collection or series of standards aimed at various medical device connections used in different clinical applications. For example, ISO 80369-7 is geared towards specifications of connectors used for intravascular or hypodermic applications. ISO 80369-20 contains all common test methods which includes mechanical test methods, including resistance to separation from axial load, resistance to separation from unscrewing, resistance to overriding, and disconnection by unscrewing. Since not all medical device connectors can be evaluated using all of the methods stated in ISO 80369-20, the test methods that are applicable to each type of connector are specified in the respective part. In general, the new standards under ISO 80369 were created to improve the safety of medical device connections by further specifying connectors by end-use applications.

What about testing other components of the syringe, like the needles themselves?

Testing the needles themselves is also critically important and often involves the determination of parameters such as needle flexural strength, penetration force, and pull-out force.  For example, ISO 9626 Annex C and Annex D specify a test method for determining needle stiffness and resistance to breakage, respectively, via a three-point bend test. For single-use hypodermic needles, ISO 7864 Annex D and Annex E specify a test method for measuring needle penetration and drag force, and the bond strength between the needle and the hub, respectively. Depending on the type of syringe, there may be variations in standards requirements. For example, for prefilled glass barrel syringes, ISO 11040-4 has a slight variation in requirements for both needle penetration testing, outlined in Annex F, and needle pull-out force outlined in Annex G.

Are there any specific challenges with syringe, Luer, and auto-injector testing that manufacturers face?

One of the biggest challenges associated with mechanical testing of syringes, Luers, and auto-injectors is the need to have one system that can easily adapt to the variety of required test methods. One of the main contributing factors of a system’s adaptability is the software and the ability to run a variety of test methods, all conforming to standards requirements. In addition, with such a wide range of measurements captured in any given test, choosing the appropriate load cell can be a challenge. This is especially the case for axial and torsional tests that require a biaxial load cell. For example, in ISO 11040-4 the torque required to unscrew the rigid cap in Annex G.5 is very low in the range of 0.1 N-m. However, in ISO 11040-4 Annex C flange breakage resistance, the axial load measurement can be up to 2,500 N. Thus, it is important for manufacturers to understand both torque and axial measurement requirements for their products in order to choose the optimal biaxial load cell.

What Instron systems help manufacturers comply with ISO 80369-20 and other testing standards in this area?

Instron offers two types of systems capable of performing the biaxial testing required in ISO 80369-20. The Torsion Add-On for our 5900 Series Electromechanical Universal Testing Systems can be used to perform simple bi-axial testing, such as Luer disconnection by unscrewing and Luer disconnection by axial loading. In addition, Instron offers fatigue bi-axial testing systems such as the ElectroPuls, E3000 Linear Torsion System, that are also capable of performing the tests outlined in ISO 80369-20.

ElectroPuls

Are there any difficulties when testing syringes of various sizes?

Actually, it is very simple to test syringes of different sizes, especially if the ASTM or ISO standard specifies syringe dimensions. For example, Instron supplies a full line of fixtures for testing to all ten annexes in ISO 11040-4. The ISO 11040-4 standard specifies a total of six different possible diameters for testing glass prefilled syringes. Using a combination of adjustable parts, drilled adapters, and advanced screw side action grips, the user is able to test all syringe sizes with minimal changes to the test setup.

Auto-injectors are used in a wide variety of applications. Could you summarize the main parts of ISO 11608 that define the performance requirements for injector pens and needles?

There are a total of five parts under ISO 11608, which specify test methods and requirements for needle-based injection systems. ISO 11608-3, Part 3 specifies requirements and test methods for finished containers; while ISO 11608-4, Part 4 specifies requirements and test methods for electronic and electromechanical pen-injectors. Lastly, ISO 11608-5, Part 5, specifies requirements for automated injection systems, such as auto-injector pens. Auto-injectors are subjected to strict quality controls because they are devices used to administer a correct dose, in a short amount of time, by an untrained person or patient themselves.  ISO 11608-5 requires physical testing of all of the manual steps leading up to using an automated injector sequence to ensure initiation of each step is within the limits specified by the auto-injector manufacturer. The most common measurements to quantify are: (1) removal force of the auto-injector safety cap; (2) activation force to start the auto-injector fluid expulsion; (3) displacement to start the auto-injector fluid expulsion; and (4) the time between initial fluid ejection to final fluid ejection, known as total ejection time.  

About Elayne Gordonov

Elayne is Instron’s Biomedical Market Manager focused on testing requirements and product development for the medical device and biomaterials industries. Elayne has worked at Instron for over 5 years, starting as an Application Engineer in 2012. Prior to Instron, Elayne received her Bachelors of Science degree from Rutgers University studying Biomedical Engineering with a concentration in materials science.