Measuring syringe plunger force using a texture analyzer instrument

A syringe’s design affects the pull and push forces required for drawing and ejecting a fluid into or from a barrel. Measurement of these forces for quality control or development purposes can be performed with a texture analyzer. The inset image shows a texture analyzer (CT3 Texture Analyzer, Brookfield Engineering) fitted with a syringe test jig.

By selecting the compression test mode, the texture analyzer measures the force required to initiate the plunger movement and the dynamic glide force required to continue extruding the medication solution from the syringe. For fluid suction, the tension test mode can measure the force required to draw fluid into the syringe barrel.

The test commences once the syringe’s plunger is centrally aligned with the texture analyzer probe holder and shaft. The plunger connector approaches the syringe plunger at a pre-test speed of 1 mm/s. The test/data collection will begin once the plunger connector is in full contact with the plunger surface and detects a trigger force of 5 g. The plunger connector exerts a force on the syringe plunger at a speed of 1 mm/s, during which time the contents in the syringe are expelled. An initial force peak is observed as the syringe contents in the barrel begins to flow. The peak is followed by a drop in force that quickly reaches a plateau as the test distance increases and the contents reach steady-state flow. When the target distance has been attained, the plunger connector withdraws from the syringe plunger and travels back to its starting position above the sample surface. The higher the initial peak force, the harder it is to initiate expelling the contents from the syringe.

About the Author
Eric Chiang, product manager, Brookfield Engineering Laboratories.