Pharmaceutical & medical
A software-controlled force tester measuring syringe ‘break-loose’ and glide force characteristics for the aspiration and injection strokes.
COVID vaccination programme, Mecmesin added a 12 specimen capacity to the syringe tester and provided software automation to run the test on the complete batch without operator intervention.
needles Hypodermic needles are tested to determine how their design influences the ease of insertion and retraction from the skin—a key factor influencing patient comfort and skin trauma. Designs of needles may differ according to the intended injection routes. Similarly, needles are tested to determine how well they pierce the elastomeric membrane of a vial closure without producing unintended rubber fragments. The characterisation of needle performance – namely for point sharpness, the effectiveness of the bevelled tip geometry and the frictional forces experienced along the shaft—is easily established by a computer-controlled compression test system. The real-time graphical force profile may be analysed for key areas of interest during the penetration (and extraction) stages, including:
resist forced or accidental disassembly. Accuracy of instrumentation reading is vital therefore in testing to these finely balanced requirements. By switching to a loadcell of a capacity close to the expected maximum load, the accuracy of the reading is optimised for the specific test being performed. Also vital, is appropriate resolution of the reading where a value indicating a ‘pass’ or ‘fail’ is needed. Again, the ability to fit a correctly matched loadcell provides this ability to differentiate between the two conditions. Measuring with optimal accuracy is all well and good as long as the correct condition is being measured. Holding the test specimen in the desired orientation and applying the representative loading precisely is achieved by the use of suitable fixtures. The grips must hold the specimen securely to avoid slippage, yet not deform it or introduce unrepresentative loads. Mecmesin’s standard interchangeable accessories enable an extensive range of medical device tests to be performed ‘off the shelf ’. However, for particularly innovative or intricate designs, Mecmesin provides a service to custom-design and manufacture bespoke fixtures exactly to the customer’s specification. Although cost-effective, simple-to-use,
manually operated force and torques testers are available—for medical and pharma industry use it is essential to have a motor-driven machine, incorporating software control. Some test standards also explicitly stipulate the use of a motor-driven tester. The motor delivers constant speeds of extension/compression or rotation, and the software enables a degree of automation, performing the procedural steps and calculating important values from the measured data. Furthermore, this sector requires software to provide traceable
Instrumentation Monthly June 2021
results, storage of raw data, a robust audit trail and full operator security.
Examination of thE problEm Syringe plunger and barrel The smooth and consistent operation of the plunger is essential when administering drugs from the syringe, whether manually or via an automated pump device. High forces or erratic movement can result in unnecessary patient discomfort. Tests on the plunger-cylinder mechanism focus not only on the design’s inherent functional performance and leakage prevention, but also support quantification of injectability and ‘syringeability’. A Universal Testing Machine is used to move
the syringe plunger at a controlled speed to aspirate and expel water, whilst the force exerted and the plunger travel are recorded. This mechanical testing enables the frictional and lubricity parameters of the plunger sealing head and barrel to be determined:
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The initial ‘break-loose’ force to start the plunger moving from its resting position.
The sustaining ‘glide’ force to keep the plunger moving.
The minimum, maximum and mean forces experienced during the return stroke of the plunger.
These are the key events that the
instrument’s software must recognise in order to fully characterise the syringe’s performance. To meet a global manufacturer’s need to increase production during the worldwide
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The initial peak force at which the needle tip first pierces the test ‘skin’ specimen, Point (A)
The intermediate cutting force as the bevelled cutting edges continue through the hole, expanding it wider, Junction (B)
The overall peak cutting force as the hole is fully opened, Heel (C)
The frictional ‘drag penetration force’ experienced as the needle shaft slides through the hole to the required depth – an indication of needle-shaft lubricity.
The tensile extraction force as the needle is withdrawn, may be measured to further differentiate designs and lubricity. To simulate real-life use of needles, a custom fixture allows adjustment of the angle of insertion into the substrate.
hub-to-syringe connection There are three main types of NIS syringe construction. Two of the most implemented are the Luer Lock syringe for detachable needles— which attach by a twist-fit thread to form the seal—and the Luer Slip syringe for detachable needles—which attach by a push fit with a small
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