Spotlight: How to verify the functionality of parenteral drug auto-injector devices

Materials World magazine
27 Sep 2019

Learn how to test for accuracy in automated dosage injectors.

An auto-injector is a medical device for administering liquid medications and is subject to stringent quality control. Parameters such as the firing time and duration of expulsion could only be measured manually. ZwickRoell has developed an actuation force, firing time, expulsion time and expulsion speed, together with the active-ingredient profile and the extended needle length. The ZwickRoell platform has an integrated precision weighing balance in the apparatus which precisely measures the volume of drug delivered from the pen during the testing process. The system carries out the testing procedure in a fully automated cycle, thereby removing the risk of error due to possible machine operator influence.

Auto-injector storage magazine

The ZwickRoell roboTest R testing apparatus performs the following standard checks – removal force of the safety cap, activation force and displacement, injection time, determination of the administered drug volume, including the last drops, effective needle length and safety function of the needle guard. The software directs the robot to remove the devices one by one from the storage magazine, feed them into the apparatus and initiate the test. The system is designed to check the auto-injector pen functionality in order to maintain product quality and ensure safe and reliable use by the patient when put in service.

Robotic test sample handling device

First, the batch of auto-injector devices is installed in the test platform storage magazine. The specimen handling system is controlled by the automation software, which directs the robot to remove the injectors one-by-one from the magazine, feed them into the test fixture in the testing machine and initiate the procedure.

Having clamped the device into the fixture, a laterally positioned tool moves into place to restrain the safety cap. The test machine crosshead moves in the vertical direction, at a pre-determined rate under computer control, to perform the safety cap removal of which the precise removal force is monitored and logged using a force transducer built into the platform. The safety cap is then automatically removed from the test space and discarded.

The subsequent movement of the machine crosshead applies a compressive force to the drug discharge button to determine the level required to activate the injector. The applied force and movement of the activation button is measured and recorded simultaneously by force and position transducers built into the testing machine. In addition, a microphone for detection of the device activation noise and a camera for time-synchronous visual recording can be incorporated and processed directly in the system software as external data channels.

The testing machine has a non-contact sensor that measures the injection time and effective needle length by means of light barriers. The dispensed drug volume is captured in a flask, mounted on a weighing balance, measured and recorded via the software. During the activation cycle, the length of the extended needle is determined using a dual laser sensor system.

Finally, the safety function of the needle guard is checked via the machine moving crosshead in conjunction with a laser–monitoring instrument after which, the device is removed from the testing platform and returned to the storage magazine by the robotic handling system.