Medical Plastic Data Service Magazine



Our 29th Year of Publication
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Drug Delivery Device Using Polymers With Improved Tribology


Improving The Patient Experience Of Your Drug Delivery Device Using Polymers With Improved Tribology




Engineering polymers are increasingly becoming an alternative to metal and ceramics in medical and pharmaceutical devices such as injection pens, inhalers, lancing devices, and surgical instruments. The portfolio of MT polymer grades supports OEMs and manufacturers as they develop and introduce innovative, reliable products. Their light weight and dimensional accuracy is achieved through precision molding. This, combined with good wear resistance and low coefficients of friction, distinguishes these plastics from metal.


Many medical and drug delivery devices contain moving parts. As these parts move, such as in an inhaler, they must effectively slide against other parts. To allow the device to function effectively they must not create noise, or even worse, wear, or have a high coefficient of friction that prevents the device from functioning smoothly. This performance has to be achieved in complex design environments including movements against different types of materials that are operating across a range of temperatures and chemical environments. These parts will work against possible presence of particulates and a range of speeds and forces in operation.


This paper reviews traditional polymers with and without external lubricants. It also includes the review of several grades of tribologically modified polymers that operate effectively without the aid of external lubricants.




If we consider the simple concept for an autoinjector shown in Figure 1, we can see that the system is comprised of several main functional elements. The casing of the unit houses a drive mechanism, release mechanism, and a needle return mechanism. The operation is triggered by the release button at the end of the device.


Figure 1: Concept device of an auto-injector


A detailed analysis of the tribological interactions between the internal parts has been done to prevent issues regarding unwanted noise generation, high friction and excessive stick-slip behavior during operation.


Figure 2: Stick-slip (ball-on-plate) Test equipment




During the last decade Celanese has gained experience in analyzing the tribological behavior of different thermoplastics with and without external lubrication and is still expanding its database.


Tribological testing devices with slow sliding speed and high pressure, like the stick-slip equipment (Figure 2) used by Celanese, are suitable for mimicking the sliding performance in medical devices.


This test equipment measures static and dynamic coefficient of friction. A measurement cycle of 45 minutes is comparatively short and facilitates the fast execution of many measurements. This allows for repetition of measurements leading to more accuracy and adding to Celanese’s database. The difference between the static and dynamic coefficient of friction results in a stick-slip effect. This stick-slip effect correlates with the risk of noise.

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Accuprec Research Labs Pvt. Ltd., India
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