Drug
Delivery Device Using Polymers With Improved Tribology
Improving The Patient Experience Of Your Drug
Delivery Device Using Polymers With Improved Tribology
INTRODUCTION
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.
THE CONCEPT DEVICE
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
MEASUREMENT OF TRIBOLOGICAL
PERFORMANCE
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. |