Medical Plastics: Let’s Leave Them To Their Own Devices!

The last few years have been particularly productive for plastic medical device designers, who have explored the benefits of using specialty plastic compounds in medical applications. Taking their cue from other industrial designers, the plastic medical device community is now utilizing wear-resistant, anti-static and elastomeric compounds that have met with great success on the factory floor. 

• surgical tools and catheters that come into contact with body tissue or fluid
• diagnostic devices that have plastic housings and/or internal components
• pharmaceutical applications where drug flow path is mission-critical

The “secret sauce” is morphology, a scientific discipline which defines structure of the polymer chains at a molecular level.  There are really only two types of morphology for plastic resins: semi-crystalline and amorphous. Amorphous materials featured a totally random orientation of the polymer chains which results in low warpage, excellent dimensional stability and relatively low, uniform shrinkage. Generally speaking,  amorphous materials have better creep reistance and overall toughness  compared to semi-crystalline polymers. Examples of amorphous plastics include:

• Acrylic
• ABS
• polycarbonate
• polysulfone
• polyethersulfone (PES)
• polyphenylsulfone (PPSU)

In contrast, semi-crystalline materials feature crystalline, regularly-ordered regions amid the random polymer chains. The creation of these regions during manufacturing, called crystallization, increases non-uniform polymer shrinkage which can lead to warpage of the plastic molded part. However, these disadvantages can be overcome with excellent wear resistance,  superlative chemical resistance and exemplary response to reinforcement.

In fact, fiber-reinforced, semi-crystalline materials typically feature very high stiffness and overall strength. Semi-crystalline polymers that are commonly used in the healthcare industry include:

• polypropylene,
• polyethylene
• nylon
• polyetheretherketone (PEEK).

One of the requirements unique to the healthcare industry is environmental exposure. In other words, the plastic itself must endure and so must the body tissue or fluids around the plastic.  Other typical requirements include:

• chemical resistance
• temperature
• humidity

Temperature and humidity are typically not much of a concern for medical applications due to the controlled environment in which most devices and applications are utilized.  But more on that later, in another blog post on this topic.