Thursday, 27 April 2017

My Top 5 Commodity Plastics For Medical Device Applications – Part 5: COC

Welcome back to the blog series about “My top 5 commodity plastics for medical device applications”. This is part 5 – Cyclo Olefin Coploymers (COC).
Here you can jump to part 1 – PVC, part 2 – PE, part 3: PP and part 4: PS.
Nr. 5 – Cyclo Olefin Copolymers (COCs)
Cyclo Olefin Copolymers (COCs) were introduced in the last decades and found their home in medical device applications in a significant way. They are amorphous and transparent copolymers made by cyclo olefins (norbornene-based) and linear olefins (ethylene-based). The typical chemical structure of such copolymers is shown in Figure 1.
What makes them so ‘special’?
It is the combination of high transparency with high impact behavior together with superior moisture barrier properties which results in excellent stability in terms of dimensions and processing. Furthermore, COCs exhibit stronger shatter resistance than glass and their thermal resistance is significantly improved in relation to polyethylene and polypropylene. These also show a better transmittance at visible and near-ultraviolet wavelengths. Their birefringence is lower than that of polystyrene and polycarbonate.

Figure 1: Chemical structure of Cyclo Olefin Coploymers (COCs)
The superior properties of COCs are very much due to the presence of the norbornene unit and its bridged-ring structure which prevents crystallization. In addition, adjustment of the norbornene content allows tailoring of the thermal properties with higher content leading to higher heat resistance.
A comparison in properties, processing and compounding can be found in Table 1 [1].
Table 1: Characteristics, processing and compounding of Cyclo Olefin Coploymers (COCs)
How do COCs perform in terms of sterilization?
Sterilization of COC based applications can be done by using gamma radiation and ethylene oxide. Depending on the amount of norbornene, copolymers will have a higher glass transition temperature which makes them suitable for steam and dry heat sterilization.
What about biocompatibility?
COCs have a low amount of extractables which give them excellent biocompatibility. There are COC grades available which fulfill the United States Pharmacopeia (USP) Class VI and/or ISO 10993.
Where is COC used in medical device applications?
COCs rose to fame in healthcare through their usage in blister packs. COCs proved particularly suitable for this application due to their good film extrusion, thermoformability together with good barrier properties and low moisture uptake. Figure 2 shows a cross section of a blister film which uses COCs [2]. This is a chlorine- and fluorine-free film which represents a good alternative to PVC-based films.

Figure 2: Cross-section of a COC based blister film

In general, blister packs consist of two components: a thermoformable film, which composes the cavity transporting the pharmaceutical product, and a lidding made of aluminum or plastic that seals the cavities after filling.
Apart of blaster packs, COC is used for syringes, vials and ampoules, petri dishes and specialized labware. Furthermore, you can find COCs in needleless injectors, injector pens, and inhalers.
Table 2:  Examples of medical applications using COCs adapted from [1]

Where to get COC for your medical device applications?
Table 3 lists the suppliers for COCs. 
Table 3: Suppliers of COCs [1]
Thanks for reading! Have a beautiful day & till next time!

P.S.S.  New to my blog – check out my ‘start here’ section.
[1] Vinny R. Sastri: Plastics in Medical Devices, 2014
[2] Amcor – Polybar®:

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