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!
Greetings,
Herwig

P.S. Back to part 1 – PVC, part 2 – PE, part 3: PP and part 4: PS

P.S.S.  New to my blog – check out my ‘start here’ section.

Literature:

[1] Vinny R. Sastri: Plastics in Medical Devices, 2014

[2] Amcor – Polybar®: https://www.amcor.com/products_services/polybar_blister_packaging

My Top 5 Commodity Plastics for Medical Device Applications – Part 4: PS

Welcome back to the blog series ”My top 5 commodity plastics for medical device applications”. This is part 4 – Polystyrene (PS).

 

Here you can jump to part 1 –PVC, part 2 – PE and part 3: PP.

Nr. 4 – Polystyrene (PS)

Polystyrene has long found its way in medical device applications and is widely used. PS is an amorphous polymer and is available in two forms: crystal clear polystyrene also referred to as General Purpose Polystyrene (GPPS) and as High Impact Polystyrene (HIPS).

HIPS is usually modified using polybutadiene elastomers. Depending on the added amount a high-impact grade (6-12% elastomers) or a medium-impact grade (2-5% elastomers) may be obtained.

A comparison in properties of GPPS and HIPS can be found in Table 1 [1].

Table 1: overview properties of GPPS and HIPS

Similarly to PP, PS can be found in three different structures: atactic (A-PS), isotactic (I-PS) and syndiotactic (S-PS). The A-PS is the most commercially available structure followed by S-PS. In applications with rather demanding specifications S-PS is usually preferred due to its superior properties i.e. high melting point (270°C), good chemical resistance and very low dielectric constant. Furthermore, S-PS has high flow capability which facilitates processing and enables thin-wall applications. Virgin S-PS is brittle. Thus, when toughness is required S-PS is usually reinforced with glass or alloyed with other polymers.  S-PS is produced in a continuous polymerization process using metallocene-based catalysts similarly to polyolefins.

How does PS perform in terms of sterilization?

Steam and autoclave sterilization are not applicable to PS due to its low heat distortion temperatures (85 °C at 1.85 MPa / 95 °C at 0.46 MPa). These will cause warp and disfigure. On the other hand, PS can be sterilized by Ethylene Oxide. This is valid for both types – GPPS and HIPS. PS shows a great stability to gamma radiation due to its high aromatic content. The aromatic ring has free electron clouds which are able to absorb the radiation inhibiting the generation of free radicals. No significant shift in color is generally observed either.  Therefore, PS can also be sterilized by irradiation.

What about biocompatibility?

PS is usually not used for applications where biocompatibility is required. However, there are biocompatible grades available from specific manufactures [2]. These allow using the versatility of polystyrene under the ISO 10993 compliance of the medical market.

Where is PS used in medical device applications?

GPPS can be processed over injection moulding leading to applications in labware, diagnostic equipment (e.g. petri dishes, test tubes and IVD products), and device components. GPPS processed by extrusion is used for packaging. As for HIPS is rather used in trays, bottles, containers, and medical components. Generally, HIPS is preferred over GPPS when impact resistance is of greater importance. Table 2 gives an overview of medical applications using PS. Since the properties of PP have been improving over the last decade, this becomes more and more competitive with PS, especially due to the relatively lower cost of PP.



Table 2:  Examples of applications using PS adapted from [1]

Where to get PS for your medical device applications?

Table 3 lists suppliers for GPPS and HIPS.

  Table 3: Suppliers of PS [1]



Table 3: Suppliers of PS [1]

Thanks for reading! Have a beautiful day & till part 5: COC!

Greetings,

Herwig

P.S. New to my blog – check out my ‘start here’ section.

Literature:

1] Vinny R. Sastri: Plastics in Medical Devices, 2014

[2] Trinseo - STYRON™ 2678 MED Polystyrene Resin: http://www.trinseo.com/News-And-Events/Trinseo-News/2016/June/Trinseo-Introduces-Biocompatible-Polystyrene-for-Medical-Devices



My Top 5 Commodity Plastics For Medical Device Applications – Part 3: PP

Welcome back to the blog series, “My top 5 commodity plastics for medical device applications”. This is part 3 – PP. Here you can jump to part 1 – PVC and part 2 – PE.

Nr. 3 – Polypropylene (PP)

Polypropylene commonly known as PP can nowadays fulfill the requirements of a multitude of applications ranging from packaging, automotive to healthcare. It can usually be found under three different structures:

• Isotactic PP (I-PP): all methyl groups are on one side of the polymer chain.
• Syndiotactic PP (S-PP): the methyl groups are alternatively located along the polymer chain.
• Atactic PP (A-PP): the methyl groups are randomly distributed along the polymer chain.

I-PP is the structure most commercially available. S-PP is difficult to manufacture and A-PP has nearly no commercial use due to its poorly defined physical and mechanical properties in comparison to I-PP. This is a result of the random distribution of the methyl groups along the polymer chain. I-PP is semi crystalline and exhibits higher chemical resistance as well as higher tensile strength together with a higher melting point in comparison to A-PP and S-PP. The latter shows thermoplastic elastomeric behavior and is more ductile compared to I-PP.

All PP structures are nowadays produced with the support of either metallocene or Ziegler-Nata type of catalysts. Metallocene catalysts are based on cyclopentadiene or other polyaromatic compounds bonded to a metal element e.g. zirconium or hafnium. Interesting to see is that PP produced in the presence of metallocene catalysts shows a superior transparency compared to PP conventional produced with Ziegler-Nata catalysts. This is due to the formation of crystals which are smaller than the wavelength of light. In terms of processing, metallocene based PP is advantageous due to its narrower molecular weight distribution which results in reduced levels of distortion during injection moulding for example. The narrow molecular weight distribution also facilitates the production of dimensional stable parts.

By adding additives, properties of “virgin” PP can be enhanced. Nucleating agents such as talcum and sorbitols are commonly used to increase the stiffness and chemical resistance of PP. During injection moulding, such nucleating agents reduce the time of the processing cycles. As a consequence, throughput and productivity are increased.

Additionally, we can distinguish between Polypropylene Homopolymer (PP-H) and Polypropylene Copolymer (PP-C). The PP-H has a good strength-to-weight ratio, combined with high stiffness and strength. Also, it has a good chemical resistance which allows it to be used in applications which need to have corrosion resistance. On the other hand, PP Copolymer has an ethylene built in improving the impact performance, as well as toughness, especially low-temperature toughness. Stress cracking performance is improved too. 

Comparing PP to PE, it has a higher processing temperature (220-230°C; softening point: 130°C) and a more narrow processing window compared to PE (LDPE: processing temperature of 160°C). Reason for the high softening point is the CH3 group in the side chain. It takes more energy to move them since they are taking more space and blocking the other chain movements. 

How does PP perform in terms of sterilization?

Steam sterilization (123°C of saturated water vapor) and autoclaving of PP may be applied only in a limited cycle scenario due to the lower heat distortion temperature of PP (100°C in case of I-PP). Ethylene Oxide (EtO) can be applied for sterilizing PP. In case of radiation sterilization, PP needs to be stabilized by free radical scavengers which help preventing degradation and discoloration as a side effect of the high energy concentration. 

What about biocompatibility?

General testing according ISO 10993 showed that PP can be used without influencing basic immunological functions of the human body. No negative physiological, allergic or toxic reactions are expected [2]. PP biocompatible grades are available and suppliers are listed at the end of this blog post.

Where is PP used in medical device applications?

There are three major reasons why PP is very useful in medical device applications as well as in packaging applications:

• high clarity
• good barrier properties
• and radiation resistance.

PP is mostly used in the production of disposable hypodermic syringes. In this case, PP needs to be transparent and most importantly radiation-resistant, because the manufacturing of large quantities of these medical devices require cost-effective sterilization procedures such as radiation [4]. Both, the barrel and plunger of the syringe are made of PP [3].

Further applications are found in medical labware. Herein, PP needs to have high clarity, chemical resistance and toughness. PP is used for labware application such as centrifuge tubes, pipettes, containers and sample cups.

Non-woven fabrics made out of PP play an important role in applications such as surgical gowns, drapes, sterilization wraps, face and surgical masks.

In Europe, parental nutrition devices and dialysis films can be named as an emerging market for PP as well [1].

PP is also used for medical devices requiring biocompatibility. Among those are, for example, the PP meshes used in general surgery, plastics reconstructive surgery as well as in hernial repair operations [5]. In this regard, heart valve structures, wound dressings and catheters are also application examples.Table 1 shows medical device applications of PP.

Table1:  Examples of applications using PP based on [1]

Where to get PP for your medical device applications?

Table 2: HC grade certified thermoplastics suppliers of PP [1]

This was part 3 of the series. The next part will be PS.

Thanks for reading! Have a beautiful day & till next time!
Greetings,
Herwig

P.S. New to my blog – check out my ‘start here’ section.

Literature:

[1] Vinny R. Sastri: Plastics in Medical Devices, 2014

[2] Archita Datta Majumdar, Biocompatible plastics and their importance in the medical device industry, (http://multibriefs.com/briefs/exclusive/biocompatible_plastics_medical_industry.html#.WNmD-bm7qWg)

[3] http://www.madehow.com/Volume-3/Syringe.html

[4] http://en.bgs.eu/services/radiation-sterilization-contamination-control/application-fields/medical-devices-and-diagnostics/
[5] Van Der Velden MA, Klein WR. A modified technique for implantation of polypropylene mesh for the repair of external abdominal hernias in horses: a review of 21 cases. Vet Quart, 1994

[6] https://www.machinedesign.com/community/article/21837192/whats-the-difference-between-polypropylene-types