Materials

PVC – A Material of Choice for Life-Saving Devices

PVC can be easily welded to itself or with other plastics by heated tool welding and vibration welding. The strong bond strengths obtained enable the fabrication of collection bags or oxygen tents without the need for adhesives.
 

PVC is thermally responsive. This means tubes can be designed to be stiff enough for insertion, but will then quickly soften in the body, thereby reducing trauma during use and removal.

Last but not least, PVC is very cost effective.

Limitations of PVC

Like all materials, PVC has its limitations.

PVC is made of macromolecules that are highly flexible due to the internal rotation of the main chain carbon-carbon bonds. Consequently, PVC has a low softening temperature compared with other plastics of a similar molecular structure.

PVC will degrade by chain scission when exposed to the highenergy radiation needed in some sterilization processes. Chain scission will lead to the formation of radicals that can react with oxygen to form oxidized products, leading to discoloration. Tinting agents that correct the color of the product after exposure to radiation help offset the color change, but the transparency of the device is lost. For some PVC formulations, the color can revert close to the original color after a few weeks of storage.

Ortho and terephthalate plasticizers are widely used in flexible PVC devices because of their compatibility with PVC. Some alternative plasticizers may be less compatible and will tend to migrate to the surface. One may have decreasing content of plasticizer near the surface and an accumulation on the exterior of the surface. Surfaces will feel greasy and look dirty. The PVC below the surface will become brittle in time and may be destroyed by movements.

Flexible formulations are susceptible to staining by substances based on oleophilic solvents, which may result in a loss of clarity, transparency, and gloss if the medical device is not stored in a clean environment.

Flexible PVC may stiffen at low temperature, which may be a limitation for some liquids needing to be stored at very low temperatures.

Further, PVC is not suitable for some sensitive drug-delivery systems because of adsorption issues and loss of active ingredients.

PVC cannot be used for implants because of tissue interactions over prolonged periods of contact.

Additives and chlorine - the Achille’s heel

It is important to stress that the controversy over PVC does not stem from a lack of functionality or patient safety. On the contrary, PVC has a track record of billions of safe patient days of human exposure through more than seven decades of use.

The concerns partly relate to the chlorine content of PVC and partly to the plasticizers that are necessary to soften the material. Taking the latter first: The discussion over the pros and cons of phthalates, namely DEHP, in medical devices is ongoing around the world, and the jury is still out. In the EU, however, the
discussion has more or less ended. New regulation requires strong justification from medical device manufacturers for the continued use of DEHP.

For almost all applications, alternative plasticizers for PVC are available and are being used. Four of these are now included in the European Pharmacopeia, which sets the safety and quality guidelines for medical products in Europe and beyond.

A notable exception is blood bags, where more R&D is needed to replace DEHP. In Europe, some uncertainties remain on how the blood bags will be classified in the EU Medical Device Regulation to be applied on May 26, 2021, which raises some doubts on how the DEHP-free blood bags will have to be certified by the notified bodies. In the meantime, it is crucial for patient safety that blood bags plasticized with DEHP continue to be available.

Regarding the chlorine content of PVC, concerns have been raised about the potential emission of waste substances from PVC incineration. Unlike most PVC applications, which are found in building and construction, the majority of PVC medical devices are short term, single-use products. For safety reasons, nonrecyclable medical PVC waste and other hospital waste streams are generally managed through incineration. The production of waste substances depends on incineration conditions. In modern, well-run incinerators, these substances are appropriately managed on the basis of the strict procedures and standards set up under national regulations. When we talk about chlorine it should not be forgotten that this element is essential to modern life — up to 80% of medicine depends on chlorine chemistry.