Medical Plastics 101: PVC Remains Material of Choice for Life-Saving DevicesMedical Plastics 101: PVC Remains Material of Choice for Life-Saving Devices
First applied to medical applications during WWII, PVC is the most widely used plastic in healthcare, accounting for approximately 25% of all medical-plastic compounds. Here’s why.
May 14, 2021
Few polymers used in healthcare have stoked as much controversy as polyvinyl chloride (PVC). For many years, this plastic and its additives have been scrutinized by authorities, criticized by NGOs, and been subjected to substitution campaigns. Paradoxically, PVC is praised by R&D departments as well as the wider medical device community for its unique technical properties. Forecasts show that PVC will remain the material of choice for a range of existing life-saving medical applications such as tubing and containers, especially blood bags, and will play a key role in tomorrow’s innovative healthcare solutions. The use of PVC in healthcare is expected to see healthy growth in the coming years.
In this article, I will outline new developments with respect to the environment and human health that hopefully will serve to build a new paradigm for the polymer, where concerns are replaced by a positive vision for the future of PVC. The focal points are PVC’s unique recyclability, which is essential to the implementation of a circular economy in healthcare, and the introduction of new plasticizers. Here, the European PVC industry’s decades-long commitment under the VinylPlus program is key to sustainable development.
But let’s begin with a brief explanation of why PVC, and plastics in general, were introduced in healthcare in the first place.
When plastics revolutionized healthcare
PVC is the most widely used plastic for medical devices, with a share of about 25%. The other main medical polymers are polypropylene, polyethylene, polystyrene, and ABS.
PVC began replacing glass, metal, ceramics, and rubber in medical devices during WWII.
PVC was introduced in medical applications during World War II to replace reusable medical devices made from glass, metal, ceramics, and rubber, which required cleaning and sterilization between uses. PVC and plastics enabled manufacturing a wider range of safe, low-cost, single-use medical devices that greatly reduced cross-contamination between patients and improved treatment.
Because of plastic’s smoothness and particularly its durability, the shift from traditional materials made treatments less painful and far safer for patients. The new plastic-based devices enabled doctors and nurses to improve patient care. It is doubtful, therefore, that the call for plastic-free healthcare recently proposed by NGO Healthcare Without Harm will find support among patients or healthcare professionals.
The first breakthrough came with the introduction of the blood bag. It was developed as a prototype in 1947, tested clinically at Harvard in the 1950s, and used experimentally in the Korean War, where it showed its worth. The PVC-based bag replaced fragile glass bottles and proved superior in preventing contamination and breakage. As the robust bag could withstand being dropped from the air, it helped save the lives of thousands of soldiers.
Further, the PVC blood bag enabled a revolution in blood collection and preparation. The PVC bag could withstand the high g-force of the centrifuge that separates blood into plasma, red blood cells, and platelet concentrates. This enabled the safe and easy preparation of multiple blood components from a single unit of whole blood.
The material’s robustness continues to be a key advantage. In various parts of Africa, for example, drones deliver blood much faster than would be possible by land transport. Instead of a five-hour round-trip drive to a hospital, the average time for a drone delivery is 30 minutes.
Unique properties of PVC
Since the 1960s, the medical applications of PVC have broadened well beyond blood bags. PVC formulations can cover a range of properties, spanning soft, flexible rubber to rigid engineering thermoplastics. As a consequence, PVC is used to make tubing, oxygen masks, containers for IV and dialysis fluids, IV sets, nasal cannulas, overshoes, examination and surgical gloves, blood vessels for artificial kidneys, blister packaging, mattress covers, training manikins, and many other products.
PVC's range of properties, safety, and low cost has made it a go-to material for a variety of medical devices.
Recently, PVC has shown its value in the fight against COVID-19, both with traditional medical devices and innovative solutions. PVC’s durability, weather resistance, and fire retardancy make it the perfect material for temporary testing and vaccination centers. PVC-based inflatable hoods for ventilators, gowns, gloves, and visors help protect healthcare workers from the virus.
PVC owes its success to a number of factors. If transparency and anti-kinking properties are needed, PVC is the only choice. Its versatility and ease of processing allow for the manufacturing of mono-material devices that consist of both soft and rigid parts. This property is essential to recycling, as we will see later in this article.
PVC can be used in a range of temperatures and it retains flexibility, strength, and durability at low temperatures.
PVC formulations exhibit excellent strength and toughness. For example, vinyl gloves possess very good resistance to tearing to protect both doctors and patients and help prevent the spread of infection, germs, and disease. They offer a viable alternative solution to latex allergies.
PVC is characterized by high biocompatibility and hemocompatibility, and this can be increased further by appropriate surface modification.
Materials used in medical applications must be capable of accepting or conveying a variety of liquids without themselves undergoing any significant changes in composition or properties. PVC has excellent chemical stability and thereby meets these demands.
PVC is compatible with virtually all pharmaceutical products in healthcare facilities today. It also has excellent water and chemical resistance, helping to keep solutions sterile.
Plasticized, flexible PVC medical devices can be easily sterilized via steam, autoclave, radiation (electron beam or gamma rays) or ethylene oxide methods, while maintaining key properties such as flexibility and resistance to tears, scratches, and kinks. Rigid unplasticized PVC medical devices can be sterilized using low-temperature steam (60 to 80°C), radiation, or ethylene oxide.
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 high-energy 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, non-recyclable 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.
When discussing waste management options of plastics in the context of the circular economy, it must be stressed that the trend is reduction, reuse, and recycling. Incineration, which emits CO2, and landfill, where the resources are wasted, are the least preferable options. That’s why recyclability of plastic materials is extremely important, and, as we will see, PVC’s chemical composition makes it perfect for circularity.
Accelerating sustainability in healthcare
For a long time, healthcare has been kept out of circular economy discussions because of the fear of contamination. Recently, however, the concept has garnered greater interest, especially because of the mountains of hospital plastic waste generated by COVID-19. At the peak of the epidemic, hospitals in Wuhan, China, saw their medical waste increase six-fold, and in Italy incinerators had to run non-stop to keep up with the waste flow. The solution to this crisis is to recycle plastics where reuse is not possible.
PVC recycling in general is well-established in Europe, with almost six million tons recycled since 2000 in the framework of VinylPlus. And PVC is a recyclable material. Take, for example, a PVC pipe. It can last 100 years or more, and several studies show that it can be recycled up to 10 times without adding new material. The same recyclability applies to medical-grade PVC. Actually, what is not well-known is that recycling of medical PVC is well-established. What started at one hospital in Australia more than 10 years ago has now spread to nine countries around the world.
VinylPlus has for several years supported the RecoMed recycling scheme in the UK, which involves 40 NHS hospitals. Leveraging the know-how gained in the UK, VinylPlus has recently launched the VinylPlus Med program to accelerate sustainability in healthcare in continental Europe, starting with Belgium.
PVC meets the tough requirements for medical plastics and has shown its worth for many decades as a lifesaving material. On top of that, PVC is often chosen for innovative applications in the fight against COVID-19. When it comes to additives, a range of medically approved plasticizers have been developed and are now on the market. This means it is possible to preserve PVC’s unique properties without using phthalates of concern.
The circular potential of PVC has also been outlined in this article, and with increased focus on circularity in healthcare there will be growing pressure to recycle where possible. For the relatively small quantity of non-recyclable medical PVC waste, incineration cannot be avoided. However, continuous improvement of incineration technology means its environmental impact will continue to be mitigated. It is also important to stress that incineration of plastics should be avoided in the circular economy. Thus, strenuous and expensive efforts to substitute PVC because of concerns related to waste incineration, as many NGOs suggest, is not the way forward when the future calls for an end to plastic incineration.
About the author
Ole Grøndahl Hansen is Project Manager at PVCMed Alliance.
About the Author(s)
You May Also Like