Plastics and medical devices: Changes for safety and cost
The move towards polypropylene and polyethylene in medical devices requires new manufacturing and assembly solutions such as ultrasonic and laser welding.
Didier Peret, Emerson
Plastics are ubiquitous in medical applications thanks to their light weight, durability, and flexibility, among other attributes. However, concern has increased in recent years about the possible negative effects of certain ingredients and components of certain plastics. This leads medical device companies to research and use other resins or plastic combinations without the same risks. However, they do not have the same transformation characteristic, and changes often force companies to implement new production processes, especially around assembly and assembly technologies.
For example, polyvinyl chloride (PVC) is used in 40% of all plastic-based medical devices, according to the Brussels-based PVCMed Alliance, and most IV tubing and bags available today, as well as numerous masks, breast pump kits, catheters and more. Yet dioxin, a known human carcinogen, can form during PVC manufacturing, and toxic chlorine can be released during processing and assembly. Additionally, DEHP, a phthalate plasticizer commonly used to soften PVC, is a known endocrine disrupting compound that has the potential to enter a patient’s bloodstream and potentially cause fertility and other related issues. to breeding. For these reasons, healthcare and professional organizations, including the American Medical Association, are encouraging hospitals and physicians to reduce and phase out the material.
Assembly of PVC components
The vast majority of PVC bags and other components are joined by conductive (heat) welding, radio frequency (RF) welding – also known as high frequency or dielectric welding – as well as solvent welding and adhesives. As manufacturers have begun to explore alternative materials, particularly polyolefins such as polypropylene (PP) and polyethylene (PE), they are finding that these traditional joining techniques are not efficient, while other technologies offer cost reductions, sustainability improvements and safer toxicology for the product and throughout the production process.
PP and PE are non-polar polymers, so they are insensitive to electromagnetic waves which generate heat during RF welding. Similarly, PP and PE have excellent chemical resistance and do not bond easily with solvents, and their low surface energy also means that adhesives are not very effective.
By far the most efficient technology for joining polyolefins, as well as multilayer films incorporating these and other materials to form IV bags, is ultrasonic welding. Ultrasonic welding uses high frequency vibrations to generate frictional heat between the layers, softening the plastic so that it fuses into a high quality joint when the films are held together under pressure. It is an extremely fast assembly process that can be applied to almost all thermoplastics, including PVC. Although equipment costs are higher than other technologies, there are many advantages that ensure a relatively quick return on investment:
- Energy savings: Unlike conduction welding, the tooling does not need to be preheated and stays cool when not in use.
- No Consumables: Adhesives and solvents are not required.
- Process efficiency: Welding times are short, allowing more cycles per minute.
- Non-toxic: No outgassing occurs during welding, so there is no danger to operators and no need for expensive ventilation equipment.
- Green: All of these factors contribute to a lower carbon footprint than any competitive assembly method, including solvents or bonding.
Polycarbonate (PC) is very strong, transparent and dimensionally stable, making it ideal for many healthcare applications, including tubular filter housings which are key components in kidney dialysis systems. However, it is known to contain bisphenol-A (BPA), another known endocrine disrupting chemical which, like DEHP, can potentially cause a range of adverse health effects. It has been largely eliminated from use in baby bottles and water bottles used by athletes, and activist groups continue to call for an outright ban.
One of the reasons why PC has not been completely banned is that low levels of BPA that enter the human body are easily eliminated by normal kidney function. However, according to recent studies, serum BPA levels accumulate as kidney function declines and are highest in people with chronic kidney disease who are on hemodialysis. Therefore, in dialyzer applications, manufacturers are looking for alternatives such as polypropylene.
Unfortunately, many of the limitations of PP as a PVC replacement also apply to PC applications. Polycarbonate dialyzer housings have historically been joined using mechanical fasteners and adhesives, which do not perform well given the lower yield strength and surface energy of PP.
Therefore, manufacturers here also turn to ultrasonic welding (with all the attendant advantages detailed above), as well as laser welding. In the latter process, components are pre-assembled before welding, and no vibration or movement is required to produce clean, particle-free welds. Multiple laser beams apply energy along the entire length of the weld surface. One surface freely transmits laser energy unaffected itself to the second laser-absorbing surface where the laser energy is converted to heat conducted across the interface, creating the weld. The benefits of this process include:
- Welding quality: Localized heating/melting develops excellent cosmetic properties.
- Minimal Flash and No Particles: No friction movement and precise power dissipation.
- Part design flexibility: multi-dimensional joint configurations are possible.
- Soft: there is no vibration and minimal heating protects sensitive components.
- Fast and flexible: Ideal for high volume applications.
Who to turn to for help
As the industry moves from traditional materials like PVC and polycarbonate to cheaper and safer PP and PE, manufacturers are discovering that they can simplify their products, reduce costs and improve performance by switching to ultrasonic welding or laser.
If you are looking for a new joining solution to meet market pressures that dictate a material change, if you are looking for a new, more productive solution to your joining needs, or even if you already use ultrasonic welding systems and /or laser, Emerson and its Branson brand of products can offer assistance and support. Emerson takes a process-agnostic approach to recommending the right technical solution for each application and can make transitions as smooth as possible. Every Branson welding solution is backed by deep technical knowledge, decades of application experience and a global supply chain with strong sourcing, manufacturing and customer support capabilities.
Didier Perret is Medical Business Development Manager, Branson Welding and Assembly at Emerson. He graduated in mechanical engineering from the Technicum La Chaux-de-Fonds in Switzerland. Perret has worked for Emerson since 2000 and has extensive experience in automation, production, product design and plastics assembly technologies.
The opinions expressed in this article are those of the author alone and do not necessarily reflect those of MedicalDesignandOutsourcing.com or its employees.