By Didier Perret, medical business development manager, Branson Welding and Assembly at Emerson
It is well known that plastics have revolutionized the medical market. Products that used to be made from glass, ceramics and metal are, more often than not, made of plastic materials, which professionals in the field appreciate for their light weight, durability, flexibility and many other attributes. In recent years, though, there has been increasing concern about possible negative effects of some ingredients and/or components in certain plastics, most notably polyvinyl chloride (PVC) and polycarbonate (PC). In response, medical-device developers and manufacturers are beginning to research and use other plastics, including polypropylene (PP) and polyethylene (PE), collectively known as polyolefins.
However, they are discovering that joining techniques commonly used with polycarbonate and PVC — including adhesives and mechanical fasteners — are not effective on these other resin choices. Welding techniques like conductive (heat) welding, radio-frequency (RF) welding (also known as high-frequency or dielectric welding) and solvent welding can also be problematic.
At the same time, medical-device makers, like all manufacturers, are struggling to remain profitable even as they ramp up production to meet exploding demand, contend with stringent quality and cleanliness standards, and respond to increasing pressure to operate more sustainably.
All these factors, taken together, are pushing device developers and producers toward increased use of ultrasonic and laser welding, and related processes. Didier Perret, medical business development manager, Branson Welding and Assembly at Emerson, looks at some of the issues and opportunities these methods present.
Phasing Out PVC
According to PVCMed Alliance (Brussels), PVC is used in 40% of all plastic-based medical devices, including most of the tubing and IV bags available today, as well as many masks, breast-pump kits, catheters and more. However, dioxin, a known human carcinogen, can be formed during the manufacture of PVC, and toxic chlorine may be released during processing and assembly. In addition, DEHP, a phthalate plasticizer commonly used to soften PVC, is a known endocrine-disrupting compound that, it is feared, can leach into the patient’s bloodstream and potentially cause fertility and other reproductive-related problems.
Because of these concerns, the American Medical Association, among other healthcare and professional organszations, is encouraging hospitals and physicians to reduce the use of and eventually phase out PVC. In Europe, Health Care Without Harm (HCWH), a network of hospitals and healthcare professionals, has stated that “the totality of issues revealed in relation to PVC presents a compelling case for a call for complete elimination of use of this material.”
PVC can be welded very effectively using conductive welding, RF welding, as well as solvent welding and adhesives, and many manufacturers have used these processes for years.
However, replacing PVC with PP or PE is not so simple from a joining perspective. That is because polyolefins are nonpolar, so they are impervious to the electromagnetic waves that generate heat during RF welding. Likewise, PP and PE have excellent chemical resistance and are not easily bonded using solvents, and their low surface energy also means that adhesives are not very effective.
By far the most effective technology for assembling 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 layers, softening the plastic so that it merges into a high-quality seal when the films are held together under pressure. This is an extremely fast joining process that can be applied to almost any thermoplastic, including PVC. While the initial equipment costs of ultrasonic welding are higher than those of other technologies, there are numerous benefits that ensure a relatively quick ROI:
- Energy savings … unlike conductive welding, tooling does not need to be preheated and remains cool when not in use.
- No consumables … adhesives and solvents are not required.
- Process efficiency … welding times are short, allowing more cycles per minute.
- Nontoxic … no off-gassing occurs during welding, so there is no danger to operators and no need for expensive venting equipment.
- Green … all these factors contribute to a smaller carbon footprint compared to any competing joining method, including solvents or gluing.
Replacing polycarbonate
Like PVC, PC has been used for years in medical applications such as dialyzer filter housings, drug delivery pens, intravenous access components, and cardiac bypass systems including blood oxygenators, reservoirs and filters. However, because polycarbonate contains bisphenol-A (BPA), a known endocrine-disrupting chemical, it has largely been eliminated from baby bottles and water bottles used by athletes. While activist groups continue to call for an outright ban, HCWH stated in a 2021 document that a ban is not necessary if ‘residual BPA and related structural analogues’ are eliminated.
While low levels of BPA have not been deemed especially problematic, there is still concern that direct and sustained contact with blood can lead to higher serum BPA levels, especially in patients with chronic renal disease. This, along with other material advantages, has manufacturers looking at PP and PE as potential alternatives to polycarbonate.
As in PVC replacement, ultrasonic welding is a good joining option, delivering the same benefits listed above. However, in many applications where polyolefins are replacing PC, laser welding is often considered as well. In laser welding, components are preassembled before joining, and no vibration or movement is required to produce clean, particulate-free welds.
Laser welding is versatile. It produces a clean homogeneous weld, with equally distributed strength and, importantly, reduced part stress, which helps ensure longer service life. In operation, the components are held together under pressure as the laser light passes through one part (the transmissive surface) and strikes the other absorptive surface, where laser energy is converted to heat, creating the weld.
An Emerson refinement to the process, called Simultaneous Through-Transmission Infrared (STTIr) laser welding, adds to these advantages. Unlike trace or scan lasers that must travel the entire length of the weld line, completing the weld a little at a time, STTlr involves a custom-tailored tool called a Waveguide, which directs light from laser diodes to all points on the weld lines simultaneously, even in different three-dimensional spatial planes, providing a predictable and uniform melt-down and weld collapse. Multiple beams are positioned on many axes, so that the energy is delivered along the full length of the weld surface at once. STTlr can weld dozens of different polymers, including some of the most advanced engineering materials like polycarbonate. Benefits of this process include:
- Weld quality … localized heating/melting creates welds with excellent cosmetic properties.
- Minimal flash and no particulate … no frictional motion, and power dissipates evenly and accurately.
- Part design flexibility … multidimensional joint configurations are possible.
- Gentle … no vibration, and minimal heating protects sensitive components.
- Fast and flexible … ideal for high-volume applications.
Data-gathering and standards compliance
Success in the medical-device industry requires the highest level of process consistency, scrupulous data-gathering and record-keeping, and close adherence to international standards of process control and quality. Welding equipment has been evolving in recent years to meet these demands.
Today’s advanced ultrasonic welders, such as the BransonT GSX models from Emerson, incorporate technology and features that make them ideal for medical applications. For instance, they are built with electromechanical (servo) actuators, which are far less likely to generate particulates than pneumatically actuated units. In fact, the new GSX-E1 welder qualifies for an ISO Class 5.5 cleanliness rating and is designed to ensure compliance with manufacturing regulations including ISO 13485 and medical FDA 21 CFR Part 11. And they meet the Food and Drug Administration’s (FDA) Current Good Manufacturing Practice (cGMP) requirements.
The power supplies that drive and control these welders are fully digital, providing closed-loop feedback and tighter control of critical weld parameters. They offer real-time control, process monitoring, data storage and communication capabilities that meet installation, operational and production qualification, and validation protocols.
Branson laser welders, such as the recently introduced GLX-1 model for small and micro components, are similarly connected. They are Industry 4.0/IIoT (industrial internet of things) capable, delivering actionable operational and traceability data over USB and OPC-UA interfaces.
