Sean Fenske, Editor-in-Chief, Medical Design Technology (October 2013)
Medical device designers can select from any array of component fabrication
processes for the necessary parts for a project, such as molding, machining, and even 3D printing. While extrusion may be most often associated with medical tubing, it serves as yet another method device developers need to consider for their needs. The process presents advantages that may be more cost effective than other component fabrication methods, depending on the type of part necessary.
"Due to the fact that it is a continuous process, extrusion typically is best suited for applications and products that similarly are continuous (long continuous lengths), but it can also discretized (cut pieces)," explains Aaron Updegrove, marketing manager for the Life Sciences Business at Saint-Gobain Performance Plastics (www.plastics.saint-gobain.com). "However, extrusion is also an effective manufacturing process for producing thin films that can later be processed into discrete pieces. An example of this is small diaphragms used in IV set check valves."
Like all component fabrication processes, extrusion comes with its own, unique set of challenges for both the medical device designer and the process expert supply partner. While clear communication between the two parties will help provide for realistic expectations of the outcome, there are several considerations that designers can be made aware of prior to even beginning development and planning.
Extruded components designed with screw bosses, hinges, and many other features, allows them to incorporate easily with mating components.
"It can be a challenge to thoroughly understand the design contradiction that the medical device designer is trying to solve," states Sean Lynn, engineering manager at Teleflex Medical OEM (www.teleflexmedicaloem.com). "Sometimes companies try to withhold information that's critical to the effective functioning of a medical device design. In those cases, our team must "tease out" the actual design constraints from the customer—a process that can be very involved and difficult. We need solid, complete design information to identify the optimum solution without a series of trials."
Vesta's (www.vestainc.com) Don Centell, the VP of engineering, cites a similar concern. "The biggest challenge is trying to figure out what the customer needs vs. what they are asking for. Have they called out specific radii for a multi-lumen although they will be insert molding on that end of the tubing? We often find ourselves educating the customer on what a material is capable of because they will ask for an attribute that is not realistic given the material choice."
Rodney Floding, die design/extrusion engineer at Alexandria Industries (alexandriaindustries.com), identifies a challenge more specific to medical device manufacturers due to the regulatory environment. "Process validation is important to show capability and control of the process. However, even the slightest change in process or design variation can potentially require revalidation, increasing costs and delaying time to market. This struggle can reoccur as suppliers seek out and find opportunities for continuous improvement within their manufacturing processes."
Speaking to the value of working with an extrusion expert as early in the design of a product as possible, Updegrove explains how material selection can impact the final result. "Due to the complexity and length of time associated with securing regulatory approval for a medical device, medical device OEMs are often reluctant to make changes to materials used in extruded products. This reluctance to consider and explore alternative materials often limits an extruder's ability to provide an optimized solution." Reviewing the material options early in the process alongside the extrusion expert is certainly going to result in a much better result for the OEM.
While the idea that extrusion is not just for tubing may not truly be a concern with informed design engineers, there are several misconceptions regarding the process that experts do encounter. Whether working with metal extrusion, as Alexandria Industries does, or plastic, as the other Roundtable participants handle, addressing these misunderstood aspects of extrusion may make the difference in a designer looking to the process for a future project instead of a more familiar component fabrication method.
Speaking to expectations, Centell addresses the difference between a CAD representation of an extruded part and the final result. "An extruded tube very rarely looks exactly like the CAD drawing. Setting customer expectations up front helps in setting realistic goals. Multi-lumen tubing with very thin walls will cause more distortion of the shapes than that of thicker walls. Co-extrusion and tri-layers may not have the crisp layer distinction although the requirements can still be met."
Updegrove looks to tackle the difference between molding and extrusion in terms of the consistency of the output with extrusion compared to molded parts. "A common misconception that exists in the market place is that to produce high precision components, the products need to be molded. More specifically, that extrusion is not capable of maintaining the same level of precision and consistency that exists with a molding process. The reality is that innovations and the additions of new technologies to extrusion have allowed extruded products to deliver the same levels of precision and part-to-part consistency that are usually associated with a molded product."
When looking to metals, Floding offers the benefits of extruded aluminum over the more commonly indicated (in healthcare, that is) stainless steel materials. "OEMs may consider stainless steel a cleaner, more appropriate material for the medical market. With proper finishing treatments, such as anodizing, aluminum extruded products can actually be less porous and cleaner than stainless steel. The inert chemical compounds in aluminum combined with proper finishing techniques help prevent corrosion and chemical absorption—key to preventing contamination and easing the cleaning processes in medical care applications." With HAI prevention being such a significant topic in the healthcare sector, working with materials that are more easily cleaned can offer a competitive advantage for device OEMs.
Going forward, extrusion will continue to offer medical device designers an alternative component fabrication method to molding, machining,and other processes. Just like specifying any part in a design, finding the right choice is critical to achieving the optimum result.
Floding points to the current trends in design for healthcare—shrinking devices and home healthcare—as drivers for future metal extrusion innovation. "Similar to the evolution of electronic devices over the past few decades, medical devices are shrinking in size and weight to enhance portability, mobility, and handling. This transformation is pushing OEMs to find alternative ways to fit in more technology, while using aluminum extrusions with smaller profiles to cut material costs. To support this effort, aluminum producers are continuing to create new alloys that can easily be extruded into thinner shapes, remain light in weight, and yet are strong enough to withstand the everyday wear that is common in medical or at-home environments."
While extrusion will likely continue to be most often associated with tube manufacturing, it serves as a reliable process for an array of components for medical devices. Whether maintained in long "strip" of product or cut into smaller components, the rate at which extruded components can be produced offers a significant competitive "challenge" to other fabrication methods. As always, medical device designers need to be sure to consider all processes with which to obtain the parts needed for a design and seek partners who help them achieve the best result from their decision.