Leveraging plastics’ powers

Historically, most single-use medical products were low-value consumables such as packaging, gloves, collection tubes, or tongue depressors. Today’s trend focuses on offering single-procedure alternatives for demanding medical device applications such as instruments for cardiovascular surgery or guiding and sizing components for orthopedic knee replacement procedures.

High-performance plastics are increasingly relevant for these surgical applications, in conjunction with or to replace metal. However, medical device manufacturers can’t just substitute one type of material for another. Traditional metals such as stainless steel have very different properties than plastics and use different manufacturing processes. With a history in metal-to-plastic conversion for healthcare applications, our experience teaches that failures typically fall into three main – yet avoidable – categories:

• Incorrect material selection
• Specification of a metal product design for the plastic component(s)
• Inexperienced, improper conversion supply chain Following are some current best practices to avoid pitfalls.

Choosing the right medical plastic

Numerous plastic materials are available, each with different performance capabilities. A good place to start is a basic categorization using an industry standard Plastics Pyramid. (See sidebar below)

Regardless of the material’s position on the pyramid, a critical consideration for designers is that the material supplier supports its use for the medical application in question (some do not), and that the material is biologically safe. Standardized biocompatibility testing is required by global regulator’s prior to clearing a device for commercial use. Some material suppliers proactively support their materials by testing in advance and offering those data to customers. More proactive suppliers have a Master Access File of their material on file with the U.S. Food and Drug Administration (FDA). This file contains all relevant toxicological and safety data for FDA reviewers, reducing the risk of regulatory delays when launching a new device.

Plastic choice can also affect ergonomics and surface quality as plastics containing reinforcements may appear rough. Ixef PARA, a gamma-sterilizable plastic material from Solvay used in spinal surgical kits, supports a smooth, aesthetic surface finish. Ixef PARA is also used in single-use instruments featuring an easy-grip handle with waffle-style pattern. When injection molded, this material supports cross-hatched, polished, or whirled patterns and product branding with a logo or image.

Plastic single-use instruments provide functionality too, such as color coding. During surgery, blood can cover instrument labels or make lettering hard to read. Plastics formulated in different colors allow designers to communicate characteristics such as size or function, eliminating potential confusion; especially important in kits where several instruments may appear similar. In today’s globally-connected world it’s also key to patient safety with surgeons in Berlin, Boston, Beijing, or Buenos Aries, because color-coding doesn’t require translation.

Plastics-centric design

During design, ensure that the part design and conversion process(es) are optimized in a plastics-centric manner. It’s unfortunately common for a medical device company’s first effort at plastics conversion to fail due to a traditional metal part design being specified and realized in plastic.

Differences can also appear in assembly. Like metal parts, molded plastic products can use threaded fasteners; however, plastic parts can also incorporate snap fits, flash joining, welding, and solvent bonding. With metal, joining or welding requires high heat. However, the heat from a hot plate may be enough to join or weld plastic.

Remember, however, that plastics have different tolerances that could affect product assembly.

Supply chain

Before replacing metal with plastic, it’s essential to understand all manufacturing considerations and ramifications. Metal instruments feature shapes and structures that are most frequently made by machining, sometimes casting, followed by secondary operations such as milling, boring, anodizing, or polishing. These processes are typically combined into a job shop workflow well suited for low-volume, high-variability production outputs.

A shift to single-procedure instrumentation brings the aspect of increased part volumes. Many instrument categories can then support conversion to more efficient mass production methods. In the case of plastics, part volumes commonly support moving to injection molding. This high-volume process supports greater design freedom and reduced part cost, allowing designers to achieve intricate features and sophisticated geometries not possible with metal manufacturing methods.

Secondary processes using plastic components – printing, joining, packaging, sterilization – can often be efficiently incorporated in line or via dedicated production cells specific to the medical device.

Plastics capabilities have grown and improved throughout medical device supply chains during the past decade. Many machine houses and contract manufacturers have incorporated molding into their operations. Their experience and advice are critical early in the product development process to ensure successful conversion to an all plastic or plastic-metal hybrid single-procedure device.

Collaboration

Designers who plan to develop single-use instruments should consider incorporating plastics but need to do more than substitute one type of material for another. In addition to choosing the right polymer, it’s essential to understand the many design and manufacturing differences between metal and plastic materials. Supply chains developed within the industry with plastics expertise assist and enable designers to take advantage of the benefits. By collaborating with material suppliers committed to healthcare, as well as their supply chain partners, medical device manufacturers can create new, innovative designs while increasing efficiency, controlling costs, and helping reduce the risk of HAIs.

Solvay

About the author: Dane Waund is the global marketing manager – healthcare, for Solvay’s Specialty Polymers business unit.