Lubrication 101

While the healthcare industry has had a long-standing reputation of being slow to adopt change, a recent shift has brought new innovative thinking to the industry. As new players such as Amazon, Uber, and Apple enter the space, patients are demanding better care and options, forcing innovation. One prominent example is medical device design. Patients have been demanding smaller and more portable devices, creating new challenges for designers and engineers. They’ve also had to consider new options and application methods for product finishing, as well as cleaning options that meet strict guidelines for medical devices.

Proper cleaning

Designers and engineers have much to consider for cleaning medical device components, especially as medical device design has evolved and components keep getting smaller and smaller. First, it’s important that the cleaning method meets the highest standards of cleanliness as it can impact device performance in the finishing process. With smaller devices and components, meeting high cleanliness standards presents a challenge because some traditional cleaning methods – water, for example – can leave spots behind. Water’s high surface tension also inhibits its ability to reach, and therefore clean, small spaces.

Luckily, major advances in cleaning chemistries in the past decade give medical device designers and engineers more options for cleaning this new wave of medical devices and components. New cleaning solvents satisfy strict regulatory requirements for medical component manufacturing and meet equally strict environmental standards, offering an overall lower cost-per-part cleaned.

Non-migrating lubricants

While guaranteed satisfactory device performance is extremely important, equally as important is knowing that the lubricating material will not migrate into the human body. Since non-migrating lubrication is mandatory, many medical device manufacturers are finding success by using polytetrafluoroethylene (PTFE) or dry lubricants because they stay where they’re applied – on the instrument, not the patient. By staying in place, PTFE also can lubricate for multiple actuations and can be annealed to the instrument (substrate) so that it is semi-permanent.

Recent designs emphasize single-use devices that simplify procedures. This often involves a device design that is minimally invasive, making it smaller and more complex with many small parts. The higher the part count, the more likely stacked tolerances will be an issue. These occur when the tolerances of individual components stack up against each other and affect device performance. Similar to stiction, stacked tolerances can be common when dealing with multi-part mechanical assemblies with moving parts.

Addressing tolerance issues can be tricky. One option is to design everything with tighter tolerances; however, this is not cost-effective as it generally drives production costs higher, requiring more sophisticated machinery and machine operator attention. An alternative is to lubricate the components to reduce movement friction, minimize actuation forces, and reduce force required for the device to complete its designed movement cycle.

Applying lubricants

Design changes in medical devices have created new challenges and opportunities for innovative finishing options, requiring new ways to apply materials to medical parts and devices. While a material might be a good fit and provide many benefits for a medical device design, it might seem impossible to apply. Today, novel application methods are solving these challenges. Some solutions include:

Dipping: Frequently used in high volume production, dipping provides consistency and uniformity in coating nearly any external and internal surface. Small parts, wire coils, and unique geometries can be coated via this method.

Wiping/brushing: Covering longer, ongoing surfaces including rods, tubing, or sheeting can be accomplished through wiping or brushing. It can also be used if only small, select areas of a larger part require coating.

Spraying: Handheld spray guns or automatic spray heads can apply diluted dispersions. Spraying can be used for various devices and is more selective than dipping, since material is applied to small areas with more precision.

The durability of PTFE dry lubricant coatings can be increased by using heat to melt and fuse the coating to the surface. This process also turns the lubricant clear, leaving an invisible coating on the device’s surface. Consulting a coatings provider can lead to recommendations on which processes are best for each application.

Carrier fluids

Just as important as a good lubricant is a good carrier fluid that enables application. The consistency of these coatings is important to ensure optimal device performance. A carrier solution can be applied in various ways, providing dilution and application for the lubricant. For example, medical-grade silicone is provided in concentrated form, so a carrier fluid must be used to dilute the lubricant, allowing application of a very thin film of silicone to a surface by dipping or spraying.

In the past, carrier fluids have posed safety concerns and environmental risks. As with solvents used for cleaning, flammability was a serious concern with older carrier fluids, particularly in high-production volume manufacturing. Additionally, commonly used silicones traditionally do not work well with less flammable, low-toxicity carrier fluids. The amount of silicone that could be mixed in carrier fluids was very low – only 1% to 2% – far lower than needed for most medical devices. Breakthroughs in carrier fluid chemistries have produced medical grade formulas with nonpyrogenic properties, ISO 10993 certification, and full compatibility with sterilizing processes. There are few, if any, toxicity or handling issues with PTFE materials, and nonflammable carrier fluids can be used.

Conclusion

While many trends impact today’s medical device design, it’s important to consider the implications on product finishing to select the best, most cost-effective solution. Today’s solvents, lubricants, and coatings have come a long way, and innovations have kept pace with trends in miniaturization, automation, and application. By examining safety, application method, and overall effectiveness, you can make confident decisions about which solutions will work best for your needs.

MicroCare Medical

Jay Tourigny, senior vice president at MicroCare Medical. Tourigny can be reached at 860.515.3011 or jaytourigny@microcare.com