The PTFE coating enables surgical instruments to overcome static friction. #medical
Use ISO 10993 certified dry lubricant to ensure that the lubricant is suitable for medical equipment. Image source: All photos are provided by MicroCare
In the medical device industry, manufacturing engineers usually design small, complex medical tools and equipment whose moving parts can swing, twist, pivot, or slide. Surgical staplers, forceps, retractors, clips, scissors, cutters, and snares are all examples of tools that must start smoothly without sticking or rubbing. But as these tools become more complex, engineers must consider how stacking tolerances affect the assembly and ultimately the function of the device.
Overtightened components caused by stacking tolerances may restrict their operation and require excessive force to start.
For example, when assembling a medical stapler, the tolerances of each metal stamping, spring or other moving part in the device may start to combine, making the assembly of the stapler more difficult and slow. Stacking tolerances can also cause problems for end users. Over-tightened components caused by stacking tolerances may reduce or restrict the movement of the equipment and require excessive force to start or operate the equipment.
Dipping can provide a consistent and uniform lubricant coating for any surface geometry, including internal surfaces.
Some equipment manufacturers choose to use functional coatings to reduce the impact of stacking tolerances and related static friction by using silicone oil or grease during assembly. But these lubricants are expensive, messy, and difficult to use, which complicates the process and cleanroom verification. The use of dry coatings for lubrication, such as PTFE (polytetrafluoroethylene) suspended in a high-purity, non-flammable carrier fluid, provides a simpler, cheaper and clean room-friendly option. PTFE is a non-stick lubricant made of a non-migrating synthetic polymer composed of carbon and fluorine. In addition to providing lubricity, it also helps parts to withstand water, oil, chemicals, wear, and high temperatures. PTFE coatings are commonly used for disposable medical devices that function outside the body. PTFE is an easy-to-apply method that reduces the coefficient of friction and reduces the force required to drive most equipment by up to 30%.
However, not all dry lubricants are the same, and one lubricant is not suitable for every application. The following are some of the key factors to consider when choosing a lubricating coating for medical devices.
Ideally, the PTFE carrier liquid disperses the coating on the treated surface and then quickly evaporates, leaving a very thin, dry, and uniform layer of dry lubricant on the surface of the treated part. The carrier fluid should be of low viscosity to wet all surfaces and conform to the surface geometry of the processed part, including the inner surface. This ensures a highly consistent surface coating in high-volume production environments, even on complex geometries or components.
Look for an ISO 10993 certified dry lubricant to ensure that the lubricant is suitable for medical equipment. The carrier fluid should be solvent-based to prevent bacterial growth and other water-related bioburden issues. The carefully selected carrier fluid has pyrolytic inertness and fast drying characteristics, so it will not remain on the finished part, leaving only the lubricating film exposed to the assembled EtO (ethylene oxide), ultrasonic or radiation sterilization process.
The coating should not migrate or transfer from the treated parts to the packaging or other untreated surfaces. This transfer may affect the subsequent application of surface treatments (such as marking or drugs), or cause dyeing on packaging or other cosmetic issues that are unacceptable in the medical industry. It should stay where it is applied to reduce the additional housekeeping costs that are common when oil is used. This characteristic is an essential attribute, especially when the coating is applied to a manufacturing clean room environment and has been validated.
Dry lubricants should be safe to use and effective on a variety of materials, including metal, glass, plastic, and ceramic parts commonly used in medical devices. It should dry to a uniform, durable surface without any staining or unsightly clumps, dripping or running, otherwise it may obscure the required unique device identification (UDI) markings.
Choose a non-flammable dry lubricant carrier fluid. This reduces transportation and storage costs while maintaining a safe working area when applying it to equipment. This is especially important for high-volume, high-speed production facilities. Many mechanical assembly operations are prone to electrostatic discharge, so the safety during use is not flammable.
Dry lubricants should be easy to apply and integrate into the internal assembly process. It should come with factory-accurate calibration and ready-to-use packaging provided by the supplier, minimizing waste of labor for mixing or inconsistent ingredients. There is no need to outsource the coating process, thereby increasing its cost-effectiveness.
Dry lubricants are usually applied using one of three methods. Knowledgeable coating partners can recommend the best process for your specific application.
Dipping is most commonly used in mass production and is suitable for complex components or small parts, metal stampings, coils and irregularly shaped coatings. Dipping can provide a consistent and uniform coating on almost any surface geometry and internal surface. The coating level is determined by the percentage concentration of solids, the removal speed and the number of applications. For most applications, one dip is usually sufficient.
Wiping or brushing is most commonly used for low to medium production runs. It can be used to coat continuous surfaces such as rods, tubes or sheets. In addition, wiping and brushing are suitable for coating small selected areas of larger parts. A variant of this method is pan coating followed by wiping.
It can be sprayed manually using a handheld spray gun or an automatic high volume low pressure (HVLP) spray head. Some aerosol sprays have a very tight spray pattern for precise lubrication, which is helpful for hinges and pivot points. Generally, a continuous thin coating allows the surface to dry between applications, which is better than a single thick coating application, which may take longer to dry and may cause uneven coverage and poor adhesion.
Air drying is best done in a dust-free place. The drying time of the coating depends on the thickness of the carrier fluid and lubricant application. Increasing the temperature of the processed parts can reduce the drying time, especially on the inner surfaces of complex components.
When more durable or permanent coatings are required, thermal curing or melt coatings are used in certain applications. The short heat treatment process turns the coating into a harder finish, thereby extending the service life. Heating makes many dry lubricants completely transparent, so there seems to be nothing on the surface of the device. This is especially useful if the coating needs to be semi-permanent, or needs to be invisible on the device.
In some cases, lubricating coatings are also used in manufacturing equipment and assembly jigs themselves to help speed up the production of plastic and metal parts. They are used for chains and pulleys, metal extrusions, machine window and door rails, chutes and slides, conveyor belts, and almost any other surface or component that requires a clean, durable, and smooth coating for optimal performance. Lubricant coatings are also used to release plastic parts from their injection mold cavities without leaving an oil film.
The surgical tool must be started smoothly without static friction.
Dry lubricants provide a cost-effective solution to manufacturing challenges such as stacking tolerances, close-fitting parts, and friction on complex mechanical components. When specifying lubricant coatings, equipment and component manufacturers should look for suppliers who provide expert advice to help them simplify the selection process. This includes personalized consultation, in-laboratory testing, and the ability to provide ready-made and custom formulations to ensure that they provide the correct dry lubricant coating for their finished products.
Jay Tourigny is the senior vice president of MicroCare Medical, a company that provides cleaning and lubrication solutions for medical equipment. He has worked in the industry for more than 30 years and holds a number of US patents for cleaning-related products that are used in medical and precision cleaning applications every day. For more information, please visit www.microcare.com.
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