Powered Surgical Tool Reliability: Protecting Against Moisture & Corrosion

Powered reusable surgical tools have gained popularity thanks to their ability to reduce procedure times and improve patient outcomes. An array of sensor, feedback, and control components make these advances possible. These parts are prone to corrosion from saline, steam sterilizations, or other contaminants. In order to ensure reliable performance over several years of surgeries and re-use, device OEMs need to protect their tools against moisture ingress. This blog post will explain how moisture, corrosion, and other harsh conditions can compromise reusable surgical tools and offer mitigation strategies to ensure long service life.

• Moisture Ingress. Often moisture ingress will occur at the distal end of the tool. One way to prevent this situation is to apply a dynamic seal between the handpiece chassis and the shaft motor. To ensure the seal is tight and long-lasting, control runout and the surface finish. In addition, mating points on motor housings are also susceptible to moisture ingress. They can be sealed using a hermetic laser weld, sealed threads, or O-rings.
• Mechanical Component Failure. Because gears, shafts, and bearings must resist fatigue, wear, and corrosion failures, material selection is key. Precipitation hardened or austenitic stainless steel protects against corrosion from saline or steam, and martensitic stainless steel has less corrosion resistance but increased strength and surface hardness. Lightly loaded components such as bearing retainers can be made from polyetheretherketone (PEEK) or polyamide-imide (PAI). Cemented carbides or ceramics can also be considered. Lubrication washout is also a common cause of failure. The lubricant should have a maximum listed operating temperature well above sterilization temperature, low water washout (per ASTM D1264 or similar), and favorable corrosion testing (per ASTM D5969 or similar).
• Electrical Failure. Printed circuit boards (PCBs), Hall sensors, or relevant electrical connections often fail due to moisture. Potting, transfer molding, and conformal coatings can protect components by encapsulating the electronics within a moisture-resistant barrier.
• Magnetic Circuit Failure. High temperatures and moisture can damage motor windings or permanent magnets. Magnet wire with high temperature and heavy-build insulation should be used, and the formed coils should be molded or potted similarly to the PCB. Sintered NdFeB magnets must be SH or UH grade and protected via electroplating or an epoxy coating, and SmCo magnets are another option to avoid corrosion and demagnetization problems.

It Pays to Collaborate With Your Motor Designer

Powered surgical hand tools are increasingly sophisticated devices, and the electric motors at the heart of these tools are susceptible to various failures due to the presence of moisture during surgeries or sterilizations for re-use. To maximize the device’s reliability in the threat of moisture, the tool designer and motor designer should collaborate on a thorough protection strategy. Portescap, a market leader, has been collaborating with surgical device OEMs for decades to design custom solutions for their specific applications. Its autoclavable motors have industry-leading performance and reportedly last through thousands of reprocessing or sterilization cycles, during which they have been used in tens of millions of surgeries worldwide.

For more information, contact an engineer.