by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Selecting the right rotary shaft seal for a medical application involves many different factors including sanitation and sterilization concerns, material compliance to both national and international standards, and patient safety. While some medical applications still depend on elastomeric sealing solutions, FDA-approved PTFE rotary shaft seals provide far more benefits.

Rotary Shaft Seals in Medical Applications

Rotary shaft seals are tasked with retaining media and protecting from outside contamination in the presence of rotating or swiveling motion. In the context of medical devices, sealing solutions are critical for the reliable operation of many different devices in hospitals rooms, treatment centers, operating rooms, and at-home health.

Medical devices that depend on rotary shaft seals include …

  • Tissue cutting tools
  • Biopsy tools
  • Ablation equipment
  • Surgical wash units
  • Surgical equipment
  • Blood pumps
  • Infusion pumps
  • Dialysis equipment
  • Endoscopes
  • Disposable stent handpieces
  • Hospital beds
  • Patient lifts

In each of these devices, the failure of a seal could lead to serious patient injury or even death. There is no room for mistakes in choosing the right seal and appropriate seal material.

Choosing a Sealing Solution for Medical Applications

When choosing a rotary shaft seal for a medical application, there are several key characteristics that must be considered. It is important to take into account the pressures involved, including not only the potential for high pressures but vacuum pressures as well. Temperatures, including operating temperature and the possibility for temperature spikes, are also critical, as well as the type of media, lubricant, and cleaning chemicals the seal will be in contact with. The expected PV value, based on pressure and speed, will also significantly affect the type of seal and material chosen. And no less important is the choice of an appropriate medical grade seal material.

Medical Grade Seal Materials

Medical applications, whether in vitro or not, severely constrain the choice of seal material. Selecting the right material for a seal involves compliance with various national and international regulations along with the properties discussed in the previous section. Medical grade materials are in compliance with the appropriate USP (U.S. Pharmacopeial Convention) standards related to medical materials. 

In the United States, these standards are enforced by the FDA (Food and Drug Administration) but are also used in over 140 other countries. These standards look at both the biological response for materials that either come into direct or indirect contact with medical patients, and medical grade materials are usually USP Class VI compliant. Such materials are believed by the scientific community to significantly reduce the risk of harming a patient due to a reaction to a toxic material.

ASTM International (American Society for Testing and Materials) also has standards that relate to medical devices, including ASTM F1980-16 Standard Guide for Accelerated Aging of Sterile Barrier Systems for Medical Devices. There is also the ISO (International Standards Organization) 10993 standard that focuses on patient safety and may apply to rotary shaft seals depending on their application. 

PTFE Rotary Seals

FlouroSeal PTFE rotary shaft seals offer several advantages over other medical-grade seal materials, including significantly lower friction that means more efficient energy usage, and less heat generation. A smaller coefficient of friction also means reduced breakout friction and a much lower startup torque. The fact that PTFE is self-lubricating means dry running is possible, which is especially beneficial in applications where lubrication can be an issue. 

PTFE has excellent wear characteristics, dimensional stability, and excellent performance even in extreme temperatures (e.g., a continuous operating temperature of 500°F). And because of PTFE’s chemical compatibility and thermal performance, PTFE seals can handle exposure to hot water, steam, and aggressive cleaning chemicals used in sanitation and sterilization procedures. And because PTFE is non-wetting, it can be self-cleaning in some situations.

FlouroSeal PTFE is available in grades that are FDA and USP Class VI compliant, making them an excellent choice for rotary shaft seals used in medical devices. In addition, the type of seal is not limited by using PTFE, either. Not only are PTFE rotary shaft seals available in hydrodynamic, plain, and multi-lip configurations, but they are also available as spring-energized seals.

Limitations of PTFE

PTFE does have its limitations in medical applications. For example, high-energy radiation can cause a breakdown of its molecular structure, making it inadvisable to use in applications that depend on radiation for sterilization. 

It is also important that the shaft meet certain conditions to ensure the longevity and performance of the seal. Most experts recommend a surface finish of 2 and 16 RMS with a Rockwell hardness between 55C and 65C, but this can vary depending on the PTFE additives used.

Conclusion

FDA-approved PTFE medical grade materials are an excellent choice for rotary shaft seals for medical devices. Low friction, chemical compatibility, thermal properties, dry running, and dimensional stability all support its use for even the most demanding medical applications. If you are working on a medical sealing solution, contact the experts here at Advanced EMC. We can help you navigate the various regulations and find a reliable, safe rotary shaft seal.

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