by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Spring-Energized Seals for the Medical Industry

Spring-energized seals, when designed correctly, provide a highly-reliable sealing solution for medical applications where failure can be fatal. Selecting the right seal jacket material and energizer is critical, but also complex. In this week’s blog post, we will discuss spring-energized seals in the medical industry, the best materials, how they are used, and more!

Spring-Energized Seals in the Medical Industry

Spring-energized seals are regularly used in equipment that involves rotary motion, including a variety of surgical instruments such as high- and low-speed handpieces, surgical saws, bone shavers, oscillating saws, and bone drills.  They are also seen in rotary catheter systems, centrifuges, and both small motors and small pumps. 

Reciprocating equipment also may require spring-energized energized seals, with typical applications including respirators, oxygen compressors, dialysis machines, syringe pumps, and blood analysis equipment. In addition, spring-energized seals work exceptionally well in cryogenic applications.

How Spring-Energized Seals Work

A spring-energized seal makes use of an energizer, most often in the form of a spring, to enable the seal lip to stay in contact with the mating surface. For high pressure applications, the pressure of the media is usually able to keep the seal lip in contact with the mating surface and the springer-energizer then takes over for high pressures. On the other hand, when used in applications involving low pressures, the spring-energizer is responsible for keeping the seal lip in contact with the sealing surface at all times. 

Seal Jacket Materials

There is a wide variety of seal jacket materials that can be used, but the choices are significantly limited for medical applications. The materials used must be FDA, USP Class VI, and ISO 10993-5 compliant. This significantly limits what materials can be used for the polymer jacket. The three most common choices are these: UHMW PE, PTFE, and PEEK.

UHMW PE

UHMW PE (Ultra High Molecular Weight Polyethylene) is a high-performance engineering polymer that possess the following characteristics:

  • Low coefficient of friction
  • Good chemical compatibility
  • Low moisture absorption
  • Good dimensional stability
  • Good operating temperature range up to 180°F
  • Can withstand extended exposure to hot water and steam
  • Self-lubricating

In addition, it exhibits excellent wear and abrasion resistance. UHMW PE is also known for its high purity and is also commonly used in orthopedic implants, in part because of its strength and toughness.

PTFE

PTFE (Polytetrafluoroethylene), often referred to as Teflon, has the following properties:

  • Extremely low coefficient of friction
  • Excellent chemical compatibility
  • Good dimensional stability
  • No moisture absorption
  • Excellent operating temperature range up to 450°F
  • Self-lubricating
  • Can withstand extended exposure to hot water and steam
  • Low cost

The primary weakness of virgin PTFE is its wear resistance, making it best adapted to light-service duty applications. However, wear resistance can be significantly improved through mineral additives.

PEEK

PEEK (polyether ether ketone) offers these properties:

  • Extremely low coefficient of friction
  • Excellent chemical compatibility
  • Moderate moisture absorption
  • Good dimensional stability
  • Wide operating temperature range up to 480°F
  • Self-lubricating
  • Can withstand extended exposure to hot water and steam

It is also extremely tough, abrasion resistant, and known for its outstanding heat resistance. In addition, PEEK is also used quite often in medical implants because of its biocompatibility, stiffness, strength, and toughness. 

Spring Energizers

Spring energizer materials are either metal or elastomeric, with metal being the most common. For medical applications, the three most commonly used metals for the spring energizers are stainless steel, Elgiloy, and Hastelloy.

Metal energizers are ideal for several reasons, with the first being their natural stiffness. They also work well in applications that involve autoclaving because of their thermal characteristics and contribution to maintaining the shape of the seal jacket. In addition, a metal spring helps to dissipate heat, reducing the potential effects of thermal deformation in the seal jacket. 

In the medical industry, the energizing spring will fall into one of these categories: canted coil, helical, or cantilever. Because spring loads can be customized, canted coil springs (also known as slanted coil springs) can serve in a variety of operating conditions. Heavy force canted coil springs perform extremely well in high pressure applications but may experience more wear than other configurations. Springs designed to provide more of a light force are ideal for high-speed applications but should not be used in cryogenic environments or with vacuum pressures.

In general, helical springs for medical applications involving cryogenic temperatures, vacuum pressures, and high pressures with only moderate wear, but are not recommended for high speed applications. Helical springs work extremely well on seals interacting with lightweight gases or fluids.

Cantilever springs offer excellent performance in vacuum pressure conditions but, as with helical springs, should not be used in high speed applications. However, a high degree of wear is to be expected. And, because the energizing force will be concentrated at the very front of the seal, they work extremely well for scraping and exclusion applications. 

Choosing the Right Spring-Energized Seal 

Dynamic sealing solutions for medical applications can prove extremely tricky for several reasons. For example, seals can be exposed to a variety of fluids and media, which can include bodily fluids and materials such as adipose, hemoglobin, proteins, carbohydrates, and general bioburden. For such applications, PTFE with its natural hydrophobic properties is an excellent option.

For seals which may be exposed to abrasive materials such as bone shavings, wear and abrasion resistant polymers such as UHMW PE and PEEK work very well, although there are FDA-approved fillers for PTFE that can enhance its wear properties. 

Cleaning, sterilization, and disinfection are critical factors in deciding on an appropriate sealing solution. Sterilization in particular is the most aggressive of the tree, and may involve the use of autoclaves (also known as steam sterilizers) that require elevated temperatures and pressures. There are other methods, such as dry heat, plasma gas, VHP (Vaporized Hydrogen Peroxide), and chemical sterilization. 

Chemical sterilization may use bleach, ozone, hydrogen peroxide, or EtO (ethylene oxide). While all three materials have good chemical neutrality and handle heat quite well, warpage may occur due to residual stresses and should be considered when developing the seal jacket molding process. 

There may also be issues with the use of lubricants, therefore many medical sealing applications require the use of a self-lubricating material of which PTFE, UHMW PE, and PEEK all qualify. However, for the lowest coefficient of friction and least slip-stick behavior or startup torque, PTFE is optimal.

Conclusion

Many different factors go into choosing the right spring-energized seal for a mission-critical medical application, and engineers must consider factors such as pressure, sterilization methods, lubricants, chemical compatibility, wear, and other. There are, however, proven sealing solutions for medical industry applications.

If you need a reliable seal for  the complex environment of a medical application, contact the sealing group at Advanced EMC. We can put our years of experience in polymers, spring energizers, and mission critical sealing solutions to work for you. Contact us today!

by Jackie Johnson Jackie Johnson No Comments

A Growing Medical Market

There are many factors that contribute to the rapidly growing medical plastics market. There is an increased demand for advanced medical devices, a rise in disposable income and changing lifestyles, and a demand for affordable and efficient healthcare systems.

These and more are currently driving the medical market, with a current estimated net worth of 22.8 billion USD.

And it is only growing.

Experts suggest that by 2024, the market will grow to a whopping 31.7 billion, with a CAGR of 6.8%.

Medical Plastics Market

Source: Markets and Markets, Medical Plastics Market

Applications of Medical Grade Plastics

Plastic packaging is widespread across many industries, but no more so than in the medical field. Within the next few years, packaging is expected to grow at a CAGR of 7.8%, due to the increased use in pharmaceutical packaging, device packaging, and more.

Surprisingly though, it is devices such as medical implants and machinery that are generating the largest revenue and driving the industry forward. A perfect storm of an ever-growing population and an increase in chronic diseases, along with the lower manufacturing cost of these devices has led to the largest growth in the medical plastics industry.

Global medical polymers market

Source: Grand View Research, Medical Polymers Market Size

An Industry Standard

Since the 1980s plastics have dominated the medical device industry on account of their low manufacturing cost, flexibility, ease of replacement, and low risk of infection.

Plastics also provide radiolucency, enable light-weighting, and reduce stress-shielding. Because they are radiolucent, polymer-based surgical devices allow surgeons to have an unobstructed view.

All these combine to make medical-grade plastics the gold standard in the industry. Which in turn creates a very lucrative market.

In Conclusion

The medical-grade plastic industry has taken off in an incredibly short amount of time. With increasingly easy to manufacture products coupled with an ever-expanding market, the industry will only get bigger over time. Want to learn more? Contact us today! 

 

by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Medical Engineering in the Age of COVID-19

Medical Engineering in the Age of COVID-19

Due to the COVID-19 pandemic, there has been an increase in worldwide demand for thermal scanners, respirators, and ventilators. This has been accompanied by an increased need for medical disposables such as gloves, respirators, medical masks, face shields, single-use syringes, and drapes. As a result, medical engineering and manufacturing both have temporarily shifted their focus and the results are fascinating.

3D printed hand sanitizer clasp

Additive Manufacturing

Shortages of some items have led to innovative design and manufacturing, much of it involving additive manufacturing using polymer materials. For example, Old Dominion University has been 3D printing masks and mask components made from PLA and designed so that they can be easily sterilized and reused. Europe has already seen companies in the 3D printing industry volunteer their equipment and knowledge to aid in manufacturing replacement parts for critical equipment such as oxygen and respirator valves, and many other countries are doing the same thing. 

Ventilator Designs

Many countries, including the United States, are worried about a potentially deadly shortage of ventilators. Various technology firms worldwide such as Nvidia are working to design critical care devices that can be produced both quickly and inexpensively. NASA has been given permission to start production of their emergency use ventilator that can be manufactured and built quickly, with the only drawback being its limited lifespan. 

In addition, ventilator manufacturers such as Medtronic have ramped up production and publicly shared their design specifications for one of their ventilator models so others can help meet this critical need.

Innovation

Engineers all over the world are looking for ways to make the treatment of COVID-19 patients easier and safer for medical personnel. For example, engineers in the Boston area have teamed up local doctors to develop a 3D printed bracket that will hold the tube and respirator hookup together in ventilator patients. The goal is to prevent release of the COVID-19 virus into air when these connections come undone, as they often do. 

Others at Boston University are looking at polymer nasal swabs that will do a better job of collecting mucus for COVID-19 tests, which could increase the reliability of testing and help with testing material shortages. At the Oxford Institute of Biomedical Engineering, engineers are leveraging wearable technology to allow nurses to track the vitals of COVID-19 patients who are not on ventilators and thus must remain mobile to recover.

Conclusion

The COVID-19 pandemic has changed how much of the world lives, and has affected a shift in the focus of many engineers. Trademarks of this shift include the use of additive manufacturing for PPE and replacement parts for life-saving equipment, a fresh look at ventilator designs that emphasizes manufacturability and availability, and the birth of innovative approaches to medical issues related to the pandemic. And, in this midst of this, companies like Advanced EMC are still working hard to make available the right polymer seals and bearings needed for medical equipment.