by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Dynamic Sealing Solutions for Implantable Medical Devices

According to Coherent Market Insights, the US market for implantable medical devices is estimated to be valued at $23.07 billion and reach  $35.38 billion by 2033. In particular, high-demand areas include orthopedic, cardiovascular, and neurostimulation devices. Many of these devices require seals that can perform in wet, dynamic, corrosive environments for millions of cycles. In addition, these seals must maintain patient safety, device longevity, and device reliability. 

In this blog post, we explore polymer solutions for implantable medical device sealing by reviewing commonly used polymers in medical applications and discussing how to choose the right one for this purpose. 

Implantable Medical Devices

Polymers are used in a wide range of medical devices, from insulin pumps and drug delivery to artificial hearts and blood pumps to implantable electronics. And in each case, it is not enough that an approved material is used, but that the most suitable polymer is used. And this is true of lip seals, o-rings, gaskets, diaphragms, backup rings, and spring-energized seals.

Materials for Medical Implant Seals

For a material to be considered for use in implants, it must comply with these standards:

  • USP Class VI — Requires three in vivo tests: a systemic injection test, an intracutaneous test, and an implantation test where material is implanted into rabbit muscle tissue and observed after 7 days. 
  • ISO 10993-5 — Cytotoxicity testing (in vitro cell testing, separate from USP Class VI)
  • ISO 10993-1 — Full biocompatibility risk assessment framework recognized by the FDA

While a number of materials are used in implantable devices, certain polymers stand out as particularly effective.

PTFE Seals for Implantable Devices

PTFE (Polytetrafluoroethylene) is well known for its chemical resistance, biocompatibility, self-lubrication, and extremely low coefficient of friction. Virgin/Unfilled PTFE (USP Class VI grade) is often the first choice, but pure PTFE has high creep under compression. Creep limits its usability in dynamic sealing applications. There are specific FDA-approved (meeting 21 CFR 177.1550) PTFE blends that exhibit excellent wear resistance in aqueous media and excellent performance when used as part of an implantable device. There are PTFE-filled compounds that are USP Class VI and ISO 10993-5 compliant for use in short and long-term implantable devices including pumps and catheters. 

PTFE is suitable for long-term implants and is widely used as the jacket material in spring-energized seals, and it works extremely well in dynamic applications with low loads.  It also has a lower wear-debris risk than other polymers. It does have its drawbacks, however. It will degrade when exposed to gamma radiation, making gamma sterilization impossible, but it can be used with EtO (Ethylene Oxide) sterilization. PTFE’s use in high-pressure sealing applications is limited, and it has low wear resistance unless a filled grade is used. 

UHMW-PE Seals for Implantable Devices

UHMW PE (Ultra-High Molecular Weight Polyethylene) can be another option. In fact, it has been used in orthopedic applications (like joint replacements and spinal discs) for over 30 years. FDA-approved UHMW PE is known for its low friction and excellent impact strength, although it lacks high load-bearing capacity. It has moderate creep resistance, an advantage over PTFE, and can handle Gamma sterilization with oxidation management. In addition, it has about 4x the wear resistance of PTFE. Unlike PTFE, it can be sterilized using EtO and gas plasma. It works moderately well with high-pressure sealing applications, but the variety of filled grades is limited. It does work well in dynamic applications with moderate pressure.

PEEK Seals for Implantable Devices

PEEK (Polyether ether ketone) offers high compression strength, self-lubrication, and low friction can be achieved with the use of certain fillers (e.g., carbon fiber or graphite). It also offers excellent creep resistance, very high wear resistance, and a low risk of wear debris. PEEK is fully compatible with autoclave and EtO sterilization and is well adapted to high-pressure sealing. It is primarily used for static seals that are high-load and long-duration, but also works extremely well for dynamic seals (especially reciprocating motion),

Choosing the Right Material for an Implantable Medical Device Seal

Medical implant seal experts recommend PTFE when friction is the primary design constraint, which is often the case in low-power motors, fine rotary seals, or applications requiring the softest possible lip contact. UHMWPE is the preferred option when wear life is critical and gamma sterilization is required, particularly in reciprocating or slow rotary applications. Finally, PEEK (especially carbon-filled) works extremely well when there is a need for maximum creep resistance for long-duration implantation, high contact pressures, or sterilization flexibility across all methods.

Conclusion and the Future of Medical Seals

Whether protecting critical electronics or ensuring a drug pump never leaks, specialized polymer seals are vital to medical engineering. If you are evaluating options for sealing solutions for implantable medical devices, contact Advanced EMC today and speak with one of our experts.

Spring Energized PTFE Seal composite bushings
by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

How Self-Lubricating Plain Polymer Bearings Keep Equipment Running Without Oil

Conventional bearings seize when oil runs out, but there are engineering polymer bearings that do not seize, nor do they experience stick-slip behavior. Where oil-free operation is required (e.g., food processing, pharma, wet/submerged environments), self-lubricating, high-performance polymers are the solution. This blog post discusses self-lubricating polymer plain bearings, including how they work, what the best naturally self-lubricating polymer options are, and how to select the right material.

The Problem with Conventional Lubrication

When the oil film fails at the contact surface, serious issues begin to develop for plain bearings, including adhesive wear, heat buildup, and seizure. The cost of failure of plain bearings is expensive and includes not only the cost of repairs but also unplanned downtime, contamination, and potential compliance risks. And while lubrication is necessary, there are some industries where adding lubrication to a bearing is simply impractical. These include food and beverage (NSF H1 and FDA), cleanrooms, and underwater applications. 

How Self-Lubricating Polymer Bearings Work

The core mechanism of self-lubricating bearings lies in the natural self-lubricating nature of the polymer (such as PTFE, UHMW-PE, and POM). There are two phases to the self-lubricating process: the run-in phase and the steady-state phase.

The Run-In (Break-In) Phase: When a new polymer bearing is installed, the metal shaft, no matter how highly polished it may be, has microscopic peaks and valleys called asperities. When the shaft begins to rotate against the bearing under a load, these asperities act like microscopic sandpaper. The asperities shear off a very thin layer of the polymer, and during this phase, the wear rate and friction are slightly higher. The image below shows an example of the asperities and their interaction with the lubricant film using PTFE as an example.

Steady-State Phase: The sheared polymer debris do not disappear. Rather, they get compacted into the valleys of the metal shaft’s surface. This process creates the transfer film. Once this film is fully established, the bearing is no longer rubbing against metal. Instead, it is rubbing against a thin layer of its own polymer material. Because polymer-on-polymer friction is exceptionally low, the wear rate drops dramatically, and the bearing can operate indefinitely without a need for external grease or oil, continuously replenishing the film as needed.

Key Polymer Materials (~150 words)

There are several polymers that have inherent self-lubricating properties due to their molecular structure, with no fillers or additives needed. Four of them are commonly used for plain bearings.

PTFE (Polytetrafluoroethylene)

PTFE has a fluorine-carbon backbone with extremely weak intermolecular forces, giving it one of the lowest coefficients of friction of any solid material (μ ≈ 0.04–0.10). The downside of PTFE for bearings tends to be its poor wear resistance, low load capacity, and tendency to creep in its pure form. However, it is available as a bearing-grade polymer that possesses additives to enhance the strength, stiffness, and wear of unfilled PTFE without sacrificing its low friction and natural lubricity. These fillers include carbon fiber, bronze, and graphite.

UHMWPE (Ultra-High Molecular Weight Polyethylene)

UHMWPE is heavily used in extreme bearing, wear pad, and sliding applications in its virgin, unfilled state. While cross-linked or oil-filled versions exist for specialty uses, its natural abrasion resistance is so remarkably high that it rarely needs compounding to function as a heavy-duty wear surface. Its low friction, excellent toughness, and good wear resistance make it an excellent choice for ebarings, and it is widely used in food processing and orthopedic implants.

Bearing-Grade POM (Acetal/Delrin)

Bearing-grade POM is naturally slippery because of its smooth, crystalline surface and low surface energy. While it is not as low-friction as PTFE, it does offer better dimensional stability and is load-capable without any additives. Virgin POM is hard, slick, and makes an excellent light-duty bearing, but at higher speeds or loads, it can generate excess heat or squeal (caused by slip-stick). The most common bearing-grade acetal has about 10-20% PTFE fibers as an additive. These fibers effectively smear across the contact surface during operation. This further lowers the coefficient of friction and increases the limiting PV  value associated with virgin acetal.

Real-World Payoff

Using a self-lubricating plain polymer bearing eliminates the need for re-lubrication intervals, which leads to significant labor and downtime savings. In addition, self-lubricating bearings pose no issues with lubricant contamination, having a direct impact on product quality as well as compliance benefits. In addition, these beatings result in an extended service life in wet, abrasive, or chemically aggressive environments where oil-lubricated bearings fail rapidly. In fact, as an example, consider a conveyor bushing in a food plant. The voice of a lubrication-free bearing means operation exceeds the service life of traditional greased bronze bearings by 3x.

Conclusion

Self-lubricated plain bearings are a proven engineering solution to bearing lubrication issues, not a compromise. The combination of the right material with correct design and proper run-in can provide you with reliable oil-free operation. Advanced EMC encourages you to evaluate your highest-maintenance lubrication points as retrofit candidates for replacement with self-lubricating solutions. For more information on self-lubricating bearings, contact us today!