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April 16, 2020

Seal Strength Testing


Empower Others for Success is a key value at PCL in our mission to deliver solutions that enable life-changing medical innovation.  That’s why we appreciate how often our customers reach out to us with questions about package testing and best practices. We welcome the opportunity to help them understand the methods and how to apply them appropriately to improve project outcomes and product quality.

In this blog, we’ll cover seal strength testing – what it is, why it’s important, and how to establish acceptance criteria.


Why do we consider seal strength testing?

It’s important to know how much force is required to open a sterile barrier package.

First, we should consider if the end user has any expectations around how weak or strong the seals should be. When the end-user peels open a package to aseptically present a device, a package that opens too easily may cause that user to question whether the seals were fully intact, and ultimately discard the device for patient safety reasons.  On the flip side, a package that is too difficult to open may result in delamination, tearing, or fracturing upon opening, rendering it impossible to aseptically present the device without contaminating it.

Furthermore, package seals are also responsible for keeping the packaging intact through the rigors of sterilization, distribution, handling, and storage, until the point of use or expiration date. Seals that are too weak may be susceptible to premature opening during transportation (i.e. heavy devices bouncing around in a package may force the seal open from the inside), or long-term storage (i.e. products on a warehouse shelf for months or years), or from other stresses imposed during the finished product’s life cycle.


Seal Strength and the 4 Pillars of Packaging Validation (ISO11607)

Requirements and expectations for seal strength are provided in ANSI/AAMI/ISO11607-1&2:2019 Packaging for Terminally Sterilized Medical Devices, an FDA-recognized consensus standard.  That standard has two parts.  The first part covers design and performance requirements (and related requirements of materials and suppliers), while the second part covers manufacturing and control & monitoring requirements.  To make the content more intuitive, we developed the 4 Pillars of Packaging Validation – Make, Ship, Store, and Use.  From a packaging engineering standpoint, we must consider the demands of all 4 pillars for compliance to ISO11607.

  • In the ‘Make’ pillar, we need to ensure repeatable and reproducible seal quality during production.
  • In the ‘Ship’ + ‘Store’ pillars, we need to ensure that packages maintain integrity of the sterile barrier after transportation and storage (shelf life/aging).
  • At the ‘Use’ pillar, we need to ensure that end-users can effectively open the sterile barrier and present the device with aseptic technique.


Measuring Seal Strength

ASTM F88 (aka “peel strength testing”) is a common seal strength test method. For this test, we take a 1-inch wide cut from the seal, clamp the test specimen into the jaws of our peel test stand, and then use our peel test stand to pull the seal apart. The peel test stand uses a gage to measure the amount of force that is required to peel apart a seal. Typical seal strength is between 1 to 2 pounds per inch, but should be uniquely established for the application.

ASTM F1140 (aka “burst testing”) is another common test that measures seal strength by internally pressurizing a sterile barrier system until it ruptures (a package inflates like a balloon until it pops).  The amount of internal pressure at rupture is recorded.  Note that the burst test method does not give you a way to measure the strength of a particular seal on the package, since all package seals experience the same force until the weakest spot on the weakest seal eventually gives way.  Therefore, care should be taken to consider whether this method is appropriate for your application.


Consider Seal Strength Testing as part of ‘Risk management’

Like any other test, you should consider medical package seal strength during risk management.  What are the consequences of a bad seal being made?  Why would that happen?  What’s the likelihood of that happening?  If it were to happen, would it be identified and contained before there are any consequences? Think through a risk management approach that considers the production environment, performance demands of the packaging system during its lifecycle, and the needs of end-users.


Differing opinions on acceptance criteria

There are different schools of thought on acceptance criteria for peel strength testing.

One school of thought that PCL has used successfully over the last several years is similar to the work of Geoff Pavey with Oliver Healthcare Packaging, who recently has been spearheading an ASTM F.02 committee working group to develop a consensus on this topic.

PCL’s preferred approach is to first optimize your sealing process, then apply process engineering statistics to OQ test data.  Results can be used to calculate a lower-bound and upper-bound specification limit using the one-sided tolerance limit calculation, which takes into account your desired confidence & reliability (allowing you to link it back to your risk assessment). Packages with artificially weak seals may then be created and subjected to transit testing and aging validations, which demonstrate the capability of worse-case packages to maintain integrity.  Likewise, packages for usability studies can be created to match routine conditions or artificial extremes.  Of course, your production PQ study will demonstrate repeatability and reproducibility under expected routine conditions.

In this way, we have used seal strength testing effectively across all 4 Pillars of Packaging Validation!


At the end of the day, it’s all about patient safety

Seal strength testing allows packaging engineers to design packages with desired seal strength, to verify seal strength specifications at different life cycle stages (in production, after sterilization, after transportation, and after long term storage), and to establish control & monitoring programs for quality assurance over time.   Ultimately, seal strength testing is critical to protecting patient safety, by ensuring that products remain sterile until the point of use or expiry date, and that devices may be aseptically opened and dispensed without contamination.  Are you confident in your seal strength data?  Can you rely on those results to make critical project decisions?

Don’t burst in panic, PCL can peel apart the mystery.  Contact us today to talk about your project!

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