In-depth knowledge of pack-testing standards and packaging materials is essential when developing packaging for medical devices, kits and other products that require sterilization.

“SPMC Learning Tools: A Guide to Gels and Sterile Barrier Integrity Measures,” a webinar sponsored by the Sterilization Packaging Manufacturers Council (SPMC), offers packaging engineers a close look at polymeric gels (film imperfections) and package integrity testing for medical applications.

This Packaging Digest webinar, which captures the information in two SPMC white papers—Package Integrity Testing and Polymeric Gels in Flexible Medical Device Packaging—was broadcast live in September 2019 by Informa Markets and will be available online until Sept. 11, 2020. Click here to register for the one-hour, view-on-demand webinar.

In the webinar, speaker Henk Blom, vp of research and technology at Paxxus, defines a gel as “a visible dome-shaped imperfection in the film matrix due to the embedding of an incompatible material” (per “Polyethylene Gels: A Primer” by N. Aubee, R. Saetre and T. Tikuisis, TAPPI 2006).

Blom describes three varieties of gels—unmelt/mixing gels, cross-linked and oxidized gels, and cross-contamination gels—with attention to common causes of each type and how to identify the various gels.

In addition, Blom provides an update on “ASTM D7310-11 Standard Guide for Defect Detection and Rating of Plastic Films Using Optical Sensors,” which is under review by a multidisciplinary group comprising resin suppliers, extrusion equipment suppliers, optical equipment companies and others. The proposed revision to the standard is available from ASTM (WK67177).

Bill Cassidy, product development manager at Amcor, provides further education on gels. He explores package integrity concerns, including gels in the context of weld seals, peelable seals, form-fill-seal and surface printing.

The webinar segues to package integrity testing, with Chetan Joshi, process engineer at Technipaq, addressing package integrity versus seal strength. Joshi notes that theses are two distinct package attributes, and that a package with acceptable seal strength may still fail integrity testing if it has a seal channel or a pinhole in its material.

Joshi also highlights the necessity of maintaining sterility of the device in the package until the point of use and the role of package integrity in assuring patient safety. He explains how porous and nonporous materials prevent microbial contamination: Porous microbial barriers create a “tortuous path” that allows air to enter the package but filters microbes, and nonporous microbial barriers block air that may carry microbes into the package.

The final portion of the webinar, presented by Ryan Killing, new product engineer at PPC Flexible Packaging,provides a guide to package integrity test methods, including dye, bubble emission (submersion), visual, vacuum decay and trace gas testing.

This portion of the webinar provides tables with descriptions and key points about a range of ASTM methods for testing seal integrity and whole package integrity. A Text Method Selection matrix depicts which test methods are appropriate for porous material, nonporous material, rigid trays, flexible packaging, clear material and opaque material.

At the conclusion of the live webinar, the speakers fielded questions from attendees. This Q&A, edited for clarity and brevity, is presented below.

Do gels create a high risk of contamination in an automated system of transport on conveyors, lifts, packaging and transportation?

Cassidy: No, they do not increase risk of contamination. The gels are completely embedded in the polyolefin film, so there’d be no increased risk. In fact, if you were to take your fingernail and try to remove it, you’d find that the gel is completely embedded in the film.

How do porous packages block microbes?

Joshi: Porous packaging materials act as filters for microbes. There are three mechanisms by which filtration occurs. These are: interception, inertial impaction and diffusion. You can read up more on these three mechanisms in the SPMC white paper [Package Integrity Testing], which is on the SPMC website now.

Do gels continue to form after a film is wound into a roll and put in storage?

Cassidy: The answer to that question also is no. As a result of the extrusion process, the amount of gels and the gel size produced as the result of that process is basically final. Regardless of how long you keep the roll in storage or pouches in storage, temperature and humidity are completely independent. So no, the gel size and frequencies will remain the same over time.

Do resin pellets have gels, or does that only happen when extruded into a thin film?

Blom: That’s a very good question. Resin pellets themselves can have gels in them, so this would obviously happen at the resin manufacturer level, and you could create additional gels during the extrusion process. So if the resin came with gels, and your resin extrusion process wasn’t optimized, you could in fact create more gels. But very often, the resins are clean from gels, and most often they are created during the extrusion process, although not exclusively.

How do I get more information on these tests without having to buy each standard?

Blom: That’s a great question, as well. You saw a partial list of test methods, as Ryan was going through some of those. There are more. The easiest way to get all of them is to become a member of ASTM and to join Committee F02. As part of your membership in ASTM, you get free access to one of the standards books, and the standard book that you would be looking for is ASTM Volume 15.10.That book has all of the test methods that ASTM F02 has oversight for and monitors and keeps current.

How does folding Tyvek cause failures in integrity testing?

Killing: Bending or folding of Tyvek can cause separation of the fibers. The microbial barrier is still there, but the pressure from the bubble test will easily allow the air to escape and represent a hole. It’s not because there’s an integrity breach, but the fibers themselves have separated, so the fluid or the air can escape. So it’s beneficial, as much as possible, to not stress the Tyvek.

Where is ASTM F1140?

Joshi: ASTM F1140 is the test method for burst strength testing, and again that is a seal strength test method. So the burst strength method does not assess package integrity. It is similar to peel strength testing. Peel strength testing gives an idea of strength in that sample or in a localized area. Burst strength testing gives us an idea of seal strength around the package, but it does not assess integrity failures, like seal channels or pinholes.

Does the white paper also provide guidance on selection of appropriate seal strength tests?

Blom: The white papers that we created do not address that question specifically. There is an ASTM task group that is addressing that question right now. It was generated around the question of where did the one-pound minimum peel strength come from? Geoff Pavey, from Oliver-Tolas, and a large group of others in the industry are dealing with that right now.