Top 5 Seal Quality Tests For Sterile Packaging
What is package integrity?
A package is a wrapped object or group of objects. The state of integrity is a state of being whole and undivided. Thus, package integrity testing has to do with testing how well a package stays complete and undivided to keep wrapped objects protected and sterile. In the context of package integrity and package integrity testing, a product package is considered both the product packaging itself and the product’s contents. Package integrity and container-closure integrity are terms that are used interchangeably. These terms are the same, depending upon the definition of container-closure integrity. In the past, container–closure integrity referred to a package that had passed or could pass a microbiological challenge test. Package integrity and container-closure integrity are synonymous under the USP 1207 definition of container-closure integrity. The USP 1207 guidance defines container–closure integrity as the absence of package leaks that risk product quality. In other words, the package is intact such that any small leaks of concern are absent. Medical device package integrity testing and package integrity testing standards for assessments such as the ASTM peel test and residual seal force test are covered in this article. Learn what are seal quality tests and more!
What are package seal quality tests, and how do they relate to leak tests?
Package seal quality tests are benchmarks used to characterize and monitor the quality and consistency of various package seals. Examples of seal quality benchmarks include seal attributes (e.g., burst force), package component assembly parameters (e.g., application force). These benchmarks provide quantitative assurance of a packaging seal’s ability to protect its contents. However, these quantitative benchmarks do not guarantee or prove package integrity. Indeed, a package that meets seal quality requirements can have leak defects in package areas other than the seal when assessed. For example, a plastic bottle that meets seal quality closure tests may have a puncture within a thin area of the bottle’s neck that allows product leakage. Alternatively, packaging that meets initial leak tests may later develop seal defects that result in product contamination before use. For example, a poorly assembled container that fails seal quality testing could pass leak tests at the time of product manufacture and develop leaks later before reaching the end-user. Thus, seal quality testing (like ASTM peel testing) is not the same as leak testing, and both sets of tests must be performed to ensure package integrity testing standards are met.
What tests are useful for package seal quality characterization and monitoring?
The following five tests are used to determine seal quality package integrity testing standards are met for various product packaging types and assemblies.
#1: Closure Application Torque Test
Torque is a force created through rotational movement. The closure application torque test applies to medical device, cosmetic, or pharmaceutical packaging that utilizes containers with a screw-thread cap. Closure torque testing measures two torque forces. The first force is the torque exerted when threading the cap onto the product container. The second force measured is the torque required to start screw-cap removal. Common medical products that require closure application torque testing are eyedrops. The torque needed for threading caps is kept within an optimal range to prevent leakage from loose caps or thread distortion from over-torqued caps. The cap removal forces are lower than cap closure forces because of material stress relaxation over time. However, cap removal forces must be strong enough to prevent excessive stress-relaxation during shipping, storage, or distribution to prevent product contamination and leakage. A properly designed screw-thread caps retain their sealing force until the time of product use. Multiple-dose packages have additional cap seal requirements. Indeed, cap design, opening forces, and reclosure forces must protect the product after repeated cap openings and closures. Closure application torque testing is performed with automated equipment that locks the bottle and cap into fixtures and applies and removes caps at uniform speeds. Closure application torque testing is only needed to ensure package integrity testing standards are met for capped packages.
#2: Package Burst Test
Package burst testing can assess the package integrity testing standards are met for flexible bags and pouches formed by heat-sealing processes. Burst testing is simple and involves inserting a pressure source into the flexible packaging under test. Then pressure is applied until the package’s seal breaks. Package burst strength testing reveals the most likely location for package failure and the pressure at which seal failure occurs when a package is exposed to a pressure differential. However, burst testing cannot measure package seal uniformity. This test is particularly crucial for packages exposed to sterilization under differential pressure and packages that will be shipped through air transport or transport at high altitudes. Package burst tests are described in ASTM F2054 and ASTM F1140. ASTM F2054 burst testing uses a restraining plate to limit package expansion during inflation, while ASTM F1140 uses no restraints. ASTM F1140 better simulates pressures experienced by the package during a typical sterilization cycle or product shipment. However, the weakest area of the packaging seal can only be revealed using a restraining plate, as this ensures that the stress is uniformly applied to all seal areas. Factors that can influence burst test results include the package’s inflation rate and the detection limits of pressure-sensing mechanisms.
#3 Package Seal Strength Test (Peel Test)
Seal strength, also known as peel strength, measures the force needed to peel apart two bonded packaging surfaces. Seal strength testing (ASTM peel testing) is useful for packages with two bonded flexible surfaces (e.g., a pouch or bag) or between a flexible material and a rigid material (e.g., a lidded tray). ASTM peel tests provide the maximum seal force needed to open the seal and an average seal force. Package seal strength results are used to provide a measure of seal quality and monitor packaging assembly consistency over time. Stress-strain instrumentation set to extension force mode is used to measure seal strength. Factors that influence ASTM peel test results include the peel angle, the pull direction, and the pull speed. Additional information on ASTM F88 steal strength testing can be found here.
#4: Residual Seal Force (RSF) Test
RSF tests are essential for filled vials of all dimensions. Residual seal force (RSF) testing indirectly measures the compressive force of an elastomeric closure on a glass or plastic vial. This elastomeric closure force indicates vial capping consistency and closure pressure. Indeed, a more tightly capped vial yields a higher RSF value. A stress-strain instrument set to compression force is used for RSF testing. In this test, a metal tool called a cap anvil fits on top of the sealed vial package. Then a constant compressive strain is exerted onto the anvil to create a plot of elastomeric closure stress as a function of time (or compressive distance). The residual seal force test value (reported in newtons or pound-force units) is the point in the stress-response curve immediately before the end of the graph’s slope change. Factors that influence RSF test results include cap anvil design, test compression rate, the elastomeric closure’s viscoelastic properties, and the elastomeric closure’s dimensions. Testing is most consistent if any plastic tops over the elastomeric vial closures are removed before assessment.
#5: Airborne Ultrasound Test
Flexible pouch seals and rigid tray seals made of metallic or plastic laminates can be airborne ultrasound tested. An airborne ultrasound test checks seal quality by passing an ultrasound signal through a package’s seal. Poorly sealed areas in a package will not transmit as much ultrasonic energy as well sealed areas. The presence and location of seal defects such as seal channels, wrinkles, incompletions, and bond weaknesses can be identified with airborne ultrasound testing. Airborne ultrasound testing is noncontact and does not require package preparation or a coupling media (such as a gel). As a result, airborne ultrasound is utilized to assess seals during and outside of manufacturing processes. Airborne ultrasound testing systems utilize transducers to capture the intensity of the signal that passes through an air gap and the package seal under test. Factors influencing airborne ultrasound test results include package material construction, seal structure (e.g., smooth versus textured surface), ultrasound scanning speed, and ultrasound scanning signal strength. Additional information on the airborne ultrasound method can be found in ASTM F3004.
Summary
Overall, package integrity testing has to do with testing how well a package stays complete and undivided to keep wrapped objects protected and sterile. In the context of package integrity and package integrity testing, a product package is considered both the product packaging itself and the contents of the product. Package seal quality tests are benchmarks used to characterize and monitor the quality and consistency of various package seals. Seal quality testing is not the same as leak testing, and both sets of tests must be performed to fully evaluate and ensure package integrity. The top five tests used to assess seal quality are closure application torque testing, package burst testing, package seal strength testing (peel testing), residual seal force (RSF) testing, and airborne ultrasound testing. Seal quality test selection is based on the type of product packaging used. All in all, ensure you choose a contract manufacturing organization that can support you with appropriate package integrity testing for your unique medical, parenteral, or cosmetic product needs.
MycoScience is a contract manufacturing organization specializing in Preservative Efficacy Testing and Microbial Aerosol Challenge Testing. MycoScience also offers Sterilization Validations, Bioburden Testing, Cleaning Validations, Accelerated Aging, Microbiology Testing, Cytotoxicity Testing, Bacterial Endotoxin Testing, EO Residual Testing, Package Integrity Testing & Environmental Monitoring services medical devices and allied industries. MycoScience is an ISO 13485 certified facility.
References
Michael J. Akers. Sterile Drug Products Formulation, Packaging, Manufacture, and Quality. Drugs and the Pharmaceutical Sciences. Informa Healthcare. 2010.
United States Pharmacopeial Convention. <1207> Package Integrity Evaluation- Sterile Products. Rockville, MD, USA. 2021. (USPC <1207>).
United States Pharmacopeial Convention. <1207.3> Package Seal Quality Test Technologies. Rockville, MD, USA. 2021. (USPC <1207.3>).
