Term package strength testing generally refers the package seal quality. Package strength concerns the force required to separate two components of the package. It could be the force to separate two flexible components of a pouch, or a flexible lid and a thermoform tray or a measure of the compressive force exerted by an elastomeric closure onto a parenteral vial finish after capping. These forces may be measured in pounds per inch width, as in the seal/peel test per ASTM F88; or in pounds per square inch, as in package burst testing methods. Alone, these tests of package strength values do not necessarily prove the integrity of the entire package but serves as a means to characterize and monitor package seal quality.
Routine package strength test programs are:
Package Strength Testing by Burst Testing
The package burst testing is performed by internally pressurizing a test package and applying increased pressure until the package seal(s) burst. The package burst strength test result (reported in pressure units) provides an indication of relative seal strength and evaluates the most likely location and mode of package failure when the package is exposed to a pressure differential. Pressure differentials leading to seal failure may occur during the sterilization processes and transportation (low pressure/high altitude exposure). Package burst tests are performed via ASTM F2054 or ASTM F1140 – or with or without restraining plate fixtures.
Package Seal Strength Testing
Package seal strength testing measures the force required to peel apart two bonded materials – applicable to testing seals between two bonded, flexible materials, for example a pouch or between a flexible material and rigid material in the case of a Tyvek lidded tray. The average force results provide a measure of seal strength between the bonded materials and the results are useful for monitoring the consistency of the sealing process over time – Test method reference is ASTM F88.
Leakage and Torque Testing
Closure application torque should be tested to designate and optimum application range to prevent leakage from loose closures and to prevent component distortion and compromised seals from closure that may have been over-torqued. Application torque degrades over time due to stress relaxation and some closure “back off” that may occur as a function of time and other environmental variables. A properly designed and applied closure will retain sufficient sealing force until the package is opened at the time of use. Closures that back off excessively during shipping, storage, or distribution increase the risk of product leakage and may not meet CPSC standards. Vacuum leakage testing (ASTM D4991) and altitude simulation (ASTM D6653) can assist in the development process. Torque degradation studies (ASTM D2063) can help you assess how much closure retention torque may be lost after exposure to temperature cycling, compression and vibration.
Residual Seal Force Testing
Often performed in conjunction with helium leak testing or vacuum decay leak testing, Residual seal force is not a leak test, but is an indirect measure of the compressive force exerted by the stopper on the vial’s land surface. A consistent and sufficiently significant RSF value provides a useful indicator of capping process consistency. A slow, constant rate of strain is applied to the top of a capped vial and the resistance to compression is monitored and reported. The appropriate amount of compressive force is required to ensure a quality seal. Vials capped at an insufficient force may leak from the sealing surface. On the other hand, vials capped at an excessive force may experience cracking and bulging, also risking the integrity of the closure system.
This nondestructive test check seal quality by passing an ultrasound signal through a sealed area of the package. Poorly sealed areas do not transmit as much ultrasonic energy as properly sealed areas- this technology can be used to check for the presence and location of seal defects such as incomplete seals, channels, wrinkles, seal contaminants or weak bonds.
Regardless of sterile medical device or a parenteral drug product, package integrity should be reevaluated when changes are required in package design, package materials, or manufacturing /processing conditions.
Package Strength Testing of Medical Devices
In order to consistently produce packaging capable of protecting its contents throughout the stated shelf life, it is important to evaluate the strength characteristic. Not only does strength play a key role in a shelf life package validation, but it also allows the medical device manufacturer to determine the consistency of their sealing process and adherence to design specifications.
There is occasional confusion regarding the differences between a package’s strength versus the integrity of a package. Package strength relates to the force required to separate two components of the package such as the force required to separate two flexible components of a pouch or the force required to separate a flexible lid from a thermoformed tray. These forces are commonly measured in pounds of force per inch width, as in the seal/peel test; or in pounds per square inch, as in the burst test method. Alone, package strength values do not necessarily prove the integrity of the entire package. As an example, while a seal strength measurement may be within the design specification that same seal may have a channel leak that would be found using dye leak testing indicating a breach in package integrity. It is the combination of strength and integrity testing that proves out the ability of a package to do its intended job. The main cause for failing package strength testing is the sealing parameters. If a proper process validation of the sealer is not performed, then the medical device manufacturer can expect failure during strength testing.
ASTM Test Standards for Packaging Strength
ASTM D3330 – Package Strength Testing by Peel Adhesion Testing
ASTM F88 – Package Strength Testing by Seal Peel Testing
ASTM F1140 – Package Strength Testing by Burst Testing