Dye Penetration Testing Methods For Porous vs. Nonporous Packaging
Dye penetration test standards, edge dip method, dye injection method, and more are covered in this article.
What is dye penetration testing useful for, and how does it work?
Medical devices and products can be contaminated through packaging leaks. These leaks are often found at small pinholes in the packaging or breaks in the seals between packaging components. Defects in seal channels can be detected via the dye penetration procedures described. Dye penetration tests are qualitative pass/fail tests. Packaging with any indication of a leak will be rejected. Note that dye penetration testing methods can qualitatively verify and locate leakage sites. However, these methods are not quantitative, and the dye penetration test results can’t infer leak size. Dye penetration detection of pinhole and channel leaks relies on capillary action. Capillary action is the tendency for liquids to rise against the force of gravity when in small tubes. Capillary action occurs when the adhesive forces between the liquid and the surface of the tube walls are greater than the cohesive forces between the liquid molecules. An example of capillary action in everyday life is a paper towel’s ability to absorb liquids. Capillary action is also how water is transported through plants. Since a pinhole or channel leak is essentially a tube and the dye penetrant solution has a surface tension less than the surface energy of flexible packaging materials, the dye penetrant will readily wet the surface of the pinhole or channel. The dye penetrant solution does not need to be “pushed” into the channel or hole for leak detection due to capillary action.
What types of packages can be tested with dye penetration, and what are the differences between porous and nonporous packaging materials?
Both transparent and opaque packages can be tested for seal leaks through dye penetration testing for nonporous packaging materials. However, porous dye penetration testing methods can only detect package edge seal leaks between a transparent and porous material. You will not be able to use dye penetration testing on permeable packaging if you do not have at least one transparent material in your packaging system. Both nonporous and porous packages that are fully packaged medical devices, empty packages, or seal edge samples can be tested. Commercial fully packaged and terminally sterilized medical devices are evaluated using dye penetration testing to ensure packaging systems meet FDA package integrity requirements.
What are the dye penetration testing conditions?
For a package to be tested with dye penetration, it must be free of any condensation or liquid water. Water on packaging can obstruct a channel, hole, or potential leak and make these leaks undetectable with a dye penetrant. If any condensation or liquid water is found, the package must be thoroughly dried at its typical storage temperature before testing.
Additionally, dye solutions must have good contrast to the transparent or opaque packaging material. Most commonly, a blue dye such as toluidine blue or Triton X is used. Make sure that your packaging material has good contrast with the dye penetrant used before testing.
How is dye penetration testing for nonporous packaging materials performed?
There are two types of dye application methods for nonporous materials, Method A and Method B. Toluidine blue is the most common dye indicator used for the dye penetrant solution for both methods.
Dye Penetration Test Method A
Method A detects seal channel leaks. Method A can detect and locate leaks equal to or greater than a channel formed by a 50-micrometer wire in the edge seals of a nonporous package. Channel leaks are detected by applying a dye penetrant solution to the seal edge. Allow the dye penetrant solution to contact the seal edge for approximately 5 seconds. Channels can be visually identified within this time. If the package has a transparent side, the seal is examined visually through this side. If the package is opaque, the outside seal edge is placed against an absorbent surface for approximately 5 seconds. Then the absorbent surface is examined for the presence of stains indicating a seal channel leak. During testing, the package is rotated, and each seal edge is tested with the dye penetrant solution.
Dye Penetration Test Method B
Method B detects holes or leaks on package surfaces. Method B can see and locate a leak equal to or greater than 10-micrometers in a nonporous flat sheet. Holes are detected by placing a flat sheet of packaging material onto an absorbent surface. If testing a package, the surface of the package inspected is cut so that the packaging material can lay flat upon the absorbent surface. Common absorbent surfaces used are white chromatography paper, white filter paper, or white paper towels. An uneven spot on the absorbent surface can inhibit consistent contact between the sample and the absorbent surface and interfere with leak detection. Thus, absorbent surfaces and package surfaces must be flat to ensure Method B testing accuracy. After the package and absorbent surface are in contact, a dye penetrant solution is spread across the surface of the package sample. The dye penetrant solution should contact all areas of the package material’s surface. Next, a small roller is used to apply pressure to the sample to ensure adequate contact between the absorbent surface and the bottom surface of the sample being tested. Finally, the flat packaging sheet is carefully removed, and the absorbent surface is inspected for staining from the dye. The presence of a stain indicates a hole or leak.
How is dye penetration testing for porous packaging materials performed?
There are three types of dye application methods. These methods are injection, edge dip, and eyedropper techniques. In all three dye application methods, Toluidine blue is recommended as the dye indicator for the dye penetrant solution.
Dye Injection Method
The first and most common method for dye penetration testing is the dye injection method. In this method, the dye penetrant solution is injected via a hypodermic needle. Flexible tubing is attached to the syringe instead of a needle to prevent accidental puncturing of the packaging material during testing. For the dye injection method, dye solution is injected to cover the longest package edge to a depth of 1/4 inch. Following administration of the dye, the seal area is visually examined through the transparent side of the package. Any channels in the seals will be readily detected within five seconds. This process is then repeated for the remaining sides of the package.
For all dye penetration testing, evaluation of the dye must occur within five seconds of application maximum. The visual examination must be performed within five seconds of dye application, as prolonged exposure of the dye solution on the packaging can result in dye wicking through the porous packaging material. When evaluating package seals, technicians look for penetration of the dye solution across the seal. If penetration occurs, this indicates that there is a leakage in the package.
Edge Dip Method
The second method for dye penetration testing is the edge dip method. The edge dip method differs from the dye injection method. For the edge dip method, a container with a length long enough to accommodate the longest edge of the package seal is selected. A dye solution is then poured up to 1/4 inch in height within this container. If the package tested has excessive material beyond the seal (such as a Chevron style opening), a modification excess material will be removed from the package. Excess material will be cut such that only 1/8 inch of material is remaining from the seal. Once extra material has been removed, an edge of the package under evaluation will be dipped just long enough to wet the entire packaging edge thoroughly. Any seal channels are detected within five seconds. This process is repeated for the remaining sides of the package.
Eyedropper Method
The third and final method for dye penetration testing is the eyedropper method. The eyedropper method differs from both the edge dip and dye injection methods. For the eyedropper method, a package needs to have an unsealed area beyond the outer edge of the seal. Once the unsealed area is confirmed, the eyedropper method can begin. First, a dye solution is poured into an open container. Next, a finger or the end of a paperclip is used to brush back the long edge of the porous material away from the transparent edge. An eyedropper or pipette is then inserted into the dye solution. With the transparent side of the package facing the technician, a bead of dye solution is placed along the top edge of the package between the transparent and porous material. The entire package border is wetted with this dye solution, and the seal is evaluated within five seconds for any leaks. This method is repeated for all sides of the package.
What conditions can cause false positives for dye penetration testing of porous materials?
Wicking, the movement of a liquid into the body of fibrous material, can result in a false-positive result if the dye penetrant solution is left for more than five seconds. Thus, dye penetrant testing technicians must detect seal leaks before the dye wicking into the packaging material. Bending or folding the packaging material can also result in false positives for flexible, porous packaging materials. Some sterilization procedures can alter the hydrostatic head of some porous materials and result in false-positive results. Such hydrostatic head material alteration is known as oxidative sterilization. Check the sensitivity of your packaging materials to modifications following sterilization.
Summary
A dye penetration test is a pass or a fail method of detecting defects in packaging seals. There are two methods of dye penetration testing for nonporous material, Method A and Method B. Method A is used to detect channel leaks in seal edges. In contrast, Method B is used to find holes in the packaging surface. There are three methods of dye penetration testing for porous materials: dye injection method, edge dip, and eyedropper methods. If leakage is detected, a qualitative description or sketch of the leakage site is provided. Overall, dye penetration testing is an important testing parameter to prove the integrity of your medical device packaging. Ensure you choose a contract manufacturing and testing organization capable of providing appropriate package integrity tests, like dye penetration testing, for your unique medical device or medical product.
MycoScience is a contract manufacturing organization specializing in sterile syringe and vial filling. MycoScience also offers Preservative Efficacy Testing, Sterilization Validations, Bioburden Testing, Cleaning Validations, Microbial Aerosol Challenge Testing, 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
American Society for Testing and Materials. Standard Test Method for Detecting Seal Leaks in Porous Medical Packaging by Dye Penetration. West Conshohocken, PA, United States. (ASTM F1929-15).
American Society for Testing and Materials. Standard Test Method for Detecting Leaks in Nonporous Packaging or Flexible Barrier Materials by Dye Penetration. West Conshohocken, PA, United States. (ASTM F3039-15).
