Package Testing: A Touchy Subject
Device manufacturers are finding the task of choosing the right leak-testing equipment to be a difficult one.
William Leventon, Contributing Editor
Medical device packagers are showing a demand for sensitive, and in some cases, hypersensitive, leak-testing equipment. Even though the industry offers many options in leak-testing equipment, there is little guidance on how to choose the right one.
"Medical device packagers usually want to detect the smallest hole possible," reports Stephen Franks, executive vice president of T.M. Electronics Inc. (Worcester, MA), which manufactures pressure-decay and mass-flow test instrumentation.
The demand for very sensitive test equipment comes from "companies wanting to be overprotected. In case something goes wrong, they don't want to have any liability issues," says J. P. DeLuca, director of helium leak detection for Alcatel Vacuum Products Inc. (Hingham, MA).
In response to this need, advertisements trumpet the sensitivity of various types of leak-testing equipment. But as device packagers consider the alternatives, how do they know how much sensitivity is enough and how much is overkill? According to those involved in package integrity testing, it may be a mistake to think that more sensitivity means more insurance against contamination.
MEETING THE CHALLENGE
Leak Detection Associates's Seal Integrity Monitoring System uses helium as a tracer gas to evaluate package integrity.
To check a package's microbial barrier, some manufacturers use a challenge test. In one version, the tester sprays the surface of a package with an aerosol mixture containing microbes. In another version, the package is immersed in a microbe bath. After exposure, the tester cleans the surface and checks the interior to see if any microbes got inside.
The test is simple enough but far from ideal. "If you're not careful enough about cleaning the outside of the package, bugs will get in when you open it and you'll get a false positive," explains Darrell Morrow, chairman and CEO of Leak Detection Associates Inc. (Blackwood, NJ). In addition, Morrow notes, the test is difficult to conduct, poses biohazards, and produces subjective, variable results.
As a result, FDA allows device packagers to replace the microbial challenge test with some physical tests. According to T.M. Electronics's Franks, the leak rates detected by these tests range from about 10–1 to 10–11 cm3/sec. The less sensitive end of the range consists of test methods such as visual inspection and bubble testing. Test methods such as helium leak testing that require sophisticated equipment are at the more sensitive end. And as far as cost is concerned, as the sensitivity of the equipment increases, so does the price.
|Nondestructive package integrity testers from iTi can detect holes as small as 10 µm in only a few seconds.|
A relatively new midrange alternative is acoustic micro imaging (AMI) equipment from Sonoscan Inc. (Elk Grove Village, IL). Using ultrasound, AMI sees flaws as small as 5 µm in the x-y plane and less than 0.1 µm in the z direction, according to Jack Richtsmeier, the company's business development manager.
In addition to detecting leaks, AMI provides information such as leak geometry and location, which may help users get to the source of their packaging problem. On the downside, however, the equipment is relatively expensive and struggles with complex package geometries. "Our technology likes planar surfaces because it depends on reflected signals," explains Richtsmeier. "The more planar the surface, the cleaner the signal."
Sonoscan is currently working on an AMI testing method that will be submitted to the ASTM's committee on package integrity. "Within a year or two, we'll have a bona fide test method that people can reference," Richtsmeier says.
THE ULTIMATE TEST
|The Alcatel ASM 142 offers four levels of operator interface, a memorization command, and multicolor display.|
For device packagers who want to detect the smallest package flaws, helium leak-testing equipment provides sensitivity down to the size of a helium atom. According to DeLuca, Alcatel's helium detection system can detect a leak rate of 5 x 10–12 atm cm3/sec, which corresponds to a hole size of about 100 Å.
In addition to extreme sensitivity, the equipment has some advantages over old helium systems, notes DeLuca. For one thing, the new system features dry technology that requires no oil in the vacuum line, eliminating the possibility of oil finding its way into packages. The system is also easier to use than its predecessors.
"The evolution of electronics has allowed us to design systems that are very simple," says DeLuca. "Now the machines are so user-friendly that all you have to do is hit the cycle switch, and the machine will take care of the rest."
Though helium testing equipment has been around for some time, it's not widely used for package integrity testing. Leak Detection Associates's Morrow thinks that may change. "The helium leak test is probably the only test besides microbial challenge that has the sensitivity to tell you whether you have a sterile barrier," he says. "In the next couple of years, I think there will be significant growth in the level of awareness of this technology."
But some packagers are dubious about the technology's prospects. "People who want to detect the smallest possible holes would be driving toward helium mass spectrometry," Franks says. "However, most people don't want to be there because of the cost and complexity of the equipment involved."
To further complicate the matter, leak-testing methods for nonporous packages can't be used on porous packages. If such attempts were made, "there would be more leaking through the porous member than there would be through any defect in the package," explains Ron Pilchik, business manager for the medical package integrity test unit of Mocon Inc. (Minneapolis).
So device manufacturers turn to other methods to test porous packages. The most common method is a simple visual inspection of the package. But this method, which relies on people rather than machines, isn't as sensitive or reliable as many would like.
Another common method for testing porous packages is known as dye penetration. In this procedure, the packager injects dye into the package, then holds it up to see if any dye comes through the seal area.
"If there are any holes, channels, or breaches in the seal, the dye, through capillary action, will rapidly show you where they are," notes John Spitzley, associate packaging fellow for Medtronic Inc. (Minneapolis). According to Spitzley, the dye penetration test is effective, inexpensive, and fairly easy, but it's also destructive and messy. He believes the ideal test for porous packages would be nondestructive and quick, with higher sensitivity than that offered by conventional methods.
Earlier this year, Mocon introduced a system that tests for defects in porous packaging. The Pac Guard 460 finds leaks as small as 50 µm with the help of patented technology that masks the porous part of the package, making it "virtually nonporous," says Pilchik.
The Pac Guard 460 pushes carbon dioxide, instead of helium, into the package through its porous component. After a special test fixture isolates the porous top part from the nonporous bottom part, the bottom chamber is evacuated. An alarm sounds if the system's infrared sensor detects carbon dioxide in the bottom chamber.
No medical device manufacturers are using the Pac Guard 460 yet. Mocon is working on an ASTM procedure for the new test, which Pilchik expects to be approved for use by early next year. "They seem to have an effective piece of equipment," says Spitzley, adding that the Pac Guard 460 is less expensive and less complex than the system's predecessor, a defunct helium system from True Technology.
MAKING A CHOICE
No matter what kind of package you have, there are plenty of ways to test it for leaks. However, the question that remains is, "How do you choose from among all the options?"
Logic might lead you to the equipment that detects the smallest holes. But in this case, logic may not be the best guide. "There is no correlation between the size of a [package] defect and the probability that a microbe can find the defect and contaminate the inside of a package," asserts Donald Barcan, a packaging consultant based in Long Valley, NJ.
Barcan's conclusion is based on studies that failed to find such a relationship. In these studies, microbes were sprayed on packages with relatively large holes, but the packages still remained sterile. "That's why the FDA hasn't attempted to correlate microbial contamination with defect size."
Packagers are driven to look for the smallest possible leaks because, says Barcan, "Nobody wants to be on the wrong end of a lawsuit."
Franks thinks some packagers may be led astray by advertisements touting the sensitivity of certain types of leak-testing equipment. "It's really misleading to the user," he says.
The fact is that there are no industry standards that specifically address test sensitivity. "The only standard that everybody operates on is that any defect is totally unacceptable," says Barcan. "But then the question becomes, 'What equipment do you use to detect defects?' And that raises the question of how sensitive you need to be. At this point, that question can only be answered on a manufacturer-by-manufacturer basis."
So when it comes to leak testing, medical device manufacturers are pretty much on their own in their search for the right method and sensitivity level. "According to ISO 11607, you have to show that your package will still be sterile after it's been through its normal process handling and aging cycle," says Franks. "But how do you get there? That's a maze."