Pharmaceutical and Medical Packaging News
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Originally Published January 2001
Manifold Methods Put Packages to the Test
Package test methods abound. Here's the scoop on several of them.
by William Leventon
There is almost no limit to what medical device manufacturers will do to their packages. They will rip them apart, blow them up, fry them, freeze them, even sniff them. As strange as this may sound, it's all done for a good reason: to find out what kind and what level of protection packages will provide for the devices inside.
Package-testing methods come in many different and ingenious forms. Some check seal strength. Others test overall package integrity. Still others measure the effects of external conditions. None tells the whole story about a package, but each of the following methods provides information that may be crucial in determining whether or not a package is up to its job.
SEAL-STRENGTH TESTING
One of the most common package-checking methods is the peel test. Mark-10 Corp. (Hicksville, NY) sells a peel-test setup that includes a force gauge, a test stand, and a set of gripping fixtures. The test is performed on a 1-in.-wide strip cut from a package. To determine seal strength, the grippers pull the two ends of the strip apart at a steady speed, while the gauge measures the force exerted on the strip.
The force value yielded by the test is less important than repeatability of results, says Bill Fridman, president of Mark-10. To improve repeatability, Fridman recommends that the separation force be applied to the seal at a steady rate. In addition, the tests should always be performed with the same equipment. "Consistency of setup using the same machine will greatly improve the repeatability and accuracy of the test," he says.
Equipment manufactured by Sonoscan Inc. uses high-frequency ultrasound to detect air gaps within and between various materials. The red areas in this image indicate voids or trapped air between sealed layers of a medical pouch.
While many manufacturers perform their own peel tests, those concerned about how FDA and others will view their test methods should consider an independent laboratory. "When the results come from an officially accredited lab, it adds credibility to the test," Fridman notes.
The downside of the tensile test is what it doesn't tell you about your seal. "If you just test a 1-in. strip, how do you know what the rest of the seal area is like?" asks Jim Zynda, sales manager for Carleton Technologies Inc. (Orchard Park, NY). "If you test only two or three locations around the perimeter of a pouch, you could miss the weak point of the seal."
For manufacturers who want to evaluate the entire seal, Carleton offers burst-testing equipment. "The burst test allows you to pressurize the entire seal area," says Zynda. "If there are any voids or weak spots, you'll find them."
In a burst test, air is forced into a package at a slow, steady rate until it bursts. The process yields a burst value, which is usually expressed in inches of water.
Before packaging operations begin, Zynda suggests that companies establish an average burst value for each package size. Normally, this is done by testing 50 to 100 samples of the same package. "The burst value is a quality control tool," Zynda explains. "You want to have the lowest burst value that will allow your packages to survive the production, sterilization, packaging, and shipping processes."
For better test results, many manufacturers use restraints that limit package deformation. Left unrestrained during testing, packages balloon into a variety of different shapes, which causes test results to vary. "That's always the big problem—variation," says Mark Strode, packaging laboratory supervisor for Edwards Lifesciences Corp. (Irvine, CA). Restraining fixtures overcome that problem by helping to ensure that each package is stressed in the same way.
Test variation is also reduced by well-calibrated pressure gauges and regulators. "Calibration is overlooked more than anything else," Strode says. "People collect data with an uncalibrated or poorly calibrated unit, use that data to make a decision, and then find out later that the data are all messed up."
Walk-in thermal chambers simulate outside temperatures. Photo courtesy of FDC Packaging Inc.
INTEGRITY CHECK
Burst testing checks package seals but not overall package integrity. For that, performance of a leak test is necessary. A common leak-testing method called force decay employs a vacuum chamber. As a package expands inside the chamber, it presses against two plates. Under the bottom plate is a sensor that measures the force exerted by the expanding package. If there are no leaks in the package, the force measurement will remain constant once the package reaches its expansion limit. If the package is leaking, however, it will start to contract and the measured force will drop. Force decay testers start at about $12,000.
Unlike burst testing, force decay is a nondestructive test method. "If the package is good, it can continue on down the production line and be used. It hasn't been damaged in any way," says Rick Reardon, business manager for the force-decay testing line at iTi Qualitek Inc. (North Billerica, MA).
On the downside, force decay won't tell you anything about the location of a leak. In addition, the method can't be used to test packages made of Tyvek and other porous materials. Because these packages won't hold air, they won't expand in the test chamber.
Before starting the test, manufacturers should determine what size holes they have to find. "If your package can be used even if it has a 20-µm hole in it, there isn't a lot of value in searching for a submicron hole," Reardon says.
For manufacturers who must find extremely small package holes, Leak Detection Associates Inc. (LDA; Williamstown, NJ) offers equipment for performing a helium leak test. In this test, a helium-filled package is put into a vacuum test chamber. When the test chamber is evacuated, instruments detect helium that has seeped through the package.
Why helium? "Because of its size, helium will go through any defects in the package," explains Darrell Morrow, chairman and CEO of LDA. "If helium can't get through, then nothing can get through."
According to Jean-Pierre De Luca, director of helium leak detection at Alcatel Vacuum Products Inc. (Hingham, MA), helium's characteristics, such as being inert, mixable with any gas or material, and light in weight, make it "the perfect tracer gas for leak detection purposes." De Luca's company offers a helium leak detector, which is designed with a built-in, temperature-compensated, calibrated leak, that is capable of detecting leaks as small as 100 Å with a high level of repeatability. "This capability," he says, "gives the user maximum flexibility for very demanding applications."
Helium package testing is often the choice of manufacturers who must deliver devices in a sterile condition. In cases like this, says Morrow, some studies show that only a helium test can give manufacturers a high level of confidence in a package's microbial barrier. "Tests using other gases are 1000 to 100,000 times less sensitive than what they need," he says.
What's more, some helium tests can find the locations of leaks. One method features a sniffer probe that sucks gas into a leak detector. Since it only works when in close proximity to a leak, the probe sniffs out leak locations in the seal area.
These capabilities don't come cheaply. According to Morrow, LDA's helium test system costs about $90,000. For those who don't need its high sensitivity and leak-finding capability, a $5000 bubble-test unit might do the trick. LDA also tests packages for some small manufacturers who need helium testing but can't afford the equipment.
Like force decay, helium leak testing doesn't work with porous materials such as Tyvek. And like the burst test, the helium method suffers when packages expand too much during testing. When packages assume a spherical shape, stresses on the seals may cause leaks. Therefore, Morrow recommends keeping package deformation below 10% during testing.
ULTRASONIC TESTING
Though not a new technology, helium testing is fairly new to the medical packaging market. The same is true of ultrasonic package testing. For manufacturers who want detailed, nondestructive information about package flaws, Sonoscan Inc. (Elk Grove Village, IL) offers an acoustic microimaging (AMI) system. In AMI, acoustic pulses enter the sample, and echoes return from different levels in the material. An electronic gate lets users study specific material interfaces by excluding echoes from other levels. "We can actually differentiate between the layers and see which ones are disbonded," says Jack Richtsmeier, Sonoscan's business development manager.
The ultrasonic pulses detect air gaps in packaging material. Voids, cracks, disbonds, and similar defects produce high contrast and are easily distinguished from the background. "Our technology offers an acoustic image," says Richtsmeier. "We not only detect the presence of flaws, but also can map them. We're also able to show you the specific geometry of the flaw so you can tell if it's a channel, a void, or something else."
Inside the laboratory at TCP/Reliable.
By zeroing in on the bond layer, AMI can also help manufacturers find an optimal dwell time for sealing techniques. "Too little time may not produce adequate bonding or may result in flaws," Richtsmeier explains. "If the dwell time is too long, you're wasting too much time on a specific product. Our technology can help customers find a dwell time that's both adequate and profitable."
In the production process, AMI can be used either on- or off-line to check for voids, gaps, or seal integrity. Due to the time required for the imaging process, however, AMI is probably better suited for batch sampling or off-line inspection.
"It takes the system 10 to 20 seconds to produce an image," Richtsmeier says. "If you only make several dozen parts per hour, we can do on-line inspection. But we can't yet keep up with processing speeds of hundreds of feet per minute."
AMI has other disadvantages as well. For one thing, package geometry sometimes limits what the system can see. And like several other test methods, AMI doesn't work well with Tyvek. "Tyvek is made up of mostly voids or air, and that's exactly what the system is designed to see," Richtsmeier says.
The cost of the equipment, which ranges from $100,000 up to about $250,000 for systems that are integrated with production processes, can also be a limiting aspect. For manufacturers who can't justify such an expenditure, Sonoscan offers contract testing services.
ENVIRONMENTAL IMPACT
Once a package leaves the factory, how will the environment affect it? FDC Packaging Inc. (Medfield, MA) can help manufacturers find out by conducting thermal tests on their packages. "We simulate the outside shipping environment inside a lab," says Lawrence Gordon, president of the company. FDC's test chambers can expose packages to temperatures ranging from –40° to 200°F. During the test, thermocouples inside the package record temperature information.
Of course, a thermal test is only as good as its temperature range. "There are some extreme events that won't be accounted for," Gordon says. "Can the temperature get down to –50°F in Alaska? And if so, will the package arrive in Alaska that day when it is –50°F? If it does, what will happen? Well, we would say that –50°F is pretty unlikely, so you might not want to test for it."
Manufacturers who tackle thermal testing should try to follow the same procedures every time. Gordon points to studies showing as much as a 4% variation in the results of a test performed in the same laboratory from one time to the next. This happens because procedures differ each time, he says.
Because of the specialized nature of the testing, and the size and expense of the test equipment, most medical device manufacturers turn thermal package testing over to outside labs. For those who decide to do that, Gordon suggests using a facility certified by the International Safe Transit Association.
Sometimes thermal tests are run in combination with shock and vibration testing. "The amount of shock and vibration a package can take depends in part on temperature," explains Sanford Cook, president of TCP/Reliable Inc. (Edison, NJ), an ISTA-certified laboratory that does thermal testing, as well as shock and vibration testing. "If you use polystyrene or rigid styrene materials at 70°F, for example, they might be totally different than they would be at 20° below zero."
Cook's company simulates the conditions—temperature, shock, and vibration—that a package may encounter on a trip from one place to another. "Let's say a package is being shipped from New Jersey to Los Angeles. We have a pretty good feel for what that trip will entail in terms of shock and temperature. We've run accelerometer tests that have given us data for trucks traveling on bumpy roads, medium roads, and good highways." The company also has thermal data and shock and vibration data from aircraft.
According to Cook, many people make the mistake of testing only at the highest and lowest temperatures that their packages might encounter. Instead, Cook believes packages should be subjected to temperature shocks, or alternating high and low temperatures.
"Materials are much more vulnerable to a series of different temperatures than they are to one continuous, extreme temperature," he says. "If you shock the material back and forth, its modulus of elasticity will change when the temperature changes."
CONCLUSION
Whether you're testing for temperature resistance, integrity, seal strength, or some other package quality, the results will be better if you develop a regular preventive maintenance program for your test equipment, says Mark Strode, who supervises a variety of package tests at Edwards Lifesciences. "Keep the equipment in tip-top shape and you'll eliminate almost all the problems that can come up and bite you."
