Originally Published PMPN September 2002
MedicalCleaning Up Package Integrity Testing
Can nondestructive integrity tests displace tried-and-true destructive tests?
Daphne Allen, Editor
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Some
emerging nondestructive tests for integrity, however, promise to provide just
as much detail as these accepted ASTM standards do, without the mess and waste.
And, in some instances, nondestructive trace-gas sensing techniques and acoustic
micro imaging can recognize leaks much smaller than destructive tests can.
DESTRUCTIVE DOWNFALLS
Since the popular destructive integrity tests are easy to use and backed by ASTM methods, there may be little incentive to abandon them. However, some question the science behind them, since typical bubble and dye tests involve subjective evaluations. "With bubble immersion and dye penetration tests, the operator relies on a visual pass-or-fail determination," says Pat Nolan, vice president of DDL Inc. (Eden Prairie, MN), a full-service medical package-testing laboratory. "These tests are too subjective."
And since bubble and dye tests involve conditions that destroy or taint the packages, the packaged devices may be destroyed, too. Companies therefore must plan to waste a certain amount of packaging material and a number of devices during audit tests.
PRESSURE AND VACUUM
One established means of testing the integrity of nonporous packages nondestructively involves applying pressure or vacuum to packages inside airtight chambers to reveal leaks.
According to Steve Franks of T.M. Electronics (TME; Bolyston, MA), in pressure decay testing, the initial pressure applied to the package in the chamber is measured against a final pressure, and the change in pressure represents a measure of leakage. Vacuum testing involves similar measurements. Pressure decay and vacuum tests can detect very small leaks, as small as 10 µm. TME offers the MDT-500C for such testing, and InterTech Development (Skokie, IL) and Uson LP (Houston) offer similar models.
"Force decay testing is a fail-safe, quick, accurate method, offering higher repeatability and faster response time than traditional destructive test methods, especially bubble immersion," says Jacques Hoffmann, president of InterTech. His firm has customized several models and related handling equipment, even units for 100% in-line testing at the end of a form-fill-seal machine.
And the method accomplishes what medical and pharmaceutical packaging engineers are looking for—minimal testing waste, reiterates John Fallon, vice president of business development for Uson. To this end, Uson has just introduced a scalable leak tester called Vector, which features universal hardware and software that allows a single tester to perform multiple tests, such as pressure decay and vacuum decay tests and others. "The Vector has the capability to perform test applications that have historically required 10 separate leak testers. And, since final test and inspection (including leak testing) is frequently a bottleneck in the manufacturing process, the Vector will make it possible for a plant to significantly increase production rates," Fallon explains.
Packaging Technologies & Inspection (PTI; Tuckahoe, NY) offers vacuum differential
technology featuring a dual-transducer system. "The absolute transducer
calculates decay in a manner similar to other systems, but the second transducer,
a differential vacuum transducer, measures very minute differences," explains
PTI's Tony Stauffer. "It is 100 times more precise than single-transducer
systems."
Despite the benefits of pressure or vacuum testing, Franks advises that the methods have limitations. "Methods that use pressure or vacuum apply forces to the seal. Users should do a burst seal-strength test to establish the seal limits before applying test pressures for leaks. For peelable seals, the test pressure on the package should be 25–30% of the burst pressure to prevent moving the seals during testing. For welded seals, the pressures can be higher, but the package must be restrained to prevent the package walls from expanding under pressure and causing wall-material failures. This is covered in ASTM F2095."
VISUAL TESTING
Perhaps the lowest-cost nondestructive testing method is visual inspection
(ASTM F1886). However, even the ASTM standard acknowledges that the method can
only be expected to reveal channels as small as 75 µm, with a 60–100%
probability.
Van der Stähl Scientific (Wrightwood, CA), a provider of package- sealing equipment, supplies, and services, uses the visual method along with other tests for integrity and seal strength. "Our engineers were using their unaided eyes, as the ASTM method instructs, but we didn't feel the method has the attributes of repeatable science," says president Charlie Webb. "We turned to a powerful microscope, but we found that backlighting samples washes them out."
Webb then turned to side lighting, eventually designing his own system. The viú is a patent-pending system that "greatly exaggerates the topography of the flexible-pouch seal area by using polychromatic side lighting in concert with a 3¥ magnification," Webb says. "It provides the packaging engineer strong visual acuity as to the nature of basic seal integrity. As the operator views the seal area through the 3¥ lens, seal anomalies are exaggerated." Working with a lighting consultant, his team determined which light wavelengths work best. "This tool has provided us with the means to develop protocols for evaluating terminally sterile seals," says Webb.
TRACE-GAS SENSING
When True Technology introduced its Seal Check system for nondestructive testing of porous and nonporous medical packages a few years ago, interest in trace-gas sensing increased because of the firm's aggressive marketing and trade show demonstrations. But budgets for the firm's high-priced technology did not. Making few sales, True Technology eventually closed, selling the technology to Mocon (Minneapolis), which now offers trace-gas sensing at a more affordable price tag.
Medical package consultant Donald Barcan, president of Donbar Industries Inc.
(Long Valley, NJ), sees a clear reason for the difference in price. "True
Technology's system featured a sensing probe that moved across the entire
package, including the seal, and recorded the leak rate at every point of the
package. Such a feature enabled the system to pinpoint the exact point at which
a package leaks. My understanding is that currently marketed systems do not
feature such a probe, and instead just report either a pass or a fail result.
This is not necessarily negative, but just a limitation."
Darrell Morrow believes that trace- gas sensing offers several benefits over other nondestructive integrity-testing methods. His firm, Leak Detection Associates Inc. (Blackwood, NJ), has offered trace-gas sensing systems years before and after True Technology, and its current model is the SIMS 1282+. "Packaging can become distorted through vacuum-pressure differentials, so such testing may not be completely nondestructive," he explains. And, when compared with destructive tests such as dye penetration and bubble immersion, trace-gas sensing appears to be considerably more sensitive. "Trace-gas sensors can detect leaks a fraction of a micron in size. Dye and bubble tests don't even pick up leaks that have been established as the largest holes that can be present and still maintain sterility, such as those put forth by Lee Kirsch, associate professor of pharmaceutics and industrial pharmacy at The University of Iowa's College of Pharmacy." Morrow points to Kirsch's research published in the PDA Journal of Pharmaceutical Science and Technology, as well as to round-robin tests that have shown that defects leaking at 10-4 cm3/sec were not detected using a vacuum bubble test. "That's two decades short of a sterile barrier," Morrow says.
Ron Pilchik, business manager of Mocon's medical package integrity group, has been working on getting ASTM to accept a testing method for trace-gas sensing. He reports that a method using CO2 leak detection is "almost through the ASTM" process. "In round-robin tests we proved that trace-gas sensing detects 100% of 4-mil (100 µm) channels and 2-mil (50 µm) pinholes. And test results are easier to interpret than dye or bubble results. In dye penetration tests, says Pilchik, "the dye often wicks on Tyvek. Mocon offers the PacGuard 400 for nonporous packages and the PacGuard 500 for trays with porous lids.
Both Morrow and Pilchik add that steps can be taken to minimize or even eliminate the effects that trace-gas sensing has on packages, making the test nondestructive. "You can pump CO2 into the package under extremely low pressure and evacuate it under extremely low vacuum," says Pilchik. Morrow says that to avoid the distortion that can occur when gas exits the package faster than air can get in, an air-helium mixture of 90% air and 10% helium can be used. "Our system can detect trace gases with only 10% helium," he says. Pilchik, however, says that helium may not work for packages made of Tyvek.
ULTRASOUND
Two companies are currently promoting the use of noncontact ultrasound to detect defects in medical and pharmaceutical packages. Sonoscan Inc. (Elk Grove Village, IL) introduced its system in 2000, calling it acoustic micro imaging (AMI). PTI unveiled its Pti 525 ABUS (airborne ultrasound) at MD&M East 2002 in New York City.
PTI's Stauffer says that ultrasound can detect defects in heat-seal joints and layers, determine integrity of heat seals, detect voids in heat-sealed layers, detect delaminations, and detect foreign materials or inclusions in seals.
Both systems employ a transducer that scans the seal areas of a package. Sonoscan's unit requires a fluid couplant for ultrasound to travel from the transducer to the sample, while PTI's unit transmits ultrasound through air. (There is some debate over which method is most sensitive.)
According to Sonoscan, the pulse travels through homogeneous, or sealed, areas of the package but is reflected back when it hits a void or other defect. Sonoscan also employs Thru-Scan imaging. The transducer above the pouch still pulses ultrasound into the sample, but a second transducer located beneath the sample collects only the ultrasound that has traveled completely through the sample. Any waves not passing through are considered to have encountered a delamination or leak. At the high frequencies used in AMI, Sonoscan says submicron gaps can be visualized. (For more details on Sonoscan's method, see "Acoustic Images Fine-Tune Parameters")
Stauffer offers another explanation. "The total energy of the ultrasonic signal through well-sealed material is identified and recorded. If there is an air or other gas gap between layers of solid materials, i.e., a partially delaminated package material structure, the total transmitted amount of energy drops accordingly."
THE IDEAL METHOD
To Franks, 100% in-line testing is the ideal. "This would be the most effective use of nondestructive tests. It would provide maximum use of the technology, prevent waste, and provide lower costs by not requiring the use of large amounts of labor."
But before nondestructive tests become the norm, ASTM or FDA would have to
urge industry toward their use. "An ASTM method will lend credibility to
the testing method," says DDL's Nolan. "Manufacturers want to
be able to reference published standards." And he adds that nondestructive
methods would be legitimized if FDA were to require more measurable, repeatable
science in the methods used to test medical packages.
Until either ASTM or FDA speaks out, though, most device companies are likely
to be just as conservative as Ethox Corp. (Buffalo, NY), a full-service contract
manufacturing, sterilization, and testing company. "There is a certain
amount of consistency and predictability to using established methods like dye
and immersion testing," explains Gary Benson, manager of sterilization
and laboratory sales. "But we do see the need for nondestructive methods
for both the product and package sides of our business. We have manufactured
millions of blood and media bags over the lifetime of the company, and having
a standardized nondestructive test available would equate to sizable cost saving
in manufacturing. Although we are active members of ASTM and AAMI, we do not
foresee an immediate investment into any new test methods, unless positioned
with the right partner, until the validation methods for nondestructive test
are no longer under debate, and when we better understand what FDA will be expecting
in years to come."
Copyright ©2002 Pharmaceutical & Medical Packaging News
