Page 220 - Biomedical Engineering and Design Handbook Volume 2, Applications

STERILE MEDICAL DEVICE PACKAGE DEVELOPMENT 199

the seal/peel test per ASTM F-88 only evaluates a 1-in segment of the package, there may be other
areas of the package which are not sealed adequately to prevent contamination of the product. In fact,
the seal width that was actually measured may be within the strength specification but may have a
channel leak that could breach the package and negate integrity.
Likewise, the ASTM F-1140 burst test method as referenced by ISO 11607 also has its pitfalls.
This method evaluates the whole package by applying pressure to all areas of the package; however,
the pressure is not applied equally at all points due to package irregularities and distortions. This can
lead to a relatively high degree of variability between tests. Further, the burst test may not detect
breaches in the package, such as pinholes and channel leaks, even though the burst test values have
met the performance specification.
Even though the package strength specifications are confirmed, the package integrity is not nec-
essarily proven. Seal integrity is defined as condition of the seal, which ensures that it presents a
microbial barrier to at least the same extent as the rest of the packaging. This definition does not
refer to the strength of the seal. Package integrity is independent of package strength, although a
strong package seal is a convincing indicator of a safe package with seal integrity. Further, if the
entire seal area is proven to be homogeneous and continuous, then one could say that the package
seals provide integrity. However, this says nothing about the package surfaces that may have pinholes
or leaks not detected by seal strength tests. Other mechanical tests may be appropriate for determin-
ing package seal homogeneity.
Seal strength is important in the overall scheme of developing the package process, but the seal
strength performance specification is used most effectively to monitor the process, not to determine
ultimate acceptance. Seal strength is also an important determinant for establishing package process
parameters. In fact, the ISO 11607 standard requires that the seal strength shall be determined at the
upper and lower limits of the defined critical sealing process variables and shall be demonstrated to
be suitable for the intended purpose. To restate, seal strength is an important performance attribute
for the package and provides suitable guidance in establishing statistical process control limits, but
is not the absolute determinant of the acceptability of the package for its intended use. Package
integrity at the point of final use is the principal acceptance criterion for a sterile medical device
package. However, both performance attributes are essential to the package design and development
process.

7.6.3 Determining Package Strength
Package seal strength measurements are fundamental indicators of the package formation process.
At a minimum the seal strength serves as a gauge that a sealing process is under control and that the
process is producing acceptable sterile barrier systems (packages).
The performance specification or benchmark for the package may be based on the seal and burst
test values of packages produced on a specific validated production line. These tests are performed
using standardized test methods developed by the American Society for Testing and Materials
(ASTM-International). The seal strength test procedure is described in ASTM F88, “Seal Strength of
Flexible Barrier Materials,” and is the industry’s definitive method for characterizing seal strength.
This test covers the measurement of the strength of a seal of a given width at a specific point of the
o
package. It does not measure the seal continuity. Other methods such as the 180 peel test may be used
to determine the seal continuity or peeling characteristics. The seal strength test is performed by cut-
ting a 1-in-wide strip from the seal of the package. The strip is placed in the tensile test machine by
clamping each leg of the sample in the grips, aligning the specimen so that the seal is perpendicular
to the direction of pull as shown in Fig. 7.1.
The seal is pulled apart at a rate of 10 to 12 in/min. The peak force required to pull the seal com-
pletely apart is recorded. It would be appropriate to perform the test at several points of the package,
including the manufacturer’s seals (produced by the vendor of the package) and the production seals
(produced by the manufacturer of the product). Typical seal strength values lie in the range between
1 and 4 lb. The optimum seal strength varies according to the type of package being tested and its
specific applications.