Page 210 - Biomedical Engineering and Design Handbook Volume 2, Applications

STERILE MEDICAL DEVICE PACKAGE DEVELOPMENT 189

7.4.1 Thermoform Trays (Semirigid)
Thermoform trays are made from a variety of plastics by molding them to the desired shape through
the thermoforming process. Trays are particularly suited for devices with irregular shapes and high
profiles since the tray can be designed to accommodate these device characteristics. Trays are ideal
for procedure kits that contain several devices as they can be molded with special flanges, undercuts,
and snap fits or ridges for securing the components. Semirigid trays are self-supporting.
When designing a tray for a medical device, several criteria must be considered in the selection
of the material:

• Tensile strength
• Stiffness
• Impact resistance
• Clarity
• Ease of forming and cutting
• Heat stability
• Compatibility with sterilization processes
• Cost, on a yield basis, versus performance
• Product compatibility
• Ability to be sealed with lidding material
When using a tray for a sterile medical device, in order to perform the most basic protection func-
tion, the tray must be sealed to prevent loss of sterility. This is accomplished by using a lidding mate-
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rial that is sealed around the flange area of the tray. Until the advent of Tyvek into the market, it
was difficult to provide lidding material that would provide a means for terminal sterilization using
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the common sterilization methods of the day. However, Tyvek has allowed widespread use of ther-
moform trays for many applications.
7.4.2 Flexible Formed Pouches

This type of package is one in which a flexible material is drawn using the thermoform process into
a flexible “tray.” The package, essentially, is a formed pouch that allows containment of high-profile
devices. These packages are generally not self-supporting.
Characteristics of the formed flexible packages are

• Relatively low cost, suitable to high-volume, low-cost devices
• May be made to be heat sealable
• Ease of forming
• Available for form-fill-seal operations
• Suited to relatively simple tray configurations
• Can conform to product
• Good visibility of product
• Cannot be preformed into a package
• Offer little structural protection
• Limited variety of materials available
• Relatively lower heat resistance
Like the semirigid tray, this package type must also be sealed using a lidding material or top web. The
top web material must be designed with the particular barrier properties needed to be compatible with