Page 212 - Biomedical Engineering and Design Handbook Volume 2, Applications

STERILE MEDICAL DEVICE PACKAGE DEVELOPMENT 191

of the necessary information for the selection of materials for the specific medical device. Consult the
references for additional information.

7.5.1 Primary Materials
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Tyvek . Tyvek , a spun-bonded olefin, is used in almost every major form of sterile package,
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including peelable pouches, header bags, and lid stock of thermoform trays and kits. Tyvek is a
fibrous web material composed entirely of extremely fine, continuous strands of high-density poly-
ethylene. This material has exceptional characteristics that distinguish it from other materials.
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The product characteristics of Tyvek include
• Outstanding porous microbial barrier
• Strength
• Moisture resistance
• Inertness to most chemicals
• Air permeability
• Clean peeling seals
• Low linting due to continuous filaments
• Low fiber tear

It has superior dry and wet strength and dimension stability. Its excellent puncture and tear resis-
tance and toughness allow for a wide range of applications for medical devices, particularly irregu-
larly shaped and bulky products. This material has an unusual fiber structure that allows for rapid gas
and vapor transmission but at the same time provides a barrier to the passage of microorganisms.
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Tyvek is used most often with ethylene oxide (EtO) sterilization methods because of its unique
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property of high porosity and microbial barrier. Tyvek provides several other attributes useful to
package integrity and aesthetics:
• Water repellency—repels water but is porous to moisture vapor
• Chemical resistance—resists usual agents of age degradation (e.g., moisture, oxidation, rot,
mildew, and many organic chemicals)
• Radiation stability—unaffected by common levels of radiation used for sterilization
• Low-temperature stability—retains strength and flexibility at subzero temperatures
• High-temperature stability—can be used in steam sterilization methods
• Aesthetic qualities—bright, white, clean appearance for printing
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Since Tyvek does not readily adhere to other plastics, except other polyolefins, through the appli-
cation of heat and pressure, it has been made a more versatile packaging material by applying coat-
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ings that enable it to bond with a wide variety of plastics. There are several grades of Tyvek used
for medical packaging applications, including 1059B, 1073B, and 2FS.
The DuPont TM Medical Packaging has published two very useful documents to help in designing
a package system that is in compliance with the ISO 11607 standard. They are
• “Technical Reference Guide for Medical Packaging,” first published in 2002; reissued in 2007
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• “DuPont TM Tyvek Compliance to ISO 11607-1:2006”
• These documents can be found at: http://www2.DuPont.com/Medical_Packaging/en_US/
tech_info/index.html
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Another breathable material which may provide an alternative to Tyvek has been developed by
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Oliver Medical called Ovantex . Ovantex/F is a material made of a proprietary blend of synthetic
fibers and cellulose-based components. The barrier properties of this material are superior to medical