Critical health role for silicones

Hazleton has over 30 years of technical and management experience with Dow
Corning's silicone businesses. He has served as Midland plant manager, vice
president and director of manufacturing and engineering, and general manager of
the Fluids, Resins and Process Industries Business. In the early 1990s, Hazleton
became president of Dow Corning Europe, a director of Dow Corning, then
president. He was named CEO in 1993 and chairman in 1994. Hazleton holds
bachelor's and master's degrees in chemical engineering from Purdue University
and a master's in business administration from Central Michigan University.

The future of life-saving and life-enhancing devices for optimal patient care depends on the availability of innovative biomaterials, says Hazleton. Dow Corning looks ahead to an ongoing role in the health-care industry.

Design News: How are silicones used in medical applications?

Hazleton: Silicones have a long health-care history. Since the mid-1950s, hydrocephalus shunts have saved the lives of hundreds of thousands of infants. Scleral sponges help repair detached retinas, and other silicones treat wounds and help heal scars. High-tear-strength silicone rubber forms an insulator for pacemaker and defibrillator leads, and silicone adhesives are used in transdermal drug delivery patches. Other uses include implantable ports, catheters, tracheotomy and feeding tubes, and voice prostheses. Silicone fluids lubricate syringes, antifoams aid pharmaceutical manufacturing, and tubing is used in IV.

Q: What physical properties make silicones useful in health care?

A: Silicones are polymers of alternating silicon and oxygen atoms. This structure yields a number of properties associated with silicone elastomers, including softness, flexibility, and lubricity. Depending on polymer length and chemical sidegroups, silicones exist in a variety of forms: fluids, antifoams, low- and high-durometer rubbers, resinous materials, and adhesives. Some silicones provide clarity, which can be important where blood flow or fluids must be observed.

Q: What about chemical or biological properties?

A: Extractable testing is one way to assess chemical properties. By using rigorous test methods, we attempt to examine "worst case" conditions for extractables. Results show low levels of extractables. These levels are below any that have shown toxicological effects. As far as biological properties, the silicones used in medical applications show very low tissue reactivity and sensitization potential, low cytotoxicity and mutagenicity, and low systemic toxicity.

Q: What other special precautions go into the design and manufacture of materials in-tended for health-care versus industrial applications?

A: With today's stringent regulatory environment, biocompatibility data are obviously vital. For example, to be designated as Silastic BioMedical Grade, each material undergoes seven intensive tests based on the Tripartite Guidance and ISO standards. We test under Good Laboratory Practices (GLPs) and produce silicones in a facility focused on health-care applications, according to bulk pharmaceutical Good Manufacturing Practices (GMPs).

Materials and processes are fully documented, from raw material testing through production, to final product testing and lot sample retention. This ensures that products continuously meet the standards to which they have been qualified. Although our customers are required to fully test their products, we help them make informed choices about raw materials, save the time and expense of additional material screening, and establish credibility.

Q: How adaptable are silicones to processing?

A: Silicone elastomers can be fabricated by extrusion, calendering, or molding processes such as injection-, transfer-, or compression-molding. High-strength liquid silicone rubber has increased processing ease via rapid injection molding. Other non-elastomeric silicones are adaptable to such processing techniques as dipping, spraying, blending, and coating.

Q: What is the outlook for silicone in health-care uses?

A: There is clearly a crisis in biomaterials availability. Although Dow Corning has been a lightning rod in that regard, the issues are not unique to our company. Numerous material suppliers have been forced to supply their products under very limited conditions or exit the health-care market en- tirely. As a result, device developers have witnessed the withdrawal of a range of organic elastomers, plastics, and polymers. Like silicones, these materials are extremely valuable in restoring and improving lives and health.

Current trends in material safety documentation, regulatory postures, and tort reform suggest the willingness of industry, govern-ment, and academia to find solutions. We hope this emerging business and regulatory environment allows Dow Corning to continue providing silicones to the industry.

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