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Introduction to Silicone Rubber

Silicone Rubber for Medical Device Applications
Sources: Charles Heide, "Silicone Rubber for Medical Applications", Medical Device and Diagnostic Industry Magazine; http://www.mddionline.com/article/silicone-rubber-medical-device-applications (November 1999)
Wacker Chemie AG, www.wacker.com.

Selecting an acceptable elastomer for medical and other applications can be a challenge. Product designers, engineers and managers have to evaluate different material properties and manufacturability to assure product reliability and costs. There are many materials and processes to choose from. It is the responsibility of the designer to make the right choice.

Medical grades of silicone are both safe and reliable since they do not melt or promote fire, are short-circuit-proof and have a high dielectric strength. In the event of a fire, they do not generate toxic vapors or residues. Silicone rubber used in medical applications also has the following UNIQUE characteristics and advantages:
-Inert, odorless, tasteless, stainless – (ideal for medical and food applications)
-Hygienic – they give bacteria and fungi little chance to spread.
-Hypo-allergenic
-Extreme temperature applications, -180ºF to 600ºF (-118ºC to 316ºC)
-Easy to clean – even with dilute acids such as vinegar.
-Can be steam sterilized and are dishwasher safe.
-Thermal resistance – (special flame retardant compounds are available)
-High resistance to weathering and oxidation
-Excellent electrical qualities – (superior dielectric and insulation characteristics in special compounds)
-Superior resistance to many chemicals
-High resistance to ozone and corona
-Superior water resistance – low water adsorption
-Lime and dirt repellent
-Colorfast and light-stable with FL color pastes
-Highly transparent and have no yellow cast
-Flexibility and Durability
-Fatigue and Compression Set Resistance
-Energy Absorption
-Long Work and Shelf Life
-Can be compounded for special properties
If you need a combination of good mechanical properties and medical safety, then ELASTOSIL® LR liquid silicone rubbers are ideal, thanks to their special chemistry. They contain no organic stabilizers, plasticizers or activators.

Silicone Defined:
Source: Julie M. Stocker

Silicon, silica, silicone-what’s the difference? Silicon is a chemical element, one of the 109 known substances that constitute the universe's matter. Second only to oxygen in its presence on earth, one-quarter of the earth’s crust is silicon. Carbon is the only element capable of producing more compounds than silicon;thus, silicon possesses immense potential for commercial application. Silicon is one of the premier semi-conducting elements and is used in many electronic devices, such as transistors and computers. However, one does not find silicon alone in nature. It always exists as silica or silicates. Silica is silicon dioxide (SiO2), commonly found in sand and quartz. Silicone is a synthetic polymer, or macro-molecule, whose backbone is a repeating chain of Si-O molecules, with various organic groups attached to the silicon. The most common silicone is PDMS, poly-dimethylsiloxane [(CH3) 2Si-O], the foundation of all silicones. Finally, silicone is also described as an elastomer – a synthetic polymer which behaves much like natural rubber – it can be stretched to several times its size and still snap back to its original length.

History of Silicones in Medical Devices
Sources: Stephen Bruner and John Freedman
Charles Heide, "Silicone Rubber for Medical Applications", Medical Device and Diagnostic Industry
Magazine; http://www.mddionline.com/article/silicone-rubber-medical-device-applications (November 1999)

After extensive use in the aerospace industry in the 1940s, silicones expanded into healthcare and medical applications during the following decade. In 1954, J.D.B. McDougall reported that various tissue cultures taken from warm-blooded animals known to be extraordinarily sensitive to foreign influences showed no deviation from the usual growth picture upon contact with liquid, semi-solid, and rubber-like silicone products. As a result of this work, silicones have been characterized as biologically and toxicologically inert and are now used in a variety of applications including pacemaker leads, hydrocephalus shunts, heart valves, finger joints, and intraocular lenses.

Silicone rubbers were first used in 1960’s for automotive, medical, aerospace and other industrial applications. Silicone became the elastomer of choice because of such properties as:
a.) inert and stable
b.) compression set resistance
c.) hypoallergenic
e.) electrically non conductive
d.) wide range of operating temperatures
f.) variety of durometer choices available
Silicone is widely used in medical applications because it is hypoallergenic and does not produce any extractables like those of other thermoplastic elastomers. Typical medical applications for Silicone are:
a.) Tubing
b.) Drains
c.) Feeding tubes
d.) Catheters
e.) Implants for long and short term use.
f.) Seals and gaskets

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