A tissue expander (occasionally "skin expander," or "Becker Expander" after the inventor of one type), is a device much like a silicone balloon that is placed under the skin. Periodically saline is added through a tube and valve just under the skin, which can be reached with a needle to inject the salt water. So the volume of the expander increases over weeks or months, and the tissue around it and skin over it get larger. Most explanations say that the skin is "stretched," but what really happens it that the connections between skin cells are put under tension and newly created skin cells migrate to fill the growing spaces; the pull on the skin seems to induce more new cells to be produced. This is basically an artificial way to induce the same kind of skin growth that happens naturally during pregnancy or when a person gains a lot of weight.

The advantages of using a tissue expander include the fact that the new skin will match the old skin around it (which may not be the case when people are treated with skin transplants from other parts of the body) and the relatively low risk. The main disadvantages are repeat visits to the doctor over the length of time it takes to gradually increase the expander's volume, and the unusual looking bulge this can create depending on where the expander is placed. This technique is most commonly used as part of breast reconstruction after a mastectomy (before a permanent saline implant is inserted), but can also be used to improve the appearance of scars and to replace skin damaged by burns, accidents, surgery, or birth defects. The expanders come in all kinds of shapes: one manufacturer offers "round, rectangular, crescent, longitudinally curved, and small oval shapes" for whatever part of the body needs more skin.

Lappé, Marc. The Body's Edge: Our Cultural Obssession with Skin. New York: Henry Holt & Company, 1996.
http://www.imaginis.com/breasthealth/reconstruction.asp
http://www.plasticsurgery.org/surgery/tisexp.htm
http://breastcarecenter.his.ucsf.edu/reconsoptions_tmast_expand.html
http://www.phudson.com/BACKGROUND/BASICS/tissueexp.html
http://www.mcghan.com/patient/bodycui.html

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