Tissue expanders are inflatable balloon-like temporary implants. They are used after a mastectomy to prepare the breast for reconstruction. The expander stretches breast skin and chest wall muscles to make room for a permanent breast implant. The expander has a small valve that health care practitioners can access by inserting a syringe through the skin. Over the next several weeks, a salt solution (saline) is periodically injected through the valve to expand the expander a little at a time.