"Tissue expanders" are medical devices that help stretch and grow the skin and tissue in the body. They are commonly used in reconstructive surgery to prepare the area for an implant or to repair damaged skin. Full definition
Patent infringement case involving tissue expanders used in connection with breast reconstructive surgery (jamsadr.com)
One of those is the Aeroform Tissue Expander System. (fortune.com)
The technique involves placing tissue expanders (interim implants) under the skin on top of a woman's pectoralis muscles after her breast tissue has been removed. (sciencedaily.com)