What is tissue expansion?
Tissue expansion is a common surgical procedure to grow extra skin through controlled mechanical overstretch. It creates skin that matches the color, texture, and thickness of the surrounding tissue.
As can be obeserved during pregnancy, skin has the remarkable ability to grow when subjected to controlled tension leading to the creation of additional soft tissue. It is this ability to stretch and generate new tissue that expanders exploit. By placing a device underneath the skin which is then slowly expands over the course of several weeks, surgeons are able to generate additional skin for reconstructive purposes. This de novo skin can then be used to repair a wide variety of congenital or acquired soft tissue defects.
The concept of tissue expansion for surgical reconstruction was first reported over fifty years ago (Neumann, 1957) although the technique did not gain popular acceptance until the 1980s (Radovan et al., 1982; Argenta et al. 1984) when it was used predominantly in delayed breast reconstruction.
Traditional tissue expansion utilises an implantable subcutaneous silicone balloon that is gradually expanded (usually on a weekly basis) by injecting saline solution through a buried filling port. Expansion continues until the desired degree of soft tissue expansion is obtained – usually a period of some months. Although widely used in a range of reconstructive applications, they have a number of inherent limitations. Firstly, they are bulky and therefore of limited use for intricate anatomical locations, particularly in the paediatric setting. Percutaneous expansion can also be uncomfortable and is poorly tolerated by some patients, especially children. Furthermore, the balloon expands equally in all directions (i.e. is isotropic), whilst in certain clinical situations, directional expansion (i.e. anisotropy) may be desirable. Such instances might include dorsal digital skin expansion prior to syndactyly release in order to avoid the need for skin grafting or intra-oral vertical ridge augmentation preceding the use of osseointegrated dental implants.
Autonomous controlled tissue expanders were developed in parallel to balloon-type devices (Austad et al., 1982). However, their impact was hindered by their limited expansion volumes and potential complications. The adoption of biocompatible osmotically active hydrogels (Weise et al. 1993) was a major advance in the evolution of autonomous controlled devices, although they were relatively crude in terms of their in vivo performance.