Figure 3.

V.A.C. mechanisms of action. An open-cell reticulated foam is placed within the wound and covered by a semi-permeable adhesive drape. The drape is adhesively secured around and over the wound to create an airtight seal. A small hole is made within the center of the drape, and the suction port and tubing connected to the collection canister are attached. Engaging the vacuum pump evacuates the air from the foam and enables (1) Macrodeformation of the foam via shrinkage, which pulls the wound edges together. At the interface between the foam and wound bed, (2) microstrain occurs in which cells are pulled into the pores of the foam while an equal and opposing force acting on the struts of the foam pushes cells away. The microstrain on the cells initiates mechanotransduction, which can stimulate cell proliferation as illustrated within the sub-inset of inset 2. Additionally, engagement of the vacuum facilitates the (3) movement of fluid out of interstitial spaces, thereby reducing edema and increasing blood flow as illustrated in inset 3. The V.A.C. system possibly (4) reduces bacterial burden; however, the mechanism by which bacteria are reduced is not fully understood. The destruction of bacteria is illustrated in inset 4. The V.A.C. system contributes to (5) wound stabilization through secondary events. Inset 5 illustrates the movement of warm air down through the semi-permeable drape into the wound space, while isolating the wound from foreign contaminants. Furthermore, the semi-permeable drape prevents evaporative water loss, which aids in keeping the wound moist to enable cell migration and nutrient transport.