MMP9 and ulcer disease: In traumatic wounds, NPWT increases local vascular endothelial-derived growth factor (VEGF) expression in humans thus promoting angiogenesis and vascular proliferation.11,12 In animal models, it has shown to increase the accumulation of granulation tissue.13 NPWT also increases blood flow in ulcers and promotes wound contraction.14 The expression of MMP-2 and MMP-9 are increased in chronic wounds15 and NPWT has shown to reduce the expression of MMP-9.16