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A number of strategies have been investigated to enhance the mechanical stability of engineered tissues. In this report, we utilized lysyl oxidase (LO) to enzymatically crosslink extracellular matrix (ECM) proteins, particularly collagen and elastin, to enhance the mechanical integrity of the ECM and thereby impart mechanical strength to the engineered tissue. Vascular smooth muscle cells (VSMCs) were liposomally transfected with the LO gene. Western analysis confirmed increased LO expression. Increased LO activity was demonstrated as increased levels of desmosine, a product of LO crosslinking, in the ECM. The mechanical effects of altered crosslink densities within tissue engineered constructs were demonstrated in a VSMC-populated collagen gel model. Smooth muscle cells transfected with lysyl oxidase were seeded in collagen gels; the tensile strength and elastic modulus in these constructs increased by approximately twofold compared to constructs seeded with mock transfected VSMCs. Compositional analysis of the ECM deposited by the transformed cells showed similar collagen and elastin levels, and cell proliferation was similar as well. Thus, increased mechanical properties were attributed to ECM crosslinking.