A surgical instrument can comprise an end effector including a plurality of jaws which can be configured to compress tissue therebetween. The end effector can further comprise one or more electrodes which can be configured to direct a flow of electrical current through the tissue in order to heat the tissue and denature collagen and/or other proteins within the tissue. As the tissue cools, the collagen and/or other proteins can renature and thereby seal the tissue. In certain embodiments, the end effector of the surgical instrument can further comprise movable portions which can apply a tension force to the tissue surrounding the tissue being sealed. In various circumstances, the tension force can reduce the over-denaturation, shrinkage, and/or other damage to the surrounding tissue caused by heat flowing from the end effector during the sealing process.