Fasteners and fastener delivery devices for affixing sheet-like materials to bone or tissue

A fastener for attachment to tissue or bone comprising:

• a first arm having a proximal end and a distal end, a second arm having a proximal end and a distal end, and a bridge connecting the first arm and second arm, wherein each of the first and second arms include a trunk portion extending over at least a portion of the length thereof, each trunk having a lateral extent larger than a lateral extent of the bridge or non-trunk arm portion adjacent thereto such that the staple includes a first change in lateral stiffness disposed proximate the bridge or non-trunk arm portion abutment with the first trunk and a second change in lateral stiffness disposed proximate the bridge or non-trunk arm portion abutment with the second trunk;
• each trunk including a first projection and a second projection, the first projection including a first proximal surface extending away from the trunk in a first direction, the first direction being such that the first proximal surface will engage the tissue or bone when the trunk is inserted therein so that a first moment is applied to the trunk in response to a pullout force on the bridge, the second projection including a second proximal surface extending away from the trunk in a second direction, the second direction being such that the second proximal surface will engage the tissue or bone when the trunk is inserted therein so that a second moment is applied to the trunk in response to a pullout force on the bridge, each of the trunks including a localized area of weakness proximate the second projection thereon.