A tissue modification apparatus includes at least a first plurality of grippers aligned in a plane adapted to secure a first edge of a patch of tissue. The plurality of grippers are each secured to a first force actuator. The first plurality of grippers are each adapted to pivot relative to the first force actuator about an axis perpendicular to the plane. In some cases, a plurality of grippers are attached to a force actuator by a passive force transfer mechanism. In some cases, individual force actuators are attached by pivoted connections to individual grippers. Methods of treating tissue can secure tensioned tissue to a frame to retain the tension during a treatment (e.g., cross-linking the tissue with a chemical cross-linker).