An end effector structure (e.g. jaws structure or similar), configured with an internal antenna for delivery of electromagnetic energy in microwave range to a straight, curved or circular end effector structure in which the portion of end effector structure includes a microwave absorbing material that absorbs microwave energy emitted by the antenna and transfers microwave energy into the heat. Such end-effector also includes surgical fasteners or staples for strengthening tissue, providing a hemostasis, tissue joint and/or welding. The microwave antenna is connected by a coaxial cable with a microwave generator. The heat generated in the microwave absorbing material is applied to the treated material (e.g. tissue) by means of capturing material in the end effector (jaw structure) and heating the tissue to the desired temperature either before, during or after a stapling procedure.