Abstract: Embodiments of the invention provide an electrosurgical jaw structure comprising first and second opposing jaws one or both of which include 3D variable resistance bodies. The jaw structure can be part of the working end of a surgical instrument. In one embodiment, the jaws can comprise first and second energy-delivery jaw surfaces having first and second 3D variable resistance bodies, with the jaw surface configured to be coupled to an Rf source. The 3D variable resistance bodies can define different temperature-resistance curves. The 3D bodies can be configured to control ohmic heating of tissue by modulating the delivery of Rf energy to tissue. Jaw structures having the 3D bodies can be used to engage and produce high strength tissue welds in targeted tissue including tissue volumes having varying tissue types. Such jaw structures can be configured to simultaneously apply different energy levels to each tissue type within the tissue volume.