A particular embodiment of the invention provides an electrosurgical working end for performing high strength welding of tissue comprising a body having a tissue contacting energy delivery surface. The body includes pixel portions and non-pixel portions distributed within the tissue contacting surface. The pixel portions comprise a positive temperature coefficient of resistance (PTCR) material with at least one pixel portion configured to switch Rf current on and off in the at least one pixel portion responsive to tissue temperature adjacent the at least one pixel portion. The pixel portions can be configured to be coupled to an Rf current source such as an Rf generator. The pixelated energy delivery surfaces are capable of highly localized modulation of Rf energy application to the engaged tissue to create high strength tissue welds.