This invention relates to the working end of a medical instrument that applies energy to tissue. In one embodiment, the instrument has a microfluidic tissue-engaging surface fabricated by soft lithography means together with optional superlattice cooling means that allows for very precise control of energy application, for example in neurosurgery applications. The tissue-engaging surface can eject a high-heat content vapor into the engaged tissue for treating tissue, while the superlattice cooling structure can prevent collateral thermal damage. Also, the superlattice cooling structure can be used to localize heat at a selected depth in tissue and prevent surface ablation. Also, the superlattice cooling structure can be used to prevent tissue sticking to a thermal energy delivery surface. In another embodiment, the tissue-engaging surface can be used in a jaw structure for sealing tissue together with hydrojet means for transecting the tissue.
