This invention relates to a novel surgical device scalable to small dimensions for thermally-mediated treatments or thermoplasties of targeted tissue volumes. An exemplary embodiment is adapted for fusing, sealing or welding tissue. The instruments and techniques utilize a thermal energy delivery means, for example an electrical energy source, to instantly elevate the temperature of a biocompatible fluid media within an electrically insulated instrument portion. The altered media which may then be a gas is characterized by a (i) a high heat content, and (ii) a high exit velocity from the working end, both of which characteristics are controlled to hydrate tissue and at the same time denature proteins to fuse, seal, weld or cause any other thermally-mediated treatment of an engaged tissue volume—；while causing limited collateral thermal damage and while totally eliminating electrical current flow the engaged tissue volume. The system can further utilize a piezoelectric material that carried fluid channels to apply compressive forces to the fluid eject the fluid from the working end of make it require less electrical energy to convert it to a gas.
