The invention relates to superparamagnetic iron oxide nanoparticles for use in sutureless thermal mediated tissue fusion. The nanoparticles are dispersed in a biocompatible solder material and heated by application of an alternating electromagnetic field. The invention furthermore relates to a pharmaceutical preparation comprising superparamagnetic iron oxide nanoparticles, preferably with a diameter of below 20 nm, and such nanoparticles coated with an organic compound and/or imbedded in a biocompatible material, for example a soldering agent. The invention likewise relates to the use of superparamagnetic iron oxide nanoparticles for the manufacture of a medicament for use in tissue fusion with an alternating electromagnetic field, and to a method of tissue fusion wherein superparamagnetic iron oxide nanoparticles dispersed in a biocompatible interface material are heated by application of an alternating electromagnetic field.