A variable-height thermal-interface assembly for transferring heat from a heat source to a heat sink comprises a slidable interface between two contacting surfaces, the slidable interface inclined diagonally relative to the z-axis. The weight has a weighted body and a clip securely attached thereto. Such devices and methods can be effectively used to deliver bioactive substances into skin. The document can be automatically aligned by the weight per se and the operations of paper placement and removal can be simplified.