Semi-closed Microfluidics Systems in the Modification of Surface Adhesion

Humankind has used adhesives since time immemorial. Birch bark, for example, was used as a natural adhesive in prehistorical time. Nowadays, synthetic adhesives are present nearly everywhere we look; they areused in clothing, furniture, vehicles, electronics, medicine etc. Most applications and thus development of adhesives are related to permanent chemical bonding. In the last decade switchable adhesives which can quickly alternate between strong bonding and delamination has aroused interest in both academia and industry.

This has been inspired by the hierarchical and fibrillar structures observed in insects’ and gecko’s feet which allow a fast animal displacement on vertical and inverted substrates. Long and slender fibres with mushroom-like tips can remarkably increase feet’s adhesive strength to surfaces due to splitting of the contact patch into multiple smaller contact spots; thisrequires greater energy for the crack propagation than in the case of a largersingle contact. Different artificial structures have mimicked this principle and rely on external stimuli such as magnetic and electric fields, mechanical impulses and environmental changes such as temperature, pH and solvent, to trigger adhesion or delamination from surfaces. In most cases the stimuli act directly on the surface modifying its chemical properties or geometry.