A microfluidic device comprising: —a first wall comprising a first substrate on which a plurality of closed patterns is grafted, —a second wall, facing the first wall, comprising a second substrate, —a plurality of nucleic acids grafted either on the first substrate or on the second substrate, wherein each nucleic acid comprises a barcode that encodes the position of the nucleic acid on said first or second substrate, wherein at least the plurality of closed patterns or the second substrate is made of an actuatable hydrogel which is swellable between a retracted state and a swollen state in which the closed patterns and the second substrate come into contact.