A micro-needle device comprising an active substance layer (3) having a plurality of active substance chambers (4) formed therein, a drive substance layer (9) having a plurality of drive substance chambers (10) formed therein and a needle support layer (5) having a plurality of micro-needles (6) extending therefrom. An activation layer (12) comprising a plurality of heating elements (14) for heating an expandable drive substance (11) located in the drive substance chambers (10) for in turn urging the second membrane (16) into the active substance chamber (4) for pressurizing and urging an active substance (2) therefrom through the corresponding micro-needle (6). A plurality of membrane accommodating recesses (25) extend into the needle support layer (5) for accommodating the first membrane (15) as the active substance in the corresponding active substance chamber (10) is pressurized. A puncturing member (33) with a piercing point (35) extends into each membrane accommodating recess (25). A barrier grating (41) extends across each active substance chamber (4) for preventing contact between the second membrane (16) and the corresponding puncturing member (33).