An apparatus (200, 300, 400, 500) for delivering a substance (433, 533) to skin tissue (250,450), comprising: - a housing (210, 310, 410, 510) defining a flat lower surface configured to contact a skin surface of the skin tissue (250, 450); - at least one opening (280, 380, 480, 580) provided in the flat lower surface (260, 360, 460, 560) of the housing (210, 310,410, 510); - a delivery arrangement (230, 330, 430, 530) provided in the housing (210, 310, 410, 510), the delivery arrangement configured to deliver the substance (433, 533) under elevated pressure through the at least one opening (280, 380, 480, 580) onto the skin surface of the skin tissue (250, 450); and - at least one low-pressure channel (222, 322, 422, 522) provided in the flat lower surface (260, 360, 460, 560) of the housing (210, 310,410, 510) proximal to and surrounding at least a portion of the at least one opening (280, 380, 480, 580), wherein the low-pressure channel (222, 322, 422, 522) is configured to apply a reduced pressure sufficient to maintain contact between the flat lower surface of the housing and the surface of the skin tissue (250, 450) in order to position the at least one opening (280, 380, 480, 580) against the surface of the skin tissue (250, 450) when the reduced pressure sufficient to maintain contact between the flat lower surface of the housing and the surface of the skin tissue (250, 450) is provided in the low-pressure channel (222,322,422,522), characterized in that the at least one opening (280, 380, 480, 580) and the at least one low-pressure channel (222, 322, 422, 522) are in coplanar alignment along the flat lower surface (260, 360, 460, 560) of the housing (210, 310, 410, 510), such that a portion of the flat lower surface (260, 360, 460, 560) of the housing (210, 310, 410, 510) separates the at least one opening (280, 380, 480, 580) from the at least one low-pressure channel (222, 322, 422, 522). - a housing (210, 310, 410, 510) defining a flat lower surface configured to contact a skin surface of the skin tissue (250, 450); - at least one opening (280, 380, 480, 580) provided in the flat lower surface (260, 360, 460, 560) of the housing (210, 310,410, 510); - a delivery arrangement (230, 330, 430, 530) provided in the housing (210, 310, 410, 510), the delivery arrangement configured to deliver the substance (433, 533) under elevated pressure through the at least one opening (280, 380, 480, 580) onto the skin surface of the skin tissue (250, 450); and - at least one low-pressure channel (222, 322, 422, 522) provided in the flat lower surface (260, 360, 460, 560) of the housing (210, 310,410, 510) proximal to and surrounding at least a portion of the at least one opening (280, 380, 480, 580), wherein the low-pressure channel (222, 322, 422, 522) is configured to apply a reduced pressure sufficient to maintain contact between the flat lower surface of the housing and the surface of the skin tissue (250, 450) in order to position the at least one opening (280, 380, 480, 580) against the surface of the skin tissue (250, 450) when the reduced pressure sufficient to maintain contact between the flat lower surface of the housing and the surface of the skin tissue (250, 450) is provided in the low-pressure channel (222,322,422,522),