A device for delivering fluid into the body is provided. The device may comprise a reservoir including at least one wall for retaining fluid and a plunger (400), wherein the plunger is articulated with a drive screw (300) having a distal end (304) that rotates within the plunger and displaces the plunger in a linear direction. The device may further comprise a reusable part having a motor, one or more gears and a receiving portion, and also a disposable part having a reservoir, a plunger and a drive screw having a proximal end capable of engaging with the receiving portion upon connecting the reusable part and the disposable part
