A device for repetitive needleless injection of a liquid into a surface includes a handheld unit that includes at least a cell that is fillable with the liquid. A propulsion mechanism is configured to apply a sequence of pressure pulses to the liquid. Each pulse ejects a micro jet of the liquid from the cell via an orifice between the cell and the exterior of the handheld unit with a velocity that is sufficient to enable the micro-jet to penetrate into the surface. A reservoir is connected to the cell by a conduit to enable the liquid to flow from the reservoir to the cell to replace the liquid that is ejected in the micro-jet. A controller is configured to operate the propulsion mechanism repeatedly so as to eject the sequence of the micro-jets.