Methods are provided for hermetically sealing an opening in a reservoir of a containment device. The method comprises applying a polymeric material to an opening in a reservoir of a containment device, the reservoir comprising reservoir contents (such as a drug or a sensor) to be hermetically isolated within the reservoir, the applied polymeric material closing off the opening and forming a temporary seal; and adhering a hermetic sealing material onto the polymeric material to hermetically seal the opening. The reservoir can be a micro-reservoir. The containment device can comprises an array of two or more of reservoirs, and the method comprises hermetically sealing each of the two or more reservoirs.