Two or more expandable fusion devices are capable of being installed inside an intervertebral disc space. A tubular sheath includes a distal end portion situated on a proximal end side of the operating section having a circular-section portion having a circular cross-section perpendicular to a longitudinal central axis and a pair of flat portions formed by cutting the opposite sides of the circular-section portion and in sliding contact with the proximal end portions of the forceps. A blocking material or an injection pin are used to interrupt the flow of molding compound through an injection molding system, and thereby prevent molding compound from flowing onto the known bad substrate sites. Other microfluidic devices include an array of reaction chambers formed by intersecting vertical and horizontal flow channels, with the ability to regulate temperature at the reaction chambers.