The Food and Drug Administration has approved a device by ThermoGenesis Corp. that separates and stores adult stem cells from bone marrow, a critical step in the evolution of the Rancho Cordova company. The FDA on Monday approved the company’s MarrowXpress device for use in clinical laboratories or during operations to concentrate bone marrow cells. Stem cells for bone marrow are used in the U.S. for clinical trials of treatments for blood disorders, some heart diseases, peripheral artery disease and diabetes. The company expects the device to also soon be used by researchers who are studying vascular and orthopedic injuries. ThermoGenesis stock increased almost 16 percent in trading Monday on Nasdaq, after the announcement.