A method of preparing a stem-cell containing solution includes: (1) storing a mixture of a blood sample and a divalent cation chelating agent at a temperature between 2 and 12 degrees Celsius for a period of from 3 hours to 72 hours so as to have the mixture with two or more separate layers, wherein a liquid in one of the separate layers contains platelets and stem cells； (2) collecting the liquid into a container； (3) centrifuging the liquid in the container until multiple particles suspended in the liquid are deposited at a bottom of the container, wherein the particles contain the stem cells and the platelets； and (4) re-suspending the particles in a buffer or liquid.
