Bone marrow aspiration devices and methods are disclosed for use in preparing a substrate. In general, the device includes an elongate penetrating element, a chamber adapted to retain a substrate, and a fluid extraction mechanism that is effective to pull fluid through the elongate penetrating element, into the chamber, and through the substrate. The device is particularly advantageous in that it will allow for the removal of fluids from a patient's body and the preparation of a substrate in a single process, thereby providing a more efficient method and device for preparing a substrate.