A method for forming an extracellular matrix material (ECM) material includes providing at least an ECM composition containing ECM particles varying in their capacity for migration through a fluid medium, including at least one population of expanded ECM particles. The ECM composition is combined in a fluid medium to form a flowable ECM composition. The flowable ECM composition is subjected to a centrifugal force in a mold for a period of time sufficient to distribute the ECM particles according to differences in their physical characteristics. The ECM composition is dried to form a dried ECM material having a density gradient extending from a less dense region to a more dense region. The dried ECM material may formed as a porous, substantially acellular ECM material expandable in an aqueous fluid environment by at least 100% in volume.
