This invention provides compositions and methods useful for the processing of a tissue sample and the preparation of cells, cell aggregates and/or tissue fragments. The invention provides two-stage filer devices and two-membrane devices. Cell aggregates and/or tissue fragments prepared using such devices and according to methods of the present invention can be used in a variety of assay systems, including, but not limited to, drug validation assays, drug screening assays, proliferation assays, metabolic assays, metastasis assays, angiogenesis assays, binding assays, biochemical assays, cellular assays, genetic assays, and the like.
