Image Number 6 for United States Patent #6368858.
Cells in a matrix or in the matrix in a vessel are grown to form a multicellular aggregate. Pressure is exerted on the growing cells by the matrix or the matrix together with the vessel due to growing cellular mass displacing the matrix. A value representing pressure exerted on the cells is calculated and the pressure is modulated to control growth of the multicellular aggregate, or to produce a multicellular aggregate of a pre-selected size or a pre-selected size and shape. Matrices include agarose, alginate and collagen gels, and the pressure exerted on the cells can be non-isotropic. The cells may be tumor cells, or liver, pancreatic, brain, skin, bone or muscle cells, and cell growth can be in vitro or in vivo. When collagen forms the matrix, the matrix may contain glycosaminoglycan.