Tissue grinders produce homogenates by a combination of shearing and compression actions. The tissue sample is progressively ground (sheared) into smaller pieces at the rounded end of the pestle as the spinning pestle is lowered into the tube. As the pestle is forced lower into the tube, the sample is displaced and forced between the straight outside wall of the pestle and the inside wall of the tube, compressing the tissue cells until they rupture. When the tube is pulled away from the pestle, a slight vacuum is created that pulls the sample back past the compression area, resulting in an additional homogenization stroke. The degree of homogenization is controlled by the clearance between the pestle’s and tube’s cylindrical section (radial distance usually 0.002 - 0.003 inches), the rotational speed of the pestle, and the number of compression strokes made.
