Cell alignment is induced by cyclic changes in cell length: studies of cells grown in cyclically stretched substrates

Many types of cells, when grown on the surface of a cyclically stretched su bstrate, align away from the stretch direction. Although cell alignment has been described as an avoidance response to stretch, the specific deformati on signal that causes a cell population to become aligned has not been iden tified. Planar surface deformation is characterized by three strains: two n ormal strains describe the length changes of two initially perpendicular li nes and one shear strain describes the change in the angle between the two lines. The present study was designed to determine which, if any, of the th ree strains was the signal for cell alignment. Human fibroblasts and osteob lasts were grown in deformable, rectangular, silicone culture dishes coated with ProNectin, a biosynthetic polymer containing the RGD ligand of fibron ectin, 24 h after plating the cells, the dishes were cyclically stretched a t 1 Hz to peak dish stretches of 0% (control), 4%, 8%, and 12%. After 24 h of stretching, the cells were fixed, stained, and their orientations measur ed. The cell orientation distribution was determined by calculating the per cent of cells whose orientation was within each of eighteen 5 degrees angul ar intervals. We found that the alignment response was primarily driven by the substrate strain which tended to lengthen the cell (axial strain). We a lso found that for each cell type there was an axial strain limit above whi ch few cells were found. The axial strain limit for fibroblasts, 4.2 +/- 0. 4% (mean +/- 95% confidence), was lower than for osteoblasts. 6.4 +/- 0.6%. We suggest that the fibroblasts are more responsive to stretch because of their more highly developed actin cytoskeleton. (C) 2001 Orthopaedic Resear ch Society. Published by Elsevier Science Ltd. All rights reserved.