The Fibroblast Muscles (IMAGE) Ecole Polytechnique Fédérale de Lausanne Caption In the migration phase of wound healing fibroblasts (upper left corner) have thin contractile fibers (red) and form only small attachment points (green) with a soft extracellular matrix. When they pull on a stiffened matrix fibroblasts release a growth factor that turns them into contractile cells. Fibroblast strength is increased by recruiting a smooth muscle protein (blue) into their fibers which become extraordinary thick (and turn purple in this picture) and terminate in enormous anchor points (green). Note that both cells have been photographed at the same magnification. Credit EPFL/LCB Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.