Popeye's Matrix (IMAGE) Ecole Polytechnique Fédérale de Lausanne Caption Contractile fibroblasts secrete and organize extracellular matrix fibers (blue) that are loaded with growth factor complexes (green), resulting in a turquoise overlay color. The contractile fibers inside the cells are visualized by detecting a smooth muscle protein (red). The cells' nuclei are visualized in yellow. 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.