von Willebrand Factor (IMAGE) Washington University School of Medicine Caption The building blocks of von Willebrand Factor remain separate at the slightly basic pH of 7.4 (left). In a more acidic environment (right), the VWF building blocks self-assemble into long chains and form the protein's signature helical tubules. This shape is vital to blood clotting. When VWF in the blood finds sites of injury, its helical tube unfurls to catch platelets and form blood clots. Credit J. Evan Sadler, M.D., Ph.D. 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.