The Investigation of Fluid Shear Stress and Subsequent Conformational Changes of von Willebrand Factor Observed in an Optical Trap

Open Access
Author:
Candela, Xavier Joseph
Area of Honors:
Bioengineering
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Keefe B Manning, Thesis Supervisor
  • Keefe B Manning, Honors Advisor
  • Peter J Butler, Faculty Reader
Keywords:
  • vWF
  • optical trap
  • fluid shear
  • von Willebrand Factor
  • LVADs
Abstract:
Thousands of ventricular assist devices (VADs) are implanted in patients with advanced heart failure in the U.S. each year. One complication associated with the use of these devices is the development of Acquired von Willebrand Syndrome (AVWS), a condition that arises when von Willebrand Factor (vWF) fails to adequately recruit platelets and arrest bleeding. Elevated shear stress levels introduced by the VADs are believed to cause the conformational change and subsequent enzymatic cleavage of the protein. Determining the threshold shear stresses necessary to induce a conformational change in the vWF protein would allow makers of cardiac prosthesis devices to avoid introducing such forces, and thus, reduce the incidence of AVWS. In the present study an optical trap was used to quantify the relationship between shear stress values and the degree of conformational change observed in the vWF protein. VWF was extracted from human plasma, purified through column chromatography, identified using a Western Blot and imaging, and finally attached to polystyrene beads. The polystyrene beads are then fixed in place by the use of an optical trap. The stiffness of the trap is calculated then software is used to track the motion of a bead within a flow chamber of DPBS solution by movement of a piezoelectric stage. Bead displacements and the phase shift between fluid velocity and bead motion were measured for vWF-coated beads under low, moderate, and high shear conditions. A difference in bead displacement between the three shear conditions is observed. This is presumably caused by an increase in the effective radius of the bead due to the characteristic unraveling of the vWF protein under significant amounts of shear stress.