Development of a Magnetic Bead Microrheometry System to Study Thrombus Rheology

Open Access
Rogers, Andrew Mark
Area of Honors:
Bachelor of Science
Document Type:
Thesis Supervisors:
  • Keefe B Manning, Honors Advisor
  • Peter J Butler, Thesis Supervisor
  • Steven Deutsch, Faculty Reader
  • Magnetic Bead Microrheometry
  • Thrombus
  • Hydrogel
The primary objective of this study was to develop a magnetic bead microrheometry system to measure spatially heterogeneous thrombus elasticity. Elasticity of a thrombus may affect the time and location of embolism, leading to stroke or heart attack. Previous studies in thrombus rheology studied entire thrombi as one homogeneous material, but have not accounted for the heterogeneous composition of thrombi. The spatial variation in magnetic force developed by a computer controlled electromagnet was calibrated by measuring the displacement of 45 µm fluorescent paramagnetic beads embedded in polyacrylamide hydrogels of homogeneous tunable elasticity. Nm-scale displacements of beads were measured using bead tracking software that cross-correlated bead position between recorded frames. Polyacrylamide hydrogels with an elasticity of 0.2 kPa and 1.61 kPa were used to calibrate the working area of the system and gather displacement data for beads in that area. These values were chosen to represent the upper and lower bounds of previous thrombus rheology studies. This force distribution in the gel due to magnetic force on the bead was then derived by integrating the total force of the gel on the bead after a prescribed displacement using finite element analysis. The force calculations were interpolated to map force as a function of position within the working area in order to test samples of spatially non-uniform elasticity. By studying thrombus rheology using magnetic bead microrheometry, localized measurements of elasticity can be used to correlate with local cellular and fibrin composition and flow dynamics on thrombus elasticity.