Mechanotransduction of Magnetically Applied Forces Leads to Mechanical Stiffening of Platelet-Rich Plugs

The mechanobiology of platelets governs early hemostasis, where their contractile forces compact and stiffen the nascent plug. However, the dynamic changes in the stiffness of a nascent platelet-rich plug have been difficult to measure. Here, we introduce a microfluidic assay integrating microscale blocks with magnetic microposts to assess platelet forces and plug stiffness. Rotation of a multipole ring magnet beneath the microfluidic channel generates oscillatory motion in the magnetic microposts. As blood enters the channel and platelets aggregate around the blocks and microposts, the oscillatory motion is progressively dampened, providing a direct measure of plug stiffness. Additionally, the deflections of the microposts are used to quantify platelet-generated forces during intermittent periods without magnetic actuation. With this approach, we find that the rate of stiffening and overall plug stiffness correlate not only with the magnitude of platelet forces, but also with the magnitude of the magnetically applied load. In contrast, pharmacological inhibition with acetylsalicylic acid or blebbistatin markedly reduced the process of plug stiffening, indicating that platelet activation and myosin-based contractility are required. Together, these findings establish a novel microfluidic platform for probing platelet biomechanics under pathophysiological shear and demonstrate that platelet mechanotransduction governs the mechanical maturation of early hemostatic plugs.