Proplatelet elongation is caused by cytoplasmic dynein-dependent microtubule sliding, and not tubulin polymerization. Primary mouse MKs were (A) untreated, incubated with (B) 100 nM nocodazole (microtubule polymerization inhibitor), or (C) 1 mM EHNA (cytoplasmic dynein inhibitor) before infusion into the microfluidic bioreactor. Whereas nocodazole treatment had no visible effect on shear-induced proplatelet production and proplatelet elongation compared with no-drug controls (Thon et al¹² ), inhibition of cytoplasmic dynein visibly reduced both. Scale bars are 50 µm.