Bioreactor-derived hiPSC-PLTs manifest structural and functional properties of human blood PLTs. (A) The hiPSC-MKs reach maximal diameter (20-60 µm) on culture day 15. (B) The hiPSC-MKs are ultrastructurally similar to primary human MKs and contain a lobulated nuclei, invaginated membrane system, glycogen stores, organelles, and characteristic secretory granules. (C) The hiPSC-MKs in static culture begin producing proPLTs at 6 hours postpurification and reach maximal proPLT production at 18 hours. White arrows denote proPLT-producing MKs. (D) The hiPSC-MKs under physiological shear stress (∼600 mPa) begin producing proPLTs immediately upon trapping and extend/release proPLTs within the first 2 hours of culture. Insert shows multiple PLT-sized swellings denoted by white arrows along single proPLT extension. (E) Percent proPLT-producing hiPSC-MKs under physiological shear stress are increased significantly to ∼90% over static cultures (∼10%). (F) ProPLT extension rates under physiological shear stress are ∼19 µm/min. Data are represented as a box-and-whisker plot where light gray indicates the upper quartile and dark gray indicates the lower quartile. (G) Bioreactor-hPLTs display forward and side scatter, and surface biomarker expression is characteristic of human blood PLTs. (H) Bioreactor-hPLTs are ultrastructurally similar to human blood PLTs and contain a cortical MT coil, open canalicular system, dense tubular system, mitochondria, and characteristic secretory granules (both panels). Top right insert, lower panel shows peripheral MT coil. (I) Bioreactor-hPLTs are anucleate, morphologically to human blood PLTs, and display comparable MT expression. (J) Bioreactor-mPLTs form filpodia/lamellipodia on activation and are spread on a glass surface. Scale bars represent 1 µm (B), 50 µm (C-D), 0.5 µm (H), and 5 µm (I-J).