Proplatelet extension across the endothelial barrier (red) and subsequent release of (pre)platelets by megakaryocytes (green), as occurring in bone marrow sinusoids in vivo, has been very difficult to reproduce in vitro. The microfluidic bioreactor design by Thon and colleagues now recapitulates many critical aspects of this process, enabling platelet production and its high-resolution real-time visualization in vitro.¹  Bone marrow cryosection was probed with anti-CD105 (Alexa Fluor 647; red), anti-GPIb (Alexa Fluor 488; green) antibodies and counterstained with 4′,6 diamidino-2-phenylindole (blue).