Granular platelet-sized polyphosphate nanoparticles (polyP NPs) were encapsulated in sterically stabilized liposomes, forming a potential, targeted procoagulant nanotherapy resembling human platelet dense granules in both structure and functionality. Dynamic light scattering (DLS) measurements reveal that artificial dense granules (ADGs) are colloidally stable and that the granular polyP NPs are encapsulated at high efficiencies. High-resolution scanning transmission electron microscopy (HR-STEM) indicates that the ADGs are monodisperse particles with a 150 nm diameter dense core consisting of P, Ca, and O surrounded by a corrugated 25 nm thick shell containing P, C, and O. Further, the ADGs manifest promising procoagulant activity: Detergent solubilization by Tween 20 or digestion of the lipid envelope by phospholipase C (PLC) allows for ADGs to trigger autoactivation of Factor XII (FXII), the first proteolytic step in the activation of the contact pathway of clotting. Moreover, ADGs' ability to reduce the clotting time of human plasma in the presence of PLC further demonstrate the feasibility to develop ADGs into a potential procoagulant nanomedicine.