Which of the following is NOT an example that activates platelets?

Platelet activation is a critical component of hemostasis, and it is typically triggered by various stimuli. The correct answer is the negative charge because it does not directly activate platelets in the same way as the other options listed.

Exposed collagen is one of the key factors that activate platelets. When vascular injury occurs, the collagen layer beneath endothelial cells is exposed, leading to platelet adherence and activation. This interaction involves specific receptors on platelets that recognize collagen, initiating aggregation and the release of clotting factors.

Foreign material can also serve as a stimulus for platelet activation. When platelets encounter biomaterials, such as those found in medical devices or implanted materials, they identify these as foreign and begin to activate, which is crucial in both normal hemostatic processes and pathological conditions, such as thrombosis.

Wettable surfaces contribute to platelet activation as well. These surfaces enhance the adhesion and spreading of platelets, leading to the formation of a thrombus. Wettable surfaces allow proteins to adsorb, which can then interact with platelets, promoting activation and stabilization of the clot.

While a negative charge can influence the behavior of platelets at a biochemical level, it does not actively activate them like the other stimuli do. Therefore, the inclusion of