Provided herein are methods and materials for assessing platelet activity and/or the ability of substances (e.g., small molecule compounds and compositions comprising the same) to inhibit or activate platelet activity. For example, this document provides methods and materials that can include (a) applying abnormal flow conditions (e.g., oscillatory shear stress) to a sample of platelets (e.g., a blood sample or platelet-rich plasma sample) to stimulate the platelets, and (b) assessing the activity of the platelets. In some embodiments, the activity of the platelets can be assessed by measuring the amount of superoxide radial or the rate and/or level of platelet aggregation within the sample.