Figure 3.

Contact angle measurement with ImageJ’s Contact Angle plugin. Following the manual selection of the first 2 points (red arrows) to determine the baseline, the periphery of the blood sample was marked to calculate the contact angle between the surface and blood. It is important to point out that an ellipse best-fit analysis poses itself between the circle best fit (green arrow) and an absolute best-fit function. Sometimes the drop is not perfectly symmetric or there is a slight effect due to gravity. In this case, an almost-circle (blue arrow) analysis can provide useful results.