Influence of evaporation rate on cracks’ formation of a drying drop of whole blood

The influence of the drying rate on pattern formation of a dried drop of whole blood is investigated. A range of relative humidity (RH) between 12.0% and 66.5% is studied. Drops of whole blood of same volume are gently deposited on microscope glass substrates. A top-view camera operates at a typical frame rate of 10 frames per second, which is sufficient to monitor the drying regime of the drop (deposition, gelation, and fracturation). Also, the evolution of the morphological structure of patterns made up of cracks and their arrangement in the corona region is studied. For this purpose, a manual segmentation is used as a reference method for the validation of our automatic developed segmentation method. This automatic segmentation method enables automatic extraction and morphological characterization of patterns. We show that the evaporation rate influences structural distribution of plaques, and consequently, the final plaques diameter at the end of the evaporation process. At low drying rate (high RH), plaques diameter show good agreement between automatically and manually segmented plaques with a slight difference. Also, automatic segmentation overestimates angular deviation. Our experimental results also show that the length of the corona region remains constant whatever is the RH levels.