Desiccation of a sessile drop of blood: Cracks, folds formation and delamination

The drying of a deposited drop of blood leads to the formation of a complex pattern. Numerous coupled mechanisms are involved in this process, such as evaporation, flow motion, adhesion, gelation, crack formation and delamination. In this paper, we focus on the mechanisms related to the formation of cracks. The dynamics of fracture, the mean space cracking and delamination are examined. The initial crack spacing appears to be correctly predicted by the Allain and Limat model implemented for open geometries. The final pattern is highly dependent on the wettability of the substrate. Indeed, whereas a wetting situation leads to a ring-like deposit with regularly spaced radial cracks at the periphery and small-scaled disordered fractures at the centre, a non-wetting situation reveals a complex shape composed of radial cracks and folds due to the development of buckling instabilities. The different behaviours encountered were analysed with a stability diagram obtained for colloidal suspensions, and a good agreement was found. The study reveals numerous analogies between model suspensions and the fluid considered.