The story of the three bloods: the effect of coagulation on drying blood droplets

Abstract

In order to pursue criminals as quickly and efficiently as possible, forensic analysts must glean a wealth of information from a limited set of evidence in a short amount of time. This research aims to expand the information acquired from a crime scene by increasing understanding of blood drying behavior. Blood is a mixture of biological colloids and proteins, the drying of which has been examined for some time. These experiments overwhelmingly use anticoagulants such as EDTA and tri-sodium citrate to extend the lifetime and transportability of the blood by preventing coagulation, making it easier to perform laboratory experiments. While experiments using anticoagulated blood produce useful information for personalised medicine, they may be of limited relevance for the typical crime scene. To extend the usefulness of blood droplet research to reallife crime scenes where coagulation naturally occurs, fresh blood coagulation and a coagulation-like process utilised by the medical community for clotting assays were introduced to small whole blood droplets. Gravimetrics, optical coherence tomography, and image analysis of drying time-lapses for various geometries were used to examine three major areas: evaporation dynamics, cracking patterns, and substrate adhesion. Experiments found important differences in the delamination, internal dynamics, and final morphology of the droplets which may impact forensic conclusions, though the drying time and evaporation rate were found to be identical across all treatments