Figure 3. Average values (n=3) for surface average roughness (µm), maximum height (µm), skewness, and kurtosis of the right side of degrading bloodstains of various volumes at varying time points after deposition. Inlet images show topographical scans from 4 µL bloodstain (stain #2), 11 µL bloodstain (stain #1) and 20 µL bloodstain (stain #1) at 10 minutes and 120 minutes after deposition.
As the bloodstain desiccated, the surface average roughness decreased until approximately 20 minutes, and then increased slightly until plateauing at about 35-40 minutes (Figure 3, d). The maximum height of the bloodstains typically decreased until 20 minutes, which remained consistent until 120 minutes (Figure 3, b). A sharp decrease in height occurred as the bloodstain began to flatten out, and the rise around ~15 minutes corresponded with the formation of the RBC ‘donut’ (Figure 3). This trend was more difficult to confirm in the larger volumes of blood due to the lack of time points prior to 10 minutes. Kurtosis increased until approximately 20 minutes, and also plateaued at about 40 minutes (Figure 3, a). Interestingly, 11 μL displayed the greatest kurtosis values at almost every time point in the short-term experiments. The skewness values decreased up to 20 minutes, before increasing up to 40 minutes, where the values then plateaued (Figure 3, c). Similar to the kurtosis trends, the 11 μL bloodstains had higher relative skewness values. Kurtosis and skewness displayed opposite trends within the first 40 minutes, which was corroborated by the correlation coefficient (r = -0.70). Lastly, height distributions for the short-term experiments were assessed. The height of the bloodstain was higher at earlier time points and decreased sharply around 25-30 minutes (Figure 4). Interestingly, we observed variance in size distributions between volumes and replicates, with the maximum frequency ranging between approximately 30 – 60 µm.