The use of liver biomechanics in forensic pathology

Stiffness and plasticity of human tissues are routinely assessed during forensic autopsy and have recently been identified as a promising metric for estimating time since death in animal models. In this study, the biomechanical state of the human liver is investigated concerning pathology, age at death, sex, liver weight, autolysis, and blood congestion. Additionally, its use for biomechanical time since death estimation is evaluated. The storage, loss, and complex shear moduli of 54 human liver parenchyma samples collected during routine forensic autopsies, were determined using a rheometer. All samples were microscopically analyzed for signs of pathology, autolysis, and blood congestion. High-grade fatty liver samples (n = 6) exhibited significantly higher storage moduli, and complex shear moduli compared to healthy (n = 27), low-grade fatty liver (n = 14), and cirrhotic (n = 7) samples (p ≤ 0.02). High-grade fatty liver samples also had significantly higher loss moduli compared to healthy and cirrhotic samples (p ≤ 0.04). The rheological properties of the human liver were unrelated to age at death (p ≥ 0.26), liver weight (p ≥ 0.13), and sex (p ≥ 0.32). Autolysis significantly increased the loss moduli of healthy liver samples (p = 0.01). Blood congestion significantly lowered the loss moduli of healthy (p = 0.03) and fatty (p < 0.01) samples, as well as storage moduli (p = 0.01), and complex shear moduli (p = 0.01) of fatty samples. A significant positive correlation between the post-mortem interval and the loss modulus was observed for healthy samples, if only samples without signs of blood congestion were included (p = 0.02; n = 9). When stored at 4 °C for an average of eight days post-mortem, liver biomechanics was significantly altered by fatty infiltration, autolysis, blood congestion, and the post-mortem interval, while liver weight, age at death, and sex had no relevant impact.