Effect of freezing on mechanical properties of ovine brain tissue

Freezing at -20 °C impacts the mechanical properties of post mortem brain tissue, which has implications for forensic science, particularly for estimating the post mortem interval (PMI). Freezing is examined as a method that may offer an extended window for forensic analysis by halting tissue degradation processes or allow tissue transfer to specialized departments. A rheological examination of samples from various brain regions of 21 ovine brains (frontal lobe, anterior deep brain, posterior deep brain, parietal lobe, superior colliculus, medulla, pons, cerebellum) was conducted. The brain tissue was tested on the day of sacrifice, after short term freezing (<16 days) and long-term freezing (95-110 days) to track the changes in mechanical properties. The results showed nearly complete overlap in storage, loss and complex shear moduli between samples tested on the day of sacrifice and their frozen counterparts for all locations, with no statistically significant differences (p > 0.05) between the moduli of the three groups. Freezing had no statistically significant impact on the tissue's mechanical properties across all tested locations. The study thus provides new insights regarding the preservation of ovine brain samples for up to 110 days for forensic biomechanical analyses.