The Mechanical Characterisation of Bovine Embolus Analogues Under Various Loading Conditions

Embolus Analogues (EAs) can provide understanding of the mechanical characteristics of blood clots of cardiac origin. Bovine EAs (n = 29) were fabricated with varying concentrations of thrombin (0-20 NIHU/ml blood). Histological staining confirmed that EA composition compared sufficiently with human samples reported in literature. EAs were mechanically described under seven testing conditions: tensile, compression, shear wave ultrasound elastography (SWE), parallel plate rheometry, indentation, creep and relaxation. The Young modulus of bovine EAs in tension varied from 7 kPa (5% strain) to 84 kPa (50% strain). The compressive Young modulus increased with increasing thrombin concentration, which was in agreement with the SWE results. There was no significant difference in Young modulus throughout the clot (p < 0.05). The EAs displayed a non-linear response under parallel plate rheometry, creep and stress relaxation. The 3rd order Mooney-Rivlin constitutive equation and Standard Linear Solid model were used to fit the non-linear stress-strain response and time-dependent properties, respectively. This is the first study in which bovine EAs, with and without addition of thrombin, are histologically and mechanically described with corresponding proposed constitutive equations. The equations and experimental data determined can be applied for future numerical and experimental testing of mammalian EAs and cardiac source clots.