Biaxial and failure properties of passive rat middle cerebral arteries.

Rodents are commonly used as test subjects in research on traumatic brain injury and stroke. However, study of rat cerebral vessel properties has largely been limited to pressure-diameter response within the physiological loading range. A more complete, multiaxial description is needed to guide experiments on rats and rat vessels and to appropriately translate findings to humans. Accordingly, we dissected twelve rat middle cerebral arteries (MCAs) and subjected them to combined inflation and axial stretch tests around physiological loading conditions while in a passive state. The MCAs were finally stretched axially to failure. Results showed that MCAs under physiological conditions were stiffer in the axial than circumferential direction by a mean (±standard deviation) factor of 1.72 (±0.73), similar to previously reported behavior of human cerebral arteries. However, the stiffness for both directions was lower in rat MCA than in human cerebral arteries (p<0.01). Failure stretch values were higher in rat MCA (1.35±0.08) than in human vessels (1.24±0.09) (p=0.003), but corresponding 1st Piola Kirchhoff stress values for rats (0.42±0.09 MPa) were considerably lower than those for humans (3.29±0.64 MPa) (p<0.001). These differences between human and rat vessel properties should be considered in rat models of human cerebrovascular injury and disease.