Variation in nerve fiber strain in brain tissue subjected to uniaxial stretch

Diffuse axonal injury (DAI) is the most frequent type of closed head in jury involved in vehicular accidents, and is characterized by structural and functional damage of nerve fibers in the white matter that may be caused by their overstretch. Because nerve fibers in the white matter have a undulated network-like structure embedded in the neuroglia and extracellular matrix, and are expected to be much stiffer than other components, the strain in the nerve fiber is not necessarily equal to that in the white matter. In this study, the authors have measured strain of the nerve fibers running in various directions in porcine brain tissue subjected to uniaxial stretch and compared them with global strain (tissue strain). The nerve fiber strain had a close correlation with their direction, and was smaller than surrounding global strain. Tensile strain appeared in the fibers ranging from 0 to 60 degrees relative to stretch direction while strain was compressive in those ranging from 60 to 90 degrees. The tensile and compressive strain at maximum stretch was 0.07 and -0.03, respectively, for nerve fibers, while it was 0.33 and -0.12, respectively, for the whole tissue. Roughly speaking, the maximum neural fiber strain was approximately 1/3 of its surrounding tissue strain in respective fiber direction, indicating that the local strain in the neural fibers is not equal to global strain in the brain tissue. Consideration of neural fiber alignment in the white matter is important in studying the mechanical aspects of pathogenesis in DAI.