Influence of pia-arachnoid complex on the indentation response of porcine brain at different length scales.

Brain tissues are surrounded by two tightly adhering thin membranes known as the pia-arachnoid complex (PAC), which is pivotal in regulating brain mechanical response upon mechanical impact. Despite the crucial role of PAC as a structural damper protecting the brain, its mechanical contribution has received minimal attention. In this work, the mechanical contribution of PAC on brain tissues against mechanical loading is characterized by using a custom-built indentation apparatus. The indentation responses of the isolated and PAC-overlaid brains are quantitatively compared at different length scales and strain rates. Results show that PAC substantially affects the indentation response of brain tissues at micro- and macro-scales and provides better protection against mechanical impact at a relatively small (μm) length scale. The modulus of the PAC-overlaid brain shows a threefold stiffening at the microscale compared with that of the isolated brain (with instantaneous shear modulus distribution means of 0.85 ± 0.14 kPa versus 2.64 ± 0.43 kPa at the strain rate of 0.64 s-1 and 1.40 ± 0.31 kPa versus 4.02 ± 0.51 at 1.27 s-1). These findings indicate that PAC seriously affects the mechanical response of brain tissues, especially at the microscale, and may have important implications for the studies of brain injury.