Background The pia arachnoid complex (PAC) is a cerebrospinal fluid-filled tissue conglomerate that surrounds the brain and spinal cord. Pia mater adheres directly to the surface of the brain while the arachnoid mater adheres to the deep surface of the dura mater. Collagen fibers, known as subarachnoid trabeculae (SAT) fibers, and microvascular structure lie intermediately to the pia and arachnoid meninges. Due to its structural role, alterations to the biomechanical properties of the PAC may change surface stress loading in traumatic brain injury (TBI) caused by sub-concussive hits. The aim of this study was to quantify the mechanical and morphological properties of ovine PAC. Methods Ovine brain samples (n = 10) were removed from the skull and tissue was harvested within 30 min post-mortem. To access the PAC, ovine skulls were split medially from the occipital region down the nasal bone on the superior and inferior aspects of the skull. A template was used to remove arachnoid samples from the left and right sides of the frontal and occipital regions of the brain. 10 ex-vivo samples were tested with uniaxial tension at 2 mm s −1 , average strain rate of 0.59 s −1 , until failure at < 5 h post extraction. The force and displacement data were acquired at 100 Hz. PAC tissue collagen fiber microstructure was characterized using second-harmonic generation (SHG) imaging on a subset of n = 4 stained tissue samples. To differentiate transverse blood vessels from SAT by visualization of cell nuclei and endothelial cells, samples were stained with DAPI and anti-von Willebrand Factor, respectively. The Mooney-Rivlin model for average stress–strain curve fit was used to model PAC material properties. Results The elastic modulus, ultimate stress, and ultimate strain were found to be 7.7 ± 3.0, 2.7 ± 0.76 MPa, and 0.60 ± 0.13, respectively. No statistical significance was found across brain dissection locations in terms of biomechanical properties. SHG images were post-processed to obtain average SAT fiber intersection density, concentration, porosity, tortuosity, segment length, orientation, radial counts, and diameter as 0.23, 26.14, 73.86%, 1.07 ± 0.28, 17.33 ± 15.25 µm, 84.66 ± 49.18°, 8.15%, 3.46 ± 1.62 µm, respectively. Conclusion For the sizes, strain, and strain rates tested, our results suggest that ovine PAC mechanical behavior is isotropic, and that the Mooney-Rivlin model is an appropriate curve-fitting constitutive equation for obtaining material parameters of PAC tissues.

中文翻译：

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单轴张力下绵羊软膜蛛网膜复合物生物力学特性的离体量化

背景软脑膜蛛网膜复合体 (PAC) 是一种充满脑脊液的组织团块，围绕着大脑和脊髓。软脑膜直接粘附在大脑表面，而蛛网膜则粘附在硬脑膜的深层表面。被称为蛛网膜下小梁 (SAT) 纤维的胶原纤维和微血管结构位于软脑膜和蛛网膜的中间。由于其结构作用，PAC 生物力学特性的改变可能会改变由亚震荡撞击引起的创伤性脑损伤 (TBI) 的表面应力负荷。本研究的目的是量化绵羊 PAC 的机械和形态特性。方法 从头骨中取出羊脑样本 (n = 10)，并在死后 30 分钟内收获组织。要访问 PAC，绵羊的头骨从枕骨区向内侧分裂，向下到头骨上部和下部的鼻骨。使用模板从大脑额叶和枕叶区域的左侧和右侧移除蛛网膜样本。10 个离体样品在 2 mm s -1 的单轴张力下进行测试，平均应变速率为 0.59 s -1 ，直到在提取后 < 5 小时失败。力和位移数据是在 100 Hz 下获得的。PAC 组织胶原纤维微观结构使用二次谐波生成 (SHG) 成像对 n = 4 染色组织样本的子集进行表征。为了通过细胞核和内皮细胞的可视化将横向血管与 SAT 区分开来，分别用 DAPI 和抗血管性血友病因子对样品进行染色。平均应力-应变曲线拟合的 Mooney-Rivlin 模型用于模拟 PAC 材料特性。结果 弹性模量、极限应力和极限应变分别为 7.7 ± 3.0、2.7 ± 0.76 MPa 和 0.60 ± 0.13。就生物力学特性而言，在大脑解剖位置上没有发现统计学意义。对 SHG 图像进行后处理以获得平均 SAT 纤维交叉密度、浓度、孔隙率、弯曲度、段长度、方向、径向计数和直径为 0.23、26.14、73.86%、1.07 ± 0.28、17.33 ± 15.25 µm、84.186 °, 8.15%, 3.46 ± 1.62 µm, 分别。结论 对于测试的尺寸、应变和应变率，我们的结果表明绵羊 PAC 的机械行为是各向同性的，