We have investigated the laser micromachining of microsieves with 3D micropore geometries. We hypothesize that mechanical cues resulting from the positioning and machining of ablated holes inside a pyramidal microcavity can influence the direction of neuronal outgrowth and instruct stem cell-derived neural networks in their differentiation processes. We narrowed the number of variations in device fabrication by developing a numerical model to estimate the stress distribution in a cell interacting with the laser-tailored unique 3D geometry of a microsieve’s pore. Our model is composed of two components: a continuous component (consisting of the membrane, cytoplasm, and nucleus) and a tensegrity structural component (consisting of the cytoskeleton, nucleoskeleton, and intermediate filaments). The final values of the mechanical properties of the components are selected after evaluating the shape of the continuous cell model when a gravity load is applied and are compared to the shape of a cell on a glass substrate after 3 h. In addition, a physical criterion implying that the cell should not slip through a hole with a bottom aperture of 3.5 μm is also set as a constraint. Among all the possible one- or multi-hole configurations, six cases appeared promising in influencing the polarization process of the cell. These configurations were selected, fabricated, and characterized using scanning electron microscopy. Fabricated microsieves consist of a 20 μm thick Norland Optical Adhesive 81 (NOA81) foil with an array of inverted pyramidal microcavities, which are opened by means of KrF 248 nm laser ablation. By changing the position of the laser beam spot on the cavities (center, slope, or corner) as well as the direction of laser beam with respect to the NOA81 microcavity foil (top side or back side), different ablation configurations yielded a variety of geometries of the 3D micropores. In the one-hole configurations when the shot is from the top side, to make the desired diameter of 3.5 μm (or less) of an opening, 1500 laser pulses are sufficient for the center and slope openings. This requirement is around 2000 laser pulses when the aperture is positioned in the corner. In back side ablation processes, the required number of pulses for through-holes at the center, slope, and corner positions are 1200, 1800, and 1800 pulses, respectively. In conclusion, we developed a microsieve platform that allows us to tailor the 3D topography of individual micropores according to the selection of cases guided by our numerical stress distribution models.

中文翻译：

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细胞中机械应力与微机械线索相互作用的计算研究以及神经片上系统中此类线索的微加工

我们研究了具有 3D 微孔几何形状的微筛的激光微加工。我们假设由锥体微腔内烧蚀孔的定位和加工产生的机械线索可以影响神经元生长的方向，并在其分化过程中指导干细胞衍生的神经网络。我们通过开发一个数值模型来估计与激光定制的微筛孔的独特 3D 几何形状相互作用的细胞中的应力分布，从而缩小了设备制造中的变化数量。我们的模型由两部分组成：连续部分（由膜、细胞质和细胞核组成）和张拉整体结构部分（由细胞骨架、核骨架和中间丝组成）。在评估施加重力载荷时连续电池模型的形状后，选择组件机械性能的最终值，并与 3 小时后玻璃基板上的电池形状进行比较。此外，物理标准暗示电池不应滑过底部孔径为 3.5 的孔 μ m 也被设置为约束。在所有可能的单孔或多孔配置中，有六种情况似乎有希望影响电池的极化过程。使用扫描电子显微镜选择、制造和表征这些配置。制造的微筛由 20  μ米厚的 Norland Optical Adhesive 81 (NOA81) 箔，带有倒金字塔形微腔阵列，这些微腔通过 KrF 248 nm 激光烧蚀打开。通过改变激光束点在空腔上的位置（中心、斜面或角）以及激光束相对于 NOA81 微腔箔（顶面或背面）的方向，不同的烧蚀配置产生了多种3D微孔的几何形状。在单孔配置中，当从顶部射出时，要获得所需的 3.5  μ直径米（或更小）的开口，1500 个激光脉冲足以用于中心和斜坡开口。当孔径位于角落时，此要求约为 2000 个激光脉冲。在背面烧蚀工艺中，中心、斜坡和拐角位置的通孔所需脉冲数分别为1200、1800和1800个脉冲。总之，我们开发了一个微筛平台，允许我们根据我们的数值应力分布模型指导的案例选择来定制单个微孔的 3D 形貌。