The aim of this work was to study the initial events of Escherichia coli adhesion to polydimethylsiloxane, which is critical for the development of antifouling surfaces. A parallel plate flow cell was used to perform the initial adhesion experiments under controlled hydrodynamic conditions (shear rates ranging between 8 and 100/s), mimicking biomedical scenarios. Initial adhesion studies capture more accurately the cell-surface interactions as in later stages, incoming cells may interact with the surface but also with already adhered cells. Adhesion rates were calculated and results shown that after some time (between 5 and 9 min), these rates decreased (by 55% on average), from the initial values for all tested conditions. The common explanation for this decrease is the occurrence of hydrodynamic blocking, where the area behind each adhered cell is screened from incoming cells. This was investigated using a pair correlation map from which two-dimensional histograms showing the density probability function were constructed. The results highlighted a lower density probability (below 4.0 × 10⁻⁴) of the presence of cells around a given cell under different shear rates irrespectively of the radial direction. A shadowing area behind the already adhered cells was not observed, indicating that hydrodynamic blocking was not occurring and therefore it could not be the cause for the decreases in cell adhesion rates. Afterward, cell transport rates from the bulk solution to the surface were estimated using the Smoluchowski-Levich approximation and values in the range of 80–170 cells/cm².s were obtained. The drag forces that adhered cells have to withstand were also estimated and values in the range of 3–50 × 10⁻¹⁴ N were determined. Although mass transport increases with the flow rate, drag forces also increase and the relative importance of these factors may change in different conditions. This work demonstrates that adjustment of operational parameters in initial adhesion experiments may be required to avoid hydrodynamic blocking, in order to obtain reliable data about cell-surface interactions that can be used in the development of more efficient antifouling surfaces.

中文翻译：

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分析初始细菌粘附力以评估防污表面的性能。

这项工作的目的是研究大肠杆菌的初始事件对聚二甲基硅氧烷的附着力，这对防污表面的发展至关重要。平行板流动池用于在受控的流体动力学条件（剪切速率介于8和100 / s之间）下进行初始粘附实验，以模仿生物医学场景。最初的粘附研究可以更准确地捕获细胞与表面的相互作用，因为在以后的阶段中，进入的细胞可能与表面相互作用，但也可能与已经粘附的细胞相互作用。计算了粘合率，结果表明，经过一段时间（5至9分钟），这些速率从所有测试条件的初始值开始降低（平均降低55％）。这种减少的常见解释是发生了流体动力阻塞，其中每个粘附细胞后面的区域都从进入的细胞中筛选出来。这是使用一对相关图进行研究的，该对图绘制了显示密度概率函数的二维直方图。结果突出显示了较低的密度概率（低于4.0×10^-4）在不同剪切速率下，给定孔周围是否存在孔，而与径向无关。没有观察到已经粘附的细胞后面的阴影区域，这表明没有发生流体动力阻塞，因此它不可能是细胞粘附速率降低的原因。然后，使用Smoluchowski-Levich近似估计从大体积溶液到表面的细胞迁移速率，得出的值在80-170个细胞/ cm ² .s的范围内。还估计了粘附细胞必须承受的阻力，其值在3–50×10 ^-14范围内N被确定。尽管质量流量随流速增加，但阻力也随之增加，并且这些因素的相对重要性可能会在不同条件下发生变化。这项工作表明，可能需要在初始附着力实验中调整操作参数以避免流体动力学阻塞，以便获得有关细胞表面相互作用的可靠数据，这些数据可用于开发更有效的防污表面。