Cell motility plays important roles in a range of biological processes, such as reproduction and infections. Studies have hypothesized that the ulcer-causing bacterium Helicobacter pylori invades the gastric mucus layer lining the stomach by locally turning nearby gel into sol, thereby enhancing its locomotion through the biological barrier. In this work, we present a minimal theoretical model to investigate how heterogeneity created by a swimmer affects its own locomotion. As a generic locomotion model, we consider the swimming of a spherical squirmer in a purely viscous fluid pocket (representing the liquified or degelled region) surrounded by a Brinkman porous medium (representing the mucus gel). The use of the squirmer model enables an exact, analytical solution to this hydrodynamic problem. We obtain analytical expressions for the swimming speed, flow field, and power dissipation of the swimmer. Depending on the details of surface velocities and fluid properties, our results reveal the existence of a minimum threshold size of mucus gel that a swimmer needs to liquify in order to gain any enhancement in swimming speed. The threshold size can be as much as approximately $30\%$ of the swimmer size. We contrast these predictions with results from previous models and highlight the significant role played by the details of surface actuations. In addition to their biological implications, these results could also inform the design of artificial microswimmers that can penetrate into biological gels for more effective drug delivery.

中文翻译：

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在Brinkman介质封闭的粘性流体中喷出。

细胞运动在一系列生物学过程（例如生殖和感染）中起重要作用。研究假设，溃疡致病菌幽门螺杆菌通过将附近的凝胶局部转化为溶胶而侵入衬在胃部的胃粘液层，从而增强其通过生物屏障的运动。在这项工作中，我们提出了一个最小的理论模型来研究游泳者产生的异质性如何影响其自身的运动。作为一个通用的运动模型，我们考虑在一个充满粘性的流体袋（代表液化或去凝胶的区域）中游走一个球形的蓄水器，该流体袋被Brinkman多孔介质（代表粘液凝胶）包围。蓄水器模型的使用为该流体动力学问题提供了精确的分析解决方案。我们获得了游泳者的游泳速度，流场和功率耗散的解析表达式。根据表面速度和流体特性的详细信息，我们的研究结果表明，游泳者必须液化最小阈值大小的粘液凝胶，以提高游泳速度。阈值大小可能约为$30％$游泳者的大小。我们将这些预测与先前模型的结果进行对比，并强调了表面驱动细节所起的重要作用。除了它们的生物学意义外，这些结果还可以为人造微泳器的设计提供参考，该微泳器可以渗透到生物凝胶中以更有效地进行药物递送。