Department of Polymer Science and Engineering, University of Massachusetts, Amherst, Massachusetts 01003, United States.
Department of Physics, University of Massachusetts, Amherst, Massachusetts 01003, United States.
ACS Appl Mater Interfaces. 2021 Apr 21;13(15):17196-17206. doi: 10.1021/acsami.1c00245. Epub 2021 Apr 6.
Bacterial swimming in flow near surfaces is critical to the spread of infection and device colonization. Understanding how material properties affect flagella- and motility-dependent bacteria-surface interactions is a first step in designing new medical devices that mitigate the risk of infection. We report that, on biomaterial coatings such as polyethylene glycol (PEG) hydrogels and end-tethered layers that prevent adhesive bacteria accumulation, the coating mechanics and hydration control the near-surface travel and dynamic surface contact of cells in gentle shear flow (order 10 s). Along relatively stiff (order 1 MPa) PEG hydrogels or end-tethered layers of PEG chains of similar polymer correlation length, run-and-tumble travel nanometrically close to the coating's surface in the flow direction in distinguishable runs or "engagements" that persist for several seconds, after which cells leave the interface. The duration of these engagements was greater along stiff hydrogels and end-tethered layers compared with softer, more-hydrated hydrogels. Swimming cells that left stiff hydrogels or end-tethered layers proceeded out to distances of a few microns and then returned to engage the surface again and again, while cells engaging the soft hydrogel tended not to return after leaving. As a result of differences in the duration of engagements and tendency to return to stiff hydrogel and end-tethered layers, swimming experienced 3 times the integrated dynamic surface contact with stiff coatings compared with softer hydrogels. The striking similarity of swimming behaviors near 16-nm-thick end-tethered layers and 100-μm-thick stiff hydrogels argues that only the outermost several nanometers of a highly hydrated coating influence cell travel. The range of material stiffnesses, cell-surface distance during travel, and time scales of travel compared with run-and-tumble time scales suggests the influence of the coating derives from its interactions with flagella and its potential to alter flagellar bundling. Given that restriction of flagellar rotation is known to trigger increased virulence, bacteria influenced by surfaces in one region may become predisposed to form a biofilm downstream.
细菌在靠近表面的流动中游动对于感染的传播和设备定植至关重要。了解材料特性如何影响鞭毛和运动依赖的细菌-表面相互作用是设计新的医疗设备以降低感染风险的第一步。我们报告称，在生物材料涂层（如聚乙二醇（PEG）水凝胶和末端键合层）上，这些涂层可以防止粘性细菌聚集，涂层力学和水合作用控制着温和剪切流中细胞的近表面运动和动态表面接触（约 10 s）。在相对较硬的（约 1 MPa）PEG 水凝胶或具有相似聚合物相关长度的末端键合 PEG 链的层上，在流动方向上，翻滚运动纳米级地靠近涂层表面，在几秒钟后，细胞离开界面。在较硬的水凝胶和末端键合层上，这些结合的持续时间比较软、更水合的水凝胶更长。离开硬水凝胶或末端键合层的游动细胞会前进到几微米的距离，然后再次返回到表面进行再次结合，而与软水凝胶结合的细胞在离开后往往不会返回。由于结合持续时间的差异以及返回硬水凝胶和末端键合层的趋势，游动细胞与硬涂层的动态表面接触积分是与软水凝胶相比增加了 3 倍。在 16nm 厚的末端键合层和 100μm 厚的硬水凝胶附近游泳行为的惊人相似性表明，只有高度水合涂层的最外层几纳米会影响细胞的运动。与翻滚运动时间相比，材料刚度范围、运动过程中的细胞-表面距离以及运动时间尺度表明，涂层的影响源于其与鞭毛的相互作用及其改变鞭毛束的潜力。由于已知限制鞭毛旋转会引发毒力增加，因此在一个区域受表面影响的细菌可能会更容易在下游形成生物膜。
