Oscillatory Diffusion - A New Diffusion Mechanism for Particulates in Porous Media

细菌生物膜是由嵌入在称为细胞外聚合物(EPS)的分泌物质网络中的细菌形成的。生活在生物膜中的细菌是许多人类传染病的罪魁祸首，包括囊性纤维化、结核病、鼻窦炎、龋齿、心脏病、尿路感染以及受污染的医疗器械和植入物的感染。细菌生物膜在食品污染、水净化、温室气体产生和环境污染物分解等方面发挥着核心作用。处理生物膜的方法涉及纳米颗粒或抗生素液体，它们可以被包裹在称为脂质体的小蛋白胶囊中，这种胶囊可以渗透到生物膜中，并将化学物质释放到细菌菌落上。研究小组发现，暴露在超声波下可以提高纳米颗粒穿透生物膜的速度。该奖项将支持对导致渗透率提高的潜在流体力学机制进行详细的实验和理论研究。研究人员提出，超声波产生的振荡流加上颗粒通过的多孔介质阻碍了它们的运动，从而导致了一种新型的扩散传输，称为振荡扩散。该奖项将支持实验，以测量超声波对纳米颗粒在水凝胶中扩散增强的影响，水凝胶是生物膜的模型，并检查单个颗粒的详细运动。将开发一个数学模型来连接这两个实验的结果。这个项目的目标是提高对振荡扩散现象的理解，在振荡扩散现象中，观察到声激励以增强颗粒在多孔介质中的扩散。目标应用包括使用超声波来增强纳米颗粒和脂质体在生物膜中的扩散。生物膜中颗粒和化学物质运输的主要机制是扩散，它通过细胞群体感应(群体感应)调节矿物质和营养物质向细菌菌落的供应，并调节细菌基因调节反应。这种振荡扩散现象是研究人员最近发现的，他们使用中等强度的超声波将充满抗生素化学物质的脂质体注射到生物膜中，以缓解生物膜。超声波还被证明可以增强纳米颗粒在阿尔加水凝胶中的渗透，阿尔加水凝胶是生物膜蛋白质基质的模型。该奖项将支持两个实验组件和一个建模组件。纳米粒子整体扩散实验将测量超声诱导的纳米粒子在水凝胶中的扩散系数和声流速度。单个颗粒跟踪实验将跟踪受振荡流场影响的多孔床中单个颗粒的运动，以更好地了解单个颗粒水平上的现象。这些实验研究的数据将被用来改进和验证振荡扩散的随机模型。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

A bacterial biofilm is formed of bacteria embedded in a network of a secreted material called extracellular polymeric substance (EPS). Bacteria living in biofilms are responsible for many human infectious diseases, including cystic fibrosis, tuberculosis, sinusitis, tooth decay, heart disease, urinary tract infections, and infections from contaminated medical devices and implants. Bacterial biofilms play a central role in food contamination, water purification, greenhouse gas generation, and breakdown of environmental contaminants. Methods for treating biofilms involve nanoparticles or antibiotic liquids that can be encapsulated in small protein capsules called liposomes, which can penetrate into the biofilm and release a chemical onto the bacterial colonies. The research team has found that exposure to ultrasound can enhance the rate of penetration of nanoparticles into a biofilm. This award will support a detailed experimental and theoretical investigation of the underlying hydrodynamic mechanisms responsible for enhanced penetration. The investigators propose that the combination of oscillatory flow produced by the ultrasound plus hindered motion of the particles by the porous medium through which they travel results in a novel type of diffusive transport termed oscillatory diffusion. The award will support experiments to measure the effect of ultrasound on diffusion enhancement of nanoparticles in a hydrogel, which is a model of a biofilm, and to examine the detailed motion of individual particles. A mathematical model will be developed to connect the results of these two experiments. The goal of this project is to improve understanding of the oscillatory diffusion phenomenon, in which acoustic excitation is observed to enhance diffusion of particulates in a porous medium. The target application involves the use of ultrasound to enhance diffusion of nanoparticles and liposomes in a biofilm. The primary mechanism for transport of particles and chemicals in biofilms is diffusion, which regulates supply of minerals and nutrients to bacterial colonies and bacteria gene regulation response via cell population sensing (quorum sensing). The oscillatory diffusion phenomenon was recently discovered by the investigators using moderate-intensity ultrasound to inject liposomes filled with antibiotic chemicals into a biofilm for biofilm mitigation. Ultrasound was also shown to enhance penetration of nanoparticles into an algar hydrogel, which models a biofilm protein matrix. This award will support two experimental components and one modeling component. A nanoparticle bulk diffusion experiment will measure ultrasound-induced nanoparticle diffusion coefficient and acoustic streaming velocity in a hydrogel. An individual particle tracking experiment will track motion of individual particles in a porous bed subject to an oscillating flow field to better understand the phenomenon at the individual particle level. The data from these experimental studies will be used to improve and validate a stochastic model of oscillating diffusion.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.