Physical nature of particle transport in elastically responsive hydrogels: one and two particle microrheology

现代临床诊断工具的设计利用病原体（如病毒）扩散到水凝胶中，其中病原体与功能化单元接触并产生可检测的光学或机械信号。大自然利用凝胶状的粘液膜有效地保护各种组织免受细菌和病毒的入侵，这种粘液膜几乎无法穿透特定的病原体。该项目结合了广泛的模拟和分析论证，以回答有关热驱动示踪粒子如何在弹性网络中扩散的物理问题，这些示踪粒子比典型的网状物更大。特别是，我们解决了示踪颗粒的大小和形状与其在凝胶网络中的迁移率之间的联系，并跟进了以下问题：颗粒的最大尺寸是多少，这样它仍然可以渗透到凝胶中并扩散？示踪形状起什么作用？示踪剂的运动与周围的凝胶网络之间的关系是什么？凝胶的空间无序对示踪剂迁移率有什么影响？最后，示踪剂的可变形程度起了什么作用，也就是说，我们能否检测到硬核与软核示踪剂颗粒运动之间的显著差异？凝胶中两种相邻示踪剂的相关运动也会被问到类似的问题，这种设置通常用于两颗粒微流变学。示踪剂的扩散特性将根据系综和时间平均粒子位移，非高斯性和非遍历性参数，以及扩散粒子的相关和概率分布函数来量化。该项目的结果将为微流变学实验的分析提供重要的输入，并允许对异质结构和弹性响应环境中颗粒扩散的物理化学特性有新的见解，例如活生物细胞内部、多细胞组织、黏液膜或用于临床诊断工具的凝胶。

Designs for modern clinical diagnostic tools utilise the diffusion ofpathogens such as viruses into hydrogels, in which pathogens get in contactwith functionalised units and give rise to detectable optical or mechanicalsignals. Nature effectively protects various tissues from bacterial andviral invasion using gel-like mucus films, which are almost impenetrableto specific pathogens. This project combines extensive simulations andanalytical arguments to answer the physical question on how thermallydriven tracer particles, which are larger than the typical network mesh,diffuse in elastic networks. In particular, we address the connectionbetween the size and shape of the tracer particle and its mobility in thegel network and follow up on questions such as: What is the maximal sizeof the particle such that it can still penetrate into and diffuse throughthe gel? Which role does the tracer shape play? What are the correlationsbetween the motion of the tracer and the surrounding gel network? Whicheffect does spatial disorder of the gel have on the tracer mobility? And finally,which role is played by the degree of deformability of the tracer, thatis, can we detect significant differences between motion of hard-coreversus soft-core tracer particles? Similar questions will be asked for thecorrelated motion of two vicinal tracers in the gel, a setup typically usedin two-particle microrheology. The diffusive characteristics of the tracerwill be quantified in terms of the ensemble and time averaged particledisplacements, the non-Gaussianity and non-ergodicity parameters, as wellas the correlation and probability distribution functions of the diffusingparticles. The results of this project will provide an important input forthe analysis of microrheology experiments and allow novel insights intothe physico-chemical properties of particle diffusion in heterogeneouslystructured and elastically responsive environments, such as those insideliving biological cells, in multicellular organisations, in mucus films,or gels used for clinical diagnostic tools.