Department of Chemical and Biomolecular Engineering, Lehigh University, 111 Research Dr., Iacocca Hall, Bethlehem, PA 18015, USA.
Lab Chip. 2017 Jun 13;17(12):2085-2094. doi: 10.1039/c7lc00222j.
A microfluidic device is designed to measure repeated phase transitions, gelation and degradation, on a single sample by exchanging the surrounding fluid while minimizing shear stress. This device enables quantitative microrheological characterization of material properties over multiple phase transitions, determining whether the material returns to the same equilibrium state. Fluid exchange is accomplished by using a two layer design, the sample is trapped in the first layer and the second layer is a well for the exchanging fluid. Fluid enters the sample chamber symmetrically creating equal pressure around the sample, trapping it in place. Multiple particle tracking (MPT) microrheology, a passive microrheological technique, measures the dynamic rheological properties during each phase transition. Combining rheological characterization and sample manipulation using microfluidics is termed μrheology. The utility of this technique is demonstrated by characterizing several phase transitions of a fibrous colloidal gel, hydrogenated castor oil. Gelation and degradation is induced by an osmotic pressure gradient created by contact with a glycerine based gelling agent and water, respectively. Several transitions are measured using a single sample. Nine transitions, five gel-sol and four sol-gel, are the maximum number of transitions characterized in a single sample. This microfluidic device and measurement technique is widely applicable and can be easily adapted to any system where solvent exchange is used to induce a change in material properties.
设计了一种微流控装置，通过在最小化剪切应力的同时交换周围流体，在单个样品上测量重复的相转变、胶凝和降解。该装置能够在多个相转变过程中对材料性能进行定量微流变学表征，确定材料是否回到相同的平衡状态。通过使用两层设计来实现流体交换，样品被捕获在第一层中，第二层是用于交换流体的井。流体对称地进入样品室，在样品周围产生相等的压力，将其固定在原位。多粒子跟踪（MPT）微流变学是一种被动微流变技术，可在每个相转变过程中测量动态流变学性质。使用微流控技术对流变学特性和样品操作进行组合称为μrheology。通过对氢化蓖麻油纤维胶体凝胶的几种相转变进行表征，证明了该技术的实用性。凝胶化和降解分别是通过与基于甘油的凝胶剂和水接触产生的渗透压梯度诱导的。使用单个样品测量了几个转变。五个凝胶-溶胶和四个溶胶-凝胶的九个转变是在单个样品中表征的最大转变数。这种微流控装置和测量技术具有广泛的适用性，可以很容易地适应任何使用溶剂交换来诱导材料性能变化的系统。
