Microaligned collagen matrices by hydrodynamic focusing: controlling the pH-induced self-assembly

The hierarchical structure of type I collagen flbrils is a key contributor to the mechanical properties of the extracellular matrix (ECM). It is known that the process of in vitro flbrillogenesis strongly depends on the pH of the collagen solution. To date, there are few methods available for precisely controlling and investigating the dependence of collagen flbril assembly on the local pH. The objective of this work was to create highly deflned pH gradients to systematically determine the efiects of local pH on microscale collagen flbrillogenesis and alignment. We use a micro∞uidic mixing device to create a difiusion controlled pH gradient, which in turn initiates the self-assembly and concurrent ∞ow-alignment of soluble collagen. Finite element method simulations of the hydrodynamic and difiusive phenomena are used to calculate the local concentrations of the components involved in the reaction. We develop a model to analytically calculate the local pH in the micro∞uidic device from these concentrations. A comparison with the experimental results from polarized light microscopy are in good agreement with the simulations.