Measuring 3D Forces during Capillary Network Remodelling

Abstract

Patterning of capillary networks is essential for the proper systemic distribution of cells, nutrients, and oxygen in developing as well as adult healthy and unhealthy tissues. Mechanical models describing the relation between blood flow and angiogenesis, vessel pruning, etc. had been introduced in biology at earlier times with great success [1]. Along with these studies, in vitro models of sprouting angiogenesis have shown mechanical descriptions of the interaction of endothelial cells/extracellular matrix (ECM) [2, 3]. Nevertheless, the lack of appropriate methods for in vivo and in situ force measurement had hampered the study of the forces that capillary wall components apply on the ECM during formation/pruning of capillaries. Here, we show that, by developing a new method for imaging and measuring forces in vivo and in situ, we can describe mechanically the remodelling of capillary networks. We introduced a multiphoton imaging system that surpasses the simultaneous channel acquisition problems that the present commercial systems have, but retains the ability of deep imaging with subcellular resolution. To quantify the forces we introduced a reference system in the chorioallantoic membrane (CAM) of the chicken embryo by adding a tunable biocompatible fluorescent nanofibres matrix (electrospun polylactic acid fibres in a predesigned arrangement) that was minimally invasive and able to deform following the deformation of the CAM stroma. We numerically modelled the system as fibres on an elastic material (CAM) and, by characterising mechanically the system, we could retrieve forces on the nN/nm scale. We also identified the formation of new functional connections and found an oscillatory behaviour of the forces that we interpret with a simple biomechanical model of damping oscillations, where the periodicity depends on the matrix structure. The damping term drives the system to a quiescent state.