On the Auxiliary Driving Mechanism for Blood Circulation

Abstract

This thesis discusses a driving mechanism for blood circulation over and above the pressure gradient. Fluid commonly flows in response to an external pressure gradient. However, when a tunnel-containing hydrogel is immersed in water, spontaneous flow occurs through the tunnel without any pressure gradient. This flow was observed in a wide range of plant- and animal-derived hydrogels. The flow appears to be driven by axial concentration gradients originating from surface activities of the tunnel wall. Those activities include: (i) hydrogel-water interaction (ii) material exchange across the tunnel boundary. Unlike pressure-driven flow, this surface-induced flow (SIF) has two distinct features: incident infrared energy substantially increases flow velocity; and, narrower tunnels generate faster flow with faster velocity. Thus, surface activities in hydrogel-lined tunnels may confer kinetic energy on the enclosed fluid, with infrared radiation as an energy source. The existence of the surface-induced flow mechanism was tested in a blood circulation system. In the three-day-old chick embryo vitelline-circulation model, it was found that blood flow continued for up to an hour after the heart stopped beating. Albeit at a slower velocity, postmortem blood flow was directional, following the same course as the original blood flow, i.e., from artery to vein. Infrared radiation appears to supply energy for driving this flow: when infrared energy was applied to the postmortem blood-flow model, velocity increased by 300%. Alternative explanations such as gravitationally driven flow, vascular contraction or convection flow could be ruled out. This finding implies that a mechanism beyond the pressure gradient, potentially SIF mechanism, helps drive the blood circulation, using infrared energy as a fuel.