Activity gradient-induced crossflow filtration in a perivascular space

In active fluids, the micro-structural elements convert the chemical energy into mechanical energy by activating their molecular motors to move their flagella (or pili). When the activity of the microorganisms decreases or increases, the overall fluid motion can develop without any external force. In this analytical study, we have investigated the transport characteristics in a micro-vasculature consisting of a core region filled with an active liquid, surrounded by a porous perivascular region filled with a non-active liquid, considering the decreasing activity of the microorganisms. We have obtained the velocity field and volume flow rate across the core layer and perivascular layer of fluids, considering the liquids in both regions as Newtonian, and they carry similar fluid properties. A creeping flow analysis is carried out for the core layer, and a Darcy model is employed for the porous outer layer. It has been observed that a significant amount of mass transport is occurring in the perivascular space due to activity gradient-induced core flow. Depending upon the porosity and sinusoidal behavior of the perivascular space, significant differences in the flow rate are observed. This study may have significant applications in biomedical engineering, including targeted drug delivery, thrombus removal, and real-time vascular diagnostics. The use of self-propelled micro-swimmers enables precise navigation in the blood flow, enhancing therapeutic efficacy with minimal invasiveness.