Smart magnetic fluids

Abstract

This thesis is centred around the problem that heart failures become more common when other dis-eases could be treated better. Although surgery could fix the immediate effects of heart failures, therecovery after the surgery is hindered by the heart not being able to pump enough blood. There aresolutions available but they are not implemented due doing more harm then good to the heart. Thisthesis will look into a way to aid the recovering heart by applying a compressional force to the outsideof the heart. Previous attempts on fixing this problem could not follow the motion of the heart closeenough due to the lack of actuation resolution, i.e. the local differentiation of the actuation applied tothe heart. This caused damage to the heart muscle, which in the end causes death due to too littleblood flow.Due to lack of actuation resolution of the previous solutions, the focus of this thesis will be on the dis-tribution of the actuation and not the actuation to the heart itself. A baseline for the requirements wasneeded to make an informed decision about the different solutions to distribute the actuation. This wasdone using a MatLab script. This gave the actuation characteristics of a compression of 20 percent witha pressure of 20 [kPa] when a compression jacket of 5 [mm] thickness around the heart is used. Therelative high compression together with the pressure directed the solution for such an actuator towardsfluids.Common fluid actuators that would have a high local differentiation in actuation require lots of pumpsor lots of valves, both of these options have as a downside that they take up to much space. That iswhere smart fluids have an advantage by decreasing the size of a pump or a valve by including thefluid in the active volume. Two of these smart fluids that seem promising are; Ferrofluids and magnetorheological fluids. Ferrofluids are activated by a magnetic field and will cause a change in internalpressure similar to how gravity affects internal pressure in a fluid. The only difference is that it couldbe about four to five orders of magnitude stronger over small distances of about a tenth of a millimetre.The magneto rheological fluid changes its viscosity in the direction perpendicular to the magnetic fieldwith the change being related to the strength of the applied field.The thesis will discuss the use of Ferrofluids as an active fluid in a pump, and magneto rheologicalfluids, MRF, as the active fluid in a valve. Ferrofluids are not feasible to be used as individual unitsas they barely meet the requirements of 20 [kPa] of pressure with the flow rate needed to actuate thejacket, without taking the fluidic losses of such a jacket into account. Whereas the MRF based valvecould achieve a pressure difference of 20 [kPa] over the valve, without being of the limits of the op-erational value of the fluid. This is enough to have both a fully opened valve and a closed one usingthe pressure needed from the requirements. Therefor the thesis recommends the further research intoimplementing a full actuation system for a heart assist device using valves based on MRF.