Using fibrinogen barriers to restrict the motion of shear-driven supported lipid bilayers

Abstract

About 70% of all drug targets are proteins situated in the cell-membrane. However, the cellmembrane offers a very complex environment in which to study just a single type of interaction with a specific type of protein, being made up of hundreds of different lipids, over 200 different proteins and oligosaccharides. There exist for this reason some different simplified models of cell membranes, where only the base of the cell-membrane is used, a bilayer often made up of just one type of lipids. A certain protein could then be incorporated into the lipid bilayer and be studied. One simplified model of the cell-membrane is a supported lipid bilayer, which is a lipid bilayer formed on a solid support. SLBs, which is the model used in this work, are formed in microfluidic channels, due to the high level of controllability it offers with laminar flows, but also requiring only small quantities of samples. It was shown by Jönsson et. al that an SLB could be made to move in a desired direction in the microfluidic channel, by having a relatively high bulk flow in the channel above the formed SLB. This proved very useful as molecules incorporated into an SLB was shown to accumulate at the front of the moving bilayer, an increasing concentration of for example a certain protein to be studied means an increase in signal strength. An increase in signal strength could for example mean that things could be studied which would otherwise drown in noise due to too low concentrations. A microfluidic channel is made of glass and PDMS, both materials on which SLBs can form. This means that an SLB when moving along the channel floor could also start moving up along the walls of the channels, thus taking with it incorporated molecules which could have been accumulated at the front. In a microfluidic channel the flow profile is such that bulk flow velocity is highest in the middle of the channel and goes down to zero at the walls, this reduce the effectiveness of the accumulation as some accumulated molecules close to the walls are continuously left behind. Fibrinogen is a protein which with the right conditions could be made to adsorb densely on the channel surface. When fibrinogen is densely packed, it forms a barrier stable enough to restrict the motion of a moving SLB. Fibrinogen barriers are studied within this work as a means of constricting the moving SLB to the center of the microfluidic channel in order to stop it from moving up the channel walls and also to increase the effectiveness of the accumulation as the zero bulk flow regions are avoided. Some results from this study are that fibrinogen indeed can form a barrier dense enough to withstand a moving bilayer, and that accumulation at the front is more effective when fibrinogen barriers are used.