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 cellmembraneoffers a very complex environment in which to study just a single type ofinteraction with a specific type of protein, being made up of hundreds of different lipids, over200 different proteins and oligosaccharides. There exist for this reason some differentsimplified models of cell membranes, where only the base of the cell-membrane is used, abilayer often made up of just one type of lipids. A certain protein could then be incorporatedinto the lipid bilayer and be studied. One simplified model of the cell-membrane is asupported lipid bilayer, which is a lipid bilayer formed on a solid support. SLBs, which is themodel used in this work, are formed in microfluidic channels, due to the high level ofcontrollability it offers with laminar flows, but also requiring only small quantities ofsamples. It was shown by Jönsson et. al that an SLB could be made to move in a desireddirection in the microfluidic channel, by having a relatively high bulk flow in the channelabove the formed SLB. This proved very useful as molecules incorporated into an SLB wasshown to accumulate at the front of the moving bilayer, an increasing concentration of forexample a certain protein to be studied means an increase in signal strength. An increase insignal strength could for example mean that things could be studied which would otherwisedrown in noise due to too low concentrations. A microfluidic channel is made of glass andPDMS, both materials on which SLBs can form. This means that an SLB when moving alongthe channel floor could also start moving up along the walls of the channels, thus taking withit incorporated molecules which could have been accumulated at the front. In a microfluidicchannel the flow profile is such that bulk flow velocity is highest in the middle of the channeland goes down to zero at the walls, this reduce the effectiveness of the accumulation as someaccumulated molecules close to the walls are continuously left behind. Fibrinogen is aprotein which with the right conditions could be made to adsorb densely on the channelsurface. When fibrinogen is densely packed, it forms a barrier stable enough to restrict themotion of a moving SLB. Fibrinogen barriers are studied within this work as a means ofconstricting the moving SLB to the center of the microfluidic channel in order to stop it frommoving up the channel walls and also to increase the effectiveness of the accumulation as thezero bulk flow regions are avoided. Some results from this study are that fibrinogen indeedcan form a barrier dense enough to withstand a moving bilayer, and that accumulation at thefront is more effective when fibrinogen barriers are used.