Cell membranes are characterised by complex lipid composition and asymmetric distribution of lipids (lipids facing the outside of the cell are different from the lipids that are facing the inside of the cell). We developed a model system that captures these features. It is based on TiO2-supported four-component lipid bilayers containing the canonical mixture of high-melting and low-melting phosphatidylcholines + cholesterol, plus phosphatidyl serine (PS). PS strongly interacts with TiO2, leading to its asymmetric distribution and mimicking the cytoskeleton-cell membrane interactions. The goal of this proposal is to quantify the distribution of all lipid components in these asymmetric cell membrane mimics by neutron reflectometry. Additional insight is gained by comparing it to that in membranes prepared on SiO2 from the same liposomes.