And so this is the bilayer membrane, this is the internal compartment and it is separated from the external compartment by this bilayer membrane. Now the question is, how do we build these liposomes? Well, if we want to build a liposome that is about 50 nm in diameter, this is the method that we have to follow. But you should know that we can also build larger liposomes if we use other techniques. So let's suppose we have an aqueous solution and then we have a second solution that contains the phospholipid that we want to use to actually create that bilayer membrane. So what we do is we basically mix these two solutions and because the phospholipids won't mix very well in the aqueous solution, we basically form these two separate layers.