Nanostructured lipid aggregates offer enormous potential as tools for membrane structural biology and biophysics. Styrene-Maleic Acid Lipid Particles have a number of attractive characteristics including stability, ease of preparation and cost. In this proposal we wish to probe the role of charge on both the polymer and the lipid species in determining disc size, shape and stability. In our initial studies we used pH 8, 200mM salt since these are standard solution conditions when the discs are used in membrane protein purification. Here we will perturb these conditions, which will alter both the extent of charge screening and the hydrophobicity of the stabilizing polymer. We will study SMALP size and shape as a function of lipid composition at selected pH and salt concentrations to enable us to determine the fundamental biophysical parameters that underlie membrane behaviour in the discs