Determination of the shear modulus of spin-coated lipid multibilayer films by the spontaneous embedment of submicrometer-sized particles

A novel submicrometer particle embedment technique has been used to determine the shear modulus of 1,2-dipalmitoyl-sn-glycero-3-phosphotidylcholine (DPPC) lipid multibilayers. The depth of the spontaneous embedment of polystyrene and silica spherical particles of 200 nm nominal size has been determined from atomic force microscopy measurements on colloidal particles dispersed onto the surfaces of the DPPC multibilayers. The standard JKR model was used to relate the shear modulus of the lipid multibilayer films to the depth of embedment of the particles. The thus-determined modulus of the DPPC is within the range of reported literature values. Gold particles are also considered, and it is found that for the smallest particles (13 nm) complete engulfment by the DPPC multibilayer film takes place.