A novel method for measuring rigidity of submicron-size liposomes with atomic force microscopy.

There are many useful colloidal drug delivery systems that use liposomes. The rigidity of the carrier particle is one of the most important properties affecting drug delivery effectiveness, assessed by particle stability, release profile of encapsulated drug, and blood circulation time. However, it is difficult to evaluate the rigidity of such fine particles; so far, no useful methods have been reported. We demonstrate a unique method to evaluate the rigidity of liposomes using atomic force microscopy (AFM) and dynamic light scattering (DLS) in this report. We showed that the combination of two types of particle-size measurements, tapping mode AFM in buffer solution with another conventional method such as DLS, is useful for evaluating the rigidity of submicron-size particles such as liposomes.