Visualising nanoscale restructuring of a cellular membrane triggered by polyelectrolyte microcapsules

Polymer-based multilayer microencapsulation technology represents one of the promising strategies for intracellular drug delivery, however, membrane processes involved in vehicle internalisation are not fully understood. Here we employed a scanning probe microscopy technique called Scanning Ion Conductance Microscopy (SICM) to study these complex processes at nanoscale resolution in real time. We were able to image topography simultaneously with local elastic modulus throughout the whole course of microcapsule internalisation in A549 cell culture without disrupting the internalisation process. The imaging revealed that capsules triggered the formation of membrane protrusions in their vicinity, which is an important but not a sufficient step towards full capsule internalisation. A crucial aspect appeared to be nanoscale restructuring of these protrusions into smooth thin layers extending over the surface of capsules. Simultaneous mapping of elastic modulus during capsule internalisation allowed monitoring the structural changes during extension of the membrane sheets over the surface of the capsule and the subsequent post-internalisation phenomenon of capsule buckling. To our knowledge these are the first experimental data capturing the interactions between the cellular membrane and microcapsules in their whole complexity with nanoscale resolution. The methodology established here has the potential to provide new insights into interactions at the interface between the nanostructured materials and cellular membrane under physiological conditions.