Maintaining sidedness and fluidity in cell membrane coatings supported on nano-particulate and planar surfaces

Supported cell membrane coatings meet many requirements set to bioactive nanocarriers and materials,provided sidedness and fluidity of the natural membrane are maintained upon coating.However,the properties of a support-surface responsible for maintaining correct sidedness and fluidity are unknown.Here,we briefly review the properties of natural membranes and membrane-isolation methods,with focus on the asymmetric distribution of functional groups in natural membranes(sidedness)and the ability of molecules to float across a membrane to form functional domains(fluidity).This review concludes that hydrophilic sugar-residues of glycoproteins in the outer-leaflet of cell membranes direct the more hydrophobic inner-leaflet towards a support-surface to create a correctly-sided membrane coating,regardless of electrostatic double-layer interactions.On positively-charged support-surfaces however,strong,electrostatic double-layer attraction of negatively-charged membranes can impede homogeneous coating.In correctly-sided membrane coatings,fluidity is maintained regardless of whether the surface carries a positive or negative charge.However,membranes are frozen on positively-charged,highly-curved,small nanoparticles and localized nanoscopic structures on a support-surface.This leaves an unsupported membrane coating in between nanostructures on planar support-surfaces that is in dual-sided contact with its aqueous environment,yielding enhanced fluidity in membrane coatings on nanostructured,planar support-surfaces as compared with smooth ones.