Membrane additives generally affect the bending stiffness. The single most investigated system in this respect is cholesterol in membranes containing phosphatidylcholine (Meleard et al., 1997, Oradd et al., 2009 and Song and Waugh, 1993). The influence of cholesterol on the bending stiffness of a lipid bilayer depends on the saturation of the lipid\'s hydrocarbon tails. Cholesterol appears to interact more favorably with saturated than with unsaturated lipid tails (Simons and Vaz, 2004). The stronger interaction with saturated Dacomitinib leads to a more condensed structure and increases the bending stiffness. It is indeed observed that membranes composed of phosphatidylcholine with one (and even more so with two) saturated tails exhibit an increase in the bending stiffness as function of cholesterol content, whereas for phosphatidylcholine with two mono-unsaturated chains the bending stiffness remains largely unaffected (Gracia et al., 2010, Henriksen et al., 2006, Pan et al., 2008a and Pan et al., 2009). Fewer data exist for additives other than cholesterol. Softening of the membrane was reported for both the small amphiphilic molecule salicylate in stearoyloleoylphosphatidylcholine (SOPC) (Zhou and Raphael, 2005), for the peptide magainin in palmitoyloleoylphosphatidylcholine (POPC) (Bouvrais et al., 2008), and for the antibiotic azithromycin (Fa et al., 2007). Softening is also a characteristic feature of adding a short-chained cosurfactant to the membrane (Safinya et al., 1989). On the other hand, the cryoprotector trehalose induces a small increase of the bending stiffness of a dioleoylphosphatidylethanolamine (DOPE) lipid layer cleavage furrow forms an inverted hexagonal phase (Di Gregorio and Mariani, 2005). Modeling of rigid inclusions in membranes can rationalize both membrane softening and rigi