The effect of electrostatics on the contact mechanics of adherent phospholipid vesicles

Abstract

Adhesion of cells on biomaterial surface is resulted from the complex interplay of specific recognitions and colloidal interactions. Thus understanding the role of electrostatic interactions in bioadhesion may help to elucidate the physiochemical basis of cell signaling pathway on therapeutic devices. In this report, high-resolution reflection interference contrast microscopy, cross-polarized light microscopy and contact mechanics modeling are applied to probe the equilibrium adhesion of giant phospholipid vesicles on 3-amino-propyl-triethoxy-silane coated glass. Simultaneously, the effects of vesicle wall thickness, pH, osmotic stress and surface chemistry on the electrostatic interactions at the membrane–substrate interface are evaluated. The results show that both unilamellar vesicles (ULV) and multilamellar vesicles (MLV) strongly adhere on the cationic substrates at neutral pH. In the presence of electrostatic interactions, ULV is slightly deformed on the substrate as the dimension of its adhesive–cohesive zone is only 6–10% higher than the theoretical value of a rigid sphere with the same mid-plane diameter. The variances of contact angle and capillary length at different locations surrounding MLV are ten times higher than those of ULV. The adhesion energy of ULV with mid-plane diameter of 45 and 20 μm is determined as 3.8×10 −12 and 8.6×10 −12 J/m 2, respectively, from the truncated sphere model. Moreover, the increase of osmotic stress induces irregular pattern in ULV's adhesion disc and raises the adhesion energy by 10-fold. Finally, the reduction of pH further enhances the electrostatic attractions/repulsions between vesicle surface and cationic or anionic substrates and leads to an increase of adhesion strength.