Studies on the Mechanical Properties of Polyunsaturated Membrane with Varying Cholesterol Content Using Atomic Force Microscopy

Lipid composition and cholesterol (Chol) content in the eye lens membrane changes dramatically with age, decreasing the unsaturation of phospholipid acyl chain and increasing the Chol content. In this study, we employ atomic force microscopy (AFM) to study the mechanical properties of polyunsaturated lipid membranes with varying Chol content. We prepared supported lipid membranes composed of 1-palmitoyl-2-arachidonoyl-sn phosphatidylcholine (PAPC) and Chol with a Chol/PAPC mixing ratio of 0, 0.125, and 0.25. Supported Chol/PAPC membranes were prepared by fusion of small unilamellar vesicles (SUVs) on top of a flat mica surface. SUVs made of different Chol/PAPC mixing ratios were prepared with the rapid solvent exchange (RSE) method followed by probe-tip sonication. We measured the membrane’s mechanical properties using breakthrough (BT) force, the amount of force required to puncture the membranes, and the area compressibility modulus (KA). In addition, we measured the surface roughness of the membranes at different Chol content. No significant difference in the membrane surface roughness was measured with increasing Chol content for these membranes; however, BT force and KA for membrane decreased when Chol/PAPC mixing ratio increased from 0 to 0.25. Our results showed that membrane elasticity increases with an increase in Chol content in the PAPC membrane