Abstract
The influence of cholesterol concentration on the formation of buckling structures is studied in a physisorbed polymer-tethered lipid monolayer system using epifluorescence microscopy (EPI) and atomic force microscopy (AFM). The monolayer system, built using the Langmuir-Blodgett (LB) technique, consists of 3 mol % poly(ethylene glycol) (PEG) lipopolymers and various concentrations of the phospholipid, 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine (SOPC), and cholesterol (CHOL). In the absence of CHOL, AFM micrographs show only occasional buckling structures, which is caused by the presence of the lipopolymers in the monolayer. In contrast, a gradual increase of CHOL concentration in the range of 0–40 mol % leads to fascinating film stress relaxation phenomena in the form of enhanced membrane buckling. Buckling structures are moderately deficient in CHOL, but do not cause any notable phospholipid-lipopolymer phase separation. Our experiments demonstrate that membrane buckling in physisorbed polymer-tethered membranes can be controlled through CHOL-mediated adjustment of membrane elastic properties. They further show that CHOL may have a notable impact on molecular confinement in the presence of crowding agents, such as lipopolymers. Our results are significant, because they offer an intriguing prospective on the role of CHOL on the material properties in complex membrane architecture.
Highlights
Buckling and wrinkling of thin elastic materials in response to lateral stress represents a fascinating topic of materials science and is of great significance in various technical applications [1,2]Importantly, these stress relaxation processes are critically dependent on the stiffness of the underlying substrate [3]
The current work shows that CHOL has a significant influence on the buckle delamination processes in physisorbed polymer-tethered membranes containing phospholipids, poly(ethylene glycol) (PEG) lipopolymers and CHOL
In the absence of CHOL and at low mol % PEG lipopolymers, membrane buckling caused by lipopolymers is very limited
Summary
Buckling and wrinkling of thin elastic materials in response to lateral stress represents a fascinating topic of materials science and is of great significance in various technical applications [1,2]. Our group reported that physisorbed polymer-tethered membranes containing phospholipids, and lipopolymers represent another model membrane system, in which membrane buckling phenomena can be investigated under well-controlled conditions [15,16] In this model system, the elastic properties can be modified through adjustment of lipopolymer molar concentration in the membrane [17,18]. Physisorbed polymer-tethered lipid bilayers, which are compartmentalized by buckling structures, show fascinating length scale-dependent lipid diffusion properties with remarkable parallels to those found in plasma membranes [19] These dynamic properties are intriguing in light of the recently reported fabrication of such membrane systems with either a static lipopolymer concentration gradient or sharp boundaries between regions of low and high lipopolymer concentrations [20]. The current work is intriguing in light of the important role of CHOL on membrane elasticity and functionality in biological membranes
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