Lipid Bilayer Phase Transformations Detected Using Microcantilevers

Abstract

We report the use of microcantilevers to measure the phase transition temperature (T(m)) of supported lipid bilayers or lipid monolayers. During the solid-liquid phase transition, a supported lipid bilayer or monolayer undergoes a conformational change in which the lipid acyl chains transition from an ordered state to a disordered state. This process is accompanied by a free energy change, which is coupled to changes in the surface stress in the underlying solid support layer. These surface stress changes can be readily detected using microcantilevers. The surface stress of the solid-like phase of 1-myristoyl-2-palmitoyl-sn-glycero-3-phosphocholine (MPPC) decreases linearly as the temperature increases and abruptly jumps at the main phase transition temperature. This phase transition temperature corresponds well with that found for free membranes. For an MPPC monolayer, this phase transition temperature is shifted, indicating that the existence of the solid support affects the monolayer structure. The addition of cholesterol into the bilayer decreases the phase transition temperature by ~0.38 °C per mol % of cholesterol. Differences in MPPC stability when it is either a bilayer or a monolayer can be detected through these sensitive surface stress measurements.

Probing the association of triblock copolymers with supported lipid membranes using microcantilevers

“…Initially, the SLB was formed on the coverslip by injecting a uorescent LUV solution (POPC with 0.5 mol% TR-DHPE) at a rate of 10 ml min À1 for 10 min into the microuidic channel using a syringe pump followed by PBS buffer to remove excess vesicles. Then, the triblock copolymer (F68 or F98) solution at a concentration of 100 mM was injected at various temperatures (25,30,35, or 40 C), followed by PBS buffer. The uidity of the lipids with and without the triblock copolymers was characterized by FRAP using confocal microscopy (Olympus IX81).…”

“…The reason lies in the asymmetric environment of the SLBs. 25 The proximal leaet of the SLB is conned by a thin water layer and the solid support. The energy penalty for disrupting this connement is too great.…”

“…This leaet asymmetry has been reported to cause the differences in the surface tension, lipid diffusion, and phase transition temperature between SLBs and free membranes. [25][26][27][28][29][30][31] In this work, F68 and F98 Pluronics were chosen because they have the same HLB value but the lengths of their lipophilic PPO blocks differ. Thus, the effect of the length of the lipophilic block on polymer-lipid association and copolymer conformation can be studied.…”

Influence of Cholesterol and Bilayer Curvature on the Interaction of PPO–PEO Block Copolymers with Liposomes

“…Numerous studies have focused on developing a basic understanding of polymer-membrane association mechanisms, using lipid bilayer systems as model membranes. [14][15][16][17][18][19][20][21][22][23][24] Cheng et al suggested that the hydrophobic PPO block inserts into the membrane interior whereas the hydrophilic PEO block weakly adsorbs onto the membrane surface. 14 Smallangle X-ray scattering experiments and coarse-grained molecular dynamic simulations indicate that the PPO block length is the key determinant for association with lipid membranes.…”

Influence of the Headgroup on the Interaction of Poly(ethylene oxide)-Poly(propylene oxide) Block Copolymers with Lipid Bilayers

“…Pure POPC liposomes were used as controls because phosphatidylcholine is one of the major components found in eukaryotic cell membranes and is widely used as the basic constituent in model membranes. [29][30][31][32] POPG, on the other hand, is a relatively minor component in eukaryotic cell membranes and is mostly found in bacterial cell membranes. 33 Nevertheless, given that POPG has the same phase transition temperature and almost the same chemical structure except for the headgroup as POPC, it can be considered as a simple model to study how the presence of net charge and hydroxyl groups affect membrane interactions with the copolymers.…”