Advances on Planar Lipid Bilayers and Liposomes 

About: Advances on Planar Lipid Bilayers and Liposomes is an academic journal. The journal publishes majorly in the area(s): Lipid bilayer & Membrane. Over the lifetime, 190 publications have been published receiving 1472 citations.

Chapter Five Liposome-Based Biomembrane Mimetic Systems: Implications for Lipid–Peptide Interactions

Abstract: The fundamental structural unit of biological membranes is mostly a highly dynamic, liquid-crystalline phospholipid bilayer that acts as a permeability barrier The concept of a characteristic lipid composition for a given cell membrane is well-accepted and is of considerable interest, when studying the molecular mechanism(s) of membrane damage by membrane-active agents such as toxins or antimicrobial peptides Despite the wealth of information and experimental data we still do not fully understand at a molecular level how these peptides disrupt the barrier function of cell membranes Therefore, lipid model membranes mimicking the more complex biological membranes have attracted scientists from various fields Structural and thermodynamic characterization of these biomembrane mimetic systems such as liposomes is a prerequisite for the understanding of lipid–peptide interactions The focus of this contribution will be on how X-ray scattering techniques contribute to the characterization of liposomes and in turn to the elucidation of the mechanisms of peptide–membrane interaction First, we summarize the current models for the mode of action of antimicrobial peptides as well as general aspects of model membranes followed by a detailed description of X-ray scattering in combination with a global data analysis The applicability of this new approach is exemplary shown on selected model membrane and lipid–peptide systems demonstrating a tight coupling between the peptide properties and those of the lipid bilayer

Steric Stabilizers for Cubic Phase Lyotropic Liquid Crystal Nanodispersions (Cubosomes)

Abstract: Lyotropic liquid crystalline nanostructured particles, such as cubosomes, have grown in popularity as drug delivery systems in the last few years These systems require steric stabilizers to maintain colloidal stability in an aqueous medium, with Pluronic®F127, a block copolymer, being the most commonly employed stabilizer However, in recent years, alternative, more effective stabilizers, as well as rationally designed systems with opportunities for further biofunctionalization have been reported The purpose of this chapter is to collate and collectively interpret studies in the field of steric stabilization of this important emerging class of nanoparticles for drug and medical imaging agent delivery

Chapter Seven Electroporation of Planar Lipid Bilayers and Membranes

Abstract: Strong external electric field can destabilize membranes and induce formation of pores thus increasing membrane permeability. The phenomenon is known as membrane electroporation, sometimes referred to also as dielectric breakdown or electropermeabilization. The structural changes involving rearrangement of the phospholipid bilayer presumably lead to the formation of aqueous pores, which increases the conductivity of the membrane and its permeability to water-soluble molecules which otherwise are deprived of membrane transport mechanisms. This was shown in variety of experimental conditions, on artificial membranes such as planar lipid bilayers and vesicles, as well as on biological cells in vitro and in vivo. While studies of electroporation on artificial lipid bilayers enabled characterization of the biophysical processes, electroporation of biological cells led to the development of numerous biomedical applications. Namely, cell electroporation increases membrane permeability to otherwise nonpermeant molecules, which allows different biological and medical applications including transfer of genes (electrogene transfer), transdermal drug delivery and electrochemotherapy of tumors. In general, the key parameter for electroporation is the induced transmembrane voltage generated by an external electric field due to the difference in the electric properties of the membrane and the external medium, known as Maxwell–Wagner polarization. It was also shown that pore formation and the effectiveness of cell electroporation depend on parameters of electric pulses like number, duration, repetition frequency and electric field strength, where the later is the crucial parameter since increased transmembrane transport due to electroporation is only observed above a certain threshold field. Two main theoretical approaches were developed to describe electroporation. The electromechanical approach considers membranes as elastic or viscoelastic bodies, and applying principles of electrostatics and elasticity predict membrane rupture above critical membrane voltage. A conceptually different approach describing formation and expansion of pores is based on energy consideration; it is assumed that external electric field reduces the free energy barrier for formation of hydrophilic pores due to lower polarization energy of water in the pores compared to the membrane. Combined with stochastic mechanism of pores expansion it can describe experimental data of bilayer membranes. Still, the molecular mechanisms of pore formation and stabilization during electroporation are not fully understood and rigorous experimental conformation of different theories is still lacking. The focus of this chapter is to review experimental and theoretical data in the field of electroporation and to connect biophysical aspects of the process with the phenomenological experimental observations obtained on planar lipid bilayers, vesicles and cells.

Chapter 9 The Biologically Relevant Lipid Mesophases as “Seen” by X-Rays

Abstract: The biologically significant state of membranes is the fluid crystalline state. As most liquid crystal compounds, lipid membranes display a rich polymorphism. However, only few phases are biologically relevant. In this review, I give an overview of all lipid mesophases which play a role in nature and illustrate how X-ray-scattering techniques contribute to the determination of their structural as well as mechanical properties. This includes to know about lipid/water composition, monolayer thickness, interfacial area per lipid, molecular shape, membrane curvatures, and bending rigidity. Under excess water condition – as biological membranes are – only four types of stable mesophases exist, i.e., the lamellar fluid phase Lα, the bicontinuous cubic phases, the columnar inverted hexagonal phase HII, and further one micellar cubic phase. Besides these, I give a brief description of the so-called “mesh” phase, which has been recently suggested to be host for the membrane fusion stalk intermediate.

Theory of Phase Transitions: From Magnets to Biomembranes

Abstract: This chapter presents an overview of the theory of phase transitions and critical phenomena in the framework of “idealized” classical models, such as the Ising model—a system of magnetic moments living on a cubic lattice and having only two accessible states and a magnetic interaction restricted to nearest-neighboring sites only. For these models, statistical physics gives a detailed description of the behavior of various thermodynamic quantities in the vicinity of the transition temperature. The predictions of the named models were confirmed by the most precise experiments on magnets. Real systems, however, are more complex and additional features, such as anisotropy, defects, and dilution have to be taken into account. These features highly affect the transitional behavior of the ideal model or even suppress it. Here, we address this issues in terms of magnetic systems and discuss their application to biomembranes.