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Physiological basis and concepts of electromyography
Published in Kumar Shrawan, Mital Anil, Electromyography in Ergonomics, 2017
The basic structure of a cell membrane is shown in Figure 2.1. The membrane comprises a double layer of phospholipids. Both surfaces of this layer are covered with proteins. In addition, proteins are embedded into the lipid bilayer, permeating it either fully or partially. The bilayer structure of the cell membrane and the properties of the lipid molecules are important for the means by which an exchange between the intracellular and the interstitial compartments is restricted. Lipid molecules are elongated and unsymmetrical in structure. They possess a polar head and a non-polar tail (Eckert and Randall, 1983). The polar heads are hydrophilic, i.e. water soluble, whereas the non-polar tails are hydrophobic, i.e. water insoluble. Within the double layer the lipid molecules are positioned in such a way that the hydrophobic ends face each other in the middle of the membrane whereas the hydrophilic ends are immersed in the aqueous solutions present in the intracellular and extracellular spaces. The hydrophobic property of the tails in the inner lipid layer means that the membrane represents an almost insuperable barrier for water, water-soluble molecules, and ions.
Monolayers and Multilayers
Published in Victor M. Starov, Nanoscience, 2010
Hernán Ritacco, Iván López-Montero, Francisco Monroy, Francisco Ortega, Ramón G. Rubio
A bilayer is a special type of amphiphile aggregate built as two tail-to-tail faced monolayers which constitute the complementary leaflets of the bilayer. Insight on the optimal molecular packing inside a bilayer can be gained from very simple energetic considerations [73]. The major forces that govern the self-assembling of a lipid bilayer derive from the hydrophobic attraction at the hydrocarbon–water interface, which induces the molecules to associate, and the hydrophilic, ionic, or steric repulsion of the head groups, which imposes the opposite requirement that they remain in contact with water. These two interactions compete as opposing forces at the interfacial region between the bilayer aggregate and the surrounding medium, the first tending to decrease the interfacial area per molecule and the other tending to increase it, so giving rise to an effective headgroup area a exposed to the aqueous subphase.
Detection and Description of Tissue Disease: Advances in the Use of Nanomedicine for Medical Imaging
Published in Dan Peer, Handbook of Harnessing Biomaterials in Nanomedicine, 2021
Jason L. J. Dearling, Alan B. Packard
The materials used in the preparation of liposomes must provide structural strength and stability while at the same time reducing interactions with proteins in order to extend the circulation time. The stability and mechanical strength of liposomes is based on a rigid bilayer that requires lipids with a high phase-transition temperature. The bilayer is typically comprised of a common lipid such as phosphatidyl choline and a mixture of the fatty acids stearate and oleate. Addition of a small amount of cholesterol increases the fluidity of the bilayer by modifying its crystalline nature. Keeping the formulation simple is also beneficial, as mixtures of lipids with different phase transition temperatures can lead to instability in vivo.
Temperature and oxidation-sensitive dioleoylphosphatidylethanolamine liposome stabilized with poly(ethyleneimine)/(phenylthio)acetic acid ion pair
Published in Journal of Biomaterials Science, Polymer Edition, 2023
Fanyu Zhao, Garima Sharma, Jin-Chul Kim
Self-assemblies are spontaneously formed by an entropy-driven process when amphiphilic molecules are dispersed in an aqueous phase [1, 2]. The molecular shape of amphiphilic molecules, characterized by its packing parameter, is a determinant factor affecting the self-assembling structure [3, 4]. The amphiphilic molecules, such as phospholipids, assemble into bilayer vesicles called liposomes. The most commonly used phospholipid for the preparation of liposomes is phosphatidylcholine (PC). Since PC has a packing parameter of around 1, it can form liposomes by itself without any helper molecules [5, 6]. Another phospholipid frequently used in preparing liposomes is dioleoylphosphatidylethanolamine (DOPE). Unlike PC, DOPE has a packing parameter greater than 1, and it tends to constitute a reversed hexagonal phase in an aqueous solution [7–9]. However, DOPE can also build bilayer vesicles with the aid of a helper molecule [10–12]. The helper molecule should be amphiphilic to be inserted between the phospholipid heads and fill the space between the heads.
Formation of planar hybrid lipid/polymer membranes anchored to an S-layer protein lattice by vesicle binding and rupture
Published in Soft Materials, 2020
Christian Czernohlavek, Bernhard Schuster
There are significant efforts to design synthetic membranes as mimics of biomembranes.[1] The building blocks of bio-inspired systems constitute unique, predictable and tunable properties, diversity, and the possibility to fabricate ultrathin two-dimensional structures in the square-micrometer range with an astonishing variety of functionalities at the nanoscale.[2–7] Moreover, these natural building blocks like, e.g., lipids, proteins, and polymers self-assemble spontaneously into supramolecular structures.[8–10] One of the most important template for bio-inspired architectures is the cell envelope structure of prokaryotes, which is a complex layered structure comprising of a cell membrane and in many cases of a monomolecular array of protein subunits forming the outermost surface layer (S-layer).[4,9,11,12] The importance of cell membranes in biological systems as a barrier, preserver of the physical integrity of the cell and host for integral membrane proteins has prompted the development of membrane platforms that recapitulate fundamental aspects of membrane biology, especially the lipid bilayer environment.[7,13,14] This environment is of utmost importance for integral membrane proteins like channels, proton pumps, and (G protein-coupled) receptors, which are responsible for carrying out important specific membrane functions.[15–19]