- Digestion of fat is mainly done in the small intestine.
- Bile salts emulsify the fat and pancreatic lipase hydrolyzes them to release fatty acids and glycerol.
- Micelles are temporary compounds formed during the fat digestion and absorption process.
How are micro-micelles formed?
Micelles are formed by self-assembly of amphiphilic molecules. The structures contain hydrophilic/polar region (head) and hydrophobic/nonpolar region (tail). Micelles are formed in aqueous solution whereby the polar region faces the outside surface of the micelle and the nonpolar region forms the core.
What is a micelle in microbiology?
A micelle (rarely micella, plural micellae) is an aggregate of surfactant molecules dispersed in a liquid colloid. A typical micelle in aqueous solution forms an aggregate with the hydrophilic "head" regions in contact with surrounding solvent, sequestering the hydrophobic tail regions in the micelle centre.
What is a micelle formed by phospholipids?
Scheme of a micelle formed by phospholipids in an aqueous solution. A micelle (/maɪˈsɛl/) or micella (/maɪˈsɛlə/) (plural micelles or micellae, respectively) is an aggregate (or supramolecular assembly) of surfactant molecules dispersed in a liquid colloid.
Where is a micelle?
A micelle, then, is a spherical structure in which the nonpolar tails of amphipathic molecules hide on the inside and are shielded from water by the polar heads that line the outside. Micelles have important roles in fat and vitamin absorption in the intestine.
Why does micelle formation take place?
When soap is dissolved in water and clothes are put in the soapy solution, soap molecules converge in a typical fashion to make a structure; called micelle. The hydrophobic ends of different molecules surround a particle of grease and make the micelle; which is a spherical structure.
What is a micelle in anatomy?
Micelles are lipid molecules that arrange themselves in a spherical form in aqueous solution. The formation of a micelle is a response to the amphipathic nature of fatty acids, meaning that they contain both hydrophilic and hydrophobic regions.
Are micelles in the blood?
Upon injection into the bloodstream, micelles are immediately surrounded by blood components, particularly albumin. We hypothesized that albumin might host the hydrophobic PCL block of PEG-PCL in its hydrophobic pocket and thus facilitate PEG-PCL micelle dissociation.
What is the function of a micelle?
Micelles help the body absorb lipid and fat soluble vitamins. They help the small intestine to absorb essential lipids and vitamins from the liver and gall bladder. They also carry complex lipids such as lecithin and lipid soluble vitamins (A, D, E and K) to the small intestine.
What are micelles give one example?
Micelles are the clusters or aggregated particles formed by association of colloids in solution. Soaps and detergents form micelles when temperatureis above Kraft temperature and concentration is above critical micelle concentration (CMC). For soaps, CMC is about 10−4 to 10−3 M.
How are micelles formed in digestion?
Lipases break down the lipids into fatty acids and glycerides. These molecules can pass through the plasma membrane of the cell, entering the epithelial cells of the intestinal lining. The bile salts surround long-chain fatty acids and monoglycerides, forming tiny spheres called micelles.
What is a micelle quizlet?
Micelles are structures composed of a monolayer of amphipathic molecules. In a biological system, the molecules tend to arrange themselves in such a manner that the inner core of these structures are hydrophobic and the outer layers are hydrophilic in nature.
How does the body break down lipids?
Lipids are not water soluble, which means that water cannot absorb them or break them down. Most of the body's digestive enzymes are water-based, so the body has to use special enzymes to break down fat throughout the digestive tract. The body begins breaking down fat in the mouth, using enzymes in saliva .
How are lipids transported through the body?
Lipids are transported as lipoproteins in the blood. Lipoproteins: Lipoproteins consists of an inner core of hydrophobic lipids surrounded by a surface layer of phospholipids, cholesterol, and outer proteins (apolipoprotein). Lipoproteins are a lipid + a protein (compound lipid).
How does fat enter the bloodstream?
Short- and medium chain fatty acids are absorbed directly into the blood via intestine capillaries and travel through the portal vein. Long-chain fatty acids, on the other hand, are too large to be directly released into the tiny intestine capillaries.
What is the structure of a micelle?
The structures contain hydrophilic/polar region (head) and hydrophobic/nonpolar region (tail) [1]. Micelles are formed in aqueous solution whereby the polar region faces the outside surface of the micelle and the nonpolar region forms the core. Micelles can deliver both hydrophilic and hydrophobic agents.
What is a micelle?
Micelles are amphiphilic nanocarriers that are effective in delivering drugs for targeting. Loading with hydrophobic drugs makes the hydrophobic core of micelles more suitable for targeting, which increases their half-life and bioavailability (Cho, 2015 ).
Why are polymeric micelles important?
Polymeric micelles have attracted much attention in drug delivery because of their ability to solubilize hydrophobic molecules, their small particle size, good thermodynamic solution stability, extended release of various drugs, and prevention of rapid clearance by the reticuloendothelial system (RES).
What are micelles made of?
Micelles are composed of amphiphilic macromolecules that contain both hydrophilic and hydrophobic segments (Sutton, Nasongkla, Blanco, & Gao, 2007 ). Depending on the size of these segments, micelles with various morphologies, including spheres, rods, tubules, lamellae, and vesicles, can be created ( Choucair & Eisenberg, 2003 ). A micelle consists of a core and a shell, where hydrophobic end groups form the core and hydrophilic head groups form the outer shell ( Fig. 1.4 ), or vice versa ( Haley & Frenkel, 2008 ). Amphiphilic micelles are formed through self-assembly of unimers with hydrophilic and hydrophobic segments in solution. In aqueous solutions, water-insoluble (hydrophobic) drugs are encapsulated during self-assembly ( Kedar et al., 2010 ). While in nonaqueous solutions, water-soluble (hydrophilic) drug molecules, including proteins, peptides, and nucleic acids, are encapsulated during assembly ( Allen, 1998; Momekova et al., 2007 ). Micelle nanoparticles range in size from 5 to 100 nm ( Oerlemans et al., 2010 ). Many different polymers can be used to create micelles; however, the selection is limited for drug delivery applications because the micelle must be biocompatible and biodegradable. PEG is commonly used to fabricate micelles because it is neutral, nontoxic, and water soluble. Other hydrophilic polymers used include poly ( N -vinyl pyrrolidone) (PVP) and pNIPAM ( Chung, Yokoyama, Aoyagi, Sakurai, & Okano, 1998; Chung, Yokoyama, & Okano, 2000; Chung et al., 1999 ). Degradable hydrophobic polyesters are commonly used to make the hydrophobic segment of the amphiphilic macromolecule ( Sutton et al., 2007 ). Micelles are intrinsically stealth particles when formed with a hydrophilic outer shell, and they are able to avoid uptake by the MPS without further modification.
What are polymeric micelles?
Micelles/polymeric micelles are composed of amphiphilic macromolecules with a hydrophobic core and hydrophilic shell with the size ranging from 20 to 80 nm (Lu and Park, 2013 ). Traditional micelles are lipid-based. Basically, the hydrophilic heads of phospholipids forms the shell and the fatty acid tails of phospholipids forms the hydrophobic core of the micelle that can accommodate phytochemicals ( Wang et al., 2014, p. 365). Polymeric micelles are emerging as a powerful tool in nanomedicine platform for cancer therapy due to their tunable size, in vivo stability, and efficiency in solubilizing water insoluble anticancer drugs with increased blood circulation times ( Sutton et al., 2007, p. 1029). Other potent pharmacokinetic benefits include reduced systemic toxicity and patient morbidity. Functionalized micelles as a recent advancement play an important role in cancer therapy by site-specific drug release at the target site ( Sutton et al., 2007, p. 1029). Micelles are more advantageous than liposomes owing to its rapid accumulation into tumors due to its smaller size ( Weissig et al., 1998, p. 1552). Like liposomes, micelles can be conjugated or functionalized with carbohydrates, peptides, mAbs, aptamers, and polymers for targeting and improving the pharmacological behaviors of payloads ( Liu et al., 2012, p. 2521).
What are mixed micelles?
Mixed micelles are mixtures of amphiphile systems (including surfactants, polymers, and copolymers) that form micellar aggregates. They exhibit characteristics properties different from the individual amphiphile. They are fascinating from a scientific as well as industrial standpoint because the properties of mixed micelles can be tuned to the desired requirements through simple composition variations, rather than through synthesis of new materials. Mixed micelles have been widely used in pharmaceutical industries for solubilization of hydrophobic drugs, which in turn improve their therapeutic efficacy. The mixed micelles stabilized drugs have been successfully administrated by various ways such as parenteral, oral, and dermal routes (Hendradi et al., 2003; Mrestani et al., 2010; Sznitowska et al., 2008 ). The use of these small mixed micelles (usually having diameters smaller than 60 nm) further increases their in vivo circulation as well as prevents their undesired uptake by RES ( Rupp et al., 2010 ). Therefore, they have been particularly employed for parenteral delivery of hydrophobic drugs. The interaction between micelles and lipophilic drugs leads to the formation of mixed micelles (MM), often called swollen micelles. Swollen micelles are fluid systems, but sufficiently stable to be used as delivery systems for stable drugs ( Hammad and Müller, 1998 ). For example, Valium MM and Konakion MM are two mixed micelle–based formulations currently available in the pharmaceutical market. The use of mixed micelles comprising biocompatible surfactants in the delivery of anticancer drugs has been reported ( Bhattacharjee et al., 2010 ).
How are polymeric micelles generated?
Polymeric micelles are generated by using block copolymers with amphiphilic character (Nishiyama and Kataoka , 2006 ). They spontaneously assemble into nano‐sized polymeric micelles in aqueous solution. These micelles contain a unique core–shell structure that serves as a container of hydrophobic drugs. A number of micelle–drug formulations are being examined in clinical trials. Genexol-PM, a 60 nm sized block copolymer of PDLLA–mPEG (poly ( d, l -lactide)–PEG) forming micelles containing paclitaxel was approved in Korea for cancer therapy ( Kim et al., 2007) and entered clinical trials in the United States.
How are micelles formed?
Micelles are formed by the aggregation of amphipathic molecules in polar solvents, like water . They are usually in the form of a sphere, sometimes they are in an ellipsoidal form; with the polar heads on the outside and the non polar tails on the inside. Here, the molecules orient themselves in such a way that the hydrophilic heads ...
What is the mechanism of micelle formation?
Formation of micelles takes place beyond a particular concentration of the amphipathic molecules. This threshold is called Critical Micelle Concentration (CMC). When the concentration of the molecules is much below the CMC, there is slight increase in the entropy of the system, these molecules exist as monomers.
What are the micelles in detergents?
Detergents are capable of forming micelles. These micelles function as emulsifiers, as they dissolve substances that are usually insoluble in water. The hydrophobic tails of detergents interact with insoluble dirt and oil such that, the dirt is entrapped in the hydrophobic center of these micelles.
What is the difference between a micelle and a lipid bilayer?
Here, the molecules orient themselves in such a way that the hydrophilic heads of the molecule are in close contact with the polar medium; whereas, their hydrophobic regions are away from it. Unlike lipid bilayers, micelles are usually composed of only a single layer of molecules. Here, the molecules consist of only a single hydrophobic tail ...
What is a micelle in a drug delivery system?
Micelles in Smart Drug Delivery System. Polymeric micelles are a combination of amphipathic molecules and reactive polymers. They are used as a vehicle to carry drugs that have least solubility. This method can be controlled to alter the size of the micelle produced or the amount of drug to be delivered.
How do counter ions affect micelles?
As counter-ions bind to polar heads of the amphipathic molecules, they decrease the repulsion between them, and thus, increase the stability of micelles. The CMC decreases with the increase in the number of counter-ions.
What are micelles used for?
Micelles function as emulsifiers, this property of micelles are used in the making a variety of cleaning products like detergents and micellar face washes. ScienceStruck gives you information on how micelles are formed, their structure, and function.
What are micelles in chemistry?
Micelles represent the simplest association structures frequently formed by amphiphles in aqueous solutions. Micelles normally have particle size within the 5–50 nm range. They belong to a group of association or amphiphilic colloids, which form spontaneously under certain conditions of concentration and temperature from amphiphilic or surface active agents, molecules of which consist of two clearly distinct regions with opposite affinities toward a given solvent (Mittal and Lindman, 1989 ). At low concentrations in aqueous medium, these amphiphilic molecules exist separately; however, when their concentration is increased, aggregation takes place within a rather narrow concentration range. The concentration at which the monomeric amphiphile forms micelles is called the critical micelle concentration (CMC). The number of individual molecules forming a micelle is called the aggregation number of the micelle. The formation of micelles is driven by the decrease of free energy in the system because of the removal of the hydrophobic segments from the aqueous environment and reestablishing of hydrogen bond network in water. Additional energy gain results from formation of van der Waals attraction between hydrophobic blocks in the core of the formed micelles (Jones and Leroux, 1999 ). The hydrophobic part of the amphiphilic molecules forms the core of a micelle, while the hydrophilic part forms the micelles’ shell ( Lasic, 1992 ). When used as drug carriers in the aqueous media, micelles solubilize molecules of poorly soluble nonpolar pharmaceuticals within the micelle core, while polar molecules are adsorbed on the shell of the micelle.
What are micelles made of?
Micelles consist of molecules containing two completely different regions that have opposite affinities against water. These amphiphilic molecules, which form the micelles, associate at certain temperatures and in appropriate concentrations. The core of the micelle is formed by the hydrophobic fragments of amphiphilic molecules, whereas micelle’s shell consists of hydrophilic fragments of micellar molecules. Micellar amphiphilic molecules at low concentrations exist separately in aqueous medium. The aggregation of micellar molecules takes place if their concentration is increased. But aggregation of micellar molecules happens only within a limited concentration interval. The critical micelle concentration is the concentration of a monomeric micellar amphiphile at which aggregation begins and micelles appear. The critical micellization temperature is the temperature at which aggregates appear and below which micellar molecules exist as monomers. The aggregation of amphiphilic molecules and formation of micelles happens after the removal of hydrophobic fragments of the micellar molecules from the aqueous environment and reconstitution of hydrogen bonds in water, leading to a decrease of free energy in the system. Micelles used as carriers for therapeutics in aqueous media can carry lipophilic drugs within its core while micelle’s surface binds polar molecules. Improved aqueous solubility and thus better intestinal permeability of micelles is achieved by formation of polymeric micelles. Polymeric micelles are formed of amphiphilic block copolymers and compared to conventional micelles show greater stability in vivo. Viruses use lectin receptors on host cells for their entry into the cells; the infected cells also express these lectins. In order to target viral reservoirs micelles consisted of PEG-polylactide copolymer surface modified with galactose are constructed, since galactose residues can interact with lectins.
What happens to the aggregation of amphiphilic molecules and formation of micelles?
The aggregation of amphiphilic molecules and formation of micelles happens after the removal of hydrophobic fragments of the micellar molecules from the aqueous environment and reconstitution of hydrogen bonds in water, leading to a decrease of free energy in the system.
Why are polymeric micelles important?
Polymeric micelles have attracted much attention in drug delivery because of their ability to solubilize hydrophobic molecules, their small particle size, good thermodynamic solution stability, extended release of various drugs, and prevention of rapid clearance by the reticuloendothelial system (RES).
What is the hydrophilic shell of a micelle?
Micelles are spherical amphiphilic structures that have a hydrophobic core and a hydrophilic shell.155 The hydrophilic shell makes the micelle water soluble that allows for intravenous delivery while the hydrophobic core carries a payload of drug for therapy. 156 The nanoscale dimensions (diameter less than 50 nm) 157 and the hydrophilic shell of polymeric micelles serve as protection from elimination by the reticulo-endothelial system, thereby increasing their circulation time and ability to deliver the drug to the target.
What is critical micelle concentration?
The critical micelle concentration is the concentration of a monomeric micellar amphiphile at which aggregation begins and micelles appear. The critical micellization temperature is the temperature at which aggregates appear and below which micellar molecules exist as monomers.
What is the shell of a micelle?
The core of the micelle is formed by the hydrophobic fragments of amphiphilic molecules, whereas micelle’s shell consists of hydrophilic fragments of micellar molecules. Micellar amphiphilic molecules at low concentrations exist separately in aqueous medium.
How do micelles form?
Micelles only form when the concentration of surfactant is greater than the critical micelle concentration (CMC), and the temperature of the system is greater than the critical micelle temperature, or Krafft temperature. The formation of micelles can be understood using thermodynamics: micelles can form spontaneously because of a balance between entropy and enthalpy. In water, the hydrophobic effect is the driving force for micelle formation, despite the fact that assembling surfactant molecules together reduces their entropy. Broadly speaking, above the CMC, the entropic penalty of assembling the surfactant molecules is less than the entropic penalty of caging water molecules. Also important are enthalpic considerations, such as the electrostatic interactions that occur between the charged parts surfactants.
What is a micelle?
A micelle (rarely micella, plural micellae) is an aggregate of surfactant molecules dispersed in a liquid colloid. A typical micelle in aqueous solution forms an aggregate with the hydrophilic "head" regions in contact with surrounding solvent, sequestering the hydrophobic tail regions in the micelle centre. This type of micelle is known as a normal phase micelle (oil-in-water micelle). Inverse micelles have the headgroups at the centre with the tails extending out (water-in-oil micelle). Micelles are approximately spherical in shape. Other phases, including shapes such as ellipsoids, cylinders, and bilayers are also possible. The shape and size of a micelle is a function of the molecular geometry of its surfactant molecules and solution conditions such as surfactant concentration, temperature, pH, and ionic strength. The process of forming micellae is known as micellisation and forms part of the phase behaviour of many lipids according to their polymorphism .
History
- The ability of a soapy solution to act as a detergent has been recognised for centuries. However it was only at the beginning of the twentieth century that the constitution of such solutions was scientifically studied. Pioneering work in this area was carried out by James William McBain at the University of Bristol. As early as 1913 he postulated the existence of “colloidal ions” to explain th…
Solvation
- Individual surfactant molecules that are in the system but are not part of a micelle are called "monomers." In water, the hydrophilic "heads" of surfactant molecules are always in contact with the solvent, regardless of whether the surfactants exist as monomers or as part of a micelle. However, the lipophilic "tails" of surfactant molecules have less contact with water when they ar…
Energy of Formation
- Micelles only form when the concentration of surfactant is greater than the critical micelle concentration (CMC), and the temperature of the system is greater than the critical micelle temperature, or Krafft temperature. The formation of micelles can be understood using thermodynamics: micelles can form spontaneously because of a balance between en...
Inverse Micelles
- In a non-polarsolvent, it is the exposure of the hydrophilic head groups to the surrounding solvent that is energetically unfavourable, giving rise to a water-in-oil system. In this case the hydrophilic groups are sequestered in the micelle core and the hydrophobic groups extend away from the centre. These inverse micelles are proportionally less likely to form on increasing headgroup cha…
Uses
- When surfactants are present above the CMC (Critical micelle concentration), they can act as emulsifiers that will allow a compound normally insoluble (in the solvent being used) to dissolve. This occurs because the insoluble species can be incorporated into the micelle core, which is itself solubilized in the bulk solvent by virtue of the head groups' favorable interactions with solv…
See Also
- Vesicle (biology)
- Lipid bilayer
- Surfactant
References
- J. M. Seddon, R. H. Templer. Polymorphism of Lipid-Water Systems, from the Handbook of Biological Physics, Vol. 1, ed. R. Lipowsky, and E. Sackmann. (c) 1995, Elsevier Science B.V. ISBN 0-444-81975-4
- S.A. Baeurle, J. Kroener, Modeling effective interactions of micellar aggregates of ionic surfactants with the Gauss-Core potential, J. Math. Chem. 36, 409-421 (2004).
- J. M. Seddon, R. H. Templer. Polymorphism of Lipid-Water Systems, from the Handbook of Biological Physics, Vol. 1, ed. R. Lipowsky, and E. Sackmann. (c) 1995, Elsevier Science B.V. ISBN 0-444-81975-4
- S.A. Baeurle, J. Kroener, Modeling effective interactions of micellar aggregates of ionic surfactants with the Gauss-Core potential, J. Math. Chem. 36, 409-421 (2004).
- McBain, J.W., Trans. Faraday Soc. 1913, 9, 99.
- Hartley, G.S., Aqueous Solutions of Paraffin Chain Salts, A Study in Micelle Formation, 1936, Hermann et Cie, Paris.
