Difference Between Liposome and Micelle

Key Difference – Liposome vs Micelle
 

Amphipathic molecules are composed of hydrophilic heads and hydrophobic tails. Therefore, they contain partial properties of both polar and nonpolar. Depending on the type of charge they carry and other parameters, amphipathic molecules could be of various types. Liposome and micelle are amphipathic molecules. Liposomes are composed of a bilayer of amphipathic molecules where the two layers of molecules are arranged in two concentric circles. Micelles are closed lipid monolayers where the fatty acids are either present in the core or at the surface. This is the key difference between liposomes and micelles.

CONTENTS

1. Overview and Key Difference
2. What is Liposome
3. What is Micelle
4. Similarities Between Liposome and Micelle
5. Side by Side Comparison – Liposome vs Micelle in Tabular Form
6. Summary

What is Liposome?

Liposomes are structures that consist of a bilayer of amphipathic molecules where the two layers of molecules are arranged in two concentric circles. In this arrangement of molecules, the outer layer hydrophilic heads are arranged where they are pointed outwards exposing to the outer environment.  The inner hydrophilic core is formed by the hydrophilic heads of the inner layer. The hydrophobic tails of both layers are arranged between the two concentric rings.

The formation of a liposome occurs by a process where the dry lipid molecules are hydrated through a nonpolar solvent that is followed an agitation process (mechanical induction). The major sources for liposome formation are phospholipid molecules along with cholesterol. The types of liposomes vary according to how they are formed. This criterion of liposome classification depends on the extent of mechanical agitation and the use of a polar solvent in some instances. These types of liposomes include Small Unilamellar Vesicles (SUV), Large Unilamellar Vesicles (LUV), Large Multilamellar Vesicles (MLV) and Multivesicular Vesicles (MVV).

In the human body, the liposomes are taken up by organs that are rich in the reticuloendothelial system.  Therefore the main objective of liposomes is drug delivery, which is targeted to these organs. In order to target specific tumor cells, the liposomes are coated with special polymers. The relative liposomes production process is costly. Therefore, these liposomes are used only during viral infection treatment and tumor cell killing. Drug administration is achieved via the parenteral route.

What is Micelle?

Micelle is defined as a lipid molecule that is arranged in a spherical form in aqueous solution. Micelles are formed in response to the amphipathic nature of fatty acids. Micelles are composed of both hydrophilic regions and hydrophobic regions. The hydrophilic regions are polar head groups whilst the hydrophobic regions are the long hydrophobic chains (tails). The polar head groups usually involve in the formation of the outside layer of the micelles since they have the ability to interact with water due to their polar nature. The hydrophobic tails are present inside of the structure to prevent the interaction with water due to their nonpolar nature.

Fatty acids that are produced from micelles contain a single hydrocarbon chain in opposite direction to two hydrocarbon chains. This structure enables the fatty acids to develop a spherical shape and thereby it lessens the steric hindrance that occurs within the fatty acid molecules themselves. The sizes of the micelles vary from 02 nm to 20 nm.  The size greatly depends on the composition and concentration of micelles. Due to the amphipathic nature of the molecule, micelles form spontaneously in water as well.

In the context of the human body, micelles help in absorption of lipid and fat-soluble vitamins such as vitamin A, D, E and K. They also help the small intestine in the absorption of essential lipids and vitamins derived from the liver and gallbladder.

What are the Similarities Between Liposome and Micelle?

• Both Liposome and micelles are composed of amphipathic molecules.
• Both Liposome and micelle are vesicular structures.
• Both Liposome and micelle have significant pharmaceutical applications.
• Both liposome and micelle play an important role in targeted drug delivery.
• Formation of both Liposome and micelles increases considerably beyond a particular temperature.

What is the Difference Between Liposome and Micelle?

Summary – Liposome vs Micelle

Amphipathic molecules contain partial polar and partial nonpolar properties. Liposomes and micelles fall under the category of amphipathic molecules. The liposomes are composed of a bilayer of amphipathic molecules where the two layers of molecules are arranged in two concentric circles. The formation of a liposome occurs by a process where the dry lipid molecules are hydrated through a nonpolar solvent. It is completed with physical agitation. Liposomes are used only during viral infection treatment and tumor cell killing since the production process is costly. Micelles are closed lipid monolayers where the fatty acids are either present in the core or at the surface. Micelles help in absorption of lipid and fat-soluble vitamins; vitamin A, D, E and K. This is the difference between liposome and micelle.

Reference:

1.“Structural Biochemistry/Lipids/Micelles.” Structural Biochemistry/Lipids/Micelles – Wikibooks, open books for an open world. Available here 
2.“The Significant Difference Between Micelles and Liposomes.” BiologyWise. Available here
3.Akbarzadeh, Abolfazl, et al. “Liposome: classification, preparation, and applications.” Nanoscale Research Letters, vol. 8, no. 1, 2013, p. 102., doi:10.1186/1556-276x-8-102

Image Courtesy:

1.’Liposome scheme-en’By SuperManu – Own work, (CC BY-SA 3.0) via Commons Wikimedia  
2.’Phospholipids aqueous solution structures’By Mariana Ruiz Villarreal ,LadyofHats – Own work, (Public Domain) via Commons Wikimedia