*4.6.1 Types of liposomes*

Depending upon their structure, there are two types of liposomes, unilamellar liposomes or unilamellar vesicles, which have a single phospholipid bilayer sphere enclosing an aqueous solution (**Figure 3**), or multilayer liposomes, which are multilamellar structures (**Figure 4**). In multilayer liposomes, several unilamellar vesicles will form one inside the other in diminished sizes, creating a multilamellar structure of concentric phospholipid spheres (like a Matryoshka doll) separated by layers of water. The structural components of liposomes could be:


**Figure 3.** *Single-layer liposome.*


**37**

[131] are the following.

**5. Mechanical dispersion method**

**5.1 Handshaking and non-handshaking method**

*Breaking down the Barrier: Topical Liposomes as Nanocarriers for Drug Delivery…*

Due to differences in preparation methods and lipid compositions, liposomes may be classified, according to their size, in small (<100 nm), medium (100– 250 nm), or large (>250 nm) [121, 122]. Some liposomes may be as small as <0.1 μm

In addition to the ability to entrap drugs with different solubility characteristics, it has been hypothesized that liposomes have different release kinetics. In general, multilamellar liposomes are more easily formed at larger hydrodynamic diameters, and, therefore, they have greater entrapped volumes than unilamellar liposomes. As a result of this, unilamellar liposomes with a hydrodynamic diameter of 130 nm exhibit a much faster release rate than multilamellar liposomes with two to three lamellar bilayers and a hydrodynamic diameter of 250 nm [123, 124]. The difference in the release rate is overall due to the number of phospholipid bilayers that it has to cross before being released [123, 124]. The ongoing interest of researchers in liposomal characteristics such as their stability, pharmacokinetic properties, and therapeutic efficacy has led to second-generation liposomes through the modulation of their lipid composition, size, and the charge of the vesicle. The addition of cholesterol to the lipid bilayer of liposomes reduces their permeability, increases their in vivo and in vitro stability, and can be used to anchor other molecules such as polyethylene glycol (PEG) or deoxyribonucleic acid (DNA) to the liposomes for their application in biosensing or as "stealth" drug carriers [124]. The use of phosphatidylcholine with saturated fatty acyl chains and materials that stretch transition temperatures beyond 37°C offered even greater stabilization [115, 125]. Furthermore, hydrophilic carbohydrates or polymers, such as monosialoganglioside (GM1) and PEG, were included in the liposomal composition. GM1 can

lead to the prolongation of the in vivo liposome viability time [126–129].

and Molinari [130], the choice of the method depends on factors such as the physicochemical characteristics of liposomes and/or drug components; the toxicity and concentration of the loaded drug; the type of medium in which liposomes are dispersed; the additional process during the application/delivery of liposomes; the desired size for the application; the half-life desired for successful application; costs, reproducibility, and applicability regarding large-scale production for clinical purpose; and good manufacturing practice-relevant issues. In addition, the target organ is a significant issue to be considered when planning the preparation of liposomes. Every method for preparing liposomes involves four basic stages: drying down lipids from an organic solvent, dispersing the lipid in aqueous media, purifying the resultant liposome, and analyzing the final product. The most common methods for producing liposomes, according to Gabizon et al. [123, 128] and Akbarzadeh et al.,

There are many different methods to prepare liposomes. According to Bozzuto

In order to produce liposomes, lipid molecules must be introduced into an aqueous environment. When a dry lipid layer film is hydrated, lamellae swell and grow

*DOI: http://dx.doi.org/10.5772/intechopen.86601*

*4.6.3 Preparation method (incorporating drugs)*

*4.6.2 Size of liposomes*

or as big as >1 mm in size.

*Breaking down the Barrier: Topical Liposomes as Nanocarriers for Drug Delivery… DOI: http://dx.doi.org/10.5772/intechopen.86601*

## *4.6.2 Size of liposomes*

*Role of Novel Drug Delivery Vehicles in Nanobiomedicine*

• Synthetic phospholipids (saturated and unsaturated).

results in repulsion interactions with macromolecules.

ability barriers to entrap aqueous drugs.

• Polymeric materials. Polymerized liposomes have significantly higher perme-

• Polymer-bearing lipids. Coating liposome surfaces with charged polymers

• Cationic lipids such as dioctadecyldimethylammonium bromide or chloride.

**36**

**Figure 4.** *Multilayer liposome.*

**Figure 3.**

*Single-layer liposome.*

Due to differences in preparation methods and lipid compositions, liposomes may be classified, according to their size, in small (<100 nm), medium (100– 250 nm), or large (>250 nm) [121, 122]. Some liposomes may be as small as <0.1 μm or as big as >1 mm in size.
