Liposomes

• Liposomes are tiny spherical vesicles widely used as delivery systems for bioactive molecules.

• Formed by hydrating lipid molecules in an aqueous environment, they resemble cell membranes, making them biocompatible and suitable for interaction with human cells.

Structural Composition

• Core and Bilayer: An aqueous core surrounded by one or multiple concentric lipid bilayers.

• Phospholipids: Composed of amphiphilic phospholipids, with hydrophilic "heads" facing outward and hydrophobic "tails" inward.

• Organization: Bilayers naturally form due to the amphiphilic nature of phospholipids.

Types of Liposomes

1. Small Unilamellar Vesicles (SUVs): Single bilayer, 20–100 nm diameter.

2. Large Unilamellar Vesicles (LUVs): Single bilayer, 100–1000 nm diameter.

3. Multilamellar Vesicles (MLVs): Multiple concentric bilayers, 500 nm to micrometers.

4. Multivesicular Vesicles (MVVs): Large vesicles containing smaller vesicles.

Preparation Methods

1. Thin Film Hydration: Solvent evaporation forms a thin lipid film, hydrated with an aqueous solution.

2. Sonication: Ultrasonic waves reduce vesicle size.

3. Extrusion: Liposome suspension is passed through membranes to control size.

Applications

1. Drug Delivery: Encapsulates hydrophilic and lipophilic drugs, improving bioavailability and enabling targeted delivery.

2. Vaccine Delivery: Encapsulates antigens, enhancing immune response.

3. Gene Therapy: Transports genetic material for therapeutic applications.

4. Cosmetics: Enhances skin penetration and hydration in products.

Characterization

1. Size & Lamellarity: Range from nanosized to microsized, unilamellar or multilamellar.

2. Surface Charge: Cationic, anionic, or neutral based on lipid composition.

3. Composition: Phospholipid and cholesterol content.

4. Drug Entrapment Efficiency: Encapsulation capability.

5. Release Profile: Drug release mechanism and rate.

Advantages

1. Versatility: Encapsulates hydrophilic and hydrophobic drugs.

2. Biocompatibility: Made of natural phospholipids, biocompatible and biodegradable.

3. Protection: Shields drugs from degradation.

4. Prolonged Circulation: PEGylation extends systemic circulation.

5. Passive Targeting: Exploits Enhanced Permeability and Retention (EPR) effect for tumors.

6. Reduced Toxicity: Limits drug exposure to non-target tissues.

Disadvantages

1. Stability Issues: Short shelf life and instability.

2. High Cost: Expensive production processes.

3. Variable Drug Loading: Inconsistent encapsulation efficiency.

4. Leakage: Drug may escape before reaching the target.

5. Complex Production: Requires specialized equipment.

6. Clearance: Susceptible to uptake by the reticuloendothelial system (RES).

Liposomes are a cornerstone in nanotechnology-driven drug delivery, with their design and applications continually evolving to enhance therapeutic outcomes.