This article is part of the series “Delivery Systems in Simple Terms.”
- Part 1: Nanoemulsions, Liposomes, Nanoparticles
- Part 2: Lipid‑Based Nanocarriers
- Part 3: Controlled Release & Mucosal Delivery
1. Nanoemulsions — simple delivery system
What they are
- Emulsions with droplet sizes ~20–200 nm
- Typically, oil-in-water (O/W) for drug delivery
- Thermodynamically unstable but kinetically stable
How they work
- The drug is dissolved in the oil phase
- Tiny droplet size → huge surface area
- Improves solubility, dissolution rate, and absorption
Key mechanisms
- Enhanced intestinal permeation
- Protection of the drug from degradation
- Possible lymphatic uptake (bypasses first-pass metabolism)
Advantages
- High bioavailability for poorly water-soluble drugs
- Fast onset
- Transparent or translucent
Limitations
- Requires surfactants (toxicity concerns)
- Physical instability over long storage
2. Liposomes — a membrane‑based delivery system
What they are
- Spherical vesicles made of phospholipid bilayers
- Size range: ~50 nm to several microns
- Mimic biological membranes
How they work
- Hydrophilic drugs → encapsulated in aqueous core
- Lipophilic drugs → embedded in lipid bilayer
- Fuse with cell membranes or are taken up by endocytosis
Key mechanisms
- Drug release by:
- Liposome destabilization
- Enzymatic degradation
- pH or temperature changes
Advantages
- Biocompatible and biodegradable
- Reduced toxicity
- Targeting possible (e.g., PEGylation, ligand attachment)
Limitations
- Short shelf life
- Expensive
- Leakage of the drug
3. Nanoparticles — solid nanocarrier systems
What they are
- Solid colloidal particles (10–1000 nm)
- Made from polymers, metals, or lipids
- The drug may be:
- Encapsulated
- Adsorbed
- Chemically attached
How they work
- Controlled drug release via:
- Diffusion
- Polymer degradation
- Swelling
Key mechanisms
- Enhanced permeability and retention (EPR effect) in tumours
- Cellular uptake via endocytosis
Advantages
- Precise control over release
- Targeted delivery possible
- Protection of the drug from degradation
Limitations
- Complex manufacturing
- Possible toxicity (material-dependent)
Delivery Systems in Simple Terms — Series Index
This article is Part 1 of a three‑part series “Delivery Systems in Simple Terms.”
- Part 1 — Nanoemulsions, Liposomes, and Nanoparticles (current article)
- Part 2 — Lipid‑Based Nanocarriers (SLNs and NLCs)
- Part 3 — Controlled Release, Sublingual, and Buccal Delivery
For a simple overview of absorption barriers and bioavailability fundamentals, see our previous article: Bioavailability Explained
For a broader overview of the field, see the Wikipedia article on Drug delivery.
