- Composition: Synthetic polymer with repeating ethyleneimine units (‑CH₂CH₂NH‑)
- Forms:
- Branched PEI (25%, 50%, 75% branching)
- Linear PEI (LPEI) (near 100% secondary amines)
- Molecular Weight: 0.8–750 kDa (most common: 25 kDa for transfection)
- Solubility:
- Water-soluble at all pH levels
- Soluble in methanol, ethanol, DMSO
- Charge: Highly cationic (protonatable amines, pKa ~8–11)
- Viscosity: Increases with MW (e.g., 25 kDa PEI: ~30 cP in 50% aqueous solution)
- Synthesis & Commercial Forms
- Branched PEI: Made via acid-catalyzed aziridine polymerization
- Linear PEI: Produced by hydrolysis of poly(2-ethyl-2-oxazoline)
- Commercial Variants:
- Branched: 25 kDa (gold standard for transfection), 50 kDa, 750 kDa
- Linear: 2.5 kDa, 25 kDa
- Modified: PEGylated, acylated, crosslinked versions
- Mechanism of Action
- Nucleic Acid Binding: Forms stable polyplexes via electrostatic interactions (protects DNA/RNA)
- “Proton Sponge” Effect: Buffers endosomal pH → osmotic swelling → endosomal escape
- Membrane Interaction: Disrupts cell membranes (enhances permeability)
- Biomedical Applications
- Gene Delivery: Top non-viral transfection reagent (especially 25 kDa branched PEI)
- Pros: High efficiency, works in serum, scalable
- Cons: Cytotoxic at high doses
- Tissue Engineering
- Surface coating for improved cell adhesion
- Growth factor delivery (e.g., heparin-PEI complexes)
- Antimicrobial Uses
- PEI-coated surfaces kill microbes on contact
- Antibiotic-PEI conjugates combat resistance
- Industrial Uses
- Paper industry: Wet-strength additive (0.1–1% loading)
- Water treatment: Removes heavy metals (flocculant)
- Adhesives: Epoxy curing agent
- Cosmetics: Hair conditioner (low MW PEI)
- Gene Delivery: Top non-viral transfection reagent (especially 25 kDa branched PEI)
