- Polyethyleneimine (PEI) is a synthetic polymer composed of repeating ethyleneimine units (–CH₂CH₂NH–) that exhibits a high density of amine groups, making it one of the most cationic polymers available.
- Depending on its synthesis method, PEI can exist in either a branched or linear form, with molecular weights ranging from a few hundred to several hundred thousand Daltons.
- Branched PEI contains primary, secondary, and tertiary amines, contributing to its highly charged and reactive nature, while linear PEI consists predominantly of secondary amines in a more ordered chain structure. This unique composition allows PEI to interact strongly with negatively charged molecules, such as nucleic acids, proteins, and metal ions, making it invaluable in fields ranging from gene therapy to water purification.
- One of PEI’s most notable characteristics is its high cationic charge density, which enables it to form stable electrostatic complexes with anionic biomolecules like DNA and RNA. This property is particularly useful in gene delivery, where PEI acts as a non-viral transfection agent by condensing genetic material into nanoparticles that can be taken up by cells.
- Additionally, PEI exhibits a “proton sponge” effect, where its amine groups buffer endosomal pH, leading to osmotic swelling and endosomal rupture, thereby enhancing the release of therapeutic nucleic acids into the cytoplasm.
- Beyond biomedical applications, PEI’s strong binding affinity for heavy metals and organic contaminants makes it effective in wastewater treatment, where it serves as a flocculant to remove pollutants.
- In biomedical research, PEI is widely used as a transfection reagent for delivering DNA, siRNA, and other nucleic acids into cells. Its efficiency in gene delivery has made it a gold standard in non-viral vector research, though its cytotoxicity at higher concentrations remains a limitation. To mitigate this, researchers often modify PEI with polyethylene glycol (PEG) or hydrolyzable linkages to improve biocompatibility.
- Beyond gene therapy, PEI is employed in drug delivery systems, where it coats nanoparticles to enhance cellular uptake or is used in layer-by-layer (LbL) assemblies for controlled drug release.
- Additionally, PEI-functionalized surfaces exhibit antimicrobial properties, making them useful in medical device coatings to prevent bacterial adhesion.
- PEI’s versatility extends to numerous industrial applications. In water treatment, it acts as an effective flocculant, binding to suspended particles and heavy metals for easier filtration. The polymer is also used in adhesives and coatings, where its strong adhesive properties improve the durability of paper, textiles, and composite materials. Furthermore, PEI serves as a modifier in membranes for gas separation and fuel cells, enhancing selectivity and performance. Its ability to chelate metal ions has also led to its use in catalysis, where it stabilizes metal nanoparticles in chemical reactions.
- Despite its advantages, PEI’s cytotoxicity—particularly for high-molecular-weight variants—limits its clinical use. The polymer can disrupt cell membranes and induce reactive oxygen species (ROS), leading to cell stress or death. Researchers address this by developing low-molecular-weight PEI derivatives or biodegradable analogs. Additionally, while PEI is generally stable, its reactivity with certain chemicals requires careful handling in industrial settings.
