Polyethyleneimine (PEI) is a versatile and widely used polymer in the bioprocess and biotechnology industries, primarily due to its polycationic (positively charged) nature, which allows it to interact effectively with negatively charged molecules such as DNA, RNA, proteins, and cell membranes.
What is Polyethyleneimine (PEI)?
Structure:
PEI is a polyamine composed of repeating units of ethyleneimine (-CH₂CH₂NH-). It comes in two main forms:
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Linear PEI – only secondary amines.
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Branched PEI – primary, secondary, and tertiary amines.
Molecular Weight:
Available in a wide range of molecular weights (typically 600–1,000,000 Da), affecting its performance and toxicity.
Applications in Bioprocessing and Biotechnology
1. Transfection Agent (Gene Delivery)
- An important non-viral transfection reagent for gene transfer. Why? PEI is widely used to deliver DNA or RNA into mammalian cells (Godbey et al., 1999).
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It forms PEI-DNA complexes (polyplexes) via electrostatic interaction.
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These complexes facilitate endocytosis and protect nucleic acids from degradation.
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Preferred in research, protein production, and gene therapy studies.
Why PEI is effective:
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Strong binding to DNA/RNA.
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Buffering capacity helps escape endosomes (proton sponge effect).
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Relatively cost-effective compared to viral vectors or lipofection reagents.
Commonly used form:
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Linear PEI 25 kDa (e.g., for CHO cell transfections in recombinant protein production).
2. Cell Culture Optimization
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Used to modify cell surfaces or enhance adhesion.
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In some processes, PEI is used to flocculate cells or remove DNA impurities in harvested cultures.
3. Flocculant in Downstream Processing
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Acts as a flocculating agent to aggregate and precipitate (Milburn et al, 1990):
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Cells and debris
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Host cell DNA
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Other impurities
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Enhances clarification in centrifugation or filtration steps.
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Reduces filter clogging and improves process efficiency.
4. Chromatography and Purification
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PEI can be immobilized on chromatographic media or used to pre-treat samples to:
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Reduce non-specific binding.
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Adjust surface charge properties.
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Capture or remove negatively charged contaminants (e.g., endotoxins, nucleic acids).
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5. Antimicrobial Agent / Biocide
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Due to its cationic nature, PEI disrupts bacterial membranes.
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Used in biosensors, coatings, and certain bioprocess sanitation systems.
Limitations and Considerations
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Cytotoxicity: Especially at high concentrations or high molecular weights. Must be optimized for safe use.
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Biodegradability: PEI is not readily biodegradable, raising concerns for environmental disposal.
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Regulatory acceptance: Its use in therapeutic manufacturing must be tightly controlled due to potential toxicity or residuals.
Recent Trends
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PEI derivatives and PEGylated PEI (PEI-PEG) are being explored to:
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Reduce toxicity.
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Improve solubility and targeting.
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PEI is a platform for developing non-viral gene delivery systems in cell and gene therapy.
Summary
| Feature | Description |
|---|---|
| Function | Transfection, flocculation, purification, antimicrobial |
| Form | Linear or branched; various molecular weights |
| Advantages | Effective, inexpensive, scalable |
| Challenges | Cytotoxicity, regulatory concerns |
References
Godbey, W. T., Wu, K. K., & Mikos, A. G. (1999). Poly (ethylenimine) and its role in gene delivery. Journal of Controlled Release, 60(2-3), pp. 149-160.
Milburn, P., Bonnerjea, J., Hoare, M., & Dunnill, P. (1990). Selective flocculation of nucleic acids, lipids, and colloidal particles from a yeast cell homogenate by polyethyleneimine, and its scale-up. Enzyme and Microbial Technology, 12(7), pp. 527-532. .
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