Polyethyleneimine (PEI): A Versatile Polymer with Diverse Applications in Biotechnology and Industry
Polyethyleneimine (PEI), also known as polyazacyclopropane, is a water-soluble, highly charged polymer consisting of a chain of monomers (-CH2CH2NH-).PEI contains a large number of amino groups on its surface, which are rich in positive charge in near-neutral solution.The surface of PEI can be chemically modified, e.g., acetylation, carboxylation, hydroxylation, and polyethylene glycol ( PEG), oligosaccharides, targeted modification or fluorescent labeling to achieve its functional diversity. PEG), oligosaccharides, targeted modifications or fluorescent labeling, etc. PEIs have both linear and branched structures, and linear PEIs contain only secondary amines, which are usually derived from the acidic hydrolysis of polyoxazolines. So it is difficult to obtain linear PEI with low molecular weight. Primary and secondary amines are active amines with strong nucleic acid binding ability and functional components such as targeting reagents, drugs, etc., while tertiary amines have weak binding ability but buffering effect in acidic conditions. In addition, dendrimer PEI is usually liquid, while linear PEI is solid at room temperature, insoluble in solvents such as cold water, phenol, ethyl ether, etc. Solubility improves in hot water and organic solvents (e.g., methanol, ethanol and chloroform).
1.PEI Characteristics
High adhesion and adsorption: Amino groups can react with carboxyl groups to form hydrogen bonds. Amino groups can react with carboxyl groups to form ionic bonds or with carbonyl groups to form covalent bonds. Polyethyleneimine has a structure with a hydrophilic group (amino group) and a hydrophobic group (vinyl group), which allows it to bind to different substances. Utilizing these combined binding forces, it can be widely used in adhesives, inks, coatings, and glues.
High cationicity: Polyethyleneimine exists as a polymer cation in water and can neutralize and adsorb all anionic substances, as well as chelate heavy metal ions. With its high cationicity, it can be used in the fields of paper making, water treatment, electroplating solution and dispersant.
Highly reactive: Polyethyleneimine has strongly reactive primary and secondary amines that can easily react with epoxides, acids, isocyanate compounds and acid gases. Using this property, it can be used as an epoxy resin modifier, aldehyde adsorbent, and color-fixing agent.
2.PEI synthesis method
Branched-chain polyethyleneimine is widely used, and straight-chain polyethyleneimine is mainly used for eukaryotic gene transfection vector.
With ethyleneimine as the main raw material, mainly synthesized branched chain polyethyleneimine
With oxazole derivatives as raw materials, mainly synthesized linear polyethyleneimine
3.PEI use
Polyethyleneimine as engineering plastics are widely used in electronic and electrical appliances, automobiles, aerospace, machinery, food industry, medical equipment, etc. In addition, polyethyleneimine can also be used in papermaking, water treatment, detergents, adhesives, cosmetics, etc. In the field of biological research, it is mainly used in the extensive study of non-viral gene carriers.
- Application in gene carrier
PEI in the gene carrier mainly as a polycationic non-viral gene carrier, PEI molecule every three atoms have a protonatable amino nitrogen atoms, the composition of the primary amine, secondary amine and tertiary amine groups with different pKa values, so that the PEI almost in the pH conditions have the ability to absorb protons (i.e., the role of proton sponges). This property allows PEI to absorb H+ in the acidic environment of the endosome, which increases its osmotic pressure and leads to membrane instability or even rupture, thus allowing the phagocytosed complex to escape and avoid DNA degradation.
PEI is the second polymer transfection reagent discovered in history after polylysine, and the transfection efficiency increases with the increase of molecular weight, which is usually not less than 20,000, but the cytotoxicity increases with the increase of molecular weight. The linear or multi-branched structure of large molecular weight PEI is connected with biodegradable chemical bonds such as ester bond, carbon and nitrogen double bond or disulfide bond, such as polyethylene glycol (PEG), hyaluronic acid, polyamino acid and polyester, etc., so that it can be biodegraded into small molecular weight PEI with low toxicity or non-toxicity in vivo, which can retain the higher transfection activity of PEI and reduce the toxicity of the cells at the same time. Another derivative application is to graft small molecule PEI onto polymer backbone, such as chitosan, polycaprolactone, etc., so as to improve transfection efficiency and reduce cytotoxicity.
Attachment of targeting substances to PEI vectors can enable the targeting of PEI to cells with high expression of the receptor, and at the same time promote endocytosis of the cells to improve the efficiency of gene transfection. Available targeting substances include endogenous ligands (transferrin (Tf), epidermal growth factor (ECG), arginine-glycyl-aspartate (RGD) peptide, etc.), carbohydrates such as galactose and specific antibodies.
- Application to immobilized enzymes
Immobilized enzyme refers to a technology that uses physical or chemical means to bind the enzyme in a certain area and still has enzyme catalytic activity and can be reused repeatedly. That is, the immobilized enzyme includes the carrier with non-catalytic function and the enzyme with catalytic function.PEI has a large number of amino groups on its macromolecular chain, and when pH<10, the amino groups on its molecular chain are mostly in the state of protonation, so that polyethyleneimine is also a kind of positively-charged polyelectrolyte. If it is bonded to a certain carrier, on the one hand, it can provide the active point of amino covalent enzyme fixation, on the other hand, most of the enzymes are negatively charged at pH<10, and PEI can produce a strong electrostatic adsorption, so the enzymes can be immobilized by ionic adsorption.
If PEI macromolecule chain is used as the functional branch carrier for enzyme curing, it can not only increase the interaction between the enzyme and the carrier, but also increase the adsorption amount of the enzyme, enhance the binding force of the enzyme and the carrier, improve the adsorption stability of the enzyme, so that the enzyme still has a high catalytic activity, and realize the purpose of reuse of the carrier.
- Application in drug delivery
Polymer drug carrier is a kind of biomaterial with positive charge on the surface, which can connect proteins and genes on the surface of the material or encapsulate them in the core of the material by chemical coupling or physical adsorption or encapsulation, and deliver the proteins or genes to the cells by interacting with the cell membrane.The multistage amine structure of PEI can effectively compress and encapsulate protein or gene drugs, which is often used as the gold standard for the evaluation of the transfection effect. It is often used as the gold standard for the evaluation of transfection effect.
- Application in immune adjuvant
PEI has strong adjuvant activity and is a potential vaccine adjuvant that can enhance the anti-infection and anti-tumor effects of traditional vaccines, and some PEI-based vaccines have already entered the clinical research stage.When constructing PEI vaccines, it is necessary to select different types of PEI, antigens, construction strategies, and immune pathways.
- Application in protein separation
PEI is a positively charged polymer that binds negatively charged macromolecules, such as acidic proteins and nucleic acids, which in turn form a PEI mesh structure that subsequently precipitates out as a complex to achieve crude separation.
- Applications in biomarkers
PEI, when conjugated with visualizing agents (e.g., Fe3O4 and fluorescent NPs), can be used as a biomarker to reflect specific cellular or subcellular information, such as cell migration and other behaviors, under certain conditions.
