Chemical Structure and
Properties
Polyethyleneimine (PEI) is a polymer made up of repeating units of
ethyleneimine monomers. The monomer units are connected through secondary amine
groups, which give PEI its unique branched structure. PEI is further classified
based on its average molecular weight - low (600-5,000 Da), medium
(5,000-25,000 Da) and high (>25,000 Da).
PEI has a high density of amine functional groups which makes it cationic and
water-soluble across all pH ranges. This key property arises due to the
presence of primary, secondary and tertiary amino groups along its polymer
backbone. PEI also has a high charge density that allows it to be an effective
polyelectrolyte and bind strongly with anions like DNA or RNA. Its branched
structure increases solubility and decreases viscosity compared to linear PEIs
of similar molecular weight.
Gene Delivery and Transfection
One of the major applications of PEI is in gene delivery and transfection. Due
to its high charge density, PEI can efficiently condense and compact negatively
charged nucleic acids like plasmids, siRNA and miRNA into positively charged
nanoparticles. These Polyethyleneimine gene polyplexes
can protect the genetic cargo from degradation and facilitate its cellular
uptake via endocytosis.
Once inside the cell, the polyplexes are able to escape from the endosome due
to the "proton sponge effect" of PEI. As endosomal pH decreases, the
PEI amine groups sequester protons, which leads to osmotic swelling and rupture
of the endosomal membrane. This allows the released genetic material to reach
the cytoplasm and nucleus for expression. Thanks to this unique property, PEI
remains one of the most widely used polymers for in vitro and in vivo gene
delivery applications.
Biofilm Inhibition
Bacterial biofilms are structured communities embedded in self-produced
extracellular polymeric matrices. They pose a significant challenge in
industries and healthcare due to their increased antimicrobial tolerance. PEI
stands out as an effective antibiofilm agent due to its antibacterial and
anti-adhesive properties.
At micromolar concentrations, PEI can disrupt pre-formed biofilms of both
Gram-positive and Gram-negative pathogens like Staphylococcus aureus and
Pseudomonas aeruginosa. It does so by damaging the bacterial cell membranes and
walls. PEI also suppresses initial biofilm formation by inhibiting bacterial
adhesion to surfaces. This makes it a promising candidate for combating biofilms
on medical implants and industrial piping. Researchers are exploring novel PEI
formulations for improved antibiofilm efficacy.
Water Treatment
As a cationic polyelectrolyte, PEI has found widespread use in water treatment
for the removal of contaminants like heavy metals, dyes, and inorganic/organic
anions. It works through electrostatic attraction - the positively charged
amino groups of PEI chelate/adsorb negatively charged pollutants from aqueous
solutions.
In water remediation, linear PEI is commonly used. It has high adsorption
capacities for ions like arsenic, chromium and radium due to efficient metal
coordination. PEI flocculation followed by sedimentation is also effective at
clarifying wastewater effluents. For potable water production, PEI functionalized
membranes demonstrate high heavy metal retention without loss of flux. Such
applications leverage PEI’s ability to remove even trace contaminants from
water sources.
Surface Modification and Polyethyleneimine
The versatile surface chemistry of PEI allows it to modify a range of materials
for enhanced performance. It improves cell proliferation and differentiation on
titanium and polymers used in implants/scaffolds. Amine-grafted surfaces
promote cell adhesion through interactions between PEI and extracellular matrix
proteins.
In gas separation membranes, embedding linear PEI enhances CO2 permeability
while maintaining high H2/CO2 selectivity. This arises from its strong and
reversible CO2 complexation ability. Similarly, gas sensors coated with
PEI-functionalized nanomaterials demonstrate increased sensitivity and
selectivity towards toxic/flammable gases. Such surface-engineered materials
exemplify PEI's role in facilitating gas-solid interactions.
PEI coating has also emerged as an effective way to render surfaces
antimicrobial. The bound cationic polymer can kill microbes on contact through
membrane disruption. It thus endows polymers, textiles and household items with
self-sanitizing properties. With low toxicity and cost-effectiveness, PEI
coatings present an attractive alternative to traditional biocides.
this
article provided an overview of the key applications of PEI that stem from its
simple yet versatile chemical structure. Areas like gene delivery, biofilm
inhibition, water treatment and surface modification extensively utilize PEI's
unique properties of high charge density, solubility and interaction strengths.
Moving forward, sustainable production methods and controlled release
formulations of PEI could further expand its industrial and biomedical impact.
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