5-2.1.4. Other Methods
Other methods of chemical transfection involve the use of chemicals such as polyethylenimine, chitosan, polyphosphoester, dendrimers.

5-2.1.4.1. Polyethylenimine

• Polyethylenimine (PEI) is a non-degradable, high molecular weight polymer which may accumulate in the body.
  
  
• PEI, due to its polycationic nature, condenses with the DNA molecule resulting in the formation of PEI-DNA complex which enters the cell by endocytosis, thus mediating gene transfer.
  
  
• PEI exhibit cytotoxicity due to its ability to permeabilize and disrupt cell membranes leading to necrotic cell death.
  
  
• The cytotoxicity may be reduced using various methods e.g. PEGylation and conjugation of low molecular weight polyethylenimine with cleavable cross-links such as disulfide bondsin the reducing environment of the cytoplasm.

5-2.1.4.2. Chitosan

• Chitosan, a biodegradable polysaccharide is composed of D-glucosamine repeating units and can be used as a non-viral gene carrier.
  
• It can efficiently bind and protect DNA from nuclease degradation.
  
  
• The biocompatibility and low toxicity profile makes it a safe biomedical material for clinical applications.
  
  
• Chitosan DNA nanoparticles can transfect several different cell types with relatively low transfection efficiency.
  
  
• Modified chitosans such as trimethylated chitosan and chitosan conjugated with deoxycholic acid have been developed to increase the solubility of chitosan at neutral pH which can efficiently transfect COS-1 cells.
  
  
• Chitosans with different molecular weights exhibit different DNA binding affinities. The efficiency of transfection is determined by the particle stability which is one of the rate-limiting steps in the overall transfection process.