Non-viral methods refer to gene delivery techniques that do not involve the use of viral vectors. These methods are generally considered safer and more easily customizable than viral methods, as they do not carry the risk of triggering an immune response or inserting genetic material into the host genome in an uncontrolled manner. Some common non-viral gene delivery methods include:

1. Lipid-based transfection: This method involves the formation of liposomes, which are vesicles composed of lipid bilayers. The genetic material, such as plasmid DNA or siRNA, is encapsulated within the liposomes, which can then fuse with the cell membrane and release their contents into the cell. Lipofection is a popular lipid-based transfection method.
2. Electroporation: This technique uses short, high-voltage electrical pulses to create temporary pores in cell membranes, allowing the uptake of exogenous molecules, such as DNA or RNA, into the cells. Electroporation can be performed in vitro (in cell culture) or in vivo (within living organisms).
3. Nucleofection: A specialized form of electroporation, nucleofection delivers the genetic material directly into the cell nucleus, which can improve transfection efficiency and gene expression, especially in hard-to-transfect cell types.
4. Gene gun: Also known as biolistic particle delivery, this method uses high-pressure helium gas to propel gold or tungsten particles coated with DNA into target cells or tissues. The gene gun is particularly useful for transfecting plant cells and tissues.
5. Microinjection: This technique involves the direct injection of genetic material into cells or tissues using a fine needle or a micropipette. Microinjection can be used for various applications, including the introduction of DNA or RNA into single cells, embryos, or tissues.
6. Calcium phosphate transfection: This method is based on the formation of calcium phosphate-DNA precipitates, which can be taken up by cells. Although this method has been largely replaced by newer techniques, it is still occasionally used due to its low cost and simplicity.
7. Polymer-based transfection: This approach uses cationic polymers, such as polyethylenimine (PEI) or polylysine, to form complexes with the negatively charged genetic material. These complexes can then enter cells through endocytosis.

Each non-viral method has its advantages and limitations in terms of transfection efficiency, cell type compatibility, and ease of use. The choice of the most suitable method depends on the specific experimental context and the desired outcomes. Non-viral methods are continuously being developed and refined to improve their efficiency, safety, and applicability across various research and therapeutic applications.