Physical gene delivery methods other than electroporation include biolistic particle delivery, direct microinjection, and laser-mediated transfection. Although these physical methods differ in the tools they employ, they all enable the direct transfer of nucleic acids into the cytoplasm or the nucleus by membrane penetration without using chemicals or viruses.
Biolistic particle delivery
In brief, biolistic particle delivery, also known as particle bombardment, involves projecting microscopic heavy-metal particles (often gold or tungsten) coated with nucleic acids into recipient cells at high velocity using a ballistic device (i.e., “gene gun”). Biolistic particle delivery can be used to transiently transfect dividing and non‑dividing cells in culture as well as cells in vivo, and it is often used for genetic vaccination and agriculture applications (Klein et al., 1992; Ye et al., 1990; Burkholder et al., 1993). While this technique is reliable and fast, it requires costly equipment, causes physical damage to the samples, and necessitates high cell numbers due to high mortality.
Direct microinjection delivers nucleic acids into the cytoplasm or the nucleus one cell at a time by means of a fine needle; therefore, this method is limited to ex vivo applications such as the transfer of genes into oocytes to engineer transgenic animals or the delivery of artificial chromosomes (Cappechi, 1980; Cappechi, 1989; Telenius et al., 1999). Although direct microinjection is nearly 100% efficient, it demands considerable technical skill, is extremely labor-intensive, and often causes cell death. As such, this method is not appropriate for studies that require the transfection of large number of cells.
Laser-mediated transfection, also known as phototransfection, laserfection, or optoporation, uses a laser pulse to transiently permeabilize the cell membrane (Shirahata et al., 2001; Schneckenburger et al., 2002). When the laser induces a pore in the membrane, the osmotic difference between the medium and the cytosol facilitates the entry of nucleic acids or other desired substances in the medium (ions, small molecules, proteins, semiconductor nanocrystals, etc.) into the cell. Advantages of laser-mediated transfection include high transfection efficiency and the ability to make pores at any location on the cell. However, the method requires an expensive laser-microscope system and the cells to be attached to a substrate.
In addition to the methods mentioned above, other physical delivery technologies use hydrodynamic pressure, ultrasound, or magnetic field to drive naked nucleic acids or nucleic acid-particle complexes into recipient cells.