Although the dimensions of retinal artery, arteriole and choriocapillary are 120 |m, 8-15 |m, and 10-15 |m, the smallest dimension of surgical tools such as tanoforceps used in retinal surgery is 1300 |m (personal communications with Dr. Marco A. Zarbin). The diameter of a 25-gauge needle is 500 |m. Thus, there is a need to develop better surgical devices and needles to accomplish micro- and nano-manipulations of blood vessels, and potentially nerve tissue in the eye. This forms the basis for the field of nanosurgery, which is aimed at developing tools such as nanoscalpels, nanotweezers, and nanoneedles (49). These tools are expected to allow small-vessel, cellular, and subcellular manipulations.

Nanoscalpels are based on femtosecond laser pulses. Nanoscalpels allow subcellular dissections, without collateral damage, using laser beams near the infrared region of the visual spectrum.

Nanotweezers are essentially two nanotubes arranged together to form a tweezer-like structure (50). Nanotweezers are commonly made of silicon and carbon nanoelectrodes. The principle of their action involves voltage-triggered to and fro motion of the free end of the tweezers. The application of voltage causes the two tips to bend closer, while removal of the applied voltage makes the tips to get back to the original position. Nanotweezers can potentially be used in the manipulation of subcellular components. These are currently being investigated as a means of enhancing the design of scanning probe microscopes, such as scanning tunneling microscopes (STM) and atomic force microscopes (AFM). The current tip design cannot grab an object for manipulation. It is believed that tweezers could overcome this problem.

Nanoneedles as thin as 100 nm have been developed and these might be helpful in performing nanoscale surgery. Nanoneedles are currently used for modification of AFM tips (51). AFM nanoneedles have the advantage of being able to enter the cells with relatively little force and high accuracy. Obataya et al. (52) developed ultrathin (200-300 nm) needle-like tips for AFM microscopes. These could potentially be used for protein, nucleic acid, and drug delivery in target cells. Although these approaches are exciting in terms of understanding events at the cellular level in experimental medicine, the practical applicability of such approaches in therapeutic intervention is yet to be established.

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