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Am J Physiol Cell Physiol 292: C1536-C1542, 2007. First published November 22, 2006; doi:10.1152/ajpcell.00348.2006
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METHODS IN CELL PHYSIOLOGY

Production of a uniform cellular injury by raster scanning of cells for the study of laser bioeffects

¹U.S. Army Medical Research Detachment, Brooks City-Base, Texas; and ²U.S. Army Institute of Surgical Research, Fort Sam Houston, Texas

Submitted 30 June 2006 ; accepted in final form 17 November 2006

Efforts to understand laser bioeffects in cells and tissues have been hindered by a nonuniform cellular response of the specimen, resulting in graded biochemical effects. In addition, the small beam diameters of commonly used lasers limit the number of cells expressing a response to numbers inadequate for the study of biochemical effects. For a limited emission power, expansion of the beam diameter reduces the irradiance, thus requiring longer exposure durations to produce a cellular response. Cultured human retinal epithelial cells were exposed as a single spot ("tophat" exposure) from a carbon dioxide (CO₂) laser operating at 10.6 µm or scanned with a raster system and compared with thermal injury produced with heated saline for short periods (1–9 s) at relatively high temperature (55–70°C). Cell viability and induction of the 70 kDa heat shock protein were evaluated as indicators of the cellular response. Initial attempts to use a tophat (uniform energy distribution) exposure resulted in a nonuniform cellular response (and nonuniform energy distribution) due to diffraction effects from the 2-mm selection aperture. However, raster scanning for appropriate times with the CO₂ laser yielded uniform cell viability and heat shock protein synthesis that were comparable to dipping cells in heated saline. Because scanning results in a homogeneous exposure of cells, the described scanning technique may be applied to studies of cellular responses to other lasers to evaluate photochemical and photomechanical effects.

carbon dioxide laser