Analysis of zona pellucida microdrilling by a 1.4 mum diode laser

Since the 1960s, surgical applications of lasers at the cellular level have been explored. One such application is assisted reproduction. Laser microdrilling has shown great promise in this area. It is the best means for assisted hatching of the gamete from its surrounding layer, the zona pellucida, when zona pellucida hardening factors interfere with implantation. Greater understanding of the drilling process is necessary to determine efficacy and assure safety of this procedure. Currently, the impracticality of certain experiments limit the understanding of this process. The development of a model which accurately predicts the temperature profile and the diameter of the hole created for specific laser parameters allows for extensive analysis of this process.;The peak temperatures reached in the laser-irradiated zona pellucida are in excess of 100°C according to the model formulated in this study. The temperatures remain above 43°C, the danger threshold for human tissue, for only milliseconds. The hole diameters predicted by the model differ from the measured hole diameters by more than a factor of two for all laser dosimetries examined. The model suggests that holes are created in the zona pellucida during laser microdrilling as changes in the thermal conductivity and absorption coefficient draw heat from the center of the laser beam outward in the radial direction. The changing refractive index limits temperature rise in a small area surrounding the beam axis and likely allows for hole diameters larger than the (initial) spot radius due to thermal defocusing. Finally, the steep intensity gradient in the radial direction is the key to drilling holes with sharp edges.