Zona pellucida drilling with cw mid-infrared radiation: basics and applications

Summary form only given. A mid-infrared radiation device has been developed to assist in vitro fertilization procedures. The system is used to generate openings of controlled size in the zona pellucida (ZP), a protein layer that surrounds and protects the oocyte. ZP drilling is intended for assisted fertilization and hatching. The device takes advantage of the typically high numerical aperture of microscope objectives to confine the interaction volume and thus reduce at maximum the extent of lateral damage, which is of prime importance, when performing surgical intervention at the cellular level. As the drilling procedure has to be done within the culture medium in order to preserve the fragile egg, a quasi-cw operation mode has to be preferred to avoid possible laser-induced mechanical effects, such as shock waves or cavitation bubbles. The selected mid-infrared radiation device incorporates an InGaAsP laser diode at 1.48 /spl mu/m, which penetrates deep enough the culture medium. The collimated laser beam is injected into the optical path of an inverted microscope and is focused by the microscope objective. With a 45 X objective, which has a field of view well adapted to the oocyte size, an and 8 /spl mu/m-diameter spot size is obtained at the object plane. Power levels at the focus of 50 to 70 mW and irradiation times of 5 to 60 ms are sufficient to drill apertures of appropriate size in mouse and human oocytes.