Objective

To assess the relative escape force of human epididymal sperm using a laser generated optical trap and compare it with that of human ejaculated sperm.

Design

Evaluation of the relative force generated by epididymal and ejaculated sperm using an 800-nm laser-generated optical trap system (titanium-sapphire, model 899-01; Coherent Innova, Palo Alto, CA).

Setting

University-based facility at the Beckman Laser Institute and Medical Clinic and Center for Reproductive Health, University of California, Irvine.

Interventions

A total of 2,720 sperm from 28 samples were randomly analyzed. Fifteen were ejaculated samples (1,650 sperm) obtained from men with proven fertilization, and 13 were epididymal samples (1,070 sperm) aspirated microsurgically from patients with obstructive azoospermia. An optical trap equipped with the 100x Neofluar objective was used to analyze an average of 100 sperm per patient.

Main outcome measures

Determination of mean relative escape force values in milliwatts for epididymal and ejaculated sperm samples.

Results

The mean relative escape force for epididymal sperm was 32.4 mW, significantly lower than ejaculated sperm, which was 85.1 mW. By correlating epididymal sperm relative force with fertilization in vitro at an arbitrary cutoff value of 30 mW, it was found that no fertilization occurred if a sample had < 13% of sperm at that value.

Conclusions

[1] The average relative escape force of the epididymal sperm was found to be 60% weaker than that of ejaculated sperm. [2] It is demonstrated that the noncontact laser optical trap is a sensitive tool that can evaluate single sperm force as a new physiological parameter.

Microthermometric measurements on optically-trapped Chinese Hamster Ovary (CHO) cells and sperms cells are reported, using a non-invasive microfluorometric detection technique. Within an optical tweezer system that has been outfitted with a spectral fluorescence excitation and detection capability, the changes in temperature induced by the process of sample confinement by a focused laser beam has been quantified over micron-sized spatial regions of both motile and immotile cells. Our measurement technique is based on the use of environmentally sensitive fluorophores that can be incorporated into the cell membrane and used to sense local changes in temperature when the cell membrane is perturbed optically or via other environmental stress factors. Using a cw 1 .064 tm Nd:YAG laser for trapping CHO and human sperm cells, a temperature increase of -4°C per 100 mW laser power was observed. At this infrared wavelength, cellular heating as result of laser confinement appears to be mainly due to radiation absorption by water.