Force generated by human sperm correlated to velocity and determined using a laser generated optical trap

Area of Science:

• Biophysics
• Cellular Mechanics
• Laser Manipulation

Background:

• Single beam gradient force optical traps enable precise manipulation of biological cells using laser light.
• This technology offers a non-invasive method for studying cellular properties.

Purpose of the Study:

• To investigate the relationship between human sperm motility and the laser power required to maintain them in an optical trap.
• To correlate sperm linear velocity and flagellar beat pattern with trapping laser power.

Main Methods:

• Utilized a continuous wave Nd:YAG (1.06 micron) laser focused through a microscope objective to create an optical trap.
• Measured the laser power at which human sperm were released from the trap.
• Correlated trapping power with sperm linear velocity and motility patterns (straight vs. zig-zag).

Main Results:

• Mean trapping power increased with sperm motility: slow (57 mW), medium (73 mW), and fast (84 mW).
• Zig-zag motile sperm required significantly higher mean trapping power than straight motile sperm at similar velocities.
• Two specimens showed significantly reduced trapping power upon re-measurement after 24 hours.

Conclusions:

• Optical trapping provides a quantitative method to assess human sperm motility and flagellar dynamics.
• Sperm motility characteristics, including beat pattern, directly influence the laser power needed for optical trapping.
• Potential for optical trap measurements to indicate changes in sperm viability or function over time.