Figure 1.
Microfluidic device setup, operation principle and calibration.
(A) Device setup. Four devices were patterned on a 1 mm thick agarose gel membrane, which was sandwiched between a Plexiglas manifold and a stainless steel supporting frame (Drawing credit: Andrew Darling). (B) Device layout. Each device contained three parallel channels that were 400 µm wide and 167 µm deep, and spaced 250 µm apart. Sperm are not shown to scale. This drawing is reproduced from Ref. [45] by permission of The Royal Society of Chemistry. Chemical/buffer were flowed through two side channels and a chemical gradient formed in the center channel via molecular diffusion through the agarose ridges between the center and the side channels. (C) Device characterization. Time evolution of fluorescence intensity profile across all three channels when flowing 4 kDa FITC-dextran/buffer along the source and sink channels respectively. Time (t) = 0 is defined as the time when the chemoattractant was flowed into the source channel.
Figure 2.
Differential morphology and motility of sea urchin versus mouse sperm.
An illustration of sea urchin (A) and mouse (B) sperm drawn to scale. Both sea urchin and mouse sperm use flagella having axonemes of 9 outer microtubule doublets and a single central pair of microtubules in order to move. Sea urchin sperm has a typical length scale of 50 µm, and mouse sperm 100 µm. Drawing credit: C. Rose Gottlieb. Trajectories of sea urchin (C) and mouse (D) sperm swimming in a microfluidic channel in the absence of putative chemoattractant. Each colored line represents a trajectory, and each trajectory is 2 s long and starts at t = 0.
Figure 3.
Differential chemotactic behavior of sea urchin and mouse sperm.
Trajectories of sea urchin sperm (25 sperm in each plot) when the resact concentration in the source channel is 0 (A); 100 pM (C); 10 nM (E). Trajectories of mouse sperm (39 sperm in each plot) when the progesterone concentration in the source channel is 0 (B); 2.5 µM (D); 250 µM (F). We placed the starting point of each of the trajectories at the (0, 0) coordinate. Each colored line is a cell trajectory that is 2 s long and starts at t = 0.
Figure 4.
Quantitative analysis of sea urchin and mouse sperm migration pattern.
Scatter plot of the speed of sea urchin (A) and mouse (B) sperm. Scatter plot of the velocity up the chemical gradient for sea urchin (C) and mouse (D) sperm. Scatter plot of the persistence length for sea urchin (E) and mouse (F) sperm. Cell numbers that contribute to the scatter plot are indicated. The duration of the cell track length ranges from 0.24 s to 38.0 s for sea urchin, and from 0.12 s to 13.76 s for mouse sperm.