Microfluidic mixers

A method of mixing fluid, comprising:

• introducing a fluid into an inlet microfluidic channel portion of a microfluidic mixer;
• dividing the fluid into a first portion of fluid on a first side of the inlet microfluidic channel portion and a second portion of fluid on a second side of the inlet microfluidic channel portion;
• flowing, by capillary action, the first portion through an overpass microfluidic channel;
• flowing, by capillary action, the second portion through an underpass microfluidic channel, wherein the underpass microfluidic channel extends under the overpass microfluidic channel such that a downstream end of the overpass microfluidic channel overlaps with a downstream end of the underpass microfluidic channel;
• flowing, by capillary action, the first portion of fluid from the overpass microfluidic channel into a fluid recombining channel portion along an angled recombining surface;
• flowing, by capillary action, the second portion of fluid from the underpass microfluidic channel into the fluid recombining channel portion along the angled recombining surface, thereby recombining the second portion of fluid with the first portion of fluid, wherein the angled recombining surface has an acute angle with respect to a direction of fluid flow through the fluid recombining channel portion, and wherein the angled recombining surface is between the downstream end of the overpass microfluidic channel and the downstream end of the underpass microfluidic channel;
• and
• flowing, by capillary action, the recombined first portion and second portion of fluid from the fluid recombining channel portion into an outlet microfluidic channel portion.