Single-layer microfluidic “spring” diodes via optofluidic lithography for ultra-low reynolds number applications

Abstract

Microfluidic components that are capable of autonomous "on-chip" operations at ultra-low Reynolds number (e.g., Re < 0.2) are critical to the advancement of integrated fluidic circuitry for chemical and biological applications, including point-of-care (POC) molecular diagnostics and on-site chemical detection. Previously, researchers have utilized dynamic resistive elements, such as suspended microbeads and rotational microstructures, to rectify Re < 0.2 flow; however, such systems require hydrodynamic forces to return the resistive elements to their "closed state" positions, allowing undesired reverse flow during this process. Conversely, double-layer "flap-type" check valves immediately return to their closed state in the absence of forward flow; unfortunately, such valves have exhibited limited functionality for Re < ~0.3 flow. To overcome these issues, here we introduce single-layer microfluidic "spring" diodes, which utilize free-standing polymeric microsprings that: (i) compress to promote forward flow, (ii) return to the closed position in the absence of forward flow, and (iii) remain in the closed position to obstruct reverse flow. The free-standing microspring elements were constructed in situ via optofluidic lithography processes. Experimental results revealed an improvement in Di performance with increasing Re for Re < 0.1; however, Di's were found to decrease for Re > 0.1. At maximum, we observed an experimental average Di of 4.10±0.01, corresponding to 0.075 < Re < 0.1 fluid flow.

Passive water collection with the integument: mechanisms and their biomimetic potential

“…In a technical context, directional fluid transport is often referred to as 'liquid diodes'. Technologies for such microfluidic diodes include movable parts such as flaps (Adams et al, 2005) or cylindrical discs (Sochol et al, 2013). However, inspired by the Texas horned lizard, surface structures have been fabricated for passive, directional transport .…”

“Fluidic diode” for passive unidirectional liquid transport bioinspired by the spermathecae of fleas

“…Devices for unidirectional liquid transport are commonly referred to as "liquid diodes" [11] , "fluid diodes" [24] or "microfluidic diodes" [25,26] in analogy to the electronic components. In Refs.…”

“…In Refs. [25] and [26], a moveable disc and a flap, respectively, supported microfluidic diode characteristics, thus enabling active fluid flow in the forward direction, while blocking it in the backward direction. Large-area coating of a porous cellulose substrate yields a passive fluid diode with flow direction normal to the surface [24] .…”

Directional, passive liquid transport: the Texas horned lizard as a model for a biomimetic ‘liquid diode’

“…Furthermore, we abstracted the subnatural structure fabricated in epoxy resin and applied the principle to PMMA, which is a common polymer in microfluidics. In contrast to other technologies for microfluidic diodes, movable parts like flaps [17] or cylindrical discs [18] are avoided. Conventional bulk material is applied and there is no need for superhydrophobic treatment or the application of porous substrates such as in [19].…”