Single-layer “domino” diodes via optofluidic lithography for ultra-low Reynolds number applications

Abstract

Autonomous fluidic components are critical to the advancement of integrated micro/nanofluidic circuitry for lab-on-a-chip applications, such as point-of-care (POC) molecular diagnostics and on-site chemical detection. Previously, a wide range of self-regulating microfluidic components, such as fluidic diodes, have been developed; however, achieving effective functionality at ultra-low Reynolds number (e.g., Re < 0.05) has remained a significant challenge. To overcome this issue, here we introduce single-layer microfluidic "domino" diodes, which utilize free-standing rotational microstructuresconstructed in situ via optofluidic lithography -in order to passively regulate the fluidic resistance based on the flow polarity, thereby enabling flow rectification under ultra-low Re conditions. COMSOL simulation results revealed a theoretical Diodicity (Di) of 31 for a singular domino diode component. Experimental results (for systems with four microstructures) revealed Di's ranging from 13.0±1.9 to 25.4±1.9 corresponding to 0.025 < Re < 0.030 and 0.010 < Re < 0.015 flow, respectively, which represent the largest Di's reported for Re < 0.05 fluid flow.

Single-layer microfluidic &#x201C;spring&#x201D; diodes via optofluidic lithography for ultra-low reynolds number applications

“…The increase in Di performance observed for 0 < Re < 0.1 can be attributed to the higher rates of microspring compression, which would decrease the resistance associated with the blocking structure. In contrast to our prior "domino" diodes, which have only one open state [26], the blocking structure of the "spring" diode displaced with increasing Re (for Re < 0.1), dynamically decreasing its effective fluidic resistance during this process. As a result, the pressure drop required to achieve forward flow decreased, thereby increasing the Di performance.…”

“…For Re > 0.1, however, this trend was found to reverse, with Di performance decreasing with increasing Re. This trend of an optimal performance is in contrast to the Di behavior of our prior microbead-based diodes [15,16], which revealed increasing Di with increasing Re, as well as our prior microfluidic "domino" diodes [26], which revealed decreasing Di with increasing Re. There are two distinct phenomena that likely contributed to this behavior.…”

“…Although several single-layer microfluidic circuit components have been successfully fabricated using optofluidic lithography, device functionality required changes in fluidic properties including pH and temperature, which lack the versatility associated with regulation using alternative flow characteristics, such as flow polarity or pressure [23][24][25]. Previously, we presented microfluidic "domino" diodes, which use freely-rotating microstructures (fabricated via optofluidic lithography) to rectify fluid flow [26]. Similar to the bead-based diodes, the "domino" diodes also require reverse flow to return the resistive elements to their closed positions.…”

Single-layer microfluidic current source via optofluidic lithography

“…The bulk microfluidic system was fabricated using standard soft lithography processes, as described in previous work [16,25]. Briefly, micromolded poly (dimethyl-siloxane) (PDMS), with microchannel heights of 110 μm, was thermally bonded to glass slides coated with 80 μm of PDMS(via PDMS-PDMS bonding techniques) to prevent the optofluidic components from sticking to the glass slides.…”

“…For example, optofluidic "domino diodes" are capable of passive flow rectification only [16]. While many biological experiments require precise reagent flow rates unavailable through such passive controls, building devices that function as hydraulic analogs to electronic "current sources" has proved a considerable challenge.…”