Capillary Flow-Driven and Magnetically Actuated Multi-Use Wax Valves for Controlled Sealing and Releasing of Fluids on Centrifugal Microfluidic Platforms

Abstract

Compact disc (CD)-based centrifugal microfluidics is an increasingly popular choice for academic and commercial applications as it enables a portable platform for biological and chemical assays. By rationally designing microfluidic conduits and programming the disc’s rotational speeds and accelerations, one can reliably control propulsion, metering, and valving operations. Valves that either stop fluid flow or allow it to proceed are critical components of a CD platform. Among the valves on a CD, wax valves that liquify at elevated temperatures to open channels and that solidify at room temperature to close them have been previously implemented on CD platforms. However, typical wax valves on the CD fluidic platforms can be actuated only once (to open or to close) and require complex fabrication steps. Here, we present two new multiple-use wax valve designs, driven by capillary or magnetic forces. One wax valve design utilizes a combination of capillary-driven flow of molten wax and centrifugal force to toggle between open and closed configurations. The phase change of the wax is enabled by heat application (e.g., a 500-mW laser). The second wax valve design employs a magnet to move a molten ferroparticle-laden wax in and out of a channel to enable reversible operation. A multi-phase numerical simulation study of the capillary-driven wax valve was carried out and compared with experimental results. The capillary wax valve parameters including response time, angle made by the sidewall of the wax reservoir with the direction of a valve channel, wax solidification time, minimum spin rate of the CD for opening a valve, and the time for melting a wax plug are measured and analyzed theoretically. Additionally, the motion of the molten wax in a valve channel is compared to its theoretical capillary advance with respect to time and are found to be within 18.75% of the error margin.

Reversible Thermally-Responsive Copolymer Valve for Manipulating Water Wicking

“…This indicates the thermal response cyclability of N-PNAGA/PSt samples. In contrast to other kinds of valves, the as-prepared thermally responsive valves do not require complex and expensive external equipment, , and exhibit temperature-adaptive responsiveness, , and multicycle ability, , which shed some light on developing reversible responsive valves.…”

Integrating Bio-Sensing Array with Blood Plasma Separation on a Centrifugal Platform

“…Indeed, in our handling of the disc with the separated red blood cells, we were unable to dislodge the separated red blood cells from the RBC chamber. The details of the simulation framework are presented in our previous paper describing wax valving on centrifugal microfluidic platforms [ 12 ].…”

“…The integrated CD is placed on a custom-made spin chuck and secured with a nut in the center of the spinning axis. The disc is spun by a motor (SM3450 D, Motion USA, Columbus, OH, USA) and controlled by a motor controller (BLDC Servo Motor Controller, EZSV23/EZSV17, AllMotion, Union City, CA, USA) [ 12 ]. A stroboscopic light source (DT-311A, Shimpo, Lynbrook, NY, USA) is used to illuminate the spinning disc during picture taking with a digital camera (acA800-510uc, Basler AG, Ahrensburg, Germany).…”

“…This sequence of photographs (one per disc’s revolution) is recorded as a video that is captured from a computer screen using recording software Bandicam (Bandicam Company, Irvine, CA, USA). Reproduced from [ 12 , 15 ].…”

Microvalves for Applications in Centrifugal Microfluidics

“…Active microvalves require the application of external force (other than the centrifugal, Euler, or Coriolis forces intrinsic for CD platforms) for actuation of the valves. These external actuators for turning on or off of the active valves are various and include laser [45][46][47]66], magnetic actuation [15,48,71], mechanical actuation [49][50][51][52], phase-changebased actuation [55][56][57][58]60,62,63], electrical actuation [16], thermal actuation [17,61], chemical actuation [72], and pressure actuation [12,64]. Generally, active valves are more reliable than passive valves due to the active valves' smaller degree of reliance on the precision of machining, fabrication, and constancy of material properties compared to passive valves.…”