Characterizations of gas purge valves for liquid alignment and gas removal in a microfluidic chip

Abstract

Two polydimethylsiloxane (PDMS) gas purge valves for excessive gas removal in general lab-on-a-chip applications are presented in this paper. Both valves are devised based on a three-layer configuration comprising a top layer for liquid channels, a membrane and a bottom layer for gas channels. The pneumatic valves work as a normal gateway for fluids when the membrane is bulged down (open state) by vacuum or pushed up (closed state) by pressure. In the closed state, the air in front of a liquid can be removed through a small notch or a permeable PDMS membrane by compressing the liquid. The purge valve with a small notch across its valve seat, termed surface-tension (ST) valve, can be operated with pressure under 11.5 kPa. The liquid is mainly retained by the surface tension resulting from the hydrophobic channel walls. In contrast, the purge valve with vacuum-filled grooves adjacent to a liquid channel, termed gas-permeation (GP) valve, can be operated at pressure above 5.5 kPa. Based on the principle of gas permeation, the excessive air can be slowly removed through the vent grooves. Detailed evaluations of both valves in a pneumatically driven microfluidic chip were conducted. Specifically, the purge valves enable users to remove gas and passively align liquids at desired locations without using sensing devices or feedback circuits. Finally, a rapid mixing reaction was successfully performed with the GP valves, showing their practicability as incorporated in a microfluidic chip.

Software-programmable continuous-flow multi-purpose lab-on-a-chip

“…Instead, we propose to use an orthogonal vent (Chuang et al 2012). Recall that SPLoCs contain a flexible membrane sandwiched between the fluid and control layers for valving and pumping.…”

“…Because of practical limitations working with very thin membranes, we kept membrane thickness constant at 100 μm. Increasing the permeation area can be achieved by either (1) using wider channels, which causes significant deformations in the PDMS membrane for the same applied pressure/vacuum, or (2) using different geometries for the permeation area (Chuang et al 2012). In summary, our prototype is able to expel an air slug of 15 mm in length and align the fluid from the reservoir with the valve in <25 s, using a 30 kPa vacuum applied to the orthogonal vents.…”

Normally closed plunger-membrane microvalve self-actuated electrically using a shape memory alloy wire

“…Out of several actuation mechanisms, pneumatic actuation is the most common. A positive suction is used to deflect the thin elastic membrane to open the valve, whereas pressurized air is used to seal the valve off (Amin et al 2013; Chuang et al 2012). Although the device footprint is miniaturized, the method requires off-chip apparatus that typically includes compressed air supply, gas regulators, and a vacuum pump.…”

Accelerated Biofluid Filling in Complex Microfluidic Networks by Vacuum‐Pressure Accelerated Movement (V‐PAM)

“…Besides used as a degassing module for microfluidics, vacuum‐based degassing has recently been exploited as a pumping mechanism for controlling fluid transport in point‐of‐care microfluidic devices . Vacuum can also indirectly control or pump fluids in microfluidic devices through a gas‐permeable PDMS membrane . Although these previous studies have provided an important foundation and proof that vacuum can be incorporated into microfluidic device designs to facilitate transport and filling of fluids in microfluidic channels, only simple microfluidic configurations and applications have been reported so far.…”

“…[23][24][25] Vacuum can also indirectly control or pump fl uids in microfl uidic devices through a gas-permeable PDMS membrane. [26][27][28][29][30] Although these previous studies have provided an important foundation and proof that vacuum can be incorporated into microfl uidic device designs to facilitate transport and fi lling of fl uids in microfl uidic channels, only simple microfl uidic confi gurations and applications have been reported so far. Thus, the full potential of vacuumbased fl uid transport in microfl uidics awaits for exploration.…”