Gas penetration through pneumatically driven PDMS micro valves

Abstract

Integration of valve like structures into microfluidic chips is a key factor for the usability of many microfluidic systems. One approach is utilization of thin PDMS layers as flexible membranes which can be closely packed on the microfluidic chips. These flexible membranes can be deformed by pneumatic actuation, closing or opening the fluidic channel of the corresponding valve. However, PDMS is permeable to gases and this permeability gets non-negligible for common valve layer thicknesses and pressure gradients. This factor restricts the usage of PDMS valves in microfluidic systems, as gas bubbles are strictly prohibited in many applications. Here two methods avoiding the intrusion of gas into the microfluidic channels are introduced and investigated. The first is based on an oil droplet placed in the dead end pneumatic channel of the valve, the second utilizes a parylene coating to make PDMS impermeable to gases. The parylene layer could not completely suppress the gas intrusion into the fluidics of the valve and additionally influenced the sealing capabilities of the valve. The oil droplet, in contrast, suppressed the permeability of the valve completely and provides a straight forward solution. In the experimental setup a novel valve design is introduced and characterized. Sealing capabilities, hydraulic resistance and lifetime are measured, dead and internal volume are calculated to describe the capabilities of thin membrane PDMS valves. These values are of interest if the valves are to be used industrially. The design introduced here is easy to fabricate and requires low alignment accuracy: it uses a Polycarbonate/PDMS sandwich, bonded by a APTES coating. Combining the simplicity of the valve design and the low cost fabrication methods and materials needed, the valve is perfectly suited as a disposable consumable.

Property Investigation of Replaceable PDMS Membrane as an Actuator in Microfluidic Device

“…Furthermore, to fully exploit the advantage of the elasticity of PDMS, various applications using PDMS as an actuator in microfluidic systems have been reported. These applications, including valve [17][18][19][20][21][22][23][24][25][26][27], pump [28][29][30][31][32][33][34], cell stimulator [35], cell immobilization device [36,37], cell culturing device [38], artificial cell activation device [39], and lens [40][41][42][43][44][45], have received extensive attention. The elastomeric property of PDMS enables easy integration of switches and valves into microfluidic systems.…”

“…The Mathies group [23] developed a PDMS membrane valve that enabled applications in lab-on-a-chip systems for infectious disease detection [24] and pressure-injected electrophoretic separation [25]. Microfluidic pumps [26][27][28][29] played an important role in many microfluidic devices: when vacuum was applied to the control channel, PDMS membrane was pulled into the displacement chamber and fluid was free to flow from the input channel to the output channel. Apart from that, the micro-lens made by PDMS membrane has wide applications.…”

Hypoxia-on-a-chip

“…So the pump acted as a combined flow source and oxygenator [12]. This may be problematic especially when gas bubbles are produced, as reported by Goldowsky and Knapp [13]. To enhance the oxygen transport capability an additional helical oxygenator element was placed at the center of the microfluidic system utilizing the same gas-permeable membrane also used for fluid actuation whereby the gas exchange area of this oxygenator is ten times larger than that of the pump.…”

Closed-loop control system for well-defined oxygen supply in micro-physiological systems

“…In previous fluidic designs, this pump was also used for gas exchange [8], which can cause gas bubble generation inside the channels. [9] To overcome this problem and enhance the oxygen transport capability, an additional oxygenator element was integrated in the MPS. Together with oxygen sensing spots this element can be used to control the concentration inside the MPS, as was reported in [3].…”