Tape underlayment rotary-node (TURN) valves for simple on-chip microfluidic flow control
We describe a simple and reliable fabrication method for producing multiple, manually activated microfluidic control valves in polydimethylsiloxane (PDMS) devices. These screwdriver-actuated valves reside directly on the microfluidic chip and can provide both simple on/off operation as well as graded control of fluid flow. The fabrication procedure can be easily implemented in any soft lithography lab and requires only two specialized tools—a hot-glue gun and a machined brass mold. To facilitate use in multi-valve fluidic systems, the mold is designed to produce a linear tape that contains a series of plastic rotary nodes with small stainless steel machine screws that form individual valves which can be easily separated for applications when only single valves are required. The tape and its valves are placed on the surface of a partially cured thin PDMS microchannel device while the PDMS is still on the soft-lithographic master, with the master providing alignment marks for the tape. The tape is permanently affixed to the microchannel device by pouring an over-layer of PDMS, to form a full-thickness device with the tape as an enclosed underlayment. The advantages of these Tape Underlayment Rotary-Node (TURN) valves include parallel fabrication of multiple valves, low risk of damaging a microfluidic device during valve installation, high torque, elimination of stripped threads, the capabilities of TURN hydraulic actuators, and facile customization of TURN molds. We have utilized these valves to control microfluidic flow, to control the onset of molecular diffusion, and to manipulate channel connectivity. Practical applications of TURN valves include control of loading and chemokine release in chemotaxis assay devices, flow in microfluidic bioreactors, and channel connectivity in microfluidic devices intended to study competition and predator/prey relationships among microbes.
KeywordsMicrofluidics On-chip valve Flow control Gradient formation Bacteria Protozoa Microbiological predation Valve fabrication Hydraulic valve Valve arrays Multi-channel closure
This work has been supported in part by National Institutes of Health Grants U01AI061223 and U54CA113007, National Science Foundation Grants 0120453 and 0649883, DOD CDMRP/BCRP grant BC061791, the Vanderbilt Institute for Integrative Biosystems Research and Education, and the Searle Systems Biology and Bioengineering Undergraduate Research Experience. We are especially indebted to John Fellenstein and Robert Patchin for the fabrication of the brass molds. We thank Adit Dhummakupt for assistance with the protozoa work and Allison Price and Don Berry for their editorial assistance in the preparation of this manuscript.
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