Next-generation integrated microfluidic circuits

Abstract

This mini-review provides a brief overview of recent devices that use networks of elastomeric valves to minimize or eliminate the need for interconnections between microfluidic chips and external instruction lines that send flow control signals. Conventional microfluidic control mechanisms convey instruction signals in a parallel manner such that the number of instruction lines must increase as the number of independently operated valves increases. The devices described here circumvent this "tyranny of microfluidic interconnects" by the serial encoding of information to enable instruction of an arbitrary number of independent valves with a set number of control lines, or by the microfluidic circuit-embedded encoding of instructions to eliminate control lines altogether. Because the parallel instruction chips are the most historical and straightforward to design, they are still the most commonly used approach today. As requirements for instruction complexity, chip-to-chip communication, and real-time on-chip feedback flow control arise, the next generation of integrated microfluidic circuits will need to incorporate these latest interconnect flow control approaches.

Recent developments in microfluidic large scale integration

“…Reducing the dependency on external pneumatic controllers can reduce the complexity of the chip-to-world interface for mLSI; this was the subject of two recent review papers [36,37]. Microfluidic logic circuits can eliminate the requirement of one external controller for each independently controlled valve set by utilizing a fluidic shift register [16 ,35,38].…”

Modular Platforms for Optofluidic Systems

“…Currently commercially available valves are mostly based on solenoids (Bürkert 6650, Kendrion Tri-Tech, LEE LFV, Staiger VA 204-7, Takasago VODA) and larger than 10 × 10 × 10 mm 3 , leaving potential for further development. For high-density integration of microvalves, alternative concepts based on indirect actuation have been developed [43][44][45]. Two layers of microfluidic channels are built on top of each other and coupled either by an elastomeric intermediate membrane or two non-miscible fluids.…”

Predictable Duty Cycle Modulation through Coupled Pairing of Syringes with Microfluidic Oscillators

“…One way to maintain the relationship shown in Equation (4) would be to modulate Ci together with Qi so that Pthi × Ci ≈ constant. One way to achieve this conveniently is by mounting two plastic syringes of different cross-sectional area on one syringe pump ( Figure 2), and utilizing the compliance of the syringe components [23] and resulting capacitive differences of the syringes [12]. Within the described system, as syringe outflow rate is a function of velocity and syringe cross-sectional area, and as both syringes are evacuated at the same linear velocity, we may further refine our definition of duty cycle as being a function of syringe diameter (Figure 2b).…”

“…The control systems underlying their operation, however, have typically remained external from the fluidic devices themselves [12][13][14]. An awareness that this rise in peripheral equipment cost may limit "next-generation" microfluidic systems has motivated the development of autonomous, pre-programmed, fluidic systems [1,[12][13][14][15][16][17].…”