Microfluidic chemical integrated circuits based on stimuli-responsive hydrogels for on-chip flow control

Microfluidics exhibits great capability in various research fields such as biology, chemistry or medicine. The lab-on-a-chip technology brings tremendous advantages over the conventional methods as it increases reaction kinetics, reduces reagent consumption and provides high throughput and parallelization capability. The aspect of parallelization on a large scale requires a powerful control paradigm where a large number of devices need to be manipulated by a small number of inputs. Even though, microfluidics has produced a variety of different platform technologies utilizing the most different physical effects the majority of technologies lack the ability to act on direct feedback from the process liquid. This results in a sophisticated external control unit off-chip which directly hinders high degrees of parallelization respectively integration. This work presents a microfluidic platform concept, which utilizes the volume phase transition of stimuli-responsive hydrogels on-chip to actively switch between fluid streams in a discrete operating manner. The volume phase transition combines the sensing and acting functionality in one component. Smart hydrogels are utilized in a transistor-like device which is capable to autonomously make switching decision exclusively depending on the chemical content of a fluid. The content comprising molecules and ions that exist simultaneously in a solution is viewed as carrier of chemical information. Thus, the chemo-fluidic transistor couples the molecular content of the liquid with the fluidic behavior of the system. The combination of the chemo-fluidic transistor and the analogy between electronics and microfluidic allowed the development of discrete basic circuits such as the logic gates AND, OR, NOT, and their negated counterparts rendering a complete computation. By consequently following the electronic paradigm more sophisticated modules are demonstrated such as an RS flip-flop or a chemo-fluidic oscillator circuit. The chemo-fluidic oscillator exhibits an autonomous oscillation in flow rate and concentration. The system architecture and circuitry allows a decoupling of the excitation stimulus and the emission concentration enabling future biological and medical application. This work discusses a novel concept for the implementation of microfluidic integrated circuits. Main aspects are examined such as technological requirements, the theoretical background, the signal variability and biological application of the system.