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Microfluidic chamber design for controlled droplet expansion and coalescence
The defined formation and expansion of droplets are essential operations for droplet-based screening assays. The volumetric expansion of droplets causes a dilution of the ingredients. Dilution is required for the generation of concentration graduation which is mandatory for many different assay protocols. Here, we describe the design of a microfluidic operation unit based on a bypassed chamber and its operation modes. The different operation modes enable the defined formation of sub-µL droplets on the one hand and the expansion of low nL to sub-µL droplets by controlled coalescence on the other. In this way the chamber acts as fluidic interface between two fluidic network parts dimensioned for different droplet volumes. Hence, channel confined droplets of about 30–40 nL from the first network part were expanded to cannel confined droplets of about 500 to about 2500 nL in the second network part. Four different operation modes were realized: (a) flow rate independent droplet formation in a self-controlled way caused by the bypassed chamber design, (b) single droplet expansion mode, (c) multiple droplet expansion mode, and (d) multiple droplet coalescence mode. The last mode was used for the automated coalescence of 12 droplets of about 40 nL volume to produce a highly ordered output sequence with individual droplet volumes of about 500 nL volume. The experimental investigation confirmed a high tolerance of the developed chamber against the variation of key parameters of the dispersed-phase like salt content, pH value and fluid viscosity. The presented fluidic chamber provides a solution for the problem of bridging different droplet volumes in a fluidic networ
Novel Network Paradigms: Microfluidic and M2M Communications
The present thesis focuses on two appealing paradigms that are expected to characterize the next generation of communication systems: microfluidic networking and Machine to Machine (M2M) Communications. Concerning the former topic, we show how it is possible to introduce switching and routing mechanism in microfluidic systems. We define some simple mathematical models that capture the macroscopic behavior of droplets in microfluidic networks. Then, we use them to implement a simulator that is able to reproduce the motion and predict the path of droplets in a generic microfluidic system. We validate the simulator and apply it to design a network with bus topology. Finally, we prove the feasibility of attaining molecular communication in this domain by describing a simple protocol that exploits droplets length/interdistance modulation to send information.
The research activity on M2M, instead, is aimed at the investigation of two critical issues that are expected to affect Machine-Type Communication (MTC), i.e. energy efficiency and massive access. Regarding energy efficiency, we address the problem of delivering a fixed data payload over a Rayleigh fading wireless channel with the purpose of minimizing the average total energy cost, given by the sum of the transmit energy and an overhead circuit energy, to complete it. This scenario is well suited for uplink cellular MTC in future 5G Internet of Things (IoT) use cases, where the focus is more on device energy efficiency than on throughput. We describe the optimal transmission policies to be used under various coordinated access scenarios with different levels of channel state information and transmitter/receiver capabilities, and show the corresponding theoretical bounds. In the last part of the work, we study the asymptotic performance of uncoordinated access schemes with Multi Packet Reception (MPR) and Successive Interference Cancellation (SIC) techniques for contention resolution at the receiver. The corresponding results in terms of throughput in a massive access M2M scenario are finally evaluated and discussed