Andrea Biral

Introducing purely hydrodynamic networking mechanisms in microfluidic systems

Microfluidic is a multidisciplinary field with practical applications to the design of systems, called Lab-on-a-Chip (LoC), where tiny volumes of fluids are circulated through channels with millimeter size and driven into structures where precise chemical/physical processes take place. One subcategory of microfluidic is droplet-based microfluidic, which disperse discrete volumes of fluids into a continuous stream of another immiscible fluid, which act as droplet carrier. Droplets can then be moved, merged, split, or processed in many other ways by suitably managing the hydrodynamic parameters of the LoC. A very interesting research challenge consists in developing basic microfluidic structures able to interconnect specialized LoCs by means of a flexible and modular microfluidic network. The aim of this paper is to exploit the properties of droplet-based microfluidics to realize purely hydrodynamic microfluidic elements that provide basic networking functionalities, such as addressing and switching. We define some simple mathematical models that capture the macroscopic behavior of droplets in microfluidic networks and use such models to design and analyze a simple microfluidic network system with bus topology.

Introducing purely hydrodynamic networking functionalities into microfluidic systems

Abstract Microfluidics is a multidisciplinary field with practical applications to the design of systems, called lab-on-chip (LoC), where tiny volumes of fluids are circulated through channels with millimeter size and driven into structures where precise chemical/physical processes take place. One subcategory of microfluidics is droplet-based microfluidics, in which discrete volumes of fluids disperse into a continuous stream of another immiscible fluid, which acts as the droplet carrier. Droplets can then be moved, merged, split, or processed in many other ways by suitably managing the hydrodynamic parameters of the LoC. A very interesting research challenge consists in developing basic microfluidic structures that are able to interconnect specialized LoCs or, more generally, microfluidic machines (MMs), by means of a flexible and modular microfluidic network. The aim of this paper is to exploit the properties of droplet-based microfluidics to realize purely hydrodynamic microfluidic elements that provide basic networking functionalities, such as addressing and switching. We define some simple mathematical models that capture the macroscopic behavior of droplets in microfluidic networks, and use such models to design and analyze a simple microfluidic network system with bus topology. The study points out some tradeoffs that need to be accounted for when designing a microfluidic network, and proposes a first approach to the performance analysis of this kind of network, while listing a number of open research challenges that call for further study.

Modeling, Simulation and Experimentation of Droplet-Based Microfluidic Networks

The aim of this paper is to model the “macroscopic” functioning of droplet-based microfluidic networks, i.e., the speed and trajectory of droplets across a network of microfluidic elements. To this end, we first give a quick overview of microfluidic basics and main governing rules. Based on such principles, we derive mathematical models of the fundamental components of a microfluidic network and, then, we identify the set of variables that capture the dynamic state of the system. This allows us to define a simple way to simulate the “macroscopic” evolution of the microfluidic network, predicting the path followed by the droplets in the circuits. To validate the model, we compare the simulation results with the experimental outcomes we obtained from a simple but representative microfluidic circuit, which has been realized in our laboratory, and with other circuits tested in previous works. Finally, we apply our theoretical model to a more complex usecase, consisting in a microfluidic network with bus topology, and we draw some final considerations about the performance of such a network.

Design and analysis of a microfluidic bus network with bypass channels

Microfluidics is a multidisciplinary field of research that deals with elementary hydraulic circuits with channels of micrometer size. At this scale, fluids exhibit very specific patterns that cannot be observed at the macro-scale. In particular, vortex forces become negligible, so that the behavior of fluids in the circuit becomes easily controllable and predictable. This technology is currently used in medicine and chemistry to perform specific tasks, such as blood analysis, DNA sequencing, and others. The interest on this technology has been increasing over the last few years and, recently, microfluidic circuits capable of performing simple logical operations have been proposed and experimentally tested, paving the way to a new research branch known as microfluidic networking. In this paper we analyze the design of a microfluidic network with a bus topology, where multiple microfluidic machines are connected to a main channel by means of passive switching elements, realized as T-junctions with bypass (shunt). We mathematically model the system and find the rules to be followed for proper design and dimensioning of such a microfluidic network. We then propose a preliminary performance analysis that gives some insights into the complex interrelations among the different elements of the microfluidic network.

Addressing multiple nodes in networked labs-on-chips without payload re-injection

On a droplet-based Labs-on-Chip (LoC) device, tiny volumes of fluids, so-called droplets, flow in channels of micrometer scale. The droplets contain chemical/biological samples that are processed by different modules on the LoC. In current solutions, an LoC is a single-purpose device that is designed for a specific application, which limits its flexibility. In order to realize a multi-purpose system, different modules are interconnected in a microfluidic network — yielding so-called Networked LoCs (NLoCs). In NLoCs, the droplets are routed to the desired modules by exploiting hydrodynamic forces. A well established topology for NLoCs are ring networks. However, the addressing schemes provided so far in the literature only allow to address multiple modules by re-injecting the droplet at the source every time, which is a very complex task and increases the risk of ruining the sample. In this work, we address this issue by revising the design of the network nodes, which include the modules. A novel configuration allows the droplet to undergo processing several times in cascade by different modules with a single injection. Simulating the trajectory of the droplets across the network confirmed the validity of our approach.

On the Impact of Transmitter Channel Knowledge in Energy-Efficient Machine-Type Communication

We address the problem of delivering a fixed data payload over a Rayleigh fading wireless channel, where the aim is to allocate resources to minimize the average total energy, given by the sum of the transmit energy and an overhead circuit energy. This scenario is well suited for uplink cellular machine-type communications in future 5G Internet of Things (IoT) use cases, where the focus is more on device energy efficiency than on throughput. We propose and describe the transmission policies to be used under three scenarios with different levels of channel state information (CSI) at the transmitter: non-causal CSI, causal CSI, and average CSI. For typical uplink macrocellular links, we show 1) that the strategy for causal CSI has nearly the same energy efficiency as the unachievable non-causal CSI bound, and 2) that the energy difference between this bound and the average CSI energy is about a factor of 2 to 5.

Transmitting information with microfluidic systems

In recent past, researchers have suggested the idea of extending information theory to the microfluidic domain. Along this stream, a few solutions have been proposed to support logic and computing functions as well as simple communications in droplet-based microfluidic systems. Of course, pursuing this objective, requires a deep knowledge of microfluidic basics and relies on the use of an appropriate information coding strategy. Accordingly, in this paper we introduce a possible scheme for information coding in microfluidic devices, evaluate its performance by means of some preliminary experimental results and draw a number of considerations.

Asymptotic throughput analysis of massive M2M access

5G systems are expected to be able to handle channel access from a massive number of low cost machine-type devices (MTDs), requiring intermittent connectivity to a network. Ideally, these devices should be able to transmit their short message either immediately without prior connection establishment (random access) or with a lightweight connection establishment (access reservation). In this paper, we analyze the capacity of a system where a large number of devices transmit simultaneously to a single receiver, capable of performing multiple packet reception (MPR) by means of advanced decoding techniques, such as successive interference cancellation (SIC). We derive a simplified mathematical model that allows us to determine the average number of signals that can be successfully decoded by the receiver as a function of the number of overlapping transmissions and the MPR capabilities of the system. We observe that, according to our analysis, a receiver capable of performing perfect SIC and MPR can theoretically decode an arbitrarily large number of simultaneous transmissions by proportionally reducing the per-user data rate, in such a way that the aggregate system capacity remains almost constant.

Uplink Resource Allocation in Cellular Systems: An Energy-Efficiency Perspective

In this work we address the problem of optimal resource allocation in the uplink of a wireless cellular network with Rayleigh fading channels, where the aim is to minimize the average total energy spent for packet delivery. The devices are assumed to transmit over orthogonal resources where the total energy used for each resource is modeled as the sum of the transmit energy and an overhead circuit energy. We first derive the optimal allocation for the single-user case when varying our assumptions on both the Channel State Information available at the transmitter and the Automatic Repeat reQuest capabilities. Then, we generalize the analysis to the multi-user case and compare the results obtained for the different scenarios.