In recent years, progresses in nanotechnology have established the foundations for implementing nanomachines capable of carrying out simple but significant tasks. Under this stimulus, researchers have been proposing various solutions for realizing nanoscale communications, considering both electromagnetic and biological communications. Their aim is to extend the capabilities of nanodevices, so as to enable the execution of more complex tasks by means of mutual coordination, achievable through communications.However, although most of these proposals show how devices can communicate at the nanoscales, they leave in the background specific applications of these new technologies. Thus, this paper shows an overview of the actual and potential applications that can rely on a specific class of such communications techniques, commonly referred to as molecular communications. In particular, we focus on health-related applications. This decision is due to the rapidly increasing interests of research communities and companies to minimally invasive, biocompatible, and targeted health-care solutions. Molecular communication techniques have actually the potentials of becoming the main technology for implementing advanced medical solution.Hence, in this paper we provide a taxonomy of potential applications, illustrate them in some details, alongwith the existing open challenges for them to be actually deployed, and draw future perspectives.

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This paper considers the scenario of a targeted drug delivery system, which consists of deploying a number of biological nanomachines close to a biological target (e.g., a tumor), able to deliver drug molecules in the diseased area. Suitably located transmitters are designed to release a continuous flow of drug molecules in the surrounding environment, where they diffuse and reach the target. These molecules are received when they chemically react with compliant receptors deployed on the receiver surface. In these conditions, if the release rate is relatively high and the drug absorption time is significant, congestion may happen, essentially at the receiver site. This phenomenon limits the drug absorption rate and makes the signal transmission ineffective, with an undesired diffusion of drug molecules elsewhere in the body. The original contribution of this paper consists of a theoretical analysis of the causes of congestion in diffusion-based molecular communications. For this purpose, it is proposed a reception model consisting of a set of pure loss queuing systems. The proposed model exhibits an excellent agreement with the results of a simulation campaign made by using the Biological and Nano-Scale communication simulator version 2 (BiNS2), a well-known simulator for molecular communications, whose reliability has been assessed through in vitro experiments. The obtained results can be used in rate control algorithms to optimally determine the optimal release rate of molecules in drug delivery applications.

In this paper, we present a communication protocol between a pair of biological nanomachines, transmitter and receiver, built upon molecular communications in an aqueous environment. In our proposal, the receiver, acting as a control node, sends a connection setup signal to the transmitter, which stokes molecules, to start molecule transmission. The molecules transmitted by the transmitter propagate in the environment and are absorbed by the receiver through its receptors. When the receiver absorbs the desired quantity of molecules, it releases a tear-down signal to notify the transmitter to stop the transmission. The proposed protocol implements a bidirectional communication by using a number of techniques originally designed for the TCP. In fact, the proposed protocol is connection-oriented, and uses the TCP-like probing to find a suitable transmission rate between transmitter and receiver so as to avoid receiver congestion. Unlike the TCP, however, explicit acknowledgments are not used, since they would degrade the communication throughput due to the large delay, a characteristic feature of molecular communications. Thus, the proposed protocol uses implicit acknowledgments, and feedback signals are sent by the receiver to throttle the transmission rate at the transmitter, i.e., explicit negative feedbacks.We also present the results of an extensive simulation campaign, used to validate the proposed protocol and to properly dimension the main protocol parameters.

This paper presents a software platform, named BiNS2, able to simulate diffusion-based molecular communications with drift inside blood vessels. The contribution of the paper is twofold. First a detailed description of the simulator is given, under the software engineering point of view, by highlighting the innovations and optimizations introduced. Their introduction into the previous version of the BiNS simulator was needed to provide to functions for simulating molecular signaling and communication potentials inside bounded spaces. The second contribution consists of the analysis, carried out by using BiNS2, of a specific communication process happening inside blood vessels, the atherogenesis, which is the initial phase of the formation of atherosclerotic plaques, due to the abnormal signaling between platelets and endothelium. From a communication point of view, platelets act as mobile transmitters, endothelial cells are fixed receivers, sticky to the vessel walls, and the transmitted signal is made of bursts of molecules emitted by platelets. The simulator allows evaluating the channel latency and the footprint on the vessel wall of the transmitted signal as a function of the transmitter distance from the vessels wall, the signal strength, and the receiver sensitivity. IntroductionThe capabilities of manipulating matter at the molecular scale has inspired a huge research effort for many years and has led to the design of sophisticated devices, commonly referred to as nanomachines. The potentials of these nano-devices span numerous areas [1][8][13], including medical science [2][14], environmental control, and material science. The technological progress has stimulated a lot of research focusing on different types of nanomachines, such as those related to the usage of carbon nanotubes and nanowires [51], and those making use of biological methods, which are the object of our analysis. Although full-fledged biological nanomachines do not yet exist, recently biochemists have done many progresses in this area, and now they are able to create at least functional cell components, such as artificial ribosomes, which can be used for the synthesis of proteins [49][50].However, the research regarding nanomachine networked coordination is still at an early stage.In the last years, some possible solutions for allowing nanomachines to exchange information have been proposed [1]. Clearly, achieving the objective of exchanging information at the nanoscale requires a deep exploration of the feasible mechanisms that allow designing the basic components of a communications system, such as an information encoder, a transmitter, a communication medium, a receiver, and an information decoder [13].Due to the heterogeneity of different environments and communication techniques that can be used at the nanoscale, it is unfeasible to identify general models, valid for most of nanocommunication systems. For example, signaling within a lymph node, or within blood vessels, or between brain cells, make use of mechanisms specific for each ...