Page 104 - ITU Journal Future and evolving technologies Volume 2 (2021), Issue 3 – Internet of Bio-Nano Things for health applications

ITU Journal on Future and Evolving Technologies, Volume 2 (2021), Issue 3

nisms [13]. There are ive transport mechanisms which cations, calcium signaling and quorum sensing in bacte‑
include free diffusion, gap junction channels, molecular ria are examples of this method [16]. Quorum sensing is
motors, self‑propelling microorganisms and random col‑ a population‑proportional stimulation and response sys‑
lision of nanomachines. Molecular communication sys‑ tem that bacteria use to coordinate with each other.
tems can be classi ied with various criteria as shown in Medical applications, such as Targeted Drug Delivery
Fig. 1: (TDD), activation of the immune system and tissue engi‑
a) Scale: The molecular communication scale refers to the neering, are one of the most important application cat‑
distances at which bio‑nanomachines interact with each egories of molecular communication. In such scenar‑
other by releasing molecules and is divided into three cat‑ ios, rate control mechanisms play an essential role. In
egories: intracellular, intercellular and inter‑organ [14]. TDD, rate control is indispensable to maintain the drug
Similarly, bio‑nanomachines are divided into three cate‑ concentration between the Least Effective Concentration
gories, short‑range such as molecular motors, medium‑ (LEC) and the Maximum Tolerated Concentration (MTC).
range such as ion signaling and transmission through dif‑ Moreover, bio‑nanomachines generally bear a limited re‑
fusion, and inally long‑range transmission such as trans‑ source, therefore releasing the drug molecules at the opti‑
mission based on bacteria, neurons and pheromone sig‑ mal rate is of signi icant importance. Controlling the rate
naling [7]. Pheromone is a chemical agent secreted or ex‑ of activators or antagonists is also indispensable in the
creted, leading to the stimulation of a collective response immune system activity scenario i.e., to intensify or re‑
in members of a species. duce the activity of the immune system. The rate control
b) Energy consumption: Molecules are either dispersed is required as well in tissue engineering scenarios to en‑
in the environment or released directionally by chemi‑ sure the prolonged exposure of the damaged tissue to the
cal energy consumption, which is called Passive Molecu‑ growth factors. Considering the importance of rate con‑
lar Communication (PMC) and Active Molecular Commu‑ trol in therapeutics applications, this paper aims to re‑
nication (AMC) [15, 14], respectively. view the state‑of‑the‑art literature on rate control using
c) Communication type: Molecular communications can molecular communication.
be divided into two categories: wired and wireless. The organization of this paper is as follows: Rate con‑
i) Wired: Refers to methods that require a physical link trol in molecular communication with a layer architec‑
to transmit signals [8] and they are also called Walkway‑ ture perspective is investigated in Section 2. Section 3
based methods [16]. For example, microtubules are presents the therapeutic applications of rate control. Sec‑
provided in micro‑dimensions to connect nanomachines. tion 4 reviews the recent advancements and current re‑
Data transfer between nanomachines is done through search on releasing rate control in DDS. Research oppor‑
the movement of molecular motors that walk on micro‑ tunities are presented in Section 5. Section 6 concludes
tubules. Another example of wired molecular communi‑ this paper.
cation is neuronal messaging that is placed in the category
of inactive molecular communication [17]. 2. RATE CONTROL IN MOLECULAR COMMU‑
ii) Wireless: Wireless methods refer to methods that re‑ NICATION
quire only a luidic medium (such as air, water and blood)
without the need for electrical conductors or physical Molecular communication architecture can be examined
links to transmit information [8]. Most current molecular from the perspective of communication networks [18, 14,
communication methods mimic wireless communication 19]: molecular physical layer, molecular link layer, molec‑
samples. This is due to the similarity of natural biologi‑ ular network layer, molecular transport layer and molec‑
calcommunicationsystemswithwirelesscommunication ular application layer. Since our paper is focused on rate
systems. Of course, the fundamental difference is that the control in molecular communication, we review the ex‑
distribution of molecules is slow compared to the propa‑ isting works in the transport layer. This layer provides
gation of radio waves. One example of this method is cal‑ the functions needed for end‑to‑end transmission and is
cium signaling. In this method, the propagation of waves responsible for providing reliability, In‑sequence deliv‑
between cell junctions is carried out in densely packed ery, congestion control and low control. Rate control
cell tissue. Calcium waves are commonly used to trans‑ in molecular communication is carried out for two pur‑
mit short‑range information between cells where infor‑ poses: Flow control and congestion control.
mation is coded in the concentration of calcium ions. An‑
other example of wireless data transmission is the use of 2.1 Flow control
bacteria [17]. The wireless method can be divided into
two categories: A) Flow‑based: In this method, molecules Flow control is a function in which the sender adjusts
are released through diffusion in a luidic medium such the transmission rate of the molecular transmission layer
as blood low. Intra‑body hormonal communication is based on the receiver’s characteristics. Flow control can
the most important example of this method [16]. B) be started by the sender or receiver [19]:
Diffusion‑based: In this method, molecules are propa‑ i) Transmitter initiated low control: The easiest form of
gated by diffusion in a luidic medium and molecules only low control is that the sender uses a very low transmis‑
follow the rules of random walk. Pheromonal communi‑ sion rate so that there are no losses. This requires prior

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