Page 77 - 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

test bed structure similar to [177]. The BER in train‑ 5.1.4 Molecule release mechanism
ing and testing data sets was ≈ 0.032 and ≈ 0.074, re‑
spectively. The proposed network achieved BER less than The transmission of molecules requires a pumping action.
SBRNN and a simple detector, where pH difference of last Therefore, nano‑pumps, as described in [167], can be
and irst values within a bit‑interval was used as the de‑ used for this purpose. Moreover, by applying mechanical
cision metric. Table 7 shows a brief description of the loads to the CNTs, molecular lows can also be achieved.
experimental works and concluding remarks on the out‑
comes of the experiments. 5.1.5 Biocompatibility
Since these nano‑machines are expected to perform their
5. CHALLENGES IN PRACTICAL DESIGN OF task inside the human body, they should be biocompati‑
TRANSMITTER AND RECEIVER, AND ble and should not produce any immunological response
FUTURE RESEARCH DIRECTIONS or toxic effects while performing their task in an environ‑
ment of living cells. For example, a biocompatible poly‑
5.1 Transmitter design mer like chitosan conjugated with anticancer agents is
used for gradual drug release in cancerous tissues. Ensur‑
Most of the existing works consider the transmitter to be ing biocompatibility requires interdisciplinary research.
an ideal point source that can release molecules in the di‑
rection of the receiver. This is a very weak assumption, 5.2 Receiver design
which has been employed for analytical tractability to an‑
alyze the system performance. However, for realizing a The types of receiver considered in the literature are
practical spherical transmitter, the following issues must mostly passive receiver, absorbing receiver, and reactive
be taken into consideration: receiver. Passive receivers are assumed to be a hypothet‑
ical sphere transparent to the arriving molecules. This
implies that the passive receiver can count the number
5.1.1 Energy of molecules within its closed boundary without affect‑
ing their propagation in the environment. In contrast
The transmitter requires some energy for its operation
to the passive receiver, an absorbing receiver can count
for example encoding the transmitted information, con‑
and absorb the molecules once they hit the surface. On
trolling the number of emitted molecules, etc. There‑ the other hand, reactive 14
fore, it should have the capability of harvesting energy. receivers have receptors on
For health applications within IoBNT, this energy harvest‑ their surface that can bind to the molecules through a re‑
versible reaction. In such a scenario, counting the num‑
ing can be done by using the chemical molecules present
ber of bound receptors can provide the information of re‑
in the environment. For example, glucose is the natural ceived molecules.
source of energy in all organisms. Similarly, the transmit‑
ter can also use some chemical to energize itself. Note that passive and absorbing receivers are dif icult to
develop in practice. Thus, a reactive receiver can be con‑
5.1.2 Molecule synthesis sidered for the practical design of the receiver. It is also
important to note that the functioning of the reactive re‑
The transmitter is expected to release the signaling ceiver is similar to the cells which can bind respective lig‑
molecules to communicate with the receiver. Hence, the ands and provide transduction of extracellular signals to
very irst requirement is the synthesis of molecules in the intracellular signals. Bio‑FET can also be used as a re‑
required amount. To achieve this, a controlled chemical ceiver to realize MC.
reaction is required. On the other hand, the signaling
molecules/drug particles can also be loaded beforehand 5.2.1 Receptor design
so that there is no requirement for molecule synthesis.
Thus, for biomedical applications e.g., drug delivery, the Since the receiver is expected to bind the signaling
required number of chemical molecules should be calcu‑ molecules at its receptor, the design of receptors is im‑
lated before inserting the nano‑machine inside the human portant. The selectivity and sensitivity of the receptors to
body. the intended molecule can be done by selecting the proper
material for the receptor. Selectivity means the receptor
should bind only that molecule, which is used for signal‑
5.1.3 Modulator ing. Sensitivity means the response time of the receptors.
The response time should not be very high otherwise it
As discussed in the previous sections, various types of
modulation schemes have been proposed in the litera‑ will limit the data rate of the MC system. As discussed in
[18], aptamers and DNAs can be appropriate to be used
ture, e.g., to transmit information, the number of released
as receptors. Various types of aptamers and correspond‑
molecules is varied, or the release time of the molecules is ing ligand/signaling molecules are available [190], [191],
varied. Hence, a unit at the transmitter is required to con‑
[192].
trol the concentration or release time of the molecules.
14 Binding and unbinding of molecules is possible in such receivers.

© International Telecommunication Union, 2021 65