Page 26 - 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

tain the continuous operation of BNTs. EH from multiple introduced application has toxic, injurious, or adverse ef‑
resources can reduce the variance at power output with fects on the living cells and biochemical processes. Se-
the addition of alternative complementary procedures in cond, an implanted IoBNT application should be able
a modular fashion as investigated in [161]. to operate without its performance being degraded by
the co‑existing biochemical processes. Performance
3.3.3 Energy Storage degradation usually follows when an IoBNT application
alters the metabolic activities, because such alternation
Storage of energy is also important when BNTs can‑ invokes the immune response that might in turn lead to
not continuously satisfy their power requirements via the rejection of the deployed application. Rejection can
EH and WPT techniques. There has been conside- occur in the form of expulsion of the IoBNT application
rable interest in miniaturizing the energy storage from the organism, encapsulation of the BNTs with
technologies to make them size‑compatible with MEMS biological cells and tissues, or in lammation or death of
and NEMS devices. Some of the efforts have been the surrounding tissues. In the case of MC, performance
devoted to develop micro‑batteries, miniaturized ver- degradation may also happen as a result of cross‑talk
sions of conventional thin‑ ilm lithiumion batteries, caused by the natural biochemical signaling.
bene iting from novel nanomaterials [162]. There are Biocompatibility concerns both materials used in the
even a few studies focusing on nanoscale versions of physical architecture of BNTs, and the networking, energy
lithium batteries [163, 145]. However, they suffer from harvesting, power transfer, and interfacing processes of
low energy density, short lifetimes, and potential the IoBNT. In terms of materials, synthetic biology‑based
toxicity in in vivo applications. More promising solution BNTs can be considered highly biocompatible, as they
is micro‑supercapacitors (MSCs), which provide adopt living cells and cellular components as the sub‑
icantly higher energy storage capacity, higher strate [24]. Likewise, luorescent protein‑ and DNA‑based
charge/discharge rates, and more importantly, scalability BNTs are also of biological origins, and thus, can be ex‑
and lexibility, which are crucial for their integration pected to offer similar levels of biocompatibility [108].
into BNTs [164, 165, 166]. However, depending on their exact biological origin and
Several types of materials have been considered for the their overall amount in the body, they may still trigger
design of MSC electrode to improve the energy density. the immune response. For example, a virus‑based syn‑
Carbon nanomaterials, such as CNTs and graphene, are thetic BNT can be labeled as foreign agent and attacked
the most widely researched materials due to their abun‑ by the immune system, unless it is designed to possess
dance and stability, which is re lected to an extended life‑ a kind of stealth proteins that help escape the immune
time [164]. Due to its extremely high surface‑to‑volume control [171]. For arti icial BNTs based on nanomateri‑
ratio, high mobility and lexibility, graphene has attracted als, biocompatibility is more challenging. There is still
particular attention [167, 168]. Additionally, conducting no consensus on a universal test of biocompatibility for
polymers, such as PEDOT/PSS, and graphene/conducting nanomaterials, leading to con licting results in the litera‑
polymer heterostructures are also considered as lexible ture about almost all materials. Complexity of the biologi‑
electrodes for MSCs [164]. The research in MSCs is still at cal systems and reproducibility problem for in vivo and in
early stages; however, we believe that with the increase vitro tests are the main causes of the ongoing ambiguity.
of energy density and further reduction of sizes, they can Nonetheless, many polymers (e.g., PMMA, Parylene), gold,
be a viable candidate for energy storage units in BNTs. titanium, and some ceramics are widely known to be bio‑
compatible [172, 173, 174]. Carbon‑based materials, e.g.,
3.4 Biocompatibility and Co‑existence CNT and graphene, have been reported as both biocom‑
patible and toxic in different works, preventing a gene-
Biological processes are complex, and intertwined, often ralization over these nanomaterials. This is attributed
through intricate relationships that are yet to be unco- to large variations in their physicochemical properties,
vered. Perturbation of homeostasis maintained by e.g., size, shape, surface characteristics, adopted in
these relationships may result in serious disorders. Even different works [175, 176]. However, it has been
more complicated is the fact that the composition of the repeatedly re‑ ported that their biocompatibility can be
physiological environment and the interactome may have modulated with chemical manipulation [175]. For
a large variance among different members of the same example, surface functionalization with dextran is
species. For example, gut microbiome is known to be shown to reduce the toxicity of graphene oxide (GO),
composed of different types of bacteria in different hinting at strategies to make carbon‑based
people [169]. Therefore, the evaluation of in vivo nanomaterials suitable for safe in vivo applications
IoBNT applications in terms of biocompatibility is very [177, 176]. Similarly, nanoparticles are shown to be
challenging, however, must be considered seriously. detoxi ied upon the functionalization of their surfaces
Biocompatibility constraints for IoBNT can be viewed with smart/benign ligands [178].
from two angles [170]. First, an IoBNT application, along In terms of processes, attention must be paid to the
with all the communication methods and devices therein, communication, bio‑cyber interfacing, energy harvesting,
should not disrupt the homeostasis of the organism it is transfer and storage processes. In EM‑based and acous‑
implemented in. Such disruption might occur when the tic communication and power transfer processes, for ex‑

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