Preprint Article

|  Biomimicry in Nanotechnology: A Comprehensive Review |
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|  Mehedi Hasan Himela,b, Bejoy Sikdera, Tanvir Ahmeda,b, Sajid Muhaimin Choudhurya ∗ |
|  Biomimicry has been utilized in many branches of science and engineering to develop devices for enhanced and better performance. The application of nanotechnology has made life easier in modern times. It has offered a way to manipulate matter and systems at the atomic level. As a result, the miniaturization of numerous devices has been possible. Of late, the integration of biomimicry with nanotechnology has shown promising results in the fields of medicine, robotics, sensors, photonics, etc. Biomimicry in nanotechnology has provided eco-friendly and green solutions to the energy problem and in textiles. This is a new research area that needs to be explored more thoroughly. This review illustrates the progress and innovations made in the field of nanotechnology with the integration of biomimicry. |

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††footnotetext: a Department of Electrical and Electronic Engineering,
Bangladesh University of Engineering and Technology, Dhaka 1205, Bangladesh.
††footnotetext: b Department of Computer Science and Engineering, BRAC
University, Mohakhali CA, Dhaka 1212, Bangladesh. ††footnotetext: ∗
Corresponding Author<EMAIL_ADDRESS>
##  1 Introduction

Nature, through billions of years of evolution, has often provided unique but
elegant designs and structures that have inspired researchers and engineers to
invent new technologies to enhance the capabilities of existing ones. The term
’Biomimetics’ or ’Biomimicry’, coined by American biophysicist Otto Schimt in
the 1950s1, 2 is composed of two words that are derived from Greek words
’bios’(life) and ’mimesis’(imitation). Biomimicry is the emulation of natural
structures, designs, and elements with a view to develop novel devices with
the desired functionalities.

The evolving field of Biomimicry is highly multidisciplinary, and it is found
on almost every engineering scale, from microscopic applications to
macroscopic applications. The idea of mimicking nature to solve complex
problems is implemented in every branch of science and engineering. Photonic
structures are prevalent in nature such as the moth-eye, the structural
coloring of insects, etc. provided many inspirations for the construction of
novel photonic materials. Photosynthesis of plants and trees has provided the
idea for newer energy harvesting methods. Mimicking the human brain’s activity
to solve problems such as object identification, pattern recognition, etc. has
led to a new computation algorithm called ’Neural Network’ which is now
successfully implemented in many branches of science to solve complicated
problems. Japan’s "Shinkansen" or high-speed bullet train, when faced with the
alarming problem of loud tunnel boom noise, was redesigned taking inspiration
from nature: the front of the train was remodeled like a kingfisher’s face to
achieve better aerodynamics. We are now able to make wind turbines with
improved energy efficiency and performance, thanks to the "tubercles" (large
bumps) design found in Humpback whales. Airplanes nowadays are designed almost
like birds and advanced robotic shapes are looking more and more like humans.
To push the limits of new innovations or to solve a complex engineering
problem, humans have always looked at nature to seek answers throughout their
extant.

Engineered biomimicry includes three methodologies: bioinspiration,
biomimetics ,and bioreplication3. Bioinspiration is the implementation of an
idea taken from nature without reproducing the actual structure/mechanism. For
example, both helicopters and bumblebees hover but the mechanisms are
different. Biomimetics requires the reproduction of the actual mechanism to
obtain a certain functionality. Robots that walk on four or more legs are
instances of biomimetics. However, the distinction between these two is very
slight, and differentiating them is not an easy task. The third approach
bioreplication is the direct replication of a biological structure to obtain
certain functionality. All of these methodologies exploit natural instances to
develop structures or devices with desirable functionalities4.

As biomimicry enable researchers to exploit natural solution to solve a
problem, nanotechnology provides the method for observing matter at a
nanoscale level. Nanotechnology is the manipulation of matter at the nanometer
$(10^{-9}m)$ scale. It is one of the most promising technologies of this
century which has paved the way for many extraordinary innovations such as
nano-sensors, nano-robots, etc. There is a close relationship between
nanotechnology and biomimicry. All biological systems are comprised of units
that are observed at the nanoscale and biology inspires the creation of new
devices and systems to enhance the capabilities of the existing technology.
Hence the integration of nanotechnology and biomimicry can be proved very
essential in the amelioration of science and technology.

M Simovic-Pavlovic et al. have discussed the advancements of MEMS and NEMS in
their work, along with designing new nanodevices for advanced materials and
sensing applications5. PP Vijayan et al. have discussed the scope of
biomimetic functionalities such as self-healing, self-cleaning, etc., for
everyday materials6. L Zhang et al. and ES Kim et al. have discussed the
advancements of biomimetic tissue engineering and regenerative nanomedicine in
their review works7,8. T Li et al. and C Guido et al. have reviewed the recent
progress of biomimetic cell membrane-coated nanoparticles and nanocarriers for
cancer therapy9,10. Z Jakšić et al. and A Giwa et al. have reviewed the
development of biomimetic nanomembranes11,12 while R Bogue has reviewed
biomimetic nano-adhesives13. N Soudi et al. have reviewed biomimetic
photovoltaic solar cells14, Y Saylan et al. have reviewed biomimetic molecular
recognition and biosensing15, and S Rauf et al. have reviewed biomimetic
optical nanosensors16. While many accomplished researchers and scientists of
different fields have reviewed biomimicry in nanotechnology in specific areas,
to our knowledge, there exists no comprehensive review of biomimicry in the
general field of nanotechnology that encompasses different areas of the field
in a single study. With that inspiration, in this work, we’ll review various
applications, advancements, and advantages of biomimicry in the field of
nanotechnology.

A comprehensive overview of this review paper has been given in table 1 which
summarizes the application of biomimicry in various fields of nanotechnology.

Table 1: Overview Fields |  Applications |  Biological Inspiration |  Significant Instances |  Features
---|---|---|---|---
Nano- sensor |  Optical Nanosensor |  • Built-in IR sensing
capabilities of snakes and vampire bats17 • Wide field-of-view of the
common housefly18 • Camouflage capabilities
of cephalopods 19 |  • Heat sensors20 • Aircraft wing deflection
measurement sensor18 • Vapor sensors21 |  • Temperature sensing • Chemical sensing • Light-weight • Low cost • Better form factor
Peptide Nanosensor |  • Peptide bonds |  • Nanoelectronic noses for
distinguishing chemical
vapors22 |  • Linking peptides to
nanosensors
Tactile Nanosensor |  • Human skin
neuroreceptors |  • Skin attachable adhesives
or E-skins23 |  • Reversible adhesion23 • Ease of deformability23
Stimuli Responsive Nanosensor |  • Venus flytrap |  • Thermo-responsive self-folding
microgrippers24 |  • Self-actuating action without
any external power sources24 • Contains stimuli responsive
hydrogel/polymers25
Nano- medicine |  Tissue Engineering |  • Human Bone Extracellular Matrix (ECM) |  • Generation of bony tissues26 |  • Self-assembling
nanostructured gel26
• Extracellular
matrix proteins26, 27, 28, 29, 30 |  • Cell attachment, proliferation, differentiation and ultimately tissue generation. |  • Creates scaffolds that mimic
natural tissues26, 27, 28, 29, 30
• Native Tissue ECM31 |  • Hydrogels maintain cell structure , repair bond32, 31 |  • Hydrogels provide strong
mechanical support33 and
adjust themselves to match the shape of injury31
Surgery |  • Reconstruction of tissues |  • Vascularized composite tissue allotransplantation (VCA)34 • Tissue engineering |  • Recovering tissues lost from
injury34
Nanoparticles |  • Encapsulation of dendritic cells35 |  • Encapsulation of internal influenza proteins on the VLPs35 |  • Mimicking virus properties
increased vaccine effectiveness36
• Nanocage |  • Protein cage nanoparticle, encapsulin37 |  • Protein based nanocages to
deliver drugs to specific sites
of human body37
Nano- robots |  Bacteria Inspired Nanorobots |  • Bacteria38 |  • Self-assembled flagellar
nanorobotic swimmers38 |  • Imitates the rotary motion of
helical bacteria flagella for
propulsion38
Platelet-Camouflaged Nanorobots |  • Hybrid Red Blood
Cells39, Platelets38 |  • Flagellar
nano-swimmers40 |  • Platelet imitating properties like binding to toxins or special kinds of pathogens39
Table 1 Overview(contd.) Fields |  Applications |  Biological Inspiration |  Significant Instances |  Features
---|---|---|---|---
Nano Energy Harvest |  Solar Energy |  • Photosynthesis • Plant Leaves41 |  • Gratzel Cell42, 43 • Nano leaves and Nano trees44 |  • Anthocyanin to recreate photosynthesisv42, 41 • Thin photovoltaic film converts light into energy43
• Butterfly Wings45 • Compound Eye of insects46, 47 |  • Solar energy harvesting45, 46 |  • Increase of optical path length via light trapping45 • Wide angular field and decreases the reflectance46, 47
Ocean Energy |  • Kelp |  • Bio-inspired Triboelectric nanogenerator (BITENG)48, 49, 50, 51, 52 |  • Mimics the gentle sway of kelps53
Nano- photonics |  Anti-reflecting Coating |  • Moth-Eye |  • Integration of Moth-Eye nanostructures into solar cells 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67 • Superhydrophobic Surface in foldable displays 67 |  • Increase of External Quantum and Power conversion Efficiency of Solar cells • Incident angle and polarization independent reflectance. • Foldable displays exhibit excellent mechanical resilience with good thermal and chemical resistant.
Anti-reflective Transparent Nanostrcutures |  • Transparent Wings of Greta Oto • Cicada Cretensis 68, 69, 70 |  • Omnidirectional anti-reflective glass 71 |  • Less than 1% reflectivity irrespective of angle of incidence for S-P linearly polarized light.
Textile Engineering |  Water Repellent Textile |  • Lotus Leaf72, 73, 74, 75, 76 |  • Superhydrophobic Surfaces on Cotton Textiles. 77 |  • Superhydrophobic, Antibacterial and UV-blocking fabric.
• Carnauba Palm (Copernicia Prunifera) |  • Water repellent nano-coating on cotton, nylon and cotton-nylon fabrics.78 |  • Significant hydrophobicity during 30 sec and even after washing. • Environment friendly water repellent textiles exhibiting good air permeability and antibacterial effect.
Textile dyeing |  • Prodigiosin79, 80 |  • Production of pyrrole structure pigment by cell metabolization.81 |  • Better mass transfer rate for positive charged substances.

##  2 Biomimicry and Nanosensors

Nanosensors are nano-devices used for sensing physical, real-life quantities
that can later be converted into detectable signals. Although nanosensors are
used in a variety of domains, they have a similar workflow: (i) binding, (ii)
signal generation, and (iii) processing. Major advantages of using nanosensors
(from their macro counterpart) are increased sensitivity and specificity,
lower cost, and better response times. Taking inspiration from mother nature,
researchers, and scientists are now trying to design nanosensors that very
closely emulate nature’s sophisticated way of effortlessly binding to an
analyte or generating signals. While there are many works that review
nanosensors in light of specific applications82838485, there still ceases to
exist any comprehensive review on "biomimicry and nanosensors". In this
section, we’ll review some of the nanosensors which were designed friration
from the biosphere, specifically in the following domains: optical
nanosensing, peptide nanosensing, tactile nanosensing, and stimuli responsive
nanosensing.

Fig. 1: Biomimicry in nanosensors. a) Venus flytrap86 A) Thermo-responsive
self-folding microgrippers24 [inspired by (a)] b) Common housefly87 B)
aircraft wing deflection sensor18 [inspired by (b)] c) Peptide bonds88 C)
Nano-electronic noses22 [inspired by (c)] d) Human skin neuroreceptors89 D)
Skin attachable adhesives (E-skins)23 [inspired by (d)]. (Images in this
figure were reproduced from the cited original work, with permission from
their corresponding publishers.)

###  2.1 Biomimetic Optical Nanosensors

Research in the field of nanosensors have paved the way for the successful
implementation of chemical, infrared and mechanical sensors, all of which have
vast applications in modern-day technology, from tensile strength of wires to
the design of an aerospace vehicle90.
Many biological creatures have “built-in” infrared (IR) sensing capabilities.
Emulating this particular characteristic has led to the fabrication of a
biomimetic IR receptor micro-sensor. Some families of pythons, boas, and even
beetles have infrared sensing organs, which sometimes convert the IR into
heat, which in turn results in a thermal-sensitive system. In the inspired
sensor, the incident IR radiation warms a liquid, thus inducing a mechanical
deformation of the membrane, which is spotted in a capacitor91. This is
possible because temperature change can be detected by closely monitoring the
changes in the capacitance. The main advantage of such a sensor is that it can
be used at room temperature without any additional active cooling, unlike the
other photo detectors.
Recently, another optical sensor that is inspired by the common housefly has
been developed which can be used for aircraft wing deflection. The
functionality of a compound eye is the wider field-of-view detection and other
image processing techniques. The advantage of such a sensor is its low weight,
less power consumption, faster computation, and better form factor. Many
animals use their ability to change their coloration for communication,
predator capturing, camouflage, etc. This ability to change color has pushed
engineers to make sensors that change color in presence of certain chemicals,
hence acting as a chemical sensing sensor. The iridescent scales of some
butterflies also show variation in their optical properties when exposed to
different kinds of vapors92. These phenomena about the natural system inspired
researchers to build photonic vapor sensors. Another device which consisted of
periodic ridges and lamella deposited on a silicon wafer showed strong
reflectance in well-defined spectral regions. These are some of the prime
examples of how researchers, scientists and engineers have mimicked Mother
Nature’s light exploitation techniques to fabricate optical nanosensors.

###  2.2 Biomimetic Peptide Nanosensors

By coupling peptide to a common nanomaterial surface (grapheme, carbon
nanotube) a peptide nanosensor is created, which is capable of distinguishing
chemically camouflaged mixtures of vapors and detecting chemical warfare
agents to parts-per-billion level 22.

###  2.3 Biomimetic Tactile Nanosensors

Tactile wearable sensors that can receive information upon physical contact
have gained a lot of attention from researchers and have potential usage in
healthcare, robotic, and wearable device applications. Researchers are now
working on tactile nanosensors that are based on biological tactile systems93.
The main challenge of such a device is mimicking the human skin
mechanoreceptors- receiving and transducing physical stimuli to electrical
signals i.e. action potentials, and biomimetic signal processing mechanism94.

###  2.4 Biomimetic Stimuli Responsive Grippers

Inspired by the Venus flytrap, many stimuli-responsive, biomimetic shape-
changing robots/actuators have been proposed by combining stimuli-responsive
hydrogels, polymer, or their hybrid combination25. These grippers actually
have far-reaching applications in the fields of biosensors, smart medicine,
robotics, and surgery. Hydrogels and polymers are best suited for this purpose
because they have the same moduli ranges ($\sim$KPa) of biological tissues and
they can extend up to several orders of magnitude in volume when perturbed
with external stimuli. This extending and shrinking mechanism mimics the self-
actuating action without any external electrical power sources. The main
material for this type of gripper is N-isopropylacrylamide (NIPAM) based
stimuli-responsive hydrogels, and liquid crystalline material-based stimuli-
responsive hydrogels.

##  3 Biomimicry in Nano Medicine

Biomimicry means technological achievements that have been developed using
inspiration found in nature. The application of nanotechnology in healthcare
is referred to as nanomedicine, and biomimicry is the inspiration for it
because the human body is a gift of nature and riddled with questions and
answers. In the sense of understanding natural structures and using this
knowledge to perform and develop many tasks, nanomedicine may be regarded as a
specialized division of biomimicry. Biomimicry assists in bone regeneration by
use of self-assembled nanostructure tissues26, hydrogels32, 33, 95, 31 or
electrospinning96.Skin97, 98 and nerve restoration are another important
aspect of biomimicry application in nanomedicine99. Biomimetic nanorobots are
another application of biomimicry in nanomedicine. Inspired by platelets 100,
101 and platelet-membrane-cloaked nanomotors performs the task of the
adsorption and isolation of platelet-targeted biological agents102.

###  3.1 Tissue Engineering and Surgery

Plastic surgery is used to reconstruct tissues lost from injury, but it has
evolved so much from the surgical practice of 30 years ago. Previously,
doctors used synthetic implants using silicone103, cellulose104 etc but they
could interact with the host in a harmful manner, resulting in infection and
rare tumors. And those implants did not mimic biological tissues. Vascularized
composite tissue allotransplantation(VCA) was the first reconstructive
milestone, but it had inevitable probabilities like transplant rejection.
Tissue engineering then became the best alternative solution since this
process does not have those limitations34. Research of the self-assembling
biomaterials that mimic complex biological structures has also been going on
for a long time. Molecules that self-assemble into a nanostructured gel and
mimic the key characteristics of human bone extracellular matrix (ECM). This
is extremely important for the generation of bony tissues26.

Biomimetic materials also support a microenvironment for cell attachment,
proliferation, differentiation, and ultimately tissue regeneration. For
example, the most abundant ECM protein in our body is collagen105. A number of
natural micromolecules ( collagen27 , silk fibrin28 , fibrinogen , synthetic
polymers ( poly[glycolic acid]29, poly[L-lactic acid]30 , poly[lactic-co-
glycolic acid] have been processed using electrospinning. This technique
builds scaffolds that mimic natural tissues. To produce good scaffolds the
biomaterial has to be both biocompatible and support cell growth. This will
allow the scaffold to continue the metabolic functions. Moreover, It must
promote integration with host tissue and allow vascularization96.

Since the early 90s, multiple biomaterials have been exploited for cartilage
and bone applications. And recently, hydrogels have become popular due to
their network of interacting hydrophilic polymer chains that has striking
similarities with native tissue ECM31. Hydrogels maintain cell structure32 and
provide strong mechanical support33. In the case of bone repair, hydrogels
bond with the natural ECM strongly95. And hydrosols can be injected at the
injury site, and they adjust themselves to match the shape of the injury31.
Artificial bone substitutes have been produced from mineral compositions,
ceramic or material, bio-glass, or other fiber materials to mimic the organic
tissue fraction as boney tissues106. However, due to inability to fully master
the level of growing fully functional bone with cortical bone components, bone
replacement surgical techniques such as non-vascularized or vascularized bone
transfer or the Masquelet technique to support bone construction by
maintaining flap coverage are used106, 107, 108.

Skin is also an important part of the human body that can receive damage from
various sources, such as burns and infections. When a skin defect reaches the
deep dermal layer, the self-regeneration potential of the skin is obstructed,
and artificial skin substitutes using biomimicry can assist in skin repair97.
Artificial skin substitutes have been constructed with different compositions
and material properties, mimicking the organization of normal skin109.
Examples are the collagen matrix bonded to flexible nylon fabric/silicone
rubber epidarmis109 or collagen-elastin matrix98. Biomimetic scaffolds can
also be used for nerve replacement by mimicking the inner structure and
surface structure of original nerves99.

###  3.2 Biomimetic Nanorobots in Medical Science

One exciting current application of biomimicry is the development of
biomimetic nanorobots. These are micro-nanoscale robots for biomedical
operations. Industrial robots are used mainly for the automation of dangerous
tasks, but biomedical nanorobots are designed to tackle biological events.
Biomimetic nanorobot design has recently started to take inspiration from
nature, especially from the circulating cells such as platelets and
leukocytes. Human platelets become the main source of inspiration owing to
their work to tackle immune evasion100, 101, pathogen interactions, and
hemostasis. The platelet membrane cloaking method is the wrapping of natural
platelet cell membranes onto the surface of nanostructures and nanodevices110.
These platelet-membrane-cloaked nanomotors are enclosed by human platelets and
do the adsorption and isolation of platelet-targeted biological agents102.
These PL-motors possess a membrane coating containing multiple functional
proteins related to platelets. These PL-motors evade the body’s immune system
and display rapid locomotion in whole blood. PL-motors can also effectively
absorb Shiga toxin using a Vero cell assay and also show binding to pathogens
that can be used for rapid bacteria isolation102.

Minimally invasive surgery (MIS) and natural orifice transluminal endoscopic
surgery (NOTES) is gradually taking the place of open surgery as this will
decrease patient trauma and recovery length. Viewing the inside of a patient’s
lumen is a must for MIS. And now soft endoscopic nanorobots, inspired by
nature, are being used for reaching distant surgical targets. Robot bodies are
composed of soft materials that will reduce the potential of damaging tissue
or organs. They are also bendable and flexible enough to move inside the
patient’s lumen. The Meshworm design developed by Bernth et al was inspired by
the earthworm 111. The robot is made up of three segments of a soft plastic-
silicone mesh composite. The total length of all segments is 50 cm and each
segment is actuated by tendon wound mounted on DC motors, which are small
enough to be embedded inside biomimetic meshworms. A PID controller controls
the length of each tendon, and a USB camera is mounted at the tip.

Then there can be nanorobots that has hybrid cell membranes – combination of
red blood cell (RBC) and platelet(PL) membranes. This shows better binding
than PL-motors and neutralization of PL-adhering pathogens(Staphylococcus
aureus bacteria) and neutralization of pore-forming toxins($\alpha$\-
toxin)112. Some drugs can be carried by platelets because of the site-specific
adhesion of platelets. PL - motors can also be used for this purpose113.

Fig. 2: Biomimicry in Nanomedicine. A) Earthworm, B) A meshworm equipped with
an endoscopic camera111 [inspired by (A), C) Schematic diagram of how a
combination of nanoelements and growth factor administration may allow
regeneration of large critical defect bone114, 115, D) Encapsulation of
internal influenza proteins on the Virus-Like-Particles (VLPs)35 (Images in
this figure were reproduced from the cited original work, with permission from
their corresponding publishers.)

###  3.3 Nanoparticles

Nanoparticles(NPs) are usually defined as particles having a diameter of
between 1 and 100 nm. Nanoparticles have unique material characteristics owing
to their submicroscopic size. For example, these nanoparticles can be used for
the better activity of different medicines. Many cancer vaccines suffer from
the inability to mount a T cell response. But viruses possess this size and
the immune system can recognize these physical properties. So, mimicking these
properties with nanoparticles produces a better platform for vaccine design. A
viral mimicking vaccine platform capable of encapsulating dendritic cells
showed a threefold better reaction than normal cases35. A controlled immune
response towards a specific virus-cell is also possible, which results in a
vaccine that is active against the specific virus at a greater rate
Encapsulation of internal influenza proteins on the interior of virus-like
particles(VLPs) results in a vaccine that provides protection against 100
times lethal doses of an influenza36. Protein-based nanocages are also of
particular interest to researchers because of their excellent ability to
deliver a drug to specific sites of the human body. A protein cage
nanoparticle, encapsulin, isolated from Thermotoga Maritima, has been
developed for multifunctional delivery nanoplatforms for both chemical and
genetic engineering37.

Nanoparticles increase the bioavailability of compounds via their large
surface-to-volume ratio. Many different nanoparticle systems have been created
over the years to influence wound care in the medicine industry. Nanoparticles
can also be tunable to react to external stimuli such as temperature116,
ultrasound117 or light118 which paves the way for targeted affinities toward
certain tissues. Degradable nanoparticles such as polymeric NPs accelerate
wound healing by controlling inflammation, fibroblast, and osteoclast
activity119 and they can also be used as antibacterial agents and stem
cells120.

##  4 Biomimicry and Nano-robots

The recent research explosion in nanotech, with the new discoveries in the
bio-molecular field, has brought about a new era in nanorobotics. Nanorobots
of any nanostructure can currently handle the task of actuation, intelligence,
information processing, sensing, etc. at the nano-scale. Some of the important
functionalities of a nanorobot are (i) decentralized intelligence or “Swarm
intelligence” (ii) self-assemble and replication at nano-scale (iii) signal
processing at nano-scale (iv) nano to macro interface architecture121. In this
section, we review some of the recent approaches in this field.

Fig. 3: Biomimicry in nanorobots. a) Bacillus subtilis, a Gram-positive
bacterium122 A) Bacteria inspired flagellar curly swimmer nanorobot38
[inspired by (a)] b) SEM image from normal circulating human blood showing red
blood cells, several white blood cells, and many small disc-shaped
platelets123 B) Fluorescent images of PL-motors covered with rhodamine-labeled
platelet membranes. Scale bars, 20 µm (left) and 1 µm (right)40 [inspired by
(b)]. (Images in this figure were reproduced from the cited original work,
with permission from their corresponding publishers.)

###  4.1 Biomimetic Bacteria Inspired Nanorobots

Wireless nanorobots have had far-reaching biomedical applications. But so far
most of the micro/nano swimmers have been imitating the rotary motion of
helical bacteria flagella for propulsion, while none of them have the ability
to reform itself in presence of different external stimuli. Recently, magnetic
actuation of self-assembled flagellar nanorobotic swimmers has been
discovered124.

###  4.2 Biomimetic platelet-camouflaged nanorobots

While the main purpose of the industrial and life-sized robots is to work in a
controlled manner, do some pre-determined tasks that are set beforehand, the
task of biomedical nanorobots is to handle the different biological
environments, adapt and improvise to the situation. In 2017, a study was
published on a biologically interfaced nanorobot, which is made of magnetic
helical nanomotors and is cloaked with the plasma membrane of human platelets
102. This kind of nanorobots show platelet imitating properties, like binding
to toxins or special kinds of pathogens.
A different but kind of similar study in 2018, reported the design,
construction, and evaluation of a dual-cell membrane functionalized nanorobot
for removal of biologically threat agents39. In this study, the nanorobots
consisted of gold nanowires and camouflaged in hybrid RBC and platelet
membranes. This kind of nanorobots can fight against biological threats with
no apparent biofouling while imitating natural cells. In the figure 3, the
preparation and characterization of such a nanorobot are shown.

##  5 Biomimicry and Nano Energy Harvest Technology

The population of our beautiful world is expected to increase to 9 billion by
2050125. This will result in an increase in the global energy consumption rate
of 40.8 TW in 2050126. But our fossil energy reserve is decreasing at an
alarming rate, and it is extremely urgent to search for other alternative
energy sources. Of these sources , solar energy has been the most researched,
and the main focus is now to convert as much solar energy as possible to
electrical energy.

###  5.1 Solar Energy

Energy is a must for humankind. The current focus of the world is on non-
polluting sources of energy, and solar energy is the most desirable of them.
98% of photovoltaic cells are silicon based127 but solar cells require 99.999%
pure silicon, which is very energy intensive and its production steps also
create hazardous byproducts.

Biomimicry is now being used to harvest solar energy from sunlight. The
photosynthesis process used by plants leaves no waste. So the inspiration is
there to use biomimicry in the solar cell. One such cell is the Gratzel cell
42 in which Gratzel used anthocyanin to recreate photosynthesis. This cell
does not use silicon or other heavy metals, and this is much greener for the
environment. The downside is that they are not as efficient as silicon cells.

A Gratzel solar cell( also known as a dye-sensitized solar cell or DSSC)
mimics the photosynthetic system by having $T_{i}O_{2}$ as $NADP^{+}$ and
$CO^{2}$, iodide as a water molecule, and -triiodide as oxygen. They harvest
the solar energy together in nano-scale systems 42. A basic DSC cell has an
energy conversion efficiency of 1% under direct radiation. But using thymol
that has 10% of the mass of the dye from cyanin 3-glucoside and cyanin
3-rutinoside improved the efficiency128. The efficiency of DSSCs has exceeded
12% after the last twenty years of development. The amount of light absorbed
within the dye is an important part of determining efficiency. For this
reason, suitable structures can improve the power conversion efficiency
further129,130.

Another approach to improving the efficiency of DSC cells has been the
modification and optimization of titania photoelectrodes. One approach was to
use sphere voids and large-sized solid particles as scattering center131,132
or use multilayer structure133 on the surface of the photoanode. These steps
resulted in an increase in the optical path length of the photoanode and a
subsequent increase in the light absorption efficiency. Another option is to
use new structural materials that can increase the optical path length via
light trapping. Butterfly wings have microstructures that are effective solar
collectors or blocks. Solar heat is absorbed at a faster rate at the ribs in
the wing, which increases the body temperature faster. Then scientists
discovered that honeycomb structures are less reactive than cross-ribbing
structures, and that this structure also has a greater advantage in terms of
light trapping. Scales have a high refractive index, and so total internal
reflection occurs more, and nearly all incident light is absorbed. So,
inspired by this, a butterfly wing scale titania film photoanode improved the
light absorptivity of the DSC photoanode 45. This structure showed perfect
light absorptivity and a higher surface area. This increased the total light
harvesting efficiency and dye absorption.
Bioreplication has also become recently popular due to its application in
solar-energy harvesting. Its application in solar energy is based on two
observations, The first observation is the wide angular field that many
insects, such as flies have. Each eye of a fly is a compound eye, consisting
of multiple elementary eyes. These are arranged radially on a carved surface.
The second observation is the almost halving of the reflectance, which is
calculated by the simulation of a prismatic compound lens adhering to a
silicon solar cell46.
This experimental technique called the Nano4Bio technique47 has been designed
to replicate the layer of a compound eye from the actual specimen. The idea is
that by covering the surface of a solar cell with numerous replicas, the
angular field of view of the solar cell will increase. The Nano4bio technique
can produce multiple replicas simultaneously of multiple biotemplates.
Solar cell efficiency is mainly bound by light-harvesting efficiency, and some
research is being done to use the photosynthetic leaf structures to increase
the solar cell efficiency. Using nano-structured poly-carbonate thin-film
inspired by the leaves of Salvinia cucullata and Pistia stratiotes helped to
design a crystalline Si semiconductor with 18.1% power conversion efficiency
(PCE)134. The light-trapping coating inspired by the epidermal cells in leaves
helped in the fabrication of the graphene/Si Schottky junction135. The leaf
anatomy combined upper and lower epidermis, palisade, and spongy mesophylls.
This upper epidermal layer increases path length and allows light to traverse
deep into the leaf. The middle layer has spongy mesophylls that scatter the
light, and this scattered light has a higher chance of absorption by the lower
part of the chlorophylls.

###  5.2 Ocean Energy

Ocean waves are a great source of renewable energy as they cover almost 70% of
the earth. But unlike solar and wind, ocean wave energy harnessing techniques
have not developed so much yet136, 137, 138. The integration of offshore wind
power plants with ocean wave energy technology could enable power generation
in a low-cost and more efficient way, which is obstructed by the deficit of
matured wave energy harvesting technology139, 140.
To collect energy from wave energy, inspiration from kelp, a marine seaweed,
has enabled the design of a triboelectric nanogenerator (TENG). Using the
conjunction of triboelectric and electrostatic induction effects, TNG can
convert mechanical energy into electrical energy48, 49, 50, 51, 52. Kelp-
inspired TENG is made of vertically free-standing polymer strips which could
sway independently to cause a contact separation with the neighboring strips,
with the vibration of TENG in water mimicking the gentle sway of kelp. A
single unit of BITENG (Bio-inspired TENG) provides an output short circuit
current of about $10\mu A$ and an open circuit voltage of 260V with the
maximum power density of $25\mu Wcm^{-2}$ which is high enough to drive 60
LEDs53. A network of BITENG can collect more energy from ocean waves and be
integrated with the offshore windmill for generating electricity.

###  5.3 Nano Leaves and Nano Trees

Another emerging application of biomimicry in the field of energy harvesting
is nano leaves and stems of artificially created trees or plants44. The nano
leaves are distributed throughout artificial trees and plants, and they can
supply a whole household’s electricity demand in optimum condition141, 142,
143. Nano leaf has two sides, one side has a very thin photovoltaic film that
converts the light from the sun into energy. On the other side, thin thermo-
voltaic films convert the heat from solar energy into electricity43. So, the
sunlight then converts into electricity when it falls onto the nano leaves.
Nano leaves convert both visible light and electrical light. When nano leaves
feel strong winds, they can also convert wind energy to electrical energy. So
nano leaves can create electricity in three ways144, directly convert solar
energy to electricity but can also convert wind energy and solar heat to
electricity.

Inspired by the leaf structure in nature, a biomimetic nanoleaf was developed
for the first time41. The fabricated nano leaves contain thin lamina and
parallel veins, forming a monocot leaf structure. CuO nanowires with a high
density on a conductive Cu mesh were used as the veins to support the layered
double hydroxide(LDH) nanosheet lamina and promote charge transfer.

Fig. 4: Biomimicry and nano energy harvest. a) Compound eye of fly, A)
Nano4Bio technique developed to replicate the corneal layer of a compound eye
from an actual specimen recreated from 47 [inspired by (a)], b) Photograph of
monocot leaf41, B) Biomimetic nano leaf 41 [inspired by (b)], c) Images of
kelp plant 53, C) Schematic diagrams of a TENG-unit, the kelp-inspired TENG
design and the networks53[inspired by (c)],d) Schematic of leaf anatomy which
inspired the light-trapping coating 135, D) Light management mechanism in
bilayer light-trapping scheme with all-dielectric sphere135[inspired by (d)].
(Images in this figure were reproduced from the cited original work, with
permission from their corresponding publishers.)

##  6 Biomimetic Nanostructures and Photonics

Fig. 5: Biomimetic structures in Nanophotonics. a) Actual and SEM images of
the eyes of a moth145146 A) i) Moth eye inspired anti-reflective nano cones.
Upper one is the pointed cone and its SEM image. Lower one is the rounded cone
and its SEM image. The scale bars in the SEM images are all 500 nm [inspired
by (a)] ii) Measured reflectance and transmittance of the moth eye inspired
nano cones and the bare structures147 [inspired by (a)] b) SEM image of
Cryptotympana atrata [cicada species] wing surfaces148149 B) i-iv) Photographs
and SEM image of an omnidirectional anti-reflective glass inspired from Cicada
Cretensis scale71 [inspired by (b)] v) Reflectance sprectra of a pristine
(green lines) and laser treated at one (red lines) or both sides (blue lines)
fused silica plate 71. Reflectance in both cases decreases with the
introduction of biomimetic anti-reflection coating [inspired by (b)](Images in
this figure were reproduced from the cited original work, with permission from
their corresponding publishers.)

Over the years, nature, through evolution, has inspired photonics researchers
by providing a great variety of biological nanostructures. This has enabled
them to design new devices and modify the existing ones to enhance
performance. Prevalent biological photonic structures are developed and
optimized to perform necessary tasks for that creature, such as camouflage,
courtship, warning or attractant to conspecifics, pollination, and so on150,
151, 152. Structural coloration and iridescence of insects, birds’ feathers,
plants 153, 151, 154, 155, 156, densely arrayed triangular hairs on Saharan
ants’ for thermoregulation 157], anti-reflecting coating of the moth and
butterfly eyes 158, 159 and on the transparent wings of hawkmoth160, the
apparent ’metallic’ view of fish-scale 150etc. are the instances of photonic
structures existent in nature. In this section, we’ll review the applications
of such natural structures in the area of nanophotonics. Mainly we’ll review
how biomimetic structures can improve the absorption, reflectance, and
transmittance spectra. Figure 5 summarizes the applications of a few such
biomimetic structures in nanophotonics.

In 1967, Bernhard discovered that the reflection over the visible range (400
to 800 nm) from the corneas of night flying moths is reduced because of their
having tiny conical burls 161, 162. This has led to the discovery of the
artificial moth eye, which is a very fine array of protuberances. The working
of an artificial moth-eye surface may be understood with the help of the
surface layer, which has a gradually changing refractive index having a value
from unity to that of the bulk. Due to the presence of gradually varying
refractive index layers, the net reflectance is the resultant of an infinite
series of reflections at each incremental change in the index. Each of these
reflections has different phase factors because of the change in depth of
different layers. Now if this occurs over a distance of $\frac{\lambda}{2}$,
all the phases will be present, which will result in destructive interference
and so the net reflectance will be zero.

###  6.1 Moth-Eye Nanostructures

The spacing of the protuberances of the moth-eye must be small enough that the
array cannot be resolved by the incident light; otherwise, the array will work
as a diffraction grating and the light will simply be redistributed into the
diffracted orders158. The optical property of an artificial moth-eye surface
depends on the height of the protuberances and their spacing. The pattern of
the moth-eye array is the photo-resist interference fringe at the intersection
of two coherent laser beams162. The advantage of moth eye anti-reflection
coating applied to a high-quality optical component comes at larger angles of
incidence. In the case of normal incidence, the moth-eye has the same
performance as conventional multilayer coating techniques. But at a larger
angle of incidence performance of the former is better than the latter. In a
work presented in 2013, a group showed the comparative study of three
different anti-reflecting structures (ARS) for broadband and angle-independent
anti-reflection54 both theoretically and experimentally. These structures
were: single diameter nanorods (ARS I), dual diameter nanorods (ARS II), and
biomimetic nanotips (ARS III) which take after the submicron structure of
moth’e eyes. The simulations were done using finite difference time domain
calculations. All the structures were made of Si. The structures along with
the refractive index profile are shown in figure 6 (a)-(b).

Fig. 6: (a) Schematic diagram of three types of Si ARS with corresponding
geometrical parameters. (b) The refractive index profile for each ARS. The
refractive index of air, Si and mixture of air/Si is represented by $n_{air}$,
$n_{s}$, $n_{1/2}$ respectively. $n_{z}$ represents the gradient index of
refraction as a function of depth, which is in the z direction. (c)
Reflectance and absorption as a function of wavelength for three types of ARS
with a reference planar Si substrate. R stands for reflectance and A stands
for absorption. (d) Reflectance data for Si wayfer, ARS I, ARS II, ARS III as
a function of angle of incidence (AOI) for unpolarized light, s-polarized
light, and p-polarized light of 633nm wavelength light. The spectrum is almost
independent of incident angle for biomimetic ARS.

The three structures, along with a planar Si wafer (used as reference) were
simulated using FDTD to obtain the results of reflectance and absorption over
250-1100nm. Figure 6(c) shows the resulting reflectance and absorption over
the mentioned wavelength region. From figure 6(c) it is seen that ARS-III has
the lowest reflectance value among the others and in the case of absorption
shown in figure 6(b), it has almost 98 % absorption over the wavelength range.

The dependence of reflectance on the angle of incidence (AOI) was studied from
5∘ to 85∘ using unpolarized, s-polarized, and p-polarized light of 633nm
wavelength. It is seen from figure 6(d) that irrespective of polarization, the
reflectance of ARS III structure shows almost no AOI dependence below brewster
angle ($\sim 75^{\circ}$). From these results, it is concluded that ARS III
inspired by the structure of moth eyes, has shown better performance as anti-
reflector than both ARS I and ARS II.

In the case of the solar cell, the greater the absorption of the incident
light, the greater the efficiency. So moth-eye is integrated into solar cells
to increase the efficiency of solar cells. As we have seen earlier, moth-eye
anti-reflecting coating has virtually zero dependence of reflectance on the
angle of incidence. This property can be exploited in an organic solar cell to
enhance performances55. Forberich et al 55 fabricated a type of organic solar
cell with a moth-eye anti-reflective coating as an effective medium at the
air-substrate interface.

The organic solar cell consisted of a thin ($\sim$ 20 nm) layer of poly
(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonate) (PEDOT:PSS
Baytron, Bayer AG) on indium tin oxide (ITO) coated on a glass substrate. The
moth-eye was introduced at the air-glass interface.

Fig. 7: Measured reflection with and without moth eye from a layer stack of
(a) glass/ITO/PEDOT and (b) P3HT:PCBM solar cell.55

The measurement results are shown in figure 7(a) and (b). From the reflectance
vs wavelength curve for glass/ITO/PEDOT stacks, both curves show oscillatory
behavior due to interference in the dielectric slab. However, in the case of
moth eye/glass/ITO/PEDOT, the overall reflection is reduced due to the
introduction of the moth-eye layer. Figure 7(b) shows the result of state-of-
the-art P3HT/PCBM solar cells with and without moth eyes.

Here it is observed that the highest reduction of reflection occurs in the
range of 350 to 600 nm wavelength range. And beyond that, the reflection
becomes almost identical. This happens because, in the case of longer
wavelengths, most of the incident light is reflected from the metal electrode,
and so the reduction of reflection at the air-glass interface has no
significant effect on the overall reflection. From the measured incident angle
dependence of external quantum efficiency (EQE) of the P3HT:PCBM solar cell
with a moth-eye anti-reflective coating, it is found that at 0∘ incident i.e.,
normal incident, the EQE increases by around 3.5% with the introduction of
moth eyes in a complete solar cell. In fact, EQE is greater with moth eyes
than with the normal solar cell for all angles of incidence.

Zhu et al 56 reported a nanocone solar cell. It had an efficient optical
property with a great processing advantage over nanowire and thin-film solar
cells. The work found that the nanocone arrays had shown absorption above 93%
which was much greater than the nanowire arrays (75%) or thin films(64%) in
the range of 400-600 nm of wavelength57,58.

In another work, biomimetic nanostructured antireflection coatings with
polymethyl methacrylate (PMMA) layers were integrated with silicon crystalline
solar cells. The structure could reduce the average reflectance of solar cells
from 13.2% to 7.8%. As a result, power conversion efficiency increased from
12.85% to 14.2%59.

The anti-reflector moth eye used in perovskite solar cells can improve
performance significantly. All-inorganic carbon-based perovskite solar cells
(PSCs) have drawn increasing interest among researchers due to their low cost
and the balance between bandgap and stability60. However, due to the
reflection at the air/glass interface, such PSCs suffer an optical loss of
about 10% of the incident photons163, 164. This optical loss results in a
reduction in the short circuit current density $(J_{sc})$ for PSCs. The
inclusion of moth-eye antireflection (AR) nanostructures with wide-range-
wavelength AR property has paved the way to solve the optical loss issue of
the above-mentioned PSCs and enhance the power conversion efficiency (PCE)60,
61, 62, 63, 64, 65, 66. Compared to the conventional AR, the additional
benefit of moth-eye ARs is the enhancement of broadband antireflection through
the tuning of structural and geometrical parameters i.e. height, periodic
distance, shape, and arrangement66. Such modulation of optical properties of
moth-eye ARs gives rise to new directions to increase the PCE of PSCs. 300 nm
and 1000 nm inverted moth-eye structured polydimethylsiloxane (PDMS) films
were fabricated using soft lithography and reported in 65. The former one
abated the optical loss at the air/glass interface and enhance the solar cell
efficiency by about 21% from 19.66% and $J_{sc}$ from 23.83 mA/cm2 to 25.11
mA/cm2. The 1000 nm moth-eye structured PDMS films exhibit elegant coloration
due to the interference originating from the diffraction grating effect.
Ormostamp-based moth-eye AR has been fabricated using the nano-imprinting
method and included on the glass side of the all-inorganic carbon-based
CsPbIBr2 PSCs in 60. This resulted in an increase of $J_{sc}$ from 10.89
mA/cm2 to 11.91 mA/cm2 and PCE increased from 9.17 % to 10.08 %. The solar
cell also showed excellent adaptability to higher temperatures up to 200∘.

A superhydrophobic surface is another application of moth-eye structures apart
from the anti-reflection coatings. Moth-eye textured surfaces, due to their
roughness, possess enhanced water-repellent properties, resulting in a
superhydrophobic surface. Such structures have been utilized to fabricate
foldable displays for various electronic devices. The transmission property of
the structures remains almost invariant under different bending, thermal, and
chemical conditions. Hence, the resulting displays show very good anti-
reflective function, excellent mechanical resilience, and foldability, as well
as superhydrophobicity with good thermal and chemical resistance67.

###  6.2 Anti-reflective Transparent Nanostructures:

Greta Oto, commonly known as glasswing butterfly, and the cicada Cretensis
species possesses unique transparent wings with broadband and omnidirectional
anti-reflection property. This property originates from the presence of
nanopillars having periodicity in the range of 150-250 nm on the wing’s
surface resulting in a gradient of refractive index between air and wing’s
membrane68, 69, 70. This property inspired the fabrication of omnidirectional
anti-reflective glass which can show reflectivity smaller than 1% irrespective
of incident angles in the visible spectrum for S-P linearly polarized
configurations71. Such biomimetic anti-reflective transparent materials have a
pervasive application including display, solar windows, optical components,
and devices165, 166, 167, 168, 169, 170, 171, 172. Single-step laser texturing
approach, nanosecond, and femtosecond laser processing systems are used to
fabricate such anti-reflective transparent structures71, 173, 174.

##  7 Biomimetic Nanotechnology in Textile Engineering

Textile has been an integral part of human civilization for a long time.
Humans started using textiles to protect themselves from the cold and other
adverse conditions. With time, the trend and manufacturing process in textile
has amended tremendously. Natural elements showing superhydrophobicity, self-
cleaning property, structural color, and fine quality of fabric have inspired
textile engineers and researchers to develop more sophisticated textiles with
enhanced performances and functionalities. In this section, we’ll review some
of the research work related to nano-biomimicry in the field of textile
engineering.

Fig. 8: a) i) A natural super-hydrophobic surface Lotus Leaf ii) SEM image of
the upper leaf side prepared by ‘glycerol substitution’ with the hierarchical
surface structure consisting of papillae, wax clusters, and wax tubules. iii)
Wax tubules on the upper leaf side. (iv) Upper leaf side after critical-point
(CP) drying and dissolution of wax tubules, which make the stomata visible. v)
CP dried underside leaf shows convex cells without stomata.75 A) A 5$\mu$L
water droplet on the surface of i) untreated ii) the Cot-OTES iii) Cot-Ag-
OTES. It is observed from these figures that with Ag coating the contact angle
is greater than the other two and shows superhydrophobicity. This is inspired
by the superhydrophobicity of the lotus leaf. SEM figure of iv)-v) untreated
and vi)-vii) Cot-Ag samples. The water droplets are seen in the cases of vi)
and vii). viii) UV-transmission spectra for different types of cotton samples.
The UV blocking performance is better in the case of Ag-coated
samples.77(Images in this figure were reproduced from the cited original work,
with permission from their corresponding publishers.)

###  7.1 Water Repellent Textile

Superhydrophobicity and self-cleaning properties are prevalent in nature in
various plants. The most common and notable example is the lotus. Due to the
higher contact angle ($\geq 150^{\circ}$), virtually no wetting of the surface
takes place on a superhydrophobic surface, leading to the property of self-
cleaning. Whenever rain falls on a lotus leaf, the water droplets roll off as
a result of a higher contact angle, and on its way, it collects the dirt or
other material, cleaning the surface and keeping the leaves dry and free of
pathogens72, 74, 73, 76.
Nanotex was founded in 1998. It was based on the idea of superhydrophobicity
i.e., repelling water from a surface. They implemented this natural process
using nanotechnology, where nano molecules bonded to the textiles provided an
efficient stain-repellent mechanism. This eventually led to the removal of
stains and dirt. This technology is now used in over 100 brands around the
world. In another research work published in 2013, the superhydrophobicity of
lotus leaves inspired the development of a simple coating method using silver
nanoparticles (AgNPs). This could facilitate the bionic creation of
superhydrophobic surfaces on cotton textiles with the functionality of water
repellency, antibacterial, and UV blocking77.

In this work, NaOH-soaked cotton fiber was immersed into the aqueous solution
which resulted in the formation of Silver cellulosate which finally formed
AgNPs through reduction of Ag cellulosate by $C_{6}H_{6}O_{8}$ solution. This
Ag-coated cotton fabric was then immersed into the prehydrolyzed OTES
(octyltriethoxysilane) and the final fabric was called "Cot-Ag-OTES". This
fabric was then subjected to ultraviolet-visible reflectance
spectrophotometry, scanning electron microscopy, energy dispersive X-ray
spectroscopy, and X-ray diffractometry for characterization. The
superhydrophobicity was determined by measuring a 5$\mu$L water droplet
contact angle (CA) and shedding angle (SHA). Cot-OTES (The sample without
AgNPs) had a CA of $135^{\circ}\pm 5.2^{\circ}$ and water SHA of $31^{\circ}$.
But with the introduction of AgNps coating, the CA was found to be
$156^{\circ}\pm 3.8^{\circ}$ and SHA of $8^{\circ}$. This proves the
performance enhancement of the water repellence property of the Cot-Ag-OTES
sample.

Figure 8(A)(i-iii) show the optical micrographs of 5$\mu$L water droplets on
the surfaces of the untreated (i) Cot-OTES (ii) Cot-Ag-OTES (iii) fabric
samples. With the introduction of AgNps, the increase of contact angle and
hence the hydrophobic property is evident in this figure. SEM micrographs of
untreated and Agnps treated cotton samples are given in figure 8(A)(iv-v) and
(A)(vi-vii) respectively. In 8(A)(vii), the water droplets are visible on the
sample, ensuring the hydrophobic property. Gram-negative E.coli and gram-
positive S. aureus bacteria were used to evaluate the anti-bacterial property
of the samples. It turned out that the inhibition zone against E.coli and
S.aureus was about 2 and 3nm respectively which indicates high antibacterial
activity.

Transmittance spectra (shown in figure 8(A)(viii) of the samples in the UV
range (280-400nm) were also observed to assess the UV-blocking property. From
this figure, it is pretty clear that the transmittance is very low for AgNPs-
coated fabrics with and without the OTES layer, which manifests itself as
excellent at blocking UV. The sample Cot-Ag-OTES happened to have a
UPF(Ultraviolet Protection Factor) value of 266.01 where UPF$>$40 is
considered to be excellent against UV radiation. So the fabric produced in
this work with Silver Nanoparticles coating on cotton mimicking the lotus leaf
showed excellent performance as superhydrophobic, anti-bacterial, and UV-
blocking fabric.

Bashari et al. proposed a natural element-based water repellent nano-coating
instead of using C8 fluorochemicals compounds onto different fabrics using a
layer by layer self assembly78. To mimic the superhydrophobicity observed in
nature, various water-repellent finishing agents are used. Among them,
fluorocarbons (FCs) possess a unique property of repelling not only water but
also, oil providing a surface tension of $10-20mNm^{-1}$ while coated on a
fabric. However, it has been reported to exert a detrimental effect on the
environment and humans leading to the need for alternative green solutions.
Carnauba wax obtained from a Brazilian tree carnauba palm, formally known as
Copernicia Prunifera, is a natural water repellent agent which has been used
in this proposed method to develop hydrophobic textiles using layer-by-layer
self-assembly. This natural water-repellent nano-coating was deposited on
three types of samples, cotton, nylon, and cotton-nylon fabrics.

Characterization of the solid carnauba nanoparticles was done through various
measurements and experiments. Table 2 shows the contact angles and the
antibacterial effects of the untreated and treated samples. It is seen that
all of the treated samples have significant hydrophobicity for 30 sec and even
after washing. The coated fabrics show enhanced antibacterial effects against
Staphylococcus aureus (S.aureus) and Escherichia coli (E.coli). The coated
fabrics also show good air permeability and thus have paved the way for green
ingredient-based environmentally friendly water repellent textiles.

Table 2: Contact angle and Antibacterial Effect of different samples with water as the wetting medium. Sample | Treatment |  | Averaged Contact
---
angle (degree)
Antibacterial Effect (%)
0s |  | 30s | S. aureus | E.coli
Cotton | Untreated | 45.36 |  | 0 | - | -
Treated | 127.6 |  | 130.9 | 95.75 | 95.1
Treated After Washing | 109.9 |  | 101.7 | - | -
Nyco | Untreated | 141.6 |  | 48.7 | - | -
Treated | 132.1 |  | 135 | 95.75 | 94.6
Treated After Washing | 122.8 |  | 124.9 | - | -
Nylon 6 | Untreated | 128.6 |  | 77.3 | - | -
Treated | 127 |  | 131.4 | 97.78 | 94.1
Treated After Washing | 105.2 |  | 102.4 | - | -

###  7.2 Textile dyeing

Natural instances show a great variety of structural colors that inspired
engineers and designers to design various dyeing techniques and processes.
Biomass pigments, with their sustainability, naturality, and biocompatibility,
have become an interesting research object in cleaner production-focused
textile dyeing. Microbial pigments have the advantage of not being constrained
by season, climate, or geography175, 176, 177, 178, 179, 180, 181.
Prodigiosin, an intracellular metabolite with a pyrrole structure, has bright
colors and antibacterial function, making it attractive to the
researchers80,79.In the past pyrrole structure red pigment was insoluble in
water and had to use organic solvents to extract from the interior of thalli
which increased the cost182,183. Now, if the pyrrole structure pigment is
produced by cell metabolization, it will result in cost reduction and
extraction of microbial pigments can be avoided81. To design this trans-
membrane culture, it is required to mimic the mechanism and substance
transport through the cell membrane. Through the simulation of the artificial
membrane, the chemistry of the preparation and kinetic study of the actual
cell membrane can be conducted. Phospholipid bilayers are dynamic and closely
similar to cell membranes, and this can be used to research trans-membrane
behavior. These phospholipid membrane microbial pigments can cross the
membrane easily for smaller molecular structure media81. It was found in the
work presented in 81 for positively charged substances that the pigments had a
better mass transfer rate than negatively charged segments. The application of
electric fields also boosted the extracellular substance concentration. Using
a permeability agent also improved the permeability of pigments.

##  8 Conclusions

In this review paper, we have summarized and highlighted several state-of-the
art innovations resulted from the application of biomimicry in nanotechnology.
We briefly illustrated how biomimicry can amend various nanotechnology based
field such as nano-sensors, nano-robots, nano-energy harvest and so on. Bio-
compatiable nano robots and sensors built taking inspirations from nature will
play a crucial role in medical science and also in making human life better
and more comfortable. Photonic structures mimicked from natural instances have
paved the way for better performing photonic devices. Artificial nano leaves,
kelp-inspired TENG and using biomimetic nanoparticles in solar cell can
facilitate our energy harness capability. Using nanoparticles and natural
water repellent on fabrics might replace the existing repellent agent and will
be less toxic and more eco-friendly. In a nutshell, application of biomimicry
in nanotechnology can provide unique, eco-friendly and efficient solution to
various problems faced by humans. We deem that the biologists will discover
more astounding information in future and the nanotech researchers will
exploit them to build a better future for human civilization.

## Conflicts of interest

The authors declare no conflicts of interest.

## Acknowledgements

The authors acknowledge the support of both the Department of Electrical and
Electronic Engineering, Bangladesh University of Engineering and Technology,
and the Department of Computer Science and Engineering, Brac Univerisity.

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