J Nanopart Res (2014) 16:2277

DOI 10.1007/s11051-014-2277-6

RESEARCH PAPER

Production of gliadin-poly(ethyl cyanoacrylate)

nanoparticles for hydrophilic coating
Sanghoon Kim • Yeon Seok Kim

Received: 25 September 2013 / Accepted: 13 January 2014 / Published online: 1 February 2014
Ó Springer Science+Business Media Dordrecht (outside the USA) 2014

Abstract Cyanoacrylate nanoparticles have been consisted of hydrophilic moiety (gliadin) and hydro-
usually prepared by anionic polymerization initiated phobic moiety (PECA). The suspension containing
by hydroxyl ions derived from dissociation of water. these nanoparticles showed an excellent coating
In the current research, amine groups on the surface of capability on the surface of hydrophobic materials
gliadin aggregates were utilized as initiator for the such as glass or plastics. A simple spray coating
polymerization of ethyl cyanoacrylate (ECA). Glia- changed the wetting property of the material instantly
din, a protein found in the endosperms of wheat and dramatically. Since both protein and poly(alkyl
(Triticum aestivum L.), is not soluble in water, but cyanoacrylate) are degradable polymers, the devel-
dissolves in aqueous ethanol in the form of aggregates. oped nanoparticles are degradable.
As a result of the reaction with ECA monomers,
gliadin molecules are chemically bound to poly(ethyl Keywords Nanoparticles
Cyanoacrylate

cyanoacrylate) (PECA) chains. The nanoparticles thus Hydrophilic coating
Wetting
Protein
produced are made up of block copolymers that are

Names are necessary to report factually on available data, Introduction

however, the USDA neither guarantees nor warrants the
standard of the product, and the use of the name by USDA
implies no approval of the product to the exclusion of others Poly(alkyl cyanoacrylate) (PACA) nanoparticles
that may also be suitable. have been studied in great detail with a view to their
use as controlled release drug delivery materials
Electronic supplementary material The online version of during the last three decades (Irache et al. 2011;
this article (doi:10.1007/s11051-014-2277-6) contains supple-
mentary material, which is available to authorized users. Vauthier et al. 2003). PACA’s are biodegradable and
can be used for the production of nanoparticles via
S. Kim (&) emulsion polymerization. Currently, preparation
Plant Polymer Research, USDA/ARS/NCAUR, 1815 N.
methods of PACA nanoparticles are well understood,
University Street, Peoria, IL 61604, USA
e-mail: sanghoon.kim@ars.usda.gov whereby nanoparticles with well-defined properties
can be produced. A majority of PACA nanoparticles
Y. S. Kim are obtained through anionic polymerization of the
Engineering Laboratory, National Institute of Standards
corresponding monomer (Nicolas and Couvreur
and Technology, 100 Bureau Drive, Gaithersburg,
MD 20899, USA 2009; Bertholon et al. 2006). In most cases, hydroxyl
e-mail: yeonseok.kim@nist.gov ions in water have been utilized as initiator for the

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production of nanoparticles in previous research. The produced protein-based nanoparticle possesses

Amine groups are also a good initiator for the peculiar properties. It readily adheres to hydrophobic
polymerization of alky cyanoacrylates. In this report, surfaces and improves the wetting property instantly
amine groups of a wheat protein, gliadin, were and dramatically. This report investigates the optimum
utilized as initiator of the polymerization of alkyl condition for the production of nanoparticles, and
cyanoacrylates. Since the initiator itself is a polymer, examines their physical properties. Although any alkyl
amphiphilic copolymers were prepared as a result of cyanoacrylates can be used as a monomer for the
polymerization reaction. In other words, the reaction production of PACA nanoparticles, ethyl cyanoacry-
products are copolymers consisting of two types of late (ECA) was chosen because of its low cost and
homopolymers, protein and PACA. Since proteins are availability.
highly hydrophilic, it works as the hydrophilic end in
the resultant amphiphile molecule because of its
charges on amino acids, while polymerized alkylcy- Experimental section
anoacrylate works as the hydrophobic end because
there is no charge on its chain. In our previous Reagents
research, an animal protein, bovine serum albumin
(BSA) was employed for the production of nanopar- Ethyl cyanoacrylate (ECA) monomer (E–Z Bond,
ticles (Kim et al. 2013). Since the physicochemical viscosity; 5 cps) was purchased from K&R Interna-
properties of BSA are well documented, it served as a tional (Laguna Niguel, CA). ECA contained *0.5 %
model protein for understanding the structure of the of hydroquinone as a free radical inhibitor that
developed nanoparticles. Because of the high cost of prevents the monomer from undergoing free radical-
BSA, however, the commercialization of the devel- induced repolymerization on storage. Gliadin was a
oped nanoparticles was not feasible. Therefore, a gift from MGP Ingredients, Inc (Atchison, KS).
wheat protein (gliadin) was chosen because of its ease Ethanol and Hydrochloric acid were reagent grade.
of preparation and low production cost. The optimum
reaction condition for gliadin is much different from Purification of gliadin
that of BSA because their aggregation behaviors are
significantly different from each other. Gliadin was purified by the procedure used by Hussain
Gliadin belongs to the characteristic class of and Lukow (1997) with minor modification to obtain
proteins known as prolamins, which occur specifically a-gliadin. Gliadin powder was mixed with 5 times
in cereals (Shukla and Cheryan 2001). It is one of the larger volume of 70 % (v/v) aqueous ethanol and
main fractions of gluten found in the endosperms of stirred overnight. Then, the solution was kept over-
wheat. Traditionally, 70 % (v/v) aqueous ethanol has night without stirring, the supernatant was collected,
been used as a solvent for gliadin (Jackson et al. 1983; and ethanol was evaporated by putting the solution in a
Robertson et al. 2004). Most prolamins are enriched in hood for a week. The sedimented precipitate was
glutamine, proline, and hydrophobic amino acids; they discarded, and the residual solution was freeze dried.
are insoluble in water or buffered salt solutions, but The obtained solid was crushed to a fine powder in a
soluble in solutions containing alcohols. Gliadins mold.
show aggregate-forming behavior in aqueous ethanol
solution. They are mainly monomeric proteins with Preparation of nanoparticle suspensions
molecular weights around 28,000–55,000 and can be
classified according to their different primary struc- Particles were prepared by polymerization of ethyl
tures into the a/b, c, and x type. Each gluten protein cyanoacrylate on to the surface of gliadin aggregates.
type consists or two or three different structural 20 mg of gliadin was dissolved in 10 g of x wt%
domains; one of them contains unique repetitive (62 B x B 80) aqueous ethanol solution that was
sequences rich in glutamine and proline. Non-covalent premixed with 40 lL of 4 N HCl. Then, y lL
bonds such as hydrogen bonds, ionic bonds, and (10 B y B 200) of ECA was slowly added during
hydrophobic bonds are important for the aggregation constant stirring with a magnetic stirrer at 500 rpm.
of gliadins (Wieser 2007). Reaction time was set to 40 min to 2 h depending on

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Fig. 1 Schematic diagram

of solution calorimeter

the added amount of ECA (see ‘‘Results and Discus- heat of reaction, the calorimeter was calibrated by
sion’’ for details). As the reaction proceeded, turbidity applying a calculated amount of heat with an electric
was developed indicating nanoparticles were formed heater immersed in Dewar #1.
in the reaction medium. The reaction product was For the estimation of reaction time, reaction was
centrifuged at 100009g for 20 min. The produced performed in 150 g of 68 % aqueous ethanol which is
nanoparticle suspension (supernatant) was collected 15 times larger scale than the usual sample prepara-
and stored at room temperature for the characteriza- tion. The amounts of hydrochloric acid, gliadin, and
tion of nanoparticles. The PECA polymers initiated by ECA were all scaled up 15 times.
the hydroxyl ions without stabilizing agent form large
aggregates because of the intermolecular forces acting Particle size measurement
between their polymer chains. On the other hand,
PECA initiated by protein molecules form amphi- Dynamic light scattering (DLS) experiments were
philes, and do not form aggregates unless PECA carried out with the dispersions using a particle size
polymer chains are too large. Therefore, these two analyzer equipped with a 658 nm diode laser and an
types of polymers can be separated by centrifuge. avalanche photodiode detector (Model 90 Plus,
Brookhaven Instruments Corporation, Holtsville,
Reaction time NY, USA). For the size measurement of gliadin
aggregates, 20 mg of gliadin was dissolved in 10 g of
Reaction time was decided by monitoring the heat of x wt% (62 B x B 80) aqueous ethanol solution that
reaction in a custom-built solution calorimeter was premixed with 40 lL of 4 N HCl. Nanoparticle
(Fig. 1). Polymerization reaction was performed in samples (prepared by the procedure in the previous
Dewar #1, and the temperature variation was moni- section) were diluted twenty times with the same
tored with a thermistor connected to a Wheatstone solvent, and measurements were performed without
bridge. Dewar #2 is for the reference. In this config- filtration. All measurements were done at a 90°
uration, the same amount of heat generated in both detection angle at 20.0 °C. For each sample, ten
Dewar jars at the same time does not contribute to the DLS measurements were conducted and each run
output signal. In other words, the Wheatstone bridge lasted 20 s. All measurements were processed using
circuit cancels out the output as long as the stirring the software supplied by the manufacturer (9kpsdw,
speeds are the same for both Dewar jars. It means that v.5.31). Data from ten measurements were averaged to
only the heat generated (or absorbed) in Dewar #1 obtain the size of nanoparticles. Viscosity of acidified
(reactor) contributes to the output signal. The working aqueous ethanol was measured with Schott ViscoSys-
principle of this design is similar to that of double- tem AVS 360 viscometer (Mainz, Germany) using
beam spectrophotometers. This configuration was Ubbelohde viscometer tube.
necessary because the reaction condition for the
polymerization of alkyl cyanoacrylate requires vigor- Dynamic contact angle (DCA) measurement
ous stirring. The output of the bridge circuit was
digitized and recorded on a computer as a function of Dynamic contact angle analysis was performed using
time. For the conversion of the output voltage to the a DCA 315 (Thermo Cahn Instruments, Madison, WI,

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USA) by the Wilhelmy plate method to determine the on cover slips (12 mm dia.), and washed with flowing
effect of nanoparticle coating on surface wettability water immediately. A Zeiss Ultra 60 Field Emission-
(Lander et al. 1993). Samples for DCA analysis were Scanning Electron Microscope (FE-SEM, Carl Zeiss
prepared by dipping plates made of the material to be Inc., Thornwood, NY) at 5 kV operating voltage was
tested into the nanoparticle suspension and rinsing used to acquire surface images of the coatings. All
with a stream of distilled water a few seconds. The SEM samples were sputter coated with 3 nm of Au/PD
prepared plate was consecutively immersed in and (60/40 mass fraction %) prior to SEM imaging.
removed from distilled water at a speed of 60 mm/
min. Curves relating the interfacial tension to the
immersion depth were plotted and used to calculate the Results and discussion
receding contact angle. A representative contact angle
was calculated for each formulation using the mean Aggregate formation of gliadin in aqueous ethanol
and standard deviation of five independent measure-
ments. DCAs were determined from a simple force Gliadin belongs to prolamin; therefore, it does not
balance equation, Fm = mg ? pcL cos(h) - Fb where dissolve in water, but dissolves in 65 % (w/w) aqueous
Fm is the measured force, mg is weight of the plate, p is ethanol (i.e., 70 % (v/v) aqueous ethanol) (Bietz and
the perimeter of the meniscus formed at the interface, Wall 1980). Even in aqueous ethanol solutions, it
cL is the surface tension, pcL cos(h) is the surface forms aggregates, and the size of aggregate varies
tension force acting on the meniscus, and Fb is the depending on the content of ethanol in the solvent
buoyance force (Davies et al. 1996). When the plate is mixture. This aggregation behavior in acidified aque-
right at the surface of liquid, Fb equals zero. The ous ethanol was investigated by DLS (Fig. 2). The
surface tension cL for all samples was calculated from procedure for sample preparation was specified in the
receding contact angles (h) in distilled water. The Experimental section. As the percentage of ethanol
receding contact angles (h) were calculated from increased from 62 to 69 % (w/w), the hydrodynamic
surface tension cL of distilled water at room temper- diameter (Dh) of gliadin decreased and increased again
ature. Two materials used as plate were cover glass with higher percentage of ethanol. It means that the
(30 9 24 9 0.17 mm, Fisher Scientific, Pittsburgh, size of gliadin aggregate is the smallest in 69 %
PA) and poly(ethylene terephthalate) (PET) sheet aqueous ethanol. This behavior is similar to that of
prepared from a water bottle (30.4 9 25 9 0.13 mm, zein which shows minimum size at around 90 % (w/w)
Aquafina, Dallas, TX). aqueous ethanol (Kim and Xu 2008). The reason for
showing a minimum in the DLS data is that there is a
Thermogravimetric analysis structural inversion of aggregates (Kim et al. 2010). In
other words, the surface of gliadin aggregates in lower
For the composition analysis of produced nanoparti- than 69.5 % ethanol is hydrophilic, while that in
cles, thermogravimetric analysis (TGA) was per- higher than 69.5 % ethanol is hydrophobic. Since
formed using a TGA 2050 (TA Instruments, New gliadin also showed a similar behavior (but at different
Castle, DE). Freeze-dried samples (*3 mg) were ethanol contents), both zein and gliadin had been used
heated in a platinum TGA pan in an air atmosphere. as binder for the fabrication of polymer composites
Each sample was heated from room temperature to (Kim 2008, 2011). According to the DLS data, the
180 °C at 20 °C/min, and then held at 180 °C for hydrodynamic diameter of gliadin aggregates in
100 min. For data analysis, results were viewed as acidified 69 % ethanol is around 32 nm. Knowing
weight % vs. time. that the MW of a-gliadin ranges 28–35 kDa (Wieser
2007), while that of Bovine Serum Albumin is 67 kDa
Surface morphology of adsorbed nanoparticles (Dh = 7.6 ± 0.4 nm) (Adel et al. 2008), it is esti-
mated that each aggregate is an assembly of more than
The surface morphology of adsorbed nanoparticles on one hundred gliadin molecules.
the surface of glass was observed with a scanning When the ECA monomers are polymerized on the
electron microscopy (SEM). Samples prepared from surface of these gliadin aggregates, reaction will occur
nanoparticles with 77 % PECA content were sprayed on the surface of the gliadin aggregates. This means

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700 the pH of the reaction medium (Behan et al. 2001).

500 Neutral water supplies too much hydroxyl ion which
hyd
drophilic surface hydrophobic surface
causes formation of large chunks of poly(ethyl cya-
300
noacrylate) (PECA) aggregates instead of
nanoparticles.
D (nm)

For the production of nanoparticles, anionic poly-

merization of alkyl cyanoacrylate has been commonly
h

100
80 used with hydroxyl ions as an initiator (Vauthier et al.
60 2003). For this project, however, amine groups on the
40 surface of gliadin molecules are used as initiator. As a
result of this polymerization, copolymers are pro-
duced. Since gliadin is hydrophilic and PACA is
20
60 65 70 75 80 hydrophobic, the resultant copolymer will behave as
wt% EtOH an amphiphile. In our reaction condition, ethyl
micellar inversion cyanoacrylate (ECA) monomers will react with
Fig. 2 Gliadin is an amphiphilic biopolymer. It shows micellar aggregated gliadin, and the produced nanoparticles
inversion as the percentage of ethanol changes will look like gliadin aggregate covered with PACA
polymer chains (Fig. 3).
In order to make sure that the amine groups in
that the size of produced particles will get larger as protein molecules initiate the polymerization reaction
more monomers are involved in the polymerization. of ECA, the three chemical groups in the protein
Since the size of reaction product (i.e., nanoparticles) molecules, i.e., amine, carboxyl, and hydroxyl groups,
needs to be small to form stable suspensions, the size were examined in acidified aqueous ethanol. For this
of gliadin aggregates before the reaction with ECA purpose, a compound that contains only one of the
monomers has to be as small as possible. According to aforementioned chemical groups was added in the
Fig. 2, 65–70 % ethanol fulfills this requirement. reaction medium instead of protein. Since our reaction
Since 69 % ethanol is too close to micellar inversion, medium contains plenty of ethanol, it is obvious that
68 % ethanol was selected as a reaction medium for hydroxyl group is not the initiator. In order to examine
the polymerization of ECA. carboxyl groups, oleic acid and acetic acid were tried,
but the result was negative. On the other hand, when
Reaction scheme butyl amine was tried, it was found that the initiation
of the reaction was extremely fast. The polymerization
In the case of conventional synthesis of nanoparticles reaction was even initiated by the small amount of
from cyanoacrylates, nanoparticles are fabricated in an butyl amine vapor on the top of reaction mixture. In
aqueous medium that is acidified with hydrochloric other words, ECA was polymerized in the air, before it
acid. Since cyanoacrylates are hydrophobic mono- is immersed in the solution and mixed with butyl
mers, they are not soluble in water. Therefore, the amine. Therefore, there is no doubt that amine groups
reaction has been performed via emulsion polymeri- in protein molecules work as initiator for the poly-
zation, while the reactant mixture is vigorously stirred merization of cyanoacrylate.
(Behan et al. 2001). In our reaction scheme, amine The size of nanoparticles depends on the amount of
groups on the surface of protein (gliadin) molecules ECA monomers reacted with each protein molecule.
react with ECA. By choosing 68 % aqueous ethanol as Since the reaction rate depends on the concentration of
a reaction medium, a two-phase reaction was avoided: reactants, the required reaction time was investigated
aqueous ethanol is more hydrophobic than water, by varying the amount of ECA per 20 mg of gliadin. It
allowing both gliadin and ECA to dissolve in the same is expected that the reaction proceeds until all
reaction medium without showing phase separation. monomers are consumed for the polymerization
Acidic condition was necessary to control the size of reaction. Data from solution calorimeter show that
nanoparticles and reaction rate. It is known that the this polymerization reaction is highly exothermic and
size distribution of produced nanoparticles depends on the reaction time varies depending on the amount of

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Fig. 3 Schematic of the gliadin-ECA coploymerization reaction

Fig. 4 Effect of monomer amount on reaction time-measured Fig. 5 Hydrodynamic diameter of the produced nanoparticles
by a solution calorimeter. The amount of ECA per 20 mg of measured by DLS
gliadin was specified on each curve

nanoparticles would increase as more ECA monomers

added ECA monomer (Fig. 4). The termination of the are added to the given amount of gliadin, and the
reaction is indicated by arrows in the figure, and the additionally added ECA will increase the chain length
termination time on each curve is used as a minimum of PACA in the corona. This prediction was supported
required reaction time. The negative slope after the by the data obtained by DLS experiment (Fig. 5).
termination of reaction indicates the loss of heat to the When more than 120 lL was added to 20 mg gliadin,
surroundings. Because of the long reaction time, heat an unstable nanoparticle suspension was obtained
loss from the reaction mixture to surroundings was whereby Dh data from DLS were not reproducible.
clearly recorded, although the reaction was performed
in the Dewar jar. Composition of nanoparticles

Size of produced nanoparticles As was stated in the Introduction section, ECA can
also be polymerized with hydroxyl ions as an initiator.
Since the produced nanoparticles are the polymeriza- Therefore, there should be a competition of the two
tion reaction product of ECA initiated by the amine initiators, amine groups on gliadin molecules and
groups on the surface of gliadin aggregates, gliadin hydroxyl ions that were dissociated from water. For
molecules are in the core of the produced nanoparti- hydroxyl ion-initiated products, particles are easily
cles, while PECA chains are in the corona. Therefore, precipitated if a stabilizer (e.g., dextran) is not used
it is expected that the size of the produced (Sommerfeld et al. 1997). On the other hand, amine-

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100 100
100% gliadin Assumed no s ide reaction

PECA fraction in product (%)

Actual PECA in product (%)
80 80
63.4% gliadin
Wt. (%)

60 60
48.5% gliadin

40
32.1% gliadin 40

19.1% gliadin
20
20
13.6% gliadin
Gliadin fraction before reaction

0
0 20 40 60 80 100 0
t (min) 34.6% 51.5% 67.9% 80.9% 86.4%
ECA fraction in reactant
Fig. 6 Thermodiagram of nanoparticles obtained by heating at
180 °C. The weight fraction of gliadin in the mixture Fig. 7 Weight fraction of PECA in the product showing the
(gliadin ? ECA) is specified on each curve effect of side reaction

initiated nanoparticles form a stable suspension with- all ECA monomers were consumed by protein-initi-
out a stabilizer. Therefore, these two types of reaction ated polymerization. The difference in the PECA
products can be separated by centrifugation. After the fraction corresponds to the polymerization of ECA
centrifugation, the precipitates, i.e., hydroxyl ion- initiated by hydroxyl ion.
initiated particles, are removed from the reaction Each gliadin molecule contains many amine groups
product. It means that the weight fraction of PECA in that can be used as an initiator of the polymerization of
the prepared nanoparticle is smaller than the weight ECA. Although it is not known how many of them are
fraction of ECA in the reactant. In order to understand located on the surface of gliadin aggregates, it is
the composition of nanoparticles, TGA was performed reasonable to assume that more than one PECA chain
(Fig. 6). is attached to each gliadin molecule. Therefore,
The TGA thermogram was obtained by setting the produced nanoparticles can be described as an assem-
temperature to 180 °C and monitoring weight loss of bly of (PECA)n-gliadin star copolymers, where PECA
the nanoparticle samples. Since gliadin degrades at chains are localized on the surface of each gliadin
higher than 250 °C, while PECA begins to degrade at molecule (Gao and Matyjaszewski 2009).
around 110 °C, the weight loss at 180 °C was
supposed to be due to the degradation of PECA only. Adhesion of nanoparticles
In actual situation, gliadin contains moisture that
begins to evaporate as the sample is heated (Fig. 6). The produced nanoparticles readily adhere to hydro-
Therefore, the weight loss of the sample is due to both phobic surfaces. Simple spraying on the target surface
PECA and the moisture in gliadin. Figure 6 shows that followed by washing with flowing water induces
more decrease in the weight of product is observed as adherence of nanoparticles. The reason for washing
higher percentage of ECA is included in the reactant. with flowing water is to remove trace of ethanol from
If the polymerization reaction is initiated by protein the coated surface. The adhesion of nanoparticles (i.e.,
only, there should be no precipitation, whereby ECA coating) takes place instantly and the coated surface
fraction in the reactant is the same as PECA fraction in turns hydrophilic. Any hydrophobic surfaces such as
the product. Because of the side reaction, i.e., glass panes, plexiglases, stainless steel, porcelain, and
hydroxyl ion-initiated polymerization, however, the polymer films that were made of polyethylene,
PECA fraction in the product is always smaller than polypropylene, polystyrene, or PET, etc., could be
the ECA fraction in the reactant. This situation is coated. A demonstration of this behavior on the
presented in Fig. 7 by comparing the actual PECA window glass of a car is shown in Fig. 8. For direct
fraction in the nanoparticle with the case that assumed comparison, only front window glass was coated with

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Fig. 8 Demonstration of wetting behavior: Driver’s seat glass windows, the sprayed water formed a thin water layer
window was coated with nanoparticles, while rear passenger instead of forming water droplets
window was uncoated. When water was sprayed on both of the

nanoparticle, and both windows were sprayed with 60

water. In the case of uncoated glass, sprayed water
PS
formed droplets on the glass surface. On the other 50 glass
hand, sprayed water on the surface of nanoparticle-
Contact angle (°)

coated glass formed a thin water layer, and subse- 40

quently sprayed water did not form droplets on its
surface. It means that the hydrophilic coating on 30
window glasses greatly improves visibility on rainy
days. If no more water is sprinkled on the surface of 20
glass, the coated surface dries quickly, while uncoated
surface dries very slowly. The accelerated drying of 10
the coated surface should be caused by two reasons:
(1) in the case of a thin water layer on the coated 0
before coating 65% PECA 77% PECA 82% PECA
surface, the weight of water to be evaporated should be Coating
much less than that the water droplets on the uncoated
one. (2) The surface area per gram of water is much Fig. 9 Contact angle of nanoparticle-coated surfaces
larger in the case of a thin water layer.
For quantitative evaluation of the functionality of
produced nanoparticles, contact angle was measured PECA fraction contained in nanoparticles increases
before and after the coating. Data from a glass plate from 65 to 82 %, the size of nanoparticles increases in
and a polystyrene (PS) sheet are shown in Fig. 9. the same order. According to the data shown in Fig. 9,
Compared with glass plates, PS is more hydrophobic the effect of adhesion of nanoparticles was not
material. Therefore, its contact angle is much larger dependent on the size or percentage of PECA of
than that of the glass plate. After coating with nanoparticles. All the examined nanoparticles showed
nanoparticles, an enormous decrease in contact angle a good enough functionality as a coating material.
was observed with both PS and glass plates. The morphology of nanoparticle-coated glass sur-
The nanoparticles used in this experiment contain face was observed with SEM (Fig. 10). SEM revealed
the same amount of gliadin. In other words, as the that the nanoparticles were pretty much evenly spread

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Fig. 10 SEM image of adsorbed nanoparticles on the surface of glass plate that was coated with nanoparticles containing 77 % PECA

over the glass surface. The size of nanoparticles is in 120 °C, the cyanoacrylate part of the nanoparticle will
the range of 30–80 nm. Since nanoparticles that degrade quickly. In the case of protein moiety,
contain 77 % PECA were prepared by reacting decomposition by microorganisms is the main degra-
20 mg gliadin with 80 lL ECA, the hydrodynamic dation pathway in nature (Morihara and Oda 1992).
diameter measured by DLS was supposed to be around
90 nm. Considering the harsh condition for sputter
coating of samples, it is probable that gliadin mole- Conclusions
cules will be dehydrated and the PACA chains will not
be extended as much as those in aqueous ethanol In this article, it is shown that surface modifying
solution. Since the size of adsorbed particles is smaller nanoparticles can be produced by utilizing amine
than the wavelength of visible light and the coated groups on the surface of protein (gliadin) aggregates as
surface was not fully covered, the SEM image explains initiator for the polymerization of ethyl cyanoacry-
why the visibility of the glasses is not affected by lates. Unlike conventional reactions for the prepara-
coating. tion of cyanoacrylate nanoparticles, acidified aqueous
ethanol as a solvent offered a one-phase reaction. The
Degradation of nanoparticles produced nanoparticle has a strong adsorption char-
acteristic that changes the wetting property of hydro-
Since both protein and PACA are degradable poly- phobic materials. Since the average diameter of
mers, the developed nanoparticles are degradable. The adsorbed nanoparticles is much smaller than the
produced nanoparticles will not be used in vivo. wavelength of visible light, transparent materials such
Therefore, a reverse Knoevenagel reaction which as glass or Plexiglas can be coated with the presented
releases formaldehyde is the most possible degrada- nanoparticles without deteriorating transparency. This
tion pathway of cyanoacrylate moiety of nanoparticles characteristic is useful for improving visibility on
(Fattal et al. 1997). In addition, heat is another possible rainy days because it suppresses water-droplet forma-
degradation pathway according to the thermodiagram tion on the surface of nanoparticle-coated windows.
obtained by TGA. If any material was coated with the Since hydrophilic coating leads to the formation of a
produced nanoparticles and exposed to higher than thin water layer instead of water-droplet formation, the

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hydrophilic coating also accelerates drying. Self- Irache JM, Esparza I, Gamazo C, Agueros M, Espuelas S (2011)
cleaning by a rainfall is another advantage of hydro- Nanomedicine: novel approaches in human and veterinary
therapeutics. Vet Parasitol 180:47–71
philic coating. Jackson EA, Holt LM, Payne PI (1983) Characterisation of high
molecular weight gliadin and low-molecular-weight glu-
Acknowledgments The authors would like to express tenin subunits of wheat endosperm by two-dimensional
appreciation to Mr. Jason Adkins for his technical support electrophoresis and the chromosomal localisation of their
during this experiment. controlling genes. Theor Appl Genet 66:29–37
Kim S (2008) Processing and properties of gluten/zein com-
posite. Bioresour Technol 99:2032–2036
Kim S (2011) Production of composites by using gliadin as a
bonding material. J Cereal Sci 54:168–172
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