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Development of antimicrobial Ion Jelly fibers

  • Instituto de Biologia Experimental e Tecnológica IBET/ Instituto de Tecnologia Química e Biológica (ITQB)

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We report a method to obtain electrospun fibers based on ionic liquids and gelatin, exhibiting antimicrobial properties.
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Development of antimicrobial Ion Jelly bers
Renato dos Santos,
Angelo Rocha,
Ana Matias,
Catarina Duarte,
Isabel S´
Nuno Lourenço,
ao Paulo Borges*
and Pedro Vidinha*
We report a method to obtain electrospun bers based on ionic liquids and gelatin, exhibiting
antimicrobial properties.
The improvement of biodegradable biomaterials has greatly
impacted the development of modern biology and medicine.
The great advantage of these materials results from the fact that
they can be broken down and removed aer they have served
their purpose. The applications of this type of polymers goes
from surgical sutures and implants to more advanced
approaches, such as tissue engineering and drug delivery. To
meet this functional demand, materials should be designed so
as to exhibit certain physical, chemical, biological, biome-
chanical, and degradation properties. In this respect a wide
range of natural (e.g. collagen,
synthetic (e.g. PLGA
)) biodegradable polymers have been
Gelatin is one of the most versatile biomaterials to fulll the
above challenges. It is a widely available natural polymer that is
prepared through thermal denaturation of collagen, aer acid
or alkaline pre-treatment.
Gelatin is commonly used for
dierent pharmaceutical and medical applications due to its
biodegradability and biocompatibility in physiological envi-
For instance, it is commonly used as a plasma
as an ingredient in drug formulations,
and as a
sealant for vascular prostheses.
Over the last years, several
modications have been introduced in the gelatin structure
with the aim to achieve new physical and chemical properties.
In this respect, we have recently reported a new biomaterial
obtained by cross-linking gelatin and an ionic liquid (IL),
designated Ion Jelly.
Ion Jelly can be described as a polymeric
material that combines the chemical versatility of an IL with the
morphological and mechanical versatility of gelatin. The
interest in the use of ILs has grown exponentially in the last
decade, mostly motivated by their tailor-made properties and
wide range of applications.
The combination of ILs with
gelatin has been shown to be an interesting and promising
strategy not only to prepare transparent, exible and conduct-
ing lms for dierent electrochemical devices,
but also as an
enzyme immobilization matrix
and hydrogels.
Recently, we reported the preparation of Ion Jelly bers
trough electrospinning in order to obtain high surface area
conductive materials.
Electrospinning is a technique that uses
electrostatic charges to produce bers from polymer melts or
polymer solutions.
Solid bers are obtained from electried
jets that are continuously elongated due to the electrostatic
repulsions between the surface charges and the evaporation of
Some applications, such as drug delivery systems or
tissue engineering, usually rely on nanoscale or sub-micrometer
structures because of their unique properties, namely increased
surface area or the ability to mimic the structural dimension of
extracellular matrices.
Some of these systems are composed
of polymer bers, and electrospinning has been shown to be a
straightforward technique to produce bers that can reach
nanometer sizes.
Nevertheless, the number of reports on the
preparation of bers with intrinsic antimicrobial properties is
very limited.
Chitosan has a polycationic nature that imparts
non-toxic, biocompatible, biodegradable and bioactive proper-
to chitosan based materials, but most other polymeric
bers have a propensity not to be biodegradable.
The development of a simple and friendly methodology that
could produce biodegradable antimicrobial bers in an easy
manner would be an important step for the development and
REQUIMTE, Departamento de Qu´
ımica, Faculdade de Ciˆ
encias e Tecnologia,
Universidade Nova de Lisboa, 2829-516 Caparica, Portugal. E-mail: pm.gomes@fct.
IBB-Institute for Biotechnology and Bioengineering, Centre for Biological and
Chemical Engineering, Instituto Superior Tecnico, Av. Rovisco Pais, 1049-001
Lisboa, Portugal. E-mail:
IBET/ITQB-UNL Instituto de Biologia Experimental e Tecnol´
ogica e Instituto de
Tecnologia Qu´
ımica e Biol´
ogica, Aptd. 12, 2780 Oeiras, Portugal
CREM Centro de Recursos Microbiol´
ogicos, Faculdade de Ciˆ
encias e Tecnologia,
Universidade Nova de Lisboa, Quinta da Torre, 2829-516 Caparica, Portugal.
CENIMAT/I3N, Departamento de Ciˆ
encia dos Materiais, Faculdade de Ciˆ
encias e
Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal. E-mail:
Electronic supplementary information (ESI) available: See DOI:
Cite this: RSC Adv., 2013, 3, 24400
Received 8th August 2013
Accepted 10th October 2013
DOI: 10.1039/c3ra44258f
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application of these materials. Our goal was the development of
Ion Jelly bers displaying antimicrobial properties, based on
the combination of an antimicrobial IL with gelatin. For that
purpose, choline based ILs were synthesized, combining
choline chloride and an antimicrobial acidmandelic acid.
Concerning the use of ILs on the preparation of biomate-
rials, namely bers, there are some aspects that need to be
reected upon. One of the most important aspects is
biocompability. It is well known that the selection of both
cation and anion is crucial to obtain biocompatible ILs.
Choline ILs meet this criterion, and have been used in dierent
applications, including as cross-linking agents for collagen
based biomaterials.
In addition, choline based ILs have been
reported to be active antimicrobial agents against cocci, rods,
and fungi.
Herein we report the preparation of biocompatible Ion Jelly
bers through with intrinsic antimicrobial properties, using
All reagents and solvents were obtained commercially unless
otherwise noted, and appropriately puried if necessary.
Gelatin was purchased from Panreac (Cultimed). Choline
chloride was purchased from Alfa Aesar (98 + %). (R)-Mandelic
acid (98%) was purchased from Fluka.
Synthesis of ILs
The ILs [Ch][Ac] (choline acetate), [Ch][Ib] (choline ibuprofen-
ate), [Ch][Ma] (choline mandelate) and [Ch][Ti] (choline tiglate)
were synthesized in our laboratory and details are provided in
the ESI.
Ion Jelly preparation
Aqueous gelatin solutions (blanks) 120 mg of gelatin were
dissolved in 280 mL of distilled water to obtain a concentration
of 30% (w/w). To produce Ion Jelly bers, gelatin was main-
tained at 30% (w/w) while water was replaced respectively by
40 mL, 80 mL and 120 mL in order to yield solutions with IL
concentrations of 10, 20 and 30% (w/w). All solutions were
prepared under magnetic stirring at 40 C. The water contents
of both IL and Ion Jelly materials were determined by Karl
Fischer titration.
The Ion Jelly solution was poured into a 1 mL syringe tted with
a 23-gauge needle, which was then placed on the infusion
syringe pump (KDS100) to control the solution feed rate. A
conducting ring, 15 cm diameter, was held coaxially with the
needle tip at its center, and electrically connected to it. The
needle and ring were directly connected to the positive output of
a high-voltage supply (Glassman EL 30 kV). Aer applying the
electric potential between the metallic syringe-tip and the
collector, the solution was continuously fed to the syringe-tip at
a constant ow rate, and accelerated towards the grounded
collector target by the ensuing electric eld (a standard elec-
trospinning setup). Stainless steel grids were used as collector.
All this equipment was located inside an acrylic box in order to
control temperature and humidity, which were kept constant in
all experiments.
Dierential scanning calorimetry (DSC)
DSC results were obtained at Laborat´
orio de An´
(REQUIMTE) using a Setaram DSC131 at a scan rate of 20 C
. Two cycles were performed and samples were kept at
90 C for 5 minutes between them. The results shown are those
for the second heating cycle. Thermograms are available in
the ESI.
Quantication of IL in Ion Jelly electrospun bers
Quantication of IL [Ch][Ma] was performed in a Beckman
Coulter DU 800 spectrophotometer. The calibration curve for
the IL quantication was obtained with the absorbance
readings of four IL [Ch][Ma] standards. The blank used was a
gelatin aqueous solution. Details in the ESI.
Fiber characterization
Optical microscopy (OM) and scanning electron microscopy
(SEM) were used to evaluate ber morphology. The optical
microscope used was an Olympus BH-2. For SEM analysis, the
bers were coated with a gold/palladium alloy with a Polaron
SC502 sputter coater, and the microscope used was a Zeiss DSM
962. Samples were suspended over two strips of carbon
conductive tape.
Antimicrobial activity assessment
The agar diusion test KirbyBauer disk diusion method
was used to evaluate the antimicrobial properties of IL [Ch]
[Ma]. Paper disks (1 cm
) and Ion Jelly bers were put in agar
plates inoculated with 100 mL of the previously diluted pre-
inoculum and were incubated during the rst 3 hours at room
temperature followed by an overnight incubation at 37 C. In
the case of Ion Jelly bers, a 1 cm
stainless/plastic collector was
used. The bacteria used for the agar diusion tests were Bacillus
subtilis 168 (B. subtilis) and Escherichia coli K-12 (E. coli). Both
were pre-inoculated in 5 mL of LB medium and incubated for 16
hours in a Sanyo orbital incubator Orbi-Safe Ts. For all anti-
microbial tests, the pre-inoculums were rst diluted in LB
medium in a 1 : 50 proportion prior to the inoculation of agar
plates (containing LB medium (LAB M) with 1.6% w/v of agar
concentration), except where mentioned otherwise.
Biocompatibility assessment
Choline salts were investigated for biocompatibility using the
3-[4,5-dimethyltriazol-2-y1]-2,5-diphenyltetrazolium (MTT) cell
viability assay with CaCo-2 cell lines. All the ILs were tested in a
concentration range up to 16 000 mM. CaCo-2 cells were
cultured in 0.5% fetal bovine serum (FBS) for 24 h and then
incubated for 4 h with the ILs in a 5% FBS medium. Aer this
period, 100 mL of the colorimetric reagent MTT (0.5 g L21) was
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added to each well and lefor 4 h. MTT is reduced to a purple
formazan product by mitochondrial reductase enzymes active
in viable cells and therefore the amount of formazan product is
proportional to the number of viable cells. Reaction was
stopped with 150 mL DMSO in each well and formazan was
quantied by measurement of the absorbance at 540 nm in a
plate reader. Each sample was incubated in three dierent wells
and three dierent measurements were obtained. The ratio
between the absorbance of IL treated cells and the absorbance
of solvent treated cells (control) was used to determine the cell
viability. This parameter was represented as a function of the
base 10 logarithm of the IL concentration (mM).
Fiber production optimization
Gelatin is not oenly used in the electrospinning process
because of its high degree of hydrogen bonds. Highly polar
solvents, such as ILs, acidic conditions or temperature increase
are successful strategies for reducing intermolecular interac-
Ion Jelly (IJ) ber production through electro-
spinning was reported by Pimenta et al.,
who used [C
]. Based on the experience acquired then, using dierent
ILs, some adjustments were needed in order to obtain bers
with choline based ILs. Parameters such as polymer and IL
concentration, applied voltage, distance between the needle tip
and the collector, ow rate, solution conductivity, temperature
and humidity were tuned in order to obtain choline-based IJ
electrospun bers without defects. Details are provided in
the ESI.
The optimized conditions for the electrospinning of IJ using
choline-based ILs are presented in Table 1.
Choline based IJ bers obtained through electrospinning
have mean sizes around the lower end of the micrometer range
(Table 2). It is also evident that changing the anion of these ILs
has little or no eect on ber diameter.
IJ-ber morphology can be evaluated by SEM images. Fig. 1
reveals that the electrospinning of choline-based IJ solutions
under conditions described in Table 1 yielded sub-micrometer,
defectless and bead-free bers. In line with previous observa-
tions, images suggest that changing the IL does not have a
signicant eect on ber morphology (Fig. 24).
Thermal characterization
Both choline-based ILs and IJs were submitted to DSC analysis
to analyze their phase transitions. The thermograms (presented
in the ESI) reveal that the IJs keep their structural properties in
a wide range of temperatures. Glass transition temperatures
), displayed in Table 3, were observed for IL [Ch][Ac], IL
[Ch][Ti], but not for IL [Ch][Ib] and IL [Ch][Ma]. On the other
hand, all IJs exhibited a T
, with the exception of IJ [Ch][Ib]
(despite having a slight curve inection on the thermogram
curve around 25 C). Even though IL [Ch][Ma] did not exhibit
, the resulting IJ [Ch][Ma] has a T
¼62.3 C. Noteworthy is
the absence of endothermic peaks in the IJs curves related to
denaturation of the triple-helix crystalline structure of gelatin.
Bigi et al. veried that various gelatin samples (with and
without cross-linking) showed a denaturation temperature
around 41 C.
The absence of endothermic peaks in this
region suggests that ILs interact with gelatin in such a way as to
hamper the ability of polymer chains to renaturate upon
Antibacterial activity
One of the aims of the present work was to evaluate if IL
encapsulation in IJ electrospun bers was an eective way to
improve the antibacterial ecacy of a given IL. To evaluate this
possibility, IL [Ch][Ma] and IJ [Ch][Ma] bers were selected
for comparison of their antimicrobial properties with those of
mandelic acid, using the agar diusion test. Our results show
that there is no loss of antibacterial properties of the mandelate
anion in the IL [Ch][Ma]. However, there is a striking dier-
ence between the mandelic acid solution and IL [Ch][Ma]
regarding antibacterial ecacy (see Table 4). This outcome is
possibly related with the higher viscosity of the IL and with
reduced diusion in the paper disk matrix, or reduced perme-
ability of the IL in cell membranes, compared with
mandelic acid.
Additionally, a stainless steel square (1 cm
area) was used to
collect the IJ [Ch][Ma] bers, that were aerwards placed on an
agar plate previously inoculated with E. coli. Our results show
that IJ bers clearly enhance the antibacterial ecacy of the IL
[Ch][Ma]. In fact there is an almost four-fold increase on the IL
antimicrobial eciency aer encapsulation of the IL in elec-
trospun bers. The same amount of IL can be released in a more
ecient way because the higher surface area of the bers
improves IL diusion towards the medium and consequently
towards bacterial membranes, reducing the problem associated
Table 1 Optimized conditions for electrospinning of choline-based IJ solutions
IJ solution % IL v/v % Gelatin w/v Voltage (kV) Distance (cm) T(C) Humidity (%) Flow rate (mL h
IJ [Ch][Ac] 15 30 15 15 40 20 [0.14]
IJ [Ch][Ma] 23 30 15 15 40 20 [0.14]
IJ [Ch][Ti] 15 30 15 15 40 20 [0.14]
IJ [Ch][Ib] 23 30 15 15 40 20 [0.14]
Table 2 Mean diameters (mm) of IJ electrospun bers
IJ-solution IJ [Ch][Ac] IJ [Ch][Ma] IJ [Ch][Ti] IJ [Ch][Ib]
1.08 0.25 1.06 0.23 1.23 0.33 0.96 0.23
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to high viscosity of this IL. This strategy enabled the IL to reach
nearly the same eciency as mandelic acid (disk 2).
This antimicrobial assessment was also performed against
the Gram-positive bacteria B. subtilis. The same procedure for E.
coli was adopted. To avoid wire collector oxidation interference,
IJ bers were tested in a square-shaped plastic support instead.
For B. subtilis,IL[Ch][Ma] encapsulation of IL in
IJ bers almost tripled its antimicrobial activity. Even though
Fig. 1 SEM images of IJ electrospun bers at optimized conditions: upper left, IJ [Ch][Ma]; upper right, IJ [Ch][Ti]; bottom left, IJ [Ch][Ib]; bottom right, IJ [Ch][Ac].
Fig. 2 Agar diusion tests for IJ [Ch][Ma] (1), mandelic acid (2) and IL [Ch][Ma] (3) against E. coli. (4) Stainless steel wire control. (5) Paper disk control.
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IJ [Ch][Ma] ber membranes enhanced the IL properties, for B.
subtilis, mandelic aqueous solutions provided better results, in
opposition to the results obtained with E. coli cultures.
The results also suggest that B. subtilis is less sensitive to IL
[Ch][Ma] and IJ [Ch][Ma] than E. coli. As Gram-positive
bacteria, B. subtilis are more resistant to these antibacterials
agent due to presence of a higher amount of peptidoglycan on
the cell wall.
Biocompatibility assessment
Considering all the concerns about IL toxicity, the success and
practical applicability of any IL-Active Pharmaceutical Ingre-
dient (API) drug delivery system is dependent on toxicity
assessment. The toxicity of all choline based ILs used in this
work was evaluated using human colon adenocarcinoma cells,
Caco-2, which are a suitable and useful in vitro model for the
intestinal epithelial barrier studies.
The cytotoxicity assays
were performed as already described by Dias et al.
Caco-2 cells were seeded at a density of 2 10
cells per well in
96-well plates and their media was replaced every 48 hours.
Aer cells reached conuence 72 hours aer seeding the
medium was removed and cells were incubated for 4 h with
choline based ILs. The ILs were tested in a concentration range
of 50015000 mM. The results obtained in this work show that
none of the choline-based ILs induce cytotoxicity in intestinal
epithelial cells aer 4 h of exposure in the concentration range
Fig. 3 Agar diusion tests for IJ [Ch][Ma] (6), mandelic acid (8) and IL [Ch][Ma] (9) against B. subtilis. (7) Plastic wire control. (10) Paper disk control.
Fig. 4 Experimental cytotoxicity proles of choline-based ILs in human colon
Caco-2 cells. Conuent cells were incubated with the dierent [Ch]-ILs for 4 h
before determination of viability.
Table 3 Glass transition temperature (T
[Ch][Ac] 68.6 84.5
[Ch][Ma] 62.3
[Ch][Ti] 78.6 70.7
[Ch][Ib] ——
Table 4 Antibacterial ecacy of mandelic acid, IL [Ch][Ma] and IJ [Ch][Ma] bers against E. coli and B. subtilis
Disk/collector Agent Mandelate anion (mg) Inhibition area (cm
) Ratio 10
E. coli 1IJ[Ch][Ma] 8.05 0.71 1.55 (19.25 1.70)
2 Mandelic acid 8.15 0.03 1.47 (18.04 0.07)
3IL[Ch][Ma] 8.37 0.06 0.39 (4.66 0.03)
B. subtilis 6IJ[Ch][Ma] 8.29 0.74 1.06 (12.80 1.14)
8 Mandelic acid 9.06 0.03 3.46 (38.20 0.13)
9IL[Ch][Ma] 8.88 0.06 0.39 (4.40 0.03)
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studied, except for choline ibuprofen. [Ch][Ib] drastically
decreased cellular viability to 50% aer 4 h, with an EC50 ¼
5827 mM, calculated from the doseresponse curve using
GraphPad Prismasoware. However, this reduction was
predictable due to the inherent ibuprofen toxicity already
determined on Caco-2 cells (aer 24 h, EC50 ¼2200 mM).
Our results clearly show that the development of Ion Jelly bers
can be an interesting solution for the application of IL-APIs.
Moreover IL-APIs can also be considered non-toxic when
compared with other crystalline APIs in the market. With a wise
choice of ions, IL-APIs can be considered safe and their
encapsulation in IJ bers produced through electrospinning
can create a successful drug delivery system.
This work has been supported by Fundaç~
ao para a Ciˆ
encia e a
Tecnologia (FCT/MEC) through projects/grants PEst-C/EQB/
LA0006/2011, FCT-MEC through Strategic PEst-C/CTM/LA0025/
2013-2014, PEst-OE/EQB/LA0023/2011 PEst-OE/BIA/UI0457/
2011, PEst-OE/EQB/LA0004/2011 PTDC/EQU-EQU/104552/2008,
PTDC/EBB-EBI/099237/2008, PTDC/CTM/100244/2008, SFRH/
BPD/41546/2007 (P. Vidinha), SFRH/BPD/41175/2007 (N. Lour-
enço), and by FEDER. The NMR spectrometers are part of the
National NMR Network (RNRMN) and are funded by Fundaç~
para a Ciˆ
encia e a Tecnologia.
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... Previous studies on the production of electrospun gelatin fibers were used as reference. Zhang et al. reported that gelatin produces good fibers in a concentration between 30 and 50% (w/v) (28), while Santos et al. concluded that a concentration of 30% (w/v) was adequate for fiber formation (29). In line with these results, in this present study, uniform and smooth fibers were obtained with both 30 and 35% (w/v) gelatin. ...
... Gelatin fibers when submitted to stress conditions assumed a straight configuration (29). However, when the stress is removed, fibers assume a more disorganized configuration (Fig. 1). ...
... Gelatin is an elastomer and produces fibers with different conformations, being the helix the most typical shape observed (29)(30)(31)(32). However, variations in electrospinning parameters are responsible for other conformations, e.g. ...
Fast-dissolving delivery systems (FDDS) have received increasing attention in the last years. Oral drug delivery is still the preferred route for the administration of pharmaceutical ingredients. Nevertheless, some patients, e.g. children or elderly people, have difficulties in swallowing solid tablets. In this work, gelatin membranes were produced by electrospinning, containing an encapsulated therapeutic deep-eutectic solvent (THEDES) composed by choline chloride/mandelic acid, in a 1:2 molar ratio. A gelatin solution (30% w/v) with 2% (v/v) of THEDES was used to produce electrospun fibers and the experimental parameters were optimized. Due to the high surface area of polymer fibers, this type of construct has wide applicability. With no cytotoxicity effect, and showing a fast-dissolving release profile in PBS, the gelatin fibers with encapsulated THEDES seem to have promising applications in the development of new drug delivery systems.
... Ion jelly R , formed from gelatine and ionic liquid (including a range of cholinium-based ionic liquids), has been shown to be extremely versatile, with applications including selective membranes, gas separation, conductive coatings for textiles, development of antimicrobial fibers, solid-state electrochromic systems, and as a gas sensor ( Vidinha et al., 2008;Nuno et al., 2011;Couto et al., 2013Couto et al., , 2015Rana et al., 2013;Santos et al., 2013;Carvalho et al., 2014;Benedetti et al., 2015). Gelatine-based ionogels have also been partnered with silver oxide nanoparticles to generate microbe-resistant and highly stretchable materials that are also self-healing and have shapememory ( Singh et al., 2017). ...
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Biopolymer processing and handling is greatly facilitated by the use of ionic liquids, given the increased solubility, and in some cases, structural stability imparted to these molecules. Focussing on proteins, we highlight here not just the key drivers behind protein-ionic liquid interactions that facilitate these functionalities, but address relevant current and potential applications of protein-ionic liquid interactions, including areas of future interest.
... The developed system had enhanced thermal stability and ensured a fast release of the API. Also dos Santos et al. have reported on the production of antimicrobial ionic gel fibres with chloride mandelate [10]. ...
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A therapeutic deep eutectic system (THEDES) is here defined as a deep eutectic solvent (DES) having an active pharmaceutical ingredient (API) as one of the components. In this work, THEDESs are proposed as enhanced transporters and delivery vehicles for bioactive molecules. THEDESs based on choline chloride (ChCl) or menthol conjugated with three different APIs, namely acetylsalicylic acid (AA), benzoic acid (BA) and phenylacetic acid (PA), were synthesized and characterized for thermal behaviour, structural features, dissolution rate and antibacterial activity. Differential scanning calorimetry and polarized optical microscopy showed that ChCl:PA (1:1), ChCl:AA (1:1), menthol:AA (3:1), menthol:BA (3:1), menthol:PA (2:1) and menthol:PA (3:1) were liquid at room temperature. Dissolution studies in PBS led to increased dissolution rates for the APIs when in the form of THEDES, compared to the API alone. The increase in dissolution rate was particularly noticeable for menthol-based THEDES. Antibacterial activity was assessed using both Gram-positive and Gram-negative model organisms. The results show that all the THEDESs retain the antibacterial activity of the API. Overall, our results highlight the great potential of THEDES as dissolution enhancers in the development of novel and more effective drug delivery systems.
... The technique is able to process mixtures of polymers or polymers carrying nonspinnable materials, so allowing a high degree of flexibility in the design of functional mats or membranes [9]. Electrospinning has been used to prepare nanofibrous scaffolds for gas and liquid filtration that benefits from adjustable functionality to prepare materials incorporating antimicrobial activity [10] and [11]. ...
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The use of electrospun polyvinylpyrrolidone (PVP) nanofibers containing silver, copper, and zinc nanoparticles was studied to prepare antimicrobial mats using silver and copper nitrates and zinc acetate as precursors. Silver became reduced during electrospinning and formed nanoparticles of several tens of nanometers. Silver nanoparticles and the insoluble forms of copper and zinc were dispersed using low molecular weight PVP as capping agent. High molecular weight PVP formed uniform fibers with a narrow distribution of diameters around 500nm. The fibers were converted into an insoluble network using ultraviolet irradiation crosslinking. The efficiency of metal-loaded mats against the bacteria Escherichia coli and Staphylococcus aureus was tested for different metal loadings by measuring the inhibition of colony forming units and the staining with fluorescent probes for metabolic viability and compromised membranes. The assays included the culture in contact with mats and the direct staining of surface attached microorganisms. The results indicated a strong inhibition for silver-loaded fibers and the absence of significant amounts of viable but non-culturable microorganisms. Copper and zinc-loaded mats also decreased the metabolic activity and cell viability, although in a lesser extent. Metal-loaded fibers allowed the slow release of the soluble forms of the three metals. Copyright © 2015 Elsevier B.V. All rights reserved.
... For the purpose of this work we have chosen Ion Jelly. This particular combination of ILs with gelatin has been shown to be an interesting and promising strategy not only to prepare transparent, flexible and conducting materials for different electrochemical devices [22][23][24][25], but also as an enzyme immobilization matrix [26], separation membrane [27] and even a drug delivery system [28]. Moreover, gelatin is soluble in water above 35 1C being jellified upon cooling. ...
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Several hydrogel materials have been proposed for drug delivery systems and other purposes as interfacial materials, such as components for fuel cells and immobilization of biomolecules. In the present work, two materials, an ion sol-gel, based on 1-octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, and an ion jelly (1-ethyl-3-methylimidazolium ethylsulfate) film deposited on carbon screen-printed electrodes, were electrochemically characterized. The electrode kinetics of ion jelly and ion sol-gel materials were compared by using ferrocyanide/ferricyanide redox reaction couple as a model redox process. Diffusion coefficients were calculated and compared to those obtained with the model redox couple in non-modified electrodes. Results pointed to a decrease of two and four orders of magnitude in the diffusion coefficients, respectively, for ion jelly and ion sol-gel film modified electrodes. Heterogeneous electron transfer constants for the ferrocyanide/ferricyanide ion redox process were also determined for modified and non-modified electrodes, in which the ion sol-gel film modified electrode presented the lower values. This work sought to contribute to the understanding of these materials’ properties, with emphasis on their diffusion, conductivity, and electrochemical behavior, namely reversibility, transfer coefficients, and kinetics, and optimize the most suitable properties for different possible applications, such as drug delivery.
In this work the physicochemical properties of newly obtained mixtures (ChM) based on choline acetate (ChAc)/chloride (ChCl) as a hydrogen bond acceptor (HBA) and carboxylic acids (oxalic (OxA), malonic (MA), citric (CA), acetic (AA), formic (FA))/ urea (U) as a hydrogen bond donors (HBD) are discussed. NMR study showed slow reaction between choline and carboxylic acid, leading to obtain ester and water. After 3 weeks of synthesis, water content (wH2O) increased ca. 1.4 and 1.9 times for ChAc+FA and ChAc+OxA respectively. This factor is acid strength (as HBD) dependents. Moreover, the results clearly shown that wH2O can be rapidly determined based on the measurements of the refractive index. The densities of the examined systems are in the range 1.084–1.296 g·cm⁻³ at 298.15 K, while kinematic viscosity at the same temperature varies from ca. 19 cSt to 2190 cSt for ChAc+FA and ChAc+CA respectively. The highest conductivity was measured in ChCl+FA system and equaled 14.60 mS·cm⁻¹.
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We report the correlation between key solution properties and spinability of chitin from the ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]) and the similarities and differences to electrospinning solutions of nonionic polymers in volatile organic compounds (VOCs). We found that when electrospinning is conducted from ILs, conductivity and surface tension are not the key parameters regulating spinability, while solution viscosity and polymer concentration are. Contrarily, for electrospinning of polymers from VOCs, solution conductivity and viscosity have been reported to be among some of the most important factors controlling fiber formation. For chitin electrospun from [C2mim][OAc], we found both a critical chitin concentration required for continuous fiber formation (>0.20 wt %) and a required viscosity for the spinning solution (between ca. 450-1500 cP). The high viscosities of the biopolymer-IL solutions made it possible to electrospin solutions with low, less than 1 wt %, polymer concentration and produce thin fibers without the need to adjust the electrospinning parameters. These results suggest new prospects for the control of fiber architecture in nonwoven mats, which is crucial for materials performance.
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Ionic liquids (ILs), such as hydroxylammonium acetate ([NH3OH][OAc]), can reactively demineralize and remove proteins from shrimp shells in an efficient one-pot pulping process, thus allowing the isolation of native chitin with >80% purity and a high degree of acetylation and crystallinity. Compared to a previously reported IL extraction using 1-ethyl-3-methylimidazolium acetate, [C2mim][OAc], these less expensive ILs can achieve comparable chitin yields and purity, at up to ten times the biomass loading, although potentially result in lower molecular weight (MW) chitin. Because the IL is not recovered or recycled, the cost can additionally be further reduced by the sequential addition of hydroxylamine and acetic acid (or vice versa) to conduct the pulping process in situ. Though each methodology results in a comparable yields and purity of chitin material, the varying production costs and process safety issues are still unknown. This work presents a step toward narrowing the choices for chitin isolation technologies that can lead to an economically and environmentally sustainable process replacing the current hazardous, energy consuming, and environmentally unsafe process.
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Electrospinning is a fabrication technique, which can be used to create nanofibrous non‐wovens from a variety of starting materials. The structure, chemical and mechanical stability, functionality, and other properties of the mats can be modified to match end applications. In this review, an introduction to biopolymers and the electrospinning process, as well as an overview of applications of nanofibrous biopolymer mats created by the electrospinning process will be discussed. Biopolymers will include polysaccharides (cellulose, chitin, chitosan, dextrose), proteins (collagen, gelatin, silk, etc.), DNA, as well as some biopolymer derivatives and composites.
In this work, hydrogels obtained by mixing gelatin with ionic liquids (ILs) are prepared. Two different ILs, [emim][EtSO4] and [bmim][N(CN)2], are used to prepare hydrogels with different amounts of starting water and phosphate buffer content, which are used after a maturation period. The percentage of swelling in water and phosphate buffer, swelling and diffusion parameters are investigated in thin-film polymers (1 × 1 cm2; 1-mm thick) with different maturation times and at temperatures ranging from 4 to 37 °C. [emim][EtSO4] polymers show a moderate (100% weight increase) but quick swelling that reaches 80% of the equilibrium within 30 min. They are liquefied and dissolved at temperatures above 25 °C. [bmim][N(CN)2] polymers with short maturation times exhibit a similar behavior to the former, but more mature hydrogels register a very small swelling, abnormal kinetics and are more resistant to higher temperatures. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys., 2013
Ion Jelly materials combine the chemical versatility and conductivity of an ionic liquid (IL) with the morphological versatility of a biopolymer (gelatin). They exhibit very interesting properties, such as conductivities up to 10− 4 S cm− 1, and high thermostability up to 180 °C, and have been used successfully to design electrochromic windows. In this work we report on the preparation of Ion Jelly fibers through electrospinning in order to obtain high surface area conductive materials. We have used the IL 1-(2-hydroxyethyl)-3-methyl-imidazolium tetrafluoroborate ([C2OHmim]BF4), which exhibits conveniently high ionic conductivity (over 10− 3 S cm− 1) and electrochemical stability (electrochemical window over 6.0 V). The morphology of the obtained fibers was quantified using Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). We found that on average the effect of the IL on fiber diameter differs for lower and higher IL concentrations and that this effect was correlated with the initial conductivity and viscosity of Ion Jelly electrospinning solution. Moreover we also found that conductivities of Ion Jelly fibers are of the same order of magnitude as the conductivities of Ion Jelly dense films (~ 10− 4 S cm− 1). To the best of our knowledge, this is the first report on the incorporation of an IL into gelatin fibers using electrospinning. This opens up new opportunities for the application of gelatin fibers in electrochemical and biomedical devices.
This paper investigates electrospinning of a natural biopolymer, gelatin, and the mass concentration-mechanical property relationship of the resulting nanofiber membranes. It has been recognized that although gelatin can be easily dissolved in water the gelatin/water solution was unable to electrospin into ultra fine fibers. A different organic solvent, 2,2,2-trifluoroethanol, is proven suitable for gelatin, and the resulting solution with a mass concentration in between 5 and 12.5% can be successfully electrospun into nanofibers of a diameter in a range from 100 to 340 nm. Further lower or higher mass concentration was inapplicable in electrospinning at ambient conditions. We have found in this study that the highest mechanical behavior did not occur to the nanofibrous membrane electrospun from the lowest or the highest mass concentration solution. Instead, the nanofiber mat that had the finest fiber structure and no beads on surface obtained from the 7.5% mass concentration exhibited the largest tensile modulus and ultimate tensile strength, which are respectively 40 and 60% greater than those produced from the remaining mass concentration, i.e. 5, 10, and 12.5%, solutions.
A straightforward, cheap and unique method to produce novel fibers with a diameter in the range of 100nm and even less is related to electrospinning. For this goal, polymer solutions, liquid crystals, suspensions of solid particles and emulsions, are electrospun in the electric field of about 1kV/cm. The electric force results in an electrically charged jet of polymer solution flowing out from a pendant or sessile droplet. After the jet flows away from the droplet in a nearly straight line, it bends into a complex path and other changes in shape occur, during which electrical forces stretch and thin it by very large ratios. After the solvent evaporates, birefringent nanofibers are left. Nanofibers of ordinary, conducting and photosensitive polymers were electrospun. The present review deals with the mechanism and electrohydrodynamic modeling of the instabilities and related processes resulting in electrospinning of nanofibers. Also some applications are discussed. In particular, a unique electrostatic field-assisted assembly technique was developed with the aim to position and align individual conducting and light-emitting nanofibers in arrays and ropes. These structures are of potential interest in the development of novel polymer-based light-emitting diodes (LED), diodes, transistors, photonic crystals and flexible photocells. Some other applications discussed include micro-aerodynamic decelerators and tiny flying objects based on permeable nanofiber mats (smart dust), nanofiber-based filters, protective clothing, biomedical applications including wound dressings, drug delivery systems based on nanotubes, the design of solar sails, light sails and mirrors for use in space, the application of pesticides to plants, structural elements in artificial organs, reinforced composites, as well as nanofibers reinforced by carbon nanotubes.
Biodegradable polymers have been widely used and have greatly promoted the development of biomedical fields because of their biocompatibility and biodegradability. The development of biotechnology and medical technology has set higher requirements for biomedical materials. Novel biodegradable polymers with specific properties are in great demand. Biodegradable polymers can be classified as natural or synthetic polymers according to the source. Synthetic biodegradable polymers have found more versatile and diverse biomedical applications owing to their tailorable designs or modifications. This review presents a comprehensive introduction to various types of synthetic biodegradable polymers with reactive groups and bioactive groups, and further describes their structure, preparation procedures and properties. The focus is on advances in the past decade in functionalization and responsive strategies of biodegradable polymers and their biomedical applications. The possible future developments of the materials are also discussed.
Electrospinning provides a simple and versatile method for generating ultrathin fibers from a rich variety of materials that include polymers, composites, and ceramics. This article presents an overview of this technique, with focus on progress achieved in the last three years. After a brief description of the setups for electrospinning, we choose to concentrate on the mechanisms and theoretical models that have been developed for electrospinning, as well as the ability to control the diameter, morphology, composition, secondary structure, and spatial alignment of electrospun nanofibers. In addition, we highlight some potential applications associated with the remarkable features of electrospun nanofibers. Our discussion is concluded with some personal perspectives on the future directions in which this wonderful technique could be pursued.
The kinetics of glucose oxidase (GOD) and horseradish peroxidase (HRP) on a transparent gelatin–ionic liquid functional polymer has been investigated using a colorimetric assay of H2O2 with phenol-4-sulfonic acid and 4-aminoantipyrine, as color-generating precursors.The effect of different ionic liquids 1-ethyl-3-methyl-imidazolium ethyl sulfate ([emim][EtSO4]), 1-butyl-3-methyl-imidazolium dycianamide ([bmim][N(CN)2]), and 1-butyl-3-methyl-imidazolium chloride ([bmim][Cl]), 1-butyl-3-methyl-imidazolium tetrafluoroborate ([bmim][BF4]), gelatin type A and water on the activity of the two free enzymes was studied.The selection of the ionic liquid [emim][EtSO4] and gelatin type A with subsequent maturation of the functional polymer at water activity of 0.76 have been found as the most suitable conditions for the entrapment of both enzymes. The activity of GOD and HRP on the gelatin–[emim][EtSO4] solid disk (6.2 × 1.5 mm of diameter and thickness) formed in the bottom of the well of ELISA plate showed to be respectively 16 times and 13 times lower than in free sodium phosphate buffer. The storage stability at 4 °C of the both immobilized enzymes showed that GOD can retain up to 70% of the initial activity after 2 weeks, where HRP retained 91% of its initial activity. The drop cast deposition of the transparent gelatin–[emim][EtSO4] functional polymer containing the two enzymes (GOD, HRP) and the color-generating precursors on filter paper allowed to demonstrate their applicability on colorimetric glucose detection.
The dramatic growth in ionic liquid research over the past decade has resulted in the development of a huge number of novel ionic liquids, as well as many associated applications. The perceived environmentally friendly nature of ionic liquids, which results from their negligible vapor pressure, is now under scrutiny since although they will not evaporate into air, it is not possible to guarantee that they will never enter the environment. Toxicity research studies including ecotoxicity, have recently received broad attention and the commonly accepted notion that ionic liquids have low toxicity has been shown to be incorrect. This review attempts to highlight the progress of ionic liquid toxicity research, as well as the development of degradable and bio-renewable ionic liquids.
The present review deals with the chemistry of gelatin cross-linking under conditions that are relevant to pharmaceutical situations. Mechanistic rationalizations are offered to explain gelatin cross-linking under “stress” conditions. These include elevated temperature and high humidity conditions. In addition, the chemical interactions between gelatin and aldehydes, such as formaldehyde and other formulation excipients, are discussed. The literature on the in vitro and in vivo dissolution and bioavailability of a drug from stressed gelatin capsules and gelatin-coated tablets is reviewed. Cross-linking phenomena, occurring in stressed hard gelatin capsules and gelatin-coated tablets, could cause considerable changes in the in vitro dissolution profiles of drugs. However, in a few cases, the bioavailability of the drug from the stressed capsules is not significantly altered when compared to that obtained from freshly packed capsules. It is concluded that, as with other drug-delivery systems, careful attention should be paid to the purity and chemical reactivity of all excipients that are to be encapsulated in a gelatin shell. It is suggested that in vitro dissolution tests of hard gelatin-containing dosage forms be conducted in two stages, one in a dissolution medium without enzymes and secondly in dissolution media containing enzymes (pepsin at pH 1.2 or pancreatin at pH 7.2, representing gastric and intestinal media, respectively) prior to in vivo evaluation. Such in vitro tests may constitute a better indication of the in vivo behavior of gelatin-encapsulated formulations. Furthermore, testing for contamination with formaldehyde as well as low molecular weight aldehydes should be a standard part of excipient evaluation procedures.