Antimicrobial Activity of Silver Nanoparticles in Polycaprolactone

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Antimicrobial activity of silver nanoparticles in polycaprolactone nanofibers against Gram-positive and negative bacteria Efrén Amador Hinojos-Márquez, Juan López-Esparza, León Francisco EspinosaCristóbal, Alejandro Donohue-Cornejo, and Simón Yobanny Reyes-López Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.6b02300 • Publication Date (Web): 28 Oct 2016 Downloaded from http://pubs.acs.org on October 30, 2016

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Industrial & Engineering Chemistry Research

Antimicrobial activity of silver nanoparticles in polycaprolactone nanofibers against Gram-positive and negative bacteria Efrén Amador Hinojos-Márquez1, Juan López-Esparza1, León Francisco EspinosaCristóbal2, Alejandro Donohue-Cornejo2 and Simón Yobanny Reyes-López1*. 1

Instituto de Ciencias Biomédicas, Universidad Autónoma de Ciudad Juárez, Envolvente

del PRONAF y Estocolmo s/n, C.P. 32300, Ciudad Juárez, Chihuahua, México. 2

Departamento de Estomatología, Instituto de Ciencias Biomédicas, Universidad Autónoma

de Ciudad Juárez, Envolvente del PRONAF y Estocolmo s/n, C.P. 32300, Ciudad Juárez, Chihuahua, México.

Abstract Drug-resistance infections have increasing increased extremely fast in the last years emerging like a serious health problem in the world. Novel and better antimicrobial agents are still being developed to control associated microorganisms. However, this still represents a great challenge for antimicrobial agents. The aim of this study was to prepare and characterize polycaprolactone nanoﬁbers containing silver nanoparticles and evaluate its antimicrobial properties against various Gram-positive and negative microorganisms associated to drug-resistance infections. Polycaprolactone-silver fibers (PCL-AgNPs) were prepared by reduction in situ method of Ag+ ions by N, N-dimethylformamide in tetrahydrofuran solution with the simple addition of polycaprolactone in the solution for electrospinning. The results of dynamic light scattering and UV–visible spectroscopy showed the presence of silver nanoparticles with diameters around 10 to 15nm. STEM and energy dispersive X-ray spectroscopy confirmed the presence of silver agglomerates distributed over the surface of nanofibers. All PCL-AgNPs nanofibers samples showed good and specific antibacterial effect despite of low silver concentration; therefore, this activity might depend on particular microbiological and cell structure characteristics as well as concentration of silver on the nanofibers. PCL-AgNPs nanofibers might have a high potential for medical applications focused to the control of drug-resistance infections. 1

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Keywords: Silver nanoparticles, Polycaprolactone, Nanofibers, Electrospinning, Drug-resistance infections, Antimicrobial activity.

INTRODUCTION Nowadays the emergence of antibiotic-resistant bacterial strains has been considered a serious global health problem issue, bacterial drug resistance has increased by ineffective antimicrobial therapeutics.1 Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) are two of the most common bacteria that have shown important antibioticresistance effects producing serious intestinal, skin and other soft tissue infections, including pneumonia, endocarditis and septicemia respectively.2, 3 Other types of bacteria commonly involved in severe nosocomial infections are Pseudomonas aeruginosa (P. aeruginosa), Streptococcus pyogenes (S. pyogenes), Klebsiella pneumonia (K. pneumonia). These microorganisms have also developed high drug resistance to antibiotic therapies, suggesting a real attention in treatment guidelines4-6 and the use of novel antimicrobial agents with better bactericidal properties. Recently, it has been demonstrated that silver nanoparticles (AgNPs) have useful antiinflammatory and antibacterial effects and improve wound healing, this could be exploited to design better wound and burn dressings.7 Also, silver is currently used to control bacterial growth in diverse biomedical applications, including catheters, treatment of some dental problems and burn injuries, among others.8-10 Although Ag ions and Ag-based compounds are highly toxic to microorganisms,9 different metal–polymer complexes have been prepared to improve its antimicrobial activity, for example, the chitosan–Ag complex and the chitosan–Zn complex.11, 12 One of the most interesting semicrystalline polymers is polycaprolactone (PCL). PCL has been considered for several biomedical applications, such as sustained drug delivery systems, tissue engineered skin regeneration, scaffolds for ﬁbroblasts supporting and osteoblasts growth, nanocomposites for bone repair, ureteral substitution, and lately in electrospun composite nanofibers.11-13 The electrospinning method has been recognized as an efficient and relatively simple technique for the fabrication of polymeric nanofibers with large surface area.14, 15 Various 2


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polymers have been successfully electrospun into ultrafine particles and fibers mostly from solvent solution and molten form. The resultant composites or nanofibers maintain the properties of the polymeric, ceramic and/or metallic nanoparticles used, and also are expected to have potential applications in many fields such as biomaterials, chemistry and physics.14-18 The electrospinning technology has been used for fabricating gold and silver nanoparticlepolymer composites and other several kinds of materials have been reported with electronic, magnetic and optical properties, and their applications to catalysis and biology.17,

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Notwithstanding, most of the scaffolds obtained in the literature require two or more manufacturing steps and do not report agglomerations of nanoparticles; another disadvantage is the use of a high concentration of silver.14-20, 22, 23 Recently a novel approach was employed to incorporate silver nanoparticles into the PCL matrix in situ and to improve the release of Ag ions from the matrix so as to enhance the antimicrobial efficacy. Recent study using a novel approach synthesized and incorporated the Ag nanoparticles into the PCL matrix, with appropriate volumes of PEG and AgNO3 solutions.24 The amount of AgNO3 was measured to make the final Ag w/w concentrations of 2.6%, 3.3%, 3.8%, and 4.5%, in which were relatively high. The Ag-containing composites showed a strong antimicrobial and anti-biofilm properties against S. aureus and P. aeruginosa24 demonstrating good bactericidal property of this type of composite, however this work only used two different microorganisms (one Gram-positive and one Gram-negative respectively). Although scientific literature has already reported scarce studies about synthesis, characterization and antimicrobial activity of PCL nanofibers by electrospinning containing AgNPs against a limited number of Gram-negative and positive bacterial strains (two or three different species of microorganisms), including multidrug resistant microorganisms and high silver concentration relatively;24-26 it is necessary to re-design novel and easy routes for the preparation of PCL-AgNPs nanofibers and evaluate its antimicrobial activity involving a large variety of microorganisms that can offer a better understanding of bacterial inhibition capacity for drug-resistance infections. One of the most interesting challenges in the major studies about antimicrobial materials is to provide and design better and novel 3



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bactericidal agents with good antimicrobial activity in a wide variety of microorganisms involved in the most common infectious diseases, including drug-resistance bacteria, considered as serious health problems. The purpose of this work was to obtain PCL nanofibers containing a low concentration of AgNPs and evaluate its antimicrobial activity on several microorganisms considered as drug resistant bacteria (E. coli, S. pyogenes, K. pneumonia, S. aureus, P. aeruginosa and B. suttilis).

EXPERIMENTAL SECTION Materials. All reactants were analytical grade and used as received. High purity water was employed. Silver, nitrate (AgNO3), poly ε-caprolactone (80,000 Mw), N, Ndimethylformamide (DMF) (≥98) and tetrahydrofuran (≥99.5%) were purchased from Aldrich. Müller-Hinton agar plates were used for antibiogram test. E. coli (ATCC 25922TM), S. pyogenes (ATCC 19615TM), K. pneumoniae (ATCC13883TM), S. aureus (ATCC 25923TM), P. aeruginosa (ATCC 27853TM) and B. subtilis (ATCC 19163TM) microorganisms were obtained from American Type Culture Collection. Silver nanoparticles preparation. The synthesis of AgNPs was carried out in one step, starting with a solution with of dimethylformamide (DMF) and tetrahydrofuran (THF) in a ratio of 7:3 respectively. Silver nitrate (AgNO3) was added to the solution as a precursor salt. The mixture was placed under magnetic stirring to observe a color change (light yellow). Particle size was controlled by the initial concentrations of silver nitrate (0mM, 1 mM, 10 mM, 50 mM and 100 mM). UV–Vis absorption spectra was performed at room temperature in a Cary100 spectrophotometer (Varian Corp.) with a variable wavelength between 100–900 nm using a10 mm quartz cell. Particle size and distribution was measured in an HORIBA SZ-100 Nanoparticle Analyzer with dynamic light scattering (DLS) technology.

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Preparation and fabrication of nanofiber scaffolds. Preparation of electrospinning solution consisted of forming a viscous mixture of PCL 8% and silver nitrate solutions (0 mM, 1 mM, 10 mM, 50 mM and 100 mM) under magnetic stirring at room temperature. The resulting viscous solution was loaded into a syringe with stainless steel needle of 1.25 mm inner diameter. The needle was connected to a highvoltage generator, an aluminum foil served as the counter electrode. A dense web of fibers was collected on the aluminum foil using an electrical potential of 13 kV, a distance between the capillary and the substrate electrode of 15 cm, and a feeding rate of 8 µL/min. The electrospinning assay was performed at 22ºC. Characterization of the scaffolds. Morphology of the PCL–Ag nanocomposites was observed trough scanning electron microscope (SEM, JEOLJSM-6400), operated at 20 kV. The fibers were previously collected on carbon-coated copper grids and coated with platinum using a sputter coating. Fiber diameter was measured using SEM micrographs. FT-IR was performed with an Alpha Platinum-ATR spectrometer. Antibacterial activity. Antibacterial activitie of PCL-AgNPs nanofiber scaffolds were measured by disc diffusion method. Six different microbial species, E. coli, S. pyogenes, K. pneumoniae, S. aureus, P. aeruginosa and B. subtilis, were cultured in Müller-Hinton broth by 20 h at 37ºC before the test. According to the McFarland scale (1.3x106 CFU/mL), 100 µL of standardized suspensions of each bacterium was placed on Müller-Hinton agar plates. Disc shape samples of PCL-AgNPs (1x1cm2) were prepared and summited to the inhibition zone tests. The discs were sterilized with ultra-violet light for 2 hours and subsequently placed on E. coli, S. pyogenes, K. pneumoniae, S. aureus, P. aeruginosa and B. subtilis culture plates. The agar plates were incubated for 24 hours at 37°C. The antibacterial effect was determined by the measurement of clear zones correspondent to inhibition formed around the discs using a vernier caliper instrument.19 The antimicrobial test for all microorganisms were made in triplicate. 5



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RESULTS AND DISCUSSION Synthesis and morphology of AgNPs and nanofibers. Initial formation of AgNPs was visualized through color changes in the solutions, from colorless to light yellow. UV-Vis analysis exhibited well-defined plasmon band absorption at 415 and 440 nm for Ag 1 to 10 mM and 50 to 100 mM; at higher concentration of silver, the solution color changed from pale yellow to dark brown, immediately. Figure 1 shows representative band absorption for nano sized silver of PCL-AgNPs 100 mM. This feature is commonly known as the surface plasmon resonance peak and depends on particle size. The optical properties of AgNPs strongly depend on the characteristics of individual particles (their size and shape) and their environment, including the spatial ordering of particles. Silver has the greatest surface plasmon resonance (SPR) band intensity. The appearance of an SPR band is the result of interaction of incident light on the NP surface with conduction of electrons of the metal. According to literature, the dependence of a spectrum on particle size shows up in the increase in SPR band intensity with the increment in the particle radius. Experimental data shows that in addition to the increase in absorption, the growth of Ag particles is accompanied by the SPR band broadening and the red shift of its maximum.20 On the other hand, the initial amounts of Ag nitrate and reducing agents left no residue and the reaction was assumed to be complete. This assertion was consistent with UV-Vis spectroscopy in the wavelength range of 200-300 nm, where no residues of Ag+ could be detected. It is observed that the nanoparticles suspensions are stable for long time in the dimethylformamide solution leading to a metastable solution of single particles and a second band around 600 nm does not emerge from the coupling of surface plasmons for aggregated particles. DLS results showed uniform and well-distributed AgNPs in a rage of 10-15 nm (Figure 2).

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Figure 1. Absorption spectra for: a) PCL-Ag 1 mM, b) PCL-Ag 10 mM, c) PCL-Ag 50 mM and d) PCL-Ag 100 mM recorded immediately after reduction process.

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Figure 2. Particle size distribution curves for: a) PCL-Ag 1 mM, b) PCL-Ag 10 mM, c) PCL-Ag 50 mM and d) PCL-Ag 100 mM.

Infrared spectrum of electrospun PCL and PCL-AgNPs 100 mM fibers is shown in Figure 3. Similar spectra was obtained for PCL and PCL-AgNPs fibers. Infrared spectra for PCLAgNPs composite does not show an enhancement or different bands by the presence of AgNPs. Regarding the spectra, asymmetric and symmetric stretching bands at CH2 at 2949 and 2846 cm−1 respectively, and a strong stretching band for the carbonyl stretching mode around 1,727 cm−1 are observed and attributed to amorphous phases of the polymer. According to the literature, the band at 1294 cm−1 is assigned to the backbone C-C and C-O stretching modes in the crystalline PCL.18, 25, 26

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Figure 3. Infrared spectra of electrospun PCL and PCL–AgNPs fibers.

Table 1, shows the average diameters of PCL and PCL-AgNPs nanofibers were 260 ± 89 nm, 234 ± 66 nm, 208 ± 47 nm, 183 ± 59 nm and 159 ± 79 nm for AgNPs contents of 0, 1, 10, 50 and 100 mM, respectively. The diameters of these nanofibers decreased upon an increase in the content of the AgNPs), this phenomena is attributed to the presence of AgNPs in the solution, metal NPs increased the electrical charge and conductivity of the solution, resulting in thinner diameter of the fibers.

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Table 1. Physical characteristics of AgNPs and PCL-Ag fibers. AgNPs

Ag concentration (mM)

Diameter (nm)

Diameter (nm)

PCL-Ag 0 mM

0

0±0

260 ±8 9

PCL-Ag 1 mM

1

10.3 ± 4.2

234 ± 66

PCL-Ag 10 mM

10

10.3 ± 3.4

208 ± 47

PCL-Ag 50 mM

50

12.3 ± 6.4

183 ± 59

PCL-Ag 100 mM

100

13.8 ± 5.3

159 ± 79

Sample

PCL-Ag fibers

Diameters of AgNPs initials and PCL-Ag fiber are expressed in average and standard deviation.

Figure 4 shows SEM images of the resulting PCL-AgNPs 100 nM nanofibers. The average diameter of the PCL-AgNPs nanofibers was 159±79 nm, according to the histogram in Figure 5. It was possible to observe that the density increases with the addition of Ag nanoparticles to the solution. Thus, the ejected jets have stronger elongation forces in the electrical field; therefore, this resulted in forming thinner composite fibers.18 In this case, only a small change appears in the average diameter of the fibers probably due to the polarity of the solution. Morphologically, fibers were smooth and uniform with optimized electrospinning parameters.

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Figure 4. SEM images of fibers: a) Electrospun PCL-AgNPs 100 mM 25,000 X (zone 1); b) Electrospun PCL-AgNPs 100 mM 50,000 X (zone 1); c) Electrospun PCL-AgNPs 100 mM 5,000 X and d) Electrospun PCL-AgNPs 100 mM 50,000 X (zone 2).

Figure 5. Histogram distribution of PCL-AgNPs 100 mM fibers. 11



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Figure 6 shows STEM micrographs of the PCL-AgNPs. AgNPs can be observed on the surface of the fibers with round shape with a size distribution of 80 to 190 nm. At high magnification the presence of some large particles is noted easily, with diameter around 180 nm in white contrast, on the surface of electrospun nanofibers, which is likely due to the increased incidence of agglomerations of AgNPs. The addition polymer promotes the formation of agglomerates because of the change of polarity in the precursor solution. Several works for the preparation of nanoparticles in nanofibers by electrospinning were carried out by adding weight percent nanoparticles to a viscous polymer solution, the resultant fibers had a presence of large particles, with an approximate diameter of 200 nm, this could be attributed to the increased incidence of agglomerations of nanoparticles and poor dispersion18. Elementary analysis of PCL-AgNps nanocomposite was carried out by using SEM–EDX. Figure 6d shows a spectrum of PCL-AgNps nanocomposite obtained by elemental microprobe EDX analysis. The results show that carbon, oxygen and silver are the principal elements forming the sample. EDX analysis provides direct evidence that AgNPs are embedded in the nanofibers. In assumptions the PCL/Ag nanocomposite membranes showed uniform fiber diameter and nanoparticles distribution.

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Figure 6. STEM micrographs of the electrospun PCL-AgNPs 100 mM nanofibers composite. a) 30,000 X (zone 1); b) 50,000 X (zone2); c) 20,000 X; d) EDX spectrum. Antibacterial Properties of PCL-AgNPs nanofiberscomposite. Figure 7 illustrates the comparative results of antibacterial activities of PCL and PCLAgNPs hybrid nanofibers using an inhibition zone chart of the tested antimicrobial samples and the corresponding plates (with 0 mM, 1 mM, 10 mM, 50 mM and 100 mM of silver nitrate initial solution). The results obtained from disc diffusion method against six different microorganisms indicated that the PCL nanofiber scaffold (with 0 mM Ag+ added) did not produce any zone of inhibition against all microorganisms tested and the silver concentration was founded dependent of antimicrobial activity. Diffusion test showed zones of inhibition for E. coli, S. pyogenes, K. pneumoniae, S. aureus and P. aeruginosa, 13



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but not for B. subtilis species, this last is considered one of the most resistant bacteria to antimicrobial treatments and to PCL-AgNPs nanofibers. The presence of silver nanoparticles at the initial concentration range (1 to 100 mM) inhibited bacterial growth in a zone of around 7 to 10 mm for a specific specie, illustrating that the most sensitive bacteria to PCL-nanofiber was S. aureus followed by E. coli, P. aeruginosa, K. pneumoniae, S. pyogenes and B. subtilis respectively. It also was found that the PCL/Ag nanofibers containing higher concentration of Ag nitrate precursor had the most effective antimicrobial activity. In this case, the increment of silver concentration showed higher inhibition zones compared to the samples with those of lower Ag concentration. It is possible to consider the existence of a dose-dependent effect in five from six bacterial strains exposed to PCL-AgNPs nanofibers samples. Furthermore, the main bacteria associated to multidrug-resistance infections were analyzed according their microbiological characteristics from cell membrane. Gram-negative bacteria (E. coli, P. aeruginosa and K. pneumoniae) were found, in general, to be more sensitive to PCL-AgNPs nanofibers compared to Gram-positive strains (S. pyogenes and B. subtilis) (Figure 7). A limited and selective mechanism of PCL-AgNPs nanofibers could act against bacteria strains depending on the type of cell membrane structure.21 Tran et. al. reported that a higher concentration of Ag (2.6 to 4.5% w/w) on a polycaprolactone matrix resulted in lower bacterial inhibition; as expected in S. aureus, 2.6% of Ag concentration inhibited near 29% of colony forming units (CFU) and for 4.5% Ag concentration, around of 72%, this supports the fact that the antimicrobial effect in Gram-positive bacteria (S. aureus) depends on the Ag concentration. For the case of Gramnegative bacteria, as P. aeruginosa, all Ag composite samples showed a high antimicrobial activity with no-statistical differences indicating that this type of bacteria possess high sensibility to Ag, despite of low concentrations used.24 This work, shows that the growth inhibition effect in S. aureus and P. aeruginosa bacteria using PCL-AgNPs nanofibers (12.5100 mM) depends on the Ag concentration included on the nanofibers (10.3-41.2% for S. aureus and 9.5-62.6% for P. aeruginosa respectively) promoting good antimicrobial effect on lower Ag concentration (1-10 mM) compared to nanofibers with high Ag amount (50-100 mM); similar antimicrobial activity was also obtained in others different types of 14


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microorganisms such as E. coli, S. pyogenes and K. pneumonia bacteria. Another recent study, reported by Chih-Hao Chen et al., evaluated the antibacterial activity of AgNPs in electrospun hyaluronic acid and polycaprolactone nanofibrous membranes (HA/PCL+Ag NFMs) using S. aureus and E. coli bacteria. Authors found that the inhibition zones of HA/PCL+Ag NFMs were higher on E. coli (2.21±0.14 cm2) compared to S. aureus strains (1.66±0.02 cm2) suggesting that the lower antimicrobial activity of HA/PCL+Ag NFMs could be related to strong cell wall structure of Gram-positive bacteria (S. aureus).27 This work found that growth inhibition zones of PCL-AgNPS nanofibers on S. aureus (~10 mm) were relatively lower than E. coli strain (~8-9.5 mm), however others three species of Grampositive and Gram-negative bacteria (P. aeruginosa,K. pneumoniae, S. pyogenes) also presented great inhibition zones (7.5-9 mm, 7-8 mm and 7-7.5 mm respectively) to PCLAgNPS nanofibers when low Ag concentrations (1-10 mM) were used. Results of present work suggest that PCL-AgNPs nanofibers have the capacity to inhibit bacterial growth in many of the species with characteristics similar to the bacteria tested on this study. The inhibition mechanism might depend on the ability of AgNPs to bind to cell membranes of microorganisms and generate this antimicrobial activity, affecting thiols and amino groups into bacterial cells through Ag ions and its very known large surface area.22, 23, 28

Moreover, other specific mechanisms such as alteration of respiration and replication of

DNA processes, and the induction of a bacterial apoptosis-like response, leading the death of bacterial strains might be involved.28-30 These findings are in agreement with various studies suggesing that the bactericidal effectiveness of PCL-AgNPs nanofibers could also be related with the physical and chemical properties of the nanomaterials, such as dose, size, concentration, shape, time of exposition, administration way and more, and the other hand, particular metabolic characteristics of the microorganisms exposed to them.28, 31-34

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Figure 7. Antibacterial activity test of PCL-AgNPs at different concentrations.

In attempt to obtain more sustainable and safety composites, it is necessary to resolve the possible adverse effects of AgNPs. Previous reports related to silver-containing electrospun PCL membranes and PCL nanofibers have demonstrated that silver ions do not have similar cytotoxic effects between eukaryotic and prokaryotic cells; therefore the use of higher Ag concentration might offer comparable toxic effects due to eukaryotic cells are usually larger and show higher structural and functional redundancy than prokaryotic cells.35,

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This

difference on biological characteristics provide a ‘‘therapeutic window’’ where bacterial cells are successfully attacked, whereas harmful effects on eukaryotic cells might not be observed. However, more in vitro and in vivo studies are needed to evaluate the biocompatibility level of PCL-AgNPs nanofibers. Moreover, regarding to the concentration range, the antibacterial activity at the highest value (100 mM) only increased 1 mm compared to the lowest concentration (1 mM) suggesting that nanofibers with a minimal 16


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amount of AgNP could be employed without significant differences related to its antimicrobial activity. Studies have demonstrated that release of Ag ions from AgNP is likely by a synergic and cooperative oxidation process which could be determined from specific aqueous media and a desorption phenomenon, producing free ions with presence or absence of oxygen.37-39 It is very probable that the AgNPs on the surface of nanofibers could have similar reaction of release due to the near contact with possible aqueous media containing oxygen such as blood, serum, medical substances or simply common water, increasing the antimicrobial activity for specific medical conditions. In the present time, several works have tried to identify and reduce the potential risks on humans and environment related with the administration of AgNPs.40 It is well known that toxicity of AgNPs is associated to various physical and chemical properties such as shape, size, surface, area, presence of coatings, reactivity, composition, dispersion, time of exposition, dose, administration way and others;41-44 therefore, Ag+ ions from AgNPs have also demonstrated significant cytotoxicity in human cells. Some authors consider that AgNPs and Ag+ ions have similar level of toxicity.45,46 increasing the antimicrobial activity and toxicity when they are combined. Although Ag+ ions comes from AgNPs, they both have different mechanisms for toxicity. The AgNPs produce cellular and DNA damage and induction of carcinogenic and oxidative stresses, radical scavenging; while Ag+ ions induce to an inflammatory response and processes of metallic detoxification but with lower stress responses compared to AgNP.47 Although these characteristics of toxicity could be shown in vitro and in vivo studies, clinical studies have reported an opposite results using specific methodology. One clinical study in 2014 evaluated clinically a commercial oral nanoparticle silver colloidal product. Clinical chemistry and hematology tests as well as general changes of 60 subjects orally and voluntarily exposed to 15 mL of AgNPs (40-60 nm) using an Ag concentration of 10 and 32 ppm in a period of 16 days were evaluated. This study found no significant changes in metabolic, hematologic or urinalysis studies, lungs or abdominal organs, pulmonary reactive oxygen species or pro-inflammatory cytokine generation. Authors concluded that the commercial oral nanoparticle silver colloidal product does not generate clinically responses associated to important toxicity markers.48 The evaluation of toxicity assays, biocompatibility tests or potential environment risks or Ag+ ions release of nanofibers with AgNPs were not evaluated in this study; however, the presentation, size, 17



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concentration, distribution and other physicochemical properties including the possible approach for biomedical application as a physical barrier with antimicrobial properties, could offer an acceptable and low toxicological and environmental risks due to high antimicrobial efficiency even with low Ag concentrations Notwithstanding PCL-AgNPs nanofibers might offer a high potential use for biomedical applications related to inhibition of antibiotic-resistance microorganisms, scaffolding structure, biological barrier, guided regeneration, treatment for burns, antimicrobial bandages, and others; more studies should be developed to indicate and choose better and safe nanomaterials with novel and improved antibacterial properties. CONCLUSIONS PCL-AgNPs fibers were successfully fabricated by electrospinning in a binary solvent (DMF and THF solution) using a novel, simple method. The resulting PCL-AgNPs fibers had a smooth surface and uniform diameters (160 nm). PCL-AgNPs nanofiber scaffolds showed good antibacterial activity against a variety of Gram-positive and negative strain bacteria: E. coli, S. pyogenes, K. pneumoniae, S. aureus, and P. aeruginosa. Composite inhibition of bacteria was possible at a low AgNps concentration. PCL-AgNPs nanofibers have a potential use as antimicrobial and scaffolding agents. This composite nanofibers might revolutionize actual antimicrobial therapies against multidrug-resistance bacteria that represent a serious global health issue.

AUTHOR INFORMATION Corresponding autor * Simón Yobanny Reyes-López, Envolvente del PRONAF y Estocolmo s/n, Cd. Juárez, Chihuahua México. C.P. 32310. Tel: +55 656 688 1823, Fax: +55 656 688 1823, email: [email protected] Note The authors declare no competing financial interest. ACKNOWLEDGMENTS Authors gratefully acknowledge financial support by CONACYT (Proyecto-204873 and 18


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Graphical Abstract

Electrospun PCL-AgNPs 30,000 X

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Antimicrobial Activity of Silver Nanoparticles in Polycaprolactone

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