- Email: [email protected]
Preparation of composite alginate-based electrospun membranes loaded with ZnO nanoparticles
Carbohydrate Polymers 227 (2020) 115371
Contents lists available at ScienceDirect
Carbohydrate Polymers journal homepage: www.elsevier.com/locate/carbpol
Preparation of composite alginate-based electrospun membranes loaded with ZnO nanoparticles
T
Andrea Dodero , Marina Alloisio, Silvia Vicini, Maila Castellano ⁎
Università degli Studi di Genova, Dipartimento di Chimica e Chimica Industriale, Via Dodecaneso 31, 16146 Genoa, Italy
ARTICLE INFO
ABSTRACT
Chemical compounds studied in this article: Sodium alginate (CID: 133126842) Poly(ethylene oxide) (CID: 8200) Strontium chloride hexahydrate (CID: 159250) Zinc oxide (CID: 14806)
In the present work alginate-based nanofibrous membranes embedding zinc oxide nanoparticles (ZnO-NPs) were prepared via electrospinning technique. ZnO-NPs were synthesized by means of a “green” sol-gel method by using alginate itself as stabilizing agent and characterized through UV–vis spectroscopy, thermogravimetric and morphological analysis. Formulations containing sodium alginate, poly(ethylene oxide) and ZnO-NPs were rheologically studied to identify the most suitable ones to be electrospun; alginate molecular structure played an important role on the solution spinnability due to the polysaccharide capability to establish electrostatic interactions and hydrogen bonds with ZnO-NPs. An innovative washing-crosslinking protocol was developed to obtain stable products which composition was assessed using Fourier Transform InfraRed spectroscopy and thermogravimetric analysis. Morphological investigation combined with EDX spectroscopy proved the obtained mats were highly porous and composed by thin homogenous nanofibers with a good distribution of the used nanofillers, thus representing potential products for several purposes (e.g. biomedical, pharmaceutical and environmental applications).
Keywords: Sodium alginate Zinc-oxide nanoparticles Rheology Electrospinning Nanofibrous membranes
1. Introduction Nowadays biopolymers represent an important class of materials widely used for several purposes, such as biomedical, pharmaceutical and environmental applications (Dodero et al., 2018, Kalia & Avérous, 2011). Among these materials, alginate has attracted a lot of interest due to its biocompatibility, biodegradability, biological activity, low cost, water-solubility, and ease of production and functionalization. Alginates are a family of linear polysaccharides extracted from brown algae and composed of β-D-mannuronic acid (M-units) and α-L-guluronic acid (G-units), as shown in Fig. 1. One of the main reason of alginate success lies in its ability to undergo a thermal independent sol/ gel transition in the presence of bivalent and trivalent cations; accordingly to the commonly called “egg-box” model, such cations are able to bind the G-units of alginate skeleton thus creating a stable threedimensional network (Fig. 1) (Vicini, Castellano, Mauri, & Marsano, 2015; Vicini, Mauri, Wichert, & Castellano, 2017). The ionic gelation of alginate has been widely employed to prepare 3D hydrogels to be used as porous scaffolds and drug delivery systems for biomedical and pharmaceutical applications (Bidarra, Barrias, & Granja, 2014; Dodero, Pianella et al., 2019; Stagnaro, Schizzi, Utzeri, Marsano, & Castellano, 2018); however, such products are usually
characterized by poor and/or inadequate mechanical properties, as well as by a microstructure which limits the cell viability. To overcome such limitations, in recent years the possibility to use electrospinning technique to produce nonwoven nanofibrous membranes has been widely investigated; indeed, the obtained systems are characterized by a texture that in the microscale strongly resembles the natural extra-cellular matrix, thus offering the ideal environment to foster cell viability due to the high surface area and porosity (Jiang, Carbone, Lo, & Laurencin, 2015; Peng et al., 2016). A further advantage of electrospinning concerns the possibility to prepare nanocomposite mats by simply dispersing nanofillers within the starting polymer solutions in order to confer additional properties to the final products, such as antioxidant and antimicrobial activities. However, despite the mentioned advantages, the electrospinning process of alginate from aqueous solution is extremely difficult owing to the high viscosity, the polyelectrolyte nature, and the H-bonding between the polymer chains which usually prevent the formation of a stable jet during the processing and leading to nonhomogeneous bead-like structures. Therefore, synthetic non-toxic polymers (e.g. poly(ethylene oxide) (PEO) and poly(vinyl alcohol) (PVA)) are commonly added to alginate solutions to help the mixture processability, nevertheless they usually remain in the final products with the risk of affecting the global biological response (Bonino et al.,
Corresponding author. E-mail addresses: [email protected] (A. Dodero), [email protected] (M. Alloisio), [email protected] (S. Vicini), [email protected] (M. Castellano). ⁎
https://doi.org/10.1016/j.carbpol.2019.115371 Received 4 July 2019; Received in revised form 20 September 2019; Accepted 21 September 2019 Available online 23 September 2019 0144-8617/ © 2019 Elsevier Ltd. All rights reserved.
Carbohydrate Polymers 227 (2020) 115371
A. Dodero, et al.
Fig. 1. Chemical structure of alginate backbone and schematic representation of its chain organization in the presence of bivalent cations ("egg-box" model).
Consequently, ZnO-NPs were synthetized following a “green” sol-gel method reported in literature and slightly modified making use of alginate as stabilizing agent to obtain nanostructures which were morphologically, thermally and optically characterized to demonstrate the efficiency of the selected chemical approach. Aqueous solution of SA, PEO (used as co-spinning agent) and ZnO-NPs were carefully studied from a rheological point of view to investigate the polymer-filler interactions and establish the most promising systems to be processed on the basis of the viscosity results (Dodero et al., 2019; Vicini, Mauri, Vita, & Castellano, 2018). Moreover, an innovative washing-crosslinking method was especially developed to obtain stable alginate/ZnONPs products with the complete elimination of the used co-spinning agent without affecting the membrane structure; in particular, strontium ions were used as crosslinkers due to their biocompatibility, ability to improve the cell viability, and high affinity to alginate (Idota et al., 2016; Meka, Jain, & Chatterjee, 2016; Neves et al., 2016; Zhou et al., 2018). A thermal and spectroscopic characterization of the final products was carried out in order to assess their composition; a morphological investigation coupled with EDX spectroscopy was then conducted to define the shape and the dimension of the fibres as well as the ZnO-NPs distribution. The achieved results demonstrated the effective possibility to obtain alginate-based membranes embedded with ZnO nanoparticles via electrospinning technique, at the same time highlighting the importance of both the raw material choice and formulation properties. Above all, the prepared mats were characterized by thin and homogenous fibres with a global high porosity, thus representing a class of potential products to be used for several technological applications ranging from environmental to biomedical purposes.
Table 1 Summary of the prepared mixtures. Triton and ZnO-NPs concentrations were fixed at 1% wt and 0.25% wt, respectively. Sample
Total polymer concentration (% wt)
SA concentration (% wt)
PEO concentration (% wt)
SA LV
6 7 8 3 3.5 4 3.0 3.5 4
4.2 4.9 5.6 2.1 2.45 2.8 2.1 2.45 2.8
1.8 2.1 2.4 0.9 1.05 1.2 0.9 1.05 1.2
SA MVM SA MVG
2011; Jeong, Krebs, Bonino, Khan, & Alsberg, 2010; Kyzioł, Michna, Moreno, Gamez, & Irusta, 2017). Moreover, due to the complete solubility of alginate in water, a crosslinking reaction is required to obtain stable nanofibers, but the chemicals generally employed to the purpose (e.g. glutaraldehyde) are highly toxic and can invalidate any biomedical application (Schiffman & Schauer, 2008). In the present work, electrospinning technique was applied to prepare nanocomposite membranes using different sodium alginates (SA) and zinc oxide nanoparticles (ZnO-NPs), which usage has been scarcely investigated (Aderibigbe & Buyana, 2018) probably due to their tendency to establish strong interactions with the polymer chains and thus reducing the solution processability (Anitha, Brabu, John Thiruvadigal, Gopalakrishnan, & Natarajan, 2013; Chopra et al., 2015; Sui, Shao, & Liu, 2007). ZnO-NPs represent a very interesting material for several biomedical applications due to their properties in the pH neutral region, low toxicity and strong antibacterial capability against several bacteria (Lova, 2018, Lova et al., 2015; Schwartz et al., 2011; Xie, He, Irwin, Jin, & Shi, 2011); in order to exploit such performances, a good dispersion and stabilization of the nanoparticles within the polymer matrix are fundamental aspects that can be easily and cost-effectively achieved through their functionalization with bio-based coatings (Trandafilović, Božanić, Dimitrijević-Branković, Luyt, & Djoković, 2012; Vafaee & Ghamsari, 2007).
2. Materials and methods 2.1. Materials Low viscosity sodium alginate (SA LV) (viscosity ∼ 4 – 12 mPa⋅s, ¯ w 150 kg / mol ), 1% in H2O at 25 °C, with a M/G ratio ∼ 1.56, M medium viscosity sodium alginate (SA MVM) (viscosity ∼ 2000 mPa⋅s, ¯ w 500 kg / mol ) 2% in H2O at 25 °C, with a M/G ratio ∼ 1.56, M
Fig. 2. FE-SEM images of ZnO nanoparticles at magnification of 50,000 (a) and 100,000 (b). 2
Carbohydrate Polymers 227 (2020) 115371
A. Dodero, et al.
Fig. 3. TGA profile (a) and normalized UV–vis absorption spectrum (b) of ZnO-NPs protected by alginate chains.
¯ v = 900 kg / mol ), (Dodero, Pianella et al., 2019), poly(ethylene oxide) (M Triton™ X-100 (TR), zinc acetate dihydrate (ZnAc), sodium hydroxide (NaOH), strontium chloride hexahydrate (SrCl2) and absolute ethanol (EtOH) were purchased from Sigma Aldrich. Medium viscosity sodium alginate (SA MVG) (viscosity ∼ 200 mPa⋅s, 1% in H2O at 25 °C, with a ¯ w 400 kg / mol ) (Dodero, Pianella et al., 2019) was M/G ratio ≤ 0.67, M obtained from FMC Biopolymers.
Yasuda model according to Eq. 1:
=
+
(
0
[1 + (
) 1 n ) a] a
(1)
where η is the apparent viscosity, η∞ the infinite viscosity (i.e. viscosity at infinite shear rate), η0 the zero-shear viscosity (i.e. viscosity at zero shear rate), τ a fluid parameter referring to a characteristic time, the shear rate, n the flow index, and a the constitutive parameter (Yasuda, Armstrong, & Cohen, 1981).
2.2. Synthesis of ZnO-NPs ZnO nanoparticles were synthetized by means of a “green” sol-gel method reported in literature and slightly modified, consisting in the use of alginate as stabilizing agent (Trandafilović et al., 2012). In the prosed method, 1 mL of NaOH 1 mol/L, 2 mL of ZnAc 0.25 mol/L, and 5 mL of SA MVM 1% wt were firstly vigorously mixed together and heated up to 80 °C for 30 min. Subsequently, the obtained suspension was centrifuged at 4500 rpm for 30 min and the white deposit washed with deionized water for three times in order to remove eventual unreacted chemicals. Finally, the obtained nanoparticles were dried in oven at 50 °C under vacuum for 24 h and then stored in desiccator.
2.5. Electrospinning and crosslinking of the composite membranes The used electrospinning instrument consisted in a precision syringe pump, a high voltage-power supply, and an aluminium collector. The spinneret to collector distance was fixed at 15 cm whereas the applied voltage and the flow rate were varied from 10 to 12 kV and from 0.4 to 0.75 mL/h, respectively. The most suitable electrospinning parameters were chosen visualising the stability of the solution jet at the end of the needle using the Moticam 10 high-resolution camera. Once prepared, the membranes were firstly soaked in EtOH at 70 °C overnight and then in a 3% w/v SrCl2 medium for 30 s, washed several times with deionized water and finally dried in oven at 50 °C under vacuum for 24 h.
2.3. Preparation of alginate-based formulations SA powder was dissolved in deionized water to obtain a concentration ranging from 2.1% to 5.6% wt. The solutions were slowly stirred at room temperature for 24 h before adding PEO powder in a SA/PEO weight ratio of 70/30 to obtain formulations with a total polymer concentration in the range 3–8% wt. The obtained solutions were additionally stirred for 24 h and finally 1% wt of TR was added in order to decrease the surface tension and increase the solution spinnability, keeping the mixtures under stirring for further 24 h. A similar procedure was followed for the systems containing ZnO nanoparticles; polymer powders and TR were added to a 0.25% wt ZnO-NPs suspension previously prepared by dispersing the nanoparticles in deionized water through sonication at 59 kHz for 3 h. Table 1 summarizes the formulations prepared for each type of SA.
2.6. UV–vis spectroscopy The optical properties of the synthetized ZnO-NPs were spectroscopically investigated by means of a UV-1800 spectrophotometer (Shimadzu, Japan) at room temperature in the 200–1000 nm range starting from a 0.025% wt aqueous dispersion. 2.7. FE-SEM, EDX, FT-IR and TGA characterization The morphology of ZnO-NPs and alginate-based membranes was investigated by means of a field-emission scanning electron microscope (FE-SEM) ZEISS SUPRA 40 V P, operating at 10 kV in direct configuration (in-lens mode). A good conductivity of the samples was achieved with a thin layer of carbon sputter-coated using a Polaron E5100. EDX spectroscopy was used to evaluate both the distribution of strontium ions and nanoparticles within the obtained mats. The size of the nanoparticles and of the nanofibers was evaluated through an image statistical analysis using the open source software ImageJ. Fourier Transform InfraRed spectroscopy (FT-IR) was conducted on alginate-based membranes by means of a Bruker Vertex 70 instrument, operating in ATR mode. The thermal stability of ZnO-NPs and alginate-based membranes
2.4. Rheological characterization of alginate-based solutions The viscosity (η) of the prepared solutions was measured using a rotational rheometer Physica MCR 301 (Anton Paar, Austria GmbH) equipped with a Peltier heating system and a solvent trap; the temperature was set at 20.0 ± 0.2 °C. A plate-plate geometry with a diameter of 25 mm (PP25) was used and the gap fixed at 0.5 mm. Flow sweep tests were carried out in the shear rate ( ) range from 0.01 to 100 s−1. The experimental viscosity data were fitted with the Carreau3
Carbohydrate Polymers 227 (2020) 115371
A. Dodero, et al.
Table 2 Zero-shear viscosity values calculated for the tested formulations using the Carreau-Yasuda model. The chosen samples to be electrospun are denoted with *. Sample
Polymer concentration (%)
η0 (Pa s) Samples without NPs
η0 (Pa s) Samples with NPs
SA LV
6.0* 7.0 8.0 3.0 3.5* 4.0 3.0 3.5* 4.0
0.6 ± 0.1 – – – 6.7 ± 0.1 – – 12.2 ± 0.1 –
2.4 ± 0.1 4.8 ± 0.1 17.8 ± 2.7 8.5 ± 0.1 15.7 ± 0.1 27.8 ± 0.3 5.0 ± 0.1 12.5 ± 0.1 21.8 ± 0.2
SA MVM SA MVG
3. Results and discussion 3.1. ZnO nanoparticles characterization FE-SEM images of ZnO-NPs are reported in Fig. 2. As clearly shown, the nanoparticles tend to aggregate in irregular star-like clusters with dimensions of several hundred nanometres, where however the single nanoparticles can still be recognised (average size of 20–30 nm). The thermal degradation profile of ZnO-NPs shows (Fig. 3a) a weight loss of around 20% in the temperature range from 30 to 400 °C ascribable to the vaporization of humidity (T ≤ 100 °C) and bounded water (100 < T < 200 °C), and to the degradation of alginate (T > 250 °C) presents on the nanoparticles surface (Matinise, Fuku, Kaviyarasu, Mayedwa, & Maaza, 2017). No further degradation step can be observed in the temperature range between 400 °C and 700 °C, indicating that the prepared nanoparticles are highly stable. Fig. 3b shows the UV–vis absorption spectrum of the synthetized ZnO-NPs. The absorption peak at 352 nm is blue-shifted with respect to the typical absorption of ZnO in bulk (380 nm), which can be ascribable both to the presence of a layer of alginate on the nanoparticle surface and to quantum confinement effects (Abou Oualid, Amadine, Essamlali, Dânoun, & Zahouily, 2018; Pal, Esumi, & Pal, 2005); moreover, the sharp absorption profile of the band denotes the monodispersed nature of the nanoparticles. Such outcomes further confirm the FE-SEM results, demonstrating that despite the tendency to aggregate the prepared nanoparticles maintain their individuality and do not coalesce (Klingshirn, 2010; Talam, Karumuri, & Gunnam, 2012). The absorption peak at 263 nm can be ascribable to alginate chains present in solution (Sharma, Sanpui, Chattopadhyay, & Ghosh, 2012). Thus, it can be assumed that alginate can be successfully employed as stabilizing in the synthesis of ZnO nanoparticles through a sol-gel approach, creating a superficial layer able to protect the nanoparticles and avoid their tendency to aggregate. 3.2. Rheological properties of alginate-ZnO suspensions and spinnability A detailed rheological investigation in terms of viscosity, which is one of the main factors affecting the solution spinnability, was carried out on the prepared systems in order to select the more suitable to be electrospun; Fig. 4 shows the flow behaviour of all the mixtures listed in Table 1. The zero-shear viscosity values of each tested formulations were calculated according to Eq. 1 and listed in Table 2. For all samples a good agreement between the experimental data and theoretical curves was found (R2 > 0.99). As expected, for all SA the results indicate a significant increase of the solution viscosity with increasing the polymer concentration
Fig. 4. Flow curves of SA LV (a), SA MVM (b), and SA MVG (c) -based mixtures. The filled points represent the experimental data whereas the dash lines their fittings derived from the Carreau-Yasuda model. For the sake of comparison, the corresponding flow curves of the sample selected to be electrospun with and without ZnO-NPs are reported in the insets.
was assessed by means of thermogravimetric analysis (TGA) carried out with a Mettler-Toledo TGA/DCS1 STARe System. A dynamic mode operating in the range from 30 to 700 °C under N2 atmosphere (gas flow of 80 mL/min) with a heating rate of 10 °C/min was employed.
4
Carbohydrate Polymers 227 (2020) 115371
A. Dodero, et al.
of the nanoparticles induces an increase of the viscosity for SA LV and SA MVM-based solutions but has a negligible effect for the SA MVGbased sample. This result could be explained by taking into account the interactions that ZnO-NPs establish with the polysaccharide chains. The positively-charged ZnO nanoparticles (Sirelkhatim et al., 2015) are supposed to be predominantly linked to the negative charges present on alginate backbone through electrostatic bonds; however, the contribution of H-bonds involving the hydroxyl groups of the polysaccharide and of ZnO-NPs cannot be completely disregarded (Kanmani & Rhim, 2014; Salarbashi et al., 2016; Zheng, Monty, & Linhardt, 2015). In any case, being M-rich alginates characterized by a “straight-line molecular structure” (Fig. 1), it can be assumed that a significant number of carboxyl and hydroxyl groups are exposed to promote the interactions with ZnO-NPs; on the contrary, a higher amount of G-units creates “cavities” along the polymer chains (Fig. 1) thus reducing the availability of the aforementioned groups to form electrostatic bonds. Starting on these bases, it is reasonable that SA LV and SA MVM are likely to bind a higher number of ZnO nanoparticles than SA MVG, which in turn leads to a more significant increase of the viscosity. Considering a referring value of η0 in the 10-12 Pa⋅s range (Dodero, Pianella et al., 2019), for both the medium viscosity alginates (SA MVM and SA MVG) the nanocomposite mixtures with a total polymer concentration of 3.5% wt were selected to be electrospun. Using SA MVG, consistent membranes with a good manageability were obtained; conversely, despite of the appropriate viscosity value (Table 2), it was not possible to prepare any mats starting from SA MVM-based suspensions most likely because of the strong electrostatic interactions occurring between the polymer chains and ZnO-NPs, which somehow prevent the formation of the nanofibers. Nevertheless the viscosity was significantly lower compared to the ideal value (Table 2), the SA LV-based formulation with a concentration of 6.0% wt was successfully electrospun; quite consistent mats were obtained probably due to the fact that ZnONPs act as bridge-points between the polymer chains, which increase the solution spinnability. A higher polymer concentration did not lead to homogeneous solutions due to the difficulty to complete solubilize alginate, and consequently has not been used. 3.3. Spectroscopic and thermal characterization of the composite membranes Fig. 5 reports the FT-IR spectra collected in ATR mode for the SA MVG/ZnO-NPs-based mats compared with SA and PEO powders. Analogous results were obtained for SA LV-based mats. The spectral profiles of the composite membrane strongly resemble those of pure alginate powder (Fig. 5a) with slight differences probably due to the low amount of ZnO-NPs nanoparticles (Carp et al., 2015; Gómez-Ordóñez & Rupérez, 2011; Leal, Matsuhiro, Rossi, & Caruso, 2008). Compared to that of pure alginate powders, the large unstructured band in the 3000–3600 cm−1 range, which was attributed to the stretching vibrations of hydroxyl groups, is broader and slightly shifted to lower wavenumbers, indicating the establishment of intermolecular H-bonds between SA and ZnO-NPs. The bands at 1599 cm−1 and 1417 cm-1 were instead assigned to asymmetric and symmetric stretching vibrations of the carboxylic groups, respectively. In the fingerprint region, the signals at 1085 cm−1 and 1026 cm−1 corresponds to C–OeC vibrations whereas those falling at 940 cm−1 and 904 cm−1 are attributable to C–O vibrations. Nevertheless some signals (e.g. C–OeC and C–O vibrations) could be related to both polymers, as clearly observed in Fig. 5c the characteristic bands of PEO were not detected in the measured spectra (Çaykara, Demirci, Eroğlu, & Güven, 2005). Fig. 6a and b reports the thermal degradation profiles whereas Fig. 6c and b the correspondent derivative patterns of the prepared composite mats. Pure SA powders clearly present a multi-step degradation profile. The first weight loss, occurring in the temperature range of 30–150 °C,
Fig. 5. FT-IR spectra of SA MVG powder (a), SA MVG/ZnO-NPs-based membrane (b) and PEO powder (c).
(Dodero, Williams et al., 2019). Moreover, all samples show the typical shear-thinning behaviour of polymer solutions, characterized by a welldefined Newtonian plateau at low shear-rate followed by a significant drop of the viscosity values with increasing the shear-rate (Torres, Hallmark, & Wilson, 2014). The presence of an initial constant-viscosity region, as well as the consistence of the experimental data with the Carreau-Yasuda model, indicates that ZnO-NPs are well dispersed within the alginate-based solutions (Boyer, Guazzelli, & Pouliquen, 2011; van der Vaart et al., 2013). Comparing the η0 values of the formulations with and without ZnONPs (insets in Fig. 4 and Table 2), it can be observed that the presence 5
Carbohydrate Polymers 227 (2020) 115371
A. Dodero, et al.
Fig. 6. TGA and DTG profiles of SA LV/ZnO-NPs based membrane (a–c) and SA MVG/ZnO-NPs based membrane (b–d). Thermal degradation profiles of PEO and SA powders are also reported for comparison.
Fig. 7. FE-SEM images of SA LV/ZnO-NPs based membrane (a) and SA MVG/ZnO-NPs based membrane (b) and their corresponding diameter distribution histograms.
corresponds to the vaporization of humidity and bounded water. The second step occurs in the 240–280 °C temperature range and regards the alginate degradation to metal carbonates, which finally decomposes slowly in a third step starting from 650 °C (Castellano, Alloisio, Darawish, Dodero, & Vicini, 2019; Li, Chen, Yi, Zhang, & Ye, 2010). Contrarywise, PEO powder is characterized by a single-step degradation occurring in the 390–410 °C temperature range (Ray & Cooney, 2018). The composite membranes show a degradation profile mostly resembling that of pure SA powders, except for the presence of an additional decomposition step, which however is not attributable to PEO. In detail, this weight loss is positioned at a temperature of 330–350 °C for the SA LV-based composite mat and of 360–380 °C for the SA MVG-based
composite mat. As reported in literature (Pan et al., 2017), this supplementary degradation step can tentatively be ascribable to the crosslinking of alginate, which stabilizes the polymer and consequently delays its degradation. The difference found for SA LV and SA MVGbased samples can be related to their different composition; indeed, being the alginate crosslinking degree directly correlated to the content of G-units (the only ones involved in the crosslinking process), the higher degradation temperature found for SA MVG-based mat is in agreement with its superior crosslinking density and stability. From the FT-IR and TGA results, PEO component seemed to be completely removed from the final composite mats most likely due to the soaking process in hot EtOH. Indeed, while alginate is completely 6
Carbohydrate Polymers 227 (2020) 115371
A. Dodero, et al.
Fig. 8. EDX map of SA MVG-based mat; strontium ions and ZnO-NPs are reported in yellow and blue, respectively (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article).
insoluble in alcohol at any temperature, PEO becomes soluble above its melting point (Tm ∼ 60 °C) (Ho, Hammouda, Kline, & Chen, 2006). Thus, the combination of a hot-washing cycle in EtOH followed by the crosslinking reaction in aqueous solution containing Sr2+ ions represents a good method to obtain crosslinked electrospun mats of pure alginate.
ranging from 20 nm up to several hundred of nanometres. The rheological behaviour of sodium alginate/PEO solutions was strongly influenced by ZnO-NPs, most likely due the establishment of intermolecular hydrogen bonds and electrostatic interactions. However, the molecular composition of SA plays a key role in the intensity of such interactions. The predominance of M-units in the polymer backbone leads to the exposure of a high number of carboxylic and hydroxylic groups, increasing their availability to establish strong interactions with ZnO-NPs. On the contrary, for G-rich alginates the influence of ZnO-NPs is almost negligible due to the presence of cavities along the polymer chains, which somehow hinder the formation of the aforementioned interactions. Therefore, as far as the electrospinning process is concerned, it can be assumed that alginates with a low molecular mass and high M/G ratio or alginates with a medium molecular mass and low M/ G ratio should be preferred when used in combination with ZnO-NPs. The prepared mats were subjected to an innovative washing process with hot EtOH followed by the crosslinking with strontium ions; this procedure allowed to obtain highly stable alginate nanocomposite mats without modifying the characteristic nanofibrous structure. Indeed, the morphological characterization showed that the obtained membranes are characterized by uniform, well-organized nanofibers with a diameter in the range 70 to 150 nm and a globally high porosity; moreover, the spectroscopic and thermal investigation carried out confirmed the total elimination of poly(ethylene oxide).
3.4. Morphological and EDX characterization of the composite membranes Fig. 7 shows the FE-SEM images obtained for the composite mats based on SA LV (Fig. 7a) and SA MVG (Fig. 7b). Both the mats are characterized by a uniform morphology consisting in well-formed fibres quite symmetrically distributed in a single population, as shown in the figure insets; however, some differences can be appreciated for the two samples. For the SA LV-based product, the fibres show an average diameter of 120 nm ( ± 25%) and are characterized by a quite rough and wrinkled surface; moreover, some ZnONPs agglomerates with a diameter around 150 nm can be observed on the fibres surface. Such results can be explained by taking into account the molecular properties of this material, which is characterized by a “high” M/G ratio (∼1.56) and a “low” molecular mass ¯ w 150 kg / mol ); the predominance of M-units and short chains leads (M to a low crosslinking density, which in turn leads to nanofibrous mats with a poor stability and shape defects. On the contrary, the SA MVGbased product is characterized by well-separated and smooth fibres with an average diameter of 100 nm ( ± 30%); considering the “low” ¯ w 400 kg / mol ) M/G ratio (≤ 0.67) and the “high” molecular mass (M of this alginate type, it can be assumed that the incremented crosslinking density reduces the swelling properties of the fibres thus improving the texturing homogeneity of the mats. Individual or aggregated ZnO-NPs cannot be easily observed, but it can be supposed they are completely incorporated within the nanofibers. Fig. 8 shows the EXD results obtained for the SA MVG-based mats; similar results were obtained for SA LV-based products. The homogeneous and dense strontium ion distribution (yellow points) indicates that the samples are highly crosslinked, further confirming the validation of the proposed crosslinking method to obtained stable alginate membranes. Moreover, ZnO-NPs appear to be well dispersed within the mats (blue points), which is in agreement with morphological investigation. Above all, the electrospun mats are both characterized by a high porosity, which is a fundamental requirement for the use of these products in biomedical and pharmaceutical applications (Bandyopadhyay et al., 2010; Vafai, 2011).
Funding This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Declaration of Competing Interest None. References Abou Oualid, H., Amadine, O., Essamlali, Y., Dânoun, K., & Zahouily, M. (2018). Supercritical CO2 drying of alginate/zinc hydrogels: A green and facile route to prepare ZnO foam structures and ZnO nanoparticles. RSC Advances, 8(37), 20737–20747. https://doi.org/10.1039/C8RA02129E. Aderibigbe, B. A., & Buyana, B. (2018). Alginate in wound dressings. Pharmaceutics, 10(2), https://doi.org/10.3390/pharmaceutics10020042. Anitha, S., Brabu, B., John Thiruvadigal, D., Gopalakrishnan, C., & Natarajan, T. S. (2013). Optical, bactericidal and water repellent properties of electrospun nanocomposite membranes of cellulose acetate and ZnO. Carbohydrate Polymers, 97(2), 856–863. https://doi.org/10.1016/j.carbpol.2013.05.003. Bandyopadhyay, A., Espana, F., Balla, V. K., Bose, S., Ohgami, Y., & Davies, N. M. (2010). Influence of porosity on mechanical properties and in vivo response of Ti6Al4V implants. Acta Biomaterialia, 6(4), 1640–1648. https://doi.org/10.1016/J.ACTBIO. 2009.11.011. Bidarra, S. J., Barrias, C. C., & Granja, P. L. (2014). Injectable alginate hydrogels for cell delivery in tissue engineering. Acta Biomaterialia, 10(4), 1646–1662. https://doi.org/ 10.1016/J.ACTBIO.2013.12.006. Bonino, C. A., Krebs, M. D., Saquing, C. D., Jeong, S. I., Shearer, K. L., Alsberg, E., ... Khan, S. A. (2011). Electrospinning alginate-based nanofibers: From blends to crosslinked low molecular weight alginate-only systems. Carbohydrate Polymers, 85(1), 111–119.
4. Conclusions In the present work nanocomposite alginate-based membranes loaded with ZnO nanoparticles were successfully prepared via electrospinning technique. ZnO-NPs were synthetized by means of a “green” sol-gel method approach obtaining star-like nanostructures with a size 7
Carbohydrate Polymers 227 (2020) 115371
A. Dodero, et al.
2015.10.038. Pal, A., Esumi, K., & Pal, T. (2005). Preparation of nanosized gold particles in a biopolymer using UV photoactivation. Journal of Colloid and Interface Science, 288(2), 396–401. https://doi.org/10.1016/j.jcis.2005.03.048. Pan, Y., Wang, W., Liu, L., Ge, H., Song, L., & Hu, Y. (2017). Influences of metal ions crosslinked alginate based coatings on thermal stability and fire resistance of cotton fabrics. Carbohydrate Polymers, 170, 133–139. https://doi.org/10.1016/J.CARBPOL. 2017.04.065. Peng, S., Jin, G., Li, L., Li, K., Srinivasan, M., Ramakrishna, S., ... Chen, J. (2016). Multifunctional electrospun nanofibres for advances in tissue regeneration, energy conversion & storage, and water treatment. Chemical Society Reviews, 45(5), 1225–1241. https://doi.org/10.1039/C5CS00777A. Ray, S., & Cooney, R. P. (2018). Thermal degradation of polymer and polymer composites. Handbook of environmental degradation of materials. 185–206. https://doi.org/10. 1016/B978-0-323-52472-8.00009-5. Salarbashi, D., Mortazavi, S. A., Noghabi, M. S., Fazly Bazzaz, B. S., Sedaghat, N., Ramezani, M., ... Shahabi-Ghahfarrokhi, I. (2016). Development of new active packaging film made from a soluble soybean polysaccharide incorporating ZnO nanoparticles. Carbohydrate Polymers, 140, 220–227. https://doi.org/10.1016/J. CARBPOL.2015.12.043. Schiffman, J. D., & Schauer, C. L. (2008). A review: Electrospinning of biopolymer nanofibers and their applications. Polymer Reviews, 48(2), 317–352. https://doi.org/10. 1080/15583720802022182. Schwartz, V. B., Thétiot, F., Ritz, S., Pütz, S., Choritz, L., Lappas, A., ... Shin, H. S. (2011). Antibacterial surface coatings from zinc oxide nanoparticles embedded in poly(Nisopropylacrylamide) hydrogel surface layers. Applied and Environmental Microbiology, 22(11), 2325–2331. https://doi.org/10.1128/aem.02149-10. Sharma, S., Sanpui, P., Chattopadhyay, A., & Ghosh, S. S. (2012). Fabrication of antibacterial silver nanoparticle—Sodium alginate–chitosan composite films. RSC Advances, 2(13), 5837. https://doi.org/10.1039/c2ra00006g. Sirelkhatim, A., Mahmud, S., Seeni, A., Kaus, N. H. M., Ann, L. C., Bakhori, S. K. M., ... Mohamad, D. (2015). Review on zinc oxide nanoparticles: Antibacterial activity and toxicity mechanism. Nano-Micro Letters, 7(3), 219–242. https://doi.org/10.1007/ s40820-015-0040-x. Stagnaro, P., Schizzi, I., Utzeri, R., Marsano, E., & Castellano, M. (2018). Alginate-polymethacrylate hybrid hydrogels for potential osteochondral tissue regeneration. Carbohydrate Polymers, 185, 56–62. https://doi.org/10.1016/J.CARBPOL.2018.01. 012. Sui, X., Shao, C., & Liu, Y. (2007). Photoluminescence of polyethylene oxide-ZnO composite electrospun fibers. Polymer, 48(6), 1459–1463. https://doi.org/10.1016/j. polymer.2007.01.039. Talam, S., Karumuri, S. R., & Gunnam, N. (2012). Synthesis, characterization, and spectroscopic properties of ZnO nanoparticles. ISRN Nanotechnology, 2012, 1–6. https:// doi.org/10.5402/2012/372505. Torres, M. D., Hallmark, B., & Wilson, D. I. (2014). Effect of concentration on shear and extensional rheology of guar gum solutions. Food Hydrocolloids, 40, 85–95. https:// doi.org/10.1016/J.FOODHYD.2014.02.011. Trandafilović, L. V., Božanić, D. K., Dimitrijević-Branković, S., Luyt, A. S., & Djoković, V. (2012). Fabrication and antibacterial properties of ZnO–alginate nanocomposites. Carbohydrate Polymers, 88(1), 263–269. https://doi.org/10.1016/J.CARBPOL.2011. 12.005. Vafaee, M., & Ghamsari, M. S. (2007). Preparation and characterization of ZnO nanoparticles by a novel sol–gel route. Materials Letters, 61(14–15), 3265–3268. https:// doi.org/10.1016/J.MATLET.2006.11.089. Vafai, K. (2011). Porous media: Applications in biological systems and biotechnology. CRC Press. van der Vaart, K., Rahmani, Y., Zargar, R., Hu, Z., Bonn, D., & Schall, P. (2013). Rheology of concentrated soft and hard-sphere suspensions. Journal of Rheology, 57(4), 1195–1209. https://doi.org/10.1122/1.4808054. Vicini, S., Castellano, M., Mauri, M., & Marsano, E. (2015). Gelling process for sodium alginate: New technical approach by using calcium rich micro-spheres. Carbohydrate Polymers, 134, 767–774. https://doi.org/10.1016/j.carbpol.2015.08.064. Vicini, S., Mauri, M., Vita, S., & Castellano, M. (2018). Alginate and alginate/hyaluronic acid membranes generated by electrospinning in wet conditions: Relationship between solution viscosity and spinnability. Journal of Applied Polymer Science, 135(25), 46390. https://doi.org/10.1002/app.46390. Vicini, S., Mauri, M., Wichert, J., & Castellano, M. (2017). Alginate gelling process: Use of bivalent ions rich microspheres. Polymer Engineering and Science, 57(6), 531–536. https://doi.org/10.1002/pen.24552. Xie, Y., He, Y., Irwin, P. L., Jin, T., & Shi, X. (2011). Antibacterial activity and mechanism of action of zinc oxide nanoparticles against Campylobacter jejuni. Applied and Environmental Microbiology, 77(7), 2325–2331. https://doi.org/10.1128/aem. 02149-10. Yasuda, K., Armstrong, R. C., & Cohen, R. E. (1981). Shear flow properties of concentrated solutions of linear and star branched polystyrenes. Rheologica Acta, 20(2), 163–178. https://doi.org/10.1007/BF01513059. Zheng, Y., Monty, J., & Linhardt, R. J. (2015). Polysaccharide-based nanocomposites and their applications. Carbohydrate Research, 405, 23–32. https://doi.org/10.1016/J. CARRES.2014.07.016. Zhou, Q., Kang, H., Bielec, M., Wu, X., Cheng, Q., Wei, W., ... Dai, H. (2018). Influence of different divalent ions cross-linking sodium alginate-polyacrylamide hydrogels on antibacterial properties and wound healing. Carbohydrate Polymers, 197, 292–304. https://doi.org/10.1016/J.CARBPOL.2018.05.078.
https://doi.org/10.1016/J.CARBPOL.2011.02.002. Boyer, F., Guazzelli, É., & Pouliquen, O. (2011). Unifying suspension and granular rheology. Physical Review Letters, 107(18), 188301. https://doi.org/10.1103/ PhysRevLett.107.188301. Carp, O., AlinaTirsoaga, Jurca, B., Ene, R., Somacescu, S., & Ianculescu, A. (2015). Biopolymer starch mediated synthetic route of multi-spheres and donut ZnO structures. Carbohydrate Polymers, 115, 285–293. https://doi.org/10.1016/J.CARBPOL. 2014.08.061. Castellano, M., Alloisio, M., Darawish, R., Dodero, A., & Vicini, S. (2019). Electrospun composite mats of alginate with embedded silver nanoparticles. Journal of Thermal Analysis and Calorimetry, 137(3), 767–778. https://doi.org/10.1007/s10973-0187979-z. Çaykara, T., Demirci, S., Eroğlu, M. S., & Güven, O. (2005). Poly(ethylene oxide) and its blends with sodium alginate. Polymer, 46(24), 10750–10757. https://doi.org/10. 1016/J.POLYMER.2005.09.041. Chopra, M., Bernela, M., Kaur, P., Manuja, A., Kumar, B., & Thakur, R. (2015). Alginate/ gum acacia bipolymeric nanohydrogels-promising carrier for zinc oxide nanoparticles. International Journal of Biological Macromolecules, 72, 827–833. https://doi. org/10.1016/j.ijbiomac.2014.09.037. Dodero, A., Pianella, L., Vicini, S., Alloisio, M., Ottonelli, M., & Castellano, M. (2019). Alginate-based hydrogels prepared via ionic gelation: An experimental design approach to predict the crosslinking degree. European Polymer Journal, 118, 586–594. https://doi.org/10.1016/J.EURPOLYMJ.2019.06.028. Dodero, A., Vicini, S., Alloisio, M., & Castellano, M. (2019). Sodium alginate solutions: Correlation between rheological properties and spinnability. Journal of Materials Science, 54(10), 8034–8046. https://doi.org/10.1007/s10853-019-03446-3. Dodero, A., Williams, R., Gagliardi, S., Vicini, S., Alloisio, M., & Castellano, M. (2018). Characterization of hyaluronic acid by dynamic light scattering and rheological techniques. In AIP Conference Proceedingshttps://doi.org/10.1063/1.5046046 Vol. 1981, p. 020184. Dodero, A., Williams, R., Gagliardi, S., Vicini, S., Alloisio, M., & Castellano, M. (2019). A micro-rheological and rheological study of biopolymers solutions: Hyaluronic acid. Carbohydrate Polymers, 203, 349–355. https://doi.org/10.1016/J.CARBPOL.2018.09. 072. Gómez-Ordóñez, E., & Rupérez, P. (2011). FTIR-ATR spectroscopy as a tool for polysaccharide identification in edible brown and red seaweeds. Food Hydrocolloids, 25(6), 1514–1520. https://doi.org/10.1016/J.FOODHYD.2011.02.009. Ho, D. L., Hammouda, B., Kline, S. R., & Chen, W.-R. (2006). Unusual phase behavior in mixtures of poly(ethylene oxide) and ethyl alcohol. Journal of Polymer Science Part B Polymer Physics, 44(3), 557–564. https://doi.org/10.1002/polb.20726. Idota, Y., Kogure, Y., Kato, T., Yano, K., Arakawa, H., Miyajima, C., ... Ogihara, T. (2016). Relationship between physical parameters of various metal ions and binding affinity for alginate. Biological & Pharmaceutical Bulletin, 39(11), 1893–1896. https://doi.org/ 10.1248/bpb.b16-00127. Jeong, S. I., Krebs, M. D., Bonino, C. A., Khan, S. A., & Alsberg, E. (2010). Electrospun alginate nanofibers with controlled cell adhesion for tissue engineeringa. Macromolecular Bioscience, 10(8), 934–943. https://doi.org/10.1002/mabi. 201000046. Jiang, T., Carbone, E. J., Lo, K. W.-H., & Laurencin, C. T. (2015). Electrospinning of polymer nanofibers for tissue regeneration. Progress in Polymer Science, 46, 1–24. https://doi.org/10.1016/J.PROGPOLYMSCI.2014.12.001. Kalia, S., & Avérous, L. (2011). Biopolymers: Biomedical and environmental applications. Wiley. Kanmani, P., & Rhim, J.-W. (2014). Properties and characterization of bionanocomposite films prepared with various biopolymers and ZnO nanoparticles. Carbohydrate Polymers, 106, 190–199. https://doi.org/10.1016/J.CARBPOL.2014.02.007. Klingshirn, C. F. Claus F. (2010). Zinc oxide: From fundamental properties towards novel applications. Springer. Kyzioł, A., Michna, J., Moreno, I., Gamez, E., & Irusta, S. (2017). Preparation and characterization of electrospun alginate nanofibers loaded with ciprofloxacin hydrochloride. European Polymer Journal, 96, 350–360. https://doi.org/10.1016/J. EURPOLYMJ.2017.09.020. Leal, D., Matsuhiro, B., Rossi, M., & Caruso, F. (2008). FT-IR spectra of alginic acid block fractions in three species of brown seaweeds. Carbohydrate Research, 343(2), 308–316. https://doi.org/10.1016/J.CARRES.2007.10.016. Li, D., Chen, L., Yi, X., Zhang, X., & Ye, N. (2010). Pyrolytic characteristics and kinetics of two brown algae and sodium alginate. Bioresource Technology, 101(18), 7131–7136. https://doi.org/10.1016/J.BIORTECH.2010.03.145. Lova, P. (2018). Selective polymer distributed bragg reflector vapor sensors. Polymers, 10(10), 1161. https://doi.org/10.3390/polym10101161. Lova, P., Manfredi, G., Boarino, L., Laus, M., Urbinati, G., Losco, T., ... Comoretto, D. (2015). Hybrid ZnO:Polystyrene nanocomposite for all-polymer photonic crystals. Physica Status Solidi (C), 12(1–2), 158–162. https://doi.org/10.1002/pssc. 201400209. Matinise, N., Fuku, X. G., Kaviyarasu, K., Mayedwa, N., & Maaza, M. (2017). ZnO nanoparticles via Moringa oleifera green synthesis: Physical properties & mechanism of formation. Applied Surface Science, 406, 339–347. https://doi.org/10.1016/j.apsusc. 2017.01.219. Meka, S. R. K., Jain, S., & Chatterjee, K. (2016). Strontium eluting nanofibers augment stem cell osteogenesis for bone tissue regeneration. Colloids and Surfaces B Biointerfaces, 146, 649–656. https://doi.org/10.1016/J.COLSURFB.2016.07.012. Neves, N., Campos, B. B., Almeida, I. F., Costa, P. C., Cabral, A. T., Barbosa, M. A., ... Ribeiro, C. C. (2016). Strontium-rich injectable hybrid system for bone regeneration. Materials Science and Engineering C, 59, 818–827. https://doi.org/10.1016/J.MSEC.
8
Contents lists available at ScienceDirect
Carbohydrate Polymers journal homepage: www.elsevier.com/locate/carbpol
Preparation of composite alginate-based electrospun membranes loaded with ZnO nanoparticles
T
Andrea Dodero , Marina Alloisio, Silvia Vicini, Maila Castellano ⁎
Università degli Studi di Genova, Dipartimento di Chimica e Chimica Industriale, Via Dodecaneso 31, 16146 Genoa, Italy
ARTICLE INFO
ABSTRACT
Chemical compounds studied in this article: Sodium alginate (CID: 133126842) Poly(ethylene oxide) (CID: 8200) Strontium chloride hexahydrate (CID: 159250) Zinc oxide (CID: 14806)
In the present work alginate-based nanofibrous membranes embedding zinc oxide nanoparticles (ZnO-NPs) were prepared via electrospinning technique. ZnO-NPs were synthesized by means of a “green” sol-gel method by using alginate itself as stabilizing agent and characterized through UV–vis spectroscopy, thermogravimetric and morphological analysis. Formulations containing sodium alginate, poly(ethylene oxide) and ZnO-NPs were rheologically studied to identify the most suitable ones to be electrospun; alginate molecular structure played an important role on the solution spinnability due to the polysaccharide capability to establish electrostatic interactions and hydrogen bonds with ZnO-NPs. An innovative washing-crosslinking protocol was developed to obtain stable products which composition was assessed using Fourier Transform InfraRed spectroscopy and thermogravimetric analysis. Morphological investigation combined with EDX spectroscopy proved the obtained mats were highly porous and composed by thin homogenous nanofibers with a good distribution of the used nanofillers, thus representing potential products for several purposes (e.g. biomedical, pharmaceutical and environmental applications).
Keywords: Sodium alginate Zinc-oxide nanoparticles Rheology Electrospinning Nanofibrous membranes
1. Introduction Nowadays biopolymers represent an important class of materials widely used for several purposes, such as biomedical, pharmaceutical and environmental applications (Dodero et al., 2018, Kalia & Avérous, 2011). Among these materials, alginate has attracted a lot of interest due to its biocompatibility, biodegradability, biological activity, low cost, water-solubility, and ease of production and functionalization. Alginates are a family of linear polysaccharides extracted from brown algae and composed of β-D-mannuronic acid (M-units) and α-L-guluronic acid (G-units), as shown in Fig. 1. One of the main reason of alginate success lies in its ability to undergo a thermal independent sol/ gel transition in the presence of bivalent and trivalent cations; accordingly to the commonly called “egg-box” model, such cations are able to bind the G-units of alginate skeleton thus creating a stable threedimensional network (Fig. 1) (Vicini, Castellano, Mauri, & Marsano, 2015; Vicini, Mauri, Wichert, & Castellano, 2017). The ionic gelation of alginate has been widely employed to prepare 3D hydrogels to be used as porous scaffolds and drug delivery systems for biomedical and pharmaceutical applications (Bidarra, Barrias, & Granja, 2014; Dodero, Pianella et al., 2019; Stagnaro, Schizzi, Utzeri, Marsano, & Castellano, 2018); however, such products are usually
characterized by poor and/or inadequate mechanical properties, as well as by a microstructure which limits the cell viability. To overcome such limitations, in recent years the possibility to use electrospinning technique to produce nonwoven nanofibrous membranes has been widely investigated; indeed, the obtained systems are characterized by a texture that in the microscale strongly resembles the natural extra-cellular matrix, thus offering the ideal environment to foster cell viability due to the high surface area and porosity (Jiang, Carbone, Lo, & Laurencin, 2015; Peng et al., 2016). A further advantage of electrospinning concerns the possibility to prepare nanocomposite mats by simply dispersing nanofillers within the starting polymer solutions in order to confer additional properties to the final products, such as antioxidant and antimicrobial activities. However, despite the mentioned advantages, the electrospinning process of alginate from aqueous solution is extremely difficult owing to the high viscosity, the polyelectrolyte nature, and the H-bonding between the polymer chains which usually prevent the formation of a stable jet during the processing and leading to nonhomogeneous bead-like structures. Therefore, synthetic non-toxic polymers (e.g. poly(ethylene oxide) (PEO) and poly(vinyl alcohol) (PVA)) are commonly added to alginate solutions to help the mixture processability, nevertheless they usually remain in the final products with the risk of affecting the global biological response (Bonino et al.,
Corresponding author. E-mail addresses: [email protected] (A. Dodero), [email protected] (M. Alloisio), [email protected] (S. Vicini), [email protected] (M. Castellano). ⁎
https://doi.org/10.1016/j.carbpol.2019.115371 Received 4 July 2019; Received in revised form 20 September 2019; Accepted 21 September 2019 Available online 23 September 2019 0144-8617/ © 2019 Elsevier Ltd. All rights reserved.
Carbohydrate Polymers 227 (2020) 115371
A. Dodero, et al.
Fig. 1. Chemical structure of alginate backbone and schematic representation of its chain organization in the presence of bivalent cations ("egg-box" model).
Consequently, ZnO-NPs were synthetized following a “green” sol-gel method reported in literature and slightly modified making use of alginate as stabilizing agent to obtain nanostructures which were morphologically, thermally and optically characterized to demonstrate the efficiency of the selected chemical approach. Aqueous solution of SA, PEO (used as co-spinning agent) and ZnO-NPs were carefully studied from a rheological point of view to investigate the polymer-filler interactions and establish the most promising systems to be processed on the basis of the viscosity results (Dodero et al., 2019; Vicini, Mauri, Vita, & Castellano, 2018). Moreover, an innovative washing-crosslinking method was especially developed to obtain stable alginate/ZnONPs products with the complete elimination of the used co-spinning agent without affecting the membrane structure; in particular, strontium ions were used as crosslinkers due to their biocompatibility, ability to improve the cell viability, and high affinity to alginate (Idota et al., 2016; Meka, Jain, & Chatterjee, 2016; Neves et al., 2016; Zhou et al., 2018). A thermal and spectroscopic characterization of the final products was carried out in order to assess their composition; a morphological investigation coupled with EDX spectroscopy was then conducted to define the shape and the dimension of the fibres as well as the ZnO-NPs distribution. The achieved results demonstrated the effective possibility to obtain alginate-based membranes embedded with ZnO nanoparticles via electrospinning technique, at the same time highlighting the importance of both the raw material choice and formulation properties. Above all, the prepared mats were characterized by thin and homogenous fibres with a global high porosity, thus representing a class of potential products to be used for several technological applications ranging from environmental to biomedical purposes.
Table 1 Summary of the prepared mixtures. Triton and ZnO-NPs concentrations were fixed at 1% wt and 0.25% wt, respectively. Sample
Total polymer concentration (% wt)
SA concentration (% wt)
PEO concentration (% wt)
SA LV
6 7 8 3 3.5 4 3.0 3.5 4
4.2 4.9 5.6 2.1 2.45 2.8 2.1 2.45 2.8
1.8 2.1 2.4 0.9 1.05 1.2 0.9 1.05 1.2
SA MVM SA MVG
2011; Jeong, Krebs, Bonino, Khan, & Alsberg, 2010; Kyzioł, Michna, Moreno, Gamez, & Irusta, 2017). Moreover, due to the complete solubility of alginate in water, a crosslinking reaction is required to obtain stable nanofibers, but the chemicals generally employed to the purpose (e.g. glutaraldehyde) are highly toxic and can invalidate any biomedical application (Schiffman & Schauer, 2008). In the present work, electrospinning technique was applied to prepare nanocomposite membranes using different sodium alginates (SA) and zinc oxide nanoparticles (ZnO-NPs), which usage has been scarcely investigated (Aderibigbe & Buyana, 2018) probably due to their tendency to establish strong interactions with the polymer chains and thus reducing the solution processability (Anitha, Brabu, John Thiruvadigal, Gopalakrishnan, & Natarajan, 2013; Chopra et al., 2015; Sui, Shao, & Liu, 2007). ZnO-NPs represent a very interesting material for several biomedical applications due to their properties in the pH neutral region, low toxicity and strong antibacterial capability against several bacteria (Lova, 2018, Lova et al., 2015; Schwartz et al., 2011; Xie, He, Irwin, Jin, & Shi, 2011); in order to exploit such performances, a good dispersion and stabilization of the nanoparticles within the polymer matrix are fundamental aspects that can be easily and cost-effectively achieved through their functionalization with bio-based coatings (Trandafilović, Božanić, Dimitrijević-Branković, Luyt, & Djoković, 2012; Vafaee & Ghamsari, 2007).
2. Materials and methods 2.1. Materials Low viscosity sodium alginate (SA LV) (viscosity ∼ 4 – 12 mPa⋅s, ¯ w 150 kg / mol ), 1% in H2O at 25 °C, with a M/G ratio ∼ 1.56, M medium viscosity sodium alginate (SA MVM) (viscosity ∼ 2000 mPa⋅s, ¯ w 500 kg / mol ) 2% in H2O at 25 °C, with a M/G ratio ∼ 1.56, M
Fig. 2. FE-SEM images of ZnO nanoparticles at magnification of 50,000 (a) and 100,000 (b). 2
Carbohydrate Polymers 227 (2020) 115371
A. Dodero, et al.
Fig. 3. TGA profile (a) and normalized UV–vis absorption spectrum (b) of ZnO-NPs protected by alginate chains.
¯ v = 900 kg / mol ), (Dodero, Pianella et al., 2019), poly(ethylene oxide) (M Triton™ X-100 (TR), zinc acetate dihydrate (ZnAc), sodium hydroxide (NaOH), strontium chloride hexahydrate (SrCl2) and absolute ethanol (EtOH) were purchased from Sigma Aldrich. Medium viscosity sodium alginate (SA MVG) (viscosity ∼ 200 mPa⋅s, 1% in H2O at 25 °C, with a ¯ w 400 kg / mol ) (Dodero, Pianella et al., 2019) was M/G ratio ≤ 0.67, M obtained from FMC Biopolymers.
Yasuda model according to Eq. 1:
=
+
(
0
[1 + (
) 1 n ) a] a
(1)
where η is the apparent viscosity, η∞ the infinite viscosity (i.e. viscosity at infinite shear rate), η0 the zero-shear viscosity (i.e. viscosity at zero shear rate), τ a fluid parameter referring to a characteristic time, the shear rate, n the flow index, and a the constitutive parameter (Yasuda, Armstrong, & Cohen, 1981).
2.2. Synthesis of ZnO-NPs ZnO nanoparticles were synthetized by means of a “green” sol-gel method reported in literature and slightly modified, consisting in the use of alginate as stabilizing agent (Trandafilović et al., 2012). In the prosed method, 1 mL of NaOH 1 mol/L, 2 mL of ZnAc 0.25 mol/L, and 5 mL of SA MVM 1% wt were firstly vigorously mixed together and heated up to 80 °C for 30 min. Subsequently, the obtained suspension was centrifuged at 4500 rpm for 30 min and the white deposit washed with deionized water for three times in order to remove eventual unreacted chemicals. Finally, the obtained nanoparticles were dried in oven at 50 °C under vacuum for 24 h and then stored in desiccator.
2.5. Electrospinning and crosslinking of the composite membranes The used electrospinning instrument consisted in a precision syringe pump, a high voltage-power supply, and an aluminium collector. The spinneret to collector distance was fixed at 15 cm whereas the applied voltage and the flow rate were varied from 10 to 12 kV and from 0.4 to 0.75 mL/h, respectively. The most suitable electrospinning parameters were chosen visualising the stability of the solution jet at the end of the needle using the Moticam 10 high-resolution camera. Once prepared, the membranes were firstly soaked in EtOH at 70 °C overnight and then in a 3% w/v SrCl2 medium for 30 s, washed several times with deionized water and finally dried in oven at 50 °C under vacuum for 24 h.
2.3. Preparation of alginate-based formulations SA powder was dissolved in deionized water to obtain a concentration ranging from 2.1% to 5.6% wt. The solutions were slowly stirred at room temperature for 24 h before adding PEO powder in a SA/PEO weight ratio of 70/30 to obtain formulations with a total polymer concentration in the range 3–8% wt. The obtained solutions were additionally stirred for 24 h and finally 1% wt of TR was added in order to decrease the surface tension and increase the solution spinnability, keeping the mixtures under stirring for further 24 h. A similar procedure was followed for the systems containing ZnO nanoparticles; polymer powders and TR were added to a 0.25% wt ZnO-NPs suspension previously prepared by dispersing the nanoparticles in deionized water through sonication at 59 kHz for 3 h. Table 1 summarizes the formulations prepared for each type of SA.
2.6. UV–vis spectroscopy The optical properties of the synthetized ZnO-NPs were spectroscopically investigated by means of a UV-1800 spectrophotometer (Shimadzu, Japan) at room temperature in the 200–1000 nm range starting from a 0.025% wt aqueous dispersion. 2.7. FE-SEM, EDX, FT-IR and TGA characterization The morphology of ZnO-NPs and alginate-based membranes was investigated by means of a field-emission scanning electron microscope (FE-SEM) ZEISS SUPRA 40 V P, operating at 10 kV in direct configuration (in-lens mode). A good conductivity of the samples was achieved with a thin layer of carbon sputter-coated using a Polaron E5100. EDX spectroscopy was used to evaluate both the distribution of strontium ions and nanoparticles within the obtained mats. The size of the nanoparticles and of the nanofibers was evaluated through an image statistical analysis using the open source software ImageJ. Fourier Transform InfraRed spectroscopy (FT-IR) was conducted on alginate-based membranes by means of a Bruker Vertex 70 instrument, operating in ATR mode. The thermal stability of ZnO-NPs and alginate-based membranes
2.4. Rheological characterization of alginate-based solutions The viscosity (η) of the prepared solutions was measured using a rotational rheometer Physica MCR 301 (Anton Paar, Austria GmbH) equipped with a Peltier heating system and a solvent trap; the temperature was set at 20.0 ± 0.2 °C. A plate-plate geometry with a diameter of 25 mm (PP25) was used and the gap fixed at 0.5 mm. Flow sweep tests were carried out in the shear rate ( ) range from 0.01 to 100 s−1. The experimental viscosity data were fitted with the Carreau3
Carbohydrate Polymers 227 (2020) 115371
A. Dodero, et al.
Table 2 Zero-shear viscosity values calculated for the tested formulations using the Carreau-Yasuda model. The chosen samples to be electrospun are denoted with *. Sample
Polymer concentration (%)
η0 (Pa s) Samples without NPs
η0 (Pa s) Samples with NPs
SA LV
6.0* 7.0 8.0 3.0 3.5* 4.0 3.0 3.5* 4.0
0.6 ± 0.1 – – – 6.7 ± 0.1 – – 12.2 ± 0.1 –
2.4 ± 0.1 4.8 ± 0.1 17.8 ± 2.7 8.5 ± 0.1 15.7 ± 0.1 27.8 ± 0.3 5.0 ± 0.1 12.5 ± 0.1 21.8 ± 0.2
SA MVM SA MVG
3. Results and discussion 3.1. ZnO nanoparticles characterization FE-SEM images of ZnO-NPs are reported in Fig. 2. As clearly shown, the nanoparticles tend to aggregate in irregular star-like clusters with dimensions of several hundred nanometres, where however the single nanoparticles can still be recognised (average size of 20–30 nm). The thermal degradation profile of ZnO-NPs shows (Fig. 3a) a weight loss of around 20% in the temperature range from 30 to 400 °C ascribable to the vaporization of humidity (T ≤ 100 °C) and bounded water (100 < T < 200 °C), and to the degradation of alginate (T > 250 °C) presents on the nanoparticles surface (Matinise, Fuku, Kaviyarasu, Mayedwa, & Maaza, 2017). No further degradation step can be observed in the temperature range between 400 °C and 700 °C, indicating that the prepared nanoparticles are highly stable. Fig. 3b shows the UV–vis absorption spectrum of the synthetized ZnO-NPs. The absorption peak at 352 nm is blue-shifted with respect to the typical absorption of ZnO in bulk (380 nm), which can be ascribable both to the presence of a layer of alginate on the nanoparticle surface and to quantum confinement effects (Abou Oualid, Amadine, Essamlali, Dânoun, & Zahouily, 2018; Pal, Esumi, & Pal, 2005); moreover, the sharp absorption profile of the band denotes the monodispersed nature of the nanoparticles. Such outcomes further confirm the FE-SEM results, demonstrating that despite the tendency to aggregate the prepared nanoparticles maintain their individuality and do not coalesce (Klingshirn, 2010; Talam, Karumuri, & Gunnam, 2012). The absorption peak at 263 nm can be ascribable to alginate chains present in solution (Sharma, Sanpui, Chattopadhyay, & Ghosh, 2012). Thus, it can be assumed that alginate can be successfully employed as stabilizing in the synthesis of ZnO nanoparticles through a sol-gel approach, creating a superficial layer able to protect the nanoparticles and avoid their tendency to aggregate. 3.2. Rheological properties of alginate-ZnO suspensions and spinnability A detailed rheological investigation in terms of viscosity, which is one of the main factors affecting the solution spinnability, was carried out on the prepared systems in order to select the more suitable to be electrospun; Fig. 4 shows the flow behaviour of all the mixtures listed in Table 1. The zero-shear viscosity values of each tested formulations were calculated according to Eq. 1 and listed in Table 2. For all samples a good agreement between the experimental data and theoretical curves was found (R2 > 0.99). As expected, for all SA the results indicate a significant increase of the solution viscosity with increasing the polymer concentration
Fig. 4. Flow curves of SA LV (a), SA MVM (b), and SA MVG (c) -based mixtures. The filled points represent the experimental data whereas the dash lines their fittings derived from the Carreau-Yasuda model. For the sake of comparison, the corresponding flow curves of the sample selected to be electrospun with and without ZnO-NPs are reported in the insets.
was assessed by means of thermogravimetric analysis (TGA) carried out with a Mettler-Toledo TGA/DCS1 STARe System. A dynamic mode operating in the range from 30 to 700 °C under N2 atmosphere (gas flow of 80 mL/min) with a heating rate of 10 °C/min was employed.
4
Carbohydrate Polymers 227 (2020) 115371
A. Dodero, et al.
of the nanoparticles induces an increase of the viscosity for SA LV and SA MVM-based solutions but has a negligible effect for the SA MVGbased sample. This result could be explained by taking into account the interactions that ZnO-NPs establish with the polysaccharide chains. The positively-charged ZnO nanoparticles (Sirelkhatim et al., 2015) are supposed to be predominantly linked to the negative charges present on alginate backbone through electrostatic bonds; however, the contribution of H-bonds involving the hydroxyl groups of the polysaccharide and of ZnO-NPs cannot be completely disregarded (Kanmani & Rhim, 2014; Salarbashi et al., 2016; Zheng, Monty, & Linhardt, 2015). In any case, being M-rich alginates characterized by a “straight-line molecular structure” (Fig. 1), it can be assumed that a significant number of carboxyl and hydroxyl groups are exposed to promote the interactions with ZnO-NPs; on the contrary, a higher amount of G-units creates “cavities” along the polymer chains (Fig. 1) thus reducing the availability of the aforementioned groups to form electrostatic bonds. Starting on these bases, it is reasonable that SA LV and SA MVM are likely to bind a higher number of ZnO nanoparticles than SA MVG, which in turn leads to a more significant increase of the viscosity. Considering a referring value of η0 in the 10-12 Pa⋅s range (Dodero, Pianella et al., 2019), for both the medium viscosity alginates (SA MVM and SA MVG) the nanocomposite mixtures with a total polymer concentration of 3.5% wt were selected to be electrospun. Using SA MVG, consistent membranes with a good manageability were obtained; conversely, despite of the appropriate viscosity value (Table 2), it was not possible to prepare any mats starting from SA MVM-based suspensions most likely because of the strong electrostatic interactions occurring between the polymer chains and ZnO-NPs, which somehow prevent the formation of the nanofibers. Nevertheless the viscosity was significantly lower compared to the ideal value (Table 2), the SA LV-based formulation with a concentration of 6.0% wt was successfully electrospun; quite consistent mats were obtained probably due to the fact that ZnONPs act as bridge-points between the polymer chains, which increase the solution spinnability. A higher polymer concentration did not lead to homogeneous solutions due to the difficulty to complete solubilize alginate, and consequently has not been used. 3.3. Spectroscopic and thermal characterization of the composite membranes Fig. 5 reports the FT-IR spectra collected in ATR mode for the SA MVG/ZnO-NPs-based mats compared with SA and PEO powders. Analogous results were obtained for SA LV-based mats. The spectral profiles of the composite membrane strongly resemble those of pure alginate powder (Fig. 5a) with slight differences probably due to the low amount of ZnO-NPs nanoparticles (Carp et al., 2015; Gómez-Ordóñez & Rupérez, 2011; Leal, Matsuhiro, Rossi, & Caruso, 2008). Compared to that of pure alginate powders, the large unstructured band in the 3000–3600 cm−1 range, which was attributed to the stretching vibrations of hydroxyl groups, is broader and slightly shifted to lower wavenumbers, indicating the establishment of intermolecular H-bonds between SA and ZnO-NPs. The bands at 1599 cm−1 and 1417 cm-1 were instead assigned to asymmetric and symmetric stretching vibrations of the carboxylic groups, respectively. In the fingerprint region, the signals at 1085 cm−1 and 1026 cm−1 corresponds to C–OeC vibrations whereas those falling at 940 cm−1 and 904 cm−1 are attributable to C–O vibrations. Nevertheless some signals (e.g. C–OeC and C–O vibrations) could be related to both polymers, as clearly observed in Fig. 5c the characteristic bands of PEO were not detected in the measured spectra (Çaykara, Demirci, Eroğlu, & Güven, 2005). Fig. 6a and b reports the thermal degradation profiles whereas Fig. 6c and b the correspondent derivative patterns of the prepared composite mats. Pure SA powders clearly present a multi-step degradation profile. The first weight loss, occurring in the temperature range of 30–150 °C,
Fig. 5. FT-IR spectra of SA MVG powder (a), SA MVG/ZnO-NPs-based membrane (b) and PEO powder (c).
(Dodero, Williams et al., 2019). Moreover, all samples show the typical shear-thinning behaviour of polymer solutions, characterized by a welldefined Newtonian plateau at low shear-rate followed by a significant drop of the viscosity values with increasing the shear-rate (Torres, Hallmark, & Wilson, 2014). The presence of an initial constant-viscosity region, as well as the consistence of the experimental data with the Carreau-Yasuda model, indicates that ZnO-NPs are well dispersed within the alginate-based solutions (Boyer, Guazzelli, & Pouliquen, 2011; van der Vaart et al., 2013). Comparing the η0 values of the formulations with and without ZnONPs (insets in Fig. 4 and Table 2), it can be observed that the presence 5
Carbohydrate Polymers 227 (2020) 115371
A. Dodero, et al.
Fig. 6. TGA and DTG profiles of SA LV/ZnO-NPs based membrane (a–c) and SA MVG/ZnO-NPs based membrane (b–d). Thermal degradation profiles of PEO and SA powders are also reported for comparison.
Fig. 7. FE-SEM images of SA LV/ZnO-NPs based membrane (a) and SA MVG/ZnO-NPs based membrane (b) and their corresponding diameter distribution histograms.
corresponds to the vaporization of humidity and bounded water. The second step occurs in the 240–280 °C temperature range and regards the alginate degradation to metal carbonates, which finally decomposes slowly in a third step starting from 650 °C (Castellano, Alloisio, Darawish, Dodero, & Vicini, 2019; Li, Chen, Yi, Zhang, & Ye, 2010). Contrarywise, PEO powder is characterized by a single-step degradation occurring in the 390–410 °C temperature range (Ray & Cooney, 2018). The composite membranes show a degradation profile mostly resembling that of pure SA powders, except for the presence of an additional decomposition step, which however is not attributable to PEO. In detail, this weight loss is positioned at a temperature of 330–350 °C for the SA LV-based composite mat and of 360–380 °C for the SA MVG-based
composite mat. As reported in literature (Pan et al., 2017), this supplementary degradation step can tentatively be ascribable to the crosslinking of alginate, which stabilizes the polymer and consequently delays its degradation. The difference found for SA LV and SA MVGbased samples can be related to their different composition; indeed, being the alginate crosslinking degree directly correlated to the content of G-units (the only ones involved in the crosslinking process), the higher degradation temperature found for SA MVG-based mat is in agreement with its superior crosslinking density and stability. From the FT-IR and TGA results, PEO component seemed to be completely removed from the final composite mats most likely due to the soaking process in hot EtOH. Indeed, while alginate is completely 6
Carbohydrate Polymers 227 (2020) 115371
A. Dodero, et al.
Fig. 8. EDX map of SA MVG-based mat; strontium ions and ZnO-NPs are reported in yellow and blue, respectively (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article).
insoluble in alcohol at any temperature, PEO becomes soluble above its melting point (Tm ∼ 60 °C) (Ho, Hammouda, Kline, & Chen, 2006). Thus, the combination of a hot-washing cycle in EtOH followed by the crosslinking reaction in aqueous solution containing Sr2+ ions represents a good method to obtain crosslinked electrospun mats of pure alginate.
ranging from 20 nm up to several hundred of nanometres. The rheological behaviour of sodium alginate/PEO solutions was strongly influenced by ZnO-NPs, most likely due the establishment of intermolecular hydrogen bonds and electrostatic interactions. However, the molecular composition of SA plays a key role in the intensity of such interactions. The predominance of M-units in the polymer backbone leads to the exposure of a high number of carboxylic and hydroxylic groups, increasing their availability to establish strong interactions with ZnO-NPs. On the contrary, for G-rich alginates the influence of ZnO-NPs is almost negligible due to the presence of cavities along the polymer chains, which somehow hinder the formation of the aforementioned interactions. Therefore, as far as the electrospinning process is concerned, it can be assumed that alginates with a low molecular mass and high M/G ratio or alginates with a medium molecular mass and low M/ G ratio should be preferred when used in combination with ZnO-NPs. The prepared mats were subjected to an innovative washing process with hot EtOH followed by the crosslinking with strontium ions; this procedure allowed to obtain highly stable alginate nanocomposite mats without modifying the characteristic nanofibrous structure. Indeed, the morphological characterization showed that the obtained membranes are characterized by uniform, well-organized nanofibers with a diameter in the range 70 to 150 nm and a globally high porosity; moreover, the spectroscopic and thermal investigation carried out confirmed the total elimination of poly(ethylene oxide).
3.4. Morphological and EDX characterization of the composite membranes Fig. 7 shows the FE-SEM images obtained for the composite mats based on SA LV (Fig. 7a) and SA MVG (Fig. 7b). Both the mats are characterized by a uniform morphology consisting in well-formed fibres quite symmetrically distributed in a single population, as shown in the figure insets; however, some differences can be appreciated for the two samples. For the SA LV-based product, the fibres show an average diameter of 120 nm ( ± 25%) and are characterized by a quite rough and wrinkled surface; moreover, some ZnONPs agglomerates with a diameter around 150 nm can be observed on the fibres surface. Such results can be explained by taking into account the molecular properties of this material, which is characterized by a “high” M/G ratio (∼1.56) and a “low” molecular mass ¯ w 150 kg / mol ); the predominance of M-units and short chains leads (M to a low crosslinking density, which in turn leads to nanofibrous mats with a poor stability and shape defects. On the contrary, the SA MVGbased product is characterized by well-separated and smooth fibres with an average diameter of 100 nm ( ± 30%); considering the “low” ¯ w 400 kg / mol ) M/G ratio (≤ 0.67) and the “high” molecular mass (M of this alginate type, it can be assumed that the incremented crosslinking density reduces the swelling properties of the fibres thus improving the texturing homogeneity of the mats. Individual or aggregated ZnO-NPs cannot be easily observed, but it can be supposed they are completely incorporated within the nanofibers. Fig. 8 shows the EXD results obtained for the SA MVG-based mats; similar results were obtained for SA LV-based products. The homogeneous and dense strontium ion distribution (yellow points) indicates that the samples are highly crosslinked, further confirming the validation of the proposed crosslinking method to obtained stable alginate membranes. Moreover, ZnO-NPs appear to be well dispersed within the mats (blue points), which is in agreement with morphological investigation. Above all, the electrospun mats are both characterized by a high porosity, which is a fundamental requirement for the use of these products in biomedical and pharmaceutical applications (Bandyopadhyay et al., 2010; Vafai, 2011).
Funding This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Declaration of Competing Interest None. References Abou Oualid, H., Amadine, O., Essamlali, Y., Dânoun, K., & Zahouily, M. (2018). Supercritical CO2 drying of alginate/zinc hydrogels: A green and facile route to prepare ZnO foam structures and ZnO nanoparticles. RSC Advances, 8(37), 20737–20747. https://doi.org/10.1039/C8RA02129E. Aderibigbe, B. A., & Buyana, B. (2018). Alginate in wound dressings. Pharmaceutics, 10(2), https://doi.org/10.3390/pharmaceutics10020042. Anitha, S., Brabu, B., John Thiruvadigal, D., Gopalakrishnan, C., & Natarajan, T. S. (2013). Optical, bactericidal and water repellent properties of electrospun nanocomposite membranes of cellulose acetate and ZnO. Carbohydrate Polymers, 97(2), 856–863. https://doi.org/10.1016/j.carbpol.2013.05.003. Bandyopadhyay, A., Espana, F., Balla, V. K., Bose, S., Ohgami, Y., & Davies, N. M. (2010). Influence of porosity on mechanical properties and in vivo response of Ti6Al4V implants. Acta Biomaterialia, 6(4), 1640–1648. https://doi.org/10.1016/J.ACTBIO. 2009.11.011. Bidarra, S. J., Barrias, C. C., & Granja, P. L. (2014). Injectable alginate hydrogels for cell delivery in tissue engineering. Acta Biomaterialia, 10(4), 1646–1662. https://doi.org/ 10.1016/J.ACTBIO.2013.12.006. Bonino, C. A., Krebs, M. D., Saquing, C. D., Jeong, S. I., Shearer, K. L., Alsberg, E., ... Khan, S. A. (2011). Electrospinning alginate-based nanofibers: From blends to crosslinked low molecular weight alginate-only systems. Carbohydrate Polymers, 85(1), 111–119.
4. Conclusions In the present work nanocomposite alginate-based membranes loaded with ZnO nanoparticles were successfully prepared via electrospinning technique. ZnO-NPs were synthetized by means of a “green” sol-gel method approach obtaining star-like nanostructures with a size 7
Carbohydrate Polymers 227 (2020) 115371
A. Dodero, et al.
2015.10.038. Pal, A., Esumi, K., & Pal, T. (2005). Preparation of nanosized gold particles in a biopolymer using UV photoactivation. Journal of Colloid and Interface Science, 288(2), 396–401. https://doi.org/10.1016/j.jcis.2005.03.048. Pan, Y., Wang, W., Liu, L., Ge, H., Song, L., & Hu, Y. (2017). Influences of metal ions crosslinked alginate based coatings on thermal stability and fire resistance of cotton fabrics. Carbohydrate Polymers, 170, 133–139. https://doi.org/10.1016/J.CARBPOL. 2017.04.065. Peng, S., Jin, G., Li, L., Li, K., Srinivasan, M., Ramakrishna, S., ... Chen, J. (2016). Multifunctional electrospun nanofibres for advances in tissue regeneration, energy conversion & storage, and water treatment. Chemical Society Reviews, 45(5), 1225–1241. https://doi.org/10.1039/C5CS00777A. Ray, S., & Cooney, R. P. (2018). Thermal degradation of polymer and polymer composites. Handbook of environmental degradation of materials. 185–206. https://doi.org/10. 1016/B978-0-323-52472-8.00009-5. Salarbashi, D., Mortazavi, S. A., Noghabi, M. S., Fazly Bazzaz, B. S., Sedaghat, N., Ramezani, M., ... Shahabi-Ghahfarrokhi, I. (2016). Development of new active packaging film made from a soluble soybean polysaccharide incorporating ZnO nanoparticles. Carbohydrate Polymers, 140, 220–227. https://doi.org/10.1016/J. CARBPOL.2015.12.043. Schiffman, J. D., & Schauer, C. L. (2008). A review: Electrospinning of biopolymer nanofibers and their applications. Polymer Reviews, 48(2), 317–352. https://doi.org/10. 1080/15583720802022182. Schwartz, V. B., Thétiot, F., Ritz, S., Pütz, S., Choritz, L., Lappas, A., ... Shin, H. S. (2011). Antibacterial surface coatings from zinc oxide nanoparticles embedded in poly(Nisopropylacrylamide) hydrogel surface layers. Applied and Environmental Microbiology, 22(11), 2325–2331. https://doi.org/10.1128/aem.02149-10. Sharma, S., Sanpui, P., Chattopadhyay, A., & Ghosh, S. S. (2012). Fabrication of antibacterial silver nanoparticle—Sodium alginate–chitosan composite films. RSC Advances, 2(13), 5837. https://doi.org/10.1039/c2ra00006g. Sirelkhatim, A., Mahmud, S., Seeni, A., Kaus, N. H. M., Ann, L. C., Bakhori, S. K. M., ... Mohamad, D. (2015). Review on zinc oxide nanoparticles: Antibacterial activity and toxicity mechanism. Nano-Micro Letters, 7(3), 219–242. https://doi.org/10.1007/ s40820-015-0040-x. Stagnaro, P., Schizzi, I., Utzeri, R., Marsano, E., & Castellano, M. (2018). Alginate-polymethacrylate hybrid hydrogels for potential osteochondral tissue regeneration. Carbohydrate Polymers, 185, 56–62. https://doi.org/10.1016/J.CARBPOL.2018.01. 012. Sui, X., Shao, C., & Liu, Y. (2007). Photoluminescence of polyethylene oxide-ZnO composite electrospun fibers. Polymer, 48(6), 1459–1463. https://doi.org/10.1016/j. polymer.2007.01.039. Talam, S., Karumuri, S. R., & Gunnam, N. (2012). Synthesis, characterization, and spectroscopic properties of ZnO nanoparticles. ISRN Nanotechnology, 2012, 1–6. https:// doi.org/10.5402/2012/372505. Torres, M. D., Hallmark, B., & Wilson, D. I. (2014). Effect of concentration on shear and extensional rheology of guar gum solutions. Food Hydrocolloids, 40, 85–95. https:// doi.org/10.1016/J.FOODHYD.2014.02.011. Trandafilović, L. V., Božanić, D. K., Dimitrijević-Branković, S., Luyt, A. S., & Djoković, V. (2012). Fabrication and antibacterial properties of ZnO–alginate nanocomposites. Carbohydrate Polymers, 88(1), 263–269. https://doi.org/10.1016/J.CARBPOL.2011. 12.005. Vafaee, M., & Ghamsari, M. S. (2007). Preparation and characterization of ZnO nanoparticles by a novel sol–gel route. Materials Letters, 61(14–15), 3265–3268. https:// doi.org/10.1016/J.MATLET.2006.11.089. Vafai, K. (2011). Porous media: Applications in biological systems and biotechnology. CRC Press. van der Vaart, K., Rahmani, Y., Zargar, R., Hu, Z., Bonn, D., & Schall, P. (2013). Rheology of concentrated soft and hard-sphere suspensions. Journal of Rheology, 57(4), 1195–1209. https://doi.org/10.1122/1.4808054. Vicini, S., Castellano, M., Mauri, M., & Marsano, E. (2015). Gelling process for sodium alginate: New technical approach by using calcium rich micro-spheres. Carbohydrate Polymers, 134, 767–774. https://doi.org/10.1016/j.carbpol.2015.08.064. Vicini, S., Mauri, M., Vita, S., & Castellano, M. (2018). Alginate and alginate/hyaluronic acid membranes generated by electrospinning in wet conditions: Relationship between solution viscosity and spinnability. Journal of Applied Polymer Science, 135(25), 46390. https://doi.org/10.1002/app.46390. Vicini, S., Mauri, M., Wichert, J., & Castellano, M. (2017). Alginate gelling process: Use of bivalent ions rich microspheres. Polymer Engineering and Science, 57(6), 531–536. https://doi.org/10.1002/pen.24552. Xie, Y., He, Y., Irwin, P. L., Jin, T., & Shi, X. (2011). Antibacterial activity and mechanism of action of zinc oxide nanoparticles against Campylobacter jejuni. Applied and Environmental Microbiology, 77(7), 2325–2331. https://doi.org/10.1128/aem. 02149-10. Yasuda, K., Armstrong, R. C., & Cohen, R. E. (1981). Shear flow properties of concentrated solutions of linear and star branched polystyrenes. Rheologica Acta, 20(2), 163–178. https://doi.org/10.1007/BF01513059. Zheng, Y., Monty, J., & Linhardt, R. J. (2015). Polysaccharide-based nanocomposites and their applications. Carbohydrate Research, 405, 23–32. https://doi.org/10.1016/J. CARRES.2014.07.016. Zhou, Q., Kang, H., Bielec, M., Wu, X., Cheng, Q., Wei, W., ... Dai, H. (2018). Influence of different divalent ions cross-linking sodium alginate-polyacrylamide hydrogels on antibacterial properties and wound healing. Carbohydrate Polymers, 197, 292–304. https://doi.org/10.1016/J.CARBPOL.2018.05.078.
https://doi.org/10.1016/J.CARBPOL.2011.02.002. Boyer, F., Guazzelli, É., & Pouliquen, O. (2011). Unifying suspension and granular rheology. Physical Review Letters, 107(18), 188301. https://doi.org/10.1103/ PhysRevLett.107.188301. Carp, O., AlinaTirsoaga, Jurca, B., Ene, R., Somacescu, S., & Ianculescu, A. (2015). Biopolymer starch mediated synthetic route of multi-spheres and donut ZnO structures. Carbohydrate Polymers, 115, 285–293. https://doi.org/10.1016/J.CARBPOL. 2014.08.061. Castellano, M., Alloisio, M., Darawish, R., Dodero, A., & Vicini, S. (2019). Electrospun composite mats of alginate with embedded silver nanoparticles. Journal of Thermal Analysis and Calorimetry, 137(3), 767–778. https://doi.org/10.1007/s10973-0187979-z. Çaykara, T., Demirci, S., Eroğlu, M. S., & Güven, O. (2005). Poly(ethylene oxide) and its blends with sodium alginate. Polymer, 46(24), 10750–10757. https://doi.org/10. 1016/J.POLYMER.2005.09.041. Chopra, M., Bernela, M., Kaur, P., Manuja, A., Kumar, B., & Thakur, R. (2015). Alginate/ gum acacia bipolymeric nanohydrogels-promising carrier for zinc oxide nanoparticles. International Journal of Biological Macromolecules, 72, 827–833. https://doi. org/10.1016/j.ijbiomac.2014.09.037. Dodero, A., Pianella, L., Vicini, S., Alloisio, M., Ottonelli, M., & Castellano, M. (2019). Alginate-based hydrogels prepared via ionic gelation: An experimental design approach to predict the crosslinking degree. European Polymer Journal, 118, 586–594. https://doi.org/10.1016/J.EURPOLYMJ.2019.06.028. Dodero, A., Vicini, S., Alloisio, M., & Castellano, M. (2019). Sodium alginate solutions: Correlation between rheological properties and spinnability. Journal of Materials Science, 54(10), 8034–8046. https://doi.org/10.1007/s10853-019-03446-3. Dodero, A., Williams, R., Gagliardi, S., Vicini, S., Alloisio, M., & Castellano, M. (2018). Characterization of hyaluronic acid by dynamic light scattering and rheological techniques. In AIP Conference Proceedingshttps://doi.org/10.1063/1.5046046 Vol. 1981, p. 020184. Dodero, A., Williams, R., Gagliardi, S., Vicini, S., Alloisio, M., & Castellano, M. (2019). A micro-rheological and rheological study of biopolymers solutions: Hyaluronic acid. Carbohydrate Polymers, 203, 349–355. https://doi.org/10.1016/J.CARBPOL.2018.09. 072. Gómez-Ordóñez, E., & Rupérez, P. (2011). FTIR-ATR spectroscopy as a tool for polysaccharide identification in edible brown and red seaweeds. Food Hydrocolloids, 25(6), 1514–1520. https://doi.org/10.1016/J.FOODHYD.2011.02.009. Ho, D. L., Hammouda, B., Kline, S. R., & Chen, W.-R. (2006). Unusual phase behavior in mixtures of poly(ethylene oxide) and ethyl alcohol. Journal of Polymer Science Part B Polymer Physics, 44(3), 557–564. https://doi.org/10.1002/polb.20726. Idota, Y., Kogure, Y., Kato, T., Yano, K., Arakawa, H., Miyajima, C., ... Ogihara, T. (2016). Relationship between physical parameters of various metal ions and binding affinity for alginate. Biological & Pharmaceutical Bulletin, 39(11), 1893–1896. https://doi.org/ 10.1248/bpb.b16-00127. Jeong, S. I., Krebs, M. D., Bonino, C. A., Khan, S. A., & Alsberg, E. (2010). Electrospun alginate nanofibers with controlled cell adhesion for tissue engineeringa. Macromolecular Bioscience, 10(8), 934–943. https://doi.org/10.1002/mabi. 201000046. Jiang, T., Carbone, E. J., Lo, K. W.-H., & Laurencin, C. T. (2015). Electrospinning of polymer nanofibers for tissue regeneration. Progress in Polymer Science, 46, 1–24. https://doi.org/10.1016/J.PROGPOLYMSCI.2014.12.001. Kalia, S., & Avérous, L. (2011). Biopolymers: Biomedical and environmental applications. Wiley. Kanmani, P., & Rhim, J.-W. (2014). Properties and characterization of bionanocomposite films prepared with various biopolymers and ZnO nanoparticles. Carbohydrate Polymers, 106, 190–199. https://doi.org/10.1016/J.CARBPOL.2014.02.007. Klingshirn, C. F. Claus F. (2010). Zinc oxide: From fundamental properties towards novel applications. Springer. Kyzioł, A., Michna, J., Moreno, I., Gamez, E., & Irusta, S. (2017). Preparation and characterization of electrospun alginate nanofibers loaded with ciprofloxacin hydrochloride. European Polymer Journal, 96, 350–360. https://doi.org/10.1016/J. EURPOLYMJ.2017.09.020. Leal, D., Matsuhiro, B., Rossi, M., & Caruso, F. (2008). FT-IR spectra of alginic acid block fractions in three species of brown seaweeds. Carbohydrate Research, 343(2), 308–316. https://doi.org/10.1016/J.CARRES.2007.10.016. Li, D., Chen, L., Yi, X., Zhang, X., & Ye, N. (2010). Pyrolytic characteristics and kinetics of two brown algae and sodium alginate. Bioresource Technology, 101(18), 7131–7136. https://doi.org/10.1016/J.BIORTECH.2010.03.145. Lova, P. (2018). Selective polymer distributed bragg reflector vapor sensors. Polymers, 10(10), 1161. https://doi.org/10.3390/polym10101161. Lova, P., Manfredi, G., Boarino, L., Laus, M., Urbinati, G., Losco, T., ... Comoretto, D. (2015). Hybrid ZnO:Polystyrene nanocomposite for all-polymer photonic crystals. Physica Status Solidi (C), 12(1–2), 158–162. https://doi.org/10.1002/pssc. 201400209. Matinise, N., Fuku, X. G., Kaviyarasu, K., Mayedwa, N., & Maaza, M. (2017). ZnO nanoparticles via Moringa oleifera green synthesis: Physical properties & mechanism of formation. Applied Surface Science, 406, 339–347. https://doi.org/10.1016/j.apsusc. 2017.01.219. Meka, S. R. K., Jain, S., & Chatterjee, K. (2016). Strontium eluting nanofibers augment stem cell osteogenesis for bone tissue regeneration. Colloids and Surfaces B Biointerfaces, 146, 649–656. https://doi.org/10.1016/J.COLSURFB.2016.07.012. Neves, N., Campos, B. B., Almeida, I. F., Costa, P. C., Cabral, A. T., Barbosa, M. A., ... Ribeiro, C. C. (2016). Strontium-rich injectable hybrid system for bone regeneration. Materials Science and Engineering C, 59, 818–827. https://doi.org/10.1016/J.MSEC.
8