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Layered cryogels laden with Brazilian honey intended for wound care

Abstract

PVA cryogels are well established as candidate biomaterials for wound healing applications but are not themselves biodegradable or antimicrobial. Blending PVA with NaCMC (CMC) or gelatin (G) can increase the gel’s ability to swell and would introduce a degree of biodegradability. The incorporation of appropriate amounts of a natural antimicrobial/healing agents, such as honey (H), would contribute to the gels properties. The present work addresses the development and characterization of layered gels (PVA-H, PVA-CMC-H and PVA-G-H, with empty PVA, PVA-CMC, PVA-G gels presented as controls). The gels were characterized by FTIR, DSC, in vitro analysis of swelling and microbiological (S. aureus) effects. Addition of gelatin, NaCMC and honey to PVA diminished the PVA chains’ ability to pack into crystallites. Samples containing honey swelled less and presented higher weight loss/biodegradability than samples without honey. Only the honey-laden PVA-CMC and PVA-G presented activity against S. aureus.

Keywords:
layered hydrogel; PVA; NaCMC; gelatin; honey

1. Introduction

Infection associated with wounds to the skin affect 14 million people per year in the USA. Such infections are characterized by colonization by gram-positive bacteria such as S. aureus in the early stages of healing, which are later replaced by gram-negative organisms[11 Simões, D., Miguel, S. P., Ribeiro, M. P., Coutinho, P., Mendonça, A. G., & Correia, I. J. (2018). Recent advances on antimicrobial wound dressing: a review. European Journal of Pharmaceutics and Biopharmaceutics, 127, 130-141. http://dx.doi.org/10.1016/j.ejpb.2018.02.022. PMid:29462687.
http://dx.doi.org/10.1016/j.ejpb.2018.02...
]. Requirements for successful healing include a mechanically stable and moist environment, a capacity for absorbing wound exudate, and antimicrobial properties which act against the development of infection.

Hydrogels have been manufactured in layers to mimic the layers and function of the skin. For example, chitosan-g-poly(ethylene glycol) hydrogel reinforced with chitosan-alginate were designed to mimic the micro-environment relevant to skin tissue engineering[22 Tsao, C. T., Leung, M., Chang, J. Y., & Zhang, M. (2014). A simple material model to generate epidermal and dermal layers in vitro for skin regeneration. Journal of Materials Chemistry B, Materials for Biology and Medicine, 2(32), 5256-5264. http://dx.doi.org/10.1039/C4TB00614C. PMid:25147728.
http://dx.doi.org/10.1039/C4TB00614C...
]. A hydrogel composed of layers of alginate/chitosan/poly(-glutamic acid) increased wound epithelialization and collagen regeneration[33 Lee, Y. H., Chang, J. J., Yang, M. C., Chien, C. T., & Lai, W. F. (2012). Acceleration of wound healing in diabetic rats by layered hydrogel dressing. Carbohydrate Polymers, 88(3), 809-819. http://dx.doi.org/10.1016/j.carbpol.2011.12.045.
http://dx.doi.org/10.1016/j.carbpol.2011...
]. Layered hydrogels based on PVA (polyvinyl alcohol) have also been developed: 2-layered skin equivalent PVA or PVA-cellulose fibre blocks were prepared by freeze-thawing and presented roughness and elasticity similar to human skin[44 Morales Hurtado, M., de Vries, E. G., Zeng, X., & van der Heide, E. (2016). A tribo-mechanical analysis of PVA-based building-blocks for implementation in a 2-layered skin model. Journal of the Mechanical Behavior of Biomedical Materials, 62, 319-332. http://dx.doi.org/10.1016/j.jmbbm.2016.05.001. PMid:27236420.
http://dx.doi.org/10.1016/j.jmbbm.2016.0...
]. A PAA layer has been added to a PVA layer, with the PAA solution poured on the top of PVA swollen layer, where the chains of both polymers would entangle and form hydrogen bonding at the interface. The presence of PAA led to increased swelling, adhesion and biocompatibility while the presence of PVA underpinned the mechanical properties of the gel[55 Tavakoli, J., Mirzaei, S., & Tang, Y. (2018). Cost-effective double-layer hydrogel composites for wound dressing applications. Polymers, 10(3), 305. http://dx.doi.org/10.3390/polym10030305. PMid:30966340.
http://dx.doi.org/10.3390/polym10030305...
]. Hydrogels are potential materials for burn dressings.

PVA is a hydrophilic biocompatible polymer used to manufacture hydrogels. PVA hydrogels are capable of presenting physical properties similar to human tissue, such as elasticity[66 Jiang, S., Liu, S., & Feng, W. (2011). PVA hydrogel properties for biomedical application. Journal of the Mechanical Behavior of Biomedical Materials, 4(7), 1228-1233. http://dx.doi.org/10.1016/j.jmbbm.2011.04.005. PMid:21783131.
http://dx.doi.org/10.1016/j.jmbbm.2011.0...
]. Hydrogels can be based on chemical crosslinking or physical crosslinking, where chemical crosslinking is based on the use of crosslinking agents, such as glutaraldehyde, or based on the use of radiation[77 Reis, E. F., Campos, F. S., Lage, A. P., Leite, R. C., Heneine, L. G., Vasconcelos, W. L., Lobato, Z. I. P., & Mansur, H. S. (2006). Synthesis and characterization of poly (vinyl alcohol) hydrogels and hybrids for rMPB70 protein adsorption. Materials Research, 9(2), 185-191. http://dx.doi.org/10.1590/S1516-14392006000200014.
http://dx.doi.org/10.1590/S1516-14392006...
,88 Tontowi, A. E., Perkasa, D. P., Siswomihardjo, W., & Darwis, D. (2016). Effect of polyvinyl alcohol (PVA) blending and gamma irradiation on compressive strength of FHAp/FGel composite as candidate of scaffold. IACSIT International Journal of Engineering and Technology, 8(1), 108-116.]. Physically crosslinked PVA hydrogels can be prepared by freezing and then thawing an aqueous solution of PVA. PVA chains entangle when in solution. When frozen, ice crystals are formed. By phase separation (ice/PVA), PVA chains are pushed together forming crystallites, which are responsible for the high mechanical properties of these gels. These gels have tissue-like elasticity, toughness and are non-toxic[99 Gupta, S., Webster, T. J., & Sinha, A. (2011). Evolution of PVA gels prepared without crosslinking agents as a cell adhesive surface. Journal of Materials Science: Materials in Medicine, 22(7), 1763-1772. http://dx.doi.org/10.1007/s10856-011-4343-2. PMid:21643819.
http://dx.doi.org/10.1007/s10856-011-434...
]. Blended PVA gels incorporating several additives, such as L. bulgaricus extract[1010 El-Fawal, G. F., Yassin, A. M., & El-Deeb, N. M. (2017). The novelty in fabrication of poly vinyl alcohol/κ-carrageenan hydrogel with Lactobacillus bulgaricus extract as anti-inflammatory wound dressing agent. AAPS PharmSciTech, 18(5), 1605-1616. http://dx.doi.org/10.1208/s12249-016-0628-6. PMid:27620196.
http://dx.doi.org/10.1208/s12249-016-062...
] and neomycin sulfate[1111 Choi, J. S., Kim, D. W., Kim, D. S., Kim, J. O., Yong, C. S., Cho, K. H., Youn, Y. S., Jin, S. G., & Choi, H. G. (2016). Novel neomycin sulfate-loaded hydrogel dressing with enhanced physical dressing properties and wound-curing effect. Drug Delivery, 23(8), 2806-2812. http://dx.doi.org/10.3109/10717544.2015.1089958. PMid:26394193.
http://dx.doi.org/10.3109/10717544.2015....
], have been studied in the literature with respect to antibacterial and healing properties.

Sodium carboxymethyl cellulose (NaCMC) is a hydrophilic polymer, a polyelectrolyte, derived from cellulose. The charges of this polyelectrolyte elongate the polymer chains, increasing the water uptake capability of the network, with counterions favouring water entrance[1212 Sannino, A., Demitri, C., & Madaghiele, M. (2009). Biodegradable cellulose-based hydrogels: design and applications. Materials, 2(2), 353-373. http://dx.doi.org/10.3390/ma2020353.
http://dx.doi.org/10.3390/ma2020353...
]. NaCMC is able to form hydrogels by blending it with hydroxyethyl cellulose and chemically crosslinking with divynilsulphone[1212 Sannino, A., Demitri, C., & Madaghiele, M. (2009). Biodegradable cellulose-based hydrogels: design and applications. Materials, 2(2), 353-373. http://dx.doi.org/10.3390/ma2020353.
http://dx.doi.org/10.3390/ma2020353...
]; NaCMC can be combined with protein sericin, crosslinked by freeze-thawing, with glutaraldehyde and AlCl3 to produce hydrogels for wound dressing[1313 Nayak, S., & Kundu, S. C. (2014). Sericin-carboxymethyl cellulose porous matrices as cellular wound dressing material. Journal of Biomedical Materials Research: Part A, 102(6), 1928-1940. http://dx.doi.org/10.1002/jbm.a.34865. PMid:23853114.
http://dx.doi.org/10.1002/jbm.a.34865...
]. NaCMC can also be blended with polyethylene glycol and crosslinked with citric acid for dressing purposes, showing no cytotoxicity[1414 Capanema, N. S. V., Mansur, A. A. P., Jesus, A. C., Carvalho, S. M., Oliveira, L. C., & Mansur, H. S. (2018). Superabsorbent crosslinked carboxymethyl cellulose-PEG hydrogels for potential wound dressing applications. International Journal of Biological Macromolecules, 106, 1218-1234. http://dx.doi.org/10.1016/j.ijbiomac.2017.08.124. PMid:28851645.
http://dx.doi.org/10.1016/j.ijbiomac.201...
]. In order to present antibacterial properties, NaCMC hydrogels can be loaded with drugs. For example, NaCMC gels can be crosslinked with citric acid and loaded with MCM-41 mesoporous silica nanoparticles containing tetracycline (antibiotic), where higher particle content led to higher S. aureus inhibition[1515 Namazi, H., Rakhshaei, R., Hamishehkar, H., & Kafil, H. S. (2016). Antibiotic loaded carboxymethylcellulose/MCM-41 nanocomposite hydrogel films as potential wound dressing. International Journal of Biological Macromolecules, 85, 327-334. http://dx.doi.org/10.1016/j.ijbiomac.2015.12.076. PMid:26740467.
http://dx.doi.org/10.1016/j.ijbiomac.201...
]. In another study, NaCMC was blended to PVA to physically (freeze-thawing) form hydrogels loaded with sodium fucidate, where the addition of NaCMC increased the gels swelling capacity, vapor transmission rate and porosity[1616 Lim, S. J., Lee, J. H., Piao, M. G., Lee, M. K., Oh, D. H., Hwang, D. H., Quan, Q. Z., Yong, C. S., & Choi, H. G. (2010). Effect of sodium carboxymethylcellulose and fucidic acid on the gel characterization of polyvinylalcohol-based wound dressing. Archives of Pharmacal Research, 33(7), 1073-1081. http://dx.doi.org/10.1007/s12272-010-0714-3. PMid:20661718.
http://dx.doi.org/10.1007/s12272-010-071...
]. PVA-NaCMC-sodium fucidate hydrogel showed faster healing compared to a PVA-NaCMC gel[1717 Lee, J. H., Lim, S. J., Oh, D. H., Ku, S. K., Li, D. X., Yong, C. S., & Choi, H. G. (2010). Wound healing evaluation of sodium fucidate-loaded polyvinylalcohol/sodium carboxymethylcellulose-based wound dressing. Archives of Pharmacal Research, 33(7), 1083-1089. http://dx.doi.org/10.1007/s12272-010-0715-2. PMid:20661719.
http://dx.doi.org/10.1007/s12272-010-071...
].

Gelatin is a water-soluble protein obtained from the thermal denaturation of collagen. Gelatins with high levels of amino acids present high gel strength and melting point[1818 Mariod, A. A., & Adam, H. F. (2013). Review: Gelatin, source, extraction and industrial applications. Acta Scientiarum Polonorum. Technologia Alimentaria, 12(2), 135-147.]. Gelatin is biocompatible, biodegradable, it has the ability to form films, and is generally low cost. In order to avoid dissolution in aqueous fluids, gelatin hydrogels have to be crosslinked with glutaraldehyde, genipin or lactose. Gelatin hydrogels crosslinked with lactose have been investigated as wound dressing materials[1919 Etxabide, A., Vairo, C., Santos-Vizcaino, E., Guerrero, P., Pedraz, J. L., Igartua, M., de la Caba, K., & Hernandez, R. M. (2017). Ultra thin hydro-films based on lactose-crosslinked fish gelatin for wound healing applications. International Journal of Pharmaceutics, 530(1-2), 455-467. http://dx.doi.org/10.1016/j.ijpharm.2017.08.001. PMid:28789885.
http://dx.doi.org/10.1016/j.ijpharm.2017...
]. Chitosan/gelatin crosslinked hydrogels were loaded with phenols from Hamamelis virginiana and showed activity against P. aeruginosa and S. aureus[2020 Rocasalbas, G., Francesko, A., Touriño, S., Fernández-Francos, X., Guebitz, G. M., & Tzanov, T. (2013). Laccase-assisted formation of bioactive chitosan/gelatin hydrogel stabilized with plant polyphenols. Carbohydrate Polymers, 92(2), 989-996. http://dx.doi.org/10.1016/j.carbpol.2012.10.045. PMid:23399119.
http://dx.doi.org/10.1016/j.carbpol.2012...
]. Superabsorbent gels were prepared by esterification of PVA with gelatin[2121 Pal, K., Banthia, A. K., & Majumdar, D. K. (2007). Preparation and characterization of polyvinyl alcohol-gelatin hydrogel membranes for biomedical applications. AAPS PharmSciTech, 8(1), 21. http://dx.doi.org/10.1208/pt080121. PMid:17408220.
http://dx.doi.org/10.1208/pt080121...
]. Chitosan/gelatin/PVA irradiated hydrogels for wound dressing applications presented swelling capacity, adequate vapor transmission rate and mechanical properties[2222 Fan, L., Yang, H., Yang, J., Peng, M., & Hu, J. (2016). Preparation and characterization of chitosan/gelatin/PVA hydrogel for wound dressings. Carbohydrate Polymers, 146, 427-434. http://dx.doi.org/10.1016/j.carbpol.2016.03.002. PMid:27112893.
http://dx.doi.org/10.1016/j.carbpol.2016...
]. PVA/chitosan/gelatin hydrogels loaded with PCL microspheres containing bFGF and BSA (protein) showed no cytotoxicity, and an improved healing rate, while chitosan improved the antimicrobial properties[2323 Shamloo, A., Sarmadi, M., Aghababaie, Z., & Vossoughi, M. (2018). Accelerated full-thickness wound healing via sustained bFGF delivery based on a PVA/chitosan/gelatin hydrogel incorporating PCL microspheres. International Journal of Pharmaceutics, 537(1-2), 278-289. http://dx.doi.org/10.1016/j.ijpharm.2017.12.045. PMid:29288809.
http://dx.doi.org/10.1016/j.ijpharm.2017...
].

Honey is a bee-based product which can present more than 200 constituent components, mainly carbohydrates (most of them monosaccharides, e.g. fructose, glucose, sucrose), proteins, organic acids, vitamins and phenolic compounds. Honey’s antimicrobial characteristics are related to the H2O2 produced by enzymatic activity and to the action of complex phenols and organic acids (flavonoids)[2424 Martinotti, S., & Ranzato, E. (2018). Honey, wound repair and regenerative medicine. Journal of Functional Biomaterials, 9(2), 34. http://dx.doi.org/10.3390/jfb9020034. PMid:29738478.
http://dx.doi.org/10.3390/jfb9020034...
,2525 Meo, S. A., Al-Asiri, S. A., Mahesar, A. L., & Ansari, M. J. (2017). Role of honey in modern medicine. Saudi Journal of Biological Sciences, 24(5), 975-978. http://dx.doi.org/10.1016/j.sjbs.2016.12.010. PMid:28663690.
http://dx.doi.org/10.1016/j.sjbs.2016.12...
]. The honey composition is influenced by the flower types visited by bees, the soil composition, bee species and climatic conditions. Brazilian honey presents a considerable variability, since the local flora and climate change all over the country. The honey’s consistency, color, odor, taste and scent are constant physical-chemical characteristics in monoflower honeys. Honey’s phenolic substances and flavonoids are responsible by pharmacological properties, e.g. antimicrobian and antioxidant activities[2626 Santos, A. M. N., Moreira, A. P. D., Carvalho, C. W. P., Luchese, R., Ribeiro, E., McGuinness, G. B., Mendes, M. F., & Oliveira, R. N. (2019). Physically cross-linked gels of PVA with natural polymers as matrices for manuka honey release in wound-care applications. Materials, 12(4), 559. http://dx.doi.org/10.3390/ma12040559. PMid:30781788.
http://dx.doi.org/10.3390/ma12040559...
]. Wounded rats treated with Brazilian honey (from southwest region of Brazil) presented fastest recovery than the control group, it also treated the wounds infection[2727 Mandal, S., DebMandal, M., Pal, N. K., & Saha, K. (2010). Antibacterial activity of honey against clinical isolates of Escherichia coli, Pseudomonas aeruginosa and Salmonella enterica serovar Typhi. Asian Pacific Journal of Tropical Medicine, 3(12), 961-964. http://dx.doi.org/10.1016/S1995-7645(11)60009-6.
http://dx.doi.org/10.1016/S1995-7645(11)...
]. Brazilian honey, also from the southwest, was tested against S. aureus microorganisms and it showed antimicrobial activity, due to its phenolic compounds[2828 Guirguis, O. W., & Moselhey, M. T. H. (2012). Thermal and structural studies of poly (vinyl alcohol) and hydroxypropyl cellulose blends. Nature and Science, 04(01), 57-67. http://dx.doi.org/10.4236/ns.2012.41009.
http://dx.doi.org/10.4236/ns.2012.41009...
]. Brazilian honey shows potential to be used as wound healing agent.

Honey has been successfully incorporated in hydrogels. For example, a chitosan dressing containing 75% honey enhanced tissue regeneration[2929 El-Kased, R. F., Amer, R. I., Attia, D., & Elmazar, M. M. (2017). Honey-based hydrogel: in vitro and comparative in vivo evaluation for burn wound healing. Scientific Reports, 7(1), 9692. http://dx.doi.org/10.1038/s41598-017-08771-8. PMid:28851905.
http://dx.doi.org/10.1038/s41598-017-087...
]. A pectin-honey hydrogel promoted faster wound healing than a control[3030 Giusto, G., Vercelli, C., Comino, F., Caramello, V., Tursi, M., & Gandini, M. (2017). A new, easy-to-make pectin-honey hydrogel enhances wound healing in rats. BMC Complementary and Alternative Medicine, 17(1), 266. http://dx.doi.org/10.1186/s12906-017-1769-1. PMid:28511700.
http://dx.doi.org/10.1186/s12906-017-176...
]. PVA crosslinked with borax and loaded with honey promoted the proliferation of cells, with swelling, and permeability properties considered adequate for moderate exudative wounds[3131 Tavakoli, J., & Tang, Y. (2017). Honey/PVA hybrid wound dressings with controlled release of antibioticsStructural, physico-mechanical and in-vitro biomedical studies. Materials Science and Engineering C, 77, 318-325. http://dx.doi.org/10.1016/j.msec.2017.03.272. PMid:28532035.
http://dx.doi.org/10.1016/j.msec.2017.03...
]. Gelatin-chitosan hydrogels loaded with compounds from manuka honey presented antibacterial activity, a high wound healing rate and the absorption of exudates[3232 Abd El-Malek, F. F., Yousef, A. S., & El-Assar, S. A. (2017). Hydrogel film loaded with new formula from manuka honey for treatment of chronic wound infections. Journal of Global Antimicrobial Resistance, 11, 171-176. http://dx.doi.org/10.1016/j.jgar.2017.08.007. PMid:28830809.
http://dx.doi.org/10.1016/j.jgar.2017.08...
]. Gelatin-chitosan-honey hydrogel was effective against S. aureus and E. coli and stimulated burns healing[3333 Wang, T., Zhu, X. K., Xue, X. T., & Wu, D. Y. (2012). Hydrogel sheets of chitosan, honey and gelatin as burn wound dressings. Carbohydrate Polymers, 88(1), 75-83. http://dx.doi.org/10.1016/j.carbpol.2011.11.069.
http://dx.doi.org/10.1016/j.carbpol.2011...
]. PVP-agar-Peg gels containing 6% of honey acceletrated rats wounds contraction[3434 Oliveira, R. N., Paranhos da Silva, C. M., Moreira, A. P. D., Mendonça, R. H., Thiré, R. M., & McGuinness, G. B. (2017). Comparative analysis of PVA hydrogels incorporating two natural antimicrobials: Punica granatum and Arnica montana tinctures. Journal of Applied Polymer Science, 134(41), 45392. http://dx.doi.org/10.1002/app.45392.
http://dx.doi.org/10.1002/app.45392...
]; PVA/chitosan/montmorillonite gels loaded with 15% Iranian honey showed potential to absorb exudate and efficient wound healing[3535 Oliveira, R. N., Rouzé, R., Quilty, B., Alves, G. G., Soares, G. D. A., Thiré, R. M. S. M., & McGuinness, G. B. (2014). Mechanical properties and in vitro characterization of polyvinyl alcohol-nano-silver hydrogel wound dressings. Interface Focus, 4(1), 20130049. http://dx.doi.org/10.1098/rsfs.2013.0049. PMid:24501677.
http://dx.doi.org/10.1098/rsfs.2013.0049...
]; acrylamide hydrogels were loaded with different amounts of Indian honey (5-15%), but the gel containing 10% honey was considered the best one, due to optimized tensile strength and swelling capacity[3636 Pietrucha, K., & Verne, S. (2009). Synthesis and characterization of a new generation of hydrogels for biomedical applications. In Proceedings of the World Congress on Medical Physics and Biomedical Engineering (pp. 1-4). Berlin: Springer. http://dx.doi.org/10.1007/978-3-642-03900-3_1.
http://dx.doi.org/10.1007/978-3-642-0390...
]; carbopol 934 and chitosan gels containing 75% Egyptian honey presented high burning healing rate[3232 Abd El-Malek, F. F., Yousef, A. S., & El-Assar, S. A. (2017). Hydrogel film loaded with new formula from manuka honey for treatment of chronic wound infections. Journal of Global Antimicrobial Resistance, 11, 171-176. http://dx.doi.org/10.1016/j.jgar.2017.08.007. PMid:28830809.
http://dx.doi.org/10.1016/j.jgar.2017.08...
].

The goal of the present work was to develop layered PVA, PVA-honey (PVA-H), PVA-NaCMC (PVA-CMC), PVA-NaCMC-honey (PVA-CMC-H), PVA-gelatin (PVA-G), PVA-gelatin-honey (PVA-G-H) hydrogels and characterise their physico-chemical and functional properties in order to gain insights into their potential development as wound-care biomaterials.

2. Materials and Methods

2.1 Sample preparation

The samples were manufactured by the dissolution of PVA (Sigma-Aldrich, Mw: 85,000-124,000 Da, 99+% hydrolyzed) at 90 °C under mechanical stirring for 4h according to Table 1. For each PVA blend without honey, the amount of water used was split in half to separately dissolve the PVA and either NaCMC (Sigma-Aldrich, average Mw ~250,000, degree of substitution 0.9) or Gelatin (from bovine skin, Sigma-Aldrich, Type B). The resulting solutions were then mixed together after each solution had reached room temperature (under stirring). The NaCMC was dissolved in water under stirring at room temperature for 2h. Gelatin was dissolved at 60 °C under stirring for 4h.

Table 1
Samples composition.

The samples were prepared in three steps using 24-well plates. The composition of each layer of the samples without honey was similar (PVA or PVA-CMC or PVA-G). The first layer was obtained by pouring 1 mL of the polymer solution or the blend solution per well followed by a freeze-thaw cycle (each freeze-thawing cycle was to submit the sample to 1h at -18 °C and 30 min at room temperature). The second layer (1 mL/well) was subsequently added and freeze-thawed, followed by the addition and freeze-thawing of the third layer. The first layer was therefore subjected to 3 freeze-thawing cycles, the second layer to 2 cycles and the third layer to 1 cycle.

For the samples that were to contain honey (a commercial Brazilian honey from Southeast region, characterized as “silvestre” honey), the polymers were dissolved in the designated amounts of water from Table 1 following the procedures previously described. Honey was then added to the polymer solution or to the blend solution, according to the quantities indicated in Table 1, at room temperature under mechanical stirring for 5 minutes. The first layer of these samples was either pure PVA or a PVA based polymer blend without honey and had experienced 3 freeze-thawing cycles. The second layer was the polymer/blend with 10% honey, submitted to 2 freeze-thawing cycles; and the third layer was polymer/blend with 5% honey, submitted to 1 freeze-thawing cycle. All the samples were dried in oven at 50 °C for 24h. Regarding honeys’ thermal degradation, honey samples treated at 23 °C for short times did not degrade, but the same behavior was not observed for samples heated at 95 °C, although antiocidant activity might increase with the heating temperature[3434 Oliveira, R. N., Paranhos da Silva, C. M., Moreira, A. P. D., Mendonça, R. H., Thiré, R. M., & McGuinness, G. B. (2017). Comparative analysis of PVA hydrogels incorporating two natural antimicrobials: Punica granatum and Arnica montana tinctures. Journal of Applied Polymer Science, 134(41), 45392. http://dx.doi.org/10.1002/app.45392.
http://dx.doi.org/10.1002/app.45392...
]. Heat treated honey might present hydroxymethylfurfural, which should be lower than 80 mg/kg in tropical honeys, since it is toxic and carcinogenic. In addition, tropical honeys can present fermentation when heat treated, but it can be prevented by heating honey at 60-70 °C for 10 min or at 60-65 °C for 30 min[3535 Oliveira, R. N., Rouzé, R., Quilty, B., Alves, G. G., Soares, G. D. A., Thiré, R. M. S. M., & McGuinness, G. B. (2014). Mechanical properties and in vitro characterization of polyvinyl alcohol-nano-silver hydrogel wound dressings. Interface Focus, 4(1), 20130049. http://dx.doi.org/10.1098/rsfs.2013.0049. PMid:24501677.
http://dx.doi.org/10.1098/rsfs.2013.0049...
]. The drying temperature was low to preserve honey activities, although honey samples autoclaved at 121 °C could maintain its properties[2727 Mandal, S., DebMandal, M., Pal, N. K., & Saha, K. (2010). Antibacterial activity of honey against clinical isolates of Escherichia coli, Pseudomonas aeruginosa and Salmonella enterica serovar Typhi. Asian Pacific Journal of Tropical Medicine, 3(12), 961-964. http://dx.doi.org/10.1016/S1995-7645(11)60009-6.
http://dx.doi.org/10.1016/S1995-7645(11)...
].

2.2 Physico-chemical analysis

The physic-chemical analysis of the samples was performed by Fourier Transformed Infrared Spectroscopy (FTIR), equipment VERTEX-70 (UFRRJ), 32 scans per sample, from 4000 cm-1 to 600 cm-1. Samples representing each layer were prepared separately and submitted to the proper number of freeze-thawing cycles separately and then dried to be evaluated by FTIR. The multi-layered samples were also evaluated by FTIR.

2.3 Thermal analysis

The samples were analysed by Differential Scanning Calorimetry (DSC), where approximately 5 mg of each sample composition was submitted to 10 °C/min of heat flow from room temperature to 240 °C using a DSC Q200 TA Instruments equipment (EMBRAPA Agroindustry). The transition temperatures of the samples (glass transition temperature - Tg, melting temperature - Tm) were obtained using the second cycle of heating to overcome the samples’ thermal history. The samples degree of crystallinity (Xc) was calculated by

X c = 100 Δ H m Δ H m 100 (1)

The ΔHm is the enthalpy of melting related to the samples at the PVA melting temperature and ΔHm100 is the enthalpy of melting related to PVA 100% crystalline, 138.6 J/g[2828 Guirguis, O. W., & Moselhey, M. T. H. (2012). Thermal and structural studies of poly (vinyl alcohol) and hydroxypropyl cellulose blends. Nature and Science, 04(01), 57-67. http://dx.doi.org/10.4236/ns.2012.41009.
http://dx.doi.org/10.4236/ns.2012.41009...
].

2.4 In vitro analysis

The swelling tests proceeded in saline solution at room temperature. For each sample composition, 5 samples were cut (samples weight was standardized among the ones with the same composition) and immersed in saline solution (20 mL per sample, used to mimic the body fluids). The samples were removed from the saline solution at regular intervals (30 min, 1h, 2h, 3h, 4h, 24h, 48h, 72h and 96h). The adsorbed fluid was removed using filter paper and the samples were weighed and then returned to the media. The swelling degree (SD) was calculated according to

S D = 100 W S W D B W D B (2)

WDB is the weight of dried samples before swelling; WS is the weight of the swelled samples.

At the end of the 4 days of immersion, the samples were dried in oven at 50 °C for 24h and weighed to calculate the sample gel fraction (GF)

G F = 100 W D W D B (3)

WD is the weight of the dried samples after swelling) and weight loss (WL)/biodegradability[3434 Oliveira, R. N., Paranhos da Silva, C. M., Moreira, A. P. D., Mendonça, R. H., Thiré, R. M., & McGuinness, G. B. (2017). Comparative analysis of PVA hydrogels incorporating two natural antimicrobials: Punica granatum and Arnica montana tinctures. Journal of Applied Polymer Science, 134(41), 45392. http://dx.doi.org/10.1002/app.45392.
http://dx.doi.org/10.1002/app.45392...
],

W L = 100 W D B W D W D B (4)

For microbiological analysis, the ASTM E2180- 07 standard was adapted. A suspension of Staphylococcus aureus cells (ATCC 6538) was prepared (guaranteeing that the suspension reached 0.5 in the MacFarland scale), which correspond to 108 colony forming unit (UFC)/mL. The agar paste received 1 mL of the mentioned suspension, where the agar paste total amount of microrganisms were 106 UFC/mL. Each sample was placed in an empty well of 24 wells flat bottom polystyrene plate, and each well received 200 μL of the agar paste containing S. aureus (where duplicates for each samples composition were evaluated). The plates were incubated at 30 °C for 24h. After incubation, the media in contact with samples were placed in Falcon tubes. After that, different amounts of buffer solution were added to prepare decimal dilutions of the media in contact with samples and to subsequently, count the colony forming units (cfu) by the micro dropping technique. The bacterial calculation was performed using the optical microscope (equipment Olympus). The reduction calculation was based on ASTM Standard 20170504.

3. Results and Discussions

It was not possible to distinguish the samples layers, indicating that the system might behave homogeneously. All samples, containing honey or not, presented homogeneous morphology, similar to PVA-H, Figure 1.

Figure 1
PVA-H sample section.

3.1 Physico-chemical analysis

The FTIR spectra of all samples are shown in Figure 2. Each layer of PVA presented similar FTIR spectra of the three-layered sample. Nonetheless, the band at 1142 cm-1, related to the formation of PVA crystallites (intra- and intermolecular hydrogen bonding between the chains originated by hydrophilic forces)[77 Reis, E. F., Campos, F. S., Lage, A. P., Leite, R. C., Heneine, L. G., Vasconcelos, W. L., Lobato, Z. I. P., & Mansur, H. S. (2006). Synthesis and characterization of poly (vinyl alcohol) hydrogels and hybrids for rMPB70 protein adsorption. Materials Research, 9(2), 185-191. http://dx.doi.org/10.1590/S1516-14392006000200014.
http://dx.doi.org/10.1590/S1516-14392006...
], presented lower transmittance with increasing numbers of freeze-thawing cycles, indicating the contribution of the freeze-thawing process to the formation of PVA crystals. There were (in all PVA layers) bands at: 3273 cm-1 (OH hydrogen bonds)[77 Reis, E. F., Campos, F. S., Lage, A. P., Leite, R. C., Heneine, L. G., Vasconcelos, W. L., Lobato, Z. I. P., & Mansur, H. S. (2006). Synthesis and characterization of poly (vinyl alcohol) hydrogels and hybrids for rMPB70 protein adsorption. Materials Research, 9(2), 185-191. http://dx.doi.org/10.1590/S1516-14392006000200014.
http://dx.doi.org/10.1590/S1516-14392006...
]; 2941 cm-1 and 2909 cm-1, ν(C–H) alkyl[77 Reis, E. F., Campos, F. S., Lage, A. P., Leite, R. C., Heneine, L. G., Vasconcelos, W. L., Lobato, Z. I. P., & Mansur, H. S. (2006). Synthesis and characterization of poly (vinyl alcohol) hydrogels and hybrids for rMPB70 protein adsorption. Materials Research, 9(2), 185-191. http://dx.doi.org/10.1590/S1516-14392006000200014.
http://dx.doi.org/10.1590/S1516-14392006...
]; 1652 cm-1, ν(C=O-, from residual aldehyde)[3535 Oliveira, R. N., Rouzé, R., Quilty, B., Alves, G. G., Soares, G. D. A., Thiré, R. M. S. M., & McGuinness, G. B. (2014). Mechanical properties and in vitro characterization of polyvinyl alcohol-nano-silver hydrogel wound dressings. Interface Focus, 4(1), 20130049. http://dx.doi.org/10.1098/rsfs.2013.0049. PMid:24501677.
http://dx.doi.org/10.1098/rsfs.2013.0049...
,3636 Pietrucha, K., & Verne, S. (2009). Synthesis and characterization of a new generation of hydrogels for biomedical applications. In Proceedings of the World Congress on Medical Physics and Biomedical Engineering (pp. 1-4). Berlin: Springer. http://dx.doi.org/10.1007/978-3-642-03900-3_1.
http://dx.doi.org/10.1007/978-3-642-0390...
]; 1563 cm-1 and 1237 cm-1, ν(C=C-)[3535 Oliveira, R. N., Rouzé, R., Quilty, B., Alves, G. G., Soares, G. D. A., Thiré, R. M. S. M., & McGuinness, G. B. (2014). Mechanical properties and in vitro characterization of polyvinyl alcohol-nano-silver hydrogel wound dressings. Interface Focus, 4(1), 20130049. http://dx.doi.org/10.1098/rsfs.2013.0049. PMid:24501677.
http://dx.doi.org/10.1098/rsfs.2013.0049...
]; 1411 cm-1, δ(-CH)[3737 Abureesh, M. A., Oladipo, A. A., & Gazi, M. (2016). Facile synthesis of glucose-sensitive chitosan-poly(vinyl alcohol) hydrogel: drug release optimization and swelling properties. International Journal of Biological Macromolecules, 90, 75-80. http://dx.doi.org/10.1016/j.ijbiomac.2015.10.001. PMid:26459171.
http://dx.doi.org/10.1016/j.ijbiomac.201...
]; 1380 cm-1, ω(C-H)[3838 Pawde, S. M., & Deshmukh, K. (2008). Characterization of polyvinyl alcohol/gelatin blend hydrogel films for biomedical applications. Journal of Applied Polymer Science, 109(5), 3431-3437. http://dx.doi.org/10.1002/app.28454.
http://dx.doi.org/10.1002/app.28454...
]; 1329 cm-1, δ(CH+OH)[3535 Oliveira, R. N., Rouzé, R., Quilty, B., Alves, G. G., Soares, G. D. A., Thiré, R. M. S. M., & McGuinness, G. B. (2014). Mechanical properties and in vitro characterization of polyvinyl alcohol-nano-silver hydrogel wound dressings. Interface Focus, 4(1), 20130049. http://dx.doi.org/10.1098/rsfs.2013.0049. PMid:24501677.
http://dx.doi.org/10.1098/rsfs.2013.0049...
]; 1089 cm-1, ν(C-O)[3939 Chen, X., Chen, C., Zhang, H., Huang, Y., Yang, J., & Sun, D. (2017). Facile approach to the fabrication of 3D cellulose nanofibrils (CNFs) reinforced poly(vinyl alcohol) hydrogel with ideal biocompatibility. Carbohydrate Polymers, 173, 547-555. http://dx.doi.org/10.1016/j.carbpol.2017.06.036. PMid:28732898.
http://dx.doi.org/10.1016/j.carbpol.2017...
]; 916 cm-1, δ(-CH2)[3939 Chen, X., Chen, C., Zhang, H., Huang, Y., Yang, J., & Sun, D. (2017). Facile approach to the fabrication of 3D cellulose nanofibrils (CNFs) reinforced poly(vinyl alcohol) hydrogel with ideal biocompatibility. Carbohydrate Polymers, 173, 547-555. http://dx.doi.org/10.1016/j.carbpol.2017.06.036. PMid:28732898.
http://dx.doi.org/10.1016/j.carbpol.2017...
]; and 835 cm-1, ρ(-CH)[3939 Chen, X., Chen, C., Zhang, H., Huang, Y., Yang, J., & Sun, D. (2017). Facile approach to the fabrication of 3D cellulose nanofibrils (CNFs) reinforced poly(vinyl alcohol) hydrogel with ideal biocompatibility. Carbohydrate Polymers, 173, 547-555. http://dx.doi.org/10.1016/j.carbpol.2017.06.036. PMid:28732898.
http://dx.doi.org/10.1016/j.carbpol.2017...
].

Figure 2
FTIR spectra of: (a) PVA layers; (b) PVA-CMC layers; (c) PVA-G layers; (d) PVA 3-layered sample, honey and PVA-H 3-layered sample; (e) PVA-CMC 3-layered sample, honey and PVA-CMC-H 3-layered sample; (f) PVA-G 3-layered sample, honey and PVA-G-H 3-layered sample; (g) PVA-H layers; (h) PVA-CMC-H layers; (i) PVA-G-H layers.

The previously reported PVA bands were also observed in the PVA-CMC as well as the overlapping bands of NaCMC, showing the dispersion of NaCMC in the PVA matrix[4040 Ibrahim, M. M., Koschella, A., Kadry, G., & Heinze, T. (2013). Evaluation of cellulose and carboxymethyl cellulose/poly(vinyl alcohol) membranes. Carbohydrate Polymers, 95(1), 414-420. http://dx.doi.org/10.1016/j.carbpol.2013.03.012. PMid:23618287.
http://dx.doi.org/10.1016/j.carbpol.2013...
]; a shoulder at 2855 cm-1, ν(C-H)[4141 Hassan, E. A., Hassan, M. L., Moorefield, C. N., & Newkome, G. R. (2015). New supramolecular metallo-terpyridine carboxymethyl cellulose derivatives with antimicrobial properties. Carbohydrate Polymers, 116, 2-8. http://dx.doi.org/10.1016/j.carbpol.2014.06.056. PMid:25458266.
http://dx.doi.org/10.1016/j.carbpol.2014...
], 1585 cm-1 (non-hydrated C=O of COO- group)[4242 Juncu, G., Stoica-Guzun, A., Stroescu, M., Isopencu, G., & Jinga, S. I. (2016). Drug release kinetics from carboxymethylcellulose-bacterial cellulose composite films. International Journal of Pharmaceutics, 510(2), 485-492. http://dx.doi.org/10.1016/j.ijpharm.2015.11.053. PMid:26688041.
http://dx.doi.org/10.1016/j.ijpharm.2015...
]; 1415 cm-1, ν(COO-); 1325 cm-1, δ(C-H) of methyl groups; 1080 cm-1 ν(C-O)[4343 Shehap, A. (2008). Thermal and spectroscopic studies of polyvinyl alcohol/sodium carboxy methyl cellulose blends. Egyptian Journal of Solid, 31(1), 75-91.]. The band at 1652 cm-1 (C=O) is absent in the sample PVA-CMC[3535 Oliveira, R. N., Rouzé, R., Quilty, B., Alves, G. G., Soares, G. D. A., Thiré, R. M. S. M., & McGuinness, G. B. (2014). Mechanical properties and in vitro characterization of polyvinyl alcohol-nano-silver hydrogel wound dressings. Interface Focus, 4(1), 20130049. http://dx.doi.org/10.1098/rsfs.2013.0049. PMid:24501677.
http://dx.doi.org/10.1098/rsfs.2013.0049...
]. The band at 1560 cm-1 (carbonyl group) in the PVA-CMC sample has a different shape compared to the same band in the PVA sample, indicating a change in the balance of free associated carbonyl groups. It could relate to the polymers miscibility, although displacement of the bands related to the crystallinity of PVA (1142 cm-1, ν(C-C)) and of NaCMC (1372 cm-1, δ(CH)) and displacement of the NaCMC β-glucosidic groups were not identified. As expected, the PVA crystallinity index (ratio between the absorbance of the band at 1142 cm-1 and the band at 2905 cm-1) is lower in the blend, IPVA is ~1.45 and IPVA-CMC is ~1.36, where the presence of NaCMC diminishes the PVA chains ability to pack into crystals[4343 Shehap, A. (2008). Thermal and spectroscopic studies of polyvinyl alcohol/sodium carboxy methyl cellulose blends. Egyptian Journal of Solid, 31(1), 75-91.]. The PVA-CMC layers revealed that the increase of freeze-thawing cycles displaced the band at 1593 cm-1 (NaCMC’s ν(-COO)[4444 Ikhuoria, E. U., Omorogbe, S. O., Agbonlahor, O. G., Iyare, N. O., Pillai, S., & Aigbodion, A. I. (2017). Spectral analysis of the chemical structure of carboxymethylated cellulose produced by green synthesis from coir fibre. Ciência e Tecnologia dos Materiais, 29(2), 55-62. http://dx.doi.org/10.1016/j.ctmat.2016.05.007.
http://dx.doi.org/10.1016/j.ctmat.2016.0...
]) to 1566 cm-1, which indicate the effectiveness of the “crosslinking”[4545 Abou-Yousef, H., & Kamel, S. (2015). High efficiency antimicrobial cellulose-based nanocomposite hydrogels. Journal of Applied Polymer Science, 132(31). http://dx.doi.org/10.1002/app.42327.
http://dx.doi.org/10.1002/app.42327...
]. In addition, the two bands at 1087 cm-1 (PVA’s δ(C-O-H)[4646 Chaturvedi, A., Bajpai, A. K., & Bajpai, J. (2015). Preparation and characterization of poly(vinyl alcohol) cryogel-silver nanocomposites and evaluation of blood compatibility, cytotoxicity, and antimicrobial behaviors. Polymer Composites, 36(11), 1983-1997. http://dx.doi.org/10.1002/pc.23108.
http://dx.doi.org/10.1002/pc.23108...
]) and at 1060 cm-1 (NaCMC’s ν(OCH–O–CH2)[4747 Singh, R. K., & Khatri, O. P. (2012). A scanning electron microscope based new method for determining degree of substitution of sodium carboxymethyl cellulose. Journal of Microscopy, 246(1), 43-52. http://dx.doi.org/10.1111/j.1365-2818.2011.03583.x. PMid:22150298.
http://dx.doi.org/10.1111/j.1365-2818.20...
]) cannot be distinguished in layers submitted to more freeze-thawing cycles, where only one band at 1087 cm-1 can be observed.

The PVA-G sample presented some differences when compared to the PVA sample, e.g. the band at 1646 cm-1 was more intense in the PVA-G sample, which could be due to the gelatin ν(C=O)[3838 Pawde, S. M., & Deshmukh, K. (2008). Characterization of polyvinyl alcohol/gelatin blend hydrogel films for biomedical applications. Journal of Applied Polymer Science, 109(5), 3431-3437. http://dx.doi.org/10.1002/app.28454.
http://dx.doi.org/10.1002/app.28454...
]. There was a band at 1169 cm-1 in the PVA-G sample (absent in the PVA sample); the PVA bands at 1142 cm-1 and at 1089 cm-1 were displaced to 1136 cm-1 and to 1101 cm-1 in the PVA-G sample, respectively. The gelatin bands displacement towards higher wavenumbers could be related to reaction products, e.g. from 1680 cm-1 to 1758 cm-1 would represent the formation of esterified product[2121 Pal, K., Banthia, A. K., & Majumdar, D. K. (2007). Preparation and characterization of polyvinyl alcohol-gelatin hydrogel membranes for biomedical applications. AAPS PharmSciTech, 8(1), 21. http://dx.doi.org/10.1208/pt080121. PMid:17408220.
http://dx.doi.org/10.1208/pt080121...
]. There were bands at 640 cm-1 and at 612 cm-1 in the PVA-G sample, while there was no band in this region in the PVA sample. A band at 670 cm-1 would be attributed to the gelatin γ(N-H), although bands observed at lower wavelengths were not reported to gelatin[3838 Pawde, S. M., & Deshmukh, K. (2008). Characterization of polyvinyl alcohol/gelatin blend hydrogel films for biomedical applications. Journal of Applied Polymer Science, 109(5), 3431-3437. http://dx.doi.org/10.1002/app.28454.
http://dx.doi.org/10.1002/app.28454...
]. The PVA-G layers revealed similar bands to those of the whole PVA-G sample.

The PVA-H sample presents bands related to PVA, e.g. 3275 cm-1, 2940 cm-1, 2910 cm-1, 1564 cm-1, 1379 cm-1, 1239 cm-1, 1143 cm-1. Nonetheless, some of its bands can be related to the presence of honey in the samples, e.g. at 1646cm-1 (ν(C–H) of carboxylic acids, ν(NH3) of free amino acids, water δ(OH)[4848 Anjos, O., Campos, M. G., Ruiz, P. C., & Antunes, P. (2015). Application of FTIR-ATR spectroscopy to the quantification of sugar in honey. Food Chemistry, 169, 218-223. http://dx.doi.org/10.1016/j.foodchem.2014.07.138. PMid:25236219.
http://dx.doi.org/10.1016/j.foodchem.201...
]), 1417 cm-1 (δ(O–H) of the C–OH group and δ(C–H) of the alkenes[4848 Anjos, O., Campos, M. G., Ruiz, P. C., & Antunes, P. (2015). Application of FTIR-ATR spectroscopy to the quantification of sugar in honey. Food Chemistry, 169, 218-223. http://dx.doi.org/10.1016/j.foodchem.2014.07.138. PMid:25236219.
http://dx.doi.org/10.1016/j.foodchem.201...
]), 775 cm-1 (saccharide configuration; anomeric region of carbohydrates vibration or δ(C–H)[4949 Kędzierska-Matysek, M., Matwijczuk, A., Florek, M., Barłowska, J., Wolanciuk, A., Matwijczuk, A., Chruściel, E., Walkowiak, R., Karcz, D., & Gładyszewska, B. (2018). Application of FTIR spectroscopy for analysis of the quality of honey. BIO Web of Conferences, 10, 02008. http://dx.doi.org/10.1051/bioconf/20181002008.
http://dx.doi.org/10.1051/bioconf/201810...
]). In addition, some of the honey bands are slightly displaced in the PVA-H sample, e.g. the bands at 1054 cm-1 (ν(C–O) of the C–OH group and carbohydrate structure's ν(C–C)[4848 Anjos, O., Campos, M. G., Ruiz, P. C., & Antunes, P. (2015). Application of FTIR-ATR spectroscopy to the quantification of sugar in honey. Food Chemistry, 169, 218-223. http://dx.doi.org/10.1016/j.foodchem.2014.07.138. PMid:25236219.
http://dx.doi.org/10.1016/j.foodchem.201...
]); 1030 cm-1 (vibration of the C–OH group, carbohydrate structure's ν(C-C) and ν(C-O), phenol's C-O vibration[5050 Tahir, H. E., Xiaobo, Z., Zhihua, L., Jiyong, S., Zhai, X., Wang, S., & Mariod, A. A. (2017). Rapid prediction of phenolic compounds and antioxidant activity of Sudanese honey using Raman and Fourier transform infrared (FT-IR) spectroscopy. Food Chemistry, 226, 202-211. http://dx.doi.org/10.1016/j.foodchem.2017.01.024. PMid:28254013.
http://dx.doi.org/10.1016/j.foodchem.201...
]); 898 cm-1; 874 cm-1, displaced by ~9 cm-1; 819 cm-1, these last bands related to saccharide configuration and to anomeric region of carbohydrates vibration or δ(C–H)[4949 Kędzierska-Matysek, M., Matwijczuk, A., Florek, M., Barłowska, J., Wolanciuk, A., Matwijczuk, A., Chruściel, E., Walkowiak, R., Karcz, D., & Gładyszewska, B. (2018). Application of FTIR spectroscopy for analysis of the quality of honey. BIO Web of Conferences, 10, 02008. http://dx.doi.org/10.1051/bioconf/20181002008.
http://dx.doi.org/10.1051/bioconf/201810...
]. Some of the PVA-H bands are located in between PVA bands position and honey bands position, e.g. the band at 1336 cm-1, which is in between the honey band at 1345 cm-1 (flavanol's and phenol's δ(O-H), δ(C-O), δ(C-H) and δ(C=C)[5050 Tahir, H. E., Xiaobo, Z., Zhihua, L., Jiyong, S., Zhai, X., Wang, S., & Mariod, A. A. (2017). Rapid prediction of phenolic compounds and antioxidant activity of Sudanese honey using Raman and Fourier transform infrared (FT-IR) spectroscopy. Food Chemistry, 226, 202-211. http://dx.doi.org/10.1016/j.foodchem.2017.01.024. PMid:28254013.
http://dx.doi.org/10.1016/j.foodchem.201...
]) and the PVA band at 1329 cm-1[3535 Oliveira, R. N., Rouzé, R., Quilty, B., Alves, G. G., Soares, G. D. A., Thiré, R. M. S. M., & McGuinness, G. B. (2014). Mechanical properties and in vitro characterization of polyvinyl alcohol-nano-silver hydrogel wound dressings. Interface Focus, 4(1), 20130049. http://dx.doi.org/10.1098/rsfs.2013.0049. PMid:24501677.
http://dx.doi.org/10.1098/rsfs.2013.0049...
]); there is a shoulder at 1097 cm-1, between the PVA band at 1089 cm-1 (ν(C-O)[3939 Chen, X., Chen, C., Zhang, H., Huang, Y., Yang, J., & Sun, D. (2017). Facile approach to the fabrication of 3D cellulose nanofibrils (CNFs) reinforced poly(vinyl alcohol) hydrogel with ideal biocompatibility. Carbohydrate Polymers, 173, 547-555. http://dx.doi.org/10.1016/j.carbpol.2017.06.036. PMid:28732898.
http://dx.doi.org/10.1016/j.carbpol.2017...
]) and the honey band at 1100 cm-1 (ν(C–O) related to the C–O–C linkage[4848 Anjos, O., Campos, M. G., Ruiz, P. C., & Antunes, P. (2015). Application of FTIR-ATR spectroscopy to the quantification of sugar in honey. Food Chemistry, 169, 218-223. http://dx.doi.org/10.1016/j.foodchem.2014.07.138. PMid:25236219.
http://dx.doi.org/10.1016/j.foodchem.201...
]); 917 cm-1, which is between the PVA band at 916 cm-1[3939 Chen, X., Chen, C., Zhang, H., Huang, Y., Yang, J., & Sun, D. (2017). Facile approach to the fabrication of 3D cellulose nanofibrils (CNFs) reinforced poly(vinyl alcohol) hydrogel with ideal biocompatibility. Carbohydrate Polymers, 173, 547-555. http://dx.doi.org/10.1016/j.carbpol.2017.06.036. PMid:28732898.
http://dx.doi.org/10.1016/j.carbpol.2017...
] and the honey band at 918 cm-1 (carbohydrate’s δ(C–H)[4848 Anjos, O., Campos, M. G., Ruiz, P. C., & Antunes, P. (2015). Application of FTIR-ATR spectroscopy to the quantification of sugar in honey. Food Chemistry, 169, 218-223. http://dx.doi.org/10.1016/j.foodchem.2014.07.138. PMid:25236219.
http://dx.doi.org/10.1016/j.foodchem.201...
]; α and β anomers' νas(C-O-C)[5151 Das, C., Chakraborty, S., Acharya, K., Bera, N. K., Chattopadhyay, D., Karmakar, A., & Chattopadhyay, S. (2017). FT-MIR supported Electrical Impedance Spectroscopy based study of sugar adulterated honeys from different floral origin. Talanta, 171, 327-334. http://dx.doi.org/10.1016/j.talanta.2017.05.016. PMid:28551147.
http://dx.doi.org/10.1016/j.talanta.2017...
]). These bands displacement and the bands located in between the original PVA and honey bands could indicate physical interaction (Van der Waals or hydrogen bonding) between PVA and honey.

Since the layers of the samples presented varied composition, they were examined separately. The layer containing 5% honey presented bands similar to the PVA-H whole sample previously described, but the bands at 1336 cm-1 and at 898 cm-1 (honey’s bands[5252 Gok, S., Severcan, M., Goormaghtigh, E., Kandemir, I., & Severcan, F. (2015). Differentiation of Anatolian honey samples from different botanical origins by ATR-FTIR spectroscopy using multivariate analysis. Food Chemistry, 170, 234-240. http://dx.doi.org/10.1016/j.foodchem.2014.08.040. PMid:25306340.
http://dx.doi.org/10.1016/j.foodchem.201...
]) were absent and a shoulder at 831 cm-1 (PVA’s band[3939 Chen, X., Chen, C., Zhang, H., Huang, Y., Yang, J., & Sun, D. (2017). Facile approach to the fabrication of 3D cellulose nanofibrils (CNFs) reinforced poly(vinyl alcohol) hydrogel with ideal biocompatibility. Carbohydrate Polymers, 173, 547-555. http://dx.doi.org/10.1016/j.carbpol.2017.06.036. PMid:28732898.
http://dx.doi.org/10.1016/j.carbpol.2017...
]) was present; the band that should be at 1054-1030 cm-1 was displaced towards the PVA band (1089 cm-1[3939 Chen, X., Chen, C., Zhang, H., Huang, Y., Yang, J., & Sun, D. (2017). Facile approach to the fabrication of 3D cellulose nanofibrils (CNFs) reinforced poly(vinyl alcohol) hydrogel with ideal biocompatibility. Carbohydrate Polymers, 173, 547-555. http://dx.doi.org/10.1016/j.carbpol.2017.06.036. PMid:28732898.
http://dx.doi.org/10.1016/j.carbpol.2017...
]), it was at 1083 cm-1. The layer containing 10% honey also present the same bands as the PVA-H whole sample, but the bands at 2940 cm-1 and at 2910 cm-1 were absent. Nonetheless, there were bands at 2930 cm-1 (honey’s band[4848 Anjos, O., Campos, M. G., Ruiz, P. C., & Antunes, P. (2015). Application of FTIR-ATR spectroscopy to the quantification of sugar in honey. Food Chemistry, 169, 218-223. http://dx.doi.org/10.1016/j.foodchem.2014.07.138. PMid:25236219.
http://dx.doi.org/10.1016/j.foodchem.201...
]), 1338 cm-1, 1259 cm-1 (honey’s band[4848 Anjos, O., Campos, M. G., Ruiz, P. C., & Antunes, P. (2015). Application of FTIR-ATR spectroscopy to the quantification of sugar in honey. Food Chemistry, 169, 218-223. http://dx.doi.org/10.1016/j.foodchem.2014.07.138. PMid:25236219.
http://dx.doi.org/10.1016/j.foodchem.201...
]), 1189 cm-1 (honey’s band[5050 Tahir, H. E., Xiaobo, Z., Zhihua, L., Jiyong, S., Zhai, X., Wang, S., & Mariod, A. A. (2017). Rapid prediction of phenolic compounds and antioxidant activity of Sudanese honey using Raman and Fourier transform infrared (FT-IR) spectroscopy. Food Chemistry, 226, 202-211. http://dx.doi.org/10.1016/j.foodchem.2017.01.024. PMid:28254013.
http://dx.doi.org/10.1016/j.foodchem.201...
]). A slight displacement of PVA and of honey bands in the PVA-H layers could be observed with the increased honey content, which could indicate the effect of honey in the movement of PVA’s functional groups and vice versa. The increased level of honey in the layer also revealed more honey bands in the FTIR spectrum, as expected.

The PVA-CMC-H sample presented the same bands as the PVA-CMC and that were previously described. In addition, there were bands related to honey, e.g. 2923 cm-1, 1417 cm-1, 1056 cm-1, 1035 cm-1 and 819 cm-1. These bands are slightly displaced in the PVA-CMC-H sample. The layer containing 10% honey and the layer with 5% honey presented similar bands to PVA-CMC-H whole sample previously described, although there were slight displacements of the bands with the addition of honey, e.g. the band at 1088 cm-1[3939 Chen, X., Chen, C., Zhang, H., Huang, Y., Yang, J., & Sun, D. (2017). Facile approach to the fabrication of 3D cellulose nanofibrils (CNFs) reinforced poly(vinyl alcohol) hydrogel with ideal biocompatibility. Carbohydrate Polymers, 173, 547-555. http://dx.doi.org/10.1016/j.carbpol.2017.06.036. PMid:28732898.
http://dx.doi.org/10.1016/j.carbpol.2017...
] in PVA-CMC layer is broadened and shifted to 1074 cm-1 in the layer containing 10% honey. There is a band at ~1592 cm-1 in the PVA-CMC-H layers that is absent in the PVA-CMC layer and in the honey spectrum. The presence of a new band could indicate new bonding between the polymers and honey[5353 Yang, C., & Wöll, C. (2017). IR spectroscopy applied to metal oxide surfaces: adsorbate vibrations and beyond. Advances in Physics: X, 2(2), 373-408. https://doi.org/10.1080/23746149.2017.1296372.
https://doi.org/10.1080/23746149.2017.12...
].

The PVA-G-H sample presented the previously described PVA bands; some gelatin bands, e.g. at 1551 cm-1 and at 1337 cm-1[5454 Agarwal, T., Narayan, R., Maji, S., Behera, S., Kulanthaivel, S., Maiti, T. K., Banerjee, I., Pal, K., & Giri, S. (2016). Gelatin/Carboxymethyl chitosan based scaffolds for dermal tissue engineering applications. International Journal of Biological Macromolecules, 93(Pt B), 1499-1506. http://dx.doi.org/10.1016/j.ijbiomac.2016.04.028. PMid:27086289.
http://dx.doi.org/10.1016/j.ijbiomac.201...
]; and some honey bands previously described, e.g. at 1052, 1029, 896, 853, 817, 775 cm-1. Band displacement or the formation of bands related to a chemical reaction or interaction between honey and the polymers was not observed[2121 Pal, K., Banthia, A. K., & Majumdar, D. K. (2007). Preparation and characterization of polyvinyl alcohol-gelatin hydrogel membranes for biomedical applications. AAPS PharmSciTech, 8(1), 21. http://dx.doi.org/10.1208/pt080121. PMid:17408220.
http://dx.doi.org/10.1208/pt080121...
].

3.2 Thermal analysis

DSC analysis of the whole three-layer samples revealed that the addition of the polysaccharide (NaCMC) diminished the sample Tg and raised the sample Tm, compared to PVA, while XcPVACMC was lower than theXcPVA (Table 2). It suggests that the NaCMC chains do not contribute to polymer chain entanglement, probably working as a plasticizer in the amorphous region of the blend. In addition, the NaCMC diminished the degree of crystallinity, but more “perfect” crystals were formed (with a higher Tm). A similar effect was observed when gelatin was added to PVA, but the Tm of PVA and PVA-G was similar, indicating that gelatin contributed only as a plasticizer and to diminish the sample’s degree of crystallinity. The addition of honey to PVA diminished considerably the Tg, Tm and the Xc of the samples, indicating that honey is a physical barrier to the interaction of polymer chains. The addition of both honey and either polysaccharide or protein to PVA led to the absence of crystallinity (there is no peak related to crystal formation). Nonetheless, compared to PVA-H, PVA-CMC-H and PVA-G-H both presented higher Tg, indicating that in the presence of the coupled materials the amorphous chains need more energy to gain movement. The Tg and Tm altering with the addition of NaCMC or honey could indicate miscibility and interaction between the materials[5555 Sudhamani, S., Prasad, M., & Udaya Sankar, K. (2003). DSC and FTIR studies on Gellan and Polyvinyl alcohol (PVA) blend films. Food Hydrocolloids, 17(3), 245-250. http://dx.doi.org/10.1016/S0268-005X(02)00057-7.
http://dx.doi.org/10.1016/S0268-005X(02)...
,5656 Abdulkhani, A., Hojati Marvast, E., Ashori, A., Hamzeh, Y., & Karimi, A. N. (2013). Preparation of cellulose/polyvinyl alcohol biocomposite films using 1-n-butyl-3-methylimidazolium chloride. International Journal of Biological Macromolecules, 62, 379-386. http://dx.doi.org/10.1016/j.ijbiomac.2013.08.050. PMid:24076203.
http://dx.doi.org/10.1016/j.ijbiomac.201...
]. The addition of gelatin altered the PVA Tg and Xc also due to the miscibility of the polymers which disorganize the chains packing[3838 Pawde, S. M., & Deshmukh, K. (2008). Characterization of polyvinyl alcohol/gelatin blend hydrogel films for biomedical applications. Journal of Applied Polymer Science, 109(5), 3431-3437. http://dx.doi.org/10.1002/app.28454.
http://dx.doi.org/10.1002/app.28454...
].

Table 2
Data regarding the samples degree of crystallinity (Xc), glass transition temperature (Tg), melting temperature (Tm), swelling degree (SD), gel fraction (GF), weight loss (WL), S. aureus growth.

3.3 In vitro analysis

All the samples’ swelling degree tests presented a similar trend (Figure 3), where there is a stretching of the network by the fluid’s initial diffusion, followed by a plateau in the curves, where the polymers network reaches stability/equilibrium, when the elastic forces and the osmotic forces on the network are balanced[5757 Ganji, F., Vasheghani-Farahani, S., & Vasheghani-Farahani, E. (2010). Theoretical description of hydrogel swelling: a review. Iranian Polymer Journal, 19(5), 375-398.]. Although some samples presented significant differences between the first hours of swelling (p < 0.05), the samples reached swelling equilibrium in 24 h of immersion.

Figure 3
Samples (a) Swelling Degree and (b) Weight Loss and gel fraction.

There was a significant difference of the equilibrium of swelling degree (SD) between all the samples, although the SD of the samples PVA and PVA-CMC-H can be considered the same. In general, it can be observed that samples containing honey swelled less than samples without honey[5858 Kouchak, M., Ameri, A., Naseri, B., & Kargar Boldaji, S. (2014). Chitosan and polyvinyl alcohol composite films containing nitrofurazone: preparation and evaluation. Iranian Journal of Basic Medical Sciences., 17(1), 14-20. http://dx.doi.org/10.22038/ijbms.2014.2150. PMid:24592302.
http://dx.doi.org/10.22038/ijbms.2014.21...
], probably because honey occupies network pores created by the ice during freeze-thawing, filling space that could have been available to the saline solution[5959 Oliveira, R. N., Moreira, A. P. D., Thiré, R. M. S. M., Quilty, B., Passos, T. M., Simon, P., Mancini, M. C., & McGuinness, G. B. (2017). Absorbent polyvinyl alcohol-sodium carboxymethyl cellulose hydrogels for propolis delivery in wound healing applications. Polymer Engineering and Science, 57(11), 1224-1233. http://dx.doi.org/10.1002/pen.24500.
http://dx.doi.org/10.1002/pen.24500...
]. PVA samples swelled less than PVA-G samples (which have a low degree of crystallinity compared to PVA), and these in turn swelled less than PVA-CMC samples (which have an even lower degree of crystallinity). Samples that are less crystalline present more amorphous phase and thereby stretch more with fluid ingress, and therefore swell more[6060 Huang, M.-H., & Yang, M.-C. (2008). Evaluation of glucan/poly(vinyl alcohol) blend wound dressing using rat models. International Journal of Pharmaceutics, 346(1-2), 38-46. http://dx.doi.org/10.1016/j.ijpharm.2007.06.021. PMid:17662545.
http://dx.doi.org/10.1016/j.ijpharm.2007...
,6161 Wang, L.-C., Chen, X.-G., Zhong, D.-Y., & Xu, Q.-C. (2007). Study on poly(vinyl alcohol)/carboxymethyl-chitosan blend film as local drug delivery system. Journal of Materials Science: Materials in Medicine, 18(6), 1125-1133. http://dx.doi.org/10.1007/s10856-007-0159-5. PMid:17268861.
http://dx.doi.org/10.1007/s10856-007-015...
].

The gel fraction (GF) of all the samples without honey (Figure 3) can be considered similar (p > 0.05). Although the addition of natural polymers altered the degree of crystallinity of the samples, the amorphous chain entanglements and the crystallites formed in freeze-thawing maintained the samples’ structural integrity[6262 Ahmed, E. M. (2015). Hydrogel: preparation, characterization, and applications: a review. Journal of Advanced Research, 6(2), 105-121. http://dx.doi.org/10.1016/j.jare.2013.07.006. PMid:25750745.
http://dx.doi.org/10.1016/j.jare.2013.07...
]. The addition of honey decreased the gel fraction of the samples (p < 0.05). The gel fraction property is related to the hydrogel’s crosslinked polymers chains that remain insoluble when immersed in aqueous fluid. The PVA-H GF is significantly higher than the PVA-CMC-H GF which is, in turn, significantly higher than the PVA-G-H, GF (p < 0.05). The GF of the honey samples diminish in accordance with the decrease in the samples’ degree of crystallinity, indicating that the samples crystallites work as physical crosslinking points. The addition of the natural polymers, as well as the addition of honey, diminishes the gels’ degree of crystallinity, diminishing the gels’ GF[6363 Tahtat, D., Mahlous, M., Benamer, S., Nacer Khodja, A., Larbi Youcef, S., Hadjarab, N., & Mezaache, W. (2011). Influence of some factors affecting antibacterial activity of PVA/Chitosan based hydrogels synthesized by gamma irradiation. Journal of Materials Science: Materials in Medicine, 22(11), 2505-2512. http://dx.doi.org/10.1007/s10856-011-4421-5. PMid:21870082.
http://dx.doi.org/10.1007/s10856-011-442...
,6464 El-Naggar, A. W. M., Senna, M. M., Mostafa, T. A., & Helal, R. H. (2017). Radiation synthesis and drug delivery properties of interpenetrating networks (IPNs) based on poly(vinyl alcohol)/methylcellulose blend hydrogels. International Journal of Biological Macromolecules, 102, 1045-1051. http://dx.doi.org/10.1016/j.ijbiomac.2017.04.084. PMid:28450244.
http://dx.doi.org/10.1016/j.ijbiomac.201...
].

The samples without honey presented similar weight loss (p > 0.05), Figure 3. The PVA samples weight loss (WL) could be due to biodegradation in saline: “hydrolytic cleavage of hydrogen bonding among -OH groups of PVA chains”, as discussed by Kamoun et al.[6565 Kamoun, E. A., Kenawy, E.-R. S., Tamer, T. M., El-Meligy, M. A., & Mohy Eldin, M. S. (2015). Poly (vinyl alcohol)-alginate physically crosslinked hydrogel membranes for wound dressing applications: characterization and bio-evaluation. Arabian Journal of Chemistry, 8(1), 38-47. http://dx.doi.org/10.1016/j.arabjc.2013.12.003.
http://dx.doi.org/10.1016/j.arabjc.2013....
]. The weight loss of the PVA blends could be related to PVA hydrolytic cleavage and also to the solubility of the natural polymers in aqueous media[6666 Kenawy, E.-R., Kamoun, E. A., Mohy Eldin, M. S., & El-Meligy, M. A. (2014). Physically crosslinked poly(vinyl alcohol)-hydroxyethyl starch blend hydrogel membranes: synthesis and characterization for biomedical applications. Arabian Journal of Chemistry, 7(3), 372-380. http://dx.doi.org/10.1016/j.arabjc.2013.05.026.
http://dx.doi.org/10.1016/j.arabjc.2013....

67 Lopez, C. G., Rogers, S. E., Colby, R. H., Graham, P., & Cabral, J. T. (2015). Structure of sodium carboxymethyl cellulose aqueous solutions: A SANS and rheology study. Journal of Polymer Science. Part B, Polymer Physics, 53(7), 492-501. http://dx.doi.org/10.1002/polb.23657. PMid:26709336.
http://dx.doi.org/10.1002/polb.23657...
-6868 Shi, C., Tao, F., & Cui, Y. (2018). New starch ester/gelatin based films: developed and physicochemical characterization. International Journal of Biological Macromolecules, 109, 863-871. http://dx.doi.org/10.1016/j.ijbiomac.2017.11.073. PMid:29137995.
http://dx.doi.org/10.1016/j.ijbiomac.201...
]. The samples containing honey presented significantly higher weight loss/biodegradation than the samples without honey. The WL followed the trend: PVA-H < PVA-CMC-H < PVA-G-H (p < 0.05), hypothesised to be due to degradation (due to chains leaching out by the saline solution) and honey delivery of both samples[6969 Pereira, R. F., Carvalho, A., Gil, M. H., Mendes, A., & Bártolo, P. J. (2013). Influence of Aloe vera on water absorption and enzymatic in vitro degradation of alginate hydrogel films. Carbohydrate Polymers, 98(1), 311-320. http://dx.doi.org/10.1016/j.carbpol.2013.05.076. PMid:23987350.
http://dx.doi.org/10.1016/j.carbpol.2013...
]. It is worth noting that only the three-layered samples were evaluated.

In this study, the PVA hydrogel can be considered a negative control (non-bactericidal) against gram-positive bacteria (S. aureus), allowing bacteria to grow in its presence[7070 Bhowmick, S., & Koul, V. (2016). Assessment of PVA/silver nanocomposite hydrogel patch as antimicrobial dressing scaffold: synthesis, characterization and biological evaluation. Materials Science and Engineering C, 59, 109-119. http://dx.doi.org/10.1016/j.msec.2015.10.003. PMid:26652355.
http://dx.doi.org/10.1016/j.msec.2015.10...
]. The addition of honey inhibited the bacterial growth in the presence of the samples for PVA-CMC and PVA-G samples, Table 2. S. aureus attaches to proteins on the surface of collagen matrices and gelatin is a hydrolysed form of collagen[7171 Porayath, C., Suresh, M. K., Biswas, R., Nair, B. G., Mishra, N., & Pal, S. (2018). Autolysin mediated adherence of Staphylococcus aureus with fibronectin, gelatin and heparin. International Journal of Biological Macromolecules, 110, 179-184. http://dx.doi.org/10.1016/j.ijbiomac.2018.01.047. PMid:29398086.
http://dx.doi.org/10.1016/j.ijbiomac.201...
]. Honey itself has a bactericidal effect due to its low water activity, the presence of H2O2 and its low pH[7272 Vijaya, K. K., & Nishteswar, K. (2012). Wound healing activity of honey: a pilot study. Ayu: an International Quarterly Journal of Research in Ayurveda, 33(3), 374-377. http://dx.doi.org/10.4103/0974-8520.108827. PMid:23723644.
http://dx.doi.org/10.4103/0974-8520.1088...
]. The antibacterial effect on S. aureus in wound healing hydrogels would depend on exceeding the minimum inhibitory concentration (MIC) of the honey with respect to the amount of honey in, and released from, the samples[7373 Miorin, P. L., Levy, N. C., Jr., Custodio, A. R., Bretz, W. A., & Marcucci, M. C. (2003). Antibacterial activity of honey and propolis from Apis mellifera and Tetragonisca angustula against Staphylococcus aureus. Journal of Applied Microbiology, 95(5), 913-920. http://dx.doi.org/10.1046/j.1365-2672.2003.02050.x. PMid:14633019.
http://dx.doi.org/10.1046/j.1365-2672.20...
]. Several hydrogels containing honey present antibacterial activity[3232 Abd El-Malek, F. F., Yousef, A. S., & El-Assar, S. A. (2017). Hydrogel film loaded with new formula from manuka honey for treatment of chronic wound infections. Journal of Global Antimicrobial Resistance, 11, 171-176. http://dx.doi.org/10.1016/j.jgar.2017.08.007. PMid:28830809.
http://dx.doi.org/10.1016/j.jgar.2017.08...
,7474 Giusto, G., Beretta, G., Vercelli, C., Valle, E., Iussich, S., Borghi, R., Odetti, P., Monacelli, F., Tramuta, C., Grego, E., Nebbia, P., Robino, P., Odore, R., & Gandini, M. (2018). Pectin-honey hydrogel: characterization, antimicrobial activity and biocompatibility. Bio-Medical Materials and Engineering, 29(3), 347-356. http://dx.doi.org/10.3233/BME-181730. PMid:29578463.
http://dx.doi.org/10.3233/BME-181730...
]. The samples of the present work had 200 mg/mL of honey, but the MIC for this Brazilian honey might not be have been reached for the PVA-honey samples. The PVA-CMC-H and PVA-G-H samples presented activity against S. aureus relative to their counterparts with no honey[5959 Oliveira, R. N., Moreira, A. P. D., Thiré, R. M. S. M., Quilty, B., Passos, T. M., Simon, P., Mancini, M. C., & McGuinness, G. B. (2017). Absorbent polyvinyl alcohol-sodium carboxymethyl cellulose hydrogels for propolis delivery in wound healing applications. Polymer Engineering and Science, 57(11), 1224-1233. http://dx.doi.org/10.1002/pen.24500.
http://dx.doi.org/10.1002/pen.24500...
]. It was observed a bactericidal effect. It is known that even low concentrations of honey can stimulate wound healing[7575 Zbuchea, A. (2014). Up to date use of honey for burns treatment. Annals of Burns and Fire Disasters, 27(1), 22-30. PMid:25249844.].

4. Conclusions

It was observed that the addition of some materials to PVA diminishes the gels crystallinity and gel fraction (related to the degree of crosslinking of the gels), altering the samples ability to swell, where the samples with honey presented lower fluid uptake than samples without it, since honey can occupy and obstruct pores. Nonehteless, the samples containing honey presented significantly higher biodegradation (hydrolytic degradation/weight loss) than the samples without honey. The samples with NaCMC or gelatin and honey were the ones that presented the highest activity against S. aureus relative to their honey-free counterparts, showing potential to be used as wound care materials.

5. Acknowledgements

The authors thank Conselho Nacional de Desenvolvimento Científico e Tecnológico - CNPq (funding/project 405922/2016-7) for the financial support, Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro - FAPERJ, CAPES (“This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001”), professor Garrett Brian McGuinness and professor Mauricio Mancini, CETEM/UFRJ and EMBRAPA.

  • How to cite: Santos, G. S., Santos, N. R. R., Pereira, I. C. S., Andrade Júnior, A. J., Lima, E. M. B., Minguita, A. P., Rosado, L. H. G., Moreira, A. P. D., Middea, A., Prudencio, E. R., Luchese, R. H., & Oliveira, R. N. (2020). Layered cryogels laden with Brazilian honey intended for wound care. Polímeros: Ciência e Tenologia, 30(3), e2020031. https://doi.org/10.1590/0104-1428.06820

6. References

  • 1
    Simões, D., Miguel, S. P., Ribeiro, M. P., Coutinho, P., Mendonça, A. G., & Correia, I. J. (2018). Recent advances on antimicrobial wound dressing: a review. European Journal of Pharmaceutics and Biopharmaceutics, 127, 130-141. http://dx.doi.org/10.1016/j.ejpb.2018.02.022 PMid:29462687.
    » http://dx.doi.org/10.1016/j.ejpb.2018.02.022
  • 2
    Tsao, C. T., Leung, M., Chang, J. Y., & Zhang, M. (2014). A simple material model to generate epidermal and dermal layers in vitro for skin regeneration. Journal of Materials Chemistry B, Materials for Biology and Medicine, 2(32), 5256-5264. http://dx.doi.org/10.1039/C4TB00614C PMid:25147728.
    » http://dx.doi.org/10.1039/C4TB00614C
  • 3
    Lee, Y. H., Chang, J. J., Yang, M. C., Chien, C. T., & Lai, W. F. (2012). Acceleration of wound healing in diabetic rats by layered hydrogel dressing. Carbohydrate Polymers, 88(3), 809-819. http://dx.doi.org/10.1016/j.carbpol.2011.12.045
    » http://dx.doi.org/10.1016/j.carbpol.2011.12.045
  • 4
    Morales Hurtado, M., de Vries, E. G., Zeng, X., & van der Heide, E. (2016). A tribo-mechanical analysis of PVA-based building-blocks for implementation in a 2-layered skin model. Journal of the Mechanical Behavior of Biomedical Materials, 62, 319-332. http://dx.doi.org/10.1016/j.jmbbm.2016.05.001 PMid:27236420.
    » http://dx.doi.org/10.1016/j.jmbbm.2016.05.001
  • 5
    Tavakoli, J., Mirzaei, S., & Tang, Y. (2018). Cost-effective double-layer hydrogel composites for wound dressing applications. Polymers, 10(3), 305. http://dx.doi.org/10.3390/polym10030305 PMid:30966340.
    » http://dx.doi.org/10.3390/polym10030305
  • 6
    Jiang, S., Liu, S., & Feng, W. (2011). PVA hydrogel properties for biomedical application. Journal of the Mechanical Behavior of Biomedical Materials, 4(7), 1228-1233. http://dx.doi.org/10.1016/j.jmbbm.2011.04.005 PMid:21783131.
    » http://dx.doi.org/10.1016/j.jmbbm.2011.04.005
  • 7
    Reis, E. F., Campos, F. S., Lage, A. P., Leite, R. C., Heneine, L. G., Vasconcelos, W. L., Lobato, Z. I. P., & Mansur, H. S. (2006). Synthesis and characterization of poly (vinyl alcohol) hydrogels and hybrids for rMPB70 protein adsorption. Materials Research, 9(2), 185-191. http://dx.doi.org/10.1590/S1516-14392006000200014
    » http://dx.doi.org/10.1590/S1516-14392006000200014
  • 8
    Tontowi, A. E., Perkasa, D. P., Siswomihardjo, W., & Darwis, D. (2016). Effect of polyvinyl alcohol (PVA) blending and gamma irradiation on compressive strength of FHAp/FGel composite as candidate of scaffold. IACSIT International Journal of Engineering and Technology, 8(1), 108-116.
  • 9
    Gupta, S., Webster, T. J., & Sinha, A. (2011). Evolution of PVA gels prepared without crosslinking agents as a cell adhesive surface. Journal of Materials Science: Materials in Medicine, 22(7), 1763-1772. http://dx.doi.org/10.1007/s10856-011-4343-2 PMid:21643819.
    » http://dx.doi.org/10.1007/s10856-011-4343-2
  • 10
    El-Fawal, G. F., Yassin, A. M., & El-Deeb, N. M. (2017). The novelty in fabrication of poly vinyl alcohol/κ-carrageenan hydrogel with Lactobacillus bulgaricus extract as anti-inflammatory wound dressing agent. AAPS PharmSciTech, 18(5), 1605-1616. http://dx.doi.org/10.1208/s12249-016-0628-6 PMid:27620196.
    » http://dx.doi.org/10.1208/s12249-016-0628-6
  • 11
    Choi, J. S., Kim, D. W., Kim, D. S., Kim, J. O., Yong, C. S., Cho, K. H., Youn, Y. S., Jin, S. G., & Choi, H. G. (2016). Novel neomycin sulfate-loaded hydrogel dressing with enhanced physical dressing properties and wound-curing effect. Drug Delivery, 23(8), 2806-2812. http://dx.doi.org/10.3109/10717544.2015.1089958 PMid:26394193.
    » http://dx.doi.org/10.3109/10717544.2015.1089958
  • 12
    Sannino, A., Demitri, C., & Madaghiele, M. (2009). Biodegradable cellulose-based hydrogels: design and applications. Materials, 2(2), 353-373. http://dx.doi.org/10.3390/ma2020353
    » http://dx.doi.org/10.3390/ma2020353
  • 13
    Nayak, S., & Kundu, S. C. (2014). Sericin-carboxymethyl cellulose porous matrices as cellular wound dressing material. Journal of Biomedical Materials Research: Part A, 102(6), 1928-1940. http://dx.doi.org/10.1002/jbm.a.34865 PMid:23853114.
    » http://dx.doi.org/10.1002/jbm.a.34865
  • 14
    Capanema, N. S. V., Mansur, A. A. P., Jesus, A. C., Carvalho, S. M., Oliveira, L. C., & Mansur, H. S. (2018). Superabsorbent crosslinked carboxymethyl cellulose-PEG hydrogels for potential wound dressing applications. International Journal of Biological Macromolecules, 106, 1218-1234. http://dx.doi.org/10.1016/j.ijbiomac.2017.08.124 PMid:28851645.
    » http://dx.doi.org/10.1016/j.ijbiomac.2017.08.124
  • 15
    Namazi, H., Rakhshaei, R., Hamishehkar, H., & Kafil, H. S. (2016). Antibiotic loaded carboxymethylcellulose/MCM-41 nanocomposite hydrogel films as potential wound dressing. International Journal of Biological Macromolecules, 85, 327-334. http://dx.doi.org/10.1016/j.ijbiomac.2015.12.076 PMid:26740467.
    » http://dx.doi.org/10.1016/j.ijbiomac.2015.12.076
  • 16
    Lim, S. J., Lee, J. H., Piao, M. G., Lee, M. K., Oh, D. H., Hwang, D. H., Quan, Q. Z., Yong, C. S., & Choi, H. G. (2010). Effect of sodium carboxymethylcellulose and fucidic acid on the gel characterization of polyvinylalcohol-based wound dressing. Archives of Pharmacal Research, 33(7), 1073-1081. http://dx.doi.org/10.1007/s12272-010-0714-3 PMid:20661718.
    » http://dx.doi.org/10.1007/s12272-010-0714-3
  • 17
    Lee, J. H., Lim, S. J., Oh, D. H., Ku, S. K., Li, D. X., Yong, C. S., & Choi, H. G. (2010). Wound healing evaluation of sodium fucidate-loaded polyvinylalcohol/sodium carboxymethylcellulose-based wound dressing. Archives of Pharmacal Research, 33(7), 1083-1089. http://dx.doi.org/10.1007/s12272-010-0715-2 PMid:20661719.
    » http://dx.doi.org/10.1007/s12272-010-0715-2
  • 18
    Mariod, A. A., & Adam, H. F. (2013). Review: Gelatin, source, extraction and industrial applications. Acta Scientiarum Polonorum. Technologia Alimentaria, 12(2), 135-147.
  • 19
    Etxabide, A., Vairo, C., Santos-Vizcaino, E., Guerrero, P., Pedraz, J. L., Igartua, M., de la Caba, K., & Hernandez, R. M. (2017). Ultra thin hydro-films based on lactose-crosslinked fish gelatin for wound healing applications. International Journal of Pharmaceutics, 530(1-2), 455-467. http://dx.doi.org/10.1016/j.ijpharm.2017.08.001 PMid:28789885.
    » http://dx.doi.org/10.1016/j.ijpharm.2017.08.001
  • 20
    Rocasalbas, G., Francesko, A., Touriño, S., Fernández-Francos, X., Guebitz, G. M., & Tzanov, T. (2013). Laccase-assisted formation of bioactive chitosan/gelatin hydrogel stabilized with plant polyphenols. Carbohydrate Polymers, 92(2), 989-996. http://dx.doi.org/10.1016/j.carbpol.2012.10.045 PMid:23399119.
    » http://dx.doi.org/10.1016/j.carbpol.2012.10.045
  • 21
    Pal, K., Banthia, A. K., & Majumdar, D. K. (2007). Preparation and characterization of polyvinyl alcohol-gelatin hydrogel membranes for biomedical applications. AAPS PharmSciTech, 8(1), 21. http://dx.doi.org/10.1208/pt080121 PMid:17408220.
    » http://dx.doi.org/10.1208/pt080121
  • 22
    Fan, L., Yang, H., Yang, J., Peng, M., & Hu, J. (2016). Preparation and characterization of chitosan/gelatin/PVA hydrogel for wound dressings. Carbohydrate Polymers, 146, 427-434. http://dx.doi.org/10.1016/j.carbpol.2016.03.002 PMid:27112893.
    » http://dx.doi.org/10.1016/j.carbpol.2016.03.002
  • 23
    Shamloo, A., Sarmadi, M., Aghababaie, Z., & Vossoughi, M. (2018). Accelerated full-thickness wound healing via sustained bFGF delivery based on a PVA/chitosan/gelatin hydrogel incorporating PCL microspheres. International Journal of Pharmaceutics, 537(1-2), 278-289. http://dx.doi.org/10.1016/j.ijpharm.2017.12.045 PMid:29288809.
    » http://dx.doi.org/10.1016/j.ijpharm.2017.12.045
  • 24
    Martinotti, S., & Ranzato, E. (2018). Honey, wound repair and regenerative medicine. Journal of Functional Biomaterials, 9(2), 34. http://dx.doi.org/10.3390/jfb9020034 PMid:29738478.
    » http://dx.doi.org/10.3390/jfb9020034
  • 25
    Meo, S. A., Al-Asiri, S. A., Mahesar, A. L., & Ansari, M. J. (2017). Role of honey in modern medicine. Saudi Journal of Biological Sciences, 24(5), 975-978. http://dx.doi.org/10.1016/j.sjbs.2016.12.010 PMid:28663690.
    » http://dx.doi.org/10.1016/j.sjbs.2016.12.010
  • 26
    Santos, A. M. N., Moreira, A. P. D., Carvalho, C. W. P., Luchese, R., Ribeiro, E., McGuinness, G. B., Mendes, M. F., & Oliveira, R. N. (2019). Physically cross-linked gels of PVA with natural polymers as matrices for manuka honey release in wound-care applications. Materials, 12(4), 559. http://dx.doi.org/10.3390/ma12040559 PMid:30781788.
    » http://dx.doi.org/10.3390/ma12040559
  • 27
    Mandal, S., DebMandal, M., Pal, N. K., & Saha, K. (2010). Antibacterial activity of honey against clinical isolates of Escherichia coli, Pseudomonas aeruginosa and Salmonella enterica serovar Typhi. Asian Pacific Journal of Tropical Medicine, 3(12), 961-964. http://dx.doi.org/10.1016/S1995-7645(11)60009-6
    » http://dx.doi.org/10.1016/S1995-7645(11)60009-6
  • 28
    Guirguis, O. W., & Moselhey, M. T. H. (2012). Thermal and structural studies of poly (vinyl alcohol) and hydroxypropyl cellulose blends. Nature and Science, 04(01), 57-67. http://dx.doi.org/10.4236/ns.2012.41009
    » http://dx.doi.org/10.4236/ns.2012.41009
  • 29
    El-Kased, R. F., Amer, R. I., Attia, D., & Elmazar, M. M. (2017). Honey-based hydrogel: in vitro and comparative in vivo evaluation for burn wound healing. Scientific Reports, 7(1), 9692. http://dx.doi.org/10.1038/s41598-017-08771-8 PMid:28851905.
    » http://dx.doi.org/10.1038/s41598-017-08771-8
  • 30
    Giusto, G., Vercelli, C., Comino, F., Caramello, V., Tursi, M., & Gandini, M. (2017). A new, easy-to-make pectin-honey hydrogel enhances wound healing in rats. BMC Complementary and Alternative Medicine, 17(1), 266. http://dx.doi.org/10.1186/s12906-017-1769-1 PMid:28511700.
    » http://dx.doi.org/10.1186/s12906-017-1769-1
  • 31
    Tavakoli, J., & Tang, Y. (2017). Honey/PVA hybrid wound dressings with controlled release of antibioticsStructural, physico-mechanical and in-vitro biomedical studies. Materials Science and Engineering C, 77, 318-325. http://dx.doi.org/10.1016/j.msec.2017.03.272 PMid:28532035.
    » http://dx.doi.org/10.1016/j.msec.2017.03.272
  • 32
    Abd El-Malek, F. F., Yousef, A. S., & El-Assar, S. A. (2017). Hydrogel film loaded with new formula from manuka honey for treatment of chronic wound infections. Journal of Global Antimicrobial Resistance, 11, 171-176. http://dx.doi.org/10.1016/j.jgar.2017.08.007 PMid:28830809.
    » http://dx.doi.org/10.1016/j.jgar.2017.08.007
  • 33
    Wang, T., Zhu, X. K., Xue, X. T., & Wu, D. Y. (2012). Hydrogel sheets of chitosan, honey and gelatin as burn wound dressings. Carbohydrate Polymers, 88(1), 75-83. http://dx.doi.org/10.1016/j.carbpol.2011.11.069
    » http://dx.doi.org/10.1016/j.carbpol.2011.11.069
  • 34
    Oliveira, R. N., Paranhos da Silva, C. M., Moreira, A. P. D., Mendonça, R. H., Thiré, R. M., & McGuinness, G. B. (2017). Comparative analysis of PVA hydrogels incorporating two natural antimicrobials: Punica granatum and Arnica montana tinctures. Journal of Applied Polymer Science, 134(41), 45392. http://dx.doi.org/10.1002/app.45392
    » http://dx.doi.org/10.1002/app.45392
  • 35
    Oliveira, R. N., Rouzé, R., Quilty, B., Alves, G. G., Soares, G. D. A., Thiré, R. M. S. M., & McGuinness, G. B. (2014). Mechanical properties and in vitro characterization of polyvinyl alcohol-nano-silver hydrogel wound dressings. Interface Focus, 4(1), 20130049. http://dx.doi.org/10.1098/rsfs.2013.0049 PMid:24501677.
    » http://dx.doi.org/10.1098/rsfs.2013.0049
  • 36
    Pietrucha, K., & Verne, S. (2009). Synthesis and characterization of a new generation of hydrogels for biomedical applications. In Proceedings of the World Congress on Medical Physics and Biomedical Engineering (pp. 1-4). Berlin: Springer. http://dx.doi.org/10.1007/978-3-642-03900-3_1
    » http://dx.doi.org/10.1007/978-3-642-03900-3_1
  • 37
    Abureesh, M. A., Oladipo, A. A., & Gazi, M. (2016). Facile synthesis of glucose-sensitive chitosan-poly(vinyl alcohol) hydrogel: drug release optimization and swelling properties. International Journal of Biological Macromolecules, 90, 75-80. http://dx.doi.org/10.1016/j.ijbiomac.2015.10.001 PMid:26459171.
    » http://dx.doi.org/10.1016/j.ijbiomac.2015.10.001
  • 38
    Pawde, S. M., & Deshmukh, K. (2008). Characterization of polyvinyl alcohol/gelatin blend hydrogel films for biomedical applications. Journal of Applied Polymer Science, 109(5), 3431-3437. http://dx.doi.org/10.1002/app.28454
    » http://dx.doi.org/10.1002/app.28454
  • 39
    Chen, X., Chen, C., Zhang, H., Huang, Y., Yang, J., & Sun, D. (2017). Facile approach to the fabrication of 3D cellulose nanofibrils (CNFs) reinforced poly(vinyl alcohol) hydrogel with ideal biocompatibility. Carbohydrate Polymers, 173, 547-555. http://dx.doi.org/10.1016/j.carbpol.2017.06.036 PMid:28732898.
    » http://dx.doi.org/10.1016/j.carbpol.2017.06.036
  • 40
    Ibrahim, M. M., Koschella, A., Kadry, G., & Heinze, T. (2013). Evaluation of cellulose and carboxymethyl cellulose/poly(vinyl alcohol) membranes. Carbohydrate Polymers, 95(1), 414-420. http://dx.doi.org/10.1016/j.carbpol.2013.03.012 PMid:23618287.
    » http://dx.doi.org/10.1016/j.carbpol.2013.03.012
  • 41
    Hassan, E. A., Hassan, M. L., Moorefield, C. N., & Newkome, G. R. (2015). New supramolecular metallo-terpyridine carboxymethyl cellulose derivatives with antimicrobial properties. Carbohydrate Polymers, 116, 2-8. http://dx.doi.org/10.1016/j.carbpol.2014.06.056 PMid:25458266.
    » http://dx.doi.org/10.1016/j.carbpol.2014.06.056
  • 42
    Juncu, G., Stoica-Guzun, A., Stroescu, M., Isopencu, G., & Jinga, S. I. (2016). Drug release kinetics from carboxymethylcellulose-bacterial cellulose composite films. International Journal of Pharmaceutics, 510(2), 485-492. http://dx.doi.org/10.1016/j.ijpharm.2015.11.053 PMid:26688041.
    » http://dx.doi.org/10.1016/j.ijpharm.2015.11.053
  • 43
    Shehap, A. (2008). Thermal and spectroscopic studies of polyvinyl alcohol/sodium carboxy methyl cellulose blends. Egyptian Journal of Solid, 31(1), 75-91.
  • 44
    Ikhuoria, E. U., Omorogbe, S. O., Agbonlahor, O. G., Iyare, N. O., Pillai, S., & Aigbodion, A. I. (2017). Spectral analysis of the chemical structure of carboxymethylated cellulose produced by green synthesis from coir fibre. Ciência e Tecnologia dos Materiais, 29(2), 55-62. http://dx.doi.org/10.1016/j.ctmat.2016.05.007
    » http://dx.doi.org/10.1016/j.ctmat.2016.05.007
  • 45
    Abou-Yousef, H., & Kamel, S. (2015). High efficiency antimicrobial cellulose-based nanocomposite hydrogels. Journal of Applied Polymer Science, 132(31). http://dx.doi.org/10.1002/app.42327
    » http://dx.doi.org/10.1002/app.42327
  • 46
    Chaturvedi, A., Bajpai, A. K., & Bajpai, J. (2015). Preparation and characterization of poly(vinyl alcohol) cryogel-silver nanocomposites and evaluation of blood compatibility, cytotoxicity, and antimicrobial behaviors. Polymer Composites, 36(11), 1983-1997. http://dx.doi.org/10.1002/pc.23108
    » http://dx.doi.org/10.1002/pc.23108
  • 47
    Singh, R. K., & Khatri, O. P. (2012). A scanning electron microscope based new method for determining degree of substitution of sodium carboxymethyl cellulose. Journal of Microscopy, 246(1), 43-52. http://dx.doi.org/10.1111/j.1365-2818.2011.03583.x PMid:22150298.
    » http://dx.doi.org/10.1111/j.1365-2818.2011.03583.x
  • 48
    Anjos, O., Campos, M. G., Ruiz, P. C., & Antunes, P. (2015). Application of FTIR-ATR spectroscopy to the quantification of sugar in honey. Food Chemistry, 169, 218-223. http://dx.doi.org/10.1016/j.foodchem.2014.07.138 PMid:25236219.
    » http://dx.doi.org/10.1016/j.foodchem.2014.07.138
  • 49
    Kędzierska-Matysek, M., Matwijczuk, A., Florek, M., Barłowska, J., Wolanciuk, A., Matwijczuk, A., Chruściel, E., Walkowiak, R., Karcz, D., & Gładyszewska, B. (2018). Application of FTIR spectroscopy for analysis of the quality of honey. BIO Web of Conferences, 10, 02008. http://dx.doi.org/10.1051/bioconf/20181002008
    » http://dx.doi.org/10.1051/bioconf/20181002008
  • 50
    Tahir, H. E., Xiaobo, Z., Zhihua, L., Jiyong, S., Zhai, X., Wang, S., & Mariod, A. A. (2017). Rapid prediction of phenolic compounds and antioxidant activity of Sudanese honey using Raman and Fourier transform infrared (FT-IR) spectroscopy. Food Chemistry, 226, 202-211. http://dx.doi.org/10.1016/j.foodchem.2017.01.024 PMid:28254013.
    » http://dx.doi.org/10.1016/j.foodchem.2017.01.024
  • 51
    Das, C., Chakraborty, S., Acharya, K., Bera, N. K., Chattopadhyay, D., Karmakar, A., & Chattopadhyay, S. (2017). FT-MIR supported Electrical Impedance Spectroscopy based study of sugar adulterated honeys from different floral origin. Talanta, 171, 327-334. http://dx.doi.org/10.1016/j.talanta.2017.05.016 PMid:28551147.
    » http://dx.doi.org/10.1016/j.talanta.2017.05.016
  • 52
    Gok, S., Severcan, M., Goormaghtigh, E., Kandemir, I., & Severcan, F. (2015). Differentiation of Anatolian honey samples from different botanical origins by ATR-FTIR spectroscopy using multivariate analysis. Food Chemistry, 170, 234-240. http://dx.doi.org/10.1016/j.foodchem.2014.08.040 PMid:25306340.
    » http://dx.doi.org/10.1016/j.foodchem.2014.08.040
  • 53
    Yang, C., & Wöll, C. (2017). IR spectroscopy applied to metal oxide surfaces: adsorbate vibrations and beyond. Advances in Physics: X, 2(2), 373-408. https://doi.org/10.1080/23746149.2017.1296372
    » https://doi.org/10.1080/23746149.2017.1296372
  • 54
    Agarwal, T., Narayan, R., Maji, S., Behera, S., Kulanthaivel, S., Maiti, T. K., Banerjee, I., Pal, K., & Giri, S. (2016). Gelatin/Carboxymethyl chitosan based scaffolds for dermal tissue engineering applications. International Journal of Biological Macromolecules, 93(Pt B), 1499-1506. http://dx.doi.org/10.1016/j.ijbiomac.2016.04.028 PMid:27086289.
    » http://dx.doi.org/10.1016/j.ijbiomac.2016.04.028
  • 55
    Sudhamani, S., Prasad, M., & Udaya Sankar, K. (2003). DSC and FTIR studies on Gellan and Polyvinyl alcohol (PVA) blend films. Food Hydrocolloids, 17(3), 245-250. http://dx.doi.org/10.1016/S0268-005X(02)00057-7
    » http://dx.doi.org/10.1016/S0268-005X(02)00057-7
  • 56
    Abdulkhani, A., Hojati Marvast, E., Ashori, A., Hamzeh, Y., & Karimi, A. N. (2013). Preparation of cellulose/polyvinyl alcohol biocomposite films using 1-n-butyl-3-methylimidazolium chloride. International Journal of Biological Macromolecules, 62, 379-386. http://dx.doi.org/10.1016/j.ijbiomac.2013.08.050 PMid:24076203.
    » http://dx.doi.org/10.1016/j.ijbiomac.2013.08.050
  • 57
    Ganji, F., Vasheghani-Farahani, S., & Vasheghani-Farahani, E. (2010). Theoretical description of hydrogel swelling: a review. Iranian Polymer Journal, 19(5), 375-398.
  • 58
    Kouchak, M., Ameri, A., Naseri, B., & Kargar Boldaji, S. (2014). Chitosan and polyvinyl alcohol composite films containing nitrofurazone: preparation and evaluation. Iranian Journal of Basic Medical Sciences., 17(1), 14-20. http://dx.doi.org/10.22038/ijbms.2014.2150 PMid:24592302.
    » http://dx.doi.org/10.22038/ijbms.2014.2150
  • 59
    Oliveira, R. N., Moreira, A. P. D., Thiré, R. M. S. M., Quilty, B., Passos, T. M., Simon, P., Mancini, M. C., & McGuinness, G. B. (2017). Absorbent polyvinyl alcohol-sodium carboxymethyl cellulose hydrogels for propolis delivery in wound healing applications. Polymer Engineering and Science, 57(11), 1224-1233. http://dx.doi.org/10.1002/pen.24500
    » http://dx.doi.org/10.1002/pen.24500
  • 60
    Huang, M.-H., & Yang, M.-C. (2008). Evaluation of glucan/poly(vinyl alcohol) blend wound dressing using rat models. International Journal of Pharmaceutics, 346(1-2), 38-46. http://dx.doi.org/10.1016/j.ijpharm.2007.06.021 PMid:17662545.
    » http://dx.doi.org/10.1016/j.ijpharm.2007.06.021
  • 61
    Wang, L.-C., Chen, X.-G., Zhong, D.-Y., & Xu, Q.-C. (2007). Study on poly(vinyl alcohol)/carboxymethyl-chitosan blend film as local drug delivery system. Journal of Materials Science: Materials in Medicine, 18(6), 1125-1133. http://dx.doi.org/10.1007/s10856-007-0159-5 PMid:17268861.
    » http://dx.doi.org/10.1007/s10856-007-0159-5
  • 62
    Ahmed, E. M. (2015). Hydrogel: preparation, characterization, and applications: a review. Journal of Advanced Research, 6(2), 105-121. http://dx.doi.org/10.1016/j.jare.2013.07.006 PMid:25750745.
    » http://dx.doi.org/10.1016/j.jare.2013.07.006
  • 63
    Tahtat, D., Mahlous, M., Benamer, S., Nacer Khodja, A., Larbi Youcef, S., Hadjarab, N., & Mezaache, W. (2011). Influence of some factors affecting antibacterial activity of PVA/Chitosan based hydrogels synthesized by gamma irradiation. Journal of Materials Science: Materials in Medicine, 22(11), 2505-2512. http://dx.doi.org/10.1007/s10856-011-4421-5 PMid:21870082.
    » http://dx.doi.org/10.1007/s10856-011-4421-5
  • 64
    El-Naggar, A. W. M., Senna, M. M., Mostafa, T. A., & Helal, R. H. (2017). Radiation synthesis and drug delivery properties of interpenetrating networks (IPNs) based on poly(vinyl alcohol)/methylcellulose blend hydrogels. International Journal of Biological Macromolecules, 102, 1045-1051. http://dx.doi.org/10.1016/j.ijbiomac.2017.04.084 PMid:28450244.
    » http://dx.doi.org/10.1016/j.ijbiomac.2017.04.084
  • 65
    Kamoun, E. A., Kenawy, E.-R. S., Tamer, T. M., El-Meligy, M. A., & Mohy Eldin, M. S. (2015). Poly (vinyl alcohol)-alginate physically crosslinked hydrogel membranes for wound dressing applications: characterization and bio-evaluation. Arabian Journal of Chemistry, 8(1), 38-47. http://dx.doi.org/10.1016/j.arabjc.2013.12.003
    » http://dx.doi.org/10.1016/j.arabjc.2013.12.003
  • 66
    Kenawy, E.-R., Kamoun, E. A., Mohy Eldin, M. S., & El-Meligy, M. A. (2014). Physically crosslinked poly(vinyl alcohol)-hydroxyethyl starch blend hydrogel membranes: synthesis and characterization for biomedical applications. Arabian Journal of Chemistry, 7(3), 372-380. http://dx.doi.org/10.1016/j.arabjc.2013.05.026
    » http://dx.doi.org/10.1016/j.arabjc.2013.05.026
  • 67
    Lopez, C. G., Rogers, S. E., Colby, R. H., Graham, P., & Cabral, J. T. (2015). Structure of sodium carboxymethyl cellulose aqueous solutions: A SANS and rheology study. Journal of Polymer Science. Part B, Polymer Physics, 53(7), 492-501. http://dx.doi.org/10.1002/polb.23657 PMid:26709336.
    » http://dx.doi.org/10.1002/polb.23657
  • 68
    Shi, C., Tao, F., & Cui, Y. (2018). New starch ester/gelatin based films: developed and physicochemical characterization. International Journal of Biological Macromolecules, 109, 863-871. http://dx.doi.org/10.1016/j.ijbiomac.2017.11.073 PMid:29137995.
    » http://dx.doi.org/10.1016/j.ijbiomac.2017.11.073
  • 69
    Pereira, R. F., Carvalho, A., Gil, M. H., Mendes, A., & Bártolo, P. J. (2013). Influence of Aloe vera on water absorption and enzymatic in vitro degradation of alginate hydrogel films. Carbohydrate Polymers, 98(1), 311-320. http://dx.doi.org/10.1016/j.carbpol.2013.05.076 PMid:23987350.
    » http://dx.doi.org/10.1016/j.carbpol.2013.05.076
  • 70
    Bhowmick, S., & Koul, V. (2016). Assessment of PVA/silver nanocomposite hydrogel patch as antimicrobial dressing scaffold: synthesis, characterization and biological evaluation. Materials Science and Engineering C, 59, 109-119. http://dx.doi.org/10.1016/j.msec.2015.10.003 PMid:26652355.
    » http://dx.doi.org/10.1016/j.msec.2015.10.003
  • 71
    Porayath, C., Suresh, M. K., Biswas, R., Nair, B. G., Mishra, N., & Pal, S. (2018). Autolysin mediated adherence of Staphylococcus aureus with fibronectin, gelatin and heparin. International Journal of Biological Macromolecules, 110, 179-184. http://dx.doi.org/10.1016/j.ijbiomac.2018.01.047 PMid:29398086.
    » http://dx.doi.org/10.1016/j.ijbiomac.2018.01.047
  • 72
    Vijaya, K. K., & Nishteswar, K. (2012). Wound healing activity of honey: a pilot study. Ayu: an International Quarterly Journal of Research in Ayurveda, 33(3), 374-377. http://dx.doi.org/10.4103/0974-8520.108827 PMid:23723644.
    » http://dx.doi.org/10.4103/0974-8520.108827
  • 73
    Miorin, P. L., Levy, N. C., Jr., Custodio, A. R., Bretz, W. A., & Marcucci, M. C. (2003). Antibacterial activity of honey and propolis from Apis mellifera and Tetragonisca angustula against Staphylococcus aureus Journal of Applied Microbiology, 95(5), 913-920. http://dx.doi.org/10.1046/j.1365-2672.2003.02050.x PMid:14633019.
    » http://dx.doi.org/10.1046/j.1365-2672.2003.02050.x
  • 74
    Giusto, G., Beretta, G., Vercelli, C., Valle, E., Iussich, S., Borghi, R., Odetti, P., Monacelli, F., Tramuta, C., Grego, E., Nebbia, P., Robino, P., Odore, R., & Gandini, M. (2018). Pectin-honey hydrogel: characterization, antimicrobial activity and biocompatibility. Bio-Medical Materials and Engineering, 29(3), 347-356. http://dx.doi.org/10.3233/BME-181730 PMid:29578463.
    » http://dx.doi.org/10.3233/BME-181730
  • 75
    Zbuchea, A. (2014). Up to date use of honey for burns treatment. Annals of Burns and Fire Disasters, 27(1), 22-30. PMid:25249844.

Publication Dates

  • Publication in this collection
    04 Dec 2020
  • Date of issue
    2020

History

  • Received
    14 July 2020
  • Reviewed
    07 Sept 2020
  • Accepted
    11 Sept 2020
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