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ScienceDirect Procedia Materials Science 11 (2015) 152 – 156
5th International Biennial Conference on Ultrafine Grained and Nanostructured Materials, UFGNSM15
Nanoclay Enhanced the Mechanical Properties of Poly(Vinyl Alcohol) /Chitosan /Montmorillonite Nanocomposite Hydrogel as Wound Dressing S. Nooria, M. Kokabia,*, Z. M. Hassanb a
Polymer Engineering Department, Faculty of Chemical Engineering, Tarbiat Modares University, Tehran, P.O. Box: 14115-114, Islamic Republic of Iran b Immunology Department, Faculty of Medical Sciences, Tarbiat Modares University, Tehran, P.O. Box: 14115-331, , Islamic Republic of Iran
Abstract Polymeric hydrogels are a new class of biomaterials that have recently attracted a lot of attention for application in medical and pharmaceutical areas. They possess the most of desirable characteristics of an ideal dressing, but they have low mechanical strength to be used in under-tension positions of the body. In this study poly (vinyl alcohol) (PVA)/chitosan (CS)/montmorillonite (MMT) nanocomposite hydrogels were prepared by freezing-thawing method, as a biocompatible wound dressing. The X-ray diffraction analysis showed exfoliated morphology for prepared nanocomposite hydrogels and their mechanical properties were significantly influenced by nanoclay reinforcement. Using only 3 wt. % of nanoclay enhances the tensile modulus of nanocomposite hydrogel near 35% in compare to its neat hydrogel counterpart. Other mechanical properties such as tensile strength and elongation at break have been investigated, too. Improved mechanical properties of this system along with the other characteristics such as biocompatibility, antibacterial activity and good swelling behaviour, made it desirable candidate for wound dressing applications. © 2015The TheAuthors. Authors.Published Published Elsevier © 2015 by by Elsevier Ltd.Ltd. This is an open access article under the CC BY-NC-ND license Peer-review under responsibility of the organizing committee of UFGNSM15. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of UFGNSM15 Keywords: Nanocomposite Hydrogel; Chitosan; Poly (vinyl alcohol); Montmorillonite; Wound Dressing.
* Corresponding author. Tel/Fax: +98-21-8288-3340. E-mail address:
[email protected]
2211-8128 © 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of UFGNSM15 doi:10.1016/j.mspro.2015.11.023
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1. Introduction Hydrogels are a new class of biomaterials that have recently attracted a lot of attention for application in medical and pharmaceutical areas. The hydrogels have been investigated for various biological applications including drug delivery, tissue engineering, wound healing, antibacterial materials and thermal therapy, Satarkar et al. (2009). In wound healing applications in order to specify optimal features of an ideal wound dressing, several characteristics should be addressed such as: x Nontoxic x Biocompatible and biodegradable x Keeping the wound environment moist x Absorbing the exudate x Protecting against secondary infection x Contributing to simple gas exchange x Decreasing or removing trauma in the defected area Hydrogels fit most criteria for suitable wound dressing. They can be the most suitable dressing in debridement stage of chronic wounds, Goossens et al. (2010). However, the gel strength of hydrogels is naturally rather weak and this unfortunately limits their useful applications. To improve the mechanical properties of hydrogels several manufacturing methods were proposed, among which nanocomposite hydrogels resulted in significant improvements in the mechanical properties, Haraguchi (2007). The nanocomposites may consist of various types of nanoparticles, such as clay, ceramic, metallic or metal oxides dispersed in a hydrogel matrix. Beside all features of an ideal wound dressing which has been mentioned before, enhanced mechanical properties, make them desirable candidate for wound dressing applications, Kopecek (2009). PVA is a non-toxic, hydrophilic semi-crystalline synthetic polymer produced by polymerization of vinyl acetate to poly (vinyl acetate) and subsequent hydrolysis of poly (vinyl acetate) to PVA. Due to presence of high number of alcoholic groups in its structure, PVA is one of the most polar and hydrophilic synthetic polymers that can also form hydrogels. Cross-linked PVA attracted popular attention because of its high degree of swelling in water, inherent low toxicity, good biocompatibility and desirable physical properties, Khan et al. (2014). Cs is a cationic natural biopolymer which has desirable biological properties like biocompatibility, biodegradability, nontoxicity, excellent swelling, mucoadhesion, anticancer, stimuli responsive behaviour, coagulation and wound healing, Rebeiro et al. (2009). However, chitosan based adsorbents have weak mechanical properties and poor chemical resistance. For these reasons, much efforts have been focused on the interpenetration network (IPN), prepared by the introduction of a suitable second hydrophilic polymer such as PVA into the Cs matrix. In this work, dual-stimuli sensitive PVA/Cs/MMT nanocomposite hydrogel wound dressing solely was crosslinked by freezing-thawing as a physical method and its morphology and mechanical properties were investigated. 2. Experimental 2.1. Materials PVA with a degree of polymerization of 1700 and saponification value of greater than 98% was purchased from the Nippon Synthetic Chemical Industry Co., Ltd, Japan. Medium molecular weight Cs supplied from Sigma-Aldrich. MMT with a cation exchange capacity of about 92.6 meq/100g was supplied by Southern Clay Product Inc. USA. Acetic acid was supplied by Merck. Deionized distilled water (DDW) was used to prepare all aqueous solutions. 2.2. Preparation PVA/Cs/MMT nanocomposite hydrogels were prepared by cyclic freezing-thawing method. For this purpose, aqueous solutions of 10% by weight PVA containing 0 and 3wt. % MMT (based on polymer weight) mixed slowly at 90 oC to achieve complete dissolution. Cs was dissolved in acetic acid and a solution of 2 wt. % was added to PVA/MMT suspension. The mixture was kept under stirring to form a homogenous solution. Then the aqueous
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solutions were poured into plastic moulds and placed at -15oC for 24 h to induce crystallization. After freezing process, they were allowed to thaw for 24 h at room temperature. This cycle was repeated three times for each solution. 2.3. Characterization To characterize the morphology and the corresponding basal spacing between the silicate layers in the samples, their X-ray diffraction (XRD) patterns were recorded using Philips diffractometer (model Nexus-MPD, Netherland). The samples were cut into a dumbbell shape according to ASTM D-1822-L with a thickness of 3 mm and their mechanical properties including tensile modulus, strength and elongation at break were determined. Measurements were performed using a tensiometer (model INSTRON 5566, USA) with a constant speed of 50 mm/min at room temperature. 3. Results and Discussion 3.1. Morphology The XRD profiles of MMT and nanocomposite hydrogel are shown in Fig. 1. As seen, the X-ray profile of MMT has a characteristic diffraction peak at 2ϴ = 8.96o corresponding to d-spacing of 1.14 nm. On the other hand, X-ray profile of PVA/ Cs/ MMT sample shows no characteristic peak. The XRD results suggested an exfoliated morphology for the prepared PVA/Cs/MMT nanocomposite hydrogel.
Fig. 1. XRD patterns of MMT and PVA/ Cs/ MMT samples.
3.2 Mechanical properties As mentioned before, main interest in production of nanocomposites is to achieve the materials with better mechanical properties. Fig. 2 shows the tensile moduli for PVA/Cs and PVA/Cs/MMT hydrogels. As shown, by adding only 3 wt.% of MMT, tensile modulus of nanocomposite hydrogel increases near 35%.
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Fig. 2. Tensile Moduli of PVA/Cs and PVA/Cs/MMT Samples.
Figure 3 shows tensile strengths of samples. It exhibits 33% increase in tensile strength for PVA/CS/MMT in compare to PVA/CS counterpart. In general, mixing process of MMT with PVA/Cs hydrogel matrix yields to some sort of diffusion of the polymer chains into basal space of silicate layers of MMT and creates strong interfacial interactions which cause better mechanical properties, Mahdavi et al. (2013). Finally, Fig. 4 indicates little decrease in elongation at break values by adding MMT. Undoubtedly, this is due to high crosslinking density and network structure of nanocomposite hydrogel.
Fig. 3. Tensile Strengths of PVA/Cs and PVA/CS/MMT Samples.
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Fig. 4. Elongation at Break of PVA/Cs and PVA/Cs/MMT Samples.
4. Conclusion In this work, PVA/Cs/MMT nanocomposite hydrogel was introduced as a novel wound dressing due to significant combined properties of PVA and Cs such as biodegradability, biocompatibility, antibacterial activity, blood coagulation, good swelling and stimuli responsive behaviour. Investigation of mechanical properties of nanocomposite hydrogels indicates that the addition of MMT to hydrogel matrix gives enhanced mechanical properties to wound dressing. The results show that the nanocomposite hydrogel is the best choice for wound dressing and can fulfil the essential requirements of an ideal wound dressing to use on wounds under high stresses.
Acknowledgements The Authors wish to thank Tarbiat Modares University and IRAN Nanotechnology Initiative Council for the financial support of this work.
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