Bubble template fabrication of chitosan/poly(vinyl alcohol) sponges for wound dressing applications
Introduction
One of the widely studied polymers for wound dressing applications is chitosan, which is natural, biocompatible, biodegradable, non-toxic, and possess antibacterial and unique hemostatic capabilities [1], [2], [3]. Chitosan based fibrous materials, hydrogels, membranes, scaffolds and sponges of chitosan based materials have been fabricated and investigated for wound care in different situations (wound type, serious extent) [1]. Generally, thin films or membranes materials are used for partial skin damage and help the regeneration of new skin. On the other hand, scaffolds and spongy materials are more suitable for large wound dressing applications. Particularly in cases of full thickness of skin or flash missing during serious accidental injury or burning, immediate coverage of wound surface with dressings is necessary before skin grafting [4]. An ideal wound dressing material should have high liquid absorbing, proper gas permeation, biocompatibility, and antibacterial properties to protect the skin defect from infections, dehydration and subsequently tissue damaging. Chitosan sponges with good fluid absorption capability, cell interaction and hydrophilicity can meet the requirements such as higher gas permeation and protection of wound from infection and dehydration.
Recently, Denkbas et al. using a solvent evaporation technique prepared and characterized chitosan sponges encapsulated with a model antibiotic drug, norfloxacin, as wound dressing material. Li et al. [5] and Jayakumar et al. [6] using freeze-drying methods prepared chitosan based sponges for wound care. These sponges had a typical microporous structure and exhibited enhanced liquid absorbing capacity and cell interaction due to high surface/volume ratio. However, one major limitation for chitosan materials is its brittle behavior. Chitosan (CS) based sponges with reasonable strength and elasticity are of high interest as it allow slow drug release to a wound while the spongy form absorbs the wound fluid [2], [5]. Blends with other synthetic materials and cross-linking are believed to be an effective way to improve mechanical strength.
In this work, polyvinyl alcohol (PVA), a nontoxic, water soluble polymer, was blended with chitosan to improve the mechanical properties of chitosan [7], [8]. CS/PVA composite sponges were prepared using a facile bubble assisted freeze-drying method. A solution of NaHCO3 was added to neutralize the acidic chitosan solution, and the acid–base reaction intrinsically produced bubbles as templates for the formation of macroporous structure. Glutaraldehyde was then added to allow for cross-linking in chitosan polymers as well as PVA polymers. To our best knowledge, this is the first report of the positive use of simple chemistry generated bubbles for producing macroporous chitosan structure. This paper studied and presented the effects of PVA content and cross-linking degree on the mechanic properties, water uptake, and moisture permeability of the CS/PVA composite sponges. To evaluate the potential for wound protection, antibacterial property of CS/PVA sponges was preliminarily studied in vitro by using Escherichia coli and zone of inhibition was observed. The chitosan's unique hemostatic capability through reaction with erythrocytes [9] was also demonstrated via in vitro method and discussed.
Section snippets
Materials
Chitosan powder (Luyang Chemical Co., Ltd, Rongcheng, Shandong, China), high molecular weight (M.W. 7570), deacetylation degree of 85%, was used without further purification. Glutaraldehyde aqueous solution (25%) and polyvinyl alcohol (PVA-124, M.W. 5000–6000, degree of hydrolysis 98% were purchased from Shanghai Chemical Reagent packing plant. Sodium bicarbonate, glycerol, acetic acid and other reagents were all of analytical grade.
Fabrication of CS/PVA medical sponge
As illustrated in Scheme 1, the process of sponge fabrication
Morphology and porosity
The fabrication process intrinsically generated the open porous structure of chitosan sponge as shown in Fig. 1. CO2 bubbles formed in the acid–base reaction during the gel formation, after the vacuum treatment, promoted the formation of interconnected uniform sphere pores with dense wall. This is different from other reported fibrous structure using solvent evaporation method and freezing-drying methods. The porosity and pore size of the sponges can be easily tuned by changing bubble density
Conclusions
The present investigation involves the synthesis of CS–PVA composite sponges in view of their increasing areas of applications in wound dressing, antibacterial and haemostatic applications. Presented bubble-assisted freeze-drying method allows the fabrication of macroporous chitosan sponges. The produced CS/PVA composite sponges exhibited an enhanced water absorption capacity. Improved mechanical properties were observed by cross-linking with glutaraldehyde and introduction of PVA. Suitable
Acknowledgments
The presented work was supported by the “undergraduate research plan” grant of University of Science and Technology of China (USTC), Hefei, China. The antibacterial testing was carried out by the department of Molecular Biology and Cell Biology at USTC, Hefei, China.
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