Wound-dressing materials with antibacterial activity from electrospun gelatin fiber mats containing silver nanoparticles Pim-on Rujitanaroj a , Nuttaporn Pimpha b , Pitt Supaphol a, * a Technological Center for Electrospun Fibers and The Petroleum and Petrochemical College, Chulalongkorn University, Pathumwan, Bangkok 10330, Thailand b National Nanotechnology Center, Thailand Science Park, Phathum Thani 12120, Thailand article info Article history: Received 1 July 2008 Received in revised form 2 August 2008 Accepted 6 August 2008 Available online 16 August 2008 Keywords: Electrospinning Fibrous membrane Ag nanoparticles abstract Ultrafine gelatin fiber mats with antibacterial activity against some common bacteria found on burn wounds were prepared from a gelatin solution (22%w/v in 70 vol% acetic acid) containing 2.5 wt% AgNO 3 . Silver nanoparticles (nAg), a potent antibacterial agent, first appeared in the AgNO 3 -containing gelatin solution after it had been aged for at least 12 h, with the amount of nAg increasing with increasing aging time. The average diameters of the as-formed nAg ranged between 11 and 20 nm. Electrospinning of both the base and the 12 h-aged AgNO 3 -containing gelatin solutions resulted in the formation of smooth fibers, with average diameters of w230 and w280 nm, respectively. The average diameter of the as- formed nAg in the electrospun fibers from the 12 h-aged AgNO 3 -containing gelatin solution was w13 nm. The nAg-containing gelatin fiber mats were further cross-linked with moist glutaraldehyde vapor to improve their stability in an aqueous medium. Both the weight loss and the water retention of the nAg-containing gelatin fiber mats in acetate buffer (pH 5.5), distilled water (pH 6.9) or simulated body fluid (SBF; pH 7.4) decreased with increasing cross-linking time. The release of Ag þ ions from both the 1- and 3 h-cross-linked nAg-containing gelatin fiber mats – by the total immersion method in acetate buffer and distilled water (both at a skin temperature of 32  C) – occurred rapidly during the first 60 min, and increased gradually afterwards; while that in SBF (at the physiological temperature of 37  C) occurred more gradually over the testing period. Lastly, the antibacterial activity of these materials, regardless of the sample types, was greatest against Pseudomonas aeroginosa, followed by Staphylococcus aureus, Escherichia coli, and methicillin-resistant S. aureus, respectively. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Electrospinning (e-spinning) is a process capable of producing fibers from materials of diverse origins, including polymers, with diameters in the nano- to micrometer range [1]. A polymer liquid (i.e., melt or solution) is first loaded into a container with a small opening (used as the nozzle), and is then charged with a high electrical potential across a finite distance between the nozzle and a grounded collection device. When the electric field increases beyond a critical value – at which the repulsive electrical forces overcome the surface tension of the polymeric liquid droplet at the tip of the nozzle – a charged jet is ejected [1]. As the jet travels to the collector, it either cools down (in case of the melt) or the solvent evaporates (in case of the solution) to obtain ultrafine fibers in the form of a non-woven fabric on the collector. The morphology of the electrospun (e-spun) fibers depends on a number of factors, such as solution properties (e.g., concentration, viscosity, conductivity, surface tension, etc.), processing conditions (e.g., electrical poten- tial, collection distance, etc.), and ambient conditions (e.g., temperature, humidity, etc.) [2,3]. Some potential uses of e-spun fibers in biomedical fields are, for example, immobilization of enzymes [4], tissue-engineered scaffolds [5,6], and delivery carriers for DNA [7] and drugs [8–12]. Due to its natural abundance and inherent biodegradability in physiological environments, gelatin is widely used in food, cosmetic, pharmaceutical and medical applications [13]. Depend- ing on its usage, gelatin can be fabricated in many forms, e.g., films [14], micro- or nanoparticles [15,16], and dense or porous hydrogels [17–19]. Gelatin in the form of micro- and nanofibers can also be fabricated by gel and e-spinning techniques, respectively [20–27]. Owing to the uniqueness of the e-spun fibers (e.g., high surface area to mass or volume ratio; high porosity of the e-spun fiber mat; and flexibility for surface functionalization), e-spun gelatin fibers are of interest here. Suitable solvents for preparing an electrospinnable gelatin solution are 2,2,2-trifluoroethanol (TFE) [21,22], formic acid [23,27], 1,1,1,3,3,3-hexafluoro-2-propanol (HFP) [24,25], and acetic acid [26,27]. The average diameters of the obtained e-spun gelatin fibers were 100–1900 nm (type-A gelatin; 5–15% w/v in TFE) [21]; * Corresponding author. Tel.: þ66 2218 4131; fax: þ66 2215 4459. E-mail address: pitt.s@chula.ac.th (P. Supaphol). Contents lists available at ScienceDirect Polymer journal homepage: www.elsevier.com/locate/polymer 0032-3861/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2008.08.021 Polymer 49 (2008) 4723–4732