DSpace at VNU: Fabrication of an antibacterial non-woven mat of a poly(lactic acid) chitosan blend by electrospinning

Macromolecular Research, Vol 20, No 1, pp 51-58 (2012) DOI 10.1007/s13233-012-0010-9 www.springer.com/13233 Fabrication of An Antibacterial Non-Woven Mat of a Poly(lactic acid)/Chitosan Blend by Electrospinning Hang Thi Au1, Lan Ngoc Pham2, Thu Ha Thi Vu3, and Jun Seo Park*,1 Division of Chemical Engineering, Hankyong National University, Gyeonggi 456-749, Korea Faculty of Chemistry, Hanoi University of Science, Hanoi, Vietnam Vietnam Institute of Industrial Chemistry, Hanoi, Vietnam Received April 19, 2011; Revised July 4, 2011; Accepted July 31, 2011 Abstract: Nonwoven mats made of a poly(lactic acid)/chitosan (PLA/CS) blend and a PLA/CS blend containing silver (Ag) nanoparticles (Ag/PLA/CS) were prepared using an electrospinning technique The morphology of electrospun fibers was observed by field emission scanning electron microscopy The addition of AgNO3 to the PLA/CS blend solution improved the electrospinning ability of the PLA/CS blend The average diameters of the electrospun PLA/CS and Ag/PLA/CS blend fibers decreased as CS content increased The Ag particles were evenly distributed in PLA/CS ultrafine fibers observed under transmission electron microscopy Ag nanoparticles were spontaneously generated during the electrospinning process When the CS content in the blend increased, the size of the Ag nanoparticles on the surface of the electrospun fibers increased as well The thermal and mechanical properties of the nonwoven mats were examined by differential scanning calorimetry and a tensile tester Fourier transform infrared spectroscopy was used to characterize the molecular interactions among PLA, Ag, and CS in the blends The antibacterial activity of the nonwoven mats against Escherichia coli and Staphylococcus aureus was studied using an optical density method Keywords: chitosan, poly(lactic acid), silver nanoparticles, antibacterial activity, electrospinning Introduction in solutions, CS cannot be fabricated easily in fiber form by electrospinning.9,10 CS is brittle in film form, and its membrane permeability limits its use as a biomaterial.8 To overcome these shortcomings, many methods have been suggested for improving the morphology and ductility of CS.8 One of these methods is the preparation of blends consisting of CS and a mechanically strong polymer such as polyvinyl alcohol (PVA), poly(ethylene oxide) (PEO), or poly(vinyl pyrrolidone) (PVP).11,12 There has been considerable interest in the blending of CS with biodegradable polyesters; such blends could be used in important human clinical applications approved by the US Food and Drug Administration (FDA), e.g., in surgical sutures and some implantable devices.1 Among the many biodegradable polyesters, poly(lactic acid) (PLA) has attracted the most attention because it is obtained through the synthesis of lactic acid, which is produced from renewable resources such as corn and sugarcane PLA is an enantiomeric polyester, including poly(L-lactic acid) (PLLA) and poly(D-lactic acid) (PDLA), and has many useful characteristics such as low toxicity, excellent biocompatibility, and good mechanical properties.13 In addition, it is known to facilitate the production of uniform e-spun nanofibers without bead formation.14,15 PLA has been used with CS to prepare com- Electrospinning is a simple and low-cost method for preparing ultrafine fibers with diameters ranging from several micrometers to several hundreds of nanometers.1 The electrospun (e-spun) fibers produced by this method show great potential for a variety of biomedical applications, e.g., in the preparation of wound-dressing materials and tissueengineering scaffolds, because they have tunable porosity and smaller pore size than traditional ones.2 Chitosan (CS), a (1-4)-linked-2-amino-2-deoxy-β-D-glucopyranose, is derived from chitin, which is the second most abundant natural polysaccharide after cellulose.3,4 CS displays an unique polycationic character, chelating in the presence of active amino and hydroxyl functional groups.5-7 CS has been widely studied because it has many useful properties such as, non-toxicity, biodegradability, and biocompatibility; further, it also shows haemostatic activity and antibacterial properties.2 These characteristics render CS beneficial for use in wound dressing, drug delivery systems, vascular surgery, tissue culture, and various tissue engineering applications.5,8 However, due to its polycationic nature *Corresponding Author E-mail: jspark@hknu.ac.kr The Polymer Society of Korea 51 H T Au et al posite materials with improved toughness and with controllable biodegradability and chemical functionalities.8,16-18 A small amount of AgNO3 added to the PLA/CS blend solution could improve its electrospinning ability since the addition of AgNO3 was found to greatly change the morphology of the e-spun fibers from bead-on-fiber structure to a uniform fiber structure.19 CS can react with AgNO3 to reduce the repulsive force between ionic groups within the polymer backbones.5-7,9,12 Thus, a continuous fiber can be espun from Ag+/PLA/CS solution with high concentration of CS Moreover, silver (Ag) nanoparticles have attracted great interest because they show very strong antimicrobial activities.7,20 There are many methods for the reduction of Ag+ to Ag nanoparticles.5,6,12,20,21 Ag+ can be reduced to Ag0 by using a solvent as the reducing agent.20 The fabrication of polymeric nanofibers containing Ag nanoparticles through the heat treatment of e-spun nanofiber mats has also been reported.7,21 In the Ag/PLA/CS blend solution, the release of free silver ions from Ag+ by chitosan is more quick and rapid.6 Ag nanoparticles are formed not only spontaneously generated from Ag+ ions, but also by the reaction between chitosan and silver nitrate during the electrospinning process.5,6,12 PLA/CS containing Ag nanoparticles are also produced by the heat-annealing of e-spun Ag+/PLA/CS blends fibers The reaction between CS and Ag+ contributes to the change in average size and number of Ag nanoparticles on the surface of fibers with and without heat treatment The antibacterial activity of CS incorporating with Ag is higher than that of each component Thus, AgNO3 can be added to a PLA/CS blend to improve the electrospinning ability and antimicrobial activities In the present study, e-spun PLA/CS blend fibers and espun Ag/PLA/CS blend fibers were fabricated by using the electrospinning method Field emission scanning electron microscopy (FE-SEM) was used to study the effects of CS and AgNO3 on the microstructure of the e-spun PLA/CS and Ag/PLA/CS blend fibers The formation and shape of the Ag nanoparticles on the surface of the PLA/CS fiber was observed by transmission electron microscopy (TEM) to examine the influence of the concentration of CS in the blend on the size of Ag particles Differential scanning calorimetry (DSC) was employed to study the thermal properties of the e-spun fibers The mechanical properties of the espun PVA/CS blend fibers were evaluated using a tensile tester Fourier transform infrared (FTIR) spectroscopy was used to investigate the molecular interactions between PLA, silver, and CS in the blends The antibacterial properties of the e-spun PLA/CS and Ag/PLA/CS blend fibers were examined using the optical density method Experimental Materials CS (Mv=693,840; degree of deacetylation= 90%) was obtained from the Bio Materials Co (Korea) 52 PLA (Mv=71,210) was purchased from Acros Organics (USA) The molecular weights of PLA and CS were obtained by using the solution viscosity measurement method The intrinsic viscosities of PLA and CS were measured with an Ubbelohde viscometer at 25 oC in chloroform and 0.1 M HOAc - 0.2 M NaCl, respectively.22-25 Trifluoroacetic acid (TFA) and silver nitrate (AgNO3) were purchased from the Samchun Chemical Co (Korea) Measurement of Viscosity and Ionic Conductivity The ionic conductivities of the PLA/CS blend solutions were determined using a conductivity meter (HI 2300, Hanna instruments, Korea) under an ambient atmosphere The viscosity of each solution was measured using a viscometer (LVDVII, Brookfield USA) The solution was first placed into the viscometer chamber, and then into a water jacket Viscosity measurements were conducted using a #18 cylindrical spindle under an ambient atmosphere Electrospinning PLA and CS were dissolved in TFA at various weight ratios: PLA/CS=100/0, 70/30, 50/50, and 30/70 The total concentration of PLA and CS was 10 wt% Silver nitrate (2 wt%) was added to the PLA/CS blend solution to prepare the Ag/PLA/CS blend by electrospinning Electrospinning of the polymer blend solution was performed at room temperature, with a voltage of 12 kV, and a tip-to-collector distance of 10 cm The spinning rate was approximately 0.3 mL/h Each of the prepared solutions was stored in a standard 5-mL plastic syringe attached to a blunt 20-gauge stainless steel hypodermic needle The flow rate of the polymer solution was controlled by a syringe pump A high supply voltage was connected to the hypodermic needle, which was used as a positive electrode Heat-Annealing The non-woven mats of the PLA/CS blend containing silver nanoparticles were heated in an oven at 100 oC for 15 h Instrumentation The morphology of the non-woven mats was observed by FE-SEM using a HITACHI S-4700 (Japan) with a BAL-TEC MED_020 coating system A Tecnai_G2 TEM with carbon-coated copper grids was used to observe the Ag nanoparticles on the surface of the e-spun fibers The thermal behavior of the non-woven mats of the PLA/ CS blends and Ag/PLA/CS blends was investigated by DSC (TA Instruments, USA) The melting behavior of the nonwoven mats was examined by heating at a rate of 10 oC/min under a nitrogen flow The mechanical properties of the non-woven mats of the PLA/CS blend were determined using a Lloyd testing machine (Lloyd Instruments., UK) The non-woven mats were tested with a 0.1 N preload at a cross-head speed of mm/min The average values from three repetitions were taken as the tensile strength and the elongation at break Antibacterial Assessment The antibacterial properties of the non-woven mats of PLA/CS and Ag/PLA/CS blends were determined against Escherichia coli (E coli) and StaMacromol Res., Vol 20, No 1, 2012 Fabrication of An Antibacterial Non-Woven Mat of a Poly(lactic acid)/Chitosan Blend by Electrospinning phylococcus aureus (S aureus) by using the optical density method Difco Nutrient Broth and Brain Heart Infusion were used as the media for the E coli and S aureus, respectively These media were used as the negative controls A representative bacteria colony (0.1 mL) was cultivated in 9.9 mL of nutrient broth The bacterial solution was used as the positive control The non-woven mats of the PLA/CS and Ag/PLA/CS blends were put into the solution, and then shaken at 37 oC for 8, 16, 24, and 36 h, respectively The weight of the non-woven mats of the PLA/CS or Ag/ PLA/CS blends was 10 mg After incubation, 0.2 mL of the solution was removed and put into 96-well plates The turbidity of the solutions was measured at 600 nm with a UV spectrophotometer (Shimadza UV-vis spectrometer, Japan).26,27 Results and Discussion Viscosity and Ionic Conductivity Measurements The solution viscosity and ionic conductivity of the AgNO3/ PLA/CS blend solutions and PLA/CS blend solutions were measured for various concentrations of CS, as shown in Figure It was found that the viscosity of the polymer solutions increase with an increasing CS content in the blends This occurred because the viscous chitosan solution had a positive effect on the blend viscosity However, the effect of silver nitrate on the viscosity of the polymer solutions was not pronounced (as shown in Figure 1(a)-(b)) Figure 1(c)-(d) show the ionic conductivities of the AgNO3/PLA/CS and PLA/CS blend solutions It was found that the ionic conductivity of PLA/CS blend solutions increased with increasing CS concentration (as shown in Figure Effect of CS concentration on the viscosity of the AgNO3/PLA/CS blend (a), PLA/CS blend (b), on the ionic conductivity of the AgNO3/PLA/CS blend (c), and PLA/CS blend (d) Macromol Res., Vol 20, No 1, 2012 Figure 1(d)) This tendency is attributed to the polycationic nature of CS in the polymer blend solution When CS was dissolved in the TFA solution, the -NH2 of the CS became -NH3+ Therefore, the -NH3+ groups increased with increasing the concentration of CS in the PLA/CS blend solutions The same trend was observed for the case of the Ag+/PLA/ CS blend solutions (as shown in Figure 1(c)) Comparison of the results between line (c) and line (d) in Figure 1, when the concentration of CS was higher than 40 wt%, the ionic conductivities of the AgNO3/PLA/CS blend solutions are lower than those of the PLA/CS blend solution for the same PLA/CS weight ratios in the blend In AgNO3/PLA/CS blend solutions, the amine and hydroxyl groups of chitosan play important role in uptake of silver cations by chelation mechanism.6 This indicates that Ag+ can interact with CS to inhibit the ionizability of the amino group of CS through a chelating mechanism.5,6 Morphology of e-Spun PLA/CS Blend Fibers and eSpun Ag/PLA/CS Blend Fibers Figure shows FE-SEM micrographs of the e-spun PLA fibers and e-spun PLA/CS blend fibers The average diameter of the e-spun PLA/CS blend fibers decreased from 572 to 239 nm with an increase in the content of CS from to 70% in the blends Figure shows that the non-woven mats of the e-spun fibers exhibited an uniform fibrous structure at the PLA/CS weight ratios of 100/0 and 70/30 When the concentration of CS in the blends was increased to a ratio of PLA/CS=50/50, beads were observed in the non-woven mat (as shown in (c) in Figure 2) The e-spun fibers could hardly be formed at all when the CS content in the polymer blend was equal to or higher than PLA/CS=30/70 (as shown in (d) in Figure 2) These behaviors can be explained by supposing that, as the concentration of polycationic CS in the blend increased, the Figure FE-SEM micrographs (average diameter (Dave) and diameter distribution) of e-spun fibers of PLA/CS non-woven mats with different weight ratios of PLA to CS: (a) 100/0, (b) 70/ 30, (c) 50/50, and (d) 30/70 53 H T Au et al Figure FE-SEM micrograph (average diameter (Dave) and diameter distribution) of e-spun fibers of Ag/PLA/CS blend nonwoven mats with different weight ratios of PLA to CS: (a) 100/0, (b) 70/30, (c) 50/50, and (d) 30/70 repulsive force between the ionic groups within the polymer backbone also increased, resulting in no formation of e-spun fibers at higher concentrations of CS in the blend solution As the concentration of CS in the blend solution increased, the average diameter of the e-spun fibers of the PLA/CS blend decreased, and their diameter distribution became slightly narrower Since chitosan is an ionic polyelectrolyte, during electrospinning of the blend sample, a higher charge density on the surface of ejected jet is formed As the charges carried by the jet increase, higher elongation forces are imposed on the jet under the electric field This is because the electric field force is proportional to the charge density on the jet, thus resulting in a decreased fiber diameter with an increase in charge density.11,28 Figure shows FE-SEM micrographs of e-spun PLA fibers containing silver nanoparticles, and e-spun PLA/CS blend fibers containing Ag nanoparticles The average diameters of the e-spun fibers of Ag/PLA/CS were 361, 338, 297, and 195 nm for CS concentrations of 0, 30, 50, and 70% in the blends, respectively Comparison of Figures and shows that the diameters of the e-spun fibers of Ag/PLA/CS of Figure also decreased as the CS content increased For ratios of PLA to CS from 50/50 to 30/70, a good fibrous structure was observed in the e-spun Ag/PLA/CS blend fibers (as shown in (c) and (d) in Figure 3), whereas the espun PLA/CS blend fibers form beads, and are hard to form at the same weight ratios of PLA to CS (as shown in (c) and (d) in Figure 2) This can be explained by considering that the repulsive forces between the ionic groups within the CS backbone were decreased by adding a small amount of salt, as the amine groups of CS interacted with the Ag cations through a chelation mechanism.6 Therefore, the addition a small amount of salt improved the electrospinning ability of 54 Figure TEM micrographs of e-spun fibers of the Ag/PLA/CS blend before heat-annealing with different weight ratios of PLA to CS in the blend solution: (a) PLA/CS=100/0, (b) PLA/CS=70/ 30, (c) PLA/CS=50/50, and (d) PLA/CS=30/70 the PLA/CS blend solutions Figure shows TEM micrographs of the e-spun PLA/CS blend fibers containing silver nanoparticles with different PLA/CS weight ratios before heat-annealing The Ag nanoparticles on the surface of the e-spun fibers are spherical, with diameters of 1.08, 1.69, 3.18, and 9.47 nm for CS contents of 0%, 30%, 50%, and 70% in the blends, respectively A large number of Ag nanoparticles were observed on the surface of the e-spun PLA/CS blend fibers This indicates that Ag nanoparticles were generated during the electrospinning process In effect, Ag nanoparticles could be generated easily and grown on the surface of the metallic part when a metallic needle and an electrode were employed for the electrospinning of polymer blend solutions.21 Ag nanoparticles can be fabricated from Ag+ ions during electrospinning.7,21 The average size of the Ag nanoparticles increased, but their number decreased, with increasing CS concentration in the polymer blend solution An explanation may be that the CS can enclose and combine the Ag nanoparticles through coordination interactions between the amino and hydroxyl groups of CS and the Ag ions.5,6 Ag nanoparticles were also generated spontaneously during the electrospinning process, and their size increased but their number decreased with increasing CS content in the blend solution Figure shows TEM micrographs of the e-spun Ag/PLA/ CS blend with different PLA to CS weight ratios after heatannealing at 100 oC for 15 h Comparing the results of Figures and 4, it is seen that the average size of the Ag nanoparticles on the surface of the e-spun fibers tended to Macromol Res., Vol 20, No 1, 2012 Fabrication of An Antibacterial Non-Woven Mat of a Poly(lactic acid)/Chitosan Blend by Electrospinning Figure TEM micrographs of e-spun fibers of the Ag/PLA/CS blend with different PLA to CS weight ratios after heat-annealing at 100 oC for 15 h: (a) PLA/CS=100/0, (b) PLA/CS=70/30, (c) PLA/CS=50/50, and (d) PLA/CS=30/70 increase, and their number decreased, when the concentration of CS was increased The average diameter of the Ag nanoparticles on the surface of the PLA e-spun fibers increased from 1.08 to 2.74 nm after heat-annealing At the same weight ratios of PLA/CS in the blends, the sizes of the Ag nanoparticles on the surface of the e-spun PLA/CS blend fiber also increased with heat-annealing, but the number of Ag nanoparticles decreased The Ag nanoparticles on the surface of the e-spun fiber were still spherical, and were evenly distributed on the surface of the PLA/CS blend fibers after heat-annealing This can be explained by considering that the Ag+ ions and Ag nanoparticles on the surface of the PLA fibers, which are residual during the electrospinning process, can diffuse and aggregate to form larger Ag nanoparticles during the heat-annealing process.7 In the espun fibers of the Ag/PLA/CS blend, the residual Ag+ ions and Ag nanoparticles not only aggregated during the heatannealing process, but also combined with CS to form larger Ag nanoparticles, thus reducing the number of Ag nanoparticles in the e-spun fibers This indicates that the size of the Ag nanoparticles can be increased by increasing the concentration of CS or by the heat- annealing process DSC Analysis Figure 6(A) and (B) show DSC thermograms of the e-spun PLA/CS blend fibers and e-spun PLA/CS blend fibers containing Ag nanoparticles with different weight ratios of PLA to CS in the blends, respectively PLA and PLA/CS blends show an endothermic curve with peak of melting and slope of glass transition of PLA PLA and PLA with silver nanoparticles have quite similar melting Macromol Res., Vol 20, No 1, 2012 Figure (A) DSC thermograms of: (a) PLA nanofibers, (b) PLA/CS 70/30 nanofibers, (c) PLA/CS 50/50 nanofibers, and (d) PLA/CS 30/70 nanofibers (B) DSC thermograms of: (a) Ag/ PLA nanofibers, (b) Ag/PLA/CS 70/30 nanofibers, (c) Ag/PLA/ CS 50/50 nanofibers, and (d) Ag/PLA/CS 30/70 nanofibers point around 152 oC indicating no difference in thermal properties by the presence of silver nanoparticles in the PLA formed during electrospinning Endothermic curves of the PLA/CS blends and PLA/CS blends containing silver nanoparticles became broader and more obtuse with increasing CS concentration The endothermic heat (Hm) in the thermogram curves of the PLA/CS blend decreased with the inclusion of CS in the blends CS is amorphous polymer and interferes the formation of crystal structure of PLA in the PLA/CS blend Multi peaks in the endothermic curve of PLA/CS blends in Figure 6(A) and (B) were observed indicating different crystalline structures of PLA in the PLA/CS blends, which were formed during electrospinning The presence of rigid CS in the PLA/CS blends may affect the formation of crystalline structure of PLA in the process of nucleation and crystallization Amorphous CS also retards the rate of crystallization and makes imperfect crystal structure of PLA.2,29 Figure 6(A) shows that the slope of endothermic curves of PLA around 59 oC indicating Tg of PLA increased with content of CS in the PLA/CS blends CS is known to have very rigid structure with glass transition temperature (Tg) of 203 oC.29 This indicates there is some partial miscibility between PLA and CS in the PLA/ 55 H T Au et al Figure FTIR spectra of non-woven mats of e-spun fibers of PLA/CS blends for different weight ratios of PLA to CS: (a) PLA/CS=100/0, (b) PLA/CS=70/30, (c) PLA/CS=50/50, (d) PLA/CS=30/70, and (e) CS CS blends.30,31 Tg of blend nanofibers of PLA/CS of 30/70 was not observed in Figure 6(A) showing no crystal of PLA was formed in the PLA/CS blend fibers Figure 6(B) shows that Tg of the PLA nanofibers containing silver nanoparticles has a slight higher value than that of PLA nanofibers The presence of silver nanoparticles in PLA nanofibers might influence the mobility of PLA main chains lowering the Tg of PLA Tgs of PLA/CS blends containing silver were not observed in Figure 6(B) This is attributed to the combined effect of silver nanoparticles and rigid CS in the PLA/CS blends FTIR Spectra Figure shows the FTIR spectra of nonwoven mats of the e-spun fibers of PLA/CS blends with different weight ratios of PLA to CS It is found that the e-spun fibers of CS present strong bands at 1673 and 1532 cm-1, which are characteristic of the amide I and II absorption bands, respectively In addition, the weak peak at 1376 cm-1 is the characteristic of the amide III band of the CS vibration (see line (e) in Figure 7) The FTIR spectrum of PLA (see line (a) in Figure 7) displays characteristic absorption bands at 1755, 1188, and 1089 cm-1, which are attributed to the backbone ester group of PLA.1 As seen in lines (b), (c), and (d) in Figure 7, the relative strength of the peak at 1755 cm-1, which is attributed to the carbonyl group of PLA, decreased with increasing CS content in the PLA/CS blends, whereas the relative strength of the peak at 1673 cm-1, which is identified as the absorption of the amide I of CS, increased This behavior could be rationalized by the fact that PLA does not have enough -OH groups to form hydrogen bonds with the -OH and -NH2 groups of CS Therefore, the specific interaction between CS and PLA is weak.1,14 Figure presents the FTIR spectra for non-woven mats of the e-spun fibers of PLA/CS blends with and without silver 56 Figure FTIR spectra of non-woven mats of PLA/CS blends with and without silver; (a) PLA, (b) Ag/PLA, (c) PLA/CS (50/ 50), (d) Ag/PLA/CS (50/50), and (e) CS nanoparticles Comparing the results of e-spun Ag/PLA/CS blend and e-spun PLA/CS blend fibers, it is found that the amide I and II bending vibration bands at about 1673 and 1532 cm-1 of Ag/PLA/CS blend decreased significantly in intensity (see lines (c) and (d) in Figure 8) There was no difference in the FTIR result between the PLA and Ag/PLA blends The difference in the FTIR spectra between PLA/ CS and Ag/PLA/CS blends is attributed to the attachment of silver to the nitrogen atoms, which reduces the vibration intensity of the N-H bond.5 Tensile Tests The mechanical properties of the polymer blends depend on many factors, including the structure of the blends and the interactions between each polymer component in the blends.12,14 The mechanical strengths of nonwoven mats of the e-spun fibers of PLA/CS blends are shown in Figure CS is known to be a very brittle and rigid natural polymer, whereas PLA is a tough natural polymer Figure shows that, for the non-woven mats of e-spun fibers of the PLA/CS blend with the weight ratio 90/10, the tensile strength at break is higher than that of PLA, whereas the elongation at break is lower With the increase of rigid CS content in the blends, the tensile strength at break increased, whereas the elongation at break decreased, as seen in lines (b), (c), and (d) in Figure This indicates that the combination of mechanically strong PLA and weak CS increases the possibility e-spun PLA/CS blends being used in various applications Antibacterial Test Figure 10(A) and (B) show the result of the optical density (OD) versus culture time for the nonwoven mats of e-spun fibers of PLA/CS and Ag/PLA/CS blends against E coli and S aureus, respectively The bacterial cell was opaque, and as the bacteria propagated the bacterial solutions became turbid Hence, the antibacterial activity of the non-woven mats of the e-spun fibers could be Macromol Res., Vol 20, No 1, 2012 Fabrication of An Antibacterial Non-Woven Mat of a Poly(lactic acid)/Chitosan Blend by Electrospinning OD of the Ag/PLA/CS blend is much lower than that of the PLA/CS blend for both E coli and S aureus The OD of the Ag/PLA/CS non-woven mats is lower than that of the Ag/ PLA non-woven mat This indicates that the antibacterial activity of CS incorporating Ag (silver ions or nanoparticles) is higher than that of each of the components Thus, the presence of Ag nanoparticles in the e-spun fibers of the PLA/CS blend can significantly increase the antibacterial activity Conclusions Figure Stress-strain curves of non-woven mats of the e-spun fibers of PLA/CS blends with different PLA/CS weight ratios: (a) 100/0, (b) 90/10, (c) 80/20, and (d) 70/30 The non-woven mats of the e-spun fibers were tested with a 0.1-N preload at a crosshead speed of mm/min Figure 10 OD versus culture time for the (a) medium, (b) PLA, (c) PLA/CS 70/30 non-woven mat, and (d-g) Ag/PLA/CS blend non-woven mat with different weight ratios of PLA/CS against E coli (A) and S aureus (B) (The weight ratios of PLA to CS in (d)-(g) are 100/0, 70/30, 50/50, and 30/70, respectively) measured using optical density as the criterion The higher the antibacterial activity of the non-woven mats, the smaller the OD of the solutions.26,27,32 As observed from Figure 10(A) and (B), the OD of the PLA/CS (70/30) is much lower than that of the PLA non-woven mat In the non-woven mats of the e-spun fibers of the Ag/PLA/CS blend, the OD decreased with increasing CS content for both bacteria E coli and S aureus In other words, the antibacterial activity of the blend non-woven mats was enhanced when the CS concentration was increased, thus demonstrating the antibacterial activity of the CS in the blends to both: E coli and S aureus Comparison of the OD results for the PLA/CS and Ag/PLA/CS blends at weight ratios of PLA/CS of 70/30 shows that the Macromol Res., Vol 20, No 1, 2012 Non-woven mats of e-spun fibers of PLA/CS blends and PLA/CS blends containing Ag nanoparticles were fabricated by using the electrospinning method PLA and AgNO3 can improve the electrospinnability of the CS The mechanical properties of CS and its suitability for electrospinning can be improved by blending it with PLA and AgNO3 The results of FTIR indicated that the molecular interaction between CS and PLA is not strong and silver is attached to the nitrogen atoms of CS Ag nanoparticles were spontaneously generated in the PLA/CS blends during the electrospinning process When the CS content was increased and heat-annealing of the blends was carried out, the size of the Ag nanoparticles increased, while the number of particles decreased It was found that in Ag/PLA/CS blend, the size of Ag nanoparticles was controlled not only by the content of CS but also by heat-annealing The CS in the PLA/CS blend exhibited a good antibacterial activity against the gram-negative bacteria E coli 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Fabrication of An Antibacterial Non-Woven Mat of a Poly(lactic acid)/ Chitosan Blend by Electrospinning OD of the Ag/PLA/CS blend is much lower than that of the PLA/CS blend for both E coli and S aureus... mats of PLA/CS and Ag/PLA/CS blends were determined against Escherichia coli (E coli) and StaMacromol Res., Vol 20, No 1, 2012 Fabrication of An Antibacterial Non-Woven Mat of a Poly(lactic acid)/ Chitosan. .. 2012 Fabrication of An Antibacterial Non-Woven Mat of a Poly(lactic acid)/ Chitosan Blend by Electrospinning Figure TEM micrographs of e-spun fibers of the Ag/PLA/CS blend with different PLA to