Hindawi Publishing Corporation International Journal of Carbohydrate Chemistry Volume 2013, Article ID 539636, 10 pages http://dx.doi.org/10.1155/2013/539636

Research Article A Green Approach to Synthesize Silver in Starch-co-Poly(acrylamide) Hydrogels by Tridax procumbens Leaf Extract and Their Antibacterial Activity

Siraj Shaik,1 Madhusudana Rao Kummara,2 Sudhakar Poluru,1 Chandrababu Allu,1 Jaffer Mohiddin Gooty,3 Chowdoji Rao Kashayi,4 and Marata Chinna Subbarao Subha1

1 Department of Chemistry, Sri Krishnadevaraya University, Anantapur, Andhra Pradesh 515 003, India 2 DepartmentofPolymerScienceandEngineering,PusanNationalUniversity,Busan609-735,RepublicofKorea 3 DepartmentofMicrobiology,SriKrishnadevarayaUniversity,Anantapur,AndhraPradesh515003,India 4 Department of Polymer Science & Tech, Sri Krishnadevaraya University, Anantapur, Andhra Pradesh 515 003, India

Correspondence should be addressed to Marata Chinna Subbarao Subha; [email protected]

Received 31 August 2013; Accepted 13 November 2013

Academic Editor: Roland J. Pieters

Copyright © 2013 Siraj Shaik et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

A series of starch-co-poly(acrylamide) (starch-co-PAAm) hydrogels were synthesized by employing free radical redox poly- + merization. A novel green approach, Tridax procumbens (TD) leaf extract, was used for reduction of silver ions (Ag )into silver nanoparticles in the starch-co-PAAm hydrogel network. The formation of silver nanoparticles was confirmed byUV- visible spectroscopy (UV-Vis), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (X-RD) studies. 22% of weight loss difference between hydrogel and silver hydrogel (SNCH) clearly indicates the formation of silver nanoparticles by TGA. TEM images indicate the successful incorporation of silver nanoparticles ranging from 5 to 10 nm in size and spherical in shape with a narrow size distribution. These developed SNCHs were used to study the antibacterial activity by inhibition zone method against gram-positive and gram-negative bacteria such as Bacillus and Escherichia coli. The results indicated that these SNCHs can be used potentially for biomedical applications.

1. Introduction forces that do not prevent the penetration of water through the network [5]. Based on these properties the hydrogels have Hydrogels have three-dimensional polymeric networks that been used recently as templates for production of metallic are fabricated from polymers stabilized through physical or nanoparticles. Hence the design and development of metal chemical crosslinking. They absorb large quantities of water nanoparticles dispersed in polymer matrix have attracted without losing their structural integrity [1]. Since they mimic potential applications in various fields like electrical, optical, body tissues and respond to external stimuli, they are made or mechanical properties [6, 7] making them valuable for important and promising forms of biomaterials for various applications in areas like optics [8], photo imaging and applications including tissue engineering, controlled drug patterning [9], electronic devices [10], sensors and biosensors release devices, biosensors, and mechanical actuators [2– [11–13], catalysis [14, 15], and antibacterial and antimicrobial 4]. Due to the presence of water solubilizing groups, such coatings [16]. Silver nanoparticles (Ag NPs) have attracted as –OH, –COOH, –CONH2,–CONH–,and–SO3H, these considerable interest in biological studies because of their hydrogels show higher hydrophilicity. The three-dimensional ease of preparation, good biocompatibility, and relatively network of hydrogel provides relative stability to its structure. large surface area [17, 18]. Ag NPs have many important appli- Their swollen state results from a balance between the cations in biomedical fields, sensors, and filters [19]. Addi- dispersing forces acting on hydrated chains and cohesive tionally, silver is a potential antibacterial agent [20]andis 2 International Journal of Carbohydrate Chemistry thus used as a sterilizer for removing bacteria from drinking The developed SNCHs may be biodegradable and nontoxic water [21, 22]. For economic and efficient use of silver, silver andwerepotentialmaterialstobeusedforbiomedical composites have been developed and tested for applications. antimicrobial activity. Starch is one of the natural, renewable, and biodegradable 2. Experimental polymers produced by many plants as a source of stored energy. Starch consists of two types of molecules: amylose 2.1. Materials. AR grade soluble starch (potato), silver nitrate (normally 20–30%) and amylopectin (normally 70–80%). (AgNO3), potassium persulfate (KPS), maleic acid (MA), and The relative proportion of amylose to amylopectin depends sodium hydroxide (NaOH) were purchased from SD Fine 1 onthesourceofstarch.Itisversatileandcheapandhas Chemicals,Mumbai,India.Acrylamide(AAm),𝑁,𝑁 -meth- 1 11 many uses as thickener, water binder, emulsion stabilizer, and ylenebisacrylamide (MBA), and 𝑁,𝑁,𝑁 ,𝑁 -tetramethyl- gelling agent [23]. Starch granules are insoluble in cold water ethylenediamine (TEMED) were purchased from Aldrich but imbibe water reversibly and swell slightly [24]. Maleic Chemical Company Inc. (Milwaukee, WI, USA). All chem- acid (MA) is a nontoxic and biodegradable hydrophilic icals were used without further purification. Double-distilled substance which is used as a type of food additive in (DD) water is used throughout the experiment. processing industry. The modification of starch with MA increases its hydrophilicity by converting it into ester form by the reaction between starch and MA to form starch macro- 2.2. Preparation of Tridax procumbens (TD) Leaf Extract. monomer [25]. The chemical modification of starch with MA Leaf extracts were prepared by a green process technique, and tartaric acid improves its properties without sacrificing using the standard procedure described by Prasad et al. [39]. its biodegradability and biocompatibility [25–27]. Several Tridax procumbens leaves were collected from Tridax pro- reports are present on acrylamide (AAm) hydrogels that were cumbens plants at our university campus in Sri Krishnade- developed because of their hydrophilic and inert nature that varaya University (Anantapur, Andhra Pradesh, India), thor- makes them suitable for applications in medicine and phar- oughly washed with DD water to remove the dust particles, macy [28, 29].Polyacrylamidehasbeenusedincontactlenses and then dried in sun to remove the residual moisture. From for a long time, and it has well been evaluated as a sustained- this 20 g leaves were chopped finely and boiled in a 250 mL release wound-dressing material [30]. glass beaker along with 200 mL of sterile DD water for 10 min In continuation of our work [31]onusageofpoly- in order to extract the contents of the leaves. After boiling the mers in biomedical applications, the present research paper colour, the aqueous solution changed from watery to yellow explores a simple and facile method to synthesize starch- colour. The aqueous extract was separated by filtration with co-poly(acrylamide) (starch-co-PAAm) hydrogels and silver 2.5 𝜇m Whatman filter paper (Sigma-Aldrich, USA) and then nanocomposite hydrogels (SNCHs) by using a green process stored at room temperature. + in which the Ag ions are successfully reduced by Tridax procumbens (TD) leaf extract. Starch, MA, and AAm were 2.3. Synthesis of Starch-co-PAAm Hydrogels and Their Sil- chosen on the basis of their significant characteristics in ver Nanocomposite Hydrogels (SNCHs). Gelatinized starch biomedical fields. The most popular way used for the direct solution was prepared by mixing a quantitative amount of synthesis of metal ions into nanoparticles is through chemical starch powder in 10.0 mL of DD water and 1.0 mL of 0.5 M reductionmethodbyusingseveralreagentssuchassodium sodium hydroxide (NaOH) solution, and the mixture was ∘ borohydride, sodium hypophosphite, and sodium citrate. heated in a water bath at 90 Cfor10minwithcontinuous Several reports are presented for the development of Ag NPs magnetic stirring. A predetermined amount of MA was then by using such reducing agents [32, 33]. But these reducing added to the gelatinized starch solution and the resulting agents may have environmental problems due to their tox- ∘ mixturewasfurtherheatedinawaterbathat80Cfor4h icity, so a considerable interest to use nontoxic materials for [25]. Subsequently, a quantitative amount of acrylamide was reduction of Ag NPs is growing rapidly these days. In order to ∘ added and stirred for half an hour at 50 C, after that cross- avoid such type of toxic reagents, recently plant extracts have beenusedforproductionofAgNPsduetotheircost-effective linker (MBA) and initiator (KPS) were added according to the nature and also ambient conditions for reduction [34–37]. formulations mentioned in the Table 1.Finally,anaqueous Therefore, the development of metal nanoparticles based on solution of TEMED was added to the solution and the same natural extracts is considered the most appropriate method. temperature was maintained for another 10 min. After Recently Tridax procumbens (TD) leaf extract was used as completion of free radical polymerization, the synthesized reducing agent for preparation of Ag NPs by direct synthe- copolymeric hydrogel was taken out and immersed in sis. TD contains several flavonoids, alkyl esters, terpenes, double-distilledwateratroomtemperaturefor24htoremove sterols, fatty acids, and polysaccharides. Due to the presence the excess of unreacted monomers and reagents present in of these constituents, TD has several potential therapeutic the hydrogel network. During this period, DD water was activities like antiviral, antioxidant, and antibiotic efficacies; refreshed for every 12 h in order to leach out the residue wound-healing activity; insecticidal and anti-inflammatory effectively. Finally, the hydrogel was dried at ambient temper- activity [38].Nowwehaveusedthisextractforproduction ature for 48 h. Similarly, other hydrogels were prepared by the of Ag NPs in starch-co-PAAm hydrogel networks due to above procedure according to their feed compositions as per its natural reduction property and high biological activity. Table 1. International Journal of Carbohydrate Chemistry 3

Table 1: Various formulation parameters used in the preparation of starch-co-PAA hydrogels.

Chemicals used Hydrogel code Starch (g) Maleic acid (mM) Acrylamide (mM) MBA (mM) KPS (mM) TMEDA (mM) Starch-co-PAAm-1 0.50 14.91 14.06 0.648 1.849 0.860 Starch-co-PAAm-2 1.00 14.91 14.06 0.648 1.849 0.860 Starch-co-PAAm-3 1.50 14.91 14.06 0.648 1.849 0.860 Starch-co-PAAm-4 0.50 7.03 14.06 0.648 1.849 0.860 Starch-co-PAAm-5 0.50 21.10 14.06 0.648 1.849 0.860 Starch-co-PAAm-6 0.50 14.91 7.03 0.648 1.849 0.860 Starch-co-PAAm-7 0.50 14.91 21.10 0.648 1.849 0.860 Starch-co-PAAm-8 0.50 14.91 14.06 0.129 1.849 0.860 Starch-co-PAAm-9 0.50 14.91 14.06 0.324 1.849 0.860

O

Δ Starch-OH + maleic acid Starch OH

Acrylamide, KPS, BIS, TEMED

+ Ag Starch-co-poly(acrylamide) hydrogel TD extract

Silver nanocomposite hydrogel

Scheme 1: Formation of starch-co-poly(acrylamide) hydrogels and their silver nanocomposite hydrogels by green method.

Accurately weighed dried starch-co-PAAm hydrogels 2.5. Characterization Methods. Fourier transform infrared were equilibrated with DD water for 48 h and immediately (FT-IR) spectra of hydrogel and SNCH are recorded on Per- transferred to a beaker containing 100 mL of 5 mM AgNO3 kin Elmer (model impact 410, Wisconsin, MI, USA) spec- aqueous solution and then allowed to equilibrate for 24 h. trophotometer. The samples were crushed with potassium + During this process, most of the silver ions (Ag )were bromide (KBr) to make pellets under hydraulic pressure of −1 exchanged from solution into free network spaces of copoly- 600 kg and scanned between 4000 and 400 cm .UV-visible + meric hydrogel. The hydrogel with absorbed Ag ions was (UV-Vis) spectra of starch-co-PAAm hydrogel and SNCHs finally transferred to a beaker containing 50 mL Tridax were recorded using UV-Vis spectrophotometer (Perkin procumbens leaf extract aqueous solution and kept for 24 h for Elmer).Forthis,thegrindedsamples(10mg/mL)werestored + 0 reduction of Ag ions into silver nanoparticles (Ag ). After for 10 days to leach out Ag NPs into water (media) and then + reduction of Ag ions, the hydrogel was turned into brown the measurements were carried out. X-ray diffraction (X-RD) 0 measurements were carried out using Rikagu diffractometer colour, which confirms the formation of Ag nanoparticles in 𝜆 = 0.1546 hydrogel matrix [31, 33]. The above procedure was adopted for (Cu radiation, nm) running at 40 kV and 40 mA. all other remaining hydrogels to convert them into SNCHs. TGA curves of hydrogel and SNCH are recorded using TA instrument’s sequential thermal analyser (Model-SDT Q600, The formation of hydrogels and silver nanocomposite hydro- USA). The samples were heated from room temperature to is shown in Scheme 1. ∘ ∘ 700 C at a heating rate of 10 C per min. Scanning electron microscopy (SEM) images were taken with a high resolution 2.4. Swelling Studies. Fully dried copolymeric hydrogels were ∘ SEM instrument (MIRA LMH, H.S.) at an accelerating volt- weighed and equilibrated in DD water at 37 Cforthreedays. age of 15 kV.SEM specimens were prepared by the dry hydro- The equilibrium swelling capacity (𝑄)ofthehydrogelwas and SNCHs, coated with a thin layer of palladium and gold calculated by the following equation: alloy, and then studied for morphological variations. The size 0 and shape of Ag nanoparticles were investigated by trans- 𝑊𝑠 2 𝑄= , (1) mission electron microscopy (TEM) (FEI Tecnai G S-Twin 𝑊𝑑 200 kV) at an acceleration voltage of 15 kV. For TEM mea- surements, the samples were prepared by dropping 5–10 𝜇Lof where 𝑊𝑠 and 𝑊𝑑 are the weight of swollen hydrogel and finely grinded SNCH dispersion on a carbon-coated copper weight of the dry hydrogel, respectively. The data provided grid and dried at room temperature after removing excess is an average value of 3 individual sample readings. moisture using filter paper. 4 International Journal of Carbohydrate Chemistry

140 100

120 80 100

80 60

60 40 Swelling (g/g) Swelling Swelling (g/g) Swelling 40 20 20

0 0 Starch-co-PAAm-1 Starch-co-PAAm-2 Starch-co-PAAm-3 Starch-co-PAAm-4 Starch-co-PAAm-5 Starch variation Maleic acid variation (a) (b) 100 100

80 80

60 60

40 40 Swelling (g/g) Swelling Swelling (g/g) Swelling

20 20

0 0 Starch-co-PAAm-6 Starch-co-PAAm-7 Starch-co-PAAm-8 Starch-co-PAAm-9 Acrylamide variation MBA variation Starch-co-PAAm hydrogel Starch-co-PAAm hydrogel SNCH SNCH (c) (d)

Figure 1: Swelling behaviour of starch-co-PAAm pure hydrogels and silver nanocomposite hydrogels of various formulations.

2.6. Antibacterial Activity of Silver Nanocomposite Hydrogels. 3. Results and Discussion Antimicrobial activity studies of starch-co-PAAm hydrogel and its SNCHs were carried out by disc diffusion method40 [ , 3.1. Swelling Studies. Water uptake by hydrogels was mon- 41] on bacterial strains, namely, Escherichia coli and Bacillus. itored for an extended period of time till equilibrium was achieved. Swelling characteristics of starch-co-PAAm hydro- Nutrient agar medium was prepared by mixing peptone ∘ (5.0 g), beef extract (3.0 g), and sodium chloride (NaCl) gels and SNCH systems at 37 C were determined using (1) (5.0 g) in 1,000 mL distilled water and the pH was adjusted andareplottedasafunctionofcompositioninFigure 1.The to 7.0. Finally, agar (15.0 g) was added to this solution and this hydrogels swelled rapidly in water and attained equilibrium medium was sterilized in an autoclave at a pressure of 15 lbs within 12 h. Figure 1 shows the influence of various amounts ∘ for 30 min at 121 C.Thismediumwastransferredintosteril- of starch, MA, acrylamide, and MBA on swelling characteris- ized Petri dishes in a laminar air flow chamber. After solid- tics of the copolymeric hydrogels and their SNCHs. The order ification of the media, Escherichia coli and Bacillus culture of swelling capacity values of starch-co-PAAm hydrogels and 𝜇 SNCHsiscopolymericSNCHs> pure hydrogels. This pattern (50 L) was spread on the solid surface of the media. Paper + discs (6 mm diameter) were soaked inside the test com- of swelling is reasonable because once the Ag ions loaded pounds (20 mg/20 mL) overnight before loading them on hydrogels were treated with TD leaf extract, the reduction ∘ + 0 culture plates. The plates were incubated at 37 Cfor24h.The of Ag ions into Ag nanoparticles takes place which may inhibition zone appeared around the disc was measured and enhance the overall porosity of the gel and hence promote recorded as the antibacterial effect of Ag NPs. higher water molecules uptake capacity. The other reason can International Journal of Carbohydrate Chemistry 5

70 1.4 (f) 1.2 60 (e)

50 1

0.8 40 (d) 0.6 30 (b) Transmittance (%) Transmittance Absorbance (a.u.) Absorbance (a) (a) 0.4 (c) 20 (b) 0.2 10 4000 3500 3000 2500 2000 1500 1000 500 −1 0 Wavenumber (cm ) 250 300 350 400 450 500 550 600 Pure hydrogel (a) Wavelength (nm) SNCH (b) Starch-co-PAAm hydrogel (a) SNCH-3 (d) SNCH-5 (e) Figure 2: FTIR spectra of pure starch-co-PAAm hydrogel (a) and SNCH-8 (b) SNCH-9 (f) SNCH (b). SNCH-6 (c) Figure 3: UV-Vis spectra of (a) starch-co-PAAm hydrogel, (b) SNCH-8, (c) SNCH-6, (d) SNCH-3, (e) SNCH-5, and (f) SNCH- be that the particles have different sizes and different surface 9. charges in the gel networks that cause absolute expansion of the network. 350 It is observed from Figures 1(a), 1(b),and1(c) as the amount of starch, MA, and AAm increases, the swelling of 300 hydrogels increased. This is due to the increase in hydrophilic 250 groups (–OH, –COOH, –CONH2) and increase in hydro- (111) dynamicfreevolumetoaccommodatemoreofthesolvent 200 molecules. As the amount of MBA increased (Figure 1(d))the (b) swelling has been decreased due to the high crosslinking den- 150 sity, which tightens the polymeric chains thereby making the (200)

hydrogels rigid. (counts) Intensity 100 (a) (220) (311) 3.2. FT-IR Spectral Studies. In Figure 2,theIRspectrumof 50 starch-co-PAAm hydrogel shows the characteristic absorp- −1 tion peaks at 1118 cm andtheabsorptionbandsintherange 0 −1 of 2900–3400 cm which are attributed to –C–O and –OH 0 102030405060708090 𝜃 stretching vibrations of starch, respectively. The characteristic Diffraction angle (2 ) −1 absorption peak at 1680 cm results from –C=O stretching Starch-co-PAAm hydrogel (a) vibration of the –CONH2 group,andabroadabsorptionband SNCH (b) −1 at 3219 cm isrelatedtothe–NHasymmetricand–OH −1 Figure 4: X-RD pattern of starch-co-PAAm hydrogel (a) and its symmetric stretching vibrational group; band at 2812 cm is SNCH (b). attributed to stretching vibrations of –CH3 units. The absorp- −1 tion band at 1710 cm is due to asymmetrical stretching for –COOH group of maleic acid. The substitution of MA was + −1 in our current strategy because the Ag -loaded starch-co- alsoconfirmedbytheabsorptionbandobservedat1230cm PAAm hydrogel was readily reduced by TD leaf extract, which indicates the –C–O–O-stretching vibrations of ester. −1 −1 −1 which immediately turned into brown colour. This change in These peaks have shifted to 1110 cm ,1214cm ,1669cm , 0 −1 −1 0 colour shows that the Ag nanoparticles are entrapped inside and 2804 cm ,and3202cm in SNCH indicates that Ag the networks through strong localization and stabilization 0 nanoparticles are successfully incorporated in SNCH matri- established by the polymer matrix. The existence of Ag ces. nanoparticlesinthegelnetworkswasestimatedbyUV-visible spectroscopy analysis. Figure 3 illustrates the absorption 0 3.3. UV-Visible Spectroscopy. The formation of Ag nanopar- peaks of SNCHs in 325–500 nm ranges that are assigned to Ag ticles in the copolymeric hydrogel networks can be expected NPswhicharosefromthesurfaceplasmonresonance(SPR). 6 International Journal of Carbohydrate Chemistry

(a) (b)

Figure 5: Scanning electron microscopy images of (a) starch-co-PAAm hydrogel and (b) SNCH.

(a) (b) 50

40

30

20

Distribution (%) Distribution 10

0 024681012 diameter (nm) (c) (d)

(e)

Figure 6: Transmission electron microscopy images of SNCHs ((a), (b), and (c)), size distribution curve, (d) and electron diffraction pattern 0 of Ag nanoparticles (e).

A significant improvement in the absorption peak at 420 nm the formation of nanoparticles and their size depends on 0 was observed for Ag -loaded hydrogels due to the surface the network structure of hydrogels and their functionality. plasmon resonance band [42]. The UV-visible absorption This absorption peak was not observed in the case of starch- band is not symmetrical for all the formulations, because co-PAAm hydrogel. No additional absorption peaks around International Journal of Carbohydrate Chemistry 7

Table 2: Antibacterial activities of the synthesized hydrogels on gram-positive and gram-negative organisms.

Name of the bacteria Inhibition zone in diameter (mm) for silver nanocomposite hydrogels (pathogens) Pure Starch-co- Starch-co- Starch-co- Starch-co- Starch-co- hydrogel (c) PAAm-3 PAAm-4 PAAm-5 PAAm-8 PAAm-9 E. coli 0 4.5 3.0 4.0 3.5 2.5 Bacillus 0 5.0 3.5 4.5 4.0 3.5

120 shows the SEM micrographs of the starch-co-PAAm and SNCHs. Figure 5(a) shows a clear surface feature for the pure hydrogel, whereas Ag NPs-loaded starch-co-PAAm hydro- 100 gel (Figure 5(b)) exhibits smaller nanoparticles distributed throughout the hydrogel networks. It is worth mentioning 80 that no individual silver particles were observed outside the SNCH, indicating a strong interaction between the polymer matrix and the silver particles. 60

(b) 3.6. TEM Studies. Shape and size distribution of the synthe- Weight loss (%) Weight 40 sized Ag NPs were characterized by transmission electron microscopic (TEM) analysis. Figures 6(a) and 6(b) are the low (a) magnification images and Figure 6(c) is the high magnifica- 20 tion image obtained by transmission electron microscopy at an acceleration voltage of 15 kV. These images indicate that 0 the particles are well defined, spherical in shape with a nar- 0 100 200 300 400 500 600 700 row size distribution, and highly dispersed with an average ∘ Temperature ( C) diameter of 7 nm in size (Figure 6(d)). Moreover, the electron 0 Starch-co-PAAm hydrogel (a) diffraction pattern of Ag nanoparticles is clearly visible in SNCH (b) Figure 6(e) as three diffraction rings and from that pattern it is evident that the nanoparticles are crystalline and have a Figure 7: Thermogravimetrical analysis of (a) pure starch-co- face centered cubic (FCC) structure. PAAm hydrogel and (b) SNCH.

3.7. Thermogravimetrical Analysis. The starch-co-PAAm hydrogel and its SNCHs are characterized by thermogravi- 325–500 nm indicates that SNCH network is protecting the metrical analysis to determine the percentage of weight loss nanoparticles from the aggregation or cluster formation. This 0 0 of pure hydrogel as well as Ag nanoparticles loaded hydrogel, analysis confirms the formation of highly dispersed Ag as shown in Figure 7. The starch-co-PAAm hydrogel has nanoparticles in the copolymeric hydrogels. ∘ followed two decomposition steps below 400 Cand82% ∘ weight loss occurred below 700 C. However, two decom- 3.4. X-Ray Diffraction. The crystallinity of the hydrogel and position states and only 60% weight loss were observed in the ∘ SNCH was confirmed by the analysis of X-ray diffraction (X- case of SNCH below 700 C. The difference in decomposition RD) pattern (Figure 4). The dry powders of hydrogel and between the hydrogel and SNCH is found to be 22%, and SNCH were used for X-RD analysis. In the diffractogram, 0 it confirms the presence of Ag nanoparticles in the SNCH four diffraction peaks were obtained at an angle, 2𝜃 = 38.39, network. From these results it is concluded that SNCH 49.25, 64.10, and 77.87 which could be attributed to the Brags showed a higher thermal stability when compared with the reflections of (111), (200), (220), and (311) planes of face centred cubic (FCC) structure of Ag NPs. A broad diffraction starch-co-PAAm hydrogel due to the undecomposed remain- ∘ 0 peak 2𝜃 in both samples can be seen at 20 due to the ing weight of Ag nanoparticles present in the copolymeric amorphous nature of starch-co-PAAm hydrogel and SNCH. networks. The (200), (220), and (311) peaks were less intense compared to (111) peak. So, in this case, we might conclude that the 3.8. Antibacterial Studies. The antimicrobial activity of dif- nanoassemblies were mainly composed of (111) lattice planes. ferent molar weight ratios of SNCHs was examined against Similar type of observations was found previously in reported gram-negative and gram-positive bacteria. All SNCHs work [31, 33]. proved effective against the tested microorganisms Escheri- chia coli and Bacillus, but growth inhibitory effects varied 3.5. SEM Studies. The morphology of starch-co-PAAm from one another as shown in Figures 8(a) and 8(b).The hydrogel and SNCH was investigated with SEM. Figure 5 results indicate that starch-co-PAAm-3, starch-co-PAAm-4, 8 International Journal of Carbohydrate Chemistry

(a) (b)

Figure 8: Antibacterial activity of the SNCHs against (a) E. coli and (b) Bacillus. starch-co-PAAm-5, starch-co-PAAm-8, and starch-co- Acknowledgments PAAm-9 SNCHs exhibited greater reduction of Escherichia coli and Bacillus growth, while the pure hydrogels (c) were The authors thank University Grants Commission (UGC), generally inefficient as shown in Table 2.Theinhibitionzone New Delhi (India), for providing financial support to one follows the order starch-co-PAAm-3 > starch-co-PAAm-5 > of the authors (Siraj Shaik) under UGC-RFSMS (Letter no. starch-co-PAAm-8 > starch-co-PAAm-4 > starch-co-PAAm- F.7-290/2009 (BSR)/10-01/2009). The authors are thankful to 0 9. These results are expected due to the small sizes of Ag Professor T. P. Radhakrishnan, School of Chemistry, Univer- nanoparticles and the same order is expected for swelling sity of Hyderabad, Hyderabad, Andhra Pradesh, for helping ratio. Ag NPs adhered to the cell wall of bacteria and them in obtaining TEM images. penetrated through the cell membrane; they kill microorgan- isms instantly by blocking their respiratory enzyme systems References andhavingnonegativeeffectonhumancells. [1] K. Y. Lee and D. J. Mooney, “Hydrogels for tissue engineering,” Chemical Reviews,vol.101,no.7,pp.1869–1879,2001. 4. Conclusions [2] N. A. Peppas, P. Bures, W. Leobandung, and H. Ichikawa, “Hydrogels in pharmaceutical formulations,” European Journal In conclusion, we have demonstrated a facile and simple of Pharmaceutics and Biopharmaceutics,vol.50,no.1,pp.27–46, green methodology for preparation of starch-co-PAAm silver 2000. nanocomposite hydrogels by free radical polymerization and + 0 [3] J. Kim, I. S. Kim, T. H. Cho et al., “Bone regeneration thereby reducing Ag into Ag nanoparticles using Tridax using hyaluronic acid-based hydrogel with bone morphogenic procumbens leafextract.Themainaimofthisstudywasto protein-2 and human mesenchymal stem cells,” Biomaterials, develop a new antimicrobial/wound-dressing agent. These vol.28,no.10,pp.1830–1837,2007. antimicrobial agents are nontoxic materials which can be [4]N.A.Peppas,J.Z.Hilt,A.Khademhosseini,andR.Langer, used systemically as an alternative to conventional systemic “Hydrogels in biology and medicine: from molecular principles antibiotic, antiviral, and antifungal therapies that do not incur to bionanotechnology,” Advanced Materials,vol.18,no.11,pp. the development of resistance by the target pathogens. The 1345–1360, 2006. synthesis method adopted here is very simple and can be [5]H.F.Mark,N.M.Bikals,C.G.Overberger,andJ.I.Kroschwitz, easily implemented for any kind of scientific as well as indus- Encyclopedia of Polymer Science and Engineering,Wiley-Inter- trial application due to its cost-effective nature. A number of 0 science, New York, NY, USA, 1986. SNCHs were formulated with high dispersion rates of Ag [6] Y. Xia, P. Yang, Y. Sun et al., “One-dimensional nanostructures: nanoparticles throughout the hydrogel networks by varying synthesis, characterization, and applications,” Advanced Mate- the concentrations of carbohydrate polymer, monomers, and rials,vol.15,no.5,pp.353–389,2003. crosslinker. The synthesized are confirmed [7] W. Caseri, “Nanocomposites of polymers and metals or semi- by using various spectral, thermal, and electron microscopy 0 conductors: historical background and optical properties,” methods. These SNCHs having Ag nanoparticles concentra- Macromolecular Rapid Communications, vol. 21, no. 11, pp. 705– tions as low as 1 mg/mL showed excellent antibacterial activ- 722, 2000. ity against gram-positive and gram-negative bactericide. This [8] M. Jose-Yacam´ an,´ R. Perez,´ P. Santiago, M. Benaissa, K. Gon- resulted into inhibition of bacterial cell growth and multipli- salves, and G. Carlson, “Microscopic structure of gold particles cation. So these nanocomposites could be used as successful in a metal polymer composite film,” Applied Physics Letters,vol. antibacterialagentssuchaswound-dressingmaterials. 69, no. 7, pp. 913–915, 1996. International Journal of Carbohydrate Chemistry 9

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