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An eco-friendly synthesis, characterization and antibacterial applications of novel almond gum – poly(acrylamide) based hydrogel silver nanocomposite
Accepted Manuscript An eco-friendly synthesis, characterisation and antibacterial applications of novel almond gum – poly(acrylamide) based hydrogel silver nanocomposite I. Syed Ahamed Hussain, V. Jaisankar PII:
S0142-9418(17)30091-0
DOI:
10.1016/j.polymertesting.2017.06.021
Reference:
POTE 5070
To appear in:
Polymer Testing
Received Date: 26 January 2017 Revised Date:
11 April 2017
Accepted Date: 21 June 2017
Please cite this article as: I. Syed Ahamed Hussain, V. Jaisankar, An eco-friendly synthesis, characterisation and antibacterial applications of novel almond gum – poly(acrylamide) based hydrogel silver nanocomposite, Polymer Testing (2017), doi: 10.1016/j.polymertesting.2017.06.021. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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An eco-friendly synthesis, characterization and antibacterial applications
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of novel almond gum – poly(acrylamide) based hydrogel silver nanocomposite
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I. Syed Ahamed Hussain a,*, V. Jaisankar a a
PG and Research Department of Chemistry, Presidency College (Autonomous), Chennai 600 005, India.
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* Corresponding author: Email: [email protected]
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Abstract Polysaccharide based semi interpenetrating hydrogel (SIH) networks of cross-linked
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poly(acrylamide) was synthesised through an redox initiating free radical polymerization
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utilizing almond gum as a grafting backbone, N,N’– methylenebisacrylamide (MBA) as the
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crosslinker and ammonium persulphate (APS) – N,N,N’,N’-tetramethyl ethylenediamine
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(TEMED) as the redox initiator pair. Silver ions were introduced into the hydrogel matrix and
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silver nanoparticles of invariable size were developed insitu of the swollen hydrogel by the
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reduction of silver ions (Ag+) using azadirachta indica (neem) leaf extract. The prepared
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hydrogel - silver nanocomposite (HSN) was characterized by UV – visible diffused reflectance
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spectroscopy (DRS), fourier transform infrared spectroscopy (FT-IR), high resolution scanning
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electron microscopy (HR-SEM), energy dispersive X-ray analysis (EDX) and thermogravimetric
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analysis (TGA). The influence of pH on the swelling behavior of HSN was studied and the
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antibacterial activity of the developed nanocomposite was evaluated.
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Keywords: Green synthesis, acrylamide, almond gum, hydrogel, silver nanocomposite and
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antimicrobial activity.
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1. Introduction Hydrogels are the most distinctive class of three dimensional polymeric networks
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which possess good hydrophilic character and can hold large quantity of aqueous solution
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without undergoing dissolution. The hydrophilicity of the hydrogel is due to the presence of
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functional groups such as –OH, –COOH, –NH2, –CONH2, –SO3H within the polymer
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backbone or in lateral chains and its stability and insolubility are attributed to three
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dimensional networks developed by either physical or chemical cross-linking. These
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networks not only prevent the hydrogels from dissolution but also make them to swell in
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aqueous solution [1]. They can be derived from natural or synthetic sources and are being
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extensively explored for their potential in tissue engineering [2], wound dressing [3],
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biosensors and drug delivery devices [4-6]. Although synthetic polymers have well
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established structures suitable for such applications but natural polymers are preferred
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because of numerous advantages such as better biodegradability, easy fabrication, lower
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material cost, biocompatibility [7], hypotoxicity [8], more versatile processability and
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functionalization [9].
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Metal nanoparticles such as silver, gold and copper are reported as highly toxic to
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microorganisms [10]. In recent years, silver nanoparticles have been extensively preferred
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for the production of medical products because of its strong cytotoxicity for various
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microorganisms and its wide use in controlling infections since ancient times [11-12].
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However, the poor binding characteristic with surfaces limited its use as antibacterial
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agent. Therefore, silver nanoparticles are incorporated in the hydrogel networks for the
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preparation of hydrogel-silver nanocomposites [13]. Hydrogels with large free space among
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the cross-linked networks can not only act as a reservoir for massive nanoparticles loading,
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but also function as a nanoreactor template for the nucleation and growth of nanoparticles
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[14]. The incorporation of silver nanoparticles introduces, by synergetic effects between
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their organic and inorganic components, new properties such as enhancement in
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mechanical toughness, large deformability, high swelling/deswelling rates, excellent
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electrical conductivity, high transparency [15-17] and remarkably strong antibacterial
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activity in combination with a fairly low toxicity against human tissues [18].
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The general methods used to incorporate nanoparticles into the hydrogels includes
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gelation of preformed nanoparticles in a solution of hydrogel forming monomers, embedding of
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nanoparticles in the hydrogel networks by swelling – shrinking process, repeated heating,
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centrifugation, redispersion and entrapment of nanoparticles in hydrogel matrix followed by
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reduction with common reducing agents. However, drawbacks such as aggregation of
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nanoparticles in monomer solution before and during the gelation process, leaching of
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nanoparticles out of the network, forcing conditions for synthesis and the use of toxic chemicals
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as reducing agents limits their use in the development of potential hydrogel nanocomposites.
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This pave the way for biological methods, using plant extracts, which are cost effective and
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environmental friendly [19].
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Among the natural polymers, polysaccharides in particular have some remarkable
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characteristics and considerable research has been directed towards them for the
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production of hydrogels [20]. Almond gum is one of the natural polymers exuded from the
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trunk of the almond tree (Purnis dulcis). Carbohydrates of the almond gum are mainly
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constituted of arabinose, xylitol, galactose and uronic acid with traces of rhamnose, mannose and
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glucose, thus suggesting an arabinogalactan structure of the gum [21]. It is cheap and has many
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properties that have generated interest in its use such as water binding capacity, biodegradability,
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biocompatibility, non-toxicity, bioactivity, metal uptake capacity, fat binding capacity and
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antimicrobial activity. [22-24]. Based on the literature survey, we report on the novel synthesis of poly(acrylamide) –
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almond gum hydrogel with certain hydrophilic nature for embedding the silver ions and reducing
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it to silver nanoparticles insitu using neem plant extract [25] to obtain polysaccharide based
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hydrogel – silver nanocomposite (HSN). The structure of HSN, effect of pH and its reversibility,
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almond gum and silver nitrate concentration on the swelling behavior of HSN were studied.
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Finally the antibacterial activity was evaluated against staphylococcus aureus, escherichia
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coli and pseudomonas aeroginosa.
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2. Experimental 2.1. Materials
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Acrylamide (AM), ammonium persulphate (APS), silver nitrate (AgNO3), N,N’-
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methylenebisacrylamide (MBA), N,N,N’,N’-tetramethyl ethylenediamine (TEMED) of reagent
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grade were kindly supplied by S.D. Fine Chemicals (Mumbai, India) and used without further
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purification. Almond gum (AG) was also of reagent grade and purified before use. Double
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distilled water (DDW) was used for the synthesis of hydrogel and for the preparation of solutions
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required in this study.
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2.2. Purification of Almond Gum
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Purification of almond gum was carried out as follows [26]. The gum was dried well and
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powdered using mortar and pestle and riddled through sieve No.100. It was solubilised in double
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distilled water and concentrated by heating. The concentrated gum was precipitated in an ice
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cold ethanol. The precipitated gum was separated and dried at 60 ºC. The pure gum was finely
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grained and stored in air tight container.
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2.3 Synthesis of polysaccharide based semi interpenetrating hydrogel (SIH) SIH was prepared by an improved one pot synthesis [27] as follows. AG (0.1 g) was
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mixed in 5 ml of DDW to get a homogeneous solution. AM (1.0 g) was dissolved in 6 ml of
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DDW followed by initiator APS (0.005 g in 1 ml of DDW) and cross-linker MBA (0.01 g in 1
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ml of DDW). Both the solutions were mixed and TEMED (0.02 ml in 1 ml of DDW) was added
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which, together with APS, acts as redox-initiating pair and initiates free radical polymerization.
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The reaction mixture was stirred and heated at 60 ºC for 5 minutes. The polymerization reaction
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results in the formation of SIH within 10 minutes of reaction time. The formed hydrogel was
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equilibrated with water for 3 days to remove unreacted monomers and reagents. The hydrogel
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was dried in hot air oven to constant weight.
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2.4. Preparation of plant extract
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Azadirachta indica (neem) leaf extract was used for the green synthesis of silver
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nanoparticles because of its cost effectiveness, ease of availability and medicinal property [28].
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Fresh leaves were collected from the local region. They were surface cleaned with running tap
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water to remove adhered impurities, followed by double distilled water and air dried at room
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temperature. About 20 g of leaves were cut into small pieces and grinded well to obtain a paste.
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This paste was dispersed in 100 ml of DDW and heated for 30 minutes at 70-80 ºC. The extract
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was cooled down and filtered using Whatman’s No.1 filter paper and the filtrate was collected in
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a presterilized conical flask, stored at 4 ºC and used on the same day.
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2.5. Green synthesis of semi interpenetrating hydrogel – silver nanocomposite
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Dried hydrogel (500 mg) was equilibrated with double distilled water for 3 days at room
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temperature. The swollen SIH was transferred to beaker containing 50 ml of 0.005 M silver
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nitrate solution and allowed to equilibrate for 24 hours. These silver salt loaded hydrogel was
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transferred into another beaker containing 50 ml of neem leaf extract and allowed to stand for 12
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hours. During this period, the silver ions were reduced to silver nanoparticles which were
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confessed by the development of brown color in the hydrogel. The silver nanoparticles loaded
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SIH was dried at ambient temperature and often termed in the forthcoming sections as HSN.
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2.6. Characterisation techniques
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2.6.1. UV-Visible diffused reflectance spectra (DRS)
UV-Visible DRS of SIH and HSN were recorded on the Shimadzu 2550 spectrophoto meter using BaSO4 as the reference material.
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2.6.2. Fourier transform infrared spectra (FT-IR)
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FT-IR spectra of completely dried SIH and HSN were recorded with a Perkin Elmer FT-
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IR spectrometer – Spectrum.RX1 (USA) of scan range 500–4000 cm−1. The instrument was
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purged with dry air before data collection and during measurements to eliminate error due to
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moisture absorption.
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2.6.3. High resolution scanning electron microscopy (HR-SEM)
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HR-SEM analysis was performed using Tescan Vega3 SBU variable pressure scanning
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electron microscope with 0.2 ml of finely grinded SIH and HSN dispersions on a copper grid
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dried at room temperature after removing excess solution using filter paper.
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2.6.4. Thermogravimetric analysis
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The thermal stability of SIH and HSN were evaluated using SII EXSTAR 6000 thermal
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system (Japan) at a heating rate of 10 ºC per minute and a flow rate of 10 ml per minute under
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nitrogen atmosphere.
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2.6.5 Swelling studies The pre-weighed HSN of different AG concentrations were immersed in DDW at 37 ºC.
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After specific time intervals, the gels were taken out and the surface adhered solution was
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removed and weighed. Similarly, the swelling ability of HSN in various buffer solutions was
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studied. The swelling ratio (Q) of the gels was calculated from the equation, Q =We/Wd,
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where We is the weight of swollen hydrogel and Wd is the weight of the dry hydrogel.
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2.6.6. Antibacterial studies
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The antibacterial activity of SIH and HSN were carried out on Mueller Hinton agar
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(MHA) medium using agar disc diffusion method [29]. MHA medium was poured into the sterile
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petriplates. After the medium was solidified, the inoculums were spread on the solid plates with
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sterile swabs moistened with the bacterial suspension. The discs were placed in MHA plates and
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20 µl of samples (Concentration: 1000µg, 750µg and 500 µg) were placed in the disc .The plates
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were incubated at 37 ºC for 24 hrs. Then the antimicrobial activity of the prepared HSN against
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the test organisms was determined by measuring the diameter (mm) of zone of inhibition.
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3. Results and discussion
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3.1. Characterisation of SIH and HSN
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3.1.1 UV – Visible diffused reflectance spectra (DRS)
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The development of opaque brown color after the addition of neem leaf extract to the
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swollen hydrogel indicates the insitu formation of silver nanoparticles (Ago) by the reduction of
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silver ions (Ag+) in the entire hydrogel. This also represents that the nanoparticles were
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entangled inside the swollen hydrogel networks through strong localization and stabilization
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established from the macromolecules of polysaccharides. The perseverance of silver
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nanoparticles in the hydrogel networks was confirmed by UV – visible DRS spectral analysis.
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Silver nanoparticles loaded hydrogel have shown a distinct peak around 380 – 400 nm in the
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diffused reflectance spectra [30] (Fig. 1(a)) due to the surface plasmon resonance (SPR) effect
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caused by the quantum size of the silver nanoparticles [31] whereas the placebo hydrogel have
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shown no such peak in the diffused reflectance spectra (Fig. 1(b)).
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3.1.2. Fourier transform infrared spectra (FT-IR)
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IR spectra of the poly(acrylamide) based hydrogel (Fig. 2(a)) shows the presence of
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absorption bands characteristic to cross–linking bridges. Absorption band attribution was made
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in agreement with the values given in literature [32]. The absorption bands at 3335 and
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1647 cm–1 corresponds to –OH stretching vibrations from the cross–linking bridges and –C=O
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extension vibrations of amide groups respectively. A band at 3202 cm–1 arising from the
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stretching vibration of the amide group, which is obvious in the spectrum of polyacrylamide
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proved the presence of acrylamide in the structure of synthesised hydrogel [33]. The symmetric
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valence vibration at 2916 cm–1 is assigned to the – CH2 groups between the macromolecular
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chains and cross–linking bridges. The asymmetric stretching vibration of ester groups of AG is
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observed at 1600 cm–1. Absorption bands assigned to the deformation vibrations of the –CN,
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–OH and –CH2 groups in the 1400 to 1350 cm–1 range were also identified. Cluster of peaks
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from 500 to 1100 cm–1 range are assigned to stretching of C – O in C – O – C and C – O – H of
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glycosidic bonds. In the IR spectra of HSN (Fig. 2(b)), the peaks were shifted to lower wave
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numbers (3326, 3192, 1642, 1591 cm–1) due to the coordination between the nano-silver and
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electron rich groups (relating to –OH, –NH, –C=O, –COO–) [34, 35] present in the hydrogel
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networks. Therefore, we can confirm the presence of silver nanoparticles in the hydrogel
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networks.
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3.1.3. High resolution scanning electron microscopy (HR-SEM) The surface morphology of SIH and the HSN were investigated with HR-SEM. The SIH
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showed a smooth surface feature (Fig. 3(a)), whereas HSN showed a shrunken surface
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throughout the gel (Fig. 3(b)). The particle size analysis confirms the presence of small, highly
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dispersed and rod shaped silver nanoparticles with an average size of about 75 nm. It is noticed
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that no individual silver particles were observed outside the HSN, suggesting a strong interaction
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between the polymer matrix and the silver particles.
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3.1.4. Energy dispersive X-ray (EDX) analysis
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Fig. 4(a) and 4(b) depicts the chemical composition of SIH and HSN as obtained by
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EDX. Fig. 4(a), which is the EDX spectrum of SIH, shows the presence of C and O signals only
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confirming the high purity of SIH. Fig. 4(b) shows the EDX spectrum corresponding to the
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presence of C, O and Ag elements only. The weight percentage of Ag as obtained from EDX
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spectrum is 6.10%. It is important to notice that the prepared HSN is pure and free from
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impurities.
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3.1.5. Thermal stability
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The thermogram of HSN displayed distinctive thermal stability as shown in Fig. 5(a).
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The HSN mainly showed two stage decomposition behavior [36]. An early weight loss (8%) in
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the range 80-120 ºC was also observed and is due to the loss of absorbed moisture. The first
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major stage of decomposition is characterized by the initial decomposition temperature (IDT) in
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the range 230-260 ºC and final decomposition temperature (FDT) in the range 310-380 ºC. This
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stage resulted in 38 % weight loss. For the second major decomposition stage, the IDT range was
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420-450 ºC and FDT range was 500-580 ºC. The weight loss was around 31 % which was
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attributed to the complete degradation of the hydrogel. However, the TGA thermogram of SIH
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(Fig. 5(b)) showed two decomposition curves [37] and degradation of the hydrogel starts
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around 230 ºC and continues up to 500 ºC. It is important to note that the thermal stability
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of HSN is higher than SIH. The high thermal stability of the HSN can be attributed to the
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presence of large quantity of silver nanoparticles inside the hydrogel network.
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3.1.6. Swelling studies
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The swelling behavior of any polymer network depends upon the nature of the
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polymer, polymer – solvent compatibility and degree of cross-linking. Hence, we have chosen
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carbohydrate polymer (AG) to improve the swelling capacity of poly(acrylamide) hydrogel. The
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capability of hydrogels to swell in water is due to the hydrophilic groups present in the polymeric
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chains and its mechanical resistance is due in part to the physical or chemical cross-linking. It
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was known that polar head groups of polymeric chains such as hydroxyl, thiol, amine, and nitrile
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have high affinity for salts [38]. The loading of silver ions throughout the gel networks causes
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repulsion among the networks, which ultimately leads to an improved swelling behavior of
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hydrogel systems. Further increase in swelling capacity was observed after the addition of
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reducing agent (neem extract) to silver ions loaded SIH. This is due to the formation of silver
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nanoparticles throughout the gel networks which increases the overall porosity of system and
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makes entry for more number of water molecules inside the gel. The other reason can be that the
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formed particles have different sizes and surface charges which cause absolute expansion of the
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networks. The order of swelling observed is: HSN > Ag+ loaded SIH > SIH
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3.1.7. Effect of AgNO3 concentration on swelling capacity of SIH
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The effect of AgNO3 concentration on swelling characteristics of the SIH was studied by
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varying the concentration of AgNO3 from 0.001 to 0.02M whereas the amount of AG was kept
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constant (0.1 g). Increasing the AgNO3 concentration up to 0.005 M, the water absorbency of the
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hydrogel was increasing (Fig. 6). The reason was that the polar head groups of polymeric chains
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such as hydroxyl, thiol, amine, and nitrile groups have a high affinity for salts. A decrease in
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swelling when the AgNO3 concentration was 0.02 M may be attributed to the chelation of some
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hydroxyl and carboxylate groups of the hydrogel networks with silver nanoparticles which
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neutralizes the repulsions in the networks.
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3.1.8. Effect of AG amount on swelling capacity of HSN
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The effect of AG concentration on water absorption of the HSN was investigated by
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varying the amount of AG from 0.1 g to 0.5 g whereas the concentration of AgNO3 was kept as
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0.005 M. As shown in Fig. 7, increasing AG amount up to 0.2 g increases the swelling capacity.
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This was due to the introduction of more number of hydrophilic polymer chains inside the gel
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networks that assists in improving the swelling characteristics of gel systems. The decrease in
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swelling with further increase in AG amount (up to 0.5 g) can be attributed to the increase in
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viscosity of the medium which in turn hinders the movement of ions.
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3.1.9. Effect of pH on swelling capacity of HSN
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The swelling behavior of HSN in various pH was observed by placing 0.1 g of HSN in
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pH of 2, 4, 6, 8 and 10 solutions respectively and examining them after one hour. It was noticed
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that the amount of swelling increases with increase in pH from 2 to 6, reaches maximum at pH 8
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and then decreases (see Fig. 8). The repulsion between –COO– groups in the hydrogel is the
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main reason for the maximum swelling at pH 8 [39]. Below pH 8, the H+ ions in the external
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medium effectively suppress the ionisation of the carboxyl and hydroxyl groups of AG. This
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decreases the number of mobile ions inside the HSN which causes decrease in osmotic pressure
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and hence the swelling capacity of HSN. Above pH 8, the –OH groups can ionise to –OR which
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reacts with –COO– to form esters. This increases the number of networks inside the hydrogel and
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also decreases the hydrophilicity which is responsible for the decrease in swelling.
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3.1.10. Effect of pH reversibility on swelling capacity of HSN The reversible swelling–deswelling behavior of HSN in solutions with pH; 2 and pH; 8
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was examined (Fig. 9) by placing the HSN in pH; 2 and pH; 8 solutions alternatively for every
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half an hour and swelling capacity was determined for every half an hour. At pH; 8, the hydrogel
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swells due to anion–anion repulsive electrostatic forces, while at pH; 2, it shrinks within a few
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minutes due to protonation of the carboxylate anions. This swelling–deswelling behavior of the
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hydrogel makes HSN a suitable material for drug delivery systems.
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3.1.11. Antibacterial analysis
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The main course of this study is to unfold a new antibacterial material. The
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antibacterial activity of different molar weight ratios of HSN and SIH were examined
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against staphylococcus aureus, escherichia coli and pseudomonas aeroginosa. All HSN
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proved effective against the tested microorganisms and the growth inhibitory effects
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showed variation form one another. Fig. 10 (a and b) exhibits the antibacterial property of
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SIH and HSN. The results indicate that the HSN exhibited greater reduction of bacterial
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growth as compared to SIH due to the sustained release of silver nanoparticles form the
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hydrogel networks. Another finding reveals that the positive charge on the silver ion is
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crucial for its antimicrobial activity through the electrostatic attraction between the
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negatively charged cell membrane of the microorganism and positively charged
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nanoparticles [40]. The inhibition area of SIH and HSN for different organisms is given in
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Table. 1.
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4. Conclusion Novel almond gum / poly(acrylamide) semi interpenetrating hydrogel – silver
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nanocomposite was successfully prepared via free radical polymerization followed by insitu
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reduction of silver ions to nanosilver using neem leaf extract as a clean and green reducing agent.
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The methodology developed for the synthesis of SIH is very simple, rapid and cost effective
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which makes it easy to implement in the industries. A number of HSN were formulated with
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high dispersion rates by varying the concentrations of AG and monomer. The formed HSN was
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characterized by different techniques. In the UV – visible diffused reflectance spectra, nanosilver
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have shown good surface plasmon resonance behavior. In FT-IR spectra, shifting of peaks to
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lower wave number occurred. SEM images confirm the presence of well defined silver
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nanoparticles and its stability was further confirmed by thermal analysis. Variation in AG and
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silver ion concentration can greatly improve the swelling of corresponding HSN. The
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antimicrobial activities shown by silver nanoparticles make this method a potential route for
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metal nanoparticles preparation to be used for biomedical applications.
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Table Caption
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Table 1. Zone of Inhibition of SIH and HSN (mm)
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Figure Captions
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Fig. 1. Diffused Reflectance spectra of (a) HSN (b) SIH
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Fig. 2.
FT-IR Spectra of (a) SIH (b) HSN
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Fig. 3.
SEM image of (a) SIH (b) HSN
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Fig. 4.
EDX spectrum of (a) SIH (b) HSN
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Fig. 5.
Thermogram of (a) HSN (b) SIH
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Fig. 6.
Effect of concentration of AgNO3 (M) on swelling capacity of SIH at 37 oC
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Fig. 7. Effect of concentration of AG (g) on swelling capacity of HSN (AgNO3 – 0.005 M)
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Fig. 8.
Effect of pH on swelling capacity of HSN at 37 oC
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Fig. 9.
pH reversibility of HSN with 30 min time interval at 37 oC
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Fig. 10. Antibacterial activity of (a) SIH and (b) HSN against (i) staphylococcus aureus (ii)
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escherichia coli and (iii) pseudomonas aeroginosa
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(a)
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95 4000
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W avenumber (cm )
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85
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Table 1
Organisms
750
500
Antibiotic (Ampicillin) (1mg/ml)
[NA*]
36
[NA*]
17
[NA*]
12
07
06
37
08
07
19
07
06
10
Concentration (µg/ml) 1000
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Zone of Inhibition (mm)
04
03
Escherichia coli
06
04
Pseudomonas aeroginosa
04
[NA*]
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Staphylococcus aureus
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SIH
HSN
Staphylococcus aureus
08
Escherichia coli
11
Pseudomonas aeroginosa
08
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[NA*] – not active
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An eco-friendly synthesis, characterization and antibacterial applications of novel almond gum – poly(acrylamide) based hydrogel silver nanocomposite I. Syed Ahamed Hussain a,*, V. Jaisankar a PG and Research Department of Chemistry, Presidency College (Autonomous), Chennai 600 005, India.
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Highlights
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Hydrogel was synthesised in a shortest time via: free radical polymerization.
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Silver ions were incorporated and converted to nanosilver using green stabilizers. Swelling characteristics were studied and hydrogel silver nanocomposite showed greater swelling.
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The hydrogel silver nanocomposite showed enhanced antibacterial activity.
S0142-9418(17)30091-0
DOI:
10.1016/j.polymertesting.2017.06.021
Reference:
POTE 5070
To appear in:
Polymer Testing
Received Date: 26 January 2017 Revised Date:
11 April 2017
Accepted Date: 21 June 2017
Please cite this article as: I. Syed Ahamed Hussain, V. Jaisankar, An eco-friendly synthesis, characterisation and antibacterial applications of novel almond gum – poly(acrylamide) based hydrogel silver nanocomposite, Polymer Testing (2017), doi: 10.1016/j.polymertesting.2017.06.021. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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An eco-friendly synthesis, characterization and antibacterial applications
2
of novel almond gum – poly(acrylamide) based hydrogel silver nanocomposite
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I. Syed Ahamed Hussain a,*, V. Jaisankar a a
PG and Research Department of Chemistry, Presidency College (Autonomous), Chennai 600 005, India.
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* Corresponding author: Email: [email protected]
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Abstract Polysaccharide based semi interpenetrating hydrogel (SIH) networks of cross-linked
24
poly(acrylamide) was synthesised through an redox initiating free radical polymerization
25
utilizing almond gum as a grafting backbone, N,N’– methylenebisacrylamide (MBA) as the
26
crosslinker and ammonium persulphate (APS) – N,N,N’,N’-tetramethyl ethylenediamine
27
(TEMED) as the redox initiator pair. Silver ions were introduced into the hydrogel matrix and
28
silver nanoparticles of invariable size were developed insitu of the swollen hydrogel by the
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reduction of silver ions (Ag+) using azadirachta indica (neem) leaf extract. The prepared
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hydrogel - silver nanocomposite (HSN) was characterized by UV – visible diffused reflectance
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spectroscopy (DRS), fourier transform infrared spectroscopy (FT-IR), high resolution scanning
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electron microscopy (HR-SEM), energy dispersive X-ray analysis (EDX) and thermogravimetric
33
analysis (TGA). The influence of pH on the swelling behavior of HSN was studied and the
34
antibacterial activity of the developed nanocomposite was evaluated.
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Keywords: Green synthesis, acrylamide, almond gum, hydrogel, silver nanocomposite and
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antimicrobial activity.
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1. Introduction Hydrogels are the most distinctive class of three dimensional polymeric networks
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which possess good hydrophilic character and can hold large quantity of aqueous solution
47
without undergoing dissolution. The hydrophilicity of the hydrogel is due to the presence of
48
functional groups such as –OH, –COOH, –NH2, –CONH2, –SO3H within the polymer
49
backbone or in lateral chains and its stability and insolubility are attributed to three
50
dimensional networks developed by either physical or chemical cross-linking. These
51
networks not only prevent the hydrogels from dissolution but also make them to swell in
52
aqueous solution [1]. They can be derived from natural or synthetic sources and are being
53
extensively explored for their potential in tissue engineering [2], wound dressing [3],
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biosensors and drug delivery devices [4-6]. Although synthetic polymers have well
55
established structures suitable for such applications but natural polymers are preferred
56
because of numerous advantages such as better biodegradability, easy fabrication, lower
57
material cost, biocompatibility [7], hypotoxicity [8], more versatile processability and
58
functionalization [9].
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Metal nanoparticles such as silver, gold and copper are reported as highly toxic to
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microorganisms [10]. In recent years, silver nanoparticles have been extensively preferred
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for the production of medical products because of its strong cytotoxicity for various
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microorganisms and its wide use in controlling infections since ancient times [11-12].
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However, the poor binding characteristic with surfaces limited its use as antibacterial
64
agent. Therefore, silver nanoparticles are incorporated in the hydrogel networks for the
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preparation of hydrogel-silver nanocomposites [13]. Hydrogels with large free space among
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the cross-linked networks can not only act as a reservoir for massive nanoparticles loading,
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but also function as a nanoreactor template for the nucleation and growth of nanoparticles
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[14]. The incorporation of silver nanoparticles introduces, by synergetic effects between
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their organic and inorganic components, new properties such as enhancement in
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mechanical toughness, large deformability, high swelling/deswelling rates, excellent
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electrical conductivity, high transparency [15-17] and remarkably strong antibacterial
72
activity in combination with a fairly low toxicity against human tissues [18].
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The general methods used to incorporate nanoparticles into the hydrogels includes
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gelation of preformed nanoparticles in a solution of hydrogel forming monomers, embedding of
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nanoparticles in the hydrogel networks by swelling – shrinking process, repeated heating,
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centrifugation, redispersion and entrapment of nanoparticles in hydrogel matrix followed by
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reduction with common reducing agents. However, drawbacks such as aggregation of
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nanoparticles in monomer solution before and during the gelation process, leaching of
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nanoparticles out of the network, forcing conditions for synthesis and the use of toxic chemicals
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as reducing agents limits their use in the development of potential hydrogel nanocomposites.
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This pave the way for biological methods, using plant extracts, which are cost effective and
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environmental friendly [19].
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Among the natural polymers, polysaccharides in particular have some remarkable
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characteristics and considerable research has been directed towards them for the
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production of hydrogels [20]. Almond gum is one of the natural polymers exuded from the
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trunk of the almond tree (Purnis dulcis). Carbohydrates of the almond gum are mainly
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constituted of arabinose, xylitol, galactose and uronic acid with traces of rhamnose, mannose and
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glucose, thus suggesting an arabinogalactan structure of the gum [21]. It is cheap and has many
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properties that have generated interest in its use such as water binding capacity, biodegradability,
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biocompatibility, non-toxicity, bioactivity, metal uptake capacity, fat binding capacity and
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antimicrobial activity. [22-24]. Based on the literature survey, we report on the novel synthesis of poly(acrylamide) –
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almond gum hydrogel with certain hydrophilic nature for embedding the silver ions and reducing
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it to silver nanoparticles insitu using neem plant extract [25] to obtain polysaccharide based
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hydrogel – silver nanocomposite (HSN). The structure of HSN, effect of pH and its reversibility,
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almond gum and silver nitrate concentration on the swelling behavior of HSN were studied.
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Finally the antibacterial activity was evaluated against staphylococcus aureus, escherichia
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coli and pseudomonas aeroginosa.
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2. Experimental 2.1. Materials
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Acrylamide (AM), ammonium persulphate (APS), silver nitrate (AgNO3), N,N’-
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methylenebisacrylamide (MBA), N,N,N’,N’-tetramethyl ethylenediamine (TEMED) of reagent
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grade were kindly supplied by S.D. Fine Chemicals (Mumbai, India) and used without further
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purification. Almond gum (AG) was also of reagent grade and purified before use. Double
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distilled water (DDW) was used for the synthesis of hydrogel and for the preparation of solutions
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required in this study.
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2.2. Purification of Almond Gum
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Purification of almond gum was carried out as follows [26]. The gum was dried well and
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powdered using mortar and pestle and riddled through sieve No.100. It was solubilised in double
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distilled water and concentrated by heating. The concentrated gum was precipitated in an ice
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cold ethanol. The precipitated gum was separated and dried at 60 ºC. The pure gum was finely
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grained and stored in air tight container.
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2.3 Synthesis of polysaccharide based semi interpenetrating hydrogel (SIH) SIH was prepared by an improved one pot synthesis [27] as follows. AG (0.1 g) was
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mixed in 5 ml of DDW to get a homogeneous solution. AM (1.0 g) was dissolved in 6 ml of
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DDW followed by initiator APS (0.005 g in 1 ml of DDW) and cross-linker MBA (0.01 g in 1
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ml of DDW). Both the solutions were mixed and TEMED (0.02 ml in 1 ml of DDW) was added
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which, together with APS, acts as redox-initiating pair and initiates free radical polymerization.
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The reaction mixture was stirred and heated at 60 ºC for 5 minutes. The polymerization reaction
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results in the formation of SIH within 10 minutes of reaction time. The formed hydrogel was
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equilibrated with water for 3 days to remove unreacted monomers and reagents. The hydrogel
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was dried in hot air oven to constant weight.
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2.4. Preparation of plant extract
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Azadirachta indica (neem) leaf extract was used for the green synthesis of silver
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nanoparticles because of its cost effectiveness, ease of availability and medicinal property [28].
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Fresh leaves were collected from the local region. They were surface cleaned with running tap
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water to remove adhered impurities, followed by double distilled water and air dried at room
128
temperature. About 20 g of leaves were cut into small pieces and grinded well to obtain a paste.
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This paste was dispersed in 100 ml of DDW and heated for 30 minutes at 70-80 ºC. The extract
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was cooled down and filtered using Whatman’s No.1 filter paper and the filtrate was collected in
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a presterilized conical flask, stored at 4 ºC and used on the same day.
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2.5. Green synthesis of semi interpenetrating hydrogel – silver nanocomposite
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Dried hydrogel (500 mg) was equilibrated with double distilled water for 3 days at room
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temperature. The swollen SIH was transferred to beaker containing 50 ml of 0.005 M silver
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nitrate solution and allowed to equilibrate for 24 hours. These silver salt loaded hydrogel was
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transferred into another beaker containing 50 ml of neem leaf extract and allowed to stand for 12
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hours. During this period, the silver ions were reduced to silver nanoparticles which were
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confessed by the development of brown color in the hydrogel. The silver nanoparticles loaded
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SIH was dried at ambient temperature and often termed in the forthcoming sections as HSN.
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2.6. Characterisation techniques
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2.6.1. UV-Visible diffused reflectance spectra (DRS)
UV-Visible DRS of SIH and HSN were recorded on the Shimadzu 2550 spectrophoto meter using BaSO4 as the reference material.
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2.6.2. Fourier transform infrared spectra (FT-IR)
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FT-IR spectra of completely dried SIH and HSN were recorded with a Perkin Elmer FT-
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IR spectrometer – Spectrum.RX1 (USA) of scan range 500–4000 cm−1. The instrument was
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purged with dry air before data collection and during measurements to eliminate error due to
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moisture absorption.
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2.6.3. High resolution scanning electron microscopy (HR-SEM)
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HR-SEM analysis was performed using Tescan Vega3 SBU variable pressure scanning
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electron microscope with 0.2 ml of finely grinded SIH and HSN dispersions on a copper grid
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dried at room temperature after removing excess solution using filter paper.
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2.6.4. Thermogravimetric analysis
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The thermal stability of SIH and HSN were evaluated using SII EXSTAR 6000 thermal
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system (Japan) at a heating rate of 10 ºC per minute and a flow rate of 10 ml per minute under
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nitrogen atmosphere.
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2.6.5 Swelling studies The pre-weighed HSN of different AG concentrations were immersed in DDW at 37 ºC.
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After specific time intervals, the gels were taken out and the surface adhered solution was
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removed and weighed. Similarly, the swelling ability of HSN in various buffer solutions was
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studied. The swelling ratio (Q) of the gels was calculated from the equation, Q =We/Wd,
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where We is the weight of swollen hydrogel and Wd is the weight of the dry hydrogel.
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2.6.6. Antibacterial studies
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The antibacterial activity of SIH and HSN were carried out on Mueller Hinton agar
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(MHA) medium using agar disc diffusion method [29]. MHA medium was poured into the sterile
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petriplates. After the medium was solidified, the inoculums were spread on the solid plates with
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sterile swabs moistened with the bacterial suspension. The discs were placed in MHA plates and
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20 µl of samples (Concentration: 1000µg, 750µg and 500 µg) were placed in the disc .The plates
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were incubated at 37 ºC for 24 hrs. Then the antimicrobial activity of the prepared HSN against
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the test organisms was determined by measuring the diameter (mm) of zone of inhibition.
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3. Results and discussion
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3.1. Characterisation of SIH and HSN
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3.1.1 UV – Visible diffused reflectance spectra (DRS)
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The development of opaque brown color after the addition of neem leaf extract to the
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swollen hydrogel indicates the insitu formation of silver nanoparticles (Ago) by the reduction of
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silver ions (Ag+) in the entire hydrogel. This also represents that the nanoparticles were
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entangled inside the swollen hydrogel networks through strong localization and stabilization
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established from the macromolecules of polysaccharides. The perseverance of silver
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nanoparticles in the hydrogel networks was confirmed by UV – visible DRS spectral analysis.
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Silver nanoparticles loaded hydrogel have shown a distinct peak around 380 – 400 nm in the
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diffused reflectance spectra [30] (Fig. 1(a)) due to the surface plasmon resonance (SPR) effect
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caused by the quantum size of the silver nanoparticles [31] whereas the placebo hydrogel have
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shown no such peak in the diffused reflectance spectra (Fig. 1(b)).
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3.1.2. Fourier transform infrared spectra (FT-IR)
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IR spectra of the poly(acrylamide) based hydrogel (Fig. 2(a)) shows the presence of
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absorption bands characteristic to cross–linking bridges. Absorption band attribution was made
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in agreement with the values given in literature [32]. The absorption bands at 3335 and
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1647 cm–1 corresponds to –OH stretching vibrations from the cross–linking bridges and –C=O
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extension vibrations of amide groups respectively. A band at 3202 cm–1 arising from the
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stretching vibration of the amide group, which is obvious in the spectrum of polyacrylamide
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proved the presence of acrylamide in the structure of synthesised hydrogel [33]. The symmetric
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valence vibration at 2916 cm–1 is assigned to the – CH2 groups between the macromolecular
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chains and cross–linking bridges. The asymmetric stretching vibration of ester groups of AG is
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observed at 1600 cm–1. Absorption bands assigned to the deformation vibrations of the –CN,
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–OH and –CH2 groups in the 1400 to 1350 cm–1 range were also identified. Cluster of peaks
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from 500 to 1100 cm–1 range are assigned to stretching of C – O in C – O – C and C – O – H of
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glycosidic bonds. In the IR spectra of HSN (Fig. 2(b)), the peaks were shifted to lower wave
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numbers (3326, 3192, 1642, 1591 cm–1) due to the coordination between the nano-silver and
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electron rich groups (relating to –OH, –NH, –C=O, –COO–) [34, 35] present in the hydrogel
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networks. Therefore, we can confirm the presence of silver nanoparticles in the hydrogel
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networks.
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3.1.3. High resolution scanning electron microscopy (HR-SEM) The surface morphology of SIH and the HSN were investigated with HR-SEM. The SIH
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showed a smooth surface feature (Fig. 3(a)), whereas HSN showed a shrunken surface
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throughout the gel (Fig. 3(b)). The particle size analysis confirms the presence of small, highly
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dispersed and rod shaped silver nanoparticles with an average size of about 75 nm. It is noticed
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that no individual silver particles were observed outside the HSN, suggesting a strong interaction
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between the polymer matrix and the silver particles.
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3.1.4. Energy dispersive X-ray (EDX) analysis
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Fig. 4(a) and 4(b) depicts the chemical composition of SIH and HSN as obtained by
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EDX. Fig. 4(a), which is the EDX spectrum of SIH, shows the presence of C and O signals only
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confirming the high purity of SIH. Fig. 4(b) shows the EDX spectrum corresponding to the
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presence of C, O and Ag elements only. The weight percentage of Ag as obtained from EDX
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spectrum is 6.10%. It is important to notice that the prepared HSN is pure and free from
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impurities.
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3.1.5. Thermal stability
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The thermogram of HSN displayed distinctive thermal stability as shown in Fig. 5(a).
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The HSN mainly showed two stage decomposition behavior [36]. An early weight loss (8%) in
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the range 80-120 ºC was also observed and is due to the loss of absorbed moisture. The first
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major stage of decomposition is characterized by the initial decomposition temperature (IDT) in
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the range 230-260 ºC and final decomposition temperature (FDT) in the range 310-380 ºC. This
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stage resulted in 38 % weight loss. For the second major decomposition stage, the IDT range was
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420-450 ºC and FDT range was 500-580 ºC. The weight loss was around 31 % which was
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attributed to the complete degradation of the hydrogel. However, the TGA thermogram of SIH
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(Fig. 5(b)) showed two decomposition curves [37] and degradation of the hydrogel starts
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around 230 ºC and continues up to 500 ºC. It is important to note that the thermal stability
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of HSN is higher than SIH. The high thermal stability of the HSN can be attributed to the
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presence of large quantity of silver nanoparticles inside the hydrogel network.
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3.1.6. Swelling studies
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The swelling behavior of any polymer network depends upon the nature of the
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polymer, polymer – solvent compatibility and degree of cross-linking. Hence, we have chosen
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carbohydrate polymer (AG) to improve the swelling capacity of poly(acrylamide) hydrogel. The
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capability of hydrogels to swell in water is due to the hydrophilic groups present in the polymeric
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chains and its mechanical resistance is due in part to the physical or chemical cross-linking. It
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was known that polar head groups of polymeric chains such as hydroxyl, thiol, amine, and nitrile
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have high affinity for salts [38]. The loading of silver ions throughout the gel networks causes
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repulsion among the networks, which ultimately leads to an improved swelling behavior of
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hydrogel systems. Further increase in swelling capacity was observed after the addition of
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reducing agent (neem extract) to silver ions loaded SIH. This is due to the formation of silver
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nanoparticles throughout the gel networks which increases the overall porosity of system and
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makes entry for more number of water molecules inside the gel. The other reason can be that the
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formed particles have different sizes and surface charges which cause absolute expansion of the
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networks. The order of swelling observed is: HSN > Ag+ loaded SIH > SIH
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3.1.7. Effect of AgNO3 concentration on swelling capacity of SIH
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The effect of AgNO3 concentration on swelling characteristics of the SIH was studied by
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varying the concentration of AgNO3 from 0.001 to 0.02M whereas the amount of AG was kept
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constant (0.1 g). Increasing the AgNO3 concentration up to 0.005 M, the water absorbency of the
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hydrogel was increasing (Fig. 6). The reason was that the polar head groups of polymeric chains
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such as hydroxyl, thiol, amine, and nitrile groups have a high affinity for salts. A decrease in
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swelling when the AgNO3 concentration was 0.02 M may be attributed to the chelation of some
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hydroxyl and carboxylate groups of the hydrogel networks with silver nanoparticles which
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neutralizes the repulsions in the networks.
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3.1.8. Effect of AG amount on swelling capacity of HSN
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The effect of AG concentration on water absorption of the HSN was investigated by
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varying the amount of AG from 0.1 g to 0.5 g whereas the concentration of AgNO3 was kept as
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0.005 M. As shown in Fig. 7, increasing AG amount up to 0.2 g increases the swelling capacity.
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This was due to the introduction of more number of hydrophilic polymer chains inside the gel
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networks that assists in improving the swelling characteristics of gel systems. The decrease in
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swelling with further increase in AG amount (up to 0.5 g) can be attributed to the increase in
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viscosity of the medium which in turn hinders the movement of ions.
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3.1.9. Effect of pH on swelling capacity of HSN
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The swelling behavior of HSN in various pH was observed by placing 0.1 g of HSN in
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pH of 2, 4, 6, 8 and 10 solutions respectively and examining them after one hour. It was noticed
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that the amount of swelling increases with increase in pH from 2 to 6, reaches maximum at pH 8
268
and then decreases (see Fig. 8). The repulsion between –COO– groups in the hydrogel is the
269
main reason for the maximum swelling at pH 8 [39]. Below pH 8, the H+ ions in the external
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medium effectively suppress the ionisation of the carboxyl and hydroxyl groups of AG. This
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decreases the number of mobile ions inside the HSN which causes decrease in osmotic pressure
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and hence the swelling capacity of HSN. Above pH 8, the –OH groups can ionise to –OR which
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reacts with –COO– to form esters. This increases the number of networks inside the hydrogel and
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also decreases the hydrophilicity which is responsible for the decrease in swelling.
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3.1.10. Effect of pH reversibility on swelling capacity of HSN The reversible swelling–deswelling behavior of HSN in solutions with pH; 2 and pH; 8
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was examined (Fig. 9) by placing the HSN in pH; 2 and pH; 8 solutions alternatively for every
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half an hour and swelling capacity was determined for every half an hour. At pH; 8, the hydrogel
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swells due to anion–anion repulsive electrostatic forces, while at pH; 2, it shrinks within a few
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minutes due to protonation of the carboxylate anions. This swelling–deswelling behavior of the
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hydrogel makes HSN a suitable material for drug delivery systems.
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3.1.11. Antibacterial analysis
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The main course of this study is to unfold a new antibacterial material. The
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antibacterial activity of different molar weight ratios of HSN and SIH were examined
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against staphylococcus aureus, escherichia coli and pseudomonas aeroginosa. All HSN
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proved effective against the tested microorganisms and the growth inhibitory effects
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showed variation form one another. Fig. 10 (a and b) exhibits the antibacterial property of
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SIH and HSN. The results indicate that the HSN exhibited greater reduction of bacterial
289
growth as compared to SIH due to the sustained release of silver nanoparticles form the
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hydrogel networks. Another finding reveals that the positive charge on the silver ion is
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crucial for its antimicrobial activity through the electrostatic attraction between the
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negatively charged cell membrane of the microorganism and positively charged
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nanoparticles [40]. The inhibition area of SIH and HSN for different organisms is given in
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Table. 1.
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4. Conclusion Novel almond gum / poly(acrylamide) semi interpenetrating hydrogel – silver
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nanocomposite was successfully prepared via free radical polymerization followed by insitu
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reduction of silver ions to nanosilver using neem leaf extract as a clean and green reducing agent.
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The methodology developed for the synthesis of SIH is very simple, rapid and cost effective
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which makes it easy to implement in the industries. A number of HSN were formulated with
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high dispersion rates by varying the concentrations of AG and monomer. The formed HSN was
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characterized by different techniques. In the UV – visible diffused reflectance spectra, nanosilver
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have shown good surface plasmon resonance behavior. In FT-IR spectra, shifting of peaks to
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lower wave number occurred. SEM images confirm the presence of well defined silver
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nanoparticles and its stability was further confirmed by thermal analysis. Variation in AG and
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silver ion concentration can greatly improve the swelling of corresponding HSN. The
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antimicrobial activities shown by silver nanoparticles make this method a potential route for
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metal nanoparticles preparation to be used for biomedical applications.
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Table Caption
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Table 1. Zone of Inhibition of SIH and HSN (mm)
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Figure Captions
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Fig. 1. Diffused Reflectance spectra of (a) HSN (b) SIH
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Fig. 2.
FT-IR Spectra of (a) SIH (b) HSN
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Fig. 3.
SEM image of (a) SIH (b) HSN
326
Fig. 4.
EDX spectrum of (a) SIH (b) HSN
327
Fig. 5.
Thermogram of (a) HSN (b) SIH
328
Fig. 6.
Effect of concentration of AgNO3 (M) on swelling capacity of SIH at 37 oC
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Fig. 7. Effect of concentration of AG (g) on swelling capacity of HSN (AgNO3 – 0.005 M)
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Fig. 8.
Effect of pH on swelling capacity of HSN at 37 oC
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Fig. 9.
pH reversibility of HSN with 30 min time interval at 37 oC
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Fig. 10. Antibacterial activity of (a) SIH and (b) HSN against (i) staphylococcus aureus (ii)
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escherichia coli and (iii) pseudomonas aeroginosa
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105
(a)
RI PT
104 103
101 100 99
SC
Transmittance (%)
102
98 97
95 4000
3500
3000
M AN U
96
2500
2000
1500
1000
500
-1
W avenumber (cm )
105
90
85
EP
Transmittance (%)
95
(b)
TE D
100
80
AC C
75
4000
3500
3000
2500
2000
1500 -1
W avenumber (cm )
Fig. 2
2
1000
500
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
(a)
Fig. 3
3
(b)
ACCEPTED MANUSCRIPT
Fig. 4
AC C
EP
TE D
M AN U
SC
RI PT
(a)
4
(b)
ACCEPTED MANUSCRIPT
(a)
120 110 100 90
70
RI PT
Weight (%)
80
60 50 40
20 10 0 200
300
400
500
600
700
800
M AN U
100
SC
30
o
Temperature ( C)
(b)
60
40
EP
Weight (%)
80
TE D
100
AC C
20
0
153.52000;
278.52000;
403.52000; o
Temperature ( C)
Fig. 5
5
528.52000;
ACCEPTED MANUSCRIPT
1.5 1.4
RI PT
1.3
Swelling (g/g)
1.2 1.1 1.0
SC
0.9 0.8
0.000
0.005
M AN U
0.7 0.010
0.015
Concentration of AgNO3 (M)
AC C
EP
TE D
Fig. 6
6
0.020
ACCEPTED MANUSCRIPT
3.5
2.0
SC
Swelling (g/g)
2.5
RI PT
0.1 1.5 0.2 0.3 0.5
3.0
1.5
0.5
20
40
M AN U
1.0
60
Time (Min)
AC C
EP
TE D
Fig. 7
7
80
100
ACCEPTED MANUSCRIPT
RI PT
1.8 1.6
1.2 1.0
SC
Swelling (g/g)
1.4
0.8
0.4 0.2 0.0 1
2
3
4
M AN U
0.6
5
6
7
AC C
EP
TE D
pH
8
Fig. 8
8
9
10
11
ACCEPTED MANUSCRIPT
14
RI PT
Swelling (g/g)
13
12
10
9 0
50
100
150
200
250
M AN U
Time (min)
SC
11
AC C
EP
TE D
Fig. 9
9
300
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
Fig. 10
10
ACCEPTED MANUSCRIPT
Table 1
Organisms
750
500
Antibiotic (Ampicillin) (1mg/ml)
[NA*]
36
[NA*]
17
[NA*]
12
07
06
37
08
07
19
07
06
10
Concentration (µg/ml) 1000
RI PT
Zone of Inhibition (mm)
04
03
Escherichia coli
06
04
Pseudomonas aeroginosa
04
[NA*]
M AN U
Staphylococcus aureus
SC
SIH
HSN
Staphylococcus aureus
08
Escherichia coli
11
Pseudomonas aeroginosa
08
AC C
EP
TE D
[NA*] – not active
11
ACCEPTED MANUSCRIPT
An eco-friendly synthesis, characterization and antibacterial applications of novel almond gum – poly(acrylamide) based hydrogel silver nanocomposite I. Syed Ahamed Hussain a,*, V. Jaisankar a PG and Research Department of Chemistry, Presidency College (Autonomous), Chennai 600 005, India.
SC
Highlights
RI PT
a
Hydrogel was synthesised in a shortest time via: free radical polymerization.
M AN U
Silver ions were incorporated and converted to nanosilver using green stabilizers. Swelling characteristics were studied and hydrogel silver nanocomposite showed greater swelling.
AC C
EP
TE D
The hydrogel silver nanocomposite showed enhanced antibacterial activity.