Sodium carboxymethyl cellulose/poly(acrylamide-co-2-acrylamido-2-methylpropane sulfonic acid) semi-interpenetrating polymer network (semi-IPN) hydrogels were prepared by using free radical polymerization technique. Silver nanoparticles were formed by reduction of silver nitrate in semi-IPN hydrogels with sodium borohydrate at room temperature. UV-visible spectroscopy, thermogravimetrical analysis, X-ray diffractometry, scanning electron microscopy, and transmission electron microscopy techniques were used to characterize the formation of silver nanoparticles in hydrogels. SEM images indicated clearly the formation of group of silver nanoparticles with size range of 10–20 nm. The sizes of silver nanoparticles were also supported by transmission electron microscopy results. The semi-IPN silver nanocomposite hydrogels reported here might be a potentially smart material in the range of applications of antibacterial activity.
Nanocomposite polymer hydrogels may be defined as crosslinked three-dimensional polymer networks swollen with water or biological fluids in the presence of nanoparticles. The design and development of such materials containing metallic nanoparticles have scientific and technological research interests in recent years due to their unique and versatile properties [
The biological activity of silver, especially the antibacterial property, is size dependent [
Usually, carboxylic acid groups can be used as a transient anchoring agent for attaching silver cations to polymer hydrogels, and the silver ion is reduced with sodium borohydride to form nanoparticles [
This paper focuses on the current design and use of cellulose-based hydrogels (NaCMC/poly(AAm-co-AMPS), which usually couple their biodegradability with a smart stimuli-sensitive behavior. Sodium carboxymethyl cellulose (NaCMC) is an ionic ether of the cellulose with too many major commercial applications. It is a highly water soluble anionic polysaccharide that is widely used in pharmaceuticals, cosmetics, and food industry [
Acrylamido methyl propane sulphonic acid (AMPS) was purchased from Aldrich Chemicals (St. Louis). Sodium carboxymethyl cellulose (NaCMC) was purchased from HiMedia Chemicals, India. Acrylamide (AAm), N,N-methylenebisacrylamide (MBA), ammonium persulfate (APS), and N,N,N,N-tetra methyl ethylenediamine (TEMED) were purchased from S.D. Fine Chemicals, India. Silver nitrate (AgNO3), Sodium borohydrate (NaBH4) were purchased from Merck (Germany). All chemicals were used without further purification, and double distilled water was used for the preparation of all solutions for this study.
NaCMC/poly(AAm-co-AMPS) semi-IPN hydrogels were synthesized by employing free radical polymerization using
Various formulation parameters used in the preparation of the hydrogels.
Sample code |
AAm (gm) | NaCMC (gm) | AMPS (gm) | MBA (gm) | APS (gm) | TEMED (mM) |
---|---|---|---|---|---|---|
SIPN-1 | 0.9 |
|
0.99 | 0.09 | 0.49 | 0.860 |
SIPN-2 | 0.9 |
|
0.99 | 0.09 | 0.49 | 0.860 |
SIPN-3 | 0.9 |
|
0.99 | 0.09 | 0.49 | 0.860 |
SIPN-4 | 0.9 |
|
0.99 | 0.09 | 0.49 | 0.860 |
SIPN-5 | 0.9 | 0.10 |
|
0.09 | 0.49 | 0.860 |
SIPN-6 | 0.9 | 0.10 |
|
0.09 | 0.49 | 0.860 |
SIPN-7 | 0.9 | 0.10 |
|
0.09 | 0.49 | 0.860 |
SIPN-8 | 0.9 | 0.10 |
|
0.09 | 0.49 | 0.860 |
SIPN-9 | 0.9 | 0.10 | 0.99 |
|
0.49 | 0.860 |
SIPN-10 | 0.9 | 0.10 | 0.99 |
|
0.49 | 0.860 |
SIPN-11 | 0.9 | 0.10 | 0.99 |
|
0.49 | 0.860 |
SIPN-12 | 0.9 | 0.10 | 0.99 |
|
0.49 | 0.860 |
The loading of silver nanoparticles into the hydrogel networks has been performed using the following procedure. Accurately weighed dried copolymeric hydrogels were swelled in double distilled water for 3 days. These swollen copolymeric hydrogels were then transferred into another beaker containing 50 mL of aqueous 5 mM AgNO3 solution and then allowed to equilibrating the hydrogel for 24 hours to absorb the silver salt. During this process, most of the silver ions were loaded into free-network spaces of hydrogel. These hydrogels with absorbed silver ions were finally transferred into a beaker containing 50 mL of 10 mM NaBH4 aqueous solution and kept for 2 hours to reduce the silver ions into silver nanoparticles. After reduction of silver ions, the hydrogel was turned into brown colour, which confirms the formation of silver nanoparticles in copolymeric hydrogel matrix as shown in Scheme
Schematic representation of formation of Ag nanoparticles in the polymeric network.
Fully dried semiIPN hydrogels, silver nanocomposite hydrogels were accurately weighed and equilibrated in distilled water at 37°C for 3 days. The equilibrium swelling capacity or swelling ratio (
UV-visible spectra of semiIPN hydrogel silver nanocomposites (10 mg in 1 mL of distilled H2O) were characterized using (Lab India UV 3000+) UV-Visible spectrophotometer; X-ray diffraction measurements were also carried out for these nanocomposites using A Siemens D 5000 (Germany) Powder X-ray diffractometer to know the crystallinity of the hydrogel. Thermal properties of semiIPN hydrogels were evaluated by using SDT-Q600 thermal system at heating rage of 10°C/min under N2 atmosphere (flow rate 100 mL/min). Morphological variations of dry hydrogel, silver nanocomposite hydrogel were studied using JSM 6400 Scanning Electron Microscope (SEM) (Japan), operating at an acceleration voltage of 15 K volts coating with a thin layer of palladium gold alloy. Particle size of silver nanoparticles was performed out by using a Tecnai F 12 Transmission Electron Microscope (TEM) operating at an acceleration voltage of 15 kV.
In this study, acryl amide and AMPS were copolymerized in the presence of NaCMC to obtain NaCMC/poly (AAm-co-AMPS) semi-IPN hydrogels, where the NaCMC chains are randomly distributed throughout the gel networks. The special interest in choosing NaCMC as an interpenetrating polymer in hydrogels is due to its viscosity increasing, binding, protecting, reducing, stabilizing, and disintegration properties [
Figure
Swelling behavior of semiIPN pure hydrogels and silver nanocomposite hydrogels of various formulations.
The effect of crosslinker concentration on the swelling behavior of semi-IPN hydrogels was studied by varying the amount of crosslinker content 0.02–0.12 gm. In Figure
Generally in silver nanoparticles the conduction band and valence band lie very close to each other in which electrons move freely. These free electrons gives rise to a surface plasmon resonance (SPR) absorption band [
UV-visible spectral analysis of pure hydrogel, hydrogel loaded with AgNO3 before reduction, and silver nanocomposite hydrogels.
The semi-IPN silver nanocomposite hydrogels are characterized by thermogravimetrical analysis to determine the percentage of weight loss of pure hydrogel as well as silver nanoparticles in the hydrogel matrix. Figure
Thermogravimetric analysis of pure hydrogel and silver nanocomposite hydrogel.
The crystallographic nature of the silver nanoparticles in hydrogels was investigated by X-ray diffraction. The X-ray diffraction of pure and silver nanocomposite semi-IPN hydrogels was illustrated in Figure
X-ray diffraction pattern of pure hydrogel and silver nanocomposite hydrogel.
The scanning electron micrographs of pure hydrogel and silver nanocomposite hydrogels were shown in Figure
SEM images of pure hydrogels (a) and (b), silver nanocomposite hydrogels (c) and (d).
TEM image demonstrates a highly uniform distribution of silver nanoparticles (20 nm) as shown in Figure
TEM image of silver nanocomposite hydrogel.
In this study the bacterial effect of silver nanocomposite hydrogels mostly depends on the size of particles and the swelling ratio, which have a direct interaction with the bacteria. Antibacterial studies of pure semi-IPN hydrogel and silver nanocomposite hydrogels were tested by paper disc method using
Antibacterial activity of silver nanocomposite hydrogels.
The inhibition area follows the order SIPN-4 > SIPN-3 > SIPN-2 > SIPN-1. This behavior is expected for silver nanoparticles of small sizes (1–20 nm) and the same order is expected for swelling ratio. So that these silver nanoparticles could come out easily and could interact with lipid layer of cell membrane, thereby attaching to microbial DNA to prevent bacterial replication, which are responsible for inhibition of bacterial growth.
NaCMC/poly (AAm-co-AMPS) semi-IPN silver nanocomposite hydrogels were successfully prepared via a free radical polymerization along with varying doses of polymer, comonomer, and crosslinking agent thereby reduction of silver ions into silver nanoparticles. The developed silver nanoparticles are well characterized by using different techniques to confirm the formation of silver nanoparticles and antibacterial activity on
The authors (A. C. Babu and K. C. Rao) gratefully acknowledge the support by the Defence Research and Development Organization (DRDO) (Sanction letter no. ERIP/ER/1003839 M/1341, dated June 28, 2011) and Ministry of Defense, Government of India, New Delhi, for the financial support.