Development of CMC hydrogels loaded with silver nano-particles for medical applications
Introduction
Superabsorbent hydrogels are three-dimensional crosslinked hydrophilic, linear or branched polymers. They have the ability to absorb large quantities of water, saline or physiological solutions compared with general absorbing materials (Pourjavadi et al., 2008, Pourjavadi et al., 2004). Hydrogel networks can be formed by conventional crosslinking methods or free-radical polymerization processes. The latter are initiated by thermal and redox systems or by the use of free-radical initiators activated by irradiation in the form of E-beams, microwaves, X-rays, or light (including UV, visible, or near infrared light) (Abdel-Aal, Gad, & Dessouki, 2006). The excellent hydrophilic properties of hydrogels along with their high swelling ratio, and biocompatibility, promote their usage widely in agriculture (Ibrahim, El Salmawi, & Zahran, 2007), biomedical area as antibacterial materials (Murthy, Mohan, Varaprasad, Sreedhar, & Raju, 2008), tissue engineering (Kim et al., 2008), biosensors (Adhikari and Majumdar, 2004, Pourjavadi et al., 2007), sorbents for the removal of heavy metals (Guilherme et al., 2007) and drug delivery (Rodriguez et al., 2003, Zhang et al., 2002).
Sodium carboxymethyl cellulose (CMC) is biocompatible and biodegradable polymer. It is, therefore, often used in the biomedical field (Chang, Duan, Cai, & Zhang, 2010). Recently, much research and development efforts have been devoted to the production of hydrogels containing metal nano-particles which are highly suitable for biomedical applications (Thomas, Namdeo, Mohan, Bajpai, & Bajpai, 2008). Particularly, nanosilver based wound dressings have received approval for clinical applications but dermal toxicity is reported (AshaRani, KahMun, Hande, & Valiyaveettil, 2009). That is why combination of a gel system with silver nano-particles will be a better choice for the treatment of wounds. A gel system in a form such as three-dimensional gel (nano, micro, and hydrogel) networks are quite appropriate for the in situ production of silver nano-particles than most of the conventional non-aqueous or polymers based synthetic approaches (Mohan et al., 2010).
Silver-based nanostructure materials have gained much attention to control infections (Rai, Yadav, & Gade, 2009). The use of silver nano-particles (Ag-NPs) have exhibited improved antibacterial properties than bulk silver due to high surface area and high fraction of surface atoms, leading to incorporating more NPs inside the bacteria and promoting its efficacy in a sustained manner (Bajpai, Mohan, Bajpai, Tankhiwale, & Thomas, 2007). The main advantage of Ag-NPs is that even nanomolar concentrations are effective than micro molar concentration of silver ions (Kong & Jang, 2008). In addition, Ag-NPs have proven relatively nontoxic to human cells (Vimalaa, Mohana, Sivudua, Varaprasad, & Raju, 2010). Nano-particles can be incorporated into the hydrogel matrix by simply mixing the NPs with the preformed hydrogel, by adding the NPs during the gelation process or the NPs can be entrapped during the swelling of the material (Hamming et al., 2009, Haraguchi et al., 2003, Liu et al., 2006, Zhang et al., 2004).
The aim of the present work is to develop CMC hydrogel containing silver nano-particles inside the interconnecting polymer, i.e. networks of CMC hydrogel matrix. Cross linking of CMC is affected by epichlorohydrin in alkaline medium. Formation of silver nano-particles inside the hydrogel matrix is investigated.
Section snippets
Materials
Carboxymethyl cellulose (CMC) having high molecular weight (Mw = 10,000 Da), epichlorohydrin (ECH) (98%), PS Panreac Quimica SA, Barcelona, sodium hydroxide, trisodium citrate and silver nitrate were of laboratory grade chemicals.
Preparation of CMC hydrogels
Definite amount of CMC was dissolved in 1% NaOH solution with continuous mechanical stirring until a homogeneous viscous mixture was obtained then different concentrations of epichlorohydrin (1–10% based on weight of bath) was added drop wise with continuous stirring. The
Mechanism of CMC hydrogel post loaded with silver nano-particles
Carboxymethyl cellulose (CMC) was converted to hydrogel using epichlorohydrin (ECH) as a cross linking agent under aqueous alkaline conditions. The proposed reaction mechanism of cross linking of CMC with ECH is illustrated in Scheme 1 (Yang, Fu, Liu, Zhou, & Li, 2011). Under alkaline conditions, the hydroxyl groups of CMC become alcoholate anion. The alcoholate anion attacks the epoxy groups of ECH to form a monoether of chloropropanediol. A new epoxy group will yield by chloride displacement
Conclusion
CMC based hydrogel was successfully prepared using epichlorohydrin in alkaline medium. Also, silver nano-particles were prepared successfully using two different process: the first included synthesis of silver nano-particles inside the preformed hydrogel polymeric matrix while the in situ technique includes synthesis of silver nano-particles inside the interconnecting polymer networks of CMC hydrogel during its formation. The prepared hydrogels are characterized using swelling behavior, UV
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