- Silver nanoparticles embedded on clay have now been successfully dispersed inside plastic to create new antimicrobial films, filaments and can also be moulded into other plastic items. Silver nanoparticle-embedded plastics were found to have greater than 99% antibacterial activity against common bacterial pathogens like Escherchia coli and Staphylococcus aureus.
- Silver nanoparticles of about 10 nanometre size were deposited on clay particles of about 200-300 nanometre length.
- an inorganic clay found in volcanic sites called Montmorillonite was used. Silver nanoparticles have a tendency of agglomeration or clumping due to high surface area, so we provided clay as a platform for the silver to sit on.
- The clay–silver compound, containg 10% silver, was then loaded into the high density polyethylene plastic using a melt compounding method. “The clay is inorganic and highly hydrophilic, whereas our plastic is organic, hydrophobic and nonpolar. They are highly incompatible. So we use a compatibilizer, which gives the required adhesion between the two phases. Also, inside the twin screw extruder machine, the necessary speed, temperature and time gives uniform mixing and the silver-clay is well embedded inside the plastic.
Films and filaments
- They then converted the newly formed silver–clay–plastic nanocomposite into films, filaments and also moulded these into specimens and checked the antibacterial property. The films and filaments showed higher activity than the moulded ones. “In the moulded ones, we found that the antimicrobial silver was not available on the surface leading to the reduction in activity. But when the concentration of silver–clay complex was increased from 3% to 5%, the moulded ones also showed excellent activity against the two pathogens,” adds Joshi. The research team has got a U.S. patent.
- The team also tried other metal ions like zinc and copper in the place of silver. “Silver has a high reduction potential, meaning it can quickly go from silver ions to silver nanoparticles without the need of any external reducing agent. These silver nanoparticles interact with the bacterial cell wall and also generate oxidative stress inside the cell, thus killing it.
- The content of silver is very low in these nanocomposite plastic so no toxicity to human cells. Further, we checked the biocompatibility of the plastic with human skin and blood in vitro. In vivo tests are in progress and we hope that the new plastic can find a wide range of applications in the biomedical field and also in commodity items where this antimicrobial property can be an added advantage.