Silver nanoparticles doped carbon nanotube–hydroxyapatite composites: biocompatibility and antibacterial property investigation.
Objectives: To study the antibacterial effect of hydroxyapatite composites reinforced with silver nanoparticles (AgNPs) decorated Carbon nanotubes (CNTs) against Staphylococcus aureus and its biocompatibility with human osteoblast cells.
Methods: The reduction of silver nitrate in the presence of pristine and functionalised CNTs produced CNTs decorated with AgNPs. HA was then synthesised in the presence of AgNPs-CNTs following the wet sol-gel technique. The AgNPs-CNTs-HA powders were mixed with Polyvinyl alcohol (1:1 ratio) to obtain the final AgNPs-CNTs-HA composites. Antibacterial activity was investigated by testing the composites- AgNPs-p-CNTs-HA and AgNPs-f-CNTs-HA (n=9/treatment) against S. aureus for 24 h which was assessed in broth and on the surface of the composites by determining lactate production, the percentage of live/ dead cells and SEM observations. Biocompatibility was examined by differentiating human osteoblast cells in the presence of the composites (n=19/treatment) for 21 days. RT-qPCR was performed for genes that code differentiation (ALP, Osteocalcin (OC), RUNX-2) on day 7 and 21. LDH, ALP and protein assay along with SEM observations were also performed.
Results: Bacterial growth on the composites was reduced by 70.13 % and 87.37 % for AgNPs-p-CNTs-HA and AgNPs-f-CNTs-HA respectively compared to the control. The genes were expressed on both the days indicating that the osteoblast cells were able to proliferate and differentiate. They were upregulated (5.85 - ALP, 7.80 - OC, 1.04 - RUNX-2 fold change) on day 7 but downregulated (12.78 – ALP, 7.25 – OC, 8.42 - RUNX -2 fold change) on day 21. SEM observations showed mineralized nodule formation of the osteoblasts on the composite surface. Protein content, ALP and LDH was higher on day 21 than day 7. Slow AgNPs release was observed on both the days with a maximum release of 90 nmol/mg cell homogenate protein.
Conclusions: The results show that the composites greatly reduce bacterial activity without compromising biocompatibility.