Silver Nanoparticle (AgNP) Technology applications in trauma and orthopaedics

Over the past decade, various innovative methods of utilizing AgNP in nanomedicine have been explored. One of the most common design has been its addition to the outer layers of implants to reduce failure rates by infection. In a study by Zhao et al., AgNP were formed and deposited in titanium nanotubes via electrochemical anodization. The nanorods not only increased the surface area for interaction, but also resulted in the production of two sizes of silver nanoparticles found, 5–10 nm within and 80 nm outside. The difference in sizes is thought to have led to an initial burst of silver ions from the smaller particles followed by a slow dispersal from the larger particles, resulting in a logarithmic release of silver over 30 days. The results demonstrated effective resistance to E. coli on exposure to the modified titanium film but also showed significant osteoblast cytotoxicity. Contrary to the cytotoxicity to osteoblasts mentioned above, a study from Chen et al demonstrated desirable pro-osteogenic effects of AgNP through regulation of M1/M2 macrophages. In their in-vivo study, the release of a concentration of 0.2 ppm AgNP over 24 h demonstrated an increase in the pro-osteogenic M2 expression of macrophages via the inhibition of glucose transporter (GLUT1) expression and promotion of autophagy. Low concentrations of silver nanoparticles resulted in greater osteogenesis and increased presence of trabeculae. Tissue engineered composite bone graft development, consisting of bone morphogenetic protein 2 (BMP-2) coupled with nano silver polylactic-co-glycolic acid (PLGA) will have significant role in osteomyelitis and infected nonunion management with the ability of controlling infection whilst promoting osteogenesis. AgNP coated external fixators pins with ability to reduce pin tract associated infection is another explored role.

Osteointegration of prosthesis used in total joint replacements and prevention of peri-prosthetic infection are key mechanisms in achieving long term, functional outcomes following arthroplasty surgery. The impact of the host response on the implant is dependent on several parameters such as surface topography and surgical technique. Titanium has been the most used material due to its tribological properties such as inertness and corrosion resistance. To reduce infection, mixture of AgNP in a nanocomposite film of tantalum oxynitride (TaON) improved the resistance to a range of bacteria, reinforcing the coating's function as a broad-spectrum antibiotic agent. The combination of the two compounds and the presence of oxygen, improved the biocompatibility of the coating resulting in an significant effect on osteogenic function. Other AgNP polymers have been experimented in promoting host reactions to implants. Through a complex multi-layered method of encapsulating AgNP within polyvinyl alcohol containers, which were evenly dispersed across a chitosan coating, Mishra et al demonstrated that not only did the coating provide good antibacterial and anti-biofilm effects, but it also promoted cellular adhesion, proliferation and improved on the mechanical qualities of the implant.