While titanium hip and knee implants have restored mobility to many people, they are still subject to failure. A new alloy could help change that by adding some flexible, bacteria-killing gallium to the mix.
Regardless of whether the implant is a hip or knee replacement, there is a distinct boundary where the titanium device meets the patient’s natural bone tissue. If bacteria colonize at that interface on the surface of the implant, an infection can occur that will cause the bone/implant connection to deteriorate. When this occurs, a second surgery will be required.
Another potential problem is that the most common type of titanium used for implants, Ti-6Al-4V, is harder than bone. This means that the implant does not flex as well as the bone it is connected to, and stress is concentrated at the interface between the two. This can not only cause the connection to fail over time, but can also be a source of pain for the patient.
In an effort to address both of these issues, scientists from Flinders University in Australia recently added gallium (Ga) to Ti-6Al-4V. Not only is the metal known to have antibacterial properties, it is also more flexible than titanium (Ti).
But the researchers added only a little gallium. One of the Ti/Ga alloys they created contained just 3% gallium by weight, while the other had just 5%. For the purposes of the study, the samples were in the form of rods, not implants.
When exposed to Pseudomonas aeruginosa bacteria (which often infect implants) the two new alloys were found to eliminate 90% (+/- 5%) and 95% (+/- 3%) of the microbes, respectively, within a six-hour period, whereas a control sample of Ti-6Al-4V titanium killed only 3% (+/- 2%).
Importantly, the antibacterial effect of the two Ti/Ga alloys persisted after the initial six-hour “killing frenzy,” and no deleterious effects to human cells were observed over the 24-hour period.
Furthermore, when the alloys were subjected to strength testing, the 3% Ga version exhibited a Young's modulus that was 37% less than Ti-6Al-4V, while the 5% Ga version was 44% less. Young's modulus is a measure of how easily a material can be bent.
However, two new alloys weakTheir hardness, which is their ability to resist surface deformation, is slightly less than that of Ti-6Al-4V. Additional research may further increase their hardness.
“The alloys in this study showed very promising results and are part of ongoing efforts to improve components in orthopedic implants,” says Dr. Reza Hashemi, who led the study with Materials Engineering graduate student Rhianna McHendrie. “Compared to existing prosthetics, the addition of gallium produces a superior material with antibacterial properties to improve patient outcomes while reducing potential pain, medical complications, and long-term implant failure.”
A paper on the study was recently published in the journal: Journal of Functional Biomaterials.
Source: Flinders University