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Coating Technology Improves Implant Osseointegration
|Photo by Gary Meek|
As new waves of aging, active baby boomers enter their sixties each day and a rising number of younger patients require joint-replacement surgery, the need for more-durable and longer-lasting implants is becoming increasingly urgent. In an effort to address this demand, a research team at the Georgia Institute of Technology (Atlanta; www.gatech.edu) has developed a bioactive coating technology that facilitates osseointegration, which is essential for a successful and long-lasting implant.
When a synthetic material is implanted, the body reacts to the foreign substance by absorbing proteins on the device and consequently causing an inflammatory response, explains Andrés Garcia, professor at the university’s Woodruff School of Mechanical Engineering and member of the research team. To prevent this nonspecific absorption of proteins, the researchers applied a polyethylene glycol (PEG)–based polymer brush—which Garcia likens to the upright bristles on a toothbrush—to the implant. The polymer chain is then polymerized on the titanium surface in a straightforward reaction.
The researchers next introduced specific biological motifs to the nonfouling surface in order to target cellular receptors. Garcia notes that presenting biological motifs is not a novel idea; research has typically focused on an arginine-glycine-aspartic acid (RGD) adhesive sequence. However, recent data have emerged indicating that this approach is not effective in vivo.
“Our original hypothesis was that the reason these short peptides do not work in vivo is that they target the wrong receptors in the cell,” Garcia explains. “What we previously did was developed other biological motifs that have much higher specificity for the adhesion receptors. So, in addition to the coating, we then directly compare the peptide we developed to the standard in the field—which is the RGD motif. We showed that by having a more-specific peptide on this titanium surface, we can get a significant enhancement in biological function compared to surfaces that have RGD, [which] essentially didn’t do anything,” he continues. Garcia adds that the functionalized surfaces even outperformed unmodified titanium in the experiments.
The dual approach of the coating followed by the specific biological motif yielded better growth of bone around the implant and created a more-robust attachment and integration of the device to the bone, according to the researchers. Although pleased at the resulting osseointegration of the titanium implant, the team views the technology as a generalized platform. “We showed that we can [apply the technology beyond peptides] by varying the presentation of the bioactive molecule in terms of the density and the coating, and we showed corresponding differences in the osseointegration or the biological performance of the device,” Garcia says.
Although the Georgia Tech researchers used titanium to prove their hypothesis, the technology can be applied to a range of materials, among them are ceramics, glass, metal, and any material that has an oxide layer.