Bodyhacking

Research at the Georgia Institute of Technology shows that coating titanium joint-replacement implants with clusters of a biologically inspired material could strengthen the connection between the implant and a patients' own bone. Image credit: Gary Meek, Georgia Tech


Researchers at Georgia Tech have developed a coating technique that could strengthen the connection between titanium joint-replacement implants and a patients’ own bone. The connection, created by manipulating signals the body’s cells use to encourage growth, could extend the lifespan of implants.

Implants coated with “flower bouquet” clusters of an engineered protein that mimics the body’s own cell-adhesion material fibronectin made 50% more contact with the surrounding bone than implants coated with protein pairs or individual strands. The cluster-coated implants were fixed in place more than twice as securely as plugs made from bare titanium, which is how joints are currently attached.

Researchers believe the biologically-inspired material improves bone growth around the implant and strengthens the attachment and integration of the implant to the bone. This work also shows for the first time that biomaterials presenting biological sequences clustered together at the nanoscale enhance cell adhesion signals. These enhanced signals result in higher levels of bone cell differentiation in human stem cells and promote better integration of biomaterial implants into bone.

“By clustering the engineered fibronectin pieces together, we were able to create an amplified signal for attracting integrins, receptors that attached to the fibronectin and directed and enhanced bone formation around the implant,” says Andrés García, professor at Georgia Tech.

Total knee and hip replacements typically last about 15 years until the components wear down or loosen. For many patients, this means a second surgery to replace the first artificial joint.

In this study, Georgia Tech professor David Collard and his students coated clinical-grade titanium with a high density of polymer strands, akin to the bristles on a toothbrush. Then, García and Tim Petrie, formerly a graduate student at Georgia Tech and currently a postdoctoral fellow at the University of Washington, modified the polymer to create three or five self-assembled tethered clusters of the engineered fibronectin, which contained the arginine-glycine-aspartic acid (RGD) sequence to which integrins binds.

Georgia Tech research technician Kellie Templeman (left) and former graduate student Tim Petrie display a piece of titanium coated with a bio-inspired polymer that enhances bone formation around the metal after implantation. Image credit: Gary Meek, Georgia Tech


To evaluate the in vivo performance of the coated titanium in bone healing, the researchers drilled two-millimeter circular holes into a rat’s tibia bone and pressed tiny clinical-grade titanium cylinders into the holes. The research team tested coatings that included individual strands, pairs, three-strand clusters and five-strand clusters of the engineered fibronectin protein.

“To investigate the function of these surfaces in promoting bone growth, we quantified osseointegration, or the growth of bone around the implant and strength of the attachment of the implant to the bone,” explains García, who is also a Woodruff Faculty Fellow at Georgia Tech.

Analysis of the bone-implant interface four weeks later revealed a 50% enhancement in the amount of contact between the bone and implants coated with three- or five-strand tethered clusters compared to implants coated with single strands. The experiments also revealed a 75% increase in the contact of the three- and five-strand clusters compared to the current clinical standard for replacement-joint implants, which is uncoated titanium.

The researchers also tested the fixation of the implants by measuring the amount of force required to pull the implants out of the bone. Implants coated with three- and five-strand tethered clusters of the engineered fibronectin fragment displayed 250% higher mechanical fixation over the individual strand and pairs coatings and a 400% improvement compared to the unmodified polymer coating. The three- and five-cluster coatings also exhibited a twofold enhancement in pullout strength compared to uncoated titanium.

More information on the research is available from Georgia Tech.

For other posts on coating-related breakthroughs covered on medtechinsider, see also:
Swiss Researchers Discover Why Implant Coatings Detach
Extracellular Matrix Improves Device Biocompatibility
Laser-Deposited Coating Imparts Bone-Like Attributes to Implants




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