In this case, the polymer presented controlled amounts of an engineered protein that mimics fibronectin, a protein in the body that acts as a binding site for cell surface receptors called integrins.
It is important to control the integrins binding to the titanium implant because integrins provide signals that direct bone formation. Therefore, controlling integrin binding to the titanium will result in targeted signals that enhance bone formation around the implant.
To bind integrins to titanium, researchers previously coated titanium with a small biological signal containing the sequence arginine-glycine-aspartic acid (RGD) that binds to integrins. However, this region alone binds many different integrin receptors and with much less affinity than the full fibronectin protein.
"It has been common to mimic only very small sections of fibronectin, but when you take a small section and ignore the rest of the molecule you lose specificity and activity, and therefore signaling is impaired," said Garca.
For that reason, Garca engineered a much longer region of the same type of fibronectin that included the RGD peptide sequence as well as new sections also known to have sites that participate in integrin binding.
To evaluate the in vivo performance of the coated titanium in bone healing, chemists Raynor and Collard coated the surfaces of tiny clinical-grade titanium cylinders with the polymer brushes. Then engineers Petrie and Garca modified them with peptide sequences.
Two-millimeter circular defects were drilled into a rat's tibia bone and the cylinders were pressed into the holes. They tested three types of coatings: uncoated titanium, titanium coated with the RGD peptide and titanium coated with different densities of the engineered fibronectin fragment.
To investigate the function of these novel surfaces in promoting bone growth, the researchers quantified osseointegration, or
|Contact: Abby Vogel|
Georgia Institute of Technology Research News