Secret Ingredient Aids Bone Growth
By B.J. AlmondFor much of his career, bioengineer Antonios Mikos has worked with porous, biodegradable materials called scaffolds, which act as patterns and support for the regrowth of bone tissue. With the right chemical and physical cues, bone cells adjacent to the scaffold can be coaxed into producing new bone. As the bone grows over the scaffold, the scaffold degrades, leaving nothing but the new bone.
“Ideally, a scaffold should be highly porous, nontoxic and biodegradable, yet strong enough to bear the structural load of the bone that will eventually replace it,” said Mikos, who is director of Rice’s Center for Excellence in Tissue Engineering. He’s also the lead researcher for a breakthrough study that found that the growing bone can be enhanced by sprinkling stick-like nanoparticles throughout the scaffolding material.
“Previous research has shown that carbon nanotubes give added strength to polymer scaffolds,” Mikos said, “but this is the first study to examine the performance of these materials in an animal model.”
The researchers implanted two kinds of scaffolds into rabbits. One type was made of a biodegradable plastic called poly(propylene fumarate) (PPF), which has performed well in previous experiments. The second was made of 99.5 percent PPF and 0.5 percent single-walled carbon nanotubes. Nanotubes usually are a thousand times longer than they are wide, but the researchers used shorter segments that have fared well in prior cytocompatibility studies.
“Previous research has shown that carbon nanotubes give added strength to polymer scaffolds, but this is the first study to examine the performance of these materials in an animal model.” —Antonios Mikos
While there was no notable difference in performance of the two materials at four weeks, the nanotube composites exhibited up to threefold greater bone ingrowth after 12 weeks. And surprisingly, at 12 weeks, the composites contained about two-thirds as much bone tissue as nearby native bone, while the straight PPF contained only about one-fifth as much.
Mikos said the results indicate that the composites may go beyond being passive guides and take an active role in promoting bone growth. The researchers don’t know why this is, though Mikos postulated that changes in surface chemistry, strength or other factors might be responsible. The team is conducting further studies to find out.
The research was funded by the National Institutes of Health, the National Science Foundation, the Welch Foundation and Rice’s J. Evans-Attwell Postdoctoral Fellows Program.
The Pressure Is On