Bioengineers and bioscientists at Rice University and Radboud University in Nijmegen, Netherlands, have found that it is possible to grow denser bone tissue if stick-like nanoparticles are scattered throughout the porous material used to pattern the bone.
This first of its kind study has made a major impact in the burgeoning field of tissue engineering, which is a new discipline combining the latest research in materials science and biomedical engineering to produce tissues that can be transplanted without any risk of rejection.
For growing a new bone, usually tissue engineers place bone cells on porous, biodegradable materials called scaffolds, which act as patterns. By providing right chemical and physical cues, the cells can be coaxed into producing new bone. And after the degradation of the scaffold, it is replaced by 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. 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," said lead researcher Antonios Mikos, Rice's J.W. Cox Professor in Bioengineering, professor of chemical and biomolecular engineering and the director of Rice's Center for Excellence in Tissue Engineering.
While conducting their experiments, the researchers implanted two kinds of scaffolds into rabbits. Of which, one type was made of a biodegradable plastic called poly (propylene fumarate), or PPF, which gave a good performance in earlier experiments. The second was made of 99.5 percent PPF and 0.5 percent single-walled carbon nanotubes.
Nanotubes are about 80,000th the width of a hair. While their length is about thousand times their width, the researchers used shorter segments that have fared well in prior cytocompatibility studies.
Fifty percent of the samples were examined four weeks after implantation and fifty percent after 12 weeks. While there wasn't nay peculiar difference in performance at four weeks, the nanotube composites exhibited up to threefold greater bone ingrowth after 12 weeks than the PPF.
Moreover, it was found that the 12-week composite scaffolds contained about two-thirds as much bone tissue as the nearby native bone tissue, while the PPF contained only about one-fifth as much.
According to Mikos, the nanocomposites performed better than anticipated. In fact, the results indicate that they may go beyond passive guides and take an active role in promoting bone growth.
"We don't yet know the exact mechanism of this enhanced bone formation, but we have intensive studies under way to find out. It could be related to changes in surface chemistry, strength or other factors," said Mikos.
The research is available online and slated to appear in the journal Bone.