Researchers at Purdue
University, the University of Alberta and Canada's
National Institute for Nanotechnology have discovered
that bone cells called osteoblasts attach better to
nanotube-coated titanium than they do to conventional
titanium used to make artificial joints.
"We have demonstrated
the same improved bone-cell adhesion with other materials,
but these nanotubes are especially promising for biomedical
applications because we'll probably be able to tailor
them for specific parts of the body," said Thomas
Webster, an assistant professor of biomedical engineering
Findings are detailed
in a paper appearing in the April issue of Nanotechnology,
published by the Institute of Physics in the United
Kingdom. The paper was written by Purdue biomedical
engineering doctoral student Ai Lin Chun, Purdue chemistry
doctoral student Jesus G. Moralez, Webster and Hicham
Fenniri, a professor of chemistry at the University
of Alberta and senior research officer at the Canadian
nanotechnology institute, where Chun and Moralez are
doctoral students as well.
nanotubes were developed by Fenniri while he was an
assistant professor at Purdue.
Webster has shown
in a series of experiments that bone cells and cells
from other parts of the body attach better to various
materials that possess surface bumps about as wide
as 100 nanometers, or billionths of a meter.
used in artificial joints has surface features on
the scale of microns, or millionths of a meter, causing
the body to recognize them as foreign and prompting
a rejection response. The body's rejection response
eventually weakens the attachment of the implants
and causes them to become loose and painful, requiring
bumps mimic surface features of proteins and natural
tissues, not only prompting cells to stick better
but promoting the growth of new cells. Bone and other
tissues adhere to artificial body parts by growing
new cells that attach to the implants, so the experiments
offer hope in developing longer lasting and more natural
implants, Webster said.
Now researchers have
discovered that the self-assembling nanotubes represent
an entirely new and potentially superior material
to use for artificial body parts.
Fenniri created the
self-assembling structures by using the chemistry
of deoxyribonucleic acid, or DNA, to make a series
of molecules that are "programmed" to link
in groups of six to form tiny rosette-shaped rings.
Numerous rings then combine to create the rod-like
nanotubes, which have widths of only about 3.5 nanometers.
"He had these
nice nanotubes, and I had this work that showed nice
bone synthesis and other tissue regeneration on nanomaterials,
so we said, Wouldn't it be great to actually combine
the two to see if his material can promote new bone
growth with these nanotubes?'" Webster said.
One nanometer is roughly
the length of 10 hydrogen atoms strung together. A
human hair is more than 30,000 times wider than the
rosette nanotubes used in the study.
Self-assembly is a
well-known principle in biology in which the right
mix of molecules interact on their own to form distinctive
structures ranging from DNA to cells and organs. The
rosette-shaped rings are made of guanine and cytosine,
which are molecules called "base pairs"
that come together to form DNA.
In addition to possible
biomedical applications, the nanotubes offer promise
in the design of future materials, electronic devices
and drug delivery systems.
The researchers coated
titanium with the nanotubes and placed them in Petri
plates containing a liquid suspension of bone cells
colored with a fluorescent dye. After a few hours,
the nanotube-coated titanium was washed, and a microscope
was used to count how many of the dyed osteoblasts
adhered to the material. Out of 2,500 bone cells in
the suspension, 2,300 to 2,400 were found to adhere
to the nanotube-coated metal. That compares with about
1,500 cells adhering to titanium not coated with the
nanotubes, representing an increase of about one-third.
The quick attachment
of bone cells is critical to create a solid bond between
orthopedic implants and the body's natural bone. The
same applies to artificial parts transplanted in other
parts of the body, such as arteries and the brain.
"The reason we
are so excited is that we see improved osteoblast
function on the coated titanium compared to the plain
titanium," Webster said.
Webster has found
similar results with other materials that possess
the nano-scale surface bumps, such as ceramics, metals
and nanotubes made of carbon. The rosette nanotubes,
however, may provide a major advantage over those
materials, he said.
such as "signaling peptides," or amino acids,
such as lysine and arginine, can be easily attached
to the surface of the nanotubes, making it feasible
to tailor the nanotubes so that they are recognized
by specific cells and body parts.
"There are definite
amino acid sequences that bone cells recognize and
stick to," Webster said. "One of those sequences
is arginine, glycine and aspartic acid. There is a
lot of work in the field now to incorporate this sequence
"One of the other
reasons we were so excited about this is that we can
put this sequence on these tubes."
Attaching the sequence
of amino acids onto the nanotubes will likely increase
osteoblast adhesion even more, Webster said.
Various parts of the
body recognize and attach to different sequences.
"I think this
really points to strong biomedical applications,"
Webster said. "If the cells you are targeting
respond to protein sequence XYZ, you just put that
sequence on the nanotubes and you can promote this
Another finding in
the research is that low concentrations of the nanotubes
provide the same results as higher concentrations.
"That means you
can use very low concentrations of this and still
get statistically higher bone-cell attachment,"
Webster said. "So it's cheap. You don't need
a lot of it to get the effect that you want."
Unlike other nano-scale
materials Webster has worked with, the rosette nanotubes
automatically arrange themselves into a webbed pattern
on the surface of the titanium. The pattern resembles
those seen by natural collagen fibers in bones and
Future work will focus
on further modifying the nanotubes and conducting
The need for better
technology is growing as more artificial body parts
are used, Webster said.
For example, about
152,000 hip replacement surgeries were performed in
the United States in 2000, representing a 33 percent
increase from 1990. The number of hip replacements
by 2030 is expected to grow to 272,000 in this country
alone because of aging baby boomers.
The research has been
funded by the National Science Foundation, American
Chemical Society, Purdue Research Foundation, Whitaker
Foundation, 3M Co. and Canada's National Institute
Writer: Emil Venere, (765) 494-4709, firstname.lastname@example.org
Sources: Thomas Webster, (765) 496-7516, email@example.com
Hicham Fenniri, (780)
Related Web sites:
Hicham Fenniri: http://www.chem.ualberta.ca/faculty/fenniri.htm
Previous releases about Thomas Webster's work:
Helical rosette nanotubes:
a more effective orthopedic implant material
Ai Lin Chun1, Jesus
G. Moralez2, Hicham Fenniri2 and Thomas J. Webster1
1 Department of Biomedical
Engineering, Purdue Universit
2 National Institute
for Nanotechnology and Department of Chemistry,
National Research Council and the University of Alberta