LAFAYETTE, Ind. – Biomedical engineers at Purdue University
have shown that "vascular stents" used to
repair arteries might perform better if their surfaces
contained "nano-bumps" that mimic tiny features
found in living tissues.
The researchers already have
shown in a series of experiments that bone and cartilage
cells in petri dishes attach better to materials that
possess smaller surface bumps than are found on conventional
materials used to make artificial joints. The smaller
features also stimulate the growth of more new bone
tissue, which is critical for the proper attachment
of artificial joints once they are implanted.
Now the biomedical engineers
have seen the same kind of increased attachment for
endothelial and vascular smooth muscle cells lining
the insides of arteries, said Thomas Webster, an associate
professor of biomedical engineering at Purdue.
The stents are small metal
scaffolds that are inserted inside arteries to prop
them open during or after surgery to remove dangerous
plaque deposits from the vessels. The stents, which
are made of titanium and other metals, enable the
arteries to grow new tissue after vessel-clogging
plaque deposits have been removed. A major problem,
however, is that the body often perceives the metal
devices as foreign invaders, hindering endothelial
cells from attaching to the scaffolding and prompting
the creation of scar tissue, which can build up inside
blood vessels and interfere with blood flow.
"If a stent doesn't attach
firmly it can become loose, and parts of it will actually
break off and go down the bloodstream," Webster
said. "Essentially, what we've been trying to
do is find new materials that cause the endothelial
cells to attach better to these stents without creating
as much dangerous scar tissue."
The researchers tested discs
of titanium containing surface bumps about as wide
as 100 nanometers – or billionths of a meter. The
metals used to make conventional stents have features
about 10 times larger or none at all. The nanometer-scale
bumps mimic surface features of proteins and natural
tissues, prompting cells to stick better, Webster
"Ideally, you want endothelial
cells to quickly attach to stents and form a coating
only one cell layer thick, which we call a monolayer,"
Webster said. "Otherwise, if the metal is not
entirely coated, blood cells passing through the repaired
artery come into contact with the metal and recognize
it as foreign."
Findings will be presented
on April 28 during the Society for Biomaterials' 2005
Annual Meeting and Exposition in Memphis, Tenn. The
work was conducted by graduate student Saba Choundhary,
Webster and Karen Haberstroh, an assistant professor
of biomedical engineering.
The researchers placed titanium
discs possessing the nano-features into petri plates
containing a suspension of endothelial cells. After
one hour, the discs were washed and a microscope was
used to count how many of the dyed cells adhered to
the material. The researchers found that nearly three
times as many cells stuck to the discs containing
the nano-bumps, as compared to ordinary titanium.
"After one hour, we get
three times more endothelial cell coverage of the
metal if it has nano- features," Webster said.
Numerous surgeries involving
stents are performed annually worldwide, with sales
of "vascular biomaterials" adding up to
more than $1 billion each year.
The research has been funded
by the National Science Foundation. Webster's lab
is affiliated with the Birck Nanotechnology Center
and the Bindley Bioscience Center, which are in Purdue's
Discovery Park, the university's hub for high-tech
Further research is planned
that will replace the titanium disks with tube-shaped
pieces of the nano-featured metal, which will resemble
the actual shape of real stents.
Writer: Emil Venere, (765)
Sources: Thomas Webster, (765)
Karen Haberstroh: (765) 496-7517,
Purdue News Service: (765)