Researchers at Shanghai University's Rapid Manufacturing
Engineering Center have developed a vascular graft composed of three layers by
combining micro-imprinting and electro-spinning techniques.
This tri-layered composite has allowed scientists to utilize
separate materials that respectively possess mechanical strength and promote
new cell growth - an important problem for existing vascular grafts that have
only consisted of a single or double layer.
Vascular grafts are
surgically attached to an obstructed or otherwise unhealthy blood vessel to
permanently redirect blood flow. Traditional grafts work by repurposing
existing vessels from the patient's own body or from a suitable donor. But,
these sources are often not sufficient for a patient's requirements because of
the limited supply in a patient's body, and may be afflicted by the same
underlying conditions that necessitate the graft in the first place.
There has been a
great deal of research towards developing synthetic vessels that can mimic
natural ones, allowing new cells to grow around them and then degrade away,
thereby creating new vessels.
Yuanyuan Liu, an
associate professor at the Rapid Manufacturing Engineering Center said that the
composite vascular grafts could be better candidates for blood vessel repair.
Liu's team had previously worked with bone scaffolds, which are used to repair
bone defects, before turning their attention to cardiovascular disease, and
thus vascular grafts.
They describe their
current research in the journal AIP
from AIP Publishing.
As a rule, surrogate
scaffolds need to mimic the natural vasculature of their targeted tissue as
much as possible.
For blood vessel
surrogates, this structural mimicry can be fabricated by electrospinning, a
process which uses an electrical charge to draw liquid inputs - here a mixture
of chitosan and polyvinyl alcohol - into incredibly fine fibers.
allows for a high surface-to-volume ratio of nanofibers, providing ample space
for host cells to grow and connect. These components all naturally degrade
within six months to a year, leaving behind a new, intact blood vessel.
structure, however, isn't very rigid - the fly in the ointment for many
previous models. To compensate for this, the researchers designed a three-layer
model, in which the mixture was electrospun onto both sides of a microimprinted
middle layer of poly-p-dioxanone, a biodegradable polymer commonly used in
biomedical applications. The ends of this sheet were then folded and attached
to make a tube-like vessel.
Liu and her team
then seeded the scaffold with rat fibroblast cells, which are ideal candidates
because of their ease of cultivation and quick growth rate, to test the
scaffold's efficacy in promoting cellular expansion and integration. The
researchers found that the cells on these composite scaffolds proliferated
quickly, likely due to the functional amino and hydroxyl groups introduced by
While a good deal of
work remains before the prospect of human trials, Liu and her group are
optimistic about the future of their research. Their next project is to test
the implants in an animal model, to observe the structure's efficacy with live