R&D DIGEST

This mesh and stent device holds microcapsules of therapeutic cells. Researchers hope it will increase the safety of long-term implants.

A biomedical design contest at The
Johns Hopkins University (Baltimore)
sparked the development of a
pouch that enables cellular therapy
with the potential to treat a range of
diseases. The nylon mesh device holds
microcapsules of therapeutic cells
while allowing blood and oxygen to
flow freely through the pouch. It is designed
to stay in the body for life.

The project began when two professors
at Johns Hopkins, Aravind
Arepally, MD, and Jeff Bulte, PhD, developed
microcapsules for cellular therapy.
They needed to figure out a way to
deliver the capsules into a blood vessel
without obstructing the patient's
bloodstream.

Their requirements included a device
that could keep the encapsulated cells
alive while inside the body. Undergraduate
students decided to take on
the challenge as part of the university's
biodesign contest and created the
innovative pouch to house the cells.

The entire system consists of two
stents, a pouch, and the microcapsules.
The pouch is made of nylon mesh,
which is laser welded onto the stents.
Its 250-μm mesh openings are just
large enough to allow blood flow but
small enough to keep the microcapsules
inside.

According to Arepally, one of the
problems with current cell therapy is
that doctors can't see exactly where the
therapeutic cells are going, so they
can't monitor them and thus have no
control over them.

One of the novelties of the device is
that a doctor can go into the pouch,
remove the old capsules, and deliver
new capsules to replenish the system. A
chemical within the capsules also lets
researchers monitor the cells' location
and oxygen levels via magnetic resonance
imaging.

As a treatment for diabetes, for example,
the pouch fits inside the portal vein, a large blood vessel in the liver. A
surgeon would use catheters to insert
the compressible pouch through the
femoral vein and into the abdomen.
The pouch, as it sits between the two
stents, is filled with the microcapsules
that provide cellular therapy.

“We're taking some normal vasculature,
an artery or vein, and we're
able to part the vein by stretching it
beyond its limits to create an extra
space to house these capsules,” says
Arepally, assistant professor of radiology
and surgery at Johns Hopkins
School of Medicine.

He adds that this is possible because
of a blood vessel's flexibility,
or compliance. “The design incorporates
that compliance to stretch it a
little bit more and use the space between
the two stents to deliver cells.”

One stent is made of stainless steel,
and the other is nitinol. Eventually,
says Arepally, both will be nitinol. “We
have to change how the stents are manufactured
to incorporate them in the
pouch design, because there currently
aren't any stents that do this,” adds
Arepally. He plans on working with
device firms to create a new nitinol
stent, which could be the most challenging
design aspect thus far.

The prototypes' diameter size is
12–14 mm, but the device will need to
be 16–18 mm for human use.

The team has already demonstrated
that the microcapsules can deliver live
cells that survive. They've filed a provisional
patent on that technology, and
the next stage will be long-term animal
testing.