Mesh and Stent Combo Delivers Microcapsules

R&D DIGEST

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.

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