Growing fresh blood vessels is a much fantasized goal of biomedical engineers. It’s probably also a fantasy of dialysis patients, hemophiliacs and others with medical conditions that necessitate regular venipuncture and whose veins are a mess from being breached several times a week.
To date, most approaches for growing blood vessels have involved coaxing human cells, either from donors or the patient themselves to manufacture connective tissue. One of the biggest challenges however has been to make the tissues develop into vein shaped vessels. Some researchers have started with flat sheets of this tissue which they then roll into tubes. Others have used tubular molds. Typically, however, the scaffolding is eventually destroyed by the body’s immune system.
Now one company – Cytograft Tissue Engineering, is trying a technique that made us look twice. They’re weaving the vessels from human thread that’s been created by spinning thin strips of cultured connective tissue.
The hope is that these woven structures could be easier to mass-produce than the tubes made with other techniques.
“A long time ago we decided we were going to make strong tissues without any scaffolding,” says Nicolas L’Heureux, Cytograft’s cofounder and chief scientific officer. “Once you get it in the body, your body doesn’t see it as foreign.”
The company developed the “human textile” idea from earlier work using sheets of biological material to reconstruct blood vessels. Researchers grow the human skin cells in a flask under conditions that encourage the cells to lay down a sheet of extracellular matrix – a structural material that makes up connective tissue. They then harvest the sheets from the culture flasks and then slice the sheets into thin ribbons that can be spooled into threads which can be used by automated weaving and braiding machines to create three-dimensional structures that do not require fusing.
Weaving 48 strands of human connective tissue into a tube
“Creating textiles is an ancient and powerful technique, and combining it with biomaterials is exciting because it has so much more versatility than the sheet method,” says Christopher Breuer, a surgeon, scientist, and tissue engineer at the Yale School of Medicine. “The notion of making blood vessels or more complex shapes like heart valves, or patches for the heart, is much easier to do with fibers. There is no limit to the size or shapes that you can make.”
In other words, the biological strands could be used to weave blood vessels, patches and grafts that a patient’s body would readily accept for almost any kind of wound repair or reconstruction.
Cytograft has not yet tested its woven blood vessels in humans, but preclinical dog work has shown that the grafts are resistant to puncture damage and that very little blood leaks from the weave.
Furthermore, the implants remain intact after months. That’s partly because Cytograft’s implants contain no cells. Though the company’s earlier implants were made of extracellular matrix produced from a patient’s own cells, they now harvest the material from cells unrelated to the person receiving the graft and remove the “donor” cells completely. Without any foreign cells to trigger an immune response blood vessels can be produced ahead of time for use in any patient.
The company is also working on a technique in which the cell-produced sheets are processed into particles instead of threads. Molding the particles together could eventually produce a liver, pancreas, or kidney.
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