Tissue Engineering of Blood Vessels and Other Tissue

Tissue engineering is beginning to yield some useful products. Using skin tissue, scientists and bio-engineers can grow blood vessels for replacement and bypass surgeries.

From a snippet of a patient’s skin, researchers have grown blood vessels in a laboratory and then implanted them to restore blood flow around the patient’s damaged arteries and veins.

It is the first time blood vessels created entirely from a patient’s own tissues have been used for this purpose, the researchers report in the current issue of The New England Journal of Medicine.

Cytograft Tissue Engineering of Novato, Calif., made the vessels, in a process that takes six to nine months. Because they are derived from patients’ own cells, they eliminate the need for antirejection drugs. And because they are devoid of any synthetic materials or a scaffolding, they avoid complications from inflammatory reactions.

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Better scaffolds for growing tissues in the lab are being developed. The gel scaffold pictured above incorporates microchannels for nutrient fluid supply to the growing tissues--an artificial "blood" vessel.

The researchers have engineered tiny channels within a water-based gel that mimic a vascular system at the cellular scale and can supply oxygen, essential nutrients and growth factors to feed individual cells. The so-called gel scaffold can hold tens of millions of living cells per milliliter in a 3-D arrangement, such as in the shape of a knee meniscus, to create a template for tissue to form.

In theory, the system could accommodate many kinds of tissue.

"A significant impediment to building engineered tissues is that you can't feed the core," said Abraham Stroock, Cornell assistant professor of chemical and biomolecular engineering and one of the paper's senior authors. "Simply embedding this mimic of a microvascular system allows you to maintain the core of the tissue during culture." Gel scaffolds, he said, "are the culture flasks of the future."

The embedded microchannels allow fluid with oxygen, sugar and proteins to travel through the system. The researchers can control the distributions of these solutes over both time and space within the developing tissue, allowing the fine-tuning of the biochemical environment of the cells while the tissue develops. For example, the tissue may need to develop into bone on one side and cartilage on the other. Now the researchers can supply the right nutrients and proteins to certain parts of the growing tissue to ensure an intended outcome.

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As scientists and bio-engineers learn to mimic normal in vivo tissue growth processes in the lab, we will have more and better tissue and organ replacements available for transplant and regenerative purposes. Eventually, we will be able to grow better tissues and organs than the originals. Tissues more resistant to wear and degradation. Stronger muscles. More efficient nerves that are resistant to degenerative influences. Blood vessels that resist occlusive processes. Bones less prone to breaking etc.