The researchers use extracellular matrix sheets to make yarn, which could then be woven (as shown here), braided, or knotted to form fabric assemblies. Credit: Nicolas L'Heureux.
A twisted thread of ECM. Credit: Nicolas L'Heureux.
The phrase “human textiles” might conjure up thoughts of a creepy fashion show or disturbing line of bed linens, but that’s not where this story is going. These textiles represent a cutting-edge research effort to create medical products from biological components that are native to the human body.From sutures that help wounds heal to grafts that bypass damaged blood vessels, textiles are invaluable and common medical tools. But there is a downside. Human immune systems often consider medical materials, especially those intended to be permanent, as foreign to the body. This can lead to inflammation and rejection.A team of researchers led by Nicolas L’Heureux at the University of Bordeaux/INSERM is working on a new kind of medical textile that they hope will fly below the immune system’s radar. In tissue engineering research published earlier this month in the journal Acta Biomaterialia, the team introduced a completely biological human yarn that can be twisted, woven, braided, or knotted to produce textiles with different properties.It all starts with human fibroblastic skin cells. Fibroblasts synthesize the ingredients of the extracellular matrix , a network of interconnected fibers that give biological tissues, like human skin, their shape and structure. In past work, L’Heureux demonstrated that fibroblasts can be cultured to produce thin sheets of an extracellular matrix in the lab that he calls a cell-assembled matrix (CAM). In this new research, they turn those sheets into yarn.“We need some sort of scaffolding if we want to create most tissue and organs, because if we use only cells, the finished product will just be a blob with no shape and strength,” explains L’Heureux. “Today, we try to use scaffolds of plastic polymers or animal tissues but the body recognizes them as foreign and will try to degrade them.”The team cultured cells for 8 weeks to produce sheets of CAM 18x10 cm2 in size. Then they used a special cutting tool to create long, thin strips. The sheets were cut either straight across or in a spiral-shaped pattern to get even more length, up to 3 meters. Twisting the strips, individually or in pairs, turned them into stronger yarn-like threads that could be dried, spooled, and store for long periods of time without damage.When the researchers examined their yarn with high-resolution microscopes, they saw a dense network of fibers and microfibers, just what you’d expect from typical human connective tissue.Different medical applications require materials with specific shapes, sizes, lifetimes, strengths, densities, and other properties. In order to see whether human yarn can accommodate some of these variations, the team turned their threads into textiles by weaving, braiding, crocheting, knitting, and knotting them.Their results show that it’s not only possible to create human textiles using these techniques, but that the process is automated for mass production. In addition, the properties of individual strands of yarn can be tuned by changing the culture time, twisting rate, and strip width; and the properties of textiles can be tuned by the choice of yarn and fabrication technique.“By combining yarns of CAM with textile technologies like weaving, knitting, braiding, etc., we can produce any shape of tissue we want with the mechanical qualities we want,” says L’Heureux. The team also showed that these textiles are compatible with living cells.To test whether the yarn could actually be used in living organisms, the team performed two animal experiments. First, a wounded rat was stitched up with a CAM thread. After two weeks, the sutures on the outside of the animal had dried up and fallen off and the wound was healing normally; after one month, things looked even better. There were no signs of inflammation. Then, using a custom loom, the team then wove 50 CAM strands into a robust, flexible vascular graft that was implanted in the carotid artery of a sheep. Blood flowed through the tube normally and without leaking.Human textiles are still a long way from clinical trials, but the results are encouraging. The next steps will involve studying how textile assemblies hold up over time, how immune systems respond to textiles produced by fibroblasts from their own species, and how implanted assemblies interact with the biological processes occurring in their environment.“What is most amazing is that we can produce very strong tissues that are entirely biological and human,” says L’Heureux. “There is still a long way to go, but we have seen that tissue-engineered skin (first used in the '80s) can become a true part of medicine and can still be improved. The field moves very slowly but the goals are very ambitious.”For more information 30 years of tissue engineering, what has been achieved? by Daniel Heath for the World Economic Forum Implants by Design: Mimicking Tissue with a New Class of Materials by Kendra Redmond for Physics Buzz