Knitting with human yarn
We’ve heard about tree fibres, wool, cotton, linen, and other materials you can use to make fabrics, and we’ve gone back over 27,000 years in the process. But, looking ahead now, we’ve not yet considered making things out of our own bodies. And Nicolas L’Heureux is a Bioengineer at INSERM, in France, where he’s developed a technique to produce a “yarn” made from human tissue that can be woven, knitted or braided into new structures, like replacement repair blood vessels, as he told Chris Smith...
Nicolas - We take a small skin biopsy, and from that we can get cells. And some of these cells are specialized in building the architecture of the body, building the scaffolding of body. And we take these cells, we put them in the lab. We give them a nice little environment where they're happy and they multiply. And they work really hard at building this scaffolding that makes us strong and sturdy.
Chris - And that's actually referred to as extracellular matrix, isn't it, it's basically the cells secreting around themselves material that they then sit down in and it gives the tissue strength.
Nicolas - Exactly. It's their little house I like to call it. That's where they live. That's where they're comfortable. And this extracellular matrix, as the name says, it's outside the cells. You may have heard of the most common protein that makes up this extracellular matrix, which is collagen. It's in beauty creams and in shampoos, but it's much more useful in your body as a strength device. It's like wood on your house. And these sheets of collagen-rich extracellular matrix is what we start with. And we take these sheets that the cells nicely laid down at the bottom of the flask, where we grow them, and we get these typically 10 by 18 centimeter sheets. And from these nice sheets, we can cut ribbons. And then with the ribbons, we can use them as a yarn.
Chris - What do they look like - when you get the sheet of tissue that you then cut into these strips to use as your starting material, what does it actually look like?
Nicolas - Well, it looks a lot like a piece of paper, a little yellowish and wet. It's about the same thickness and it's probably a little stronger than a piece of paper and it is much more flexible though.
Chris - And what do you then do with it? So you've got the sheet of material. You can cut that into strips. I get that. And that would give you almost individual strands, but how do you use them?
Nicolas - So once you have a ribbon or a thread you can use the three typical textile assembly approaches, which are weaving, knitting and braiding. So we use a lot of weaving because it makes very tight constructs. As you know, you can weave a basket with vegetable fibres and be able to put water into it. So that's our favourite for making blood vessels because of course being leak-proof is quite important for blood.
Chris - We've got lots of materials that are artificial that we can knock out pretty rapidly and they work very well to do replacement parts for blood vessels. For instance, you can replace sections of someone's main body blood vessel the aorta this way, can't you? So why do we need to make things your way?
Nicolas - What really works best when you have a blocked artery is your own artery to replace it. That's what surgeons do today. They take an artery from a place where it's not critical and they transfer it somewhere else in your body where it is critical. If you run out of vessels, for example, which happens quite often because we don't have a big reserve of vessels that we don't know what to do with, the surgeons will put in plastics that are very inert chemically, but the body recognises them as foreign. And eventually the vessel will fail. It will be obstructed by the reaction of the body. What we want to do is we want to put in the same basic architecture that you find in your own vessels, and we expect the body not to see this as foreign. And in fact, we have had many studies that have shown that it is the fact it is well accepted by the host.
Chris - So are you in a stage where you've actually now made blood vessels of the sort of calibre that could be plumbed into someone's heart to bridge a blocked coronary artery, for example, and do they work at the sorts of pressures that you see in the human arterial circuit?
Nicolas - Yes, actually we have made blood vessels by weaving from 2 to about 5 millimetres in diameter, and that's exactly the right range for small vascular surgery in different places, including on the heart. And these are actually extremely strong. We probably overdid it from the engineering point of view because they are twice to three times as strong as a native artery.
Chris - And have you actually tried implanting them to see how a real living body receives them and whether it does indeed accept them?
Nicolas - So we are in the process of doing that. The problem here is that we're specializing in making human tissue. Of course, if you put human tissue into an animal for testing, it will be rejected very aggressively. So what we have been doing for a few years now is trying to make an animal tissue to be able to take this animal tissue and put it into an animal to see what's going to happen.
Chris - Of course, there's a problem with size though isn't there because the size of a mouse blood vessel is quite different to the size of a human blood vessel, and therefore what works in one might not work so well in the other.
Nicolas - Yes. And in fact, we are not attempting to do a mouse or a rat because it is very, very small. We're using sheep as our model, which have vessels that are about the size of human’s and are widely used to study vascular devices.