Nicolas L’Heureux: Artificial Blood Vessels That Are 100% Biological

Recipient of a European Research Council grant in 2022 for his project to develop artificial tissues in the treatment of pelvic organ prolapse, Nicolas L’Heureux, director of the Tissue Bioengineering Laboratory in Bordeaux, has worked for twenty years to design artificial vessels that are impermeable, resistant, and contain no synthetic products.

What research can be furthered? What has not yet been tried? These are the questions that Inserm research director Nicolas L’Heureux has asked himself every day for a long time, « like a game ». Which means that from very early on he had the idea of pushing the limits of vascular tissue engineering – a field in which he had begun working when doing his M.Sc. « When performing a cardiac or other type of bypass, preference is given to using the patient’s own vessels that are taken from one place and transplanted into another, more critical, one. An autologous graft continues to remain the best solution, but it is a limited resource. » Diseases such as stroke, hyperlipidemia, and thrombosis, which have the particularity of being systemic – in which they attack all vessels to varying degrees –, as well as aging, weaken our vessels. And the earlier the need for surgery, the greater the likelihood of a second intervention. « A transplanted artery will withstand an average of ten years and a vein six to seven years. » Which just leaves synthetic grafts.

But the artificial polyester, PET (Dacron®), or PTFE (Gore-Tex®) vessels are far from being the miracle solution. Although inert, these plastics are attacked in the first days that follow the operation by a hypervigilant innate immune system, hostile to the slightest intrusion of a foreign body. This results in chronic inflammation of the implanted tissues that will often lead to failure of the graft. « Inflammation at the extremities of the graft generates intimal hyperplasia, i.e. exaggerated healing of the vessels that forms at the joint between the native cells and the more rigid prosthesis, » specifies the researcher. This leads to compression of the vessel caused by thickening of the walls, turbulence phenomena, and gradual clogging of the inside of the vessel, which eventually becomes blocked. « And the smaller the diameter of the vessel, the more complicated it gets. »

« Next Generation » Artificial Vessels

L’Heureux therefore sought to circumvent this problem. At the Tissue Engineering Laboratory (LOEX) of Québec University Hospital, where he studied in 1989 and 1990, the young biologist began by replacing bovine cells (previously used as an animal model) with human cells in order to increase the tolerance level of the immune system. Then he reviewed the composition of the collagen gels that were used in the development of vascular grafts, adapting it to the vessels’ mechanical constraints. This gel was typically obtained by solubilizing the collagen and re-precipitating it in order to pour it into the shape of the tissue concerned. The result was a type of aspic. « The problem is that it tears and melts as soon as you handle it. » In search of a solution, the student used a freeze-drying technique that enabled him to compress the collagen, treat it to increase its density, and even roll it to form a tube around which he would be able to graft living cells.

And it was then that things took a radical turn, with L’Heureux deciding to leave a flask of cells to mature for two weeks in culture in an incubator, just to see what would happen. « In some laboratories, it is often a challenge to keep cell cultures sterile for several weeks. I wanted to know what would form and at LOEX it was not a problem. After a few adjustments, the experiment eventually produced homogeneous and relatively thick sheets of matrix. Today, this technique is routine and requires no antibiotics.  »

And what happened was surprising. Floating at the bottom of the flask was a sheet of cells and its extracellular matrix that were connected and contracting spontaneously, coming apart from the plastic backing. « For the first time, we obtained a fully biological tissue whose mechanical properties were similar to those of native tissue. I could stretch it and play with it. » By changing the cell type, L’Heureux went on to obtain a much better result, with more resistant tissue. The researcher was truly onto something.

He then increased the tests, set about rolling several sheets on tubes to obtain multiple layers, which he placed in a bioreactor to fuse the layers. Before combining two cell types, fibroblasts and muscle cells, and insert into the center of the vessel a third, endothelial cells. The next-generation artificial vessel was born. « We were finally able to synthesize vessels with remarkable properties, with no exogenous support and whose mechanical resistances were equivalent to those of the arteries – our strongest vessels. » This was followed by the publication of an article in FASEB Journal, as well as several articles and patent filings. Then large-scale, long-term animal trials began in 1995 as part of a postdoctoral fellowship at the University California San Diego (UCSD).

Back to Basics

“When I arrived in the USA, it was like another world, » explains the researcher.An ultra-enterprising, positive, visionary world. Very close to industry. « Together with another UCSD student, I raised several rounds of major funding to launch the start-up Cytograft Tissue Engineering. I held on for around fifteen years with promising results, but it was not enough. The development time was just too long compared with conventional investment scenarios. » It was then that L’Heureux decided to get back to basics. Namely, return to France to take the time to further his research again before creating value from it when the time was right. He obtained ANR funding at the Tissue Bioengineering Laboratory (Biotis) in Bordeaux in 2015, followed by a European Research Council (ERC) Advanced Grant in 2018 to develop a new model and test it in animals. « I suggested cutting the sheets into threads with which we could use textile approaches. And that’s what we did. Today we have semi-automated circular looms to manufacture highly impermeable and highly resistant vessels. »

A new era was launched. And with it, the openness to new markets. Recently, the team received ERC European Proof of Concept funding for POPTex. A project that has recently begun and aims to replace the polypropylene meshes recently withdrawn from the market with biological meshes, as part of the treatment for pelvic organ prolapse, a syndrome affecting over one in two women after the age of 45.