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Human, Woven, Tissue-Engineered Blood Vessels (TEBV) Exclusively from Cell-Assembled Extracellular Matrix (CAM).

Periodic Reporting for period 2 - HUMAN TEXTILES (Human, Woven, Tissue-Engineered Blood Vessels (TEBV) Exclusively from Cell-Assembled Extracellular Matrix (CAM).)

Reporting period: 2020-05-01 to 2021-10-31

Currently, when small diameter blood vessels are obstructed, we sometimes have to replace them. The best option is to use a “less important” vessel and transplant it within the same patient. This is done, for example, when a vein from the leg is used to replace one on the heart. We also sacrifice healthy vessels to connect people with failed kidneys to a hemodialysis machine. Of course, we do not have a large supply of vessels that can be spared, and, unfortunately, these transplanted vessels most often do not last for the rest of the life of the patient. When biological vessels are not (no longer) available, surgeons use special plastic tubing. Unfortunately, the body recognizes these so-called “biomaterials” as foreign and will try to degrade them. This will cause inflammation, fibrosis, and thrombosis that can all lead to failure of the conduit. In addition, these materials can hide microorganism from the immune system and cause deadly infection. Also, these materials are very stiff compared to biological tissues and this will add to the poor ability of these synthetic grafts to work as blood vessels, especially when diameters are smaller than 5-6 mm.

With our current eating habits and more sedentary lifestyle, disease of the blood vessels (cardiovascular) is the most important cause morbidity and mortality in the richer countries. The need for hemodialysis, which linked to diabetes and hypertension, is also very important (about 2 million worldwide) and will likely increase at the population ages. Clearly, finding better blood vessel replacements would improve the life of millions.

Our approach is to produce biological vessels in the lab by using human cells in culture. This would avoid the use of synthetic materials that the body recognized as foreign while insuring an infinite supply of replacement vessels. We have previously shown that cells can lay down a sheet of material (called extracellular matrix) in the right culture conditions. We have previously shown that this cell-assembled matrix (CAM) can be used to produce vessel by rolling the sheets and that these vessels can perform well in humans. In this project, we want to create blood vessels by weaving yarn made from CAM because this will allow the production of vessels much more rapidly (so less expensively), reliably, and with better control over their properties. Our objectives are to 1) Create and characterize CAM yarn made in the lab with human and a large animal cells, 2) Test the biocompatibility (under the skin) of theses yarns in vivo (test human in an immunosuppressed rat model and the large animal yarn in the same selected large animal species), 3) Weave small diameter vessels with human and animal yarn, characterize them in vitro, and optimize their properties, and 4) Implant large animal woven vessels in the arterial circulation of the same species and evaluate their performance for up to 1 year.
We have produced yarn from human cells and have learned a lot about their mechanical properties and biological structure. We have identified sheep (ovine) as the best large animal model to produce CAM in vitro. After much development, we are now able to make ovine CAM sheets that are as strong as human ones. As a results, we have also learned how to make various types of yarn from ovine CAM. We have also compared the two together.
We have developed a model of subcutaneous implantation of human yarn in nude rats (immunosuppressed rats). We have shown that these rats will not reject human CAM but will degrade extracellular matrix that has been denatured. With this model, we have shown that the CAM yarn is well tolerated and is still present and largely untouched after 6 months. Similarly, ovine yarn have been implanted in the subcutaneous space of sheep. In our first experiment, we recovered yarns at 1 month but we unable to confidently identify the yarn at 3 and 6 months. We will redo this experiment with a different implantation strategy to better localize the yarn after long-term implantation. Initial results show that yarns are also well tolerated. We have learned to make woven vessels with human yarn and with ovine yarn. Both vessel types have promising mechanical properties. We are in the process of understanding how production parameters influence the final vessel properties in order to be able to optimize the vessels. As a transitional model, and because this is the only way to test human vessels in vivo, we have implanted miniature human vessels in the aorta of nude rats to analyze their remodeling in the circulation. We have achieved 9 month implantations at this time. Finally, we are implanting a first series of ovine vessels (carotid implants) to establish this model and validate the basic woven vessel model before starting a series to evaluate long-term implantations and the performance of optimized vessels.
This is the first demonstration of fully human and biological textile production. The development of human textiles made from CAM yarn is an important step forward in the development of fully biological tissue-engineered constructs. While sheets of CAM have shown great potential, the ability to create textiles opens the door a series of new applications and demonstrated that we can use textile assembly methods which are faster, cheaper, more versatile, and automatable. This project is focused on blood vessels but the principle of textile-based CAM assembly has multiple applications. Because it will avoid the presence of synthetic biomaterials, this approach can replace many medical textiles in applications where inflammation is a problem. This is also the first demonstration of a large animal models CAM production that is similar to that of human CAM and creates a fantastic animal model to validate CAM-based products at a scale that is clinically relevant. Upcoming results will proved information on the in vivo durability and remodeling of the CAM in general but also information on the performance of this new generation of blood vessels produced in the lab.