Currently, cardiac tissue engineering is a very promising avenue in the search for new cardiovascular therapies. One of the open avenues is the generation of heart tissue patches that are implanted in the affected area to help it regain its functionality. This research field has advanced at great speed over the last two decades and has managed to cultivate cardiomyocytes and endothelial cells successfully in the laboratory. However, the plate culture technique is not able to recreate the myocardium in all its complexity, especially at the vascular level, which prevents its viability in vivo: without an extensive microvascular network that provides enough blood and nutrients, the tissue cannot mature properly, developes fibrosis and probably dies. More complex tissues can be generated with other techniques such as 3D bioprinting, since the bioprinter allows the detailed arrangement of several layers of different biomaterials along the three spatial axes.
Now, a research team in RegenBell has generated a patch of myocardial tissue by 3D bioprinting that, for the first time, can grow, mature and survive in the long term after being implanted into a host, in this case, an animal model. Until now, similar studies had achieved a two-week survival of the tissue, but it then died due to a lack of nutrients. Thanks to 3D bioprinting, the researchers have been able to place layers of small blood vessels that have allowed the correct integration with the host’s circulatory system, thus guaranteeing blood circulation throughout the implanted tissue and its survival. “We have been able to observe the myocardial patch under the microscope, record its beating correctly and see how new blood vessels had been generated,” explains Laura Casado, RegenBell researcher and co-first author of this work. Watch video.
Having obtained such positive results in animal models, the researchers are confident that, in the not too distant future, this myocardial patch could represent a new therapy for patients with cardiovascular problems. “We want to apply this myocardium patch on top of the heart affected area so that it regains functionality and beats correctly again,” explains Dr. Ángel Raya, leader of the study and coordinator of RegenBell, IDIBELL regenerative medicine program. Regarding its clinical application, Dr. Raya specifies that “To be able to bring this therapy to the first patient, we estimate that we would need about four more years of research in collaboration with other centers. We have applied for a European project but it has not been granted, so we will have to find other ways to move it forward”.
The perfect recipe: bioinks and printing technology
To make cardiac tissue via 3D bioprinting, a good protocol is essential: just as if we were making a cake, we need to find the ingredients and techniques, that is, the bioinks composition and layers arrangement, so that the tissue gets a good structure and stability. In this case, the researchers have discovered the best formula to make the myocardial patch: they put three layers of muscle bioink between two layers of vascular bioink and in a specific spatial disposition.
To begin with, they have perfected the basic recipe for bioink, which consists of four basic ingredients: gelatin, fibrinogen, hyaluronic acid and mTG. Gelatin provides the right consistency and plasticity, being very useful in bioprinting. Fibrinogen and hyaluronic acid fulfil the same function as in the extracellular matrix: they provide structure, flexibility and cell attachment. Finally, microbial transglutaminase, mTG, is an enzyme that promotes the creation of bonds between cell layers, which is essential for tissue stability once implanted in vivo. With this base, the two bioinks can be generated separately. On the one hand, for muscle bioink scientists added cardiomyocites, derived from induced pluripotent stem cells. On the other hand, the vascular bioink contains vascular microfragments extracted from the host’s adipose tissue via liposuction.
The RegenBell: cutting-edge regenerative medicine thanks to teamwork
This study is the result of four years of teamwork by the RegenBell stem cell potency group in collaboration with other groups in the same program. All of them are very satisfied with the results and recall the importance of basic research – scientific research that does not have a direct application – in order to find new therapies in the future. “Without all the prior knowledge about the myocardium and its vascularization, regenerative medicine would not have been able to take advantage of technological advances such as 3D bioprinting and clinical guidance to find new personalized treatments. In addition, studies like this also help us to understand the biology of heart tissue even better,” explains Dr. Raya.
In this study, cardiomyocytes have been obtained from induced pluripotent stem cells from the IDIBELL node of the National Cell Line Bank. In view of a potential application in humans, it is expected that the myocardial patch can be generated with immunocompatible cells and thus avoid possible immune rejection. In this sense, IDIBELL’s pluripotent stem cell therapy group is leading HAPLO-iPS, a European project that aims to create a bank of induced pluripotent stem cells that are immunocompatible with a large population portion and will provide multiple biomedical applications.
The Bellvitge Biomedical Research Institute (IDIBELL) is a research center established in 2004 specialized in cancer, neuroscience, translational medicine, and regenerative medicine. It counts on a team of more than 1.500 professionals who, from 73 research groups, publish more than 1.400 scientific articles per year. IDIBELL is participated by the Bellvitge University Hospital and the Viladecans Hospital of the Catalan Institute of Health, the Catalan Institute of Oncology, the University of Barcelona, and the City Council of L’Hospitalet de Llobregat.
IDIBELL is a member of the Campus of International Excellence of the University of Barcelona HUBc and is part of the CERCA institution of the Generalitat de Catalunya. In 2009 it became one of the first five Spanish research centers accredited as a health research institute by the Carlos III Health Institute. In addition, it is part of the “HR Excellence in Research” program of the European Union and is a member of EATRIS and REGIC. Since 2018, IDIBELL has been an Accredited Center of the AECC Scientific Foundation (FCAECC).