Revista nº 809

Ruiz-de-Almirón Ingeniería tisular del miocardio · 40 · Actualidad Médica · Número 809 · Enero/Abril 2020 Páginas 39 a 47 biology, engineering, chemistry, biotechnology and medicine to artificially construct biological substitutes in order to repair or re- generate damaged tissues (4), (Figure 1). To understand that it is a tissue engineering product we have to take into account three components: stem cells, growth factors and scaffolds. As for cell sources, stem cells are the primary source due to their ability to proliferate and promote tissue regeneration, relea- se a wide range of growth factors and modulate the host inmune response (5). Once we have the cell type, the behaviour and pro- liferation should be guide either by manipulating the extracellular microenvironment in which the cell is going to develop its activity or by genetically manipulating these cells to modify the synthesis of the extracellular matrix, inhibit the immune response or alter cell proliferation. Regarding the growth factors, the cell response derives from the detection of chemical signals or physical stimu- lus from the extracellular environment, wich will activate molecu- lar and biological mechanisms responsible for division, migration, differentiation, phenotype maintenance or apoptosis. Therefore, controlling the concentration, local duration and spatial distribu- tion of these factors is essential to their utility and efficacy (6). Lastly, scaffolds are used as structural support for the new mi- croenvironment of the biological substitute. They will allow cell union, migration and differentiation, as well as they favour an or- ganisation to facilitate the action of growth factors and molecular signals (3). In this regard, hydrogels appear to be the most promi- sing biomaterials due to their high hydratation, easy tunning for recreate extracellular matrix (ECM) properties and biocompatibi- lity (7). These properties favour a suitable microenvironment for cell growth, the incorporation of drugs and the controlled release of biologically active agents (8). In order to optimize the physical and mechanical properties of hydrogels, nanoparticles acting as enhancing materials have also been investigated to incorporate into different kinds of natural or synthetic polymer networks to prepare nanocomposite hydrogels for TE (7). Basic research is essential and subsequently, the translation of these pre-clinical results into clinical practice plays a crucial role. It is necessary the adaptation of the in vitro and in vivo stu- dies, as well as the biofabrication protocols to a good manufac- turing practice manufacturing process and the design of an ad- vanced therapy clinical trial obeying European requirements and regulations. In Andalusian there are two successful experience in the development and clinical translation of two tissue enginee- ring products: a novel anterior lamellar artificial cornea (9) and artificial autologous human skin (10). Also, recently Traverse et al. evaluated the safety and feasibility of a cardiac extracellular ma- trix hydrogel, in early and late post–myocardial infarction patients with left ventricular dysfunction (11). This review aim is to look over the different strategies, ele- ments and challenge of cardiac tissue engineering in the scientific literature. SYNTHESIS OF THE REVIEW This article discusses the scientific literature on scaffolding strategies for regenerative therapies by means of tissue enginee- ring. It will be analyses the cell sources, important methods of tissue engineering investigated up to know, essential points of neovascularization as well as the 3D bioprinting, and finally the future perspectives towards the achievment of transferring this strategies to the clinic. Stem cells Cells will be responsible for homeostasis and to forming the connections between the tissue matrix and the native tissue. So it is important to choose the cell type by virtue of the objective of the new tissue to be grafted. For this reason, stem cells due to their favourable proliferation characteristics, tissue regeneration, releasion a wide range of growth factors, modulation the host inmune response and serving as feeder platform for ex vivo expansion of differenciated cells (5), are the most studied to promote tissue engineering processes. Stem cells can be allogenic or autologous, but the latter are the central focus of research due to the problems of survei- llance and rejection that still present allogenic cells (3). (Table 1) shows cells with cardiac regeneration potential. As we can see, the elaboration of constructs in the labo- ratory depends mainly on avaibility of viable cells, so viability and physiological state maintained in culture must be previusly studied in order to be able to use them for clinical purposes. Classical methods based on exclusion dyes such as tripan blue are used to identify membrane alterations or the metabolic state of cells. Other protocols to analyse cell viability include a technique using quantitative analytical electron miscroscopy by X-ray emission that allows to identify, localize, and quan- tify elements both at the whole cell and at the intracellular level (22,23). Likewise, once the tissue substitute has been obtained, it must be analysed and evaluated to guarantee a structure similar to that of the native tissue to be replaced and that normal functions of the native tissue can be reproduced at both in vitro and in vivo levels by the tissue substitutes (24). Thus, the evaluation of cell viability is very important and it is a basic criteria to ensure therapeutic efficacy of tissues and approval as advanced therapy medicament (9,10). Cardiac Tissue Engineering Most common cardiovascular diseases can have as a conse- quence the formation of non-contractile conjunctive scar tissue, inflammation of the tissue's microenvironment, calcification of the grafts and degradation among others (3). This is why simple repair or regeneration focused on the reconstitution of cardiomyocytes is ineffective, as the lesion interrupts the organization of cardiac tissue and architecture, along with the coordinated interaction of cells. It will be important for the repair or regeneration both res- toration of cell types and scaffold structure to restore electrical and mechanical communication between the cardiomyocytes and the environment. Therefore, key points of regeneration are the sources of new cardiomyocytes, the role of inflamatory and inmune cells, extracellular matrix, neovascularization and lymphagenesis (25). Cardiac tissue engineering objective is to reconstitute the contractile tissue of the myocardial muscle in vitro using synthetic Figure 1 . Tissue engineering procedure. 1. Biopsy of the patient to extract cells depending on the tissue to be regenerated; 2. After surgical dissection, the isolation of the cells must be performed by mechanical fragmentation or by enzymatic digestion, so that they can subsequently be cultured in a specific culture medium.; 3. We need a stroma where the cells can be immersed and development in the same way as in their native tissue. Porous scaffold, cells, nutrients and growth factors allow the formation of the tissue in the culture medium; 4. Evaluation of cell viability;and 5. Implant.