Revista nº 809

Ruiz-de-Almirón Ingeniería tisular del miocardio · 43 · Actualidad Médica · Número 809 · Enero/Abril 2020 Páginas 39 a 47 For cardiac tissue engineering, it is crucial the develop- ment of electrically conductive hydrogels to achieve the spon- taneous beating behaviour of the heart, in order to accomplis- hed the functional regeneration (8,40). Advances in the science and applications of hydrogel sys- tems have led to develop 'smart hydrogels', which are polymeric scaffolds with tunable properties. They can be triggered by cer- tain stimulus such as temperature, electric and magnetic fields, light, pH, ions, and specific molecular recognition events such as glucose. These polymers can exhibit dramatic changes in their swelling behavior, sol-gel transition, network structure, permea- bility, or mechanical strength in response to changes in the pH, ionic strength, or temperature, as an example (41). Newly, there are some contributions about hydrogels. First one, shows up an injectable nanocomposite hydrogel, which could be potential for vascularization and tissue re- pair aplicattions. It has been developed with chitosan, gelatin, β-glycerphosphate and Arg-Gly-Asp (RGD) peptide and loaded with stromal cell-derived factor-1 and vascular endothelial growth factor (VEGF) nanoparticles to simulate the natural na- noparticles in the extracellular matrix to promote angiogenesis (42). Secondly, an injectable human amniotic membrane (hAM) matrix (43). And, lastly is about the first-in-man clinical trial per- formed with an extracellular matrix hydrogel derived from dece- llularized porcine myocardium (Ventrigel), in post–MI patients. After preclinical studies showing biocompatibility, hemocompa- tibility, and lack of arrhythmias, a multicenter trial was develo- ped to evaluate the safety, feasibility, and preliminary efficacy of percutaneous transendocardial delivery of VentriGel in early and late MI patients with left ventricular dysfunction (11). c) Decellularized scaffolds Decellularized extracellular matrices (dECM) processed in vitro could be promising biomaterials for cardiovascular tis- sue regeneration as it has the potential to overcome the need to artificially recreate the conditions from ECM deposition (35). They most effectively captures the complex array of pro- teins, glycosaminoglycans, proteoglycans, and many other ma- trix components that are found in native tissue, providing ideal cues for regeneration and repair of damaged myocardium. In addition, dECM can be used either as solid scaffolds that man- tain the native matrix structure, or as soluble materials that can form injectable hydrogels for tissue repair and regenera- tion (44). For decellularization and subsequent recellulariza- tion are required a scaffolding organ; a detergent, osmolar or enzymatic solution to remove native cell material; stem cells for repopulation; and a culture environment, or bioreactor, to promote adhesion, growth and integration of new cells (3). Generally, decellularization performed by perfusion with SDS or Triton X-100 has been done successful in small animal or- gans and whole organs. This procedure wipes out almost com- pletely cells from the tissue but leaves connective tissue archi- tecture of blood vessels intact and most of the components of the extracellular fibrillar and non-fibrillar matrix, so it allows perfusing of the remaining matrix (44, 45). For cardiovascular treatment dECM materials have been limited to repair or re- placement of heart valves, large vasculature, and congenital heart defects using patches and valves (PhotoFix, CryoValve), pericardial patches (SJM and Tutopatch) and injectable cellular ECM hydrogels with soluble ECM (Ventrigel) (44). Recently, it have been developed two engineered car- diac grafts based on decellularized scaffolds from myocardial and pericardial tissues. They were repopulated with adipose tissue mesenchymal stem cells. It was observed that decellu- larized scaffolds maintained structural integrity of the native matrix fibrils (Figure 2A,B,G,H) and type-I and type-III colla- gens, were properly marked, indicating preservation of matrix protein components (Figure 2J,K). After recellularization it was confirmed the capability to recruit cells (Figure 2C,I,F,L). The mechanical properties of cardiac tissue were evalua- ted and no significant changes were found when comparing data along the different recellularization steps. Comparative analysis of the generated acellular myocardial and pericardial tissues revealed they shared 40% of the matrisome proteins, wich are involved in cellular processes such as maintaining the ECM structure and modulating cell differentiation (co- llagens type-I, -III, -IV, -V, -VI), cell adhesion (laminin family and heparan sulfate), or survival and differentiation proces- ses (fibronectin). Immunohistological analysis showed co- rrect adhesion of the implanted graft with myocardium and hystological analysis showed functional blood vessels con- nected to host vascularization in all scaffolds of the experi- mental groups. Both engineered cardiac grafts were further evaluated in pre-clinical MI swine models and demonstrated biocompability and efficacy, improving ventricular function, as well as integration with the underlying myocardium and signs of neovascularization and nerve sprouting (46). At this moment, it is going under an interventional clinical trial (Pe- riCord) and it is based on a decellularized pericardial matrix with mesenchymal stem cells that carries them directly over myocardial infarction. d) Cell sheets This technique is based on the construction of cell sheets without scaffolding using specialized temperature-responsive polymer surfaces , wich allow to binding of cells, and the dea- tachment of the cultured cells as an intact layer without al- tering the deposited ECM (2,34). In that respect, previously Inui & Sekine et al. showed up that cocultivation with vas- cular endothelial cells (Figure 3A), treatment with vascular endothelial growth factor (VEFG) and in vitro vascularization bioreactors may favour the stacking of three-layers laminae in several stages. Recently they have been developed a new method involved the layering of cardiac cell sheets derived from human induced pluripotent stem cells cocultured with endothelial cells and fibroblasts on a vascular bed derived from porcine small intestinal tissue (Figure 3B,C). They succe- eded in engineering spontaneously beating 3D cardiac tissue Figure 2. Internal structure and protein composition of the cardiac scaffolds. SEM images of the (A) native myocardium, (G) native pericardium, (B) decellularized myocardial scaffold and (H) decellularized pericardial scaffolds, showing the intrinsical organization and spatial three-dimensional distribution of the native matrix fibrils. Native myocardium and decellularized myocardial scaffolds, respectively (D,E) and (J,K) native pericardium and decellularized pericardial scaffolds showing immunostaining for matrix proteins, type-I (green) and type-III (red) collagens and cardiac troponin I, cTnI (white). (C) recellularized myocardial and (I) pericardial scaffolds, showing the presence of cells detected using SEM and (F,L) displaying immunostaining for col-I (green) for recellularized myocardial and pericardial scaffolds. Nuclei were counterstained with DAPI (blue). Scale bars = 50 μm. Reproduced from Perea-Gil et al 46 with permission of the publisher. Copyright © 2018, Springer Nature. Creative Commons license: http://creativecommons.org/licenses/ by/4.0/.