**6. Concluding Remarks**

Decellularization is a grea<sup>t</sup> technique to generate tissue-specific ECM-derived products with multiple applications, including tissue regeneration in clinical settings. Decellularization can be achieved from many tissues, but it has to be designed in accordance with the properties of the target tissue and the intended approach, aiming to preserve specific ECM components. The literature is extensive, but mostly related to empirical experimental research data. As a consequence, a variety of decellularization protocols have been described for each one of the targeted tissues. Therefore, the challenge remains in defining broadly acceptable standardized decellularization and characterization procedures for each specific tissue that would ease the selection of standard controls and the development of future research, ultimately helping in the transfer of knowledge to clinical settings. At present, tissues' dECM scaffolds are the core of most clinical products, while research efforts are now strongly moving toward the development of postprocessing-related products, such as

bioink-related 3D structures. Therefore, we anticipate rapid growth in the number of tissue-specific dECM postprocessing-related clinical products for the coming years.

**Author Contributions:** Conceptualization, U.M. and A.A.; writing—original draft preparation, U.M. and R.R.-H., S.R.-C., N.G.-U., and A.A.; writing—review and editing, A.A.; visualization, B.O.-G.; supervision, A.A. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was supported by the Spanish "Programa Estatal de I+D+i Orientada a los Retos de la Sociedad", gran<sup>t</sup> number RTI2018-101708-A-I00. S.R.-C. was supported by Fomento de San Sebastian innovative talent programme, gran<sup>t</sup> number 0508/2019/0009. R.R.-H. was supported by Spanish State Training Subprogramme, gran<sup>t</sup> number PRE2018-084542. A.A. was supported by Spanish State Subprogramme of Incorporation Ramón y Cajal, gran<sup>t</sup> number RYC2018-025502-I, and 2019 Leonardo Grant for Researchers and Cultural Creators, BBVA Foundation, gran<sup>t</sup> number IN[19]\_CMA\_BIO\_0119. The BBVA Foundation accepts no responsibility for the opinions, statements and contents included, which are entirely the responsibility of the authors.

**Acknowledgments:** This work was performed under the Maria de Maeztu Units of Excellence Programme–Grant No. MDM-2017-0720 Ministry of Science, Innovation and Universities. And Basque Government Elkartek program (KK-2019/00093).

**Conflicts of Interest:** The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.
