Gladstone Institute for Cardiovascular Disease 2 articles published in JoVE Bioengineering Comparable Decellularization of Fetal and Adult Cardiac Tissue Explants as 3D-like Platforms for In Vitro Studies Ana C. Silva1,2,3,4, Maria J. Oliveira1,2,5, Todd C McDevitt4,6, Mário A. Barbosa1,2,3, Diana S. Nascimento1,2, Perpétua Pinto-do-Ó1,2,3 1i3S - Instituto de Investigação e Inovação em Saúde, Universidade do Porto, 2INEB - Instituto de Engenharia Biomédica, Universidade do Porto, 3Instituto de Ciências Biomédicas Abel Salazar (ICBAS), Universidade do Porto, 4Gladstone Institute of Cardiovascular Disease, 5Faculty of Medicine, University of Porto, 6University of California San Francisco The cardiac extracellular matrix (ECM) is a complex network of molecules that orchestrate key processes in tissues and organs while enduring physiological remodeling throughout life. Standardized decellularization of fetal and adult hearts permits comparative experimental studies of both tissues in a 3D context by capturing native architecture and biomechanical properties. Bioengineering Fabrication of Custom Agarose Wells for Cell Seeding and Tissue Ring Self-assembly Using 3D-Printed Molds Hannah A. Strobel1, Elizabeth L. Calamari1, Brittany Alphonse1, Tracy A. Hookway1,2, Marsha W. Rolle1 1Biomedical Engineering, Worcester Polytechnic Institute, 2Gladstone Institute for Cardiovascular Disease This protocol describes a platform for fabricating self-assembled tissue rings in variable sizes using a customized 3D-printed plastic mold. PDMS negatives are cured in the 3D-printed mold; then agarose is cast in the cured PDMS negatives. Cells are seeded into the resulting agarose wells where they aggregate into tissue rings.