PROJECT SUMMARY: In the U.S. alone, there are more than 735,000 myocardial infarctions (MI) each year, suggesting a pressing need to develop treatments for repairing injured hearts. Due to the limited regenerative capacity of adult hearts, human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CMs) have received significant attention due to their demonstrated capacity for remuscularization and restoration of contractile function upon transplantation to injured hearts. Despite the progress, the current approach is limited by low cell retention and poor integration when delivered as dissociated cells or engineered cardiac tissue patches. To address these challenges, we pioneered the use of electrically conductive silicon nanowires (e- SiNWs) to facilitate self-assembly of hiPSC-CMs to form nanowired hiPSC cardiac spheroids. Our in vivo studies showed the nanowired spheroids improve cell retention and engraftment after transplantation, presumably due to their 3D microtissue configuration and the e-SiNW enhanced electrical integration. To improve cell survival and engraftment in injured hearts, I recently developed an organoid fabrication protocol where we seed the supporting cells (e.g., endothelial cells, cardiac fibroblasts, human adipose stem cells) onto nanowired hiPSC cardiac spheroids. My preliminary data showed sizeable engraftments of nanowired cardiac organoids in ischemia/reperfusion (I/R) injured rat hearts, with rapid infiltration of host vasculature and improved organization and development of contractile structures, when compared to non-nanowired cardiac organoids. The goal of this proposal is to determine the effects of e-SiNWs and prevascularization of the organoids on hiPSC-CM engraftment and integration (Aim 1) and demonstrate the translational potential of nanowired human cardiac organoids in repairing infarcted hearts (Aim 2). The central hypotheses of this proposal are 1) the e-SiNWs can improve the contractile development of the transplanted organoids, and 2) the lumen-like vasculature in the organoids can allow for rapid anastomosis with host myocardium. The proposal is innovative in that, for the first time, we will synergize e-SiNWs and pre-vascularized, injectable 3D cardiac microtissues to develop a scalable platform to effectively engraft hiPSC-CMs and improve their integration with adult myocardium. My long-term goal is to make significant contributions towards advancing development of cell-based therapies for repairing cardiac injury. Accordingly, we will pursue the following specific aims: 1) Determine the effects of e- SiNWs and prevascularization in nanowired organoids on contractile development and vascular integration with host myocardium in healthy rat hearts, and 2) Determine therapeutic efficacy of nanowired human cardiac organoids with injured rat hearts. The proposed research would, for the first time, allow us to investigate the synergistic effect of e-SiNWs and supporting cell-types on hiPSC-CM engraftment and integration in injured hearts. This research will provide the foundation to use nanowired human cardiac organoid to pursue large animal studies and accelerate their translational applications.