Project summary One bottleneck to achieving therapeutically relevant cell concentrations at the infarct site after myocardial infarction is the poor cell engraftment and retention of vehicles at the target site. Here we propose the first-of-its- kind, tunable, replenishable scaffold of cells that allows for multiple drug delivery "waves" to address this gap. We hypothesize that cardioregenerative cell accumulation and retention in the infarcted myocardium will be enhanced by surface decorating them with proteins that cross-link the cells via layer-by-layer assembly into a scaffold. Unlike conventional delivery strategies, which do not allow the subsequent accumulation of cells or carriers after saturation of the target infarct, each dose of cells in our platform will serve as a capturing surface for the next dose of cells. This will dramatically amplify the targetable surface area for additional waves of cell attachment and will also allow the total therapeutic concentration to be adjusted based on the number of doses administered. To prevent premature cross-linking, we will use engineered proteins that form heterodimers but not homodimers. These studies are expected to result in a new class of carrier-linked network that will not only substantially enhance cellular accumulation, retention, and local drug release at the infarct site to maximize therapeutic efficacy but also allow for several cycles of drug replenishment or personalized dosing in a non- invasive manner. Here, we aim to evaluate the safety and therapeutic effectiveness of this approach and assess the effect of surface modification on stem cell function. Successful completion of the proposed studies will transform the treatment of patients suffering from myocardial infarction.