PROJECT SUMMARY The promise of human stem cell-derived cardiomyocytes (hSC-CMs) opens doors towards the feasibility of personalized medicine against cardiac diseases and for performing more accurate drug discovery studies. Moreover, hSC-CMs overcome the issue of species differences when using animal models for high throughput screening studies. However, one of the bottlenecks for scaling up the use of hSC-CMs is their ability to accurately reflect the native structure and function of adult human cardiomyocytes. Current efforts to address this critical challenge involve maturation protocols that use biophysical cues such as electrical stimulation or substrate- induced tissue alignment. Methods for electrical stimulation often utilize electrode contacts for field stimulation, bulky instrumentation for combining electrical stimuli delivery with mechanical or sustained chemical stimulation, or genetically modifying cells to be light-responsive. Although we have seen successes through these induction and stimulation approaches, the field would benefit from a stimulation approach with minimal culture contact to reduce risk of infection during long-term cultures, as well as a light-based approach with higher spatiotemporal resolution than electrode-based stimulation. Here, we propose a new paradigm for stimulating hSC-CMs towards maturation by interfacing these cells with peptide-based substrates that can induce tissue anisotropy and are engineered to convert light to stimulatory cues. Our team will develop peptides functionalized with chromophore units and cell-binding epitopes as materials that can be used for light-based stimulation of hSC- CMs, in combination with induction of tissue alignment, towards maturation. The long-term goal of this project is to establish light stimulation via engineered peptides as a viable method to stimulate cardiomyocytes and promote hSC-CM maturation in an electrodeless and non-genetic manner. We hypothesize that transient charging and other associated light-induced processes at the cardiomyocyte-biomaterial interface can influence extracellular potential, resulting in the photostimulation of hSC-CMs towards maturation. Our rationale for proposing a materials-based approach for stimulating hSC-CMs stems from previous reports of conjugated polymers being used as a photoactive substrate for triggering action potentials of other excitable cells. To test our hypothesis, we propose the following specific aims: (1) establishing design parameters for engineered peptide substrates with optimal photostimulation efficiency; (2) test the cellular- and tissue-level impact of peptide-mediated photostimulation in combination with anisotropic cues; and (3) elucidate the effect of the proposed photostimulation method, along with anisotropy cues, on hSC-CM maturation. By establishing the design rules for the proposed photoexcitable peptides for eliciting combinatorial cues to stimulate hSC-CMs and ensure their capability to excite car...