Abstract
The limited regenerative capacity of the adult mammalian heart following myocardial infarction (MI) remains a primary challenge in cardiovascular medicine. Recent advances in tissue engineering have shifted focus from purely structural scaffolds to immunomodulatory biomaterials that actively shape the immune environment. Central to this approach is the orchestration of macrophage polarization, transitioning from the pro-inflammatory M1 phenotype to the pro-reparative M2 phenotype. This study investigates the design and efficacy of a biomimetic silk-based hydrogel functionalized with RGD peptides and encapsulated mesenchymal stem cell-derived extracellular vesicles (MSC-EVs) to modulate macrophage behavior. We hypothesized that the combination of topographical cues and biochemical signaling would synergistically drive M2 polarization and enhance cardiac function. Using a rat model of MI, we characterized the immunomodulatory effects of various scaffold architectures, including varying fiber diameters and pore dimensions. Results indicated that scaffolds with larger pore dimensions (30-40 μm) and MSC-EV functionalization significantly increased the M2/M1 ratio compared to standard alginate or untreated controls. This shift was associated with enhanced fatty acid metabolism via the PPAR/JAK-STAT signaling pathway and a marked reduction in fibrotic scar area. Furthermore, the delivery of MSC-EVs via the hydrogel matrix promoted angiogenesis and cardiomyocyte survival. These findings demonstrate that precisely engineered biomaterials can serve as instructive microenvironments that leverage the immune system's inherent reparative potential, providing a promising strategy for clinical cardiac regeneration. The study concludes that sequential activation and maintenance of M2 phenotypes are essential for meaningful functional recovery in post-ischemic cardiac tissue.