EMMIs: Engineered Myometrial Microtissues for Direct Quantification of Oxytocin-Induced Contractility

models provide only indirect readouts of contractility without direct force quantification. Here, we introduce engineered myometrial microtissues (EMMIs), a platform enabling the direct, isometric measurement of contractile force in response to physiological agonists like oxytocin. By embedding and molding immortalized human myometrial smooth muscle cells within a collagen hydrogel, we induced significant structural and molecular maturation over six days. Upon maturation, EMMIs were characterized by circumferential cellular alignment, sustained expression of smoothelin, upregulation of connexin-43, and a transcriptomic shift toward a contractile phenotype. Mature EMMIs generated calcium-sensitive, dose-dependent contractions to oxytocin and potassium chloride. Genetic deletion of the oxytocin receptor abolished oxytocin-induced contractility, establishing receptor specificity. Finally, we utilized EMMIs to recapitulate clinical oxytocin desensitization, providing a direct link between prolonged oxytocin exposure and diminished contractile output. Together, these findings establish engineered myometrial microtissues (EMMIs) as a genetically manipulable, and reproducible system for investigating myometrial contractile physiology to improve obstetric outcomes. Teaser: Engineered 3D uterine tissues quantify how labor-inducing drugs weaken contractions and drive maternal hemorrhage.