Two-in-one: multifunctional poloxamer hydrogel accelerates endometrial regeneration and fertility restoration through synergistic regulation of KGF-2 and NO

A healthy endometrium is crucial for embryo implantation and pregnancy maintenance. Thin endometrium, reduced glands and fibrosis resulting from infection or mechanical injury, are the primary causes of long-term infertility and poor pregnancy outcomes. Unfortunately, these issues have not been resolved by conventional clinical methods. Keratinocyte growth factor-2 (KGF-2) is an epithelial mitogen that regulates proliferation and migration of epithelial cells. Nitric oxide (NO) is involved in maintaining vascular homeostasis and angiogenesis. Poloxamer-407 (P) hydrogel is a promising topical drug delivery system due to its excellent solution-gel transition properties in response to body temperature. In this study, therapeutic NO gas was first prepared into stabilized microbubbles (NO-MBs). Subsequently, KGF-2 and NO-MBs were encapsulated into micelles of P hydrogel to form a multifunctional temperature-sensitive (28.9-31.8°C) hydrogel (KGF-NO-MBs-P hydrogel). This hydrogel not only exhibited suitable apparent viscosity, bio-adhesive and mechanical properties for application <i>in situ</i> but also showed sustained release of KGF-2 and NO. <i>In vivo</i>, KGF-NO-MBs-P hydrogel effectively restored endometrial morphology, increased the number of glands and endometrial thickness, reversed endometrial fibrosis and improved pregnancy outcomes by synergistic regulation of KGF-2 and NO. Repair of endometrial injury was closely related to promoting neovascularization, inducing endometrial cell proliferation and epithelialization, inhibiting apoptosis and inflammation and balancing collagen subtypes. Therefore, KGF-NO-MBs-P hydrogel may be useful in promoting endometrial regeneration and fertility restoration through <i>in situ</i> microinjection. This study represented a convenient, safe and promising method for repair of endometrial injury.