Ion-Triggered In Situ Gel Combined with Melatonin Liposomes: Breaking Through the Dual Barriers of Nasal and Brain Delivery to Treat Insomnia

Background/Objectives: Insomnia severely impairs quality of life. Oral melatonin (MEL) suffers from poor brain delivery. Intranasal administration bypasses the blood–brain barrier, but rapid mucociliary clearance shortens drug retention, and MEL poor water solubility limits its nasal dissolution. Traditional in situ gels have “gelation-first, spreading-second” defects, causing uneven distribution. Herein, we developed a two-step sequential ion-triggered in situ gel combined with MEL liposomes (MEL-Lips-Gel) to enhance solubility, achieve instant uniform coating, and prolong retention for efficient nose-to-brain delivery. Methods: MEL-Lips were dispersed in alginate (first component) and calcium gluconate served as the second component. After sequential spray, the two components mix and form an ion-crosslinked gel. Rheology, in vivo fluorescence imaging, in vitro release, open-field/sucrose preference tests, and H&E staining were performed. Results: MEL-Lips showed uniform size and good encapsulation. The sequential system achieved instant widespread spreading and rapid gelation, significantly prolonged nasal retention, enabled sustained brain delivery, and reversed insomnia-induced hyperactivity and anxiety-like behaviors more effectively than oral MEL, intranasal MEL solution, liposomes alone, or non-liposomal gel, with good nasal safety. Conclusions: This sequential ion-triggered liposome-in-gel strategy synergistically overcomes rapid clearance (via gel) and poor solubility (via liposomes), enhancing nose-to-brain delivery of melatonin and providing a promising platform for insomnia therapy.