Xiaoyuan Sha,1 Leung Chan,1 Xiaoyi Fan,2 Penghao Guo,3 Tianfeng Chen,1 Lian Liu,1 Jingxiang Zhong1,4 1Department of Ophthalmology, The First Affiliated Hospital, and Department of Chemistry, Jinan University, Guangzhou, Peopleâs Republic of China; 2Department of Clinical Laboratory, The First Affiliated Hospital of Jinan University, Guangzhou, Peopleâs Republic of China; 3Department of Clinical Laboratory, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, Peopleâs Republic of China; 4Department of Ophthalmology, The Sixth Affiliated Hospital, Jinan University, Dongguan, Peopleâs Republic of ChinaCorrespondence: Lian Liu; Tianfeng Chen, Department of Ophthalmology, The First Affiliated Hospital of Jinan University; Department of Chemistry, Jinan University, 601 Huangpu Road, Guangzhou, 510632, Peopleâs Republic of China, Email liulianbb@163.com; tchentf@jnu.edu.cnPurpose: Fusarium Solani is the principal pathogen associated with fungal keratitis. As a sensitive drug to F. Solani, natamycin (NAT) was limited by the poor penetration and low bioavailability in clinical application. The aim of this study was to develop a new type of tri-block polymer nanoparticle-gel complex (Gel@PLGA-PEI-PEG@NAT) for delivering NAT and evaluate its physicochemical properties, antifungal activity, safety, penetrability, adhesion, and efficacy in treating fungal keratitis.Methods: PLGA-PEI-PEG@NAT was prepared and characterized with a nano-particle size analyzer, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). The minimum inhibitory concentration (MIC), cytotoxicity, penetrability of NAT (Natacyn® 5% ophthalmic suspension; Alcon) and PLGA-PEI-PEG@NAT with different concentrations were assessed. The eye surface retention time, ocular irritation, and curative effect of the NAT ophthalmic suspension and Gel@PLGA-PEI-PEG@NAT on a rabbit fungal keratitis model were evaluated.Results: PLGA-PEI-PEG@NAT had a particle size of 150 nm, a positive surface charge, and a sustained-release effect. The MIC for F. Solani was 2 μg/mL. A cytotoxicity test and ocular irritation test showed that PLGA-PEI-PEG@NAT and Gel@PLGA-PEI-PEG@NAT had good biocompatibility and no obvious irritation for rabbit corneas. Penetration experiments confirmed that PLGA-PEI-PEG@NAT can successfully enter corneal epithelial cells and through the cornea to enter the anterior chamber. Compared with NAT ophthalmic suspension, Gel@PLGA-PEI-PEG@NAT had stronger cornea permeation at the same concentration. The therapeutic effect and precorneal retention ability of the NAT ophthalmic suspension and Gel@PLGA-PEI-PEG@NAT on the fungal keratitis rabbit model were compared. Gel@PLGA-PEI-PEG@NAT achieved a better therapeutic effect at a lower drug concentration, and its eye surface retention time was significantly longer than that of the NAT ophthalmic suspension.Conclusion: Gel@PLGA-PEI-PEG@NAT was shown to be a safe and effective nanodrug delivery system for NAT. It has great potential to improve the cure rate of fungal keratitis, reduce the administration frequency during the treatment process, and improve patient compliance.Graphical Abstract: Keywords: fungal keratitis, natamycin, nanoparticles, ocular drug delivery, tri-block polymer