Nisin-Incorporated Solid Lipid Nanoparticles-Based In Situ Ocular Gel Using Box–Behnken Design for Enhanced Antibacterial Activity: In Vitro-Ex Vivo-In Vivo Analysis

Microbial ocular infections, namely bacterial conjunctivitis (BC), are a major concern in the biomedical field. Nisin (NIS) is an amphiphilic natural antimicrobial peptide. It showed antibacterial potential against Pseudomonas aeruginosa, which is responsible for BC. Despite this, the application of NIS in pharmaceuticals for the treatment of ocular infections is hindered by several limitations that include poor aqueous solubility and stability. The preference for solid lipid nanoparticles (SLN) shows the aptitude to enhance solubility, bioavailability, etc., of therapeutically active molecules. Therefore, the present research work intends to prepare a thermoresponsive poloxamer 407 (P-407)-based in situ ocular gel of NIS-incorporated SLN using Box Behnken Design (BBD) for improved antibacterial application. Herein, NIS-SLN was formulated with glyceryl monostearate (GMS) and Tween 80 using a HSH-probe sonication method. It resulted in the spherical shape NIS-SLN with the particle size (PS) of 158.8 ± 13.56 nm, zeta potential (ZP) of −22.48 ± 1.86 mV, and drug loading (DL) of 12.8% ± 2.84%. The formulated thermo-responsive in situ gel (ISG) pH, gelling temperature, and viscosity were found to be 7.45 ± 0.02, 36.5°C ± 0.5°C, and 465.5 ± 6.5 cps, respectively, with drug release of 68.65% ± 5.1% over 24 h. Moreover, it shows improved permeation of 66.43% ± 2.6%, which might be because of the nanoscale dimensions of SLN and Tween 80. The formulation demonstrates good stability for 3 months and improved antimicrobial potential against P. aeruginosa compared to pure NIS, possibly owing to sustained release and improved penetration of NIS. Moreover, in vivo experiments demonstrated no irritation of the gel formulation, confirming biocompatibility with the ocular region. In conclusion, the SLN incorporated thermo-responsive P-407-based in situ ocular gel provides the improved potential of NIS. In the future, it will reveal a new horizon for the delivery of NIS and other molecules for ocular disease treatment.