Ajwain Essential Oil-loaded chitosan nanoparticle hydrogel with antibacterial activity: experimental evaluation and molecular docking analysis

Ajwain ( Trachyspermum ammi ) essential oil (EO) possesses well-known antimicrobial properties; however, its high volatility and chemical instability limit its therapeutic applications. In the present study, Ajwain EO was nanoencapsulated within chitosan nanoparticles and subsequently incorporated into an HPMC hydrogel to improve its stability and antibacterial performance. GC–MS analysis revealed thymol, p-cymene, and γ-terpinene as the major constituents of the EO. Chitosan nanoparticles prepared by ionic gelation exhibited an average particle size of 132 ± 7 nm with good colloidal stability (zeta potential − 44 ± 3 mV) and demonstrated high encapsulation efficiency (68 ± 3%) and loading capacity (26 ± 2%). ATR-FTIR spectroscopy confirmed successful incorporation of EO within the polymeric matrix, while rheological analysis demonstrated shear-thinning behavior suitable for topical applications. The antibacterial activity of the developed formulations was evaluated using the AATCC 100 method against Staphylococcus aureus and Pseudomonas aeruginosa . The nanoparticle-based hydrogel (ChiNPs/HPMC-EO) exhibited significantly enhanced antibacterial activity compared with the non-nano formulation, achieving complete inhibition of both pathogens at 625 µg/mL. Molecular docking analysis further provided mechanistic insight into the interactions of the major EO constituents with key bacterial proteins involved in DNA replication, fatty acid biosynthesis, and cell wall formation. The results demonstrate that nanoencapsulation of Ajwain EO within chitosan nanoparticles incorporated into an HPMC hydrogel represents a promising strategy for enhancing the antibacterial efficacy of EOs and developing effective topical antimicrobial formulations.