Phytonanogels of <i>Alternanthera brasiliana</i> : comparative evaluation of chitosan and silver-nitrate nanogels for antimicrobial, antioxidant, and wound-healing applications

Nanogels incorporating plant-derived bioactives offer a promising strategy for transdermal therapeutics owing to their biocompatibility, stability, and capacity for controlled drug release. This study phyto-engineered nanogels using <i>Alternanthera brasiliana</i> aqueous extract and compared the performance of chitosan-based (CS) and silver nitrate-based (CP) systems. Nanogels were synthesized and characterized for particle size, zeta potential, pH, viscosity, spreadability, occlusivity, and transdermal permeation. CS-3 and CP-3 emerged as optimized formulations, exhibiting particle sizes of 170.2 ± 6.0 nm and 200.5 ± 5.2 nm, with zeta potentials of -37.4 ± 1.1 mV and -34.0 ± 1.3 mV, respectively. CS-3 demonstrated superior antimicrobial activity (19 mm and 21 mm zones of inhibition), enhanced antioxidant potential (IC₅₀ = 146.94 μg/mL), and improved wound closure (95.74% at 48 h) compared with CP-3 (antioxidant IC₅₀ = 547.18 μg/mL; wound closure 93.74%). Both nanogels showed excellent cytocompatibility and minimal haemolysis, supporting their safety for topical application. The findings highlight the synergistic interaction between chitosan and plant polyphenols, contributing to improved bioactivity compared with silver-based systems. Overall, the study identifies CS-3 as a promising biopolymeric nanogel for future transdermal biomedical applications.