Citric Acid Cross‐Linked Gum Katira–Carboxymethyl Cellulose Hydrogel: Synthesis, Characterization and Application as Bioagent Carrier

Globally, entomopathogenic nematodes (EPNs) exhibit promise as biocontrol agents against various pests, both above and below the ground. Nonetheless, existing formulations utilizing these bioagents often face challenges in maintaining viability under elevated storage temperatures. Thus, a necessity arose to develop effective moisture-retentive carriers for these bioagents. In the present study, biopolymeric and co-biopolymeric hydrogels were synthesized by cross-linking of two biopolymers, namely, gum katira (Gk) and carboxymethyl cellulose (CMC), with a green cross-linker, citric acid (CA), through an in situ cross-linking polymerization technique. Structural characterization by FT-IR and ¹³C NMR studies revealed successful cross-linking between the biopolymers and the cross-linker, whereas scanning electron microscopic (SEM) and x-ray diffraction (XRD) studies showed increased surface roughness and amorphous nature of the prepared hydrogels, respectively. The equilibrium swelling ratio and density of the prepared hydrogels were also measured. Viscoelastic behaviour analysis revealed the maximum mechanical and thermal stability of the co-biopolymeric hydrogel (Gk-CA-CMC) compared to the pure biopolymers and biopolymeric hydrogels (Gk-CA and CMC-CA). The Gk-CA-CMC was further used to develop EPN-based bioinsecticidal gel formulations, which reported more than 80% survival of immobilized bioagents and 100% infectivity to the test insect, Galleria mellonella (fourth instar larvae), after 30 days of storage at 35°C. Further research work may be carried out on the shelf life of the prepared formulation and its biocontrol potential under field conditions.