Self-assembled nano-vesicles based on mPEG-NH₂ modified carboxymethyl chitosan-graft-eleostearic acid conjugates for delivery of spinosad for Helicoverpa armigera

In this work, carboxymethyl chitosan-graft-eleostearic acid (CMCS-g-EA) was synthesized via the amide reaction between the amino groups of carboxymethyl chitosan and the carboxyl group of eleostearic acid, and then mPEG-NH₂ was grafted to CMCS-g-EA to prepare amphiphilic polymers (mPEG-CMCS-g-EA). The chemical structures of the above conjugates were characterized by FT-IR and ¹H NMR. Both CMCS-g-EA and mPEG-CMCS-g-EA based nano-vesicles were prepared by ultrasonic self-assembly method and they exhibited a low critical aggregation concentration (CAC) of 14.97 μg/mL, 16.82 μg/mL, respectively. The spinosad-loaded mPEG-CMCS-g-EA nano-vesicles (SSD@mPEG-CMCS-g-EA NVs) were spherical in shape with an average diameter of 502.8 nm and the zeta potential of −25.60 mV. The encapsulation efficiency (EE) and drug loading content (LC) of SSD@mPEG-CMCS-g-EA nano-vesicles were 42.00%, 23.07%, respectively. In vitro release revealed that the SSD@mPEG-CMCS-g-EA nano-vesicles exhibited a sustained and pH-responsive drug release property, and could significantly enhance the photostability of spinosad. Furthermore, the toxicological tests demonstrated that the SSD@mPEG-CMCS-g-EA nano-vesicles could efficiently inhibit the growth and development of Helicoverpa armigera. These results indicated that the SSD@mPEG-CMCS-g-EA nano-vesicles were highly potential for the treatment of Helicoverpa armigera.