Nano-in-micro alginate/chitosan hydrogel via electrospray technology for orally curcumin delivery to effectively alleviate ulcerative colitis

•A nanoparticles-in-microparticles system was fabricated by electrospray technology for curcumin colon-targeting oral delivery in ulcerative colitis treatment.•Encapsulation in hydrogel microparticles could avoid the immature drug release of nanoparticles in the upper gastrointestinal tract.•Curcumin-loaded in the nanoparticles-in-microparticles systems were apt to reach colitis lesion and enter into inflammatory macrophages to suppress inflammation.