Controlled Release of Dyes from Hydrogel Cargoes through pH and Magnetic Stimuli

Stimuli-responsive biomaterials capable of controlled, on-demand release are vital for next-generation therapeutic delivery. We present a dual-responsive hydrogel platform for the controlled release of dyes from hydrogel cargoes, regulated by both pH and magnetic stimuli. By integrating magneto-responsive sodium alginate hydrogels with ferrofluid, we engineer smart hydrogel cargoes capable of responding to physiological cues as well as to on-demand external triggers. In this work, we utilize the liquid-liquid encapsulation method to generate Rhodamine B dye-loaded hydrogel-based cargoes. Our system enables not only passive, pH-driven diffusion but also active, magnetically enhanced release, demonstrating for the first time dual-mode modulation of release profiles from encapsulated hydrogels within protective oil-based droplets. Upon external magnetic activation, hydrogel cargoes are extracted from their encapsulation and immersed in various aqueous environments, where their release kinetics are finely tuned by both pH-dependent swelling/shrinking and magnetic field-induced structural changes. We found that the incorporation of magnetic actuation significantly increases the effective diffusion coefficient (∼ 10^-9 m²/s) as compared to that for the pH-assisted release (∼10^-10 m²/s) of Rhodamine B from the hydrogel. This approach provides spatiotemporal control over release behavior, paving the way for advanced, remotely controllable strategies in targeted drug delivery, minimally invasive therapeutics, and adaptive biomaterials. Our findings highlight the transformative potential of multistimuli-responsive hydrogels as a versatile platform for next-generation biomedical applications.