Modified-Release Drug Delivery Systems: Stimuli-Activated

Stimuli-activated DDS release drugs in response to specific triggers.

Many use hydrogels—3D hydrophilic polymer networks—that swell or shrink to regulate release, making them smart systems.

These operate as either open-loop or closed-loop mechanisms.

Open-loop systems rely on externally applied stimuli to initiate or inhibit drug release.

Stimuli include temperature changes, ultrasound, magnetic fields, or electric currents.

But closed-loop systems are self-regulated. They detect internal physiological changes—such as shifts in pH, enzyme activity, or metabolic signals—and adjust drug release accordingly.

These systems can also be classified based on the stimulus type.

Physical triggers include osmotic, hydrodynamic, or vapor pressure; mechanical force, magnetic fields, temperature, light, ultrasound, and electrical current.

Chemical triggers involve pH variations, ion exchange, hydrolysis, or chelation.

Biological triggers include enzyme activity, inflammation, or antibody interactions.

These approaches enable precise and responsive drug delivery.