Smart microdevices for biomedical drug delivery: endogenous stimuli as the key to safer therapeutics

The landscape of drug delivery has undergone a transformative shift with the emergence of adaptive therapeutics, smart microdevices engineered to respond dynamically to specific physiological or externally applied stimuli. These stimuli-responsive systems represent a significant advancement over conventional delivery methods by offering precise spatiotemporal control over drug release, thereby enhancing therapeutic efficacy and minimizing off-target effects and systemic toxicity. This review delves into the foundational design principles and material innovations that underpin these responsive microdevices. It highlights the role of endogenous stimuli such as pH gradients, temperature fluctuations, enzymatic activity, and redox, ionic, and hypoxia-responsive elements in activating drug release mechanisms. The integration of cutting-edge microfabrication techniques, nanomaterials, and bioinspired architectures has enabled the development of devices that are not only highly sensitive and selective but also capable of navigating complex biological environments. Furthermore, the article explores and examines the challenges associated with scalability, long-term biocompatibility, biosafety, and toxicity of implanted microdevices. Emerging trends such as AI-enhanced feedback loops, wearable biosensors, and closed-loop delivery platforms are discussed as future directions that could redefine personalized medicine. By bridging engineering ingenuity with biomedical imperatives, stimuli-responsive microdevices are poised to revolutionize drug delivery, offering intelligent, patient-centric solutions that adapt in real time to the dynamic needs of the human body. Notably, stimulus-responsive microdevices may soon facilitate localized delivery of imaging contrast agents, pharmaceuticals, genes, and mRNA; enable minimally invasive surgical procedures; and assist in cellular micromanipulation.