Nanocarriers in Targeted Drug Delivery: Design Strategies to Overcome Biological Barriers

Effective drug delivery requires overcoming multiple biological barriers, including enzymatic degradation, immune clearance, and poor tissue penetration. This review systematically presents the design strategies for nanocarriers — including surface modification, stimuli-responsive release, and active targeting ligands — to enhance therapeutic index and specificity. We discuss recent advances in polymeric nanoparticles, liposomes, dendrimers, and exosome-based carriers, emphasizing their applications in cancer, infectious diseases, and neurological disorders