Barrier-Oriented Design of Next-Generation Polymeric Nanocarriers for Targeted Drug Delivery

Targeted drug delivery remains difficult because multiple biological barriers interfere with the stable transport of therapeutics to the site of action. Polymeric nanocarriers have gained broad attention as delivery platforms since their composition and surface properties can be adjusted to improve circulation behavior and cellular delivery. This review discusses the major biological barriers involved in targeted drug delivery and describes how polymeric nanocarriers are engineered to overcome them. Major carrier types, including polymeric nanoparticles and micelles, are considered with emphasis on their physicochemical and interfacial features. Particular attention is given to surface engineering and stimuli-responsive design as key strategies for barrier transport and controlled cargo release. The review also highlights representative applications in anticancer, gene, protein, and vaccine delivery, together with translational issues such as biocompatibility, stability, reproducibility, scale-up, and regulatory acceptance.