Nanostructured Polymeric Carriers for Efficient Drug Encapsulation and sustained release

Abstract

Nanostructured polymeric carriers have emerged as versatile platforms for overcoming important limitations of conventional pharmaceutical formulations, including poor aqueous solubility, physicochemical instability, rapid elimination, low bioavailability, nonspecific biodistribution, and dose-dependent toxicity. Polymeric nanospheres, nanocapsules, micelles, dendrimers, and nanogels provide structurally diverse environments in which small-molecule drugs, proteins, peptides, and nucleic acids can be physically entrapped, adsorbed, ionically complexed, or chemically conjugated. Their pharmaceutical performance can be modulated through polymer chemistry, molecular weight, crystallinity, hydrophilic–hydrophobic balance, particle size, surface characteristics, crosslinking density, drug–polymer affinity, and manufacturing conditions. Biodegradable polymers such as poly(lactic-co-glycolic acid) (PLGA), polylactic acid (PLA), polycaprolactone (PCL), chitosan, and alginate have received considerable attention, whereas amphiphilic and stimuli-responsive polymers have expanded opportunities for spatially and temporally controlled delivery. Drug release from polymeric nanocarriers generally results from interacting processes involving surface desorption, diffusion, swelling, polymer relaxation, hydrolytic degradation, erosion, and carrier disassembly. Despite substantial preclinical progress, translation remains constrained by burst release, inadequate drug loading, colloidal instability, biological barriers, scale-up difficulties, sterilization requirements, batch variability, insufficiently predictive in vitro release models, and regulatory complexity. This review critically examines nanostructured polymeric carrier architecture, polymer selection, mechanisms of drug encapsulation, fabrication strategies, characterization, sustained-release mechanisms, stimuli-responsive delivery, biomedical applications, manufacturing limitations, and future research priorities. Particular attention is directed toward relationships among material structure, encapsulation efficiency, drug loading, and release kinetics. The available literature indicates that future clinical progress will depend on establishing reproducible structure–property–performance relationships integrating therapeutic efficacy with manufacturability, stability, safety, and clinically meaningful release profiles.