Biodegradable polymers have emerged as important materials for the development of controlled drug delivery systems because they can provide sustained and site-specific drug release while gradually degrading into biologically acceptable products. Conventional drug administration often results in fluctuations in plasma drug concentrations, repeated dosing, poor patient compliance, and systemic adverse effects. Polymer-based delivery systems offer an opportunity to overcome these limitations by regulating drug encapsulation, protection, transport, and release. This review discusses the synthesis, characterization, and pharmaceutical applications of biodegradable polymers used in controlled drug delivery. Particular attention is given to naturally derived polymers, including chitosan, alginate, gelatin, collagen, and starch, as well as synthetic polymers such as poly(lactic acid), poly(glycolic acid), poly(lactic-co-glycolic acid), polycaprolactone, and related copolymers. Major synthesis approaches, including ring-opening polymerization, condensation polymerization, solvent evaporation, nanoprecipitation, emulsion techniques, and ionic gelation, are discussed. Characterization techniques such as Fourier-transform infrared spectroscopy, nuclear magnetic resonance, X-ray diffraction, differential scanning calorimetry, thermogravimetric analysis, scanning electron microscopy, particle-size analysis, and molecular-weight determination are important for establishing polymer structure and performance. Factors controlling drug release, including polymer composition, molecular weight, crystallinity, degradation rate, particle size, porosity, and drug–polymer interactions, are also considered. Recent advances in stimuli-responsive, nanoparticle-based, and targeted polymeric delivery systems are highlighted. Overall, biodegradable polymers provide a versatile platform for developing safer, longer-acting, and more effective drug delivery technologies.
