Influence of drug incorporation strategy on structure and release behavior of alginate beads: A mechanistic study

Conventional excipients used in pharmaceutical formulations often exhibit limitations such as uncontrolled drug release and adverse patient responses, highlighting the need for improved drug delivery systems. Sodium alginate beads have been widely investigated as biocompatible carriers due to their ability to form ionically crosslinked hydrogels; however, the influence of drug incorporation strategies on their structural and functional performance remains insufficiently understood. In this study, alginate beads were used as delivery systems for acetylsalicylic acid (ASA) and acetaminophen (AP), comparing encapsulation during gelation with post-synthesis impregnation. The aim was to evaluate how these strategies affect morphology, drug loading, and release mechanisms. Encapsulation resulted in higher drug loading efficiencies (66.5% for AP and 81.8% for ASA) compared to impregnation (61.4% and 73.3%, respectively), as well as a more homogeneous drug distribution within the polymeric matrix. Morphological and structural analyses confirmed that encapsulated beads exhibited more uniform and compact structures, whereas impregnated systems showed heterogeneous drug localization and surface-associated deposits. In vitro release studies revealed that encapsulation promotes controlled and sustained release, while impregnation leads to faster release due to shorter diffusion pathways. Kinetic modeling indicated that AP release follows anomalous transport involving both diffusion and polymer relaxation, whereas ASA release is predominantly diffusion-controlled. These findings demonstrate that the drug incorporation strategy governs the internal structure of alginate beads and directly determines their release behavior, providing mechanistic insight into the rational design of polymeric drug delivery systems with tunable and predictable performance.

The main objective of this study was to investigate sodium alginate beads as potential carriers for active pharmaceutical ingredients.

Sodium alginate beads were prepared by ionotropic gelation and loaded with acetaminophen or acetylsalicylic acid either by encapsulation during gelation or by post-synthesis impregnation. The beads were characterized using FTIR, SEM, and XRD. Drug loading, swelling behavior, in vitro drug release, and release kinetics were also evaluated.

Encapsulation produced beads with higher drug-loading efficiency and more homogeneous structures than impregnation. Consequently, encapsulated systems exhibited more controlled and sustained drug release, whereas impregnated beads showed faster release because of drug localization near the bead surface. Kinetic analysis indicated anomalous transport for acetaminophen and predominantly diffusion-controlled release for acetylsalicylic acid.

This study indicates that the drug incorporation strategy is a key factor governing the structural, functional, and release properties of alginate-based delivery systems.