Influence of plasticizer type on the structure and drug release characteristics of LM-pectin hydrogels

TL;DR

This study shows how different plasticizers affect the structure and drug release of LM-pectin hydrogels, influencing their performance in drug delivery.

Contribution

The study reveals how specific plasticizers alter hydrogel properties and drug release mechanisms for tailored delivery applications.

Findings

CO increased cumulative drug release by creating flexible yet crystalline matrices.

PEG1500 and PVP enabled prolonged, diffusion-controlled drug delivery.

PEG400 and PEG1000 showed non-Fickian transport due to polymer relaxation.

Abstract

This study investigated the effects of different plasticizers—castor oil (CO), polyvinylpyrrolidone (PVP), and polyethylene glycol (PEG) with varying molecular weights (MWs)—on the structure and drug-release performance of low-methoxyl pectin (LM-pectin) hydrogels. Theophylline was used as a model drug to evaluate release behavior under physiologically relevant conditions. The incorporation of plasticizers modulated polymer–polymer interactions, swelling behavior, and thermal properties, thereby affecting drug-release kinetics. CO, a hydrophobic triglyceride, created microdomain-induced diffusion pathways; PVP, containing water-affinitive lactam units, facilitated moisture-driven plasticization; and PEG (MW 400/1000/1500), with hydroxyl-terminated chains, established hydrogen bonds with pectin. Structural analyses (FTIR and DSC) revealed that CO disrupted pectin packing, leading to a flexible yet crystalline matrix and enabling the highest cumulative drug release. PVP-based hydrogels exhibited enhanced crystallinity and slower release, whereas PEG formulations showed molecular-weight-dependent behavior. Kinetic calculations confirmed similar patterns, demonstrating non-Fickian transport for PEG400 and PEG1000 (diffusion associated with polymer relaxation) and an additional diffusion-limited profile for PEG1500 attributed to network densification. Among the methods evaluated, CO improved cumulative release, while PEG1500 and PVP promoted extended, lower-rate delivery. The selection of plasticizers must correspond with the design objective: CO for high cumulative release and PEG1500 or PVP for prolonged, diffusion-controlled administration. These results highlight the critical role of the plasticizer type in tailoring hydrogel performance. The LM-pectin formulations developed herein demonstrate potential for application in controlled dermal and mucosal drug-delivery systems.

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