Supramolecular Strategy Effects on Chitosan Bead Stability in Acidic Media: A Comparative Study.

Andrew Worthen,Yakov Lapitsky,Kelly Irving

doi:10.3390/gels5010011

Abstract

Chitosan beads attract interest in diverse applications, including drug delivery, biocatalysis and water treatment. They can be formed through several supramolecular pathways, ranging from phase inversion in alkaline solutions, to the ionic crosslinking of chitosan with multivalent anions, to polyelectrolyte or surfactant/polyelectrolyte complexation. Many chitosan bead uses require control over their stability to dissolution. To help elucidate how this stability depends on the choice of supramolecular gelation chemistry, we present a comparative study of chitosan bead stability in acidic aqueous media using three common classes of supramolecular chitosan beads: (1) alkaline solution-derived beads, prepared through simple precipitation in NaOH solution; (2) ionically-crosslinked beads, prepared using tripolyphosphate (TPP); and (3) surfactant-crosslinked beads prepared via surfactant/polyelectrolyte complexation using sodium salts of dodecyl sulfate (SDS), caprate (NaC10) and laurate (NaC12). Highly variable bead stabilities with dissimilar sensitivities to pH were achieved using these methods. At low pH levels (e.g., pH 1.2), chitosan/SDS beads were the most stable, requiring roughly 2 days to dissolve. In weakly acidic media (at pH 3.0–5.0), however, chitosan/TPP beads exhibited the highest stability, remaining intact throughout the entire experiment. Beads prepared using only NaOH solution (i.e., without ionic crosslinking or surfactant complexation) were the least stable, except at pH 5.0, where the NaC10 and NaC12-derived beads dissolved slightly faster. Collectively, these findings provide further guidelines for tailoring supramolecular chitosan bead stability in acidic media.

Highlights

Chitosan is a bioderived polysaccharide that is produced through the deacetylation of chitin [1,2]
Aside from some reports comparing chitosan complexation with small multivalent ions with chitosan-based polyelectrolyte complex formation [31,40], and studying the effects of various covalent and ionic crosslink types [7,38], there is a dearth of studies that directly compare the stability of self-assembled chitosan gels prepared through disparate mechanisms. To partially address this and provide further guidelines for designing supramolecular chitosan complexes, here we investigate the stability of chitosan-based beads in acidic aqueous solutions using beads prepared by three different supramolecular mechanisms: (1) precipitation in alkaline solution, (2) complexation with anionic surfactant, and (3) ionic crosslinking with tripolyphosphate (TPP), which is a common ionic chitosan crosslinker [7,8,26,38]
Supramolecular chitosan beads were generated via dropwise addition of a 3 wt% aqueous chitosan solution into either 0.1 M NaOH or 1 wt% TPP, sodium caprate (NaC10 ), sodium laurate (NaC12 ) or sodium dodecyl sulfate (SDS) solutions through a 20-gauge syringe needle and equilibrating the resulting mixtures at 30 ◦ C for at least 24 h

Summary

Introduction

Chitosan is a bioderived polysaccharide that is produced through the deacetylation of chitin [1,2]. When its amine groups are protonated, chitosan becomes a polyelectrolyte that can be assembled into diverse, gel-like soft materials [5,6,8,9]. These range from films and coatings [17,18], to fibers [19,20], colloidal particles [8,21,22], and macroscopic gels [9,23] and beads [13,24,25,26]. These materials can be prepared using diverse supramolecular strategies, which include ionic crosslinking of chitosan with multivalent ions [18,21,26], complexation of chitosan with anionic surfactants [13,19,24]

Methods

Results

Discussion

Conclusion