Chitosan Cross-Linking with Acetaldehyde Acetals.

Alexander Pestov,Yuliya Privar,Arseny Slobodyuk,Svetlana Bratskaya,Andrey Boroda

doi:10.3390/biomimetics7010010

Abstract

Here we demonstrate the possibility of using acyclic diethylacetal of acetaldehyde (ADA) with low cytotoxicity for the fabrication of hydrogels via Schiff bases formation between chitosan and acetaldehyde generated in situ from acetals in chitosan acetate solution. This approach is more convenient than a direct reaction between chitosan and acetaldehyde due to the better commercial availability and higher boiling point of the acetals. Rheological data confirmed the formation of intermolecular bonds in chitosan solution after the addition of acetaldehyde diethyl acetal at an equimolar NH2: acetal ratio. The chemical structure of the reaction products was determined using elemental analysis and 13C NMR and FT-IR spectroscopy. The formed chitosan-acetylimine underwent further irreversible redox transformations yielding a mechanically stable hydrogel insoluble in a broad pH range. The reported reaction is an example of when an inappropriate selection of acid type for chitosan dissolution prevents hydrogel formation.

Highlights

Expanding directions of chitosan application to obtain new organic materials requires the development of versatile approaches for this aminopolysaccharide modification
The latter type of modification allows the fabrication of chitosan hydrogels for pharmaceutical and medical use with tunable swelling, which can be controlled via the type and density of the cross-linking [3,4]
Non-selective methods of cross-linker synthesis and the irregular structure of carbohydrate polyaldehydes lead to the low reproducibility of this fabrication method and of resultant hydrogels’ properties

Summary

Introduction

Expanding directions of chitosan application to obtain new organic materials requires the development of versatile approaches for this aminopolysaccharide modification This modification must be targeted toward the introduction of ionic functional groups [1] to broaden the pH window of the polymer solubility, and to cross-link macromolecules to limit the solubility in acidic media [2]. Its natural toxicity limits its use for biomedical applications [10,11] To solve this problem, recent studies suggest using the products of the partial oxidation of polysaccharides as cross-linkers [5,12,13,14,15,16,17,18,19] and their functional derivatives [20,21]. The chemical shifts were referenced to tetramethylsilane (TMS).Fourier transform infrared (FTIR) spectra were recorded using an IR Affinity-1 spectrometer with a MIRacle 10 FTIR accessory (Shimadzu, Kyoto, Japan)

Rheological Properties

Cytotoxicity Study