Ionotropic Gelation of Chitosan Flat Structures and Potential Applications

Abstract

The capability of some polymers, such as chitosan, to form low cost gels under mild conditions is of great application interest. Ionotropic gelation of chitosan has been used predominantly for the preparation of gel beads for biomedical application. Only in the last few years has the use of this method been extended to the fabrication of chitosan-based flat structures. Herein, after an initial analysis of the major applications of chitosan flat membranes and films and their usual methods of synthesis, the process of ionotropic gelation of chitosan and some recently proposed novel procedures for the synthesis of flat structures are presented.

Keywords: carbohydrate polymers; chitosan; chitosan membranes; flat chitosan; ionotropic gelation.

Figure 1

Structures of chitin, chitosan, and cellulose. Reprinted from [33] with permission from Elsevier.

Figure 2

Scheme illustrating the chemical equilibrium of chitosan in slightly acidic solution and related methods to obtain chitosan flat structures from its soluble or insoluble form.

Figure 3

Scheme of solution-cast and LBL assembly methods for the fabrication of chitosan-based flat structures starting from a chitosan polycation solution (low pH, Chit-soluble form).

Figure 4

(a) Approximate number of publications from 1985 to 1st December 2020 obtained by Web of Science using the topic keywords indicated on the labels of the graph. (b) Magnification of the area indicated by the dashed box in the graph of panel (a).

Figure 5

Sketch of (a) a flat chitosan-based asymmetric membrane for application in wound dressing. Reprinted from [51] with permission from Elsevier. (b) how the wound dressing works. Reprinted from [75] under open access CC-BY license.

Figure 6

Synthesis of a flat-structured free-standing solid polymer superamolecular hydrogel electrolyte. Reprinted under an open access CC-BY licence [135].

Figure 7

(a) Schematic of preparation process of Chit/PVA blend membranes. (b) Proposed interactions among Chit, PVA and adipic acid in the casting solution. Reprinted from [152] with permission from Elsevier.

Figure 8

Published articles each year obtained by a search in Web of Science database in December 2020 using “Chitosan” and “Ionotropic gelation” topic keywords.

Figure 9

(a) The BIG method: steps of the procedure of proton conducting Chit-PWA flat membranes formation. (b) Scheme of Chit polyelectrolyte dissolution in acid acetic solution (left) and ionotropic gelation of chitosan through cross-linking with PWA³⁻ anions (right). Reproduced from Ref. [9] under open access CC-BY license.

Figure 10

Fuel cell performance recorded for a hydrogen/oxygen fed fuel cell (25 °C, 1 mg cm⁻² Pt) with Chit/PWA flat membranes prepared by ionotropic gelation at the experimental conditions indicated on the graph. Insets: SEM cross-sections of inotropic gelled Chit/PWA flat membranes before assembly. Reproduced from Ref. [9] under open access CC-BY license.

Figure 11

(a) Experimental setup for developing chitosan-tripolyphosphate (TPP) macroscopic gels through external gelation method. (b) Scheme of the obtained homogeneous chitosan-TPP hydrogel. Reprinted with permission from ([13], 2014 American Chemical Society).

Figure 12

(a) Confocal scanning electron microscopy on chitosan gel synthetized by FITC-labeled chitosan along with (b) polymer profile through the gelling axis. Reprinted under an open access CC-BY licence [207].

Figure 13

Substrate dissipation energy as novel cell controller. (a) Stress as a function of strain for different chitosan substrates. (b) Energy at different fractions of acetylation (F_A). (c) How the substrate dissipated energy controls adhesion and spreading. (d) Critical strain as a function of F_A. (e) Scheme showing how chitosan substrate allow two possible combinations of five consecutive monomers (pentads) irrespective of sugar position behave as “energy dampers” thus dissipating shear forces (A = N-acetyl-glucosamine unit, D = glucosamine unit). Reproduced from [209] with permission of John Wiley and Sons.