Chemically Crosslinked Alginate Hydrogel with Polyaziridine: Effects on Physicochemical Properties and Promising Applications

Abstract

Alginate biopolymer is widely employed in many industrial fields thanks to its pleasing features of biodegradability, biocompatibility, low toxicity, and relatively low cost. The gelling process of alginate with divalent cations is fairly simple and thus it is used as a versatile biomaterial to tailor the desired mechanical and moisture properties. This study focused on developing new gel formulations to enhance the properties of calcium-alginate hydrogel (CA). The newly synthesized hydrogels, referred to as CA-CHEM gels, were chemically cross-linked with different ratios of pentaerythritol tris[3-(1-aziridinyl)propionate] (PTAP) through the reaction between the carboxylic groups of alginate and aziridines of PTAP. The reaction was successfully monitored by NMR. The new CA-CHEM gels were chemically characterized using FTIR-ATR, while SEM analysis confirmed the changes in the porosity and homogeneity of the network. Additionally, thermogravimetric analyses and mechanical properties showed improvement in degradation stability and in structural strength, compared to plain CA, with an increasing PTAP content up to 1 % w/w. Finally, the new CA-CHEM gels effectively controlled water absorption and release. In particular, CA-CHEM-1 performed as the most controlled system, making it promising for delivering aqueous cleaning solutions on water-sensitive surfaces such as a wooden historical musical instrument.

Keywords: Alginate hydrogel; Biopolymer; Chemical crosslinking; Gel application; Polyaziridine.

Figure 1

A sketch of the internal side of the double bass (on the left) and the wood bottom block of the instrument (on the right) with the label highlighted by a red rectangle.

Figure 2

¹H NMR spectrum of Alg (sodium alginate), PTAP (pentaerythritol tris[3‐(1‐aziridinyl)propionate]), and Alg‐PTAP. Characteristic peaks are denoted.

Figure 3

Graphical representation of the chemical structure of CA‐CHEM gels and reagents (top) and FTIR‐ATR spectra of the gels prepared with different PTAP content, in the range 2000–1300 cm⁻¹. Ester bands are marked with an asterisk at 1725 cm⁻¹.

Figure 4

SEM images of the surface of CA (a‐b), CA‐CHEM‐0.5 (c‐d), CA‐CHEM‐1 (e‐f), and CA‐CHEM‐2 (g‐h) at different magnifications.

Figure 5

TGA curves from room temperature to 350 °C (a) and DTG traces from 180 °C to 350 °C (b) curves for CA and CA‐CHEM gels obtained with different PTAP content.

Figure 6

Mechanical properties determined by tensile test (mean value±s.d.; n=5) of gels CA and CA‐CHEM‐0.5, 1, and 2 (a‐b), and fresh and aged CA and CA‐CHEM‐1 (c‐d).

Figure 7

Images before (a) and after (b) cleaning the Leopold Noiriel's double bass wood block in visible and UV light, and after processing the image with the likelihood tool (c), with the gel application area in red square; (d) ER‐FTIR spectra after Kramers‐Kronig transform of uncleaned (black) and cleaned (red) area. The marker bands of amide I and II of the animal glue are represented with dotted red lines.