Effect of Chitosan on Rheological, Mechanical, and Adhesive Properties of Pectin-Calcium Gel

Abstract

In the present study, chitosan was included in the pectin ionotropic gel to improve its mechanical and bioadhesive properties. Pectin-chitosan gels P-Ch0, P-Ch1, P-Ch2, and P-Ch3 of chitosan weight fractions of 0.00, 0.25, 0.50, and 0.75 were prepared and characterized by dynamic rheological tests, penetration tests, and serosal adhesion ex vivo assays. The storage modulus (G') and loss modulus (G″) values, gel hardness, and elasticity of P-Ch1 were significantly higher than those of P-Ch0 gel. However, a further increase in the content of chitosan in the gel significantly reduced these parameters. The inclusion of chitosan into the pectin gel led to a decrease in weight and an increase in hardness during incubation in Hanks' solution at pH 5.0, 7.4, and 8.0. The adhesion of P-Ch1 and P-Ch2 to rat intestinal serosa ex vivo was 1.3 and 1.7 times stronger, whereas that of P-Ch3 was similar to that of a P-Ch0 gel. Pre-incubation in Hanks' solution at pH 5.0 and 7.4 reduced the adhesivity of gels; however, the adhesivity of P-Ch1 and P-Ch2 exceeded that of P-Ch0 and P-Ch3. Thus, serosal adhesion combined with higher mechanical stability in a wide pH range appeared to be advantages of the inclusion of chitosan into pectin gel.

Keywords: chitosan; ionotropic gel; mechanical properties; pectin; rheology; serosal adhesion; weight loss.

Figure 1

Strain sweep of P–Ch0 (A), P–Ch1 (B), P–Ch2 (C), and P–Ch3 (D) gels at a fixed frequency of 1 Hz and 20 °C.

Figure 2

Scanning electron micrographs of the surfaces of the P–Ch0 (A,E), P–Ch1 (B,F), P–Ch2 (C,G), and P–Ch3 (D,H) gels. Magnification: (A–D)—50×, scale bar: 1.0 mm; (E–H)—2000×, scale bar: 20 μm.

Figure 3

Weight change of pectin–chitosan gels during incubation in Hank’s solution of pH 5.0 (A), 7.4 (B), and 8.0 (C). Different lowercase letters a, b, c, and d indicate significant (p < 0.05) differences between gels. * p < 0.05 vs. previous time point. n = 6.

Figure 4

The content of GalA in the incubation medium during incubation of pectin–chitosan gels in Hank’s solutions of initial pH 5.0 (A), 7.4 (B), and 8.0 (C). Different lowercase letters a, b and c indicate significant (p < 0.05) differences between gels. * p < 0.05 vs. previous time point. n = 6.

Figure 5

Change in pH level during incubation of pectin–chitosan gels in Hank’s solutions of initial pH 5.0 (A), 7.4 (B), and 8.0 (C). Different lowercase letters a, b and c indicate significant (p < 0.05) differences between gels. * p < 0.05 vs. previous time point. n = 6.

Figure 6

Change in hardness of pectin–chitosan gels during incubation in Hank’s solution of pH 5.0 (A), 7.4 (B), and 8.0 (C). Different lowercase letters a, b, c, and d indicate significant (p < 0.05) differences between gels. * p < 0.05 vs. previous time point. n = 8.

Figure 7

Change in elasticity of pectin–chitosan gels during incubation in Hank’s solution of pH 5.0 (A), 7.4 (B), and 8.0 (C). Different lowercase letters a, b, c, and d indicate significant (p < 0.05) differences between gels. * p < 0.05 vs. previous time point. n = 8.

Figure 8

Change in Young’s modulus of pectin–chitosan gels during incubation in Hank’s solution of pH 5.0 (A), 7.4 (B), and 8.0 (C). Different lowercase letters a, b, c, and d indicate significant (p < 0.05) differences between gels. * p < 0.05 vs. previous time point. n = 8.

Figure 9

The adhesion strength of pectin–chitosan gels before (A) and after 24 h of incubation in Hank’s solution at pH 5.0 (B), 7.4 (C), and 8.0 (D). Different lowercase letters a, b and c indicate significant (p < 0.05) differences between gels. * p < 0.05 vs. before incubation. n = 8.

Figure 10

The work of adhesion of pectin–chitosan gels before (A) and after 24 h incubation in Hank’s solution at pH 5.0 (B), 7.4 (C), and 8.0 (D). Different lowercase letters a, b and c indicate significant (p < 0.05) differences between gels. * p < 0.05 vs. before incubation. n = 8.

Figure 11

Representative tensile strength adhesive curve of the interaction of the P–Ch0 and P–Ch3 gels with the serosa before (A) and after 24 h incubation in Hank’s solution at pH 5.0 (B), 7.4 (C), and 8.0 (D). The deadhesion (i) and the debonding (ii) phases are shown.

Figure 12

Adhesion of human fibroblasts to the plastic surface (control) after 2 (A) and 24 h (B) of incubation.

Figure 13

Adhesion of human fibroblasts to the P–CH0 (A), P–Ch1 (B), P–Ch2 (C), and P–Ch3 (D) gels after 24 h of incubation.

Figure 14

Mechanism presentation of the network model of the P–Ch0 (A), P–Ch1 (B), P–Ch2 (D), and P–Ch3 (E) gels. (C,F) show the possible interaction of pectin and chitosan chains in P–Ch1 and P–Ch3 gels, respectively.

Figure 15

The gel probe for testing adhesion.