Effect of Cross-Linking Cations on In Vitro Biocompatibility of Apple Pectin Gel Beads

Abstract

The study aimed to compare the in vitro biocompatibility of pectin gels formed by different cross-linking cations. Hydrogel beads named CaPG, ZnPG, FePG, and AlPG were prepared from 4% solutions of apple pectin using ionotropic gelling with CaCl2, ZnCl2, FeCl3, and AlCl3, respectively. Cations influenced the gel strength of the wet gel beads in the following order (least strong) Ca2+ < Zn2+ < Fe3+~Al3+ (most strong). The swelling degree of the CaPG beads after 24 h of incubation in the RPMI-1640 medium was 104%, whereas the ZnPG, FePG, and AlPG beads swelled by 76, 108, and 134%, respectively. The strength of the pectin gel decreased significantly after incubation in the RPMI-1640 medium for 24 h, regardless of the cross-linking cation, although the FePG beads remained the strongest. All the pectin beads adsorbed serum proteins to a low degree, however the serum protein adsorption by the ZnPG and FePG beads (1.46 ± 0.87 and 1.35 ± 0.19 µg/mm2) was more than the CaPG and AlPG beads (0.31 ± 0.36 and 0.44 ± 0.25 µg/mm2). All the pectin beads reduced the production of TNF-α and IL-10 by hPBMCs in response to LPS stimulation. The IL-1β response of cells to LPS was significantly reduced by the CaPG, ZnPG, and FePG beads, whereas the AlPG beads enhanced it twofold. The CaPG, FePG, and AlPG beads had no cytotoxicity. The viability of hPBMCs and human fibroblasts incubated with ZnPG beads was 5.3 and 7.2%, respectively. Thus, the use of different cross-linking cations changed the properties of the pectin gel, which is important for biocompatibility.

Serosal Adhesion Ex Vivo of Hydrogels Prepared from Apple Pectin Cross-Linked with Fe3+ Ions

“…As shown by the initial screening, the type of cross-linking cation affects the adhesiveness of the pectin hydrogel. The type of cross-linking cation is well known to be a significant determinant of pectin gel stability [ 16 , 23 ], drug-releasing behavior [ 15 , 20 ], biocompatibility [ 24 ], and other functional properties [ 25 ]. Calcium ions are mainly used as a cross-linker to obtain ionotropic pectin hydrogels, however, Zn 2+ and Al 3+ ion cross-linking provides better control of stability and drug release rate than Ca 2+ [ 20 , 21 , 23 ].…”

“…However, we did not further consider the adhesiveness of these hydrogels due to their low biocompatibility. It was previously shown that Zn 2+ cross-linked hydrogel had a cytotoxic effect on leukocytes and fibroblasts, and Al 3+ cross-linked hydrogel enhanced the production of the inflammatory cytokine IL-1β [ 24 ].…”

“…Protein adsorption and leukocyte adhesion on the surface are one of the first events after biomaterial implantation [ 30 , 31 ]. We have previously shown that pectin hydrogels adsorb serum proteins, and adhere and activate leukocytes [ 24 , 32 , 33 ]. In the present study, serum proteins and peritoneal cells did not interfere with the serosal adhesion, suggesting different binding points.…”

Matrices of Native and Oxidized Pectin and Ferrous Bisglycinate and Their In Vitro Behavior through Gastrointestinal Conditions

“…Different studies have previously explored pectin colloidal gels crosslinked with iron, and have demonstrated that this cation produces one of the most stable forms, when compared to other most commonly used gels such as copper and calcium [28,36]. In this case, it is believed, from the FTIR analysis, that oxidation produced a greater number of carboxyl groups that could potentially participate in the ionotropic gelation, but it is possible that the number of these extra groups was not sufficient to cause a significant difference in the degree of crosslinking, and thereby affect swelling.…”

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

“…Recently, our group showed that a hydrogel made of ionically cross-linked apple pectin adhered to rat intestinal serosa ex vivo with a strength that depended on the type of cross-linking cation [23]. However, the serosal adhesion and strength of the ionotropic pectin gel were found to decrease significantly after incubation in physiological media [23][24][25]. Improvement of adhesivity and strengthening of the pectin gel network appear to be necessary to obtain promising hydrogel adhesives to treat anastomotic leakage.…”