Self-Crosslinkable Oxidized Alginate-Carboxymethyl Chitosan Hydrogels as an Injectable Cell Carrier for In Vitro Dental Enamel Regeneration

Abstract

Injectable hydrogels, as carriers, offer great potential to incorporate cells or growth factors for dental tissue regeneration. Notably, the development of injectable hydrogels with appropriate structures and properties has been a challenging task, leaving much to be desired in terms of cytocompatibility, antibacterial and self-healing properties, as well as the ability to support dental stem cell functions. This paper presents our study on the development of a novel self-cross-linkable hydrogel composed of oxidized alginate and carboxymethyl chitosan and its characterization as a cell carrier for dental enamel regeneration in vitro. Oxidized alginate was synthesized with 60% theoretical oxidation degree using periodate oxidation and characterized by Fourier Transform Infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, and Ultraviolet-visible absorption spectroscopy. Then, hydrogels were prepared at three varying weight ratios of oxidized alginate to carboxymethyl chitosan (4:1, 3:1, and 2:1) through Schiff base reactions, which was confirmed by Fourier Transform Infrared spectroscopy. The hydrogels were characterized in terms of gelation time, swelling ratio, structure, injectability, self-healing, antibacterial properties, and in vitro characterization for enamel regeneration. The results demonstrated that, among the three hydrogels examined, the one with the highest ratio of oxidized alginate (i.e., 4:1) had the fastest gelation time and the lowest swelling ability, and that all hydrogels were formed with highly porous structures and were able to be injected through a 20-gauge needle without clogging. The injected hydrogels could be rapidly reformed with the self-healing property. The hydrogels also showed antibacterial properties against two cariogenic bacteria: Streptococcus mutans and Streptococcus sobrinus. For in vitro enamel regeneration, a dental epithelial cell line, HAT-7, was examined, demonstrating a high cell viability in the hydrogels during injection. Furthermore, HAT-7 cells encapsulated in the hydrogels showed alkaline phosphatase production and mineral deposition, as well as maintaining their round morphology, after 14 days of in vitro culture. Taken together, this study has provided evidence that the oxidized alginate-carboxymethyl chitosan hydrogels could be used as an injectable cell carrier for dental enamel tissue engineering applications.

Chitosan-Based Biomaterials for Tissue Regeneration

“…Another chitosan-based hydrogel was developed by Mohabatpour and colleagues as a cell carrier for in vitro regeneration of tooth enamel [ 86 ]. The biomaterial complex of oxidized alginate and carboxymethyl chitosan was tested in 3 different compositions (4:1, 3:1 and 2:1 ratios).…”

“…In all groups, the expression of alkaline phosphatase, a marker of enamel matrix mineralization, was found, which indicated the differentiation of HAT-7 cells in ameloblasts and possible restoration of enamel. In addition, hydrogels exhibited antibacterial properties against two cariogenic bacteria: Streptococcus mutans and Streptococcus sobrinus , which are involved in the formation of dental caries [ 86 ]. Taken together, the above findings support the idea of the multifunctional nature of chitosan.…”

Alginate-Based Biomaterials in Tissue Engineering and Regenerative Medicine

“…Today, studies have focused on using alginate-based biomaterials in dental TE-RM; alginate hydrogels with non-toxicity can be deployed for directing the differentiation of dental-derived stem cells [ 97 , 98 ]. In addition, injectable hydrogels can be deployed as carriers with excellent potential to incorporate cells or growth factors for dental tissue regeneration [ 99 ]. In one study, self-crosslinkable hydrogels were constructed from oxidized alginate and carboxymethyl chitosan as cell carriers for dental enamel regeneration (in vitro), showing suitable self-healing property.…”

“…These hydrogels also exhibited antibacterial activities against Streptococcus mutans and Streptococcus sobrinus . After in vitro enamel regeneration studies, it was revealed that the dental epithelial cell line, HAT-7, had high cell viability in the injected hydrogels [ 99 ]. In addition, an injectable, non-toxic, and biodegradable scaffold was developed using oxidized alginate microbeads, which encapsulated periodontal ligament and gingival MSCs [ 97 ].…”

A Comprehensive Review of Cross-Linked Gels as Vehicles for Drug Delivery to Treat Central Nervous System Disorders

“…Schiff base cross-linking reactions are reactions between molecules containing amine, alcohol, or hydrazide moieties and an aldehyde molecule [ 87 ]. The reactions involve a dynamic covalent amine bond formation via the cross-linking of amine groups and aldehyde groups and depend on the pH, temperature, and type of aldehydes/amines involved in the reaction [ 182 , 183 ]. Enzymes form covalent bonds between polymers, they are significantly sensitive and specific in chemical reactions [ 80 ].…”