Injectable in situ Physically and Chemically Crosslinkable Gellan Hydrogel
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An injectable, in situ physically and chemically crosslinkable gellan hydrogel is synthesized via gellan thiolation. The thiolation does not alter the gellan's unique 3-D conformation, but leads to a lower phase transition temperature under physiological conditions and stable chemical crosslinking. The synthesis and hydrogels are characterized by (1)H NMR, FT-IR, CD, or rheology measurements. The injectability and the tissue culture cell viability is also tested. The thiolated gellan hydrogel exhibits merits, such as ease for injection, quick gelation, lower gelling temperature, stable structure, and nontoxicity, which make it promising in biomedicine and bioengineering as an injectable hydrogel.Keywords:
Gellan gum
The relatively weak mechanical properties of hydrogels remain a major drawback for their application as load-bearing tissue scaffolds. Previously, we developed cell-laden double-network (DN) hydrogels that were composed of photocrosslinkable gellan gum (GG) and gelatin. Further research into the materials as tissue scaffolds determined that the strength of the DN hydrogels decreased when they were prepared at cell-compatible conditions, and the encapsulated cells in the DN hydrogels did not function as well as they did in gelatin hydrogels. In this work, we developed microgel-reinforced (MR) hydrogels from the same two polymers, which have better mechanical strength and biological properties in comparison to the DN hydrogels. The MR hydrogels were prepared by incorporating stiff GG microgels into soft and ductile gelatin hydrogels. The MR hydrogels prepared at cell-compatible conditions exhibited higher strength than the DN hydrogels and the gelatin hydrogels, the highest strength being 2.8 times that of the gelatin hydrogels. MC3T3-E1 preosteoblasts encapsulated in MR hydrogels exhibited as high metabolic activity as in gelatin hydrogels, which is significantly higher than that in the DN hydrogels. The measurement of alkaline phosphatase (ALP) activity and the amount of mineralization showed that osteogenic behavior of MC3T3-E1 cells was as much facilitated in the MR hydrogels as in the gelatin hydrogels, while it was not as much facilitated in the DN hydrogels. These results suggest that the MR hydrogels could be a better alternative to the DN hydrogels and have great potential as load-bearing tissue scaffolds.
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Currently, biodegradable hydrogels are one of the most promising materials in tissue engineering. From the perspective of clinical needs, hydrogels with high strength and minimally invasive implantation are preferred for the reconstruction of load-bearing tissues. In this work, a biodegradable, high-strength, and injectable hydrogel was developed by one-step photo-cross-linking of two biomacromolecules, polyethylene glycol acrylated poly(l-glutamic acid) (PLGA-APEG) and methacrylated gellan gum (GG-MA). The hydrogels, named as PLGA/GG hydrogels, exhibited high mechanical properties. The compression stress of the hydrogels was 0.53 MPa, and the fracture energy was 7.7 ± 0.2 kJ m-2. Meanwhile, the storage modulus could reach 44.0 ± 0.6 kPa. The hydrogel precursor solution loaded with adipose-derived stem cells (ASCs) was subcutaneously injected into C57BL/6 mice and then cross-linked via in situ transdermal irradiation, which demonstrated the excellent injectability and subcutaneous gelatinization of PLGA/GG hydrogels as cell carriers. Furthermore, three-dimensional encapsulation of ASCs in hydrogels after 7, 14, and 21 days showed outstanding cytocompatibility, and the viability of ASCs was up to 84.0 ± 1.7%. The PLGA/GG hydrogels exhibited ideal behaviors of degradation, with 60 ± 5% of hydrogels degraded in phosphate buffered solution (PBS) after 11 weeks. H&E staining demonstrated that the hydrogels degraded gradually after 6 weeks and supported tissue invasion without inflammatory reactions, which indicated the laudable biodegradability of hydrogels. Hence, the biodegradable and high-strength hydrogels with well-performed injectability and biocompatibility possessed high potential applications in tissue engineering, especially in load-bearing tissue regeneration.
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Methacrylamide
Cell encapsulation
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Gellan gum (GG)-based hydrogels are advantageous in tissue engineering not only due to their ability to retain large quantities of water and provide a similar environment to that of natural extracellular matrix (ECM), but also because they can gelify in situ in seconds. Their mechanical properties can be fine-tuned to mimic natural tissues such as the nucleus pulposus (NP). This study produced different formulations of GG hydrogels by mixing varying amounts of methacrylated (GG-MA) and high-acyl gellan gums (HA-GG) for applications as acellular and cellular NP substitutes. The hydrogels were physicochemically characterized by dynamic mechanical analysis. Degradation and swelling abilities were assessed by soaking in a phosphate buffered saline solution for up to 170 h. Results showed that as HA-GG content increased, the modulus of the hydrogels decreased. Moreover, increases in HA-GG content induced greater weight loss in the GG-MA/HA-GG formulation compared to GG-MA hydrogel. Potential cytotoxicity of the hydrogel was assessed by culturing rabbit NP cells up to 7 days. An MTS assay was performed by seeding rabbit NP cells onto the surface of 3D hydrogel disc formulations. Viability of rabbit NP cells encapsulated within the different hydrogel formulations was also evaluated by Calcein-AM and ATP assays. Results showed that tunable GG-MA/HA-GG hydrogels were non-cytotoxic and supported viability of rabbit NP cells. Copyright © 2012 John Wiley & Sons, Ltd.
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Matrix (chemical analysis)
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Hydrogel materials are 3D polymeric materials that have a wide range of applications. Strain-sensor applications, one of the application areas of hydrogels, continue to attract the attention of researchers. In this study, gellan gum-graphene oxide (GG/GO) hybrid hydrogels were synthesized for strain-sensor application. FTIR, XRD, and SEM measurements and strain sensor application analyses of the synthesized hydrogels were performed. It has been observed that the GG/GO hybrid hydrogels obtained as a result of the findings are promising for strain-sensor applications.
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Strain (injury)
Characterization
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The relatively weak mechanical properties of hydrogels remain a major drawback for their application as load-bearing tissue scaffolds. Previously, we developed cell-laden double-network (DN) hydrogels that were composed of photocrosslinkable gellan gum (GG) and gelatin. Further research into the materials as tissue scaffolds determined that the strength of the DN hydrogels decreased when they were prepared at cell-compatible conditions, and the encapsulated cells in the DN hydrogels did not function as well as they did in gelatin hydrogels. In this work, we developed microgel-reinforced (MR) hydrogels from the same two polymers, which have better mechanical strength and biological properties in comparison to the DN hydrogels. The MR hydrogels were prepared by incorporating stiff GG microgels into soft and ductile gelatin hydrogels. The MR hydrogels prepared at cell-compatible conditions exhibited higher strength than the DN hydrogels and the gelatin hydrogels, the highest strength being 2.8 times that of the gelatin hydrogels. MC3T3-E1 preosteoblasts encapsulated in MR hydrogels exhibited as high metabolic activity as in gelatin hydrogels, which is significantly higher than that in the DN hydrogels. The measurement of alkaline phosphatase (ALP) activity and the amount of mineralization showed that osteogenic behavior of MC3T3-E1 cells was as much facilitated in the MR hydrogels as in the gelatin hydrogels, while it was not as much facilitated in the DN hydrogels. These results suggest that the MR hydrogels could be a better alternative to the DN hydrogels and have great potential as load-bearing tissue scaffolds.
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Gellan gum
Regenerative Medicine
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Hydrogels are known as polymer-based networks with the ability to absorb water and other body fluids. Because of this, the hydrogels are used to preserve drugs, proteins, nutrients or cells. Hydrogels possess great biocompatibility, and properties like soft tissue, and networks full of water, which allows oxygen, nutrients, and metabolites to pass. Therefore, hydrogels are extensively employed as scaffolds in tissue engineering. Specifically, hydrogels made of natural polymers are efficient structures for tissue regeneration, because they mimic natural environment which improves the expression of cellular behavior. Producing natural polymer-based hydrogels from collagen, hyaluronic acid (HA), fibrin, alginate, and chitosan is a significant tactic for tissue engineering because it is useful to recognize the interaction between scaffold with a tissue or cell, their cellular reactions, and potential for tissue regeneration. The present review article is focused on injectable hydrogels scaffolds made of biocompatible natural polymers with particular features, the methods that can be employed to engineer injectable hydrogels and their latest applications in tissue regeneration.
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Hydrogels have gained a lot of attention with their widespread use in different industrial applications. The versatility in the synthesis and the nature of the precursor reactants allow for a varying range of hydrogels with different mechanical and rheological properties. Understanding of the rheological behavior and the relationship between the chemical structure and the resulting properties is crucial, and is the focus of this review. Specifically, we include detailed discussion on the correlation between the rheological characteristics of hydrogels and their possible applications. Different rheological tests such as time, temperature and frequency sweep, among others, are described and the results of those tests are reported. The most prevalent applications of hydrogels are also discussed.
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