Hydrogel is in the spotlight as a useful biomaterial in the field of drug delivery and tissue engineering due to its similar biological properties to a native extracellular matrix (ECM). Herein, we proposed a ternary hydrogel of gellan gum (GG), silk fibroin (SF), and chondroitin sulfate (CS) as a biomaterial for cartilage tissue engineering. The hydrogels were fabricated with a facile combination of the physical and chemical crosslinking method. The purpose of this study was to find the proper content of SF and GG for the ternary matrix and confirm the applicability of the hydrogel in vitro and in vivo. The chemical and mechanical properties were measured to confirm the suitability of the hydrogel for cartilage tissue engineering. The biocompatibility of the hydrogels was investigated by analyzing the cell morphology, adhesion, proliferation, migration, and growth of articular chondrocytes-laden hydrogels. The results showed that the higher proportion of GG enhanced the mechanical properties of the hydrogel but the groups with over 0.75% of GG exhibited gelling temperatures over 40 °C, which was a harsh condition for cell encapsulation. The 0.3% GG/3.7% SF/CS and 0.5% GG/3.5% SF/CS hydrogels were chosen for the in vitro study. The cells that were encapsulated in the hydrogels did not show any abnormalities and exhibited low cytotoxicity. The biochemical properties and gene expression of the encapsulated cells exhibited positive cell growth and expression of cartilage-specific ECM and genes in the 0.5% GG/3.5% SF/CS hydrogel. Overall, the study of the GG/SF/CS ternary hydrogel with an appropriate content showed that the combination of GG, SF, and CS can synergistically promote articular cartilage defect repair and has considerable potential for application as a biomaterial in cartilage tissue engineering.

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In this study, dopamine-functionalized gellan gum (DFG) hydrogel was prepared as a carrier for retinal pigment epithelium (RPE) cell delivery via a carbodiimide reaction. The carboxylic acid of gellan gum (GG) was replaced with catechol in a 21.3% yield, which was confirmed by NMR. Sol fraction and weight loss measurements revealed that dopamine improved degradability in the GG hydrogel. Measurements of the viscosity, injection force, and compressibility also showed that dopamine-functionalized GG hydrogels had more desirable rheological/mechanical properties for improving injectability. These characteristics were confirmed to arise from the GG’s helix structure loosened by the dopamine’s bulky nature. Moreover, dopamine’s hydrophilic characteristics were confirmed to create a more favorable microenvironment for cell growth by promoting swelling capability and cell attachment. This improved biocompatibility became more pronounced when the hydrophilicity of dopamine was combined with a larger specific surface area stemming from the less porous structure of the dopamine-grafted hydrogels. This effect was apparent from the live/dead staining images of the as-prepared hydrogels. Meanwhile, the nonionic cross-linked DFG (DG) hydrogel showed the lowest protein expression in the immunofluorescence staining images obtained after 28 days of culture, supporting that it had the highest degradability and associated cell-releasing ability. That tendency was also observed in the gene expression data acquired by real-time polymerase chain reaction (RT-PCR) analysis. RT-PCR analysis also revealed that the DG hydrogel carrier could upregulate the visual function-related gene of RPE. Overall, the DG hydrogel system demonstrated its feasibility as a carrier of RPE cells and its potential as a means of improving visual function.

Cell therapies for age-related macular degeneration (AMD) treatment have been developed by integrating hydrogel-based biomaterials. Until now, cell activity has been observed only in terms of the modulus of the hydrogel. In addition, cell behavior has only been observed in the 2D environment of the hydrogel and the 3D matrix. As time-dependent stress relaxation is considered a significant mechanical cue for the control of cellular activities, it is important to optimize hydrogels for retinal tissue engineering (TE) by applying this viewpoint. Herein, a gellan Gum (GG)/Hyaluronic acid (HA) hydrogel was fabricated using a facile physical crosslinking method. The physicochemical and mechanical properties were controlled by forming a different composition of GG and HA. The characterization was performed by conducting a mass swelling study, a sol fraction study, a weight loss test, a viscosity test, an injection force study, a compression test, and a stress relaxation analysis. The biological activity of the cells encapsulated in 3D constructs was evaluated by conducting a morphological study, a proliferation test, a live/dead analysis, histology, immunofluorescence staining, and a gene expression study to determine the most appropriate material for retinal TE biomaterial. Hydrogels with moderate amounts of HA showed improved physicochemical and mechanical properties suitable for injection into the retina. Moreover, the time-dependent stress relaxation property of the GG/HA hydrogel was enhanced when the appropriate amount of HA was loaded. In addition, the cellular compatibility of the GG/HA hydrogel in in vitro experiments was significantly improved in the fast-relaxing hydrogel. Overall, these results demonstrate the remarkable potential of GG/HA hydrogel as an injectable hydrogel for retinal TE and the importance of the stress relaxation property when designing retinal TE hydrogels. Therefore, we believe that GG/HA hydrogel is a prospective candidate for retinal TE biomaterial.

Various research about cartilage regeneration using biomaterials has been done recently. Particularly, gellan gum hydrogel (GG) is reported to be suitable as a biomaterial for cartilage tissue engineering (TE) for its water uptaking ability, producibility, and environmental resemblance of native cartilage. Despite these advantages, mechanical and cell adhesion properties are still difficult to modulate.Reinforcement is essential to overcome these problems. Herein, GG was modified by physically blending with different lengths of silk fiber (SF). As SF is expected to improve such disadvantages of GG, mechanical and biological properties were characterized to confirm its reinforcement ability. Mechanical properties such as degradation rate, swelling rate, compression strength, and viscosity were studied and it was confirmed that SF significantly reinforces the mechanical properties of GG. Furthermore, in vitro study was carried out to confirm morphology, biocompatibility, proliferation, and chondrogenesis of chondrocytes encapsulated in the hydrogels. Overall, chondrocytes in the GG blended with SF (SF/GG) showed enhanced cell viability and growth. According to this study, SF/GG can be a promising biomaterial for cartilage TE biomaterial. K E Y W O R D Schondrogenesis, gellan gum, hydrogel, silk fiber, tissue engineering | INTRODUCTIONCartilage defects can occur by various causes such as injuries, diseases, aging, etc. and they are relatively difficult to regenerate naturally due to lack of blood vessel, an insufficient number of progenitor cells, and slow turnover of a cartilaginous matrix. Defected cartilage may advance to other severe chondral diseases. Therefore, the necessity of proper treatment for cartilage regeneration is highlighted. The current treatments include chondrocytes implantation, allografting, and drilling (Musumeci et al., 2013), but these procedures do not provide a high success rate due to body immune response and the complexity of the procedure. Tissue engineering (TE) for cartilage regeneration has been rapidly taken place as it emerged as an excellent approach for tissue repair. Numerous types of synthetic and natural biomaterials were produced for cartilage TE purposes (Cao et al., 2014;Ge et al., 2012;Stoddart et al., 2009). Among these types, hydrogels have gained attention recently for their excellent biocompatibility and