Hyaluronate-alginate hybrid hydrogels prepared with various linkers for chondrocyte encapsulation

Bioactive Phenylboronic Acid-Functionalized Hyaluronic Acid Hydrogels Induce Chondro-Aggregates and Promote Chondrocyte Phenotype

Hydrogels are extensively investigated as biomimetic extracellular matrix (ECM) scaffolds in tissue engineering. The physiological properties of ECM affect cellular behaviors, which is an inspiration for cell-based therapies. Photocurable hyaluronic acid (HA) hydrogel (AHAMA-PBA) modified with 3-aminophenylboronic acid, sodium periodate, and methacrylic anhydride simultaneously is constructed in this study. Chondrocytes are then cultured on the surface of the hydrogels to evaluate the effect of the physicochemical properties of the hydrogels on modulating cellular behaviors. Cell viability assays demonstrate that the hydrogel is non-toxic to chondrocytes. The existence of phenylboronic acid (PBA) moieties enhances the interaction of chondrocytes and hydrogel, promoting cell adhesion and aggregation through filopodia. RT-PCR indicates that the gene expression levels of type II collagen, Aggrecan, and Sox9 are significantly up-regulated in chondrocytes cultured on hydrogels. Moreover, the mechanical properties of the hydrogels have a significant effect on the cell phenotype, with soft gels (≈2 kPa) promoting chondrocytes to exhibit a hyaline phenotype. Overall, PBA-functionalized HA hydrogel with low stiffness exhibits the best effect on promoting the chondrocyte phenotype, which is a promising biomaterial for cartilage regeneration.

Advances in mechanically robust and biomimetic polysaccharide-based constructs for cartilage tissue engineering

The purpose of cartilage tissue engineering is to provide artificial constructs with biological functions and mechanical features that resemble native tissue to improve tissue regeneration. Biochemical characteristics of the cartilage extracellular matrix (ECM) microenvironment provide a platform for researchers to develop biomimetic materials for optimal tissue repair. Due to the structural similarity of polysaccharides into physicochemical characteristics of cartilage ECM, these natural polymers capture special attention for developing biomimetic materials. The mechanical properties of constructs play a crucial influence in load-bearing cartilage tissues. Moreover, the addition of appropriate bioactive molecules to these constructs can promote chondrogenesis. Here, we discuss polysaccharide-based constructs that can be used to create substitutes for cartilage regeneration. We intend to focus on newly developed bioinspired materials, fine-tuning the mechanical properties of constructs, the design of carriers loaded by chondroinductive agents, and development of appropriate bioinks as a bioprinting approach for cartilage regeneration.

Effect of the uronic acid composition of alginate in alginate/collagen hybrid hydrogel on chondrocyte behavior

Introduction: Developing a culture system that can effectively maintain chondrocyte phenotype and functionalization is a promising strategy for cartilage repair. Methods: An alginate/collagen (ALG/COL) hybrid hydrogel using different guluronate/mannuronate acid ratio (G/M ratio) of alginates (a G/M ratio of 64/36 and a G/M ratio of 34/66) with collagen was developed. The effects of G/M ratios on the properties of hydrogels and their effects on the chondrocytes behaviors were evaluated. Results: The results showed that the mechanical stiffness of the hydrogel was significantly affected by the G/M ratios of alginate. Chondrocytes cultured on Mid-G/M hydrogels exhibited better viability and phenotype preservation. Moreover, RT-qPCR analysis showed that the expression of cartilage-specific genes, including SOX9, COL2, and aggrecan was increased while the expression of RAC and ROCK1 was decreased in chondrocytes cultured on Mid-G/M hydrogels. Conclusion: These findings demonstrated that Mid-G/M hydrogels provided suitable matrix conditions for cultivating chondrocytes and may be useful in cartilage tissue engineering. More importantly, the results indicated the importance of taking alginate G/M ratios into account when designing alginate-based composite materials for cartilage tissue engineering.

A bionic composite hydrogel with dual regulatory functions for the osteochondral repair

Due to the avascular nature of cartilage, it is difficult to heal and regenerate spontaneously after injury. At present, tissue engineering has become a promising strategy for repairing damaged cartilage, but the use of seed cells and growth factors is limited. In addition, the importance of mechanical compatibility of scaffold materials is often ignored. In this study, osteochondral scaffold was designed as a bilayer structure with a dense γ-Polyglutamic acid/carboxymethyl chitosan/bacterial cellulose (PGA/CMCS/BC) hydrogel cartilage layer and a porous nano HA-containing PGA/CMCS/BC hydrogel osteogenic layer. In addition, bioactive ions were introduced into the hydrogel scaffold to adjust the mechanical and swelling properties of the material to match the mechanical properties of natural articular cartilage. At the same time, based on the structural characteristics of bone and cartilage, magnesium and copper ions were introduced into the double-layer hydrogel scaffold, respectively, to prepare the cartilage layer and the bone layer, which endowed the material with excellent antibacterial properties and achieved the purpose of the integrated repair of bone and cartilage. The results showed that, after adding magnesium ions, the tensile breaking strength of material was increased from 0.66 MPa to 1.37 MPa，the corresponding compression modulus of the material (strain 0-12%) increased from 0.15 MPa to 0.58 MPa whilst the maximum mass swelling rate decreased from 155% to 75%. The results of in vivo experiments show that the group with bioactive ions had a much better effect on the repair of osteochondral defects, compared with group without bioactive ions, demonstrating such double ion regulation strategy is a very practical strategy for the treatment of osteochondral defects.

Current Understanding of Hydrogel for Drug Release and Tissue Engineering

Due to their good absorption, satisfactory biocompatibility, and high safety, hydrogels have been widely used in the field of biomedicine, including for drug delivery and tissue regeneration. In this review, we introduce the characteristics and crosslinking methods of natural and synthetic hydrogels. Then, we highlight the design and principle of intelligent hydrogels (i.e., responsive hydrogels) used for drug release. Moreover, we introduce the application of the application of hydrogels in drug release and tissue engineering, and the limitations and research directions of hydrogel in drug release and tissue engineering are also considered. We hope that this review can provide a reference for follow-up studies in related fields.

Injectable Natural Polymer Hydrogels for Treatment of Knee Osteoarthritis

Osteoarthritis (OA) is a serious chronic and degenerative disease that increasingly occurs in the aged population. Its current clinical treatments are limited to symptom relief and cannot regenerate cartilage. Although a better understanding of OA pathophysiology has been facilitating the development of novel therapeutic regimen, delivery of therapeutics to target sites with minimal invasiveness, high retention, and minimal side effects remains a challenge. Biocompatible hydrogels have been recognized to be highly promising for controlled delivery and release of therapeutics and biologics for tissue repair. In this review, the current approaches and the challenges in OA treatment, and unique properties of injectable natural polymer hydrogels as delivery system to overcome the challenges are presented. The common methods for fabrication of injectable polysaccharide-based hydrogels and the effects of their composition and properties on the OA treatment are detailed. The strategies of the use of hydrogels for loading and release cargos are also covered. Finally, recent efforts on the development of injectable polysaccharide-based hydrogels for OA treatment are highlighted, and their current limitations are discussed.

Three-dimensional bioprinting of polysaccharide-based self-healing hydrogels with dual cross-linking

Three-dimensional (3D) bioprinting technique is useful to fabricate constructs with functional and biological structures for various biomedical applications. Oxidized hyaluronate (OHA) and glycol chitosan (GC) can form autonomous self-healing hydrogels when adipic acid dihydrazide (ADH) is used. We demonstrate that hyaluronate-alginate hybrid (HAH) polymers can be used for secondary physical cross-linking of OHA/GC/ADH hydrogel with calcium ions after 3D printing. The molecular weight of hyaluronate can be varied while keeping the molecular weight of alginate in HAH. The mechanical stiffness and stability of gels after 3D printing are strongly dependent on the molecular weight of HAH at the same cross-linking density. In vitro chondrogenic differentiation of ATDC5 cells encapsulated in 3D-printed constructs is dependent on the molecular weight of HAH in gels. This dual cross-linking system consisting of naturally occurring biocompatible polysaccharides may have potential in the 3D bioprinting of custom-made scaffolds for tissue engineering applications.

Chitin Hydrogels Prepared at Various Lithium Chloride/N,N-Dimethylacetamide Solutions by Water Vapor-Induced Phase Inversion

Chitin was chemically extracted from crab shells and then dissolved in N,N-dimethylacetamide (DMAc) solvent with lithium chloride (LiCl) at 3, 5, 7, and 10%. The concentrated chitin-DMAc/LiCl solutions were used for the preparation of chitin hydrogels by water vapor-induced phase inversion at 20°C. The coagulation process was investigated while altering the concentration of LiCl in the DMAc solution. The shear viscosity of the chitin solution increased with higher LiCl amounts and decreased when the concentration of LiCl was reduced by adding water to the chitin solution, implying high LiCl concentration delayed the coagulation of chitin solution in the presence of water. The viscoelasticity of the chitin solutions indicated the gel formation intensification was dependent on the dose of LiCl and chitin in the DMAc solution. After the chitin solution was coagulated, the resultant hydrogels had water contents of 387–461% and the tensile strength varied from 285 to 400 kPa when the concentration of LiCl in the hydrogel was adjusted to 3% and 7%, respectively. As for viscoelasticity, the complex modulus of the chitin hydrogels indicated that the increment of the LiCl concentration up to 7% formed the tight hydrogels. Atomic force microscopic (AFM) image revealed the formation of the entanglement network and larger domains of the aggregated chitin segments. However, the hydrogel prepared at 10% LiCl in DMAc solution exhibited weak mechanical properties due to the loose hydrogel networking caused by the strong aggregation of the chitin segments.

Regulation of the Viscoelastic Properties of Hyaluronate-Alginate Hybrid Hydrogel as an Injectable for Chondrocyte Delivery

Modulation of the viscoelastic properties of hydrogels is critical in tissue engineering applications. In the present study, a hyaluronate-alginate hybrid (HAH) was synthesized by introducing alginate to the hyaluronate backbone with varying molecular weights (700-2500 kDa), and HAH hydrogels were prepared in the presence of calcium ions at the same cross-linking density. The storage shear moduli of the HAH hydrogels increased with the concomitant increase in the molecular weight of hyaluronate in the HAH polymer. The HAH hydrogels were also modified with arginine-glycine-aspartic acid (RGD) and histidine-alanine-valine (HAV) peptides to enhance cell-matrix and cell-cell interactions, respectively. The chondrogenic differentiation of ATDC5 cells encapsulated within the HAH hydrogels was enhanced with the increase in the storage shear moduli of the gels in vitro as well as in vivo. This approach of regulating the viscoelastic properties of hydrogels using polymers of varying molecular weights at the same cross-linking density may prove to be useful in various tissue engineering applications including cartilage regeneration.

A moldable thermosensitive hydroxypropyl chitin hydrogel for 3D cartilage regeneration in vitro and in vivo

Because of poor self-repair capacity, the repair of cartilage defect is always a great challenge in clinical treatment. In vitro cartilage regeneration provides a potential strategy for functional reconstruction of cartilage defect. Hydrogel has been known as an ideal cartilage regeneration scaffold. However, to date, in vitro cartilage regeneration based on hydrogel has not achieved satisfactory results. The current study explored the feasibility of in vitro 3D cartilage regeneration based on a moldable thermosensitive hydroxypropyl chitin (HPCH) hydrogel and its in vivo fate. The thermosensitive HPCH hydrogel was prepared and characterized. Goat auricular chondrocytes were encapsulated into the HPCH hydrogel to form a chondrocyte-hydrogel construct. The constructs were injected subcutaneously into nude mice or molded into different shapes for in vitro chondrogenic culture followed by in vivo implantation. The results demonstrated that the HPCH hydrogel possessed satisfactory gelation properties (gelation time < 18 s at 37 °C), biocompatibility (cell amount almost doubled within one week), and the ability to be applied as an injectable hydrogel for cartilage regeneration. All the constructs of in vitro culture basically maintained their original shapes (in vitro to initial: 110.8%) and displayed typical cartilaginous features with abundant lacunae and cartilage specific matrix deposition. These in vitro samples became more mature with prolonged in vivo implantation and largely maintained the original shape (in vivo to in vitro: 103.5%). These results suggested that the moldable thermosensitive HPCH hydrogel can serve as a promising scaffold for cartilage regeneration with defined shapes in vitro and in vivo. STATEMENT OF SIGNIFICANCE: Because of avascular and non-nervous characteristic of cartilage, in vitro regeneration plays an important role in reconstructing cartilage function. Hydrogel has been known as an ideal cartilage regeneration scaffold. However, to date, in vitro cartilage regeneration based on hydrogel has not achieved satisfactory results. The current study demonstrated that the chondrocyte-hydrogel construct generated by high density of chondrocytes encapsulated into a thermosensitive HPCH hydrogel could successfully regenerate in vitro typical cartilage-like tissue with defined shapes and further mature to form homogeneous cartilage with their original shapes after in vivo implantation. The current study indicated that the moldable thermosensitive HPCH hydrogel could serve as a promising scaffold for in vitro and in vivo cartilage regeneration with different shapes.

Intelligent Cellulose Nanofibers with Excellent Biocompatibility Enable Sustained Antibacterial and Drug Release via a pH-Responsive Mechanism

Novel nanosized biomass-based pH-responsive cellulose nanofibers (CNF-PEI) with excellent biocompatibility were tailored by grafting polyethylenimine (PEI) onto carboxylated cellulose nanofibers (CNF-COOH); the active site (-COOH, 0.96 mmol/g) was anchored on cellulose nanofibers (CNFs) to introduce PEI with a high density (10.57 mmol/g) of amino groups. The as-prepared CNF-PEI not only maintained the good properties of CNFs but also possessed excellent biocompatibility and pH-responsive properties, offering interesting possibilities for pH-induced sustained drug release and medical dressing. The CNF-PEI showed rapid wettability conversion from hydrophilic, underwater superoleophobic (WCA = 20.7°, OCA = 159.3°) to hydrophobic, superoleophilic (WCA = 129.6°, OCA = 29.7°) in response to pH change from acidic conditions to alkaline conditions. The antibacterial activity of CNF-PEI toward Escherichia coli and Listeria monocytogenes was 100% and 94.6% under acidic conditions, respectively. Furthermore, the pH-responsive mechanism of CNF-PEI was revealed by XPS, ¹³C NMR, ¹H NMR, and AFM analyses.

Effect of matrix stiffness and adhesion ligand density on chondrogenic differentiation of mesenchymal stem cells

Adhesion ligands and mechanical properties of extracellular matrix (ECM) play significant roles in directing mesenchymal stem cells' (MSCs) behaviors, but how they affect chondrogenic differentiation of MSCs has rarely been studied. In this study, we investigated the effects of matrix stiffness and adhesion ligand density on proliferation and chondrogenic differentiation of MSCs by using UV crosslinked hydrogels comprised of methacrylated gelatin (GelMA) and poly(ethylene glycol) diacrylate (PEGDA) of different weight ratios. The PEGDA/GelMA hydrogels were fabricated by adjusting the weight ratio of PEGDA and GelMA with low or high adhesion ligand density (0.05 and 0.5% GelMA, respectively) and independent tunable stiffness (1.6, 6, and 25 kPa separately for hydrogels with 5, 10, and 15% PEGDA). MSCs presented differential behaviors to ECM by adjusting its adhesion ligand density and stiffness. Cell proliferation and chondrogenic differentiation could be enhanced with the improvement of adhesive properties and stiffness, evidenced by cell viability assay, hematoxylin-eosin staining, Safranin O staining, immunohistochemistry (Collagen types II, Col2a1), as well as the chondrogenic genes expression of Col2a1, Acan, and Sox9. This study may provide new strategies to design the scaffolds for cartilage tissue engineering.