Comprehensive review on biosynthesis of hyaluronic acid with different molecular weights and its biomedical applications

Hyaluronic acid (HA), an anionic and nonsulfated glycosaminoglycan, is the main structural component of various tissues and plays an important role in various biological processes. Given the promising properties of HA, such as high cellular compatibility, moisture retention, antiaging, proper interaction with cells, and CD44 targeting, HA can be widely used extensively in drug delivery, tissue engineering, wound healing, and cancer therapy. HA can obtain from animal tissues and microbial fermentation, but its applications depend on its molecular weight. Microbial fermentation is a common method for HA production on an industrial scale and S. zooepidemicus is the most frequently used strain in HA production. Culture conditions including pH, temperature, agitation rate, aeration speed, shear stress, dissolved oxygen, and bioreactor type significantly affect HA biosynthesis properties. In this review all the HA production methods and purification techniques to improve its physicochemical and biological properties for various biomedical applications are discussed in details. In addition, we showed that how HA molecular weight can significantly affect its properties and applications.

Three-dimensional Culture and Chondrogenic Differentiation of Mesenchymal Stem Cells in Interconnected Collagen Scaffolds

Interconnected scaffolds are useful for promoting the chondrogenic differentiation of stem cells. Collagen scaffolds with interconnected pore structures were fabricated with poly(lactic acid-co-glycolic acid) (PLGA) sponge templates. The PLGA-templated collagen scaffolds were used to culture human bone marrow-derived mesenchymal stem cells (hMSCs) to investigate their promotive effect on the chondrogenic differentiation of hMSCs. The cells adhered to the scaffolds with a homogeneous distribution and proliferated with culture time. The expression of chondrogenesis-related genes was upregulated, and abundant cartilaginous matrices were detected. After subcutaneous implantation, the PLGA-templated collagen scaffolds further enhanced the production of cartilaginous matrices and the mechanical properties of the implants. The good interconnectivity of the PLGA-templated collagen scaffolds promoted chondrogenic differentiation. In particular, the collagen scaffolds prepared with large pore-bearing PLGA sponge templates showed the highest promotive effect.

Quantitative Grafting for Structure-Function Establishment: Thermoresponsive Poly(alkylene oxide) Graft Copolymers Based on Hyaluronic Acid and Carboxymethylcellulose

A series of thermoresponsive graft copolymers, gelling at physiological conditions in aqueous solution and cell growth media, have been synthesized using quantitative coupling between a small set of amino-functionalized poly(alkylene oxide) copolymers (PAO) and the carboxylate of the biologically important polysaccharides (PSa) carboxymethylcellulose and the less reactive hyaluronate. Quantitative grafting enables the establishment of structure-function relationship which is imperative for controlling the properties of in situ gelling hydrogels. The EDC/NHS-mediated reaction was monitored using SEC-MALLS, which revealed that all PAOs were grafted onto the PSa backbone. Aqueous solutions of the graft copolymers were Newtonian fluids at room temperatures and formed reversible physical gels at elevated temperatures which were noncytotoxic toward chondrocytes. The established structure-function relationship was most clearly demonstrated by inspecting the thermogelling strength and the onset of thermogelling in a phase diagram. The onset of the thermogelling function could be controlled by the global PAO concentration, independent of graft ratio.

Fabrication of continuous apatite-graded collagen sponges via electrolysis method

Electrolysis of collagen/hydroxyapatite solution is a powerful method for obtaining collagen sponges with gradually-graded apatite contents. The porous bodies are promising scaffolds for osteochondral defects.

Collagen Scaffolds in Cartilage Tissue Engineering and Relevant Approaches for Future Development

BACKGROUND

Cartilage tissue engineering (CTE) aims to obtain a structure mimicking native cartilage tissue through the combination of relevant cells, three-dimensional scaffolds, and extraneous signals. Implantation of 'matured' constructs is thus expected to provide solution for treating large injury of articular cartilage. Type I collagen is widely used as scaffolds for CTE products undergoing clinical trial, owing to its ubiquitous biocompatibility and vast clinical approval. However, the long-term performance of pure type I collagen scaffolds would suffer from its limited chondrogenic capacity and inferior mechanical properties. This paper aims to provide insights necessary for advancing type I collagen scaffolds in the CTE applications.

METHODS

Initially, the interactions of type I/II collagen with CTE-relevant cells [i.e., articular chondrocytes (ACs) and mesenchymal stem cells (MSCs)] are discussed. Next, the physical features and chemical composition of the scaffolds crucial to support chondrogenic activities of AC and MSC are highlighted. Attempts to optimize the collagen scaffolds by blending with natural/synthetic polymers are described. Hybrid strategy in which collagen and structural polymers are combined in non-blending manner is detailed.

RESULTS

Type I collagen is sufficient to support cellular activities of ACs and MSCs; however it shows limited chondrogenic performance than type II collagen. Nonetheless, type I collagen is the clinically feasible option since type II collagen shows arthritogenic potency. Physical features of scaffolds such as internal structure, pore size, stiffness, etc. are shown to be crucial in influencing the differentiation fate and secreting extracellular matrixes from ACs and MSCs. Collagen can be blended with native or synthetic polymer to improve the mechanical and bioactivities of final composites. However, the versatility of blending strategy is limited due to denaturation of type I collagen at harsh processing condition. Hybrid strategy is successful in maximizing bioactivity of collagen scaffolds and mechanical robustness of structural polymer.

CONCLUSION

Considering the previous improvements of physical and compositional properties of collagen scaffolds and recent manufacturing developments of structural polymer, it is concluded that hybrid strategy is a promising approach to advance further collagen-based scaffolds in CTE.

Hyaluronic Acid Dictates Chondrocyte Morphology and Migration in Composite Gels

Tissue equivalent collagen-hyaluronic acid-based hydrogels are widely used for cartilage tissue engineering; however, not much importance has been given to investigate how cellular responses are altered with varying concentrations of hyaluronic acid in gels. In this study, different concentrations of hyaluronic acid dialdehyde (HAD) were combined with collagen to fabricate collagen-HAD composite (CH) gels, and the influence of HAD on cell shape, migration, viability, cytoskeletal organization, and gel contraction was examined. The microstructure and the mechanical strength of the composite gels were altered by varying HAD concentrations. Morphology of chondrocytes cultured on CH gels showed a significant increase in their aspect ratio and decrease in number of cell protrusions with increase in concentration of HAD. The organization of the cytoskeleton at the cellular protrusions was vimentin localized at the base, microtubules at the tip, and actin localized throughout the cell body. Changes in HAD concentrations altered hydrogel mechanical strength, cytoskeletal organization, and formation of cellular protrusions, all of which contributed to changes in cell morphology and migration. These changes were more evident in 3D cell-encapsulated gels than chondrocytes cultured over the 2D gels. However, viability of cells and matrix contraction, staining for adhesion protein vinculin, and hyaluronic acid receptor CD44 remained similar in all CH compositions. The changes in cell responses further influenced extracellular matrix deposition during in vitro culture. Cell responses in low HAD gels mimic the cellular behavior in damaged cartilage, whereas those in high HAD gels resembled the behavior in healthy cartilage tissue. Our study illustrates the importance of careful formulations of hydrogel compositions in designing biomimetic matrices that are used as in vitro models to study chondrocyte behavior.

Fabrication of Highly Crosslinked Gelatin Hydrogel and Its Influence on Chondrocyte Proliferation and Phenotype

Gelatin methacrylate (GelMA) hydrogels have been widely studied for biomedical applications, such as tissue engineering and drug delivery, because of their good biocompatibility and injectability. However, the quick degradation and low mechanical property of GelMA hydrogels need to be improved for further applications, especially for long-term implantation. In this study, a sequential double modification of gelatin was used to achieve high density of photocrosslinkable double bonds in gelatin derivatives. The amino groups in gelatin were first reacted with methacrylic anhydride. After this, the hydroxyl and carboxyl groups in gelatin were reacted with glycidyl methacrylate to obtain the double modified gelatin macromer. The double modified gelatin macromer was used to prepare gelatin hydrogels with high crosslinking density. The hydrogels exhibited high storage modulus and low degradation. Culture of bovine articular chondrocytes in the gelatin hydrogels showed that chondrocytes had round morphology and maintained a cartilaginous phenotype while cell proliferation was hampered. This method for increasing crosslinking density should be useful for preparation of stable hydrogels for cartilage tissue engineering.

Influence of microporous gelatin hydrogels on chondrocyte functions

Hydrogels can provide biomimetic three-dimensional microenvironments for transplanted cells and are attractive scaffolds for cartilage tissue engineering. In this study, gelatin hydrogels with microporous structures were prepared and their effects on chondrocyte functions were compared with gelatin hydrogels without microporous structures. Gelatin bulk hydrogels were prepared by photo-initiated crosslinking of gelatin methacrylate macromers. Micropores were formed in the bulk hydrogels by dissolution of gelatin microgels prepared by a cutting method. Chondrocytes cultured in gelatin hydrogels without microporous structures showed high expression and production of cartilaginous matrices and low cell proliferation. Chondrocytes cultured in gelatin hydrogels with microporous structures tended to migrate from bulk hydrogel matrices to the micropores. Chondrocytes in the microporous hydrogels showed higher proliferation and lower expression and production of cartilaginous matrices than did the chondrocytes cultured in hydrogels without microporous structures. Gelatin hydrogels without microporous structures facilitated maintenance of the cartilaginous phenotype of the chondrocytes while microporous gelatin hydrogels were beneficial for cell proliferation.

Targeting ligand-functionalized photothermal scaffolds for cancer cell capture and in situ ablation

Targeting ligands with different grafting densities were introduced into photothermal scaffolds for cancer cell specific capture and ablation.

Insight into the interactions between nanoparticles and cells

This review summarizes the latest advances in nanoparticle (NP)–cell interactions. The influence of NP size, shape, shell structure, surface chemistry and protein corona formation on cellular uptake and cytotoxicity is highlighted in detail. Their impact on other cellular responses such as cell proliferation, differentiation and cellular mechanics is also discussed.

Composite scaffolds of gelatin and gold nanoparticles with tunable size and shape for photothermal cancer therapy

Photothermal therapy (PTT) has been extensively investigated as a promising strategy for cancer therapy. For successful application of this technique, various nanomaterials have been explored as photothermal conversion agents. Gold nanoparticles (AuNPs), especially Au nanorods and Au nanostars, have received much attention for photothermal therapy because of their facile preparation and high photothermal conversion efficiency. Due to the limited accumulation and easy diffusion of free nanoparticles, incorporation of nanoparticles into scaffolds for direct implantation has been demonstrated as an attractive way for cancer therapy applications. In this study, composite porous scaffolds of gelatin and AuNPs were prepared by introducing Au nanorods and Au nanostars with average sizes of around 35.0, 65.0 and 115.0 nm in gelatin scaffolds. The composite scaffolds were used for the localized PTT application of cancer cells. Gel/AuNP composite scaffolds supported cell adhesion and showed good biocompatibility. Temperature in the composite scaffolds increased quickly upon NIR laser irradiation. Photothermal efficiency and cancer cell killing efficiency were dependent on the shape, size and amount of AuNPs in the composite scaffolds. The composite scaffolds prepared with 65.0 nm Au nanorods showed the highest photothermal efficiency and cell killing efficiency. The results indicated the importance of the shape and size modulation of AuNPs for photothermal therapy applications.

Preparation of gelatin/Fe3O4 composite scaffolds for enhanced and repeatable cancer cell ablation

Various nanomaterials have been extensively investigated for photothermal ablation of cancer cells because of their high photothermal conversion efficiency. However, the poor targeting specificity and low repeated heating efficiency of nanomaterials restrict their applications in the clinic. In this work, porous gelatin/iron oxide (Gel/Fe₃O₄) composite scaffolds were prepared by a facile ice particulate templating method for efficient and repeatable cancer cell ablation. Gel/Fe₃O₄ composite scaffolds showed controlled porous structure consisting of large pores and interconnecting small pores. The strong absorption in the near-infrared (NIR) region enabled the Gel/Fe₃O₄ composite scaffolds to elevate local temperature quickly under NIR laser irradiation. The composite scaffolds allowed cell adhesion and proliferation showing good biocompatibility. Cancer cells entrapped in the scaffolds could be efficiently killed during laser irradiation. Moreover, the therapeutic efficacy of Gel/Fe₃O₄ composite scaffolds could be enhanced by repeated laser irradiation treatment, which is important for clinical application because of the resistant and recurrent nature of cancer. The results indicated that the porous Gel/Fe₃O₄ composite scaffolds had good biocompatibility and excellent cancer cell ablation efficacy, which may provide an attractive way to use porous scaffolds for cancer therapy application.