Comparison of polysaccharides in articular cartilage regeneration associated with chondrogenic and autophagy-related gene expression

Alginate Improves the Chondrogenic Capacity of 3D PCL Scaffolds In Vitro: A Histological Approach

Polycaprolactone (PCL) scaffolds have demonstrated an effectiveness in articular cartilage regeneration due to their biomechanical properties. On the other hand, alginate hydrogels generate a 3D environment with great chondrogenic potential. Our aim is to generate a mixed PCL/alginate scaffold that combines the chondrogenic properties of the two biomaterials. Porous PCL scaffolds were manufactured using a modified salt-leaching method and embedded in a culture medium or alginate in the presence or absence of chondrocytes. The chondrogenic capacity was studied in vitro. Type II collagen and aggrecan were measured by immunofluorescence, cell morphology by F-actin fluorescence staining and gene expression of COL1A1, COL2A1, ACAN, COL10A1, VEGF, RUNX1 and SOX6 by reverse transcription polymerase chain reaction (RT-PCR). The biocompatibility of the scaffolds was determined in vivo using athymic nude mice and assessed by histopathological and morphometric analysis. Alginate improved the chondrogenic potential of PCL in vitro by increasing the expression of type II collagen and aggrecan, as well as other markers related to chondrogenesis. All scaffolds showed good biocompatibility in the in vivo model. The presence of cells in the scaffolds induced an increase in vascularization of the PCL/alginate scaffolds. The results presented here reinforce the benefits of the combined use of PCL and alginate for the regeneration of articular cartilage.

Snail Mucus-Enhanced Adhesion of Human Chondrocytes on 3D Porous Agarose Scaffolds

This study reports the preparation of a novel porous 3D scaffold from agarose-snail mucus (AGSMu) for cartilage tissue repair applications. AG is reported for its unique thermal and mechanical properties, biocompatibility, and biodegradability, making it suitable for biomedical applications. Still, it lacks the cell adhesion properties required for tissue engineering applications. SMu is a complex substance identified to contain glycosaminoglycans (GAGs) and other bioactive molecules that promote wound healing and reduce cartilage deterioration and inflammation. Hence, porous 3D blend scaffolds containing AG and SMu were prepared by the freeze-drying method, characterized, and investigated for bioactive effects on human chondrocyte (C28/I2) cells. The scaffolds had a microporous structure with an average pore size of 245 μm. FTIR spectroscopy showed that SMu was successfully incorporated into the scaffolds. The SMu increased the mechanical strength of the composite scaffolds by more than 80% compared to the pristine AG scaffold. The scaffolds were found to be biocompatible with tunable degradation. The human chondrocyte cells attached and proliferated well on the 3D scaffolds in a few days, demonstrating a marked improvement in adhesion due to the presence of SMu. Enhanced cell adhesion and mechanical properties of 3D porous AG scaffolds could make them suitable for articular cartilage repair and regeneration.

Epigenetic modification and exosome effects on autophagy in osteoarthritis

Osteoarthritis (OA) is a degenerative disease that leads to joint pain and stiffness and is one of the leading causes of disability and pain worldwide. Autophagy is a highly conserved self-degradation process, and its abnormal function is closely related to human diseases, including OA. Abnormal autophagy regulates cell aging, matrix metalloproteinase metabolism, and reactive oxygen metabolism, which are key in the occurrence and development of OA. There is evidence that drugs directly or indirectly targeting autophagy significantly hinder the progress of OA. In addition, the occurrence and development of autophagy in OA are regulated by many factors, including epigenetic modification, exosomes, crucial autophagy molecules, and signaling pathway regulation. Autophagy, as a new therapeutic target for OA, has widely influenced the pathological mechanism of OA. However, determining how autophagy affects OA pathology and its use in the treatment and diagnosis of targets still need further research.

Current application and modification strategy of marine polysaccharides in tissue regeneration: A review

Marine polysaccharides (MPs) are exceptional bioactive materials that possess unique biochemical mechanisms and pharmacological stability, making them ideal for various tissue engineering applications. Certain MPs, including agarose, alginate, carrageenan, chitosan, and glucan have been successfully employed as biological scaffolds in animal studies. As carriers of signaling molecules, scaffolds can enhance the adhesion, growth, and differentiation of somatic cells, thereby significantly improving the tissue regeneration process. However, the biological benefits of pure MPs composite scaffold are limited. Therefore, physical, chemical, enzyme modification and other methods are employed to expand its efficacy. Chemically, the structural properties of MPs scaffolds can be altered through modifications to functional groups or molecular weight reduction, thereby enhancing their biological activities. Physically, MPs hydrogels and sponges emulate the natural extracellular matrix, creating a more conducive environment for tissue repair. The porosity and high permeability of MPs membranes and nanomaterials expedite wound healing. This review explores the distinctive properties and applications of select MPs in tissue regeneration, highlighting their structural versatility and biological applicability. Additionally, we provide a brief overview of common modification strategies employed for MP scaffolds. In conclusion, MPs have significant potential and are expected to be a novel regenerative material for tissue engineering.

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.

Polysaccharide-Based Composite Scaffolds for Osteochondral and Enthesis Regeneration

The rotator cuff and Achilles tendons along with the anterior cruciate ligament (ACL) are frequently injured with limited healing capacity. At the soft-hard tissue interface, enthesis is prone to get damaged and its regeneration in osteochondral defects is essential for complete healing. The current clinical techniques used in suturing procedures to reattach tendons to bones need much improvement for the generation of the native interface tissue, that is, enthesis, for patients to regain their full functions. Recently, inspired by the composite native tissue, much effort has been made to fabricate composite scaffolds for enthesis tissue regeneration. This review first focuses on the studies that used composite scaffolds for the regeneration of enthesis. Then, the use of polysaccharides for osteochondral tissue engineering is reviewed and their potential for enthesis regeneration is presented based on their supporting effects on osteogenesis and chondrogenesis. Gellan gum (GG) is selected and reviewed as a promising polysaccharide due to its unique osteogenic and chondrogenic activities that help avoid the inherent weakness of dissimilar materials in composite scaffolds. In addition, original preliminary results showed that GG supports collagen type I production and upregulation of osteogenic marker genes. Impact Statement Enthesis regeneration is essential for complete and functional healing of tendon and ligament tissues. Current suturing techniques to reattach the tendon/ligament to bones have high failure rates. This review highlights the studies on biomimetic scaffolds aimed to regenerate enthesis. In addition, the potential of using polysaccharides to regenerate enthesis is discussed based on their ability to regenerate osteochondral tissues. Gellan gum is presented as a promising biopolymer that can be modified to simultaneously support bone and cartilage regeneration by providing structural continuity for the scaffold.

Thermosensitive Injectable Gradient Hydrogel-Induced Bidirectional Differentiation of BMSCs

Osteochondral defects threaten the quality of life of patients to a great extent. To simulate gradient changes in osteochondral tissue, a gradient-mixing injection device consisting of a controller and injection pumps is design. Bioactive glass (BG) and gellan gum (GG) are used to prepare thermosensitive injectable gradient hydrogels (B_0.5 G, B₁ G) with an upper critical solution temperature (UCST) range of 37.7-40.2 °C using this device for the first time. The mechanical properties of gradient hydrogels are significantly better than those of pure GG hydrogels. The gradients in the composition, structure, and morphology of gradient hydrogels are confirmed via physicochemical characterization. Cytocompatibility tests show that hydrogels, especially B_0.5 G gradient hydrogels, promote the proliferation of bone marrow mesenchymal stem cells (BMSCs). Most importantly, qRT-PCR shows that the different components in B_0.5 G gradient hydrogels simultaneously induce the osteogenic and chondrogenic differentiation of BMSCs. Experimental injection in porcine osteochondral defects indicates that the B_0.5 G gradient hydrogel seamlessly fills irregular osteochondral defects in a less invasive manner by controlling the temperature to avoid cellular and tissue damage arising from crosslinkers or other conditions. These results show that thermosensitive injectable B_0.5 G gradient hydrogels have the potential for less invasive integrated osteochondral repair.

Autophagy Is a Crucial Path in Chondrogenesis of Adipose-Derived Mesenchymal Stromal Cells Laden in Hydrogel

Autophagy is a cellular process that contributes to the maintenance of cell homeostasis through the activation of a specific path, by providing the necessary factors in stressful and physiological situations. Autophagy plays a specific role in chondrocyte differentiation; therefore, we aimed to analyze this process in adipose-derived mesenchymal stromal cells (ASCs) laden in three-dimensional (3D) hydrogel. We analyzed chondrogenic and autophagic markers using molecular biology, immunohistochemistry, and electron microscopy. We demonstrated that ASCs embedded in 3D hydrogel showed an increase expression of typical autophagic markers Beclin 1, LC3, and p62, associated with clear evidence of autophagic vacuoles in the cytoplasm. During ASCs chondrogenic differentiation, we showed that autophagic markers declined their expression and autophagic vesicles were rare, while typical chondrogenic markers collagen type 2, and aggrecan were significantly increased. In line with developmental animal models of cartilage, our data showed that in a 3D hydrogel, ASCs increased their autophagic features. This path is the fundamental prerequisite for the initial phase of differentiation that contributes to fueling the cells with energy and factors necessary for chondrogenic differentiation.

Advanced injectable hydrogels for cartilage tissue engineering

The rapid development of tissue engineering makes it an effective strategy for repairing cartilage defects. The significant advantages of injectable hydrogels for cartilage injury include the properties of natural extracellular matrix (ECM), good biocompatibility, and strong plasticity to adapt to irregular cartilage defect surfaces. These inherent properties make injectable hydrogels a promising tool for cartilage tissue engineering. This paper reviews the research progress on advanced injectable hydrogels. The cross-linking method and structure of injectable hydrogels are thoroughly discussed. Furthermore, polymers, cells, and stimulators commonly used in the preparation of injectable hydrogels are thoroughly reviewed. Finally, we summarize the research progress of the latest advanced hydrogels for cartilage repair and the future challenges for injectable hydrogels.

Rapid and Economical Drug-Eluting IOL Preparation via Thermoresponsive Agarose Coating for Effective Posterior Capsular Opacification Prevention

Posterior capsular opacification (PCO), the highest incidence complication after cataract surgery, is mainly due to the attachment, proliferation, and migration of the residual lens epithelial cells (LECs). Although the drug-eluting IOLs have been proved to be an effective way to prevent PCO incidence, its preparations are time consuming and require tedious preparation steps. Herein, the thermoreversible agarose is adopted to prepare drug-eluting IOL. Such functional coating can be obtained easily by simple immersion in the antiproliferative drug containing hot agarose and taken out for cooling, which not only does not affect the optical property but also can effectively decrease the PCO incidence after intraocular implantation. As a result, the proposed agarose coating provides a rapid and economical alternative of drug-eluting IOL fabrication for PCO prevention.

Preparation and characterization of a novel drug-loaded Bi-layer scaffold for cartilage regeneration

The incidence of articular cartilage defects is increasing year by year. In order to repair the cartilage tissue at the defect, scaffolds with nanofiber structure and biocompatibility have become a research hotspot. In this study, we designed and fabricated a bi-layer scaffold prepared from an upper layer of drug-dispersed gelatin methacrylate (GELMA) hydrogel and a lower layer of a drug-encapsulated coaxial fiber scaffold prepared from silk fiber (SF) and polylactic acid (PLA). These bi-layer scaffolds have porosity (91.26 ± 3.94%) sufficient to support material exchange and pore size suitable for cell culture and infiltration, as well as mechanical properties (2.65 ± 0.31 MPa) that meet the requirements of cartilage tissue engineering. The coaxial fiber structure exhibited excellent drug release properties, maintaining drug release for 14 days in PBS. In vitro experiments indicated that the scaffolds were not toxic to cells and were amenable to chondrocyte migration. Notably, the growth of cells in a bi-layer scaffold presented two states. In the hydrogel layer, cells grow through interconnected pores and take on a connective tissue-like shape. In the coaxial fiber layer, cells grow on the surface of the coaxial fiber mats and appeared tablet-like. This is similar to the structure of the functional partitions of natural cartilage tissue. Together, the bi-layer scaffold can play a positive role in cartilage regeneration, which could be a potential therapeutic choice to solve the current problems of clinical cartilage repair.

Articular cartilage and osteochondral tissue engineering techniques: Recent advances and challenges

In spite of the considerable achievements in the field of regenerative medicine in the past several decades, osteochondral defect regeneration remains a challenging issue among diseases in the musculoskeletal system because of the spatial complexity of osteochondral units in composition, structure and functions. In order to repair the hierarchical tissue involving different layers of articular cartilage, cartilage-bone interface and subchondral bone, traditional clinical treatments including palliative and reparative methods have showed certain improvement in pain relief and defect filling. It is the development of tissue engineering that has provided more promising results in regenerating neo-tissues with comparable compositional, structural and functional characteristics to the native osteochondral tissues. Here in this review, some basic knowledge of the osteochondral units including the anatomical structure and composition, the defect classification and clinical treatments will be first introduced. Then we will highlight the recent progress in osteochondral tissue engineering from perspectives of scaffold design, cell encapsulation and signaling factor incorporation including bioreactor application. Clinical products for osteochondral defect repair will be analyzed and summarized later. Moreover, we will discuss the current obstacles and future directions to regenerate the damaged osteochondral tissues.

Facile Preparation of β-Cyclodextrin-grafted Chitosan Electrospun Nanofibrous Scaffolds as a Hydrophobic Drug Delivery Vehicle for Tissue Engineering Applications

Despite advances in the bio-tissue engineering area, the technical basis to directly load hydrophobic drugs on chitosan (CTS) electrospun nanofibers (ENs) has not yet been fully established. In this study, we fabricated CTS ENs by using an electrospinning (ELSP) system, followed by surface modification using succinyl-beta-cyclodextrin (β-CD) under mild conditions. The β-CD-modified CTS (βCTS) ENs had slightly increased hydrophobicity compared to pristine CTS ENs as well as decreased residual amine content on the surface. Through FTIR spectroscopy and thermogravimetric analysis (TGA), we characterized the surface treatment physiochemically. In the drug release test, we demonstrated the stable and sustained release of a hydrophobic drug (e.g., dexamethasone) loaded on β-CD ENs. During in vitro biocompatibility assessments, the grafting of β-CD was shown to not reduce cell viability compared to pristine CTS ENs. Additionally, cells proliferated well on β-CD ENs, and this was confirmed by F-actin fluorescence staining. Overall, the material and strategies developed in this study have the potential to load a wide array of hydrophobic drugs. This could be applied as a drug carrier for a broad range of tissue engineering applications.

Alginate-Agarose Hydrogels Improve the In Vitro Differentiation of Human Dental Pulp Stem Cells in Chondrocytes. A Histological Study

Matrix-assisted autologous chondrocyte implantation (MACI) has shown promising results for cartilage repair, combining cultured chondrocytes and hydrogels, including alginate. The ability of chondrocytes for MACI is limited by different factors including donor site morbidity, dedifferentiation, limited lifespan or poor proliferation in vitro. Mesenchymal stem cells could represent an alternative for cartilage regeneration. In this study, we propose a MACI scaffold consisting of a mixed alginate-agarose hydrogel in combination with human dental pulp stem cells (hDPSCs), suitable for cartilage regeneration. Scaffolds were characterized according to their rheological properties, and their histomorphometric and molecular biology results. Agarose significantly improved the biomechanical behavior of the alginate scaffolds. Large scaffolds were manufactured, and a homogeneous distribution of cells was observed within them. Although primary chondrocytes showed a greater capacity for chondrogenic differentiation, hDPSCs cultured in the scaffolds formed large aggregates of cells, acquired a rounded morphology and expressed high amounts of type II collagen and aggrecan. Cells cultured in the scaffolds expressed not only chondral matrix-related genes, but also remodeling proteins and chondrocyte differentiation factors. The degree of differentiation of cells was proportional to the number and size of the cell aggregates that were formed in the hydrogels.

Narrative review of the choices of stem cell sources and hydrogels for cartilage tissue engineering

Stem cell-based therapy is a promising treatment for cartilage defects due to the pluripotency, abundant sources and low immunogenicity of stem cells. Hydrogels are a promising class of biomaterials for cartilage engineering and are characterized by bioactivity, degradability and elasticity as well as provide water content and mechanical support. The combination of stem cells and hydrogels opens new possibilities for cartilage tissue engineering. However, the selection of suitable types of stem cells and hydrogels is difficult. Currently, various types of stem cells, such as embryonic stem cells (ESCs), mesenchymal stem cells (MSCs), induced pluripotent stem cells (iPSCs), and peripheral blood mononuclear cells (PBMSCs), and various types of hydrogels, including natural polymers, chemically modified natural polymers and synthetic polymers, have been explored based on their potential for cartilage tissue engineering. These materials are used independently or in combination; however, there is no clear understanding of their merits and disadvantages with regard to their suitability for cartilage repair. In this article, we aim to review recent progress in the use of stem cell-hydrogel hybrid constructs for cartilage tissue engineering. We focus on the effects of stem cell types and hydrogel types on efficient chondrogenesis from cellular, preclinical and clinical perspectives. We compare and analyze the advantages and disadvantages of these cells and hydrogels with the hope of increasing discussion of their suitability for cartilage repair and present our perspective on their use for the improvement of physical and biological properties for cartilage tissue engineering.