Tissue-derived scaffolds and cells for articular cartilage tissue engineering: characteristics, applications and progress

Construction of Integral Decellularized Cartilage Using a Novel Hydrostatic Pressure Bioreactor

The decellularized extracellular matrix (ECM) of cartilage is a widely used natural bioscaffold for constructing tissue-engineered cartilage due to its good biocompatibility and regeneration properties. However, current decellularization methods for accessing decellularized cartilaginous tissues require multiple steps and a relatively long duration to produce decellularized cartilage. In addition, most decellularization strategies lead to damage of the microstructure and loss of functional components of the cartilaginous matrix. In this study, a novel decellularization strategy based on a hydrostatic pressure (HP) bioreactor was introduced, which aimed to improve the efficiency of producing integral decellularized cartilage pieces by combining physical and chemical decellularization methods in a perfusing manner. Two types of cartilaginous tissues, auricular cartilage (AC) and nucleus pulposus (NP) fibrocartilage, were selected for comparison of the effects of ordinary, positive, and negative HP-based decellularization according to the cell clearance ratio, microstructural changes, ECM components, and mechanical properties. The results indicated that applying positive HP improved the efficiency of producing decellularized AC, but no significant differences in decellularization efficiency were found between the ordinary and negative HP-treated groups. However, compared with the ordinary HP treatment, the application of the positive or negative HP did not affect the efficiency of decellularized NP productions. Moreover, neither positive nor negative HP influenced the preservation of the microstructure and components of the AC matrix. However, applying negative HP disarranged the fibril distribution of the NP matrix and reduced glycosaminoglycans and collagen type II contents, two essential ECM components. In addition, the positive HP was beneficial for maintaining the mechanical properties of decellularized cartilage. The recellularization experiments also verified the good biocompatibility of the decellularized cartilage produced by the present bioreactor-based decellularization method under positive HP. Overall, applying positive HP-based decellularization resulted in a superior effect on the production of close-to-natural scaffolds for cartilage tissue engineering. Impact statement In this study, we successfully constructed a novel hydrostatic pressure (HP) bioreactor and used this equipment to produce decellularized cartilage by combining physical and chemical decellularization methods in a perfusing manner. We found that positive HP-based decellularization could improve the production efficiency of integral decellularized cartilage pieces and promote the maintenance of matrix components and mechanical properties. This new decellularization strategy exhibited a superior effect in the production of close-to-natural scaffolds and positively impacts cartilage tissue engineering.

From materials to clinical use: advances in 3D-printed scaffolds for cartilage tissue engineering

Osteoarthritis caused by articular cartilage defects is a particularly common orthopedic disease that can involve the entire joint, causing great pain to its sufferers. A global patient population of approximately 250 million people has an increasing demand for new therapies with excellent results, and tissue engineering scaffolds have been proposed as a potential strategy for the repair and reconstruction of cartilage defects. The precise control and high flexibility of 3D printing provide a platform for subversive innovation. In this perspective, cartilage tissue engineering (CTE) scaffolds manufactured using different biomaterials are summarized from the perspective of 3D printing strategies, the bionic structure strategies and special functional designs are classified and discussed, and the advantages and limitations of these CTE scaffold preparation strategies are analyzed in detail. Finally, the application prospect and challenges of 3D printed CTE scaffolds are discussed, providing enlightening insights for their current research.

Osteochondral regeneration in rabbit using xenograft decellularized ECM in combination with different biological products; platelet-rich fibrin, amniotic membrane extract, and mesenchymal stromal cells

This study aimed to investigate the regenerative effect of decellularized osteochondral ECM xenograft in combination with various biological products in an osteochondral (OC) defect. OC tissue from the sheep femur were obtained and decellularized. The decellularized ECM (dECM) was combined with either platelet-rich fibrin (PRF), amniotic membrane extract (AME), or rabbit bone marrow-derived mesenchymal stromal cells (rBMSCs). The hybrid dECM-biological products were then utilized for the treatment of rabbit OC critical size defects. The regenerative potential of different groups was compared using; MRI, macroscopic assessment, histopathology, and histomorphometry. All characterizations analysis verified successful decellularization. Three months post-surgery, macroscopic findings indicated that dECM was better compared to controls. Also, dECM in combination with AME, PRF, and rBMSCs showed enhanced OC regeneration compared to only dECM (AME: +100%, PRF: +61%, rBMSCs: +28%). In particular, the dECM+AME group results in the best integration of new cartilage into surrounding cartilage tissue. The histomorphometric evaluations demonstrated enhancement in new cartilage formation and bone tissue (86.5 ± 5.9% and 90 ± 7.7%, respectively) for the dECM+AME group compared to other groups. Furthermore, histological results for the dECM+AME elucidated a mature hyaline cartilage tissue that covered the new and symmetrically formed subchondral bone, exhibiting a significantly higher regenerative effect compared to all other treated groups. This finding was also confirmed with MRI images. The current study revealed that in addition to the benefits of dECM alone, its combination with AME indicated to have a superior regenerative effect on OC regeneration. Overall, dECM+AME may be considered a suitable construct for treating knee OC injuries.

3D bioprinting of photo-crosslinkable silk methacrylate (SilMA)-polyethylene glycol diacrylate (PEGDA) bioink for cartilage tissue engineering

Articular cartilage damage poses huge burden on healthcare sector globally due to its extremely weak inherent regenerative ability. Three-dimensional (3D) bioprinting for development of cartilage mimic constructs using composite bioinks serves as an emerging perspective. However, difficulty in development of suitable bioink and chemical crosslinking associated inherent toxicity hamper widespread adoption of this technique. To circumvent this, a photo-polymerizable hydrogel-based bioink which helps in recapitulation of the complex cartilage microenvironment is pertinent. Herein, a photo-crosslinkable bioink containing different concentrations of silk methacrylate (SilMA) and polyethylene glycol diacrylate (PEGDA) was mixed with chondrocytes for biofabrication of 3D bioprinted cartilage constructs. The rheological properties, printability of bioink and physico-chemical characterization of printed hydrogel constructs were examined along with cartilaginous tissue formation. The printed SilMA-PEGDA hydrogel constructs possessed proper internal porous structure and demonstrated most reliable rheological properties, printability along with good mechanical, and degradation properties suitable for cartilage regeneration. Live/dead staining showed cytocompatibility of the 3D-bioprinted SilMA-PEGDA constructs. Moreover, a marked increase in cell number and DNA content was observed within the cartilaginous tissue as indicated by cell viability and DNA content quantitation. Biochemical evaluation confirmed the neocartilage formation within SilMA-PEGDA bioprinted constructs as revealed by enhanced deposition of cartilage specific extracellular matrix-sulphated GAG (sGAG) and collagen type II (>2-fold increase, p < 0.001) with time. Finally, immunohistochemical analysis indicated expression of collagen type II and aggrecan which corroborated with cartilaginous tissue formation. Taken together, we conclude that SilMA-PEGDA bioink could be suitable candidate for bioprinting chondrocytes to support cartilage tissue repair and regeneration.

Marine origin materials on biomaterials and advanced therapies to cartilage tissue engineering and regenerative medicine

The body's self-repair capacity is limited, including injuries on articular cartilage zones. Over the past few decades, tissue engineering and regenerative medicine (TERM) has focused its studies on the development of natural biomaterials for clinical applications aiming to overcome this self-therapeutic bottleneck. This review focuses on the development of these biomaterials using compounds and materials from marine sources that are able to be produced in a sustainable way, as an alternative to mammal sources (e.g., collagens) and benefiting from their biological properties, such as biocompatibility, low antigenicity, biodegradability, among others. The structure and composition of the new biomaterials require mimicking the native extracellular matrix (ECM) of articular cartilage tissue. To design an ideal temporary tissue-scaffold, it needs to provide a suitable environment for cell growth (cell attachment, proliferation, and differentiation), towards the regeneration of the damaged tissues. Overall, the purpose of this review is to summarize various marine sources to be used in the development of different tissue-scaffolds with the capability to sustain cells envisaging cartilage tissue engineering, analysing the systems displaying more promising performance, while pointing out current limitations and steps to be given in the near future.

3D printed silk-gelatin hydrogel scaffold with different porous structure and cell seeding strategy for cartilage regeneration

Hydrogel scaffolds are attractive for tissue defect repair and reorganization because of their human tissue-like characteristics. However, most hydrogels offer limited cell growth and tissue formation ability due to their submicron- or nano-sized gel networks, which restrict the supply of oxygen, nutrients and inhibit the proliferation and differentiation of encapsulated cells. In recent years, 3D printed hydrogels have shown great potential to overcome this problem by introducing macro-pores within scaffolds. In this study, we fabricated a macroporous hydrogel scaffold through horseradish peroxidase (HRP)-mediated crosslinking of silk fibroin (SF) and tyramine-substituted gelatin (GT) by extrusion-based low-temperature 3D printing. Through physicochemical characterization, we found that this hydrogel has excellent structural stability, suitable mechanical properties, and an adjustable degradation rate, thus satisfying the requirements for cartilage reconstruction. Cell suspension and aggregate seeding methods were developed to assess the inoculation efficiency of the hydrogel. Moreover, the chondrogenic differentiation of stem cells was explored. Stem cells in the hydrogel differentiated into hyaline cartilage when the cell aggregate seeding method was used and into fibrocartilage when the cell suspension was used. Finally, the effect of the hydrogel and stem cells were investigated in a rabbit cartilage defect model. After implantation for 12 and 16 weeks, histological evaluation of the sections was performed. We found that the enzymatic cross-linked and methanol treatment SF5GT15 hydrogel combined with cell aggregates promoted articular cartilage regeneration. In summary, this 3D printed macroporous SF-GT hydrogel combined with stem cell aggregates possesses excellent potential for application in cartilage tissue repair and regeneration.

Mesenchymal stem cells loaded on 3D-printed gradient poly(ε-caprolactone)/methacrylated alginate composite scaffolds for cartilage tissue engineering

Cartilage has limited self-repair ability due to its avascular, alymphatic and aneural features. The combination of three-dimensional (3D) printing and tissue engineering provides an up-and-coming approach to address this issue. Here, we designed and fabricated a tri-layered (superficial layer (SL), middle layer (ML) and deep layer (DL)) stratified scaffold, inspired by the architecture of collagen fibers in native cartilage tissue. The scaffold was composed of 3D printed depth-dependent gradient poly(ε-caprolactone) (PCL) impregnated with methacrylated alginate (ALMA), and its morphological analysis and mechanical properties were tested. To prove the feasibility of the composite scaffolds for cartilage regeneration, the viability, proliferation, collagen deposition and chondrogenic differentiation of embedded rat bone marrow mesenchymal stem cells (BMSCs) in the scaffolds were assessed by Live/dead assay, CCK-8, DNA content, cell morphology, immunofluorescence and real-time reverse transcription polymerase chain reaction. BMSCs-loaded gradient PCL/ALMA scaffolds showed excellent cell survival, cell proliferation, cell morphology, collagen II deposition and hopeful chondrogenic differentiation compared with three individual-layer scaffolds. Hence, our study demonstrates the potential use of the gradient PCL/ALMA construct for enhanced cartilage tissue engineering.

Morphology Comparison Between Goat Bone Marrow Mesenchymal Stem Cells and Adhesive Fibrin for the Repair of Annulus Fibrosus Defect of Intervertebral Discs

Introduction: The purpose of this study was to compare the histological findings of goat bone marrow mesenchymal stem cell (BMSC) transplantation and adhesive fibrin repair for annulus fibrosus defects in intervertebral discs. Material and methods: The goats were spanided into three groups: the control group, the adhesive group and the transplantation group. In the control group, surgical instruments were used to create a fibrous ring defect in the intervertebral disc of the goats. In the adhesive group, a 1.5*1.5-cm defect was also created by surgical intervention, and the broken fiber ring was then bonded with adhesive fibrin. In the transplantation group, a gelatine sponge containing the goat BMSCs was implanted into the broken annulus fibrosus, and the wound was closed layer by layer. At 6 weeks and 12 weeks after the operation, the damaged tissues were removed, and haematoxylin and eosin (HE), trichrome gelatine (Masson), Alcian blue periodic acid-Schiff (AB-PAS) and Collagen II staining was performed. Then, the tissues from the different groups were histologically compared and analyzed. Results: Goat BMSCs have a better ability to repair defects in the fibrous ring than adhesive fibrin. Over time, the number of cells or the amount of tissue following cell transplantation was greater, indicating that the degree of repair is greater with BMSCs than with adhesive fibrin. Conclusion: Histologically, repair of the defect of the fibrous ring and prevention of nucleus pulposus protrusion were more effective in the cell transplantation group than in the other two groups.

Enhanced articular cartilage decellularization using a novel perfusion-based bioreactor method

Current decellularization methods for articular cartilages require many steps, various and high amounts of detergents, and a relatively long time to produce decellularized scaffolds. In addition, such methods often damage the essential components and the structure of the tissue. This study aims to introduce a novel perfusion-based bioreactor (PBB) method to decellularize bovine articular cartilages efficiently while reducing the harmful physical and chemical steps as well as the duration of the process. This leads to better preservation of the structure and the essential components of the native tissue. Firstly, a certain number of channels (Ø 180 μm) were introduced into both sides of cylindrical articular bovine cartilage disks (5 mm in diameter and 1 mm in thickness). Next, the disks were decellularized in the PBB and a shaker as the control. Using the PBB method resulted in ∼90% reduction of DNA content in the specimens, which was significantly higher than those of the shaker results with ∼60%. Also, ∼50% sulfated glycosaminoglycan (sGAG) content and ∼92% of the compression properties were maintained implying the efficient preservation of the structure and components of the scaffolds. Moreover, the current study indicated that the PBB specimens supported the adherence and proliferation of the new cells effectively. In conclusion, the results show that the use of PBB method increases the efficiency of producing decellularized cartilage scaffolds with a better maintenance of essential components and structure, while reducing the chemicals and steps required for the process. This will pave the way for producing close-to-natural scaffolds for cartilage tissue engineering.

Fabrication and Characterization of the Core-Shell Structure of Poly(3-Hydroxybutyrate-4-Hydroxybutyrate) Nanofiber Scaffolds

Tissue engineering scaffolds with nanofibrous structures provide positive support for cell proliferation and differentiation in biomedical fields. These scaffolds are widely used for defective tissue repair and drug delivery. However, the degradation performance and mechanical properties of scaffolds are often unsatisfactory. Here, we successfully prepared a novel poly(3-hydroxybutyrate-4-hydroxybutyrate)/polypyrrole (P34HB-PPy) core-shell nanofiber structure scaffold with electrospinning and in situ surface polymerization technology. The obtained composite scaffold showed good mechanical properties, hydrophilicity, and thermal stability based on the universal material testing machine, contact angle measuring system, thermogravimetric analyzer, and other methods. The results of the in vitro bone marrow-derived mesenchymal stem cells (BMSCs) culture showed that the P34HB-PPy composite scaffold effectively mimicked the extracellular matrix (ECM) and exhibited good cell retention and proliferative capacity. More importantly, P34HB is a controllable degradable polyester material, and its degradation product 3-hydroxybutyric acid (3-HB) is an energy metabolite that can promote cell growth and proliferation. These results strongly support the application potential of P34HB-PPy composite scaffolds in biomedical fields, such as tissue engineering and soft tissue repair.

Biological perspectives and current biofabrication strategies in osteochondral tissue engineering

Articular cartilage and the underlying subchondral bone are crucial in human movement and when damaged through disease or trauma impacts severely on quality of life. Cartilage has a limited regenerative capacity due to its avascular composition and current therapeutic interventions have limited efficacy. With a rapidly ageing population globally, the numbers of patients requiring therapy for osteochondral disorders is rising, leading to increasing pressures on healthcare systems. Research into novel therapies using tissue engineering has become a priority. However, rational design of biomimetic and clinically effective tissue constructs requires basic understanding of osteochondral biological composition, structure, and mechanical properties. Furthermore, consideration of material design, scaffold architecture, and biofabrication strategies, is needed to assist in the development of tissue engineering therapies enabling successful translation into the clinical arena. This review provides a starting point for any researcher investigating tissue engineering for osteochondral applications. An overview of biological properties of osteochondral tissue, current clinical practices, the role of tissue engineering and biofabrication, and key challenges associated with new treatments is provided. Developing precisely engineered tissue constructs with mechanical and phenotypic stability is the goal. Future work should focus on multi-stimulatory environments, long-term studies to determine phenotypic alterations and tissue formation, and the development of novel bioreactor systems that can more accurately resemble the in vivo environment.

Natural polypeptides-based electrically conductive biomaterials for tissue engineering

Fabrication of an appropriate scaffold is the key fundamental step required for a successful tissue engineering (TE). The artificial scaffold as extracellular matrix in TE has noticeable role in the fate of cells in terms of their attachment, proliferation, differentiation, orientation and movement. In addition, chemical and electrical stimulations affect various behaviors of cells such as polarity and functionality. Therefore, the fabrication approach and materials used for the preparation of scaffold should be more considered. Various synthetic and natural polymers have been used extensively for the preparation of scaffolds. The electrically conductive polymers (ECPs), moreover, have been used in combination with other polymers to apply electric fields (EF) during TE. In this context, composites of natural polypeptides and ECPs can be taken into account as context for the preparation of suitable scaffolds with superior biological and physicochemical features. In this review, we overviewed the simultaneous usage of natural polypeptides and ECPs for the fabrication of scaffolds in TE.