Meniscus Tissue Engineering Research Articles

Advances in Electrospun Scaffolds Towards Meniscus: From Tissue Engineering to Repair and Regeneration

The meniscus plays a critical role in maintaining the homeostasis, biomechanics, and structural stability of the knee joint. Unfortunately, it is predisposed to damages either from sports-related trauma or age-related degeneration. The meniscus has an inherently limited capacity for tissue regeneration. Self-healing of injured adult menisci only occurs in the peripheral vascularized portion, while the spontaneous repair of the inner avascular region seems never happens. Repair, replacement, and regeneration of menisci through tissue engineering strategies are promising to address this problem. Recently, many scaffolds for meniscus tissue engineering have been proposed for both experimental and preclinical investigations. Electrospinning is a feasible and versatile technique to produce nano- to micro-scale fibers that mimic the microarchitecture of native extracellular matrix and is an effective approach to prepare nanofibrous scaffolds for constructing engineered meniscus. Electrospun scaffolds are reported to be capable of inducing colonization of meniscus cells by modulating local extracellular density and stimulating endogenous regeneration by driving reprogramming of meniscus wound microenvironment. Electrospun nanofibrous scaffolds with tunable mechanical properties, controllable anisotropy, and various porosities have shown promises for meniscus repair and regeneration and will undoubtedly inspire more efforts in exploring effective therapeutic approaches towards clinical applications. In this article, we review the current advances in the use of electrospun nanofibrous scaffolds for meniscus tissue engineering and repair and discuss prospects for future studies.

Meniscal tissue engineering via 3D printed PLA monolith with carbohydrate based self-healing interpenetrating network hydrogel

Failure of bioengineered meniscus implant after transplantation is a major concern owing to mechanical failure, lack of chondrogenic capability and patient specific design. In this article, we have, for the first time, fabricated a 3D printed scaffold with carbohydrate based self-healing interpenetrating network (IPN) hydrogels-based monolith construct for load bearing meniscus tissue. 3D printed PLA scaffold was surface functionalized and embedded with self-healing IPN hydrogel for interfacial bonding further characterized by micro CT. Using collagen (C), alginate (A) and oxidized alginate (ADA), we developed self-healing IPN hydrogels with dual crosslinking (Ca2+ based ionic crosslinking and Schiff base (A-A, A-ADA)) capability and studied their physicochemical properties. Further, we studied human stem cells behaviour and chondrogenic differentiation potential within these IPN hydrogels. In-vivo heterotopic implantation confirmed biocompatibility of the monolith showing the feasibility of using carbohydrate based IPN hydrogel embedded in 3D printed scaffold for meniscal tissue development.

Parathyroid hormone (1-34) promotes the effects of 3D printed scaffold-seeded bone marrow mesenchymal stem cells on meniscus regeneration

BackgroundCell-based tissue engineering represents a promising management for meniscus repair and regeneration. The present study aimed to investigate whether the injection of parathyroid hormone (PTH) (1-34) could promote the regeneration and chondroprotection of 3D printed scaffold seeded with bone marrow mesenchymal stem cells (BMSCs) in a canine total meniscal meniscectomy model.Methods3D printed poly(e-caprolactone) scaffold seeded with BMSCs was cultured in vitro, and the effects of in vitro culture time on cell growth and matrix synthesis of the BMSCs–scaffold construct were evaluated by microscopic observation and cartilage matrix content detection at 7, 14, 21, and 28 days. After that, the tissue-engineered meniscus based on BMSCs–scaffold cultured for the appropriate culture time was selected for in vivo implantation. Sixteen dogs were randomly divided into four groups: PTH + BMSCs–scaffold, BMSCs–scaffold, total meniscectomy, and sham operation. The regeneration of the implanted tissue and the degeneration of articular cartilage were assessed by gross, histological, and immunohistochemical analysis at 12 weeks postoperatively.ResultsIn vitro study showed that the glycosaminoglycan (GAG)/DNA ratio and the expression of collagen type II (Col2) were significantly higher on day 21 as compared to the other time points. In vivo study showed that, compared with the BMSCs–scaffold group, the PTH + BMSCs–scaffold group showed better regeneration of the implanted tissue and greater similarity to native meniscus concerning gross appearance, cell composition, and cartilage extracellular matrix deposition. This group also showed less expression of terminal differentiation markers of BMSC chondrogenesis as well as lower cartilage degeneration with less damage on the knee cartilage surface, higher expression of Col2, and lower expression of degeneration markers.ConclusionsOur results demonstrated that PTH (1-34) promotes the regenerative and chondroprotective effects of the BMSCs–3D printed meniscal scaffold in a canine model, and thus, their combination could be a promising strategy for meniscus tissue engineering.

Facile Strategy on Hydrophilic Modification of Poly(ε-caprolactone) Scaffolds for Assisting Tissue-Engineered Meniscus Constructs In Vitro.

Poly(ε-caprolactone) (PCL) derived scaffolds have been extensively explored in the field of tissue-engineered meniscus (TEM) originating from their good biosafety and biomechanical properties. However, the poor intrinsic hydrophobicity severely hindered their wide applications for the scaffold-assisted tissue regeneration. Herein, we developed a simple strategy on surface modification of three-dimensional (3D) PCL scaffolds via a simply soaking treatment of sodium hydroxide (NaOH) solutions to increase the hydrophilicity and roughness of scaffolds' surfaces. We investigated the effect of hydrolysis degree mediated by NaOH solutions on mechanical properties of 3D scaffolds, considering the importance of scaffolds' resistance to internal force. We also investigated and analyzed the biological performances of mesenchymal stromal cells (MSCs) and meniscal fibrocartilage cells (MFCs) onto the scaffolds treated or untreated by NaOH solutions. The results indicated that hydrophilic modification could improve the proliferation and attachment of cells on the scaffolds. After careful screening process condition, structural fabrication, and performance optimization, these modified PCL scaffolds possessed roughened surfaces with inherent hierarchical pores, enhanced hydrophilicity and preferable biological performances, thus exhibiting the favorable advantages on the proliferation and adhesion of seeded cells for TEM. Therefore, this feasible hydrophilic modification method is not only beneficial to promote smarter biomedical scaffold materials but also show great application prospect in tissue engineering meniscus with tunable architectures and desired functionalities.

Emerging research trends and foci of studies on the meniscus: A bibliometric analysis.

Meniscus has always been the focus of sport medicine with thousands of articles published annually. Few study has tried to analyze these papers with bibliometric methods. The purpose of this study is to statistically analyze the output of meniscus research and determine emerging research trends and hot spots. Papers related to the meniscus published from 2010 to 2019 were downloaded from the Web of Science Core Collection. Information about annual publications and journal distribution was analyzed by Excel 2016. Co-occurrence analysis of the countries/regions, institutions, authors, and keywords were performed with CiteSpace V, which was also used to perform a co-cited analysis of the references and generate corresponding knowledge maps as well as detect burst keywords. A total of 10,066 articles regarding meniscus were published between 2010 and 2019. The number of articles annual about meniscus increased from 786 to 1300. Knee Surgery Sports Traumatology Arthroscopy, the United States, University of Pittsburgh, and LaPrade RF were journal, country, institution, and author with the most publications, respectively. Makris EA et al. in 2011 was the most cited articles, with a citation of 198. Osteoarthritis, tear repair, anterior cruciate ligament, and articular cartilage were keywords with occurrence of more than 500. Meniscal extrusion, scaffold, and tissue engineering were terms with most burst strength. Meniscus-related publications showed a gradual rising trend from 2010 to 2019. Osteoarthritis, tear repairs, and the anterior cruciate ligament are the current research hot spots. Extrusion and scaffolds may be the frontiers of meniscus research in the next few years. IV.

Entrapped in cage (EiC) scaffolds of 3D-printed polycaprolactone and porous silk fibroin for meniscus tissue engineering

The meniscus has critical functions in the knee joint kinematics and homeostasis. Injuries of the meniscus are frequent, and the lack of a functional meniscus between the femur and tibial plateau can cause articular cartilage degeneration leading to osteoarthritis development and progression. Regeneration of meniscus tissue has outstanding challenges to be addressed. In the current study, novel Entrapped in cage (EiC) scaffolds of 3D-printed polycaprolactone (PCL) and porous silk fibroin were proposed for meniscus tissue engineering. As confirmed by micro-structural analysis the entrapment of silk fibroin was successful, and all scaffolds had excellent interconnectivity (≥99%). The EiC scaffolds had more favorable micro-structure compared with the PCL cage scaffolds by improving the pore size while keeping the interconnectivity almost the same. When compared with the PCL cage, the entrapment of porous silk fibroin into the PCL cage decreased the high compressive modulus in a favorable matter in the wet state thanks to the silk fibroin’s high swelling properties. The in vitro studies with human stem cells or meniscocytes seeded constructs, demonstrated that the EiC scaffolds had superior cell adhesion, metabolic activity, and proliferation compared to the PCL cage scaffolds. Upon subcutaneous implantation of scaffolds in nude mice, all groups were free of adverse incidents, and mildly invaded by inflammatory cells with neovascularization, while the EiC scaffolds showed better tissue infiltration. The results of this work indicated that the EiC scaffolds of PCL and silk fibroin are favorable for meniscus tissue engineering, and the findings are encouraging for further studies using a larger animal model.

Which Contributes to Meniscal Repair, the Synovium or the Meniscus? An In Vivo Rabbit Model Study With the Freeze-Thaw Method

Background: During meniscal tissue repair, the origin of the reparative cells of damaged meniscal tissue remains unclear. Hypothesis: Comparison of the influence between meniscal and synovial tissues on meniscal repair by the in vivo freeze-thaw method would clarify the origin of meniscal reparative cells. Study Design: Controlled laboratory study. Methods: A total of 48 mature Japanese white rabbits were divided into 4 groups according to the tissue (meniscal or synovial) that received freeze-thaw treatment. The meniscus of each group had a 2 mm–diameter cylindrical defect filled with alginate gel. Macroscopic and histologic evaluations of the reparative tissues were performed at 1, 3, and 6 weeks postoperatively. Additional postoperative measurements included cell density, which was the number of meniscal cells in the cut area per cut area (mm2) of meniscus; cell density ratio, which was the cell density of the sample from each group per the average cell density of the intact meniscus; and cell death rate, which was the number of cells stained by propidium iodide per the number of cells stained by Hoechst 33342 of the meniscal tissue adjacent to the defect. Results: The macroscopic and histologic evaluations of the non–synovium freeze-thaw groups were significantly superior to those of the synovium freeze-thaw groups at 3 and 6 weeks postoperatively. Additionally, the meniscal cell density ratio and cell death rate in the freeze-thaw groups were significantly lower than those in the non–meniscal freeze-thaw groups at 3 and 6 weeks postoperatively. Conclusion: The freeze-thawed meniscus recovered few cells in its tissue even after 6 weeks. However, the defect was filled with fibrochondrocytes and proteoglycan when the synovium was intact. On the basis of these results, it is concluded that synovial cells are the primary contributors to meniscal injury repair. Clinical Relevance: In meniscal tissue engineering, there is no consensus on the best cell source for meniscal repair. Based on this study, increasing the synovial activity and contribution should be the main objective of meniscal tissue engineering. This study can establish the foundation for future meniscal tissue engineering.

Effect of cell seeding density on matrix-forming capacity of meniscus fibrochondrocytes and nasal chondrocytes in meniscus tissue engineering.

The presence of intact menisci is imperative for the proper function of the knee joint. Meniscus injuries are often treated by the surgical removal of the damaged tissue, which increases the likelihood of post-traumatic osteoarthritis. Tissue engineering holds great promise in producing viable engineered meniscal tissue for implantation using the patient's own cells; however, the cell source for producing the engineered tissue is unclear. Nasal chondrocytes (NC) possess many attractive features for engineering meniscus. However, in order to validate the use of NC for engineering meniscus fibrocartilage, a thorough comparison of NC and meniscus fibrochondrocytes (MFC) must be considered. Our study presents an analysis of the relative features of NC and MFC and their respective chondrogenic potential in a pellet culture model. We showed considerable differences in the cartilage tissue formed by the two different cell types. Our data showed that NC were more proliferative in culture, deposited more extracellular matrix, and showed higher expression of chondrogenic genes than MFC. Overall, our data suggest that NC produce superior cartilage tissue to MFC in a pellet culture model. In addition, NCs produce higher quality cartilage tissue at higher cell seeding densities during cell expansion.

Repair of a Meniscal Defect in a Rabbit Model Through Use of a Thermosensitive, Injectable, In Situ Crosslinked Hydrogel With Encapsulated Bone Mesenchymal Stromal Cells and Transforming Growth Factor β1

Background: Meniscal injury repair with tissue engineering technique is promising. Among various scaffolds, the thermosensitive injectable hydrogel has recently attracted much attention. Purpose: (1) Evaluate the biocompatibility of thermosensitive, injectable, in situ crosslinked hydrogel and (2) determine whether the hydrogel with or without transforming growth factor β1 (TGF-β1) could support the fibrochondrogenic differentiation of bone mesenchymal stromal cells (BMSCs) and promote the repair of a critical-sized defect in rabbit meniscus. Study Design: Controlled laboratory study. Methods: The rheological and sustained release properties of the hydrogel were demonstrated. BMSCs were isolated and cultured. Cell viability, quantitative polymerase chain reaction (qPCR), and Western blot were tested in vitro. In vivo, a critical-sized defect was introduced into the meniscus of 30 rabbits. Each defect was randomly assigned to be implanted with either phosphate-buffered saline (PBS); BMSC-laden hydrogel; or BMSC-laden, TGF-β1-incorporated hydrogel. Histological and immunohistochemical analyses were performed at 8 weeks after surgery. The Ishida scoring system was adopted to evaluate the healing quantitatively. Results: The elastic modulus of the hydrogel was about 1000 Pa. The hydrogel demonstrated a sustained-release property and could promote proliferation and induce fibrochondrogenic differentiation of BMSCs after the incorporation of TGF-β1 (P < .001). At 8 weeks after surgery, a large amount of fibrocartilaginous tissue, which was positive on safranin-O staining and expressed strong type II collagen intermingled with weak type I collagen, was observed in the defect region of the BMSC-laden, TGF-β1-incorporated hydrogel group. In the BMSC-laden hydrogel group, the defect was filled with fibrous tissue together with a small amount of fibrocartilage. The mean ± SD quantitative scores obtained for the 3 groups—PBS; BMSC-laden hydrogel; and BMSC-laden, TGF-β1-incorporated hydrogel—were 1.00, 3.20 ± 0.84, and 5.00 ± 0.71, respectively (P < .001). Conclusion: The hydrogel was biocompatible and could stimulate strong fibrochondrogenic differentiation of BMSCs after the incorporation of TGF-β1. The local administration of the BMSC-laden, TGF-β1-incorporated hydrogel could promote the healing of rabbit meniscal injury. Clinical Relevance: This hydrogel is an alternative scaffold for meniscus tissue engineering.

Aligned biomimetic scaffolds based on carbon nanotubes-reinforced polymeric nanofibers for knee meniscus tissue engineering

Many strategies in tissue engineering have been developed in order to provide potential treatments for Knee meniscal injuries since it is a high incidence lesion and without effective treatment available in clinical practice. The success of this approach is directly related to the creation of a scaffold able to reproduce the complex extracellular matrix of the native meniscus with adequate mechanical properties. Here we fabricated an aligned biomimetic scaffold, based on carbon nanotube (CNT)-reinforced polymeric nanofibers. For that, scaffolds with both circumferentially and radially aligned polycaprolactone fibers were developed from a specific electrospinning setup and incorporated with two different concentrations of CNT: 0.05% and 0.10%. Characterization by scanning electron microscopy confirmed the spatial distribution and the alignment of the electrospun nanofibers as well as a decrease in average fiber size with the addition of CNT (the presence of CNT was confirmed by transmission electron microscopy). Dynamic mechanical analysis and biological assays showed an improvement in the mechanical properties related to increased CNT content without influence in mesenchymal stem cells survival. These findings suggest a potential applicability of this nanocomposite for knee meniscus tissue engineering.

Biomechanically, structurally and functionally meticulously tailored polycaprolactone/silk fibroin scaffold for meniscus regeneration

Meniscus deficiency, the most common and refractory disease in human knee joints, often progresses to osteoarthritis (OA) due to abnormal biomechanical distribution and articular cartilage abrasion. However, due to its anisotropic spatial architecture, complex biomechanical microenvironment, and limited vascularity, meniscus repair remains a challenge for clinicians and researchers worldwide. In this study, we developed a 3D printing-based biomimetic and composite tissue-engineered meniscus scaffold consisting of polycaprolactone (PCL)/silk fibroin (SF) with extraordinary biomechanical properties and biocompatibility. We hypothesized that the meticulously tailored composite scaffold could enhance meniscus regeneration and cartilage protection.Methods: The physical property of the scaffold was characterized by scanning electron microscopy (SEM) observation, degradation test, frictional force of interface assessment, biomechanical testing, and fourier transform infrared (FTIR) spectroscopy analysis. To verify the biocompatibility of the scaffold, the viability, morphology, proliferation, differentiation, and extracellular matrix (ECM) production of synovium-derived mesenchymal stem cell (SMSC) on the scaffolds were assessed by LIVE/DEAD staining, alamarBlue assay, ELISA analysis, and qRT-PCR. The recruitment ability of SMSC was tested by dual labeling with CD29 and CD90 by confocal microscope at 1 week after implantation. The functionalized hybrid scaffold was then implanted into the meniscus defects on rabbit knee joint for meniscus regeneration, comparing with the Blank group (no scaffold) and PS group. The regenerated meniscus tissue was evaluated by histological and immunohistochemistry staining, and biomechanical test. Macroscopic and histological scoring was performed to assess the outcome of meniscus regeneration and cartilage protection in vivo.Results: The combination of SF and PCL could greatly balance the biomechanical properties and degradation rate to match the native meniscus. SF sponge, characterized by fine elasticity and low interfacial shear force, enhanced energy absorption capacity of the meniscus and improved chondroprotection. The SMSC-specific affinity peptide (LTHPRWP; L7) was conjugated to the scaffold to further increase the recruitment and retention of endogenous SMSCs. This meticulously tailored scaffold displayed superior biomechanics, structure, and function, creating a favorable microenvironment for SMSC proliferation, differentiation, and extracellular matrix (ECM) production. After 24 weeks of implantation, the histological assessment, biochemical contents, and biomechanical properties demonstrated that the polycaprolactone/silk fibroin-L7 (PS-L7) group was close to the native meniscus group, showing significantly better cartilage protection than the PS group.Conclusion: This tissue engineering scaffold could greatly strengthen meniscus regeneration and chondroprotection. Compared with traditional cell-based therapies, the meniscus tissue engineering approach with advantages of one-step operation and reduced cost has a promising potential for future clinical and translational studies.

Single-cell RNA-seq analysis identifies meniscus progenitors and reveals the progression of meniscus degeneration

ObjectivesThe heterogeneity of meniscus cells and the mechanism of meniscus degeneration is not well understood. Here, single-cell RNA sequencing (scRNA-seq) was used to identify various meniscus cell subsets and investigate...

Characterization and Comparison of Postnatal Rat Meniscus Stem Cells at Different Developmental Stages.

Meniscus‐derived stem cells (MeSCs) are a potential cell source for meniscus tissue engineering. The stark morphological and structural changes of meniscus tissue during development indicate the complexity of MeSCs at different tissue regions and stages of development. In this study, we characterized and compared postnatal rat meniscus tissue and MeSCs at different tissue regions and stages of development. We observed that the rat meniscus tissue exhibited marked changes in tissue morphology during development, with day 7 being the most representative time point of different developmental stages. All rat MeSCs displayed typical stem cell characteristics. Rat MeSCs derived from day 7 inner meniscus tissue exhibited the highest self‐renewal capacity, cell proliferation, differentiation potential toward various mesenchymal lineage and the highest expression levels of chondrogenic genes and proteins. Transplantation of rat MeSCs derived from day 7 inner meniscus tissue promoted neo‐tissue formation and effectively protected joint surface cartilage in vivo. Our results demonstrated for the first time that rat MeSCs are not necessarily better at earlier developmental stages, and that rat MeSCs derived from day 7 inner meniscus tissue may be a superior cell source for effective meniscus regeneration and articular cartilage protection. This information could make a significant contribution to human meniscus tissue engineering in the future. stem cells translational medicine 2019;8:1318&1329

Nanocellulose isolation characterization and applications: a journey from non-remedial to biomedical claims

Cellulose is a renewable, biodegradable, ecofriendly and sustainable biomaterial. Global market of nanocellulose is comprehensively very high due to its utility. Extraction of nanocellulose from bacteria and plant results in different morphology and size of nanocellulose. Biocompatibility, mechanical strength, biofabrication, crystallinity, high surface area per unit mass, hydrophilicity, porosity, transparency and non-toxicity of bacterial cellulose make it more attractive. The extravagant nanoscaled three-dimensional network of cellulosic structures possess extraordinary properties for biomedical application, evidencing its usage in skin therapy, cardiovascular implants, cartilage meniscus implants, tissue engineering, bone tissue and neural implants, wound care products, drug delivery agents, tablet modification, tissue engineered urinary conduits, and synthesis of artificial cornea. Hence due to potential benefits associated with nanocellulose effective and efficient techniques are required for the isolation of nanocellulose that should be economical, ecofriendly and non-toxic.

Indirect printing of hierarchical patient-specific scaffolds for meniscus tissue engineering

The complex meniscus tissue plays a critical role in the knee. The high susceptibility to injury has led to an intense pursuit for better tissue engineering regenerative strategies, where scaffolds play a major role. In this study, indirect printed hierarchical multilayered scaffolds composed by a silk fibroin (SF) upper layer and an 80/20 (w/w) ratio of SF/ionic-doped β-tricalcium phosphate (TCP) bottom layer were developed. Furthermore, a comparative analysis between two types of scaffolds produced using different SF concentrations, i.e., 8% (w/v) (Hi8) and 16% (w/v) (Hi16) was performed. In terms of architecture and morphology, the produced scaffolds presented homogeneous porosity in both layers and no differences were observed when comparing both scaffolds. A decrease in terms of mechanical performance of the scaffolds was observed when SF concentration decreased from 16 to 8% (w/v). Hi16 revealed a static compressive modulus of 0.66 ± 0.05 MPa and dynamical mechanical properties ranging from 2.17 ± 0.25 to 3.19 ± 0.38 MPa. By its turn, Hi8 presented a compressive modulus of 0.27 ± 0.08 MPa and dynamical mechanical properties ranging from 1.03 ± 0.08 MPa to 1.56 ± 0.13 MPa. In vitro bioactivity studies showed formation of apatite crystals onto the surface of Hi8 and Hi16 bottom layers. Human meniscus cells (hMCs) and human primary osteoblasts were cultured separately onto the top layer (SF8 and SF16) and bottom layer (SF8/TCP and SF16/TCP) of the hierarchical scaffolds Hi8 and Hi16, respectively. Both cell types showed good adhesion and proliferation as denoted by the live/dead staining, Alamar Blue assay and DNA quantification analysis. Subcutaneous implantation in mice revealed weak inflammation and scaffold’s integrity. The hierarchical indirect printed SF scaffolds can be promising candidate for meniscus TE scaffolding applications due their suitable mechanical properties, good biological performance and possibility of being applied in a patient-specific approach.

Core-Shell Nanofibrous Scaffolds for Repair of Meniscus Tears.

Electrospinning is an attractive method of fabricating nanofibers that replicate the ultrastructure of the human meniscus. However, it is challenging to approximate the mechanical properties of meniscal tissue while maintaining the biocompatibility of collagen fibers. Our objective was to determine if functionalizing polylactic acid (PLA) nanofibers with collagen would enhance their biocompatibility. We therefore used coaxial electrospinning to generate core-shell nanofibers with a core of PLA for mechanical strength and a shell of collagen to enhance cell attachment and matrix synthesis. We characterized the nanostructure of the engineered scaffolds and measured the hydrophilic and mechanical properties. We assessed the performance of human meniscal cells seeded on coaxial electrospun scaffolds to produce meniscal tissue by gene expression and histology. Finally, we investigated whether these cell-seeded scaffolds could repair surgical tears created ex vivo in avascular meniscal explants. Histology, immunohistochemistry, and mechanical testing of ex vivo repair provided evidence of neotissue that was significantly better integrated with the native tissue than with the acellular coaxial electrospun scaffolds. Human meniscal cell-seeded coaxial electrospun scaffolds may have potential in enhancing repair of avascular meniscus tears. Impact Statement The success of any tissue-engineered meniscus graft relies on its ability to mimic native three-dimensional microstructure, support cell growth, produce tissue-specific matrix, and enhance graft integration into the repair site. Polylactic acid scaffolds possess the desired mechanical properties, whereas collagen scaffolds induce better cell attachment and enhanced tissue regeneration. We therefore fabricated nanofibrous scaffolds that combined the properties of two biomaterials. These novel coaxial scaffolds more closely emulated the structure, mechanical properties, and biochemical composition of native meniscal tissue. Our findings of meniscogenic tissue generation and integration in meniscus defects have the potential to be translated to clinical use.

Engineered knee meniscus construct: understanding the structure and impact of functionalization in 3D environment

The structural complexity of human knee meniscus warrants a suitable 3D microenvironment for its successful regeneration. For this, 3D porous poly-e-caprolactone (PCL) scaffold structures were prepared using freeze drying method (lyophilization). PCL was dissolved in different weight percentages (10, 15, 20% w/v, coded as P10, P15 and P20, respectively) in acetone and lyophilized to develop 3D porous structures. The scaffolds were studied for their morphological, mechanical and functional properties. Compression tests were performed to understand their compressive properties and structural integrity. Results indicate that P10 is most suitable considering the highest porosity (above 85%), uniform pore distribution, better resiliency and less than 40% compression at a load of 30 kg/cm2 for 1 min. Further, the effect of a unique combination of biomolecule (UCM) functionalization in 3D PCL scaffold (P10) on human meniscal cell attachment, growth and proliferation was studied in detail. The developed scaffolds were also characterized for dynamic mechanical properties and compared with native human meniscal tissue properties. The primary human meniscus cell attachment, growth and proliferation on to the scaffolds were studied and analyzed using SEM and Hoechst staining experiments. Extracellular matrix secretion (glycosaminoglycans and collagen) in the cell culture medium was estimated. UCM-functionalized PCL 3D porous scaffold, P10 showed better cell attachment and proliferation indicating its potential for meniscus tissue engineering applications.

Suturable regenerated silk fibroin scaffold reinforced with 3D-printed polycaprolactone mesh: biomechanical performance and subcutaneous implantation.

The menisci have crucial roles in the knee, chondroprotection being the primary. Meniscus repair or substitution is favored in the clinical management of the meniscus lesions with given indications. The outstanding challenges with the meniscal scaffolds include the required biomechanical behavior and features. Suturability is one of the prerequisites for both implantation and implant survival. Therefore, we proposed herein a novel highly interconnected suturable porous scaffolds from regenerated silk fibroin that is reinforced with 3D-printed polycaprolactone (PCL) mesh in the middle, on the transverse plane to enhance the suture-holding capacity. Results showed that the reinforcement of the silk fibroin scaffolds with the PCL mesh increased the suture retention strength up to 400%, with a decrease in the mean porosity and an increase in crystallinity from 51.9 to 55.6%. The wet compression modulus values were significantly different for silk fibroin, and silk fibroin + PCL mesh by being 0.16 ± 0.02, and 0.40 ± 0.06 MPa, respectively. Both scaffolds had excellent interconnectivity (>99%), and a high water uptake feature (>500%). The tissue's infiltration and formation of new blood vessels were assessed by means of performing an in vivo subcutaneous implantation of the silk fibroin + PCL mesh scaffolds that were seeded with primary human meniscocytes or stem cells. Regarding suturability and in vivo biocompatibility, the findings of this study indicate that the silk fibroin + PCL mesh scaffolds are suitable for further studies to be carried out for meniscus tissue engineering applications such as the studies involving orthotopic meniscal models and fabrication of patient-specific implants.

Development of decellularized meniscus extracellular matrix and gelatin/chitosan scaffolds for meniscus tissue engineering.

Meniscus tissue engineering has provided a great potential treatment for meniscal injuries. However, few scaffolds in meniscus tissue engineering have matched the mechanical properties of native meniscus. In this study, we developed a composite scaffold using decellularized meniscus extracellular matrix (DMECM) and gelatin/chitosan (G/C) to explore a preferable ratio to enhance the elastic modulus and cytotoxicity properties of scaffolds. The microstructure, porosity, cytotoxicity, and strength of the composite scaffolds were evaluated. The micro-architectures of the samples were evaluated using scanning electron microscope (SEM). Fourier Transform Infrared analysis (FTIR) was used to confirm the chemical structure with different type composite scaffolds. The compressive elastic modulus of all the scaffolds were measured by the universal tensile testing machine DNS300. Calcein-AM (fluorescent green) and propidium iodide (fluorescent red) were used to stain live cells and dead cells. Morphology and spatial distribution of cells within scaffolds were observed by confocal laser scanning microscopy FV 1000. SEM showed that the composite scaffolds had suitable porous structure. CCK-8 and live/dead staining demonstrated that the composite scaffolds had no cytotoxicity and could promote bone marrow mesenchymal stem cells (BMSCs) proliferation. The FTIR results demonstrated the successful mixing of these two elements, and the addition of DMECM improved the elastic modulus and cytotoxicity of G/C composite scaffolds. This study developed a composite scaffold using DMECM and G/C, and demonstrated that it might be suitable for meniscal tissue engineering application.

Biomechanical Stimulus Based Strategies for Meniscus Tissue Engineering and Regeneration.

Meniscus injuries are very common in the knee joint. Treating a damaged meniscus continues to be a scientific challenge in sport medicine because of its poor self-healing potential and few clinical therapeutic options. Tissue engineering strategies are very promising solutions for repairing and regenerating a damaged meniscus. Meniscus is exposed to a complex biomechanical microenvironment, and it plays a crucial role in meniscal development, growth, and repairing. Over the past decades, increasing attention has been focused on the use of biomechanical stimulus to enhance biomechanical properties of the engineered meniscus. Further understanding the influence of mechanical stimulation on cell proliferation and differentiation, metabolism, relevant gene expression, and pro/anti-inflammatory responses may be beneficial to enhance meniscal repair and regeneration. On the one hand, this review describes some basic information about meniscus; on the other hand, we sum up the various biomechanical stimulus based strategies applied in meniscus tissue engineering and how these factors affect meniscal regeneration. We hope this review will provide researchers with inspiration on tissue engineering strategies for meniscus regeneration in the future.