Cell-derived polymer/extracellular matrix composite scaffolds for cartilage regeneration, Part 1: investigation of cocultures and seeding densities for improved extracellular matrix deposition

Human Adipose-Derived Mesenchymal Stem Cell-Secreted Extracellular Matrix Coating on a Woven Nanotextile Vascular Patch for Improved Endothelial Cell Response

Biomedical implants possessing the structural and functional characteristics of extracellular matrix (ECM) are pivotal for vascular applications. This study investigated the potential of recreating a natural ECM-like structural and functional environment on the surface of biodegradable polymeric nanotextiles for vascular implants. Human adipose-derived mesenchymal stem cells (MSCs) were grown on a suitably engineered polycaprolactone (PCL) nanofibrous textile and were allowed to modify its surface through the deposition of MSC-specific ECM. This surface-modified nanotextile showed mechanical characteristics and functionality appropriate for vascular patch material. The uniformity of ECM coating significantly improved the viability, proliferation, and migration of human endothelial cells compared to bare and xenogeneic collagen-coated PCL nanotextile patches. Thus, a polymeric nanotextile, which is surface modified using MSC-driven ECM, provided a rapid and improved endothelialization, thereby suggesting its potential for vascular patch applications.

Co-culture pellet of human Wharton's jelly mesenchymal stem cells and rat costal chondrocytes as a candidate for articular cartilage regeneration: in vitro and in vivo study

BACKGROUND

Seeding cells are key factors in cell-based cartilage tissue regeneration. Monoculture of either chondrocyte or mesenchymal stem cells has several limitations. In recent years, co-culture strategies have provided potential solutions. In this study, directly co-cultured rat costal chondrocytes (CCs) and human Wharton's jelly mesenchymal stem (hWJMSCs) cells were evaluated as a candidate to regenerate articular cartilage.

METHODS

Rat CCs are directly co-cultured with hWJMSCs in a pellet model at different ratios (3:1, 1:1, 1:3) for 21 days. The monoculture pellets were used as controls. RT-qPCR, biochemical assays, histological staining and evaluations were performed to analyze the chondrogenic differentiation of each group. The 1:1 ratio co-culture pellet group together with monoculture controls were implanted into the osteochondral defects made on the femoral grooves of the rats for 4, 8, 12 weeks. Then, macroscopic and histological evaluations were performed.

RESULTS

Compared to rat CCs pellet group, 3:1 and 1:1 ratio group demonstrated similar extracellular matrix production but less hypertrophy intendency. Immunochemistry staining found the consistent results. RT-PCR analysis indicated that chondrogenesis was promoted in co-cultured rat CCs, while expressions of hypertrophic genes were inhibited. However, hWJMSCs showed only slightly improved in chondrogenesis but not significantly different in hypertrophic expressions. In vivo experiments showed that all the pellets filled the defects but co-culture pellets demonstrated reduced hypertrophy, better surrounding cartilage integration and appropriate subchondral bone remodeling.

CONCLUSION

Co-culture of rat CCs and hWJMSCs demonstrated stable chondrogenic phenotype and decreased hypertrophic intendency in both vitro and vivo. These results suggest this co-culture combination as a promising candidate in articular cartilage regeneration.

[Research progress of different cell seeding densities and cell ratios in cartilage tissue engineering]

OBJECTIVE

To review the research progress of different cell seeding densities and cell ratios in cartilage tissue engineering.

METHODS

The literature about tissue engineered cartilage constructed with three-dimensional scaffold was extensively reviewed, and the seeding densities and ratios of most commonly used seed cells were summarized.

RESULTS

Articular chondrocytes (ACHs) and bone marrow mesenchymal stem cells (BMSCs) are the most commonly used seed cells, and they can induce hyaline cartilage formation in vitro and in vivo. Cell seeding density and cell ratio both play important roles in cartilage formation. Tissue engineered cartilage with good quality can be produced when the cell seeding density of ACHs or BMSCs reaches or exceeds that in normal articular cartilage. Under the same culture conditions, the ability of pure BMSCs to build hyaline cartilage is weeker than that of pure ACHs or co-culture of both.

CONCLUSION

Due to the effect of scaffold materials, growth factors, and cell passages, optimal cell seeding density and cell ratio need further study.

Crosstalk Between Mesenchymal Stromal Cells and Chondrocytes: The Hidden Therapeutic Potential for Cartilage Regeneration

Cartilage injuries following trauma create a puzzling clinical scenario. The finite reparative potential of articular cartilage is well known, and injuries are associated with an increased risk of osteoarthritis. Cell-based therapies have spotlighted chondrocytes and mesenchymal stromal cells (MSCs) as the functional unit of articular cartilage and the progenitor cells, respectively. The available clinical treatments cannot reproduce the biomechanical properties of articular cartilage and call for continuous investigations into alternative approaches. Co-cultures of chondrocytes and MSCs are an attractive in vitro system to step closer to the in vivo multicellular environment's complexity. Research on the mechanisms of interaction between both cell types will reveal essential cues to understand cartilage regeneration. This review describes the latest discoveries on these interactions, along with advantages and main challenges in vitro and in vivo. The successful clinical translation of in vitro studies requires establishing rigorous standards and clinically relevant research models and an organ-targeting therapeutic strategy.

Post-decellularization techniques ameliorate cartilage decellularization process for tissue engineering applications

Due to the current lack of innovative and effective therapeutic approaches, tissue engineering (TE) has attracted much attention during the last decades providing new hopes for the treatment of several degenerative disorders. Tissue engineering is a complex procedure, which includes processes of decellularization and recellularization of biological tissues or functionalization of artificial scaffolds by active cells. In this review, we have first discussed those conventional steps, which have led to great advancements during the last several years. Moreover, we have paid special attention to the new methods of post-decellularization that can significantly ameliorate the efficiency of decellularized cartilage extracellular matrix (ECM) for the treatment of osteoarthritis (OA). We propose a series of post-decellularization procedures to overcome the current shortcomings such as low mechanical strength and poor bioactivity to improve decellularized ECM scaffold towards much more efficient and higher integration.

Boosting osteogenic potential and bone regeneration by co-cultured cell derived extracellular matrix incorporated porous electrospun scaffold

Implants for bone regeneration to remedy segmental bone defects, osteomyelitis, necrotic bone tissue and non-union fractures have worldwide appeal. Although biomaterials offer most of the advantages by improving tissue growth but developments are more commonly achieved via biologically derived molecules. To aid site specific bone tissue regeneration by synthetic scaffold, cell derived extracellular matrix (ECM) can be a crucial component. In this study, co-cultured bone marrow mesenchymal stem cell and osteoblastic cells derived ECM incorporated electrospun polycaprolactone (PCL) membranes were assessed for bone tissue engineering application. The preliminary experimental details indicated that, co-culture of cells supported enhanced in vitro ECM synthesis followed by successful deposition of osteoblastic ECM into electrospun membranes. The acellular samples revealed retention of ECM related biomacromolecules (collagen, glycosaminoglycan) and partial recovery of pores after decellularization. In vitro biocompatibility tests ensured improvement of proliferation and osteoblastic differentiation of MC3T3-E1 cells in decellularized ECM containing membrane (PCL-ECM) compared to bare membrane (PCL-B) which was further confirmed by osteogenic marker proteins expression analysis. The decellularized PCL-ECM membrane allowed great improvement of bone regeneration over the bare membrane (PCL-B) in 8 mm size critical sized rat skull defects at 2 months of post implantation. In short, the outcome of this study could be impactful in development and application of cell derived ECM based synthetic electrospun templates for bone tissue engineering application.[Formula: see text].

Chondrogenesis of cocultures of mesenchymal stem cells and articular chondrocytes in poly(l-lysine)-loaded hydrogels

This work investigated the effect of poly(l-lysine) (PLL) molecular weight and concentration on chondrogenesis of cocultures of mesenchymal stem cells (MSCs) and articular chondrocytes (ACs) in PLL-loaded hydrogels. An injectable dual-network hydrogel composed of a poly(N-isopropylacrylamide)-based synthetic thermogelling macromer and a chondroitin sulfate-based biological network was leveraged as a model to deliver PLL and encapsulate the two cell populations. Incorporation of PLL into the hydrogel did not affect the hydrogel's swelling properties and degradation characteristics, nor the viability of encapsulated cells. Coculture groups demonstrated higher type II collagen expression compared to the MSC monoculture group. Expression of hypertrophic phenotype was also limited in the coculture groups. Histological analysis indicated that the ratio of MSCs to ACs was an accurate predictor of the degree of long-term chondrogenesis, while the presence of PLL was shown to have a more substantial short-term effect. Altogether, this study demonstrates that coculturing MSCs with ACs can greatly enhance the chondrogenicity of the overall cell population and offers a platform to further elucidate the short- and long-term effect of polycationic factors on the chondrogenesis of MSC and AC cocultures.

Extracellular Matrix for Small-Diameter Vascular Grafts

To treat coronary heart disease, coronary artery bypass grafts are used to divert blood flow around blockages in the coronary arteries. Autologous grafts are the gold standard of care, but they are characterized by their lack of availability, low quality, and high failure rates. Alternatively, tissue-engineered small-diameter vascular grafts made from synthetic or natural polymers have not demonstrated adequate results to replace autologous grafts; synthetic grafts result in a loss of patency due to thrombosis and intimal hyperplasia, whereas scaffolds from natural polymers are generally unable to support the physiological conditions. Extracellular matrix (ECM) from a variety of sources, including cell-derived, 2D, and cannular tissues, has become an increasingly useful tool for this application. The current review examines the ECM-based methods that have recently been investigated in the field and comments on their viability for clinical applications.

Cell-derived decellularized extracellular matrix scaffolds for articular cartilage repair

Articular cartilage repair remains a great clinical challenge. Tissue engineering approaches based on decellularized extracellular matrix (dECM) scaffolds show promise for facilitating articular cartilage repair. Traditional regenerative approaches currently used in clinical practice, such as microfracture, mosaicplasty, and autologous chondrocyte implantation, can improve cartilage repair and show therapeutic effect to some degree; however, the long-term curative effect is suboptimal. As dECM prepared by proper decellularization procedures is a biodegradable material, which provides space for regeneration tissue growth, possesses low immunogenicity, and retains most of its bioactive molecules that maintain tissue homeostasis and facilitate tissue repair, dECM scaffolds may provide a biomimetic microenvironment promoting cell attachment, proliferation, and chondrogenic differentiation. Currently, cell-derived dECM scaffolds have become a research hotspot in the field of cartilage tissue engineering, as ECM derived from cells cultured in vitro has many advantages compared with native cartilage ECM. This review describes cell types used to secrete ECM, methods of inducing cells to secrete cartilage-like ECM and decellularization methods to prepare cell-derived dECM. The potential mechanism of dECM scaffolds on cartilage repair, methods for improving the mechanical strength of cell-derived dECM scaffolds, and future perspectives on cell-derived dECM scaffolds are also discussed in this review.

PLGA scaffold carrying icariin to inhibit the progression of osteoarthritis in rabbits

Icariin, the main effective component extracted from epimedium, has been shown to stimulate osteogenic differentiation and bone formation and to increase synthesis of the cartilage extracellular matrix. However, there has been little study on the effects of icariin on osteoarthritis. In this study, we loaded icariin onto poly(lactic-co-glycolic acid) (PLGA) electrospinning. The aim of this study was to explore a composite scaffold and to inhibit the progression of osteoarthritis. Our main experimental results demonstrated that the PLGA/icariin composite spinning scaffold had higher hydrophilicity, and icariin was released slowly and steadily from the scaffold. According to the results of an MTT test, immunofluorescence staining, an alkaline phosphate activating assay and a real-time polymerase chain reaction (RT-PCR) assay, the PLGA/icariin composite scaffold had good biocompatibility. In models of osteoarthritis, the results of a RT-PCR assay indicated that the PLGA/icariin scaffold promoted the synthesis of the extracellular matrix. The results of X-ray microtomography and histological evaluation demonstrated that the PLGA/icariin scaffold maintained the functional morphology of articular cartilage and inhibited the resorption of subchondral bone trabeculae. These findings indicated that the PLGA and icariin composite scaffold has therapeutic potential for use in the treatment of osteoarthritis.

Functionality of decellularized matrix in cartilage regeneration: A comparison of tissue versus cell sources

Increasing evidence indicates that decellularized extracellular matrices (dECMs) derived from cartilage tissues (T-dECMs) or chondrocytes/stem cells (C-dECMs) can support proliferation and chondrogenic differentiation of cartilage-forming cells. However, few review papers compare the differences between these dECMs when they serve as substrates for cartilage regeneration. In this review, after an introduction of cartilage immunogenicity and decellularization methods to prepare T-dECMs and C-dECMs, a comprehensive comparison focuses on the effects of T-dECMs and C-dECMs on proliferation and chondrogenic differentiation of chondrocytes/stem cells in vitro and in vivo. Key factors within dECMs, consisting of microarchitecture characteristics and micromechanical properties as well as retained insoluble and soluble matrix components, are discussed in-depth for potential mechanisms underlying the functionality of these dECMs in regulating chondrogenesis. With this information, we hope to benefit dECM based cartilage engineering and tissue regeneration for future clinical application.

STATEMENT OF SIGNIFICANCE

The use of decellularized extracellular matrix (dECM) is becoming a promising approach for tissue engineering and regeneration. Compared to dECM derived from cartilage tissue, recently reported dECM from cell sources exhibits a distinct role in cell based cartilage regeneration. In this review paper, for the first time, tissue and cell based dECMs are comprehensively compared for their functionality in cartilage regeneration. This information is expected to provide an update for dECM based cartilage regeneration.

Combating Osteoarthritis through Stem Cell Therapies by Rejuvenating Cartilage: A Review

Knee osteoarthritis (OA) is a chronic degenerative disorder which could be distinguished by erosion of articular cartilage, pain, stiffness, and crepitus. Not only aging-associated alterations but also the metabolic factors such as hyperglycemia, dyslipidemia, and obesity affect articular tissues and may initiate or exacerbate the OA. The poor self-healing ability of articular cartilage due to limited regeneration in chondrocytes further adversely affects the osteoarthritic microenvironment. Traditional and current surgical treatment procedures for OA are limited and incapable to reverse the damage of articular cartilage. To overcome these limitations, cell-based therapies are currently being employed to repair and regenerate the structure and function of articular tissues. These therapies not only depend upon source and type of stem cells but also on environmental conditions, growth factors, and chemical and mechanical stimuli. Recently, the pluripotent and various multipotent mesenchymal stem cells have been employed for OA therapy, due to their differentiation potential towards chondrogenic lineage. Additionally, the stem cells have also been supplemented with growth factors to achieve higher healing response in osteoarthritic cartilage. In this review, we summarized the current status of stem cell therapies in OA pathophysiology and also highlighted the potential areas of further research needed in regenerative medicine.

Functionalization of porous BCP scaffold by generating cell-derived extracellular matrix from rat bone marrow stem cells culture for bone tissue engineering

The potential of decellularized cell-derived extracellular matrix (ECM) deposited on biphasic calcium phosphate (BCP) scaffold for bone tissue engineering was investigated. Rat derived bone marrow mesenchymal stem cells were cultured on porous BCP scaffolds for 3 weeks and decellularized with two different methods (freeze-thaw [F/T] or sodium dodecyl sulfate [SDS]). The decellularized ECM deposited scaffolds (dECM-BCP) were characterized through scanning electron microscopy, energy dispersive X-ray spectrometer, and confocal microscopy. The efficiency of decellularization was evaluated by quantifying remaining DNA, sulfated glycosaminoglycans, and collagens. Results revealed that F/T method was more effective procedure for removing cellular components of cultured cells (95.21% DNA reduction) than SDS treatment (92.49%). Although significant loss of collagen was observed after decellularization with both F/T (56.68%) and SDS (70.87%) methods, F/T treated sample showed higher retaining amount of sulfated glycosaminoglycans content (75.64%) than SDS (33.28%). In addition, we investigated the cell biocompatibility and osteogenic effect of dECM-BCP scaffolds using preosteoblasts (MC3T3-E1). Compared to bare BCP scaffolds, dECM-BCP_F/T scaffolds showed improved cell attachment and proliferation based on immunofluorescence staining and water soluble tetrazolium salts assay (p < .001). Moreover, dECM-BCP scaffolds showed increased osteoblastic differentiation of newly seeded preosteoblasts by up-regulating three types of osteoblastic genes (osteopontin, alkaline phosphatase, and bone morphogenic protein-2). This study demonstrated that functionalization of BCP scaffold using cell-derived ECM could be useful for improving the bioactivity of materials and providing suitable microenvironment, especially for osteogenesis. Further study is needed to determine the potential of dECM-BCP scaffold for bone formation and regeneration in vivo.

Cell type-specific extracellular matrix guided the differentiation of human mesenchymal stem cells in 3D polymeric scaffolds

The tissue microenvironment has profound effects on tissue-specific regeneration. The 3-dimensional extracellular matrix (ECM) niche influences the linage-specific differentiation of stem cells in tissue. To understand how ECM guides tissue-specific regeneration, we established a series of 3D composite scaffolds containing ECMs derived from different primary cells isolated from a single animal species and assessed their impact on the differentiation of human mesenchymal stem cells (hMSCs). Synthetic microfiber scaffolds (fiber mats) were fabricated by electrospinning tyrosine-derived polycarbonates (pDTEC). The bovine primary fibroblasts, chondrocytes and osteoblasts cultured on the fiber mats produced and assembled their ECMs, infiltrating the pores of the fibrous scaffold. The composite scaffolds were decellularized to remove cellular components, preserve ECM and minimally affect polymer integrity. Characterization of the ECMs derived from different primary cells in the composite scaffolds showed overlapping but distinct compositions. The chondrogenic and osteogenic differentiation of hMSCs on the different composite scaffolds were compared. Our results showed that ECM derived from chondrocytes cultured in synthetic fiber mats promoted the chondrogenic differentiation of hMSC in the presence or absence of soluble inducing factors. ECM derived from co-culture of osteoblasts and chondrocytes promoted osteogenic differentiation in hMSCs better than ECM derived from chondrocytes. This study demonstrated that decellularized ECMs derived from different cell types formed within synthetic fiber scaffolds guide the tissue-specific differentiation of hMSCs. These composite scaffolds may be developed into models to study the mechanisms of ECM-induced tissue regeneration.

Optimization of Polymer-ECM Composite Scaffolds for Tissue Engineering: Effect of Cells and Culture Conditions on Polymeric Nanofiber Mats

The design of composite tissue scaffolds containing an extracellular matrix (ECM) and synthetic polymer fibers is a new approach to create bioactive scaffolds that can enhance cell function. Currently, studies investigating the effects of ECM-deposition and decellularization on polymer degradation are still lacking, as are data on optimizing the stability of the ECM-containing composite scaffolds during prolonged cell culture. In this study, we develop fibrous scaffolds using three polymer compositions, representing slow (E0000), medium (E0500), and fast (E1000) degrading materials, to investigate the stability, degradation, and mechanics of the scaffolds during ECM deposition and decellularization, and during the complete cellularization-decell-recell cycle. We report data on percent molecular weight (% Mw) retention of polymeric fiber mats, changes in scaffold stiffness, ECM deposition, and the presence of fibronectin after decellularization. We concluded that the fast degrading E1000 (Mw retention ≤ 50% after 28 days) was not sufficiently stable to allow scaffold handling after 28 days in culture, while the slow degradation of E0000 (Mw retention ≥ 80% in 28 days) did not allow deposited ECM to replace the polymer support. The scaffolds made from medium degrading E0500 (Mw retention about 60% at 28 days) allowed the gradual replacement of the polymer network with cell-derived ECM while maintaining the polymer network support. Thus, polymers with an intermediate rate of degradation, maintaining good scaffold handling properties after 28 days in culture, seem best suited for creating ECM-polymer composite scaffolds.

Potential of silk fibroin/chondrocyte constructs of muga silkworm Antheraea assamensis for cartilage tissue engineering

Articular cartilage damage represents one of the most perplexing clinical problems of musculoskeletal therapeutics due to its limited self-repair and regenerative capabilities. In this study, 3D porous silk fibroin scaffolds derived from non-mulberry muga silkworm Antheraea assamensis were fabricated and examined for their ability to support cartilage tissue engineering. Additionally, Bombyx mori and Philosamia ricini silk fibroin scaffolds were utilized for comparative studies. Herein, the fabricated scaffolds were thoroughly characterized and compared for cartilaginous tissue formation within the silk fibroin scaffolds seeded with primary porcine chondrocytes and cultured in vitro for 2 weeks. Surface morphology and structural conformation studies revealed the highly interconnected porous structure (pore size 80-150 μm) with enhanced stability within their structure. The fabricated scaffolds demonstrated improved mechanical properties and were followed-up with sequential experiments to reveal improved thermal and degradation properties. Silk fibroin scaffolds of A. assamensis and P. ricini supported better chondrocyte attachment and proliferation as indicated by metabolic activities and fluorescence microscopic studies. Biochemical analysis demonstrated significantly higher production of sulphated glycosaminoglycans (sGAGs) and type II collagen in A. assamensis silk fibroin scaffolds followed by P. ricini and B. mori scaffolds (p < 0.001). Furthermore, histochemistry and immunohistochemical studies indicated enhanced accumulation of sGAGs and expression of collagen II. Moreover, the scaffolds in a subcutaneous model of rat demonstrated in vivo biocompatibility after 8 weeks of implantation. Taken together, these results demonstrate the positive attributes from the non-mulberry silk fibroin scaffold of A. assamensis and suggest its suitability as a promising scaffold for chondrocyte based cartilage repair.

Biomimetic extracellular matrix mediated somatic stem cell differentiation: applications in dental pulp tissue regeneration

Dental caries is one of the most widely prevalent infectious diseases in the world. It affects more than half of the world's population. The current treatment for necrotic dental pulp tissue arising from dental caries is root canal therapy. This treatment results in loss of tooth sensitivity and vitality making it prone for secondary infections. Over the past decade, several tissue-engineering approaches have attempted regeneration of the dental pulp tissue. Although several studies have highlighted the potential of dental stem cells, none have transitioned into a clinical setting owing to limited availability of dental stem cells and the need for growth factor delivery systems. Our strategy is to utilize the intact ECM of pulp cells to drive lineage specific differentiation of bone marrow derived mesenchymal stem cells. From a clinical perspective, pulp ECM scaffolds can be generated using cell lines and patient specific somatic stem cells can be used for regeneration. Our published results have shown the feasibility of using pulp ECM scaffolds for odontogenic differentiation of non-dental mesenchymal cells. This focused review discusses the issues surrounding dental pulp tissue regeneration and the potential of our strategy to overcome these issues.

Concise review: tailoring bioengineered scaffolds for stem cell applications in tissue engineering and regenerative medicine

The potential for the clinical application of stem cells in tissue regeneration is clearly significant. However, this potential has remained largely unrealized owing to the persistent challenges in reproducibly, with tight quality criteria, and expanding and controlling the fate of stem cells in vitro and in vivo. Tissue engineering approaches that rely on reformatting traditional Food and Drug Administration-approved biomedical polymers from fixation devices to porous scaffolds have been shown to lack the complexity required for in vitro stem cell culture models or translation to in vivo applications with high efficacy. This realization has spurred the development of advanced mimetic biomaterials and scaffolds to increasingly enhance our ability to control the cellular microenvironment and, consequently, stem cell fate. New insights into the biology of stem cells are expected to eventuate from these advances in material science, in particular, from synthetic hydrogels that display physicochemical properties reminiscent of the natural cell microenvironment and that can be engineered to display or encode essential biological cues. Merging these advanced biomaterials with high-throughput methods to systematically, and in an unbiased manner, probe the role of scaffold biophysical and biochemical elements on stem cell fate will permit the identification of novel key stem cell behavioral effectors, allow improved in vitro replication of requisite in vivo niche functions, and, ultimately, have a profound impact on our understanding of stem cell biology and unlock their clinical potential in tissue engineering and regenerative medicine.

Multifunctional ECM proteins in bone and teeth

The extracellular matrix (ECM) of all tissues and organs is a highly organized and complex structure unique to the specific organ type. The ECM contains structural and functional proteins that define cellular function, organization, behavior and ultimately organ characteristics and function. The ECM was initially thought to contain only a specific set of secretory proteins. However, our group and several other groups have shown that the ECM contains functional proteins that have been previously defined as solely intracellular. In the present review, we have focused on the ECM of mineralized tissues namely bone and dentin. We provide here, a brief review of some non-classical ECM proteins that have been shown to possess both intra and extracellular roles in the formation of these mineralized matrices.

Enhancing chondrogenic phenotype for cartilage tissue engineering: monoculture and coculture of articular chondrocytes and mesenchymal stem cells

Articular cartilage exhibits an inherently low rate of regeneration. Consequently, damage to articular cartilage often requires surgical intervention. However, existing treatments generally result in the formation of fibrocartilage tissue, which is inferior to native articular cartilage. As a result, cartilage engineering strategies seek to repair or replace damaged cartilage with an engineered tissue that restores full functionality to the impaired joint. These strategies often involve the use of chondrocytes, yet in vitro expansion and culture can lead to undesirable changes in chondrocyte phenotype. This review focuses on the use of articular chondrocytes and mesenchymal stem cells (MSCs) in either monoculture or coculture for the enhancement of chondrogenesis. Coculture strategies increasingly outperform their monoculture counterparts with regard to chondrogenesis and present unique opportunities to attain chondrocyte phenotype stability in vitro. Methods to prevent chondrocyte dedifferentiation and promote chondrocyte redifferentiation as well as to promote the chondrogenic differentiation of MSCs while preventing MSC hypertrophy are discussed.

Direct and indirect co-culture of chondrocytes and mesenchymal stem cells for the generation of polymer/extracellular matrix hybrid constructs

In this work, the influence of direct cell-cell contact in co-cultures of mesenchymal stem cells (MSCs) and chondrocytes for the improved deposition of cartilage-like extracellular matrix (ECM) within nonwoven fibrous poly(∊-caprolactone) (PCL) scaffolds was examined. To this end, chondrocytes and MSCs were either co-cultured in direct contact by mixing on a single PCL scaffold or produced via indirect co-culture, whereby the two cell types were seeded on separate scaffolds which were then cultured together in the same system either statically or under media perfusion in a bioreactor. In static cultures, the chondrocyte scaffold of an indirectly co-cultured group generated significantly greater amounts of glycosaminoglycan and collagen than the direct co-culture group initially seeded with the same number of chondrocytes. Furthermore, improved ECM production was linked to greater cellular proliferation and distribution throughout the scaffold in static culture. In perfusion cultures, flow had a significant effect on the proliferation of the chondrocytes. The ECM contents within the chondrocyte-containing scaffolds of the indirect co-culture groups either approximated or surpassed the amounts generated within the direct co-culture group. Additionally, within bioreactor culture there were indications that chondrocytes had an influence on the chondrogenesis of MSCs as evidenced by increases in cartilaginous ECM synthetic capacity. This work demonstrates that it is possible to generate PCL/ECM hybrid scaffolds for cartilage regeneration by utilizing the factors secreted by two different cell types, chondrocytes and MSCs, even in the absence of juxtacrine signaling.

Stem cells catalyze cartilage formation by neonatal articular chondrocytes in 3D biomimetic hydrogels

Cartilage loss is a leading cause of disability among adults and effective therapy remains elusive. Neonatal chondrocytes (NChons) are an attractive allogeneic cell source for cartilage repair, but their clinical translation has been hindered by scarce donor availability. Here we examine the potential for catalyzing cartilage tissue formation using a minimal number of NChons by co-culturing them with adipose-derived stem cells (ADSCs) in 3D hydrogels. Using three different co-culture models, we demonstrated that the effects of co-culture on cartilage tissue formation are dependent on the intercellular distance and cell distribution in 3D. Unexpectedly, increasing ADSC ratio in mixed co-culture led to increased synergy between NChons and ADSCs, and resulted in the formation of large neocartilage nodules. This work raises the potential of utilizing stem cells to catalyze tissue formation by neonatal chondrocytes via paracrine signaling, and highlights the importance of controlling cell distribution in 3D matrices to achieve optimal synergy.

Cell-derived polymer/extracellular matrix composite scaffolds for cartilage regeneration, Part 2: construct devitalization and determination of chondroinductive capacity

This work examined the chondrogenic potential of chondrocyte and mesenchymal stem cell (MSC) coculture generated poly(ɛ-caprolactone) (PCL)/extracellular matrix (ECM) hybrid scaffolds. Five different ratios of chondrocytes and MSCs were cocultured to generate cartilage-like ECM within electrospun fibrous scaffolds for 7, 14, and 21 days. These constructs were then devitalized to isolate the chondrogenic effects of the ECM alone. Devitalization was successful at removing cellular matter from the scaffolds, yet did reduce the amount of matrix present in the scaffolds. Following devitalization, the PCL/ECM scaffolds were then cultured with MSCs in serum-free conditions with or without TGF-β3 treatment for 21 days. TGF-β3 supplemented culture caused an induction of chondrogenesis in each scaffold type, but also somewhat masked the subtle differences of the different ECM coatings. Without TGF-β3, the cartilaginous matrix generated by 1:1 cocultures of chondrocytes to MSCs for 14 days supported similar chondrogenic gene expression patterns of MSCs cultured on scaffolds generated by chondrocytes alone. These scaffold formulations had a positive chondrogenic effect on aggrecan, collagen type II, and collagen II/I expression when compared to PCL controls. This study demonstrates that it is possible to utilize cocultures of chondrocytes and MSCs to coat a polymer scaffold with cartilage-like ECM capable of supporting chondrogenic differentiation of MSCs.