In vitro and in vivo co‐culture of chondrocytes and bone marrow stem cells in photocrosslinked PCL–PEG–PCL hydrogels enhances cartilage formation

Chondrocytes (CH) and bone marrow stem cells (BMSCs) are sources that can be used in cartilage tissue engineering. Co‐culture of CHs and BMSCs is a promising strategy for promoting chondrogenic differentiation. In this study, articular CHs and BMSCs were encapsulated in PCL–PEG–PCL photocrosslinked hydrogels for 4 weeks. Various ratios of CH:BMSC co‐cultures were investigated to identify the optimal ratio for cartilage formation. The results thus obtained revealed that co‐culturing CHs and BMSCs in hydrogels provides an appropriate in vitro microenvironment for chondrogenic differentiation and cartilage matrix production. Co‐culture with a 1:4 CH:BMSC ratio significantly increased the synthesis of GAGs and collagen. In vivo cartilage regeneration was evaluated using a co‐culture system in rabbit models. The co‐culture system exhibited a hyaline chondrocyte phenotype with excellent regeneration, resembling the morphology of native cartilage. This finding suggests that the co‐culture of these two cell types promotes cartilage regeneration and that the system, including the hydrogel scaffold, has potential in cartilage tissue engineering. Copyright © 2013 John Wiley & Sons, Ltd.     

Low‐oxygen conditions promote synergistic increases in chondrogenesis during co‐culture of human osteoarthritic stem cells and chondrocytes

There has been increased interest in co‐cultures of stem cells and chondrocytes for cartilage tissue engineering as there are the limitations associated with using either cell type alone. Drawbacks associated with the use of chondrocytes include the limited numbers of cells available for isolation from damaged or diseased joints, their dedifferentiation during in vitro expansion, and a diminished capacity to synthesise cartilage‐specific extracellular matrix components with age and disease. This has motivated the use of adult stem cells with either freshly isolated or culture‐expanded chondrocytes for cartilage repair applications; however, the ideal combination of cells and environmental conditions for promoting robust chondrogenesis remains unclear. In this study, we compared the effect of combining a small number of freshly isolated or culture‐expanded human chondrocytes with infrapatellar fat pad–derived stem cells (FPSCs) from osteoarthritic donors on chondrogenesis in altered oxygen (5% or 20%) and growth factor supplementation (TGF‐β3 only or TGF‐β3 and BMP‐7) conditions. Both co‐cultures, but particularly those including freshly isolated chondrocytes, were found to promote cell proliferation and enhanced matrix accumulation compared to the use of FPSCs alone, resulting in the development of a tissue that was compositionally more similar to that of the native articular cartilage. Local oxygen levels were found to impact chondrogenesis in co‐cultures, with more robust increases in proteoglycan and collagen deposition observed at 5% O₂. Additionally, collagen type I synthesis was suppressed in co‐cultures maintained at low‐oxygen conditions. This study demonstrates that a co‐culture of freshly isolated human chondrocytes and FPSCs promotes robust chondrogenesis and thus is a promising cell combination for cartilage tissue engineering.     

A mixed co‐culture of mesenchymal stem cells and transgenic chondrocytes in alginate hydrogel for cartilage tissue engineering

To regenerate articular cartilage tissue from degeneration and trauma, synovial mesenchymal stem cells (SMSCs) were used in this study as therapeutic progenitor cells to induce therapeutic chondrogenesis. To accomplish this, chondrocytes pre‐transduced with adenoviral vectors carrying the transforming growth factor (TGF) β3 gene were selected as transgenic companion cells and co‐cultured side‐by‐side with SMSCs in a 3D environment to provide chondrogenic growth factors in situ. We adopted a mixed co‐culture strategy for this purpose. Transgenic delivery of TGF‐β3 in chondrocytes was performed via recombinant adenoviral vectors. The mixed co‐culture of SMSCs and transgenic chondrocytes was produced in alginate gel constructs. Gene expression in both SMSCs and chondrocytes were characterized. Biochemical assays in vitro and in vivo showed that release of TGF‐ß3 from transgenic chondrocytes not only induced SMSC differentiation into chondrocytic cells but also preserved the chondrocytic phenotype of chondrocytes from suspected dedifferentiation. As a result, this mixed co‐culture strategy in conjunction with TGF‐ß3 gene delivery could be a promising approach in cartilage tissue engineering. Copyright © 2012 John Wiley & Sons, Ltd.     

Dynamic three‐dimensional micropatterned cell co‐cultures within photocurable and chemically degradable hydrogels

In this paper we report on the development of dynamically controlled three‐dimensional (3D) micropatterned cellular co‐cultures within photocurable and chemically degradable hydrogels. Specifically, we generated dynamic co‐cultures of micropatterned murine embryonic stem (mES) cells with human hepatocellular carcinoma (HepG2) cells within 3D hydrogels. HepG2 cells were used due to their ability to direct the differentiation of mES cells through secreted paracrine factors. To generate dynamic co‐cultures, mES cells were first encapsulated within micropatterned photocurable poly(ethylene glycol) (PEG) hydrogels. These micropatterned cell‐laden PEG hydrogels were subsequently surrounded by calcium alginate (Ca‐Alg) hydrogels containing HepG2 cells. After 4 days, the co‐culture step was halted by exposing the system to sodium citrate solution, which removed the alginate gels and the encapsulated HepG2 cells. The encapsulated mES cells were then maintained in the resulting cultures for 16 days and cardiac differentiation was analysed. We observed that the mES cells that were exposed to HepG2 cells in the co‐cultures generated cells with higher expression of cardiac genes and proteins, as well as increased spontaneous beating. Due to its ability to control the 3D microenvironment of cells in a spatially and temporally regulated manner, the method presented in this study is useful for a range of cell‐culture applications related to tissue engineering and regenerative medicine. Copyright © 2013 John Wiley & Sons, Ltd.     

Endothelial cells stimulate osteogenic differentiation of mesenchymal stem cells on calcium phosphate scaffolds

The interaction of mesenchymal stem cells (MSCs) with endothelium in vivo is significant for regenerative processes in organisms. To design concepts for tissue engineering for bone regeneration based on this interaction, the osteogenic differentiation of human bone marrow‐derived MSCs in a co‐culture with human dermal microvascular endothelial cells (HDMECs) was studied. The experiments were focussed on the regulation of MSCs in a co‐culture with HDMECs on different calcium phosphate scaffolds. Alkaline phosphatase (ALP) activity and mRNA expression of various osteogenic markers increased significantly when cells were co‐cultured on materials with calcium phosphate scaffolds compared to tissue culture polystyrene or when MSCs were cultured alone. In addition, it was observed that the expression of osteopontin and osteocalcin was highly sensitive to the substrate for cell adhesion. Whereas these late osteogenic markers were down‐regulated in co‐cultures on polystyrene, they were up‐regulated on calcium phosphate and moreover, were differentially expressed on the three calcium phosphate scaffolds tested. To enhance the osteogenic differentiation of MSCs in a co‐culture, direct cell‐cell interactions were required. Concerning molecular mechanisms in the interactions between both cell types, it was found that connexin 43 was expressed in contact sites and more apparently, endothelial cells grew over the MSCs, which facilitated direct cellular interactions mediated by various adhesion receptors. This study revealed significant findings for the design of implant materials suitable for regeneration of bone by stimulating the functional interaction of MSCs with endothelial cells. Copyright © 2012 John Wiley & Sons, Ltd.     

Co-culturing mesenchymal stem cells from bone marrow and periosteum enhances osteogenesis and neovascularization of tissue-engineered bone

Mesenchymal stem cells (MSCs) isolated from bone marrow and periosteum are often used as cellular sources for bone tissue engineering. This study showed that co‐cultured human bone marrow stem cells (hBMSCs) and periosteal‐derived stem cells (hPCs) resulted in a synergistic effect on osteogenic differentiation both in vitro and in vivo. Compared to hBMSCs and hPCs, co‐culturing MSCs showed abundant mineralization, robust calcium deposition, steadily increasing ALP activity, and upgraded mRNA expression of osteogenic specific genes (COL1A1, BMP‐2, osteopontin, osteocalcin) in vitro. Eight weeks after implantation of cellular β‐TCP scaffolds in immunodeficient mice, similar synergistic effects were confirmed during in vivo evaluation of total new bone formation, mature bone formation, and neovascularization. Based on these findings, the use of co‐cultured hBMSCs and hPCs can be recommended as a promising new approach for bone tissue engineering applications. Copyright © 2011 John Wiley & Sons, Ltd.     

Cell–cell interaction between vocal fold fibroblasts and bone marrow mesenchymal stromal cells in three‐dimensional hyaluronan hydrogel

Mesenchymal stromal cells (MSCs) are multipotential adult cells present in all tissues. Paracrine effects and differentiating ability make MSCs an ideal cell source for tissue regeneration. However, little is known about how interactions between implanted MSCs and native cells influence cellular growth, proliferation, and behaviour. By using an in vitro three‐dimensional (3D) co‐culture assay of normal or scarred human vocal fold fibroblasts (VFFs) and bone marrow‐derived MSCs (BM‐MSCs) in a uniquely suited hyaluronan hydrogel (HyStem–VF), we investigated cell morphology, survival rate, proliferation and protein and gene expression of VFFs and BM‐MSCs. BM‐MSCs inhibited cell proliferation of both normal and scarred VFFs without changes in VFF morphology or viability. BM‐MSCs demonstrated decreased proliferation and survival rate after 7 days of co‐culture with VFFs. Interactions between BM‐MSCs and VFFs led to a significant increase in protein secretion of collagen I and hepatocyte growth factor (HGF) and a decrease of vascular endothelial growth factor (VEGF), monocyte chemotactic protein‐1 (MCP‐1) and interleukin‐6 (IL‐6). In particular, BM‐MSCs significantly upregulated matrix metalloproteinase 1 (MMP1) and HGF gene expression for scarred VFFs compared to normal VFFs, indicating the potential for increases in extracellular matrix remodelling and tissue regeneration. Application of BM‐MSCs‐hydrogels may play a significant role in tissue regeneration, providing a therapeutic approach for vocal fold scarring. Copyright © 2013 John Wiley & Sons, Ltd.     

Matrix formation is enhanced in co‐cultures of human meniscus cells with bone marrow stromal cells

The ultimate aim of this study was to assess the feasibility of using human bone marrow stromal cells (BMSCs) to supplement meniscus cells for meniscus tissue engineering and regeneration. Human menisci were harvested from three patients undergoing total knee replacements. Meniscus cells were released from the menisci after collagenase treatment. BMSCs were harvested from the iliac crest of three patients and were expanded in culture until passage 2. Primary meniscus cells and BMSCs were co‐cultured in vitro in three‐dimensional (3D) pellet culture at three different cell–cell ratios for 3 weeks under normal (21% O₂) or low (3% O₂) oxygen tension in the presence of serum‐free chondrogenic medium. Pure BMSCs and pure meniscus cell pellets served as control groups. The tissue generated was assessed biochemically, histochemically and by quantitative RT–PCR. Co‐cultures of primary meniscus cells and BMSCs resulted in tissue with increased (1.3–1.7‐fold) deposition of proteoglycan (GAG) extracellular matrix (ECM) relative to tissues derived from BMSCs or meniscus cells alone under 21% O₂. GAG matrix formation was also enhanced (1.3–1.6‐fold) under 3% O₂ culture conditions. Alcian blue staining of generated tissue confirmed increased deposition of GAG‐rich matrix. mRNA expression of type I collagen (COL1A2), type II collagen (COL2A1) and aggrecan were upregulated in co‐cultured pellets. However, SOX9 and HIF‐1α mRNA expression were not significantly modulated by co‐culture. Co‐culture of primary meniscus cells with BMSCs resulted in increased ECM formation. Co‐delivery of meniscus cells and BMSCs can, in principle, be used in tissue engineering and regenerative medicine strategies to repair meniscus defects. Copyright © 2012 John Wiley & Sons, Ltd.     

Osteogenic capacity of human BM‐MSCs,AT‐MSCs and their co‐cultures using HUVECs in FBS and PL supplemented media

Human bone marrow‐derived mesenchymal stem cells (BM‐MSCs) and human adipose tissue‐derived mesenchymal stem cells (AT‐MSCs) are the most frequently used stem cells in tissue engineering. Due to major clinical demands, it is necessary to find an optimally safe and efficient way for large‐scale expansion of these cells. Considering the nutritional source in the culture medium and method, this study aimed to analyze the effects of FBS‐ and PL‐supplemented media on osteogenesis in stem cell mono‐ and co‐cultures with human umbilical vein endothelial cells (HUVECs). Results showed that cell metabolic activity and proliferation increased in PL‐ compared to FBS‐supplemented media in mono‐ and co‐cultures for both BM‐MSCs and AT‐MSCs. In addition, calcium deposition was cell type dependent and decreased for BM‐MSCs but increased for AT‐MSCs in PL‐supplemented medium in both mono‐ and co‐cultures. Based on the effects of co‐cultures, BM‐MSCs/HUVECs enhanced osteogenesis compared to BM‐MSCs monocultures in both FBS‐ and PL‐supplemented media whereas AT‐MSCs/HUVECs showed similar results compared to AT‐MSCs monocultures. Copyright © 2013 John Wiley & Sons, Ltd.     

Cartilage graft engineering by co‐culturing primary human articular chondrocytes with human bone marrow stromal cells

Co‐culture of mesenchymal stromal cells (MSCs) with articular chondrocytes (ACs) has been reported to improve the efficiency of utilization of a small number of ACs for the engineering of implantable cartilaginous tissues. However, the use of cells of animal origin and the generation of small‐scale micromass tissues limit the clinical relevance of previous studies. Here we investigated the in vitro and in vivo chondrogenic capacities of scaffold‐based constructs generated by combining primary human ACs with human bone marrow MSCs (BM‐MSCs). The two cell types were cultured in collagen sponges (2 × 6 mm disks) at the BM‐MSCs:ACs ratios: 100:0, 95:5, 75:25 and 0:100 for 3 weeks. Scaffolds freshly seeded or further precultured in vitro for 2 weeks were also implanted subcutaneously in nude mice and harvested after 8 or 6 weeks, respectively. Static co‐culture of ACs (25%) with BM‐MSCs (75%) in scaffolds resulted in up to 1.4‐fold higher glycosaminoglycan (GAG) content than what would be expected based on the relative percentages of the different cell types. In vivo GAG induction was drastically enhanced by the in vitro preculture and maximal at the ratio 95:5 (3.8‐fold higher). Immunostaining analyses revealed enhanced accumulation of type II collagen and reduced accumulation of type X collagen with increasing ACs percentage. Constructs generated in the perfusion bioreactor system were homogeneously cellularized. In summary, human cartilage grafts were successfully generated, culturing BM‐MSCs with a relatively low fraction of non‐expanded ACs in porous scaffolds. The proposed co‐culture strategy is directly relevant towards a single‐stage surgical procedure for cartilage repair. Copyright © 2012 John Wiley & Sons, Ltd.     

In vitro generation of whole osteochondral constructs using rabbit bone marrow stromal cells,employing a two‐chambered co‐culture well design

The regeneration of whole osteochondral constructs with a physiological structure has been a significant issue, both clinically and academically. In this study, we present a method using rabbit bone marrow stromal cells (BMSCs) cultured on a silk–RADA peptide scaffold in a specially designed two‐chambered co‐culture well for the generation of multilayered osteochondral constructs in vitro. This specially designed two‐chambered well can simultaneously provide osteogenic and chondrogenic stimulation to cells located in different regions of the scaffold. We demonstrated that this co‐culture approach could successfully provide specific chemical stimulation to BMSCs located on different layers within a single scaffold, resulting in the formation of multilayered osteochondral constructs containing cartilage‐like and subchondral bone‐like tissue, as well as the intermediate osteochondral interface. The cells in the intermediate region were found to be hypertrophic chondrocytes, embedded in a calcified extracellular matrix containing glycosaminoglycans and collagen types I, II and X. In conclusion, this study provides a single‐step approach that highlights the feasibility of rabbit BMSCs as a single‐cell source for multilayered osteochondral construct generation in vitro. Copyright © 2013 John Wiley & Sons, Ltd.     

Bone marrow stromal and Schwann cells from adult rats can interact synergistically to aid in peripheral nerve repair even without intercellular contact in vitro

To better understand the use of Schwann cells (SCs) and bone marrow stromal cells (BMSCs) together for nerve repair, we studied whether interactions between these two cell types by diffusible molecules can enhance their utility. In the present study, a co‐culture system was established to allow BMSCs and SCs grow in the same culture medium but without physical contact. Before co‐culture, the adult SCs were expanded until confluent. The adult BMSCs were cultured until P10 with CD29 and CD44 positive but CD45 negative. After 4 days in culture, > 80% of the BMSCs in the co‐culture system showed both GFAP‐ and S‐100‐positive, but < 6% of the BMSCs in control culture system showed both GFAP‐ and S‐100‐positive. Meanwhile, 68.76% of the SCs in co‐culture system showed S‐100‐positive, which was > 42.03% of the SCs in control culture system. Furthermore, the in vivo study also confirmed that differentiated BMSCs exert a more beneficial effect on repairing injured sciatic nerve function and axonal regeneration than undifferentiated BMSCs. These results indicate that the two most widely used cell types for promoting peripheral nerve regeneration may interact synergistically to aid their roles in peripheral nerve repair. Copyright © 2011 John Wiley & Sons, Ltd.     

In vitro generation of a multilayered osteochondral construct with an osteochondral interface using rabbit bone marrow stromal cells and a silk peptide‐based scaffold

Tissue engineering of a biological osteochondral multilayered construct with a cartilage‐interface subchondral bone layer is a key challenge. This study presented a rabbit bone marrow stromal cell (BMSC)/silk fibroin scaffold‐based co‐culture approach to generate tissue‐engineered osteochondral grafts with an interface. BMSC‐seeded scaffolds were first cultured separately in osteogenic and chondrogenic stimulation media. The two differentiated pieces were then combined using an RADA self‐assembling peptide and subsequently co‐cultured. Gene expression, histological and biochemical analyses were used to evaluate the multilayered structure of the osteochondral graft. A complete osteochondral construct with a cartilage‐subchondral bone interface was regenerated and BMSCs were used as the only cell source for the osteochondral construct and interface regeneration. Furthermore, in the intermediate region of co‐cultured samples, hypertrophic chondrogenic gene markers type X collagen and MMP‐13 were found on both chondrogenic and osteogenic section edges after co‐culture. However, significant differences gene expression profile were found in distinct zones of the construct during co‐culture and the section in the intermediate region had significantly higher hypertrophic chondrocyte gene expression. Biochemical analyses and histology results further supported this observation. This study showed that specific stimulation from osteogenic and chondrogenic BMSCs affected each other in this co‐culture system and induced the formation of an osteochondral interface. Moreover, this system provided a possible approach for generating multilayered osteochondral constructs. Copyright © 2013 John Wiley & Sons, Ltd.     

Chondrogenic potential of injectable κ‐carrageenan hydrogel with encapsulated adipose stem cells for cartilage tissue‐engineering applications

Due to the limited self‐repair capacity of cartilage, regenerative medicine therapies for the treatment of cartilage defects must use a significant amount of cells, preferably applied using a hydrogel system that can promise their delivery and functionality at the specific site. This paper discusses the potential use of κ‐carrageenan hydrogels for the delivery of stem cells obtained from adipose tissue in the treatment of cartilage tissue defects. The developed hydrogels were produced by an ionotropic gelation method and human adipose stem cells (hASCs) were encapsulated in 1.5% w/v κ‐carrageenan solution at a cell density of 5 × 10⁶ cells/ml. The results from the analysis of the cell‐encapsulating hydrogels, cultured for up to 21 days, indicated that κ‐carrageenan hydrogels support the viability, proliferation and chondrogenic differentiation of hASCs. Additionally, the mechanical analysis demonstrated an increase in stiffness and viscoelastic properties of κ‐carrageenan gels with their encapsulated cells with increasing time in culture with chondrogenic medium. These results allowed the conclusion that κ‐carrageenan exhibits properties that enable the in vitro functionality of encapsulated hASCs and thus may provide the basis for new successful approaches for the treatment of cartilage defects. Copyright © 2013 John Wiley & Sons, Ltd.     

Co‐culture of adipose‐derived stem cells and endothelial cells in fibrin induces angiogenesis and vasculogenesis in a chorioallantoic membrane model

Neovascularization of adipose tissue equivalents is a crucial step in successful adipose tissue engineering, since insufficient vascularization results in graft resorption in an in vivo situation. A possible cellular approach to overcome this limitation is the co‐implantation of adipose‐derived stem cells (ASCs) with endothelial cells to stimulate the formation of a vascular network. We investigated the potential of ASCs derived from human abdominal fat tissue co‐cultured with endothelial progenitor cells (EPCs) from human peripheral blood to stimulate neovascularization of fibrin constructs on the chorioallantoic membrane (CAM) of fertilized chicken eggs, in direct comparison to human umbilical vein endothelial cells (HUVECs). After 9 days of incubation, cell–fibrin constructs were explanted and histologically evaluated with respect to ingrowth of avian blood vessels into the construct and formation of human blood vessels by co‐implanted endothelial cells. When administered on the CAM, ASCs successfully guided host vasculature into the construct (angiogenesis) and guided formation of capillary‐like structures by co‐implanted human endothelial cells (vasculogenesis), with HUVECs being superior to EPCs, leading to a perfused avian and human capillary network within the fibrin construct. However, the results also showed that perfused human blood vessels were only observed near the CAM compared to unperfused capillary‐like structures near the top of the construct, indicating that perfusion of the cell–fibrin construct takes longer than 9 days. In conclusion, as blood vessel formation is an essential step during adipogenic differentiation, the data support our hypothesis that cellular communication between transplanted ASCs and endothelial cells is beneficial for vasculogenesis. Copyright © 2013 John Wiley & Sons, Ltd.     

Engineering zonal cartilaginous tissue by modulating oxygen levels and mechanical cues through the depth of infrapatellar fat pad stem cell laden hydrogels

Engineering tissues with a structure and spatial composition mimicking those of native articular cartilage (AC) remains a challenge. This study examined if infrapatellar fat pad‐derived stem cells (FPSCs) can be used to engineer cartilage grafts with a bulk composition and a spatial distribution of matrix similar to the native tissue. In an attempt to mimic the oxygen gradients and mechanical environment within AC, FPSC‐laden hydrogels (either 2 mm or 4 mm in height) were confined to half of their thickness and/or subjected to dynamic compression (DC). Confining FPSC‐laden hydrogels was predicted to accentuate the gradient in oxygen tension through the depth of the constructs (higher in the top and lower in the bottom), leading to enhanced glycosaminoglycan (GAG) and collagen synthesis in 2 mm high tissues. When subjected to DC alone, both GAG and collagen accumulation increased within 2 mm high unconfined constructs. Furthermore, the dynamic modulus of constructs increased from 0.96 MPa to 1.45 MPa following the application of DC. There was no synergistic benefit of coupling confinement and DC on overall levels of matrix accumulation; however in all constructs, irrespective of their height, the combination of these boundary conditions led to the development of engineered tissues that spatially best resembled native AC. The superficial region of these constructs mimicked that of native tissue, staining weakly for GAG, strongly for type II collagen, and in 4 mm high tissues more intensely for proteoglycan 4 (lubricin). This study demonstrated that FPSCs respond to joint‐like environmental conditions by producing cartilage tissues mimicking native AC. Copyright © 2016 John Wiley & Sons, Ltd.     

Multilineage co‐culture of adipose‐derived stem cells for tissue engineering

Stem cell interactions through paracrine cell signalling can regulate a range of cell responses, including metabolic activity, proliferation and differentiation. Moving towards the development of optimized tissue‐engineering strategies with adipose‐derived stem cells (ASCs), the focus of this study was on developing indirect co‐culture models to study the effects of mature adipocytes, chondrocytes and osteoblasts on bovine ASC multilineage differentiation. For each lineage, ASC differentiation was characterized by histology, gene expression and protein expression, in the absence of key inductive differentiation factors for the ASCs. Co‐culture with each of the mature cell populations was shown to successfully induce or enhance lineage‐specific differentiation of the ASCs. In general, a more homogeneous but lower‐level differentiation response was observed in co‐culture as compared to stimulating the bovine ASCs with inductive differentiation media. To explore the role of the Wnt canonical and non‐canonical signalling pathways within the model systems, the effects of the Wnt inhibitors WIF‐1 and DKK‐1 on multilineage differentiation in co‐culture were assessed. The data indicated that Wnt signalling may play a role in mediating ASC differentiation in co‐culture with the mature cell populations. Copyright © 2012 John Wiley & Sons, Ltd.