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.     

Ectopic bone formation by aggregated mesenchymal stem cells from bone marrow and adipose tissue: A comparative study

Tissue engineered constructs (TECs) based on spheroids of bone marrow mesenchymal stromal cells (BM‐MSCs) combined with calcium phosphate microparticles and enveloped in a platelet‐rich plasma hydrogel showed that aggregation of MSCs improves their ectopic bone formation potential. The stromal vascular fraction (SVF) and adipose‐derived MSCs (ASCs) have been recognized as an interesting MSC source for bone tissue engineering, but their ectopic bone formation is limited. We investigated whether aggregation of ASCs could similarly improve ectopic bone formation by ASCs and SVF cells. The formation of aggregates with BM‐MSCs, ASCs and SVF cells was carried out and gene expression was analysed for osteogenic, chondrogenic and vasculogenic genes in vitro. Ectopic bone formation was evaluated after implantation of TECs in immunodeficient mice with six conditions: TECs with ASCs, TECs with BM‐MSC, TECs with SVF cells (with and without rhBMP2), no cells and no cells with rhBMP2. BM‐MSCs showed consistent compact spheroid formation, ASCs to a lesser extent and SVF showed poor spheroid formation. Aggregation of ASCs induced a significant upregulation of the expression of osteogenic markers like alkaline phosphatase and collagen type I, as compared with un‐aggregated ASCs. In vivo, ASC and SVF cells both generated ectopic bone in the absence of added morphogenetic proteins. The highest incidence of bone formation was seen with BM‐MSCs (7/9) followed by SVF + rhBMP2 (4/9) and no cells + rhBMP2 (2/9). Aggregation can improve ectopic bone tissue formation by adipose‐derived cells, but is less efficient than rhBMP2. A combination of both factors should now be tested to investigate an additive effect.     

Liver extracellular matrix promotes BM‐MSCs hepatic differentiation and reversal of liver fibrosis through activation of integrin pathway

In cell‐based therapies for liver injuries, the clinical outcomes are closely related to the surrounding microenvironment of the transplanted bone marrow mesenchymal stem cells (BM‐MSCs). However, whether liver‐specific ECM (L‐ECM), as one of major microenvironment signals, could regulate the therapeutic effect of BM‐MSCs through changing their biological characteristics is unclear. This study aimed to investigate the hepatogenicity and underlying mechanism of L‐ECM as well as its potential regulative role in the MSC‐based liver recovery. L‐ECM was prepared by homogenization of decellularized whole porcine liver. After three‐dimensional culture with or without the presence of L‐ECM, BM‐MSCs expressed hepatocyte‐specific genes and proteins in an L‐ECM concentration‐dependent manner. Further analysis showed that L‐ECM could activate specific types of integrins (ITGs) as well as their downstream signalling pathways. When the cell/ECM interaction was enhanced by incorporating BM‐MSCs with Mn²⁺, ITGs were activated and the hepatogenic capacity of L‐ECM was improved. The regeneration of rat livers from either acute or chronic fibrosis could also be accelerated after transplantation of Mn²⁺‐treated BM‐MSCs. L‐ECM therefore promotes hepatic differentiation of BM‐MSCs via the ITG pathway and plays a therapeutically beneficial role for stem cell‐based liver regeneration. Copyright © 2016 John Wiley & Sons, Ltd.     

Effect of donor variation on osteogenesis and vasculogenesis in hydrogel cocultures

To introduce a functional vascular network into tissue‐engineered bone equivalents, human endothelial colony forming cells (ECFCs) and multipotent mesenchymal stromal cells (MSCs) can be cocultured. Here, we studied the impact of donor variation of human bone marrow‐derived MSCs and cord blood‐derived ECFCs on vasculogenesis and osteogenesis using a 3D in vitro coculture model. Further, to make the step towards cocultures consisting of cells derived from a single donor, we tested how induced pluripotent stem cell (iPSC)‐derived human endothelial cells (iECs) performed in coculture models. Cocultures with varying combinations of human donors of MSCs, ECFCs, or iECs were prepared in Matrigel. The constructs were cultured in an osteogenic differentiation medium. Following a 10‐day culture period, the length of the prevascular structures and osteogenic differentiation were evaluated for up to 21 days of culture. The particular combination of MSC and ECFC donors influenced the vasculogenic properties significantly and induced variation in osteogenic potential. In addition, the use of iECs in the cocultures resulted in prevascular structure formation in osteogenically differentiated constructs. Together, these results showed that close attention to the source of primary cells, such as ECFCs and MSCs, is critical to address variability in vasculogenic and osteogenic potential. The 3D coculture model appeared to successfully generate prevascularized constructs and were sufficient in exceeding the ~200 μm diffusion limit. In addition, iPSC‐derived cell lineages may decrease variability by providing a larger and potentially more uniform source of cells for future preclinical and clinical applications.     

Angiogenic potential of human mesenchymal stromal cell and circulating mononuclear cell cocultures is reflected in the expression profiles of proangiogenic factors leading to endothelial cell and pericyte differentiation

Endothelial progenitors found among the peripheral blood (PB) mononuclear cells (MNCs) are interesting cells for their angiogenic properties. Mesenchymal stromal cells (MSCs) in turn can produce proangiogenic factors as well as differentiate into mural pericytes, making MSCs and MNCs an attractive coculture setup for regenerative medicine. In this study, human bone marrow‐derived MSCs and PB‐derived MNCs were cocultured in basal or osteoblastic medium without exogenously supplied growth factors to demonstrate endothelial cell, pericyte and osteoblastic differentiation. The expression levels of various proangiogenic factors, as well as endothelial cell, pericyte and osteoblast markers in cocultures were determined by quantitative polymerase chain reaction. Immunocytochemistry for vascular endothelial growth factor receptor‐1 and α‐smooth muscle actin as well as staining for alkaline phosphatase were performed after 10 and 14 days. Messenger ribonucleic acid expression of endothelial cell markers was highly upregulated in both basal and osteoblastic conditions after 5 days of coculture, indicating an endothelial cell differentiation, which was supported by immunocytochemistry for vascular endothelial growth factor receptor‐1. Stromal derived factor‐1 and vascular endothelial growth factor were highly expressed in MSC‐MNC coculture in basal medium but not in osteoblastic medium. On the contrary, the expression levels of bone morphogenetic protein‐2 and angiopoietin‐1 were significantly higher in osteoblastic medium. Pericyte markers were highly expressed in both cocultures after 5 days. In conclusion, it was demonstrated endothelial cell and pericyte differentiation in MSC‐MNC cocultures both in basal and osteoblastic medium indicating a potential for neovascularization for tissue engineering applications.     

Electrical stimulation of adipose‐derived mesenchymal stem cells and endothelial cells co‐cultured in a conductive scaffold for potential orthopaedic applications

Electrical stimulation (ES) has emerged as a useful tool to regulate cell behaviour, but the effect of ES on mesenchymal stem cell (MSC)/vasculogenic cell co‐culture has not been investigated. Herein, human adipose‐derived MSCs (AD‐MSCs) and umbilical vein endothelial cells (HUVECs) were co‐cultured in an electrically conductive polypyrrole/chitosan scaffold. Compared with AD‐MSC monoculture, calcium deposition in the co‐culture without and with ES (200 μA for 4 h/day) was 139% and 346% higher, respectively, after 7 days. As the application of ES to AD‐MSC monoculture only increased calcium deposition by 56% compared with that without ES after 7 days, these results indicate that ES and co‐culture with HUVECs have synergistic effects on AD‐MSCs' osteogenic differentiation. ES application also significantly enhanced CD31 expression of HUVECs. In HUVEC monoculture, application of ES increased CD31 expression by 224%, whereas the corresponding increase in AD‐MSC/HUVEC co‐culture with ES application was 62%. The gene expression results indicate that ES enhanced the cellular functions in AD‐MSC and HUVEC monoculture via autocrine bone morphogenetic protein‐2 (BMP‐2) and vascular endothelial growth factor (VEGF), respectively. In co‐culture, crosstalk between AD‐MSCs and HUVECs due to paracrine BMP‐2 and VEGF enhanced the cellular functions compared with the respective monoculture. With application of ES to the AD‐MSC/HUVEC co‐culture, autocrine signalling was enhanced, resulting in further promotion of cellular functions. These findings illustrate that co‐culturing AD‐MSC/HUVEC in a conductive scaffold with ES offers potential benefits for bone defect therapy.     

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.     

The effect of ex vivo dynamic loading on the osteogenic differentiation of genetically engineered mesenchymal stem cell model

Mechanical loading has been described as a highly important stimulus for improvements in the quality and strength of bone. It has also been shown that mechanical stimuli can induce the differentiation of mesenchymal stem cells (MSCs) along the osteogenic lineage. We have previously demonstrated the potent osteogenic effect of MSCs engineered to overexpress the BMP2 gene. In this study we investigated the effect of mechanical loading on BMP2‐expressing MSC‐like cells, using a special bioreactor designed to apply dynamic forces on cell‐seeded hydrogels. Cell viability, alkaline phosphatase (ALP) activity, BMP2 secretion and mineralized substance formation in the hydrogels were quantified. We found that cell metabolism increased as high as 6.8‐fold, ALP activity by 12.5‐fold, BMP2 secretion by 182‐fold and mineralized tissue formation by 1.72‐fold in hydrogels containing MSC‐like cells expressing BMP2, which were cultured in the presence of mechanical loading. We have shown that ex vivo mechanical loading had an additive effect on BMP2‐induced osteogenesis in genetically engineered MSC‐like cells. These data could be valuable for bone tissue‐engineering strategies of the future. Copyright © 2010 John Wiley & Sons, Ltd.     

Angiogenic and osteogenic regeneration in rats via calcium phosphate scaffold and endothelial cell co‐culture with human bone marrow mesenchymal stem cells (MSCs), human umbilical cord MSCs,human induced pluripotent stem cell‐derived MSCs and human embryonic stem cell‐derived MSCs

Angiogenesis is a limiting factor in regenerating large bone defects. The objective of this study was to investigate angiogenic and osteogenic effects of co‐culture on calcium phosphate cement (CPC) scaffold using human umbilical vein endothelial cells (hUVECs) and mesenchymal stem cells (MSCs) from different origins for the first time. hUVECs were co‐cultured with four types of cell: human umbilical cord MSCs (hUCMSCs), human bone marrow MSCs (hBMSCs) and MSCs from induced pluripotent stem cells (hiPSC‐MSCs) and embryonic stem cells (hESC‐MSCs). Constructs were implanted in 8 mm cranial defects of rats for 12 weeks. CPC without cells served as control 1. CPC with hBMSCs served as control 2. Microcapillary‐like structures were successfully formed on CPC in vitro in all four co‐cultured groups. Microcapillary lengths increased with time (p < 0.05). Osteogenic and angiogenic gene expressions were highly elevated and mineralization by co‐cultured cells increased with time (p < 0.05). New bone amount and blood vessel density of co‐cultured groups were much greater than controls (p < 0.05) in an animal study. hUVECs co‐cultured with hUCMSCs, hiPSC‐MSCs and hESC‐MSCs achieved new bone and vessel density similar to hUVECs co‐cultured with hBMSCs (p > 0.1). Therefore, hUCMSCs, hiPSC‐MSCs and hESC‐MSCs could serve as alternative cell sources to hBMSCs, which require an invasive procedure to harvest. In conclusion, this study showed for the first time that co‐cultures of hUVECs with hUCMSCs, hiPSC‐MSCs, hESC‐MSCs and hBMSCs delivered via CPC scaffold achieved excellent osteogenic and angiogenic capabilities in vivo. The novel co‐culture constructs are promising for bone reconstruction with improved angiogenesis for craniofacial/orthopaedic applications. Copyright © 2017 John Wiley & Sons, Ltd.     

Platelet‐rich plasma counteracts detrimental effect of high‐glucose concentrations on mesenchymal stem cells from Bichat fat pad

Diabetic patients display increased risk of periodontitis and failure in bone augmentation procedures. Mesenchymal stem cells (MSCs) and platelet‐rich plasma (PRP) represent a relevant advantage in tissue repair process and regenerative medicine. We isolated MSCs from Bichat's buccal fat pad (BFP) and measured the effects of glucose and PRP on cell number and osteogenic differentiation potential. Cells were cultured in the presence of 5.5‐mM glucose (low glucose [LG]) or 25‐mM glucose (high glucose [HG]). BFP–MSC number was significantly lower when cells were cultured in HG compared with those in LG. Following osteogenic differentiation procedures, calcium accumulation, alkaline phosphatase activity, and expression of osteogenic markers were significantly lower in HG compared with LG. Exposure of BFP–MSC to PRP significantly increased cell number and osteogenic differentiation potential, reaching comparable levels in LG and in HG. Thus, high‐glucose concentrations impair BFP–MSC growth and osteogenic differentiation. However, these detrimental effects are largely counteracted by PRP.     

Synthesis and secretome release by human bone marrow mesenchymal stem cell spheroids within three‐dimensional collagen hydrogels: Integrating experiments and modelling

Myocardial infarction results in loss of cardiac cell types, inflammation, extracellular matrix (ECM) degradation, and fibrotic scar. Transplantation of bone marrow‐derived mesenchymal stem cells (BM‐MSCs) is being explored as they could differentiate into cardiomyocyte‐like cells, integrate into host tissue, and enhance resident cell activity. The ability of these cells to restore lost ECM, remodel the inflammatory scar tissue, and repair the injured myocardium remains unexplored. We here elucidated the synthesis and deposition of ECM (e.g., elastin, sulfated glycosaminoglycans, hyaluronan, collagen type III, laminin, fibrillin, lysyl oxidase, and nitric oxide synthases), matrix metalloproteinases (MMPs) and their inhibitors (TIMPs), and other secretome (cytokines, chemokines, and growth factors) in adult human BM‐MSC spheroid cultures within three‐dimensional collagen gels. The roles of species‐specific type I collagen and 5‐azacytadine were assessed over a 28‐day period. Results revealed that human collagen (but not rat‐derived) suppressed MSC proliferation and survival, and MSCs synthesized and released a variety of ECM proteins and secretome over the 28 days. Matrix deposition is at least an order of magnitude lower than their release levels at every time point, most possibly due to elevated MMP levels and interleukins with a concomitant decrease in TIMPs. Matrix synthesis over the 28‐day period was fitted to a competitive inhibition form of Michaelis–Menten kinetics, and the production and decay rates of ECM, MMPs, and TIMPs, along with the kinetic model parameters quantified. Such an integrated experimental and modelling approach would help elucidate the critical roles of various parameters (e.g., cell encapsulation and delivery vehicles) in stem cell‐based transplantation therapies.     

Dynamic cell–cell interactions between cord blood haematopoietic progenitors and the cellular niche are essential for the expansion of CD34+, CD34+CD38− and early lymphoid CD7+ cells

Most clinical applications of haematopoietic stem/progenitor cells (HSCs) would benefit from their ex vivo expansion to obtain a therapeutically significant amount of cells from the available donor samples. We studied the impact of cellular interactions between umbilical cord blood (UCB) haematopoietic cells and bone marrow (BM)‐derived mesenchymal stem cells (MSCs) on the ex vivo expansion and differentiative potential of UCB CD34⁺‐enriched cells. UCB cells were cultured: (a) directly in contact with BM MSC‐derived stromal layers (contact); (b) separated by a microporous membrane (non‐contact); or (c) without stroma (no stroma). Highly dynamic culture events occurred in HSC‐MSC co‐cultures, involving cell–cell interactions, which preceded HSC expansion. Throughout the time in culture [18 days], total cell expansion was significantly higher in contact (fold increase of 280 ± 37 at day 18) compared to non‐contact (85 ± 25). No significant cell expansion was observed in stroma‐free cultures. CD34⁺ cell expansion was also clearly favoured by direct contact with BM MSCs (35 ± 5‐ and 7 ± 3‐fold increases at day 18 for contact and non‐contact, respectively). Moreover, a higher percentage of CD34⁺CD38^? cells was consistently maintained during the time in culture under contact (8.1 ± 1.9% at day 18) compared to non‐contact (5.7 ± 1.6%). Importantly, direct cell interaction with BM MSCs significantly enhanced the expansion of early lymphoid CD7⁺ cells, yielding considerably higher (×3–10) progenitor numbers compared to non‐contact conditions. These results highlight the importance of dynamic cell–cell interactions between UCB HSCs and BM MSCs, towards the maximization of HSC expansion ex vivo to obtain clinically relevant cell numbers for multiple settings, such as BM transplantation or somatic cell gene therapy. Copyright © 2009 John Wiley & Sons, Ltd.     

Three‐dimensional printed polycaprolactone‐based scaffolds provide an advantageous environment for osteogenic differentiation of human adipose‐derived stem cells

The capacity of bone grafts to repair critical size defects can be greatly enhanced by the delivery of mesenchymal stem cells (MSCs). Adipose tissue is considered the most effective source of MSCs (ADSCs); however, the efficiency of bone regeneration using undifferentiated ADSCs is low. Therefore, this study proposes scaffolds based on polycaprolactone (PCL), which is widely considered a suitable MSC delivery system, were used as a three‐dimensional (3D) culture environment promoting osteogenic differentiation of ADSCs. PCL scaffolds enriched with 5% tricalcium phosphate (TCP) were used. Human ADSCs were cultured in osteogenic medium both on the scaffolds and in 2D culture. Cell viability and osteogenic differentiation were tested at various time points for 42 days. The expression of RUNX2, collagen I, alkaline phosphatase, osteonectin and osteocalcin, measured by real‐time polymerase chain reaction was significantly upregulated in 3D culture. Production of osteocalcin, a specific marker of terminally differentiated osteoblasts, was significantly higher in 3D cultures than in 2D cultures, as confirmed by western blot and immunostaining, and accompanied by earlier and enhanced mineralization. Subcutaneous implantation into immunodeficient mice was used for in vivo observations. Immunohistological and micro‐computed tomography analysis revealed ADSC survival and activity toward extracellular production after 4 and 12 weeks, although heterotopic osteogenesis was not confirmed – probably resulting from insufficient availability of Ca/P ions. Additionally, TCP did not contribute to the upregulation of differentiation on the scaffolds in culture, and we postulate that the 3D architecture is a critical factor and provides a useful environment for prior‐to‐implantation osteogenic differentiation of ADSCs. Copyright © 2016 John Wiley & Sons, Ltd.     

Scaffold‐free cell sheet injection results in bone formation

We previously reported a new cell transplantation method in which mesenchymal stem cells (MSCs) were cultured as cell sheets. The cultured MSC sheets showed high alkaline phosphatase (ALP) activities and osteocalcin (OC) contents. In the present study, we transplanted such sheets by injection to assess whether the injectable MSC sheets could form bone tissue at subcutaneous sites. At 4 weeks after the subcutaneous injection, the injected areas showed hard mass formation. Each mass consisted of newly formed bone, as evaluated by radiographic, histological and gene expression analyses as well as three‐dimensional computed tomography (3D‐CT). Histological analyses revealed extracellular bone matrix together with osteocytes and active osteoblasts. Real‐time PCR analyses showed high ALP and OC mRNA expressions. We also injected the cell sheets into dead bone to determine whether the lost osteogenic potential could be rescued, and histological analyses revealed that the injected cell sheets supplied osteogenic potential to the dead bone. The present study clearly indicates that osteogenic MSC sheets can be transplanted via injection through a needle and that bone formation results in the injected areas. Owing to its usage of a needle for fabrication of in vivo bone tissue, this injection method can be applied as a minimally invasive approach for hard tissue reconstruction. Copyright © 2010 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.     

Mesenchymal stromal cells improve the osteogenic capabilities of mineralized agarose gels in a rat full‐thickness cranial defect model

The authors previously created HAp or CaCO₃ formed on or in agarose gels (HAp and CaCO₃ gels, respectively) as biocompatible and biodegradable bone graft materials. However, these gels have limitations for bone regeneration. Mesenchymal stromal cells (MSCs) have osteogenic potential and are considered useful for bone tissue engineering. The purpose of this study was to clarify the osteogenic abilities of MSCs loaded in HAp or CaCO₃ gels (MSC/HAp and MSC/CaCO₃ gels, respectively) using a rat cranial defect model compared to HAp and CaCO₃ gels alone. HAp, CaCO₃, MSC/Hap, and MSC/CaCO₃ gels were prepared for in vivo analyses and implanted into full‐thickness bone defects created in the rat cranium. All samples were assessed radiologically and histologically at 4 and 8 weeks after implantation. Using microfocus‐computed tomography, an increase in bone formation was observed in the MSC‐loaded gels compared to the gels alone. In addition, peripheral quantitative computed tomography revealed higher bone mineral contents in the MSC‐loaded gels compared to the gels alone. After transmission X‐ray diffraction analyses, the degree of apatite c‐axis orientation as a bone quality index of newly formed bone in the MSC‐loaded gels was close to that of living cranial bone. Histologically, more extensive bone formation was detected in the MSC‐loaded gels compared to gels alone. Overall, MSC/HAp and MSC/CaCO₃ gels showed equivalent efficacy for bone regeneration. These findings demonstrate that loading of MSCs into the gels strengthened their osteogenic ability and improved the quality of the newly formed bone. As a result, MSC‐loaded gels could represent viable therapeutic biomaterials for bone tissue engineering. Copyright © 2012 John Wiley & Sons, Ltd.