Biomimetic three-dimensional cultures significantly increase hematopoietic differentiation efficacy of embryonic stem cells

Stem cell-based tissue engineering is a promising technology in the effort to create functional tissues of choice. To establish an efficient approach for generating hematopoietic cell lineages directly from embryonic stem (ES) cells and to study the effects of three-dimensional (3D) biomaterials on ES cell differentiation, we cultured mouse ES cells on 3D, highly porous, biomimetic scaffolds. Cell differentiation was evaluated by microscopy and flow cytometry analysis with a variety of hematopoiesis- specific markers. Our data indicate that ES cells differentiated on porous 3D scaffold structures developed embryoid bodies (EBs) similar to those in traditional two-dimensional (2D) cultures; however, unlike 2D differentiation, these EBs integrated with the scaffold and appeared embedded in a network of extracellular matrix. Most significantly, the efficiency of hematopoietic precursor cell (HPC) generation on 3D, as indicated by the expression of various HPC-specific surface markers (CD34, Sca-1, Flk-1, and c-Kit) and colony-forming cell (CFC) assays, was reproducibly increased (about 2-fold) over their 2D counterparts. Comparison of static and dynamic 3D cultures demonstrated that spinner flask technology also contributed to the higher hematopoietic differentiation efficiency of ES cells seeded on scaffolds. Continued differentiation of 3D-derived HPCs into the myeloid lineage demonstrated increased efficiency (2-fold) of generating myeloid compared with differentiation from 2D-derived HPCs.     

Biological characterisation of vascular grafts cultured in a bioreactor

In this study, the development is described of a tissue-engineered construct mimicking the structure of a natural blood vessel. Smooth muscle cells (SMC) were cultured under pulsatile flow conditions in porous tubular scaffolds composed of crosslinked type I insoluble collagen and insoluble elastin. Under these dynamic culture conditions, average wall shear rate, systolic and diastolic pressures and pressure wave-forms comparable to conditions in the human carotid artery were obtained. Culturing of SMC in tubular scaffolds under dynamic conditions resulted in enhanced tissue formation compared to static conditions. Higher SMC numbers, a more homogeneous distribution of SMC throughout the scaffolds and higher collagen mRNA expression levels were found when cells were cultured under dynamic compared to static conditions. mRNA expression levels of markers of proliferation and apoptosis showed that the higher cell numbers in the scaffolds cultured under dynamic conditions can be explained by increased cell proliferation but not by decreased apoptosis. Glucose consumption and lactate formation by the cells showed that cell metabolism was more aerobic under dynamic compared to static conditions. Lining of the dynamically cultured constructs with a luminal monolayer of endothelial cells might result in vessels suitable for in vivo applications.     

Study of osteoblastic cells in a microfluidic environment

Bone tissue engineering consists of culturing osteoblastic cells onto synthetic three-dimensional (3D) porous scaffolds. The organization of bone cells into 3D scaffolds is crucial for ex vivo tissue formation. Diffusional rates of nutrients could be greatly improved by perfusing media through the 3D microporous scaffolds. However, bone cells cultured in vitro are responsive to a variety of different mechanical signals including fluid flow and shear stresses. In this work, we attempt to study osteoblastic cells behaviour cultured within microdevices allowing continuous and homogenous feeding of cells. We have fabricated polydimethylsiloxane PDMS microdevices with a 3D microstructured channel network. Mouse calvarial osteoblastic cells MC3T3-E1 were seeded at 2x10(6)cells/ml and cultured into the microdevices under flow rates of 0, 5, 35 microl/min. Cells attached and proliferated well in the designed microdevices. Cell viability was found around 85% up to 1 to 2 weeks for shear stress value under 5 mPa. The alkaline phosphatase (ALP) activity was enhanced 3- and 7.5-fold inside the microdevices under static and dynamic flow of 5 microl/min as compared to flat static cultures in PDMS coated Petri dishes. Therefore, osteoblastic cells could be successfully cultured inside the microdevices under dynamic conditions and their ALP activity was enhanced. These results are promising for bone cell growth and differentiation as well as future tissue regeneration using larger 3D microfluidic microdevices.     

Effect of flow perfusion on the osteogenic differentiation of bone marrow stromal cells cultured on starch-based three-dimensional scaffolds

This study aims to investigate the effect of culturing conditions (static and flow perfusion) on the proliferation and osteogenic differentiation of rat bone marrow stromal cells seeded on two novel scaffolds exhibiting distinct porous structures. Specifically, scaffolds based on SEVA-C (a blend of starch with ethylene vinyl alcohol) and SPCL (a blend of starch with polycaprolactone) were examined in static and flow perfusion culture. SEVA-C scaffolds were formed using an extrusion process, whereas SPCL scaffolds were obtained by a fiber bonding process. For this purpose, these scaffolds were seeded with marrow stromal cells harvested from femoras and tibias of Wistar rats and cultured in a flow perfusion bioreactor and in 6-well plates for 3, 7, and 15 days. The proliferation and alkaline phosphatase activity patterns were similar for both types of scaffolds and for both culture conditions. However, calcium content analysis revealed a significant enhancement of calcium deposition on both scaffold types cultured under flow perfusion. This observation was confirmed by Von Kossa-stained sections and tetracycline fluorescence. Histological analysis and confocal images of the cultured scaffolds showed a much better distribution of cells within the SPCL scaffolds than the SEVA-C scaffolds, which had limited pore interconnectivity, under flow perfusion conditions. In the scaffolds cultured under static conditions, only a surface layer of cells was observed. These results suggest that flow perfusion culture enhances the osteogenic differentiation of marrow stromal cells and improves their distribution in three-dimensional, starch-based scaffolds. They also indicate that scaffold architecture and especially pore interconnectivity affect the homogeneity of the formed tissue.     

Enhancement of viability of muscle precursor cells on 3D scaffold in a perfusion bioreactor

The aim of this study was to develop a methodology for the in vitro expansion of skeletal-muscle precursor cells (SMPC) in a three-dimensional (3D) environment in order to fabricate a cellularized artificial graft characterized by high density of viable cells and uniform cell distribution over the entire 3D domain. Cell seeding and culture within 3D porous scaffolds by conventional static techniques can lead to a uniform cell distribution only on the scaffold surface, whereas dynamic culture systems have the potential of allowing a uniform growth of SMPCs within the entire scaffold structure. In this work, we designed and developed a perfusion bioreactor able to ensure long-term culture conditions and uniform flow of medium through 3D collagen sponges. A mathematical model to assist the design of the experimental setup and of the operative conditions was developed. The effects of dynamic vs static culture in terms of cell viability and spatial distribution within 3D collagen scaffolds were evaluated at 1, 4 and 7 days and for different flow rates of 1, 2, 3.5 and 4.5 ml/min using C2C12 muscle cell line and SMPCs derived from satellite cells. C2C12 cells, after 7 days of culture in our bioreactor, perfused applying a 3.5 ml/min flow rate, showed a higher viability resulting in a three-fold increase when compared with the same parameter evaluated for cultures kept under static conditions. In addition, dynamic culture resulted in a more uniform 3D cell distribution. The 3.5 ml/min flow rate in the bioreactor was also applied to satellite cell-derived SMPCs cultured on 3D collagen scaffolds. The dynamic culture conditions improved cell viability leading to higher cell density and uniform distribution throughout the entire 3D collagen sponge for both C2C12 and satellite cells.     

Modulation of osteogenic properties of biodegradable polymer/extracellular matrix scaffolds generated with a flow perfusion bioreactor

In this study, composite scaffolds consisting of both synthetic and natural components with controllable properties were generated by incorporating mineralized extracellular matrix (ECM) and electrospun poly(ε-caprolactone) (PCL) microfiber scaffolds. Mesenchymal stem cells (MSCs) were cultured on PCL scaffolds under flow perfusion conditions with culture medium supplemented with dexamethasone to investigate the effect of culture duration on mineralized extracellular matrix deposition. MSCs differentiated down the osteogenic lineage and produced extracellular matrix with different compositions of mineral, collagen, and glycosaminoglycan with distinct morphologies at various stages of osteogenesis. To determine whether the presence and maturity of mineralized extracellular matrix influences osteogenic differentiation in vitro, PCL/ECM constructs were decellularized to yield PCL/ECM composite scaffolds that were subsequently seeded with MSCs and cultured in the absence of dexamethasone. The presence of mineralized matrix reduced cellular proliferation while stimulating alkaline phosphatase activity with increasing amounts of calcium deposition over time. PCL/ECM composite scaffolds containing the most mature mineralized matrix resulted in the most rapid increase and highest levels of alkaline phosphatase activity and calcium deposition compared to all other scaffold groups. Therefore, we demonstrate that mineralized extracellular matrix generated under controlled flow perfusion conditions can impart osteogenic properties to an osteoconductive polymer scaffold, and that the maturity of this matrix influences osteogenic differentiation in vitro, even in the absence of dexamethasone.     

Formation of three-dimensional cell/polymer constructs for bone tissue engineering in a spinner flask and a rotating wall vessel bioreactor

The aim of this study is to investigate the effect of the cell culture conditions of three-dimensional polymer scaffolds seeded with rat marrow stromal cells (MSCs) cultured in different bioreactors concerning the ability of these cells to proliferate, differentiate towards the osteoblastic lineage, and generate mineralized extracellular matrix. MSCs harvested from male Sprague-Dawley rats were culture expanded, seeded on three-dimensional porous 75:25 poly(D,L-lactic-co-glycolic acid) biodegradable scaffolds, and cultured for 21 days under static conditions or in two model bioreactors (a spinner flask and a rotating wall vessel) that enhance mixing of the media and provide better nutrient transport to the seeded cells. The spinner flask culture demonstrated a 60% enhanced proliferation at the end of the first week when compared to static culture. On day 14, all cell/polymer constructs exhibited their maximum alkaline phosphatase activity (AP). Cell/polymer constructs cultured in the spinner flask had 2.4 times higher AP activity than constructs cultured under static conditions on day 14. The total osteocalcin (OC) secretion in the spinner flask culture was 3.5 times higher than the static culture, with a peak OC secretion occurring on day 18. No considerable AP activity and OC secretion were detected in the rotating wall vessel culture throughout the 21-day culture period. The spinner flask culture had the highest calcium content at day 14. On day 21, the calcium deposition in the spinner flask culture was 6.6 times higher than the static cultured constructs and over 30 times higher than the rotating wall vessel culture. Histological sections showed concentration of cells and mineralization at the exterior of the foams at day 21. This phenomenon may arise from the potential existence of nutrient concentration gradients at the interior of the scaffolds. The better mixing provided in the spinner flask, external to the outer surface of the scaffolds, may explain the accelerated proliferation and differentiation of marrow stromal osteoblasts, and the localization of the enhanced mineralization on the external surface of the scaffolds.     

Differentiation of embryonic stem cells into neural cells on 3D poly (D, L-lactic acid) scaffolds versus 2D cultures

In this study, a highly porous poly (D, L-lactic acid) (PDLLA) scaffold was designed and fabricated using dioxane and thermal-induced phase separation (TIPS) methods (liquid-liquid and solid-liquid). Additionally, we characterized the ability of mouse embryonic stem cells (ESCs) to differentiate into neural cells in PDLLA scaffold with uniform porosity, interconnectivity, and high porosity, and then compared them with cells seeded under conventional two-dimensional (2D) culture conditions. Histochemistry staining showed the migration of differentiated cells through the scaffold. Immunofluorescence analysis of the differentiated cells by counting positive cells revealed that the PDLLA scaffold resulted in a significantly greater number of neural markers, microtubule associated protein-2, ?-tubulin III, neurofilament protein, and glial fibrillary acidic protein (the astrocyte marker) when compared to those in 2D culture condition. Moreover, the expression of Nestin, Mash1, Pax6, and HB9 increased significantly in 3D scaffolds when compared with 2D cultures as detected by semi-quantitative RT-PCR. Scanning electron microscopy of differentiated neurons on scaffolds also demonstrated favorable results for neurite outgrowth. The results of this study demonstrated a promising effect of 3D scaffold culture for neural cell differentiation from ESCs in prospective tissue engineering applications.     

Long-term cytokine-free expansion of cord blood mononuclear cells in three-dimensional scaffolds

Cord blood expansion ex vivo can be achieved in liquid suspension through the addition of cytokines at the expense of often undesirable cell differentiation. In order to derive a cytokine-free dynamic culture system, we hypothesised that a three-dimensional (3D) environment in the form of highly porous scaffolds made of poly (D,L-lactide-co-glycolide) (PLGA) or polyurethane (PU) for the biomimetic growth of cord blood mononuclear cells (CBMNCs), would facilitate expansion of hematopoietic cells without exogenous cytokines. Both scaffolds supported cellular expansion ex vivo. Cytokine-free, long-term culture was best in PU coated with collagen type I (54-fold expansion). In contrast, traditional 2D well-plate cultures collapsed within 4 days in the absence of cytokines. CBMNCs cultured in the scaffolds were visualised by scanning electron microscopy and immunophenotypic/immunostaining analysis and the studies validated the presence of a dynamic culture containing erythroid precursors (CD45(-)/CD71(+)/CD235a(+)), hematopoietic stem/progenitor cells (CD38(-)CD34(+), CD117(+)), maturing myeloid cells (CD38(+), MPO(+)), CD4(+) and CD8(+) T-lymphocytes and megakaryocytes (FVIII(+)). Colony forming unit (CFU) assays indicated that BFU-E and CFU-GM increased (p < 0.05) whereas CFU-GEMM were maintained at week 4. In conclusion, this 3D culture system is capable of long-term, cytokine-free expansion of CBMNCs, enabling the study of hematopoiesis and providing a potential platform for drug discovery and therapeutic applications ex vivo.     

Optimization of fibrin scaffolds for differentiation of murine embryonic stem cells into neural lineage cells

The objective of this research was to determine the appropriate cell culture conditions for embryonic stem (ES) cell proliferation and differentiation in fibrin scaffolds by examining cell seeding density, location, and the optimal concentrations of fibrinogen, thrombin, and aprotinin (protease inhibitor). Mouse ES cells were induced to become neural progenitors by adding retinoic acid for 4 days to embryoid body (EB) cultures. For dissociated EBs, the optimal cell seeding density and location was determined to be 250,000 cells/cm² seeded on top of fibrin scaffolds. For intact EBs, three-dimensional (3D) cultures with one EB per 400 μL fibrin scaffold resulted in greater cell proliferation and differentiation than two-dimensional (2D) cultures. Optimal concentrations for scaffold polymerization were 10 mg/mL of fibrinogen and 2 NIH units/mL of thrombin. The optimal aprotinin concentration was determined to be 50 μg/mL for dissociated EBs (2D) and 5 μg/mL for intact EBs in 3D fibrin scaffolds. Additionally, after 14 days in 3D culture EBs differentiated into neurons and astrocytes as indicated by immunohistochemisty. These conditions provide an optimal fibrin scaffold for evaluating ES cell differentiation and proliferation in culture, and for use as a platform for neural tissue engineering applications, such as the treatment for spinal cord injury.     

Chondrogenesis in perfusion bioreactors using porous silk scaffolds and hESC-derived MSCs

Tissue engineered cartilage can be grown in vitro with the use of cell-scaffold constructs and bioreactors. The present study was designed to investigate the effects of perfusion bioreactors on the chondrogenic potential of engineered constructs prepared from porous silk fibroin scaffolds seeded with human embryonic stem cell (hESC)-derived mesencyhmal stem cells (MSCs). After four weeks of incubation, constructs cultured in perfusion bioreactors showed significantly higher amounts of glycosaminoglycans (GAGs) (p < 0.001), DNA (p < 0.001), total collagen (p < 0.01), and collagen II (p < 0.01) in comparison to static culture. Mechanical stiffness of constructs increased 3.7-fold under dynamic culture conditions and RT-PCR results concluded that cells cultured in perfusion bioreactors highly expressed (p < 0.001) cartilage-related genes when compared with static culture. Distinct differences were noted in tissue morphology, including polygonal extracellular matrix structure of engineered constructs in thin superficial zones and an inner zone under static and dynamic conditions, respectively. The results suggest that the utility of perfusion bioreactors to modulate the growth of tissue-engineered cartilage and enhance tissue growth in vitro.     

Chondrogenic differentiation of adipose-derived adult stem cells by a porous scaffold derived from native articular cartilage extracellular matrix

Adipose-derived adult stem cells (ASCs) have the ability to differentiate into a chondrogenic phenotype in response to specific environmental signals such as growth factors or artificial biomaterial scaffolds. In this study, we examined the hypothesis that a porous scaffold derived exclusively from articular cartilage can induce chondrogenesis of ASCs. Human ASCs were seeded on porous scaffolds derived from adult porcine articular cartilage and cultured in standard medium without exogenous growth factors. Chondrogenesis of ASCs seeded within the scaffold was evident by quantitative RT-PCR analysis for cartilage-specific extracellular matrix (ECM) genes. Histological and immunohistochemical examination showed abundant production of cartilage-specific ECM components-particularly, type II collagen-after 4 or 6 weeks of culture. After 6 weeks of culture, the cellular morphology in the ASC-seeded constructs resembled those in native articular cartilage tissue, with rounded cells residing in the glycosaminoglycan-rich regions of the scaffolds. Biphasic mechanical testing showed that the aggregate modulus of the ASC-seeded constructs increased over time, reaching 150 kPa by day 42, more than threefold higher than that of the unseeded controls. These results suggest that a porous scaffold derived from articular cartilage has the ability to induce chondrogenic differentiation of ASCs without exogenous growth factors, with significant synthesis and accumulation of ECM macromolecules, and the development of mechanical properties approaching those of native cartilage. These findings support the potential for a processed cartilage ECM as a biomaterial scaffold for cartilage tissue engineering. Additional in vivo evaluation is necessary to fully recognize the clinical implication of these observations.     

Tubular perfusion system culture of human mesenchymal stem cells on poly-L-lactic acid scaffolds produced using a supercritical carbon dioxide-assisted process

In vitro human mesenchymal stem cell (hMSC) proliferation and differentiation is dependent on scaffold design parameters and specific culture conditions. In this study, we investigate how scaffold microstructure influences hMSC behavior in a perfusion bioreactor system. Poly-L-lactic acid (PLLA) scaffolds are fabricated using supercritical carbon dioxide (SC-CO(2) ) gel drying. This production method results in scaffolds fabricated with nanostructure. To introduce a microporous structure, porogen leaching was used in addition to this technique to produce scaffolds of average pore size of 100, 250, and 500 μm. These scaffolds were then cultured in static culture in well plates or dynamic culture in the tubular perfusion system (TPS) bioreactor. Results indicated that hMSCs were able to attach and maintain viability on all scaffolds with higher proliferation in the 250 μm and 500 μm pore sizes of bioreactor cultured scaffolds and 100 μm pore size of statically cultured scaffolds. Osteoblastic differentiation was enhanced in TPS culture as compared to static culture with the highest alkaline phosphatase expression observed in the 250 μm pore size group. Bone morphogenetic protein-2 was also analyzed and expression levels were highest in the 250 μm and 500 μm pore size bioreactor cultured samples. These results demonstrate cellular response to pore size as well as the ability of dynamic culture to enhance these effects. ? 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part A 100A:2563-2572, 2012.     

Hematopoietic progenitor cells derived from embryonic stem cells: analysis of gene expression

Rhesus monkey embryonic stem (ES) cells undergo differentiation in vitro to generate hematopoietic progenitor cells. Our previous studies demonstrated a high degree of similarity in the expression of genes associated with hematopoietic differentiation, homing, and engraftment in CD34(+) and CD34(+)CD38(-) cells from rhesus monkey ES cells and from fresh or cultured bone marrow (BM). In the present study, we compared the expression patterns of cyclins, cyclin-dependent kinases (CDKs) and CDK inhibitors (CDIs) in these cells. The expression of genes for cyclins, CDKs, and CDIs was similar among the hematopoietic progenitor cells of different origins, with only minor differences. Differentially expressed genes were also analyzed in CD34(+) lineage-negative cells derived from mouse ES cells and from BM. No difference or totally divergent results were obtained with the latter system, suggesting that this variation may be species specific. We observed, however, that CD34(+) and CD34(+)CD38(-) cells derived from ES cells expressed embryonic epsilon and zeta as well as alpha, beta, and gamma globin genes, whereas no expression of embryonic globins could be detected in the cell preparations from BM. Moreover, erythroblast-enriched CD34(-) cells derived from 4- or 5-week ES cell differentiation cultures also expressed embryonic, fetal, and adult globin genes, with greater beta gene expression, but otherwise were identical to those of the more primitive CD34(+) cells derived from 2-week ES cultures. These latter observations may reflect the presence of heterogeneous cell populations within the cell fractions that were compared, or they may represent variability among ES-cell-derived hematopoietic stem cells.     

Effect of seeding technique and scaffold material on bone formation in tissue-engineered constructs

The aim of the present study was to test the hypothesis that both scaffold material and the type of cell culturing contribute to the results of in vivo osteogenesis in tissue-engineered constructs in an interactive manner. CaCO3 scaffolds and mineralized collagen scaffolds were seeded with human trabecular bone cells at a density of 5 x 10(6) cells/cm(3) and were left to attach under standard conditions for 24 h. Subsequently, they were submitted to static and dynamic culturing for 14 days (groups III and IV, respectively). Dynamic culturing was carried out in a continuous flow perfusion bioreactor. Empty scaffolds and scaffolds that were seeded with cells and kept under standard conditions for 24 h served as controls (groups I and II, respectively). Five scaffolds of each biomaterial and from each group were implanted into the gluteal muscles of rnu rats for 6 weeks. Osteogenesis was assessed quantitatively by histomorphometry and expression of osteocalcin (OC) and vascular endothelial growth factor (VEGF) was determined by immunohistochemistry. CaCO3 scaffolds exhibited 15.8% (SD 3.1) of newly formed bone after static culture and 22.4% (SD 8.2) after dynamic culture. Empty control scaffolds did not show bone formation, and scaffolds after 24 h of standard conditions produced 8.2% of newly formed bone (SD 4.0). Differences between the controls and the scaffolds cultured for 14 days were significant, but there was no significant difference between static and dynamic culturing. Mineralized collagen scaffolds did not show bone formation in any group. There was a significant difference in the expression of OC within the scaffolds submitted to static versus dynamic culturing in the CaCO3 scaffolds. VEGF expression did not show significant differences between static and dynamic culturing in the two biomaterials tested. It is concluded that within the limitations of the study the type of biomaterial had the dominant effect on in vivo bone formation in small tissue-engineered scaffolds. The culture period additionally affected the amount of bone formed, whereas the type of culturing may have had a positive effect on the expression of osteogenic markers but not on the quantity of bone formation.