Dynamic formation of cellular aggregates of chondrocytes and mesenchymal stem cells in spinner flask

Epigenetic Priming Enhances Chondrogenic Potential of Expanded Chondrocytes

Expansion of chondrocytes presents a major obstacle in the cartilage regeneration procedure, such as matrix-induced autologous chondrocyte implantation. Dedifferentiation of chondrocytes during the expansion process leads to the emergence of a fibrotic (chondrofibrotic) phenotype that decreases the chondrogenic potential of the implanted cells. We aim to (1) determine the extent that chromatin architecture of H3K27me3 and H3K9me3 remodels during dedifferentiation and persists after the transfer to a three-dimensional (3D) culture; and (2) to prevent this persistent remodeling to enhance the chondrogenic potential of expanded bovine chondrocytes, used as a model system. Chromatin architecture remodeling of H3K27me3 and H3K9me3 was observed at 0 population doublings, 8 population doublings, and 16 population doublings (PD16) in a two-dimensional (2D) culture and after encapsulation of the expanded chondrocytes in a 3D hydrogel culture. Chondrocytes were treated with inhibitors of epigenetic modifiers (epigenetic priming) for PD16 and then encapsulated in 3D hydrogels. Chromatin architecture of chondrocytes and gene expression were evaluated before and after encapsulation. We observed a change in chromatin architecture of epigenetic modifications H3K27me3 and H3K9me3 during chondrocyte dedifferentiation. Although inhibiting enzymes that modify H3K27me3 and H3K9me3 did not alter the dedifferentiation process in 2D culture, applying these treatments during the 2D expansion did increase the expression of select chondrogenic genes and protein deposition of type II collagen when transferred to a 3D environment. Overall, we found that epigenetic priming of expanded bovine chondrocytes alters the cell fate when chondrocytes are later encapsulated into a 3D environment, providing a potential method to enhance the success of cartilage regeneration procedures.

Co-culture engineering: a promising strategy for production of engineered extracellular vesicle for osteoarthritis treatment

The therapeutic effects of extracellular vesicles (EVs) have been identified as a significant factor in intercellular communication in different disease treatments, including osteoarthritis (OA). Compared to the conventional approaches in treating OA, EV therapy is a non-invasive and cell-free method. However, improving the yield of EVs and their therapeutic effects are the main challenges for clinical applications. In this regard, researchers are using the EV engineering potential to overcome these challenges. New findings suggest that the co-culture strategy as an indirect EV engineering method efficiently increases EV production and quality. The co-culture of mesenchymal stem cells (MSCs) and chondrocytes has improved their chondrogenesis, anti-inflammatory effects, and regenerative properties which are mediated by EVs. Hence, co-culture engineering by considerable systems could be useful in producing engineered EVs for different therapeutic applications. Here, we review various co-culture approaches, including diverse direct and indirect, 2D and 3D cell cultures, as well as static and dynamic systems. Meanwhile, we suggest and discuss the advantages of combined strategies to achieve engineered EVs for OA treatment.

Sericin nano-gel agglomerates mimicking the pericellular matrix induce the condensation of mesenchymal stem cells and trigger cartilage micro-tissue formation without exogenous stimulation of growth factors in vitro

Mesenchymal stem cells (MSCs) are excellent seed cells for cartilage tissue engineering and regenerative medicine. Though the condensation of MSCs is the first step of their differentiation into chondrocytes in skeletal development, the process is a challenge in cartilage repairing by MSCs. The pericellular matrix (PCM), a distinct region surrounding the chondrocytes, acts as an extracellular linker among cells and forms the microenvironment of chondrocytes. Inspired by this, sericin nano-gel soft-agglomerates were prepared and used as linkers to induce MSCs to assemble into micro-spheres and differentiate into cartilage-like micro-tissues without exogenous stimulation of growth factors. These sericin nano-gel soft-agglomerates are composed of sericin nano-gels prepared by the chelation of metal ions and sericin protein. The MSCs cultured on 2D culture plates self-assembled into cell-microspheres centered by sericin nano-gel agglomerates. The self-assembly progress of MSCs is superior to the traditional centrifugation to achieve MSC condensation due to its facility, friendliness to MSCs and avoidance of the side-effects of growth factors. The analysis of transcriptomic results suggested that sericin nano-gel agglomerates offered a soft mechanical stimulation to MSCs similar to that of the PCM to chondrocytes and triggered some signaling pathways as associated with MSC chondrogenesis. The strategy of utilizing biomaterials to mimic the PCM as a linker and as a mechanical micro-environment and to induce cell aggregation and trigger the differentiation of MSCs can be employed to drive 3D cellular organization and micro-tissue fabrication in vitro. These cartilage micro-masses reported in this study can be potential candidates for cartilage repairing, cellular building blocks for 3D bio-printing and a model for cartilage development and drug screening.

3D culture of bovine articular chondrocytes in viscous medium encapsulated in agarose hydrogels for investigation of viscosity influence on cell functions

The mechanical properties of an extracellular microenvironment can affect cell functions. The effects of elasticity and viscoelasticity on cell functions have been extensively studied with hydrogels of tunable mechanical properties. However, investigation of the viscosity effect on cell functions is still very limited and it can be tricky to explore how viscosity affects cells in three-dimensional (3D) culture due to the lack of appropriate tools. In this study, agarose hydrogel containers were prepared and used to encapsulate viscous media for 3D cell culture to investigate the viscosity effect on the functions of bovine articular chondrocytes (BACs). Polyethylene glycol of different molecular weights was used to adjust culture medium viscosity in a large range (72.8-679.2 mPa s). The viscosity affected gene expression and secretion of cartilagenious matrices, while it did not affect BAC proliferation. The BACs cultured in the lower viscosity medium (72.8 mPa s) showed a higher level of cartilaginous gene expression and matrix secretion.

Fabricating the cartilage: recent achievements

This review aims to describe the most recent achievements and provide an insight into cartilage engineering and strategies to restore the cartilage defects. Here, we discuss cell types, biomaterials, and biochemical factors applied to form cartilage tissue equivalents and update the status of fabrication techniques, which are used at all stages of engineering the cartilage. The actualized concept to improve the cartilage tissue restoration is based on applying personalized products fabricated using a full cycle platform: a bioprinter, a bioink consisted of ECM-embedded autologous cell aggregates, and a bioreactor. Moreover, in situ platforms can help to skip some steps and enable adjusting the newly formed tissue in the place during the operation. Only some achievements described have passed first stages of clinical translation; nevertheless, the number of their preclinical and clinical trials is expected to grow in the nearest future.

Evaluating the reliability of tumour spheroid-on-chip models for replicating intratumoural drug delivery: considering the role of microfluidic parameters

Several tumour spheroid-on-chip models have already been proposed in the literature to conduct high throughput drug screening assays. The microfluidic configurations in these models generally depend on the strategies adopted for spheroid formation and entrapment. However, it is not clear how successful they are to mimic in vivo transport mechanisms. In this study, drug transport in different tumour spheroid-on-chip models is numerically investigated under static and dynamic conditions using porous media theory. Moreover, the treatment of a solid tumour at the initial stage of development is modelled using bolus injection and continuous infusion methods. Then, the results of tumour spheroid-on-chip, including drug concentration, cell viability, as well as pressure and fluid shear stress distributions, are compared with those of the solid tumour, assuming identical transport properties in all models. Finally, a new configuration of the microfluidic device along with the optimal drug concentrations is proposed, which can well imitate a given in vivo situation.

Design considerations of benchtop fluid flow bioreactors for bio-engineered tissue equivalents in vitro

One of the major aims of bio-engineering tissue equivalents in vitro is to create physiologically relevant culture conditions to accurately recreate the cellular microenvironment. This often includes incorporation of factors such as the extracellular matrix, co-culture of multiple cell types and three-dimensional culture techniques. These advanced techniques can recapitulate some of the properties of tissue in vivo, however fluid flow is a key aspect that is often absent. Fluid flow can be introduced into cell and tissue culture using bioreactors, which are becoming increasingly common as we seek to produce increasingly accurate tissue models. Bespoke technology is continuously being developed to tailor systems for specific applications and to allow compatibility with a range of culture techniques. For effective perfusion of a tissue culture many parameters can be controlled, ranging from impacts of the fluid flow such as increased shear stress and mass transport, to potentially unwanted side effects such as temperature fluctuations. A thorough understanding of these properties and their implications on the culture model can aid with a more accurate interpretation of results. Improved and more complete characterisation of bioreactor properties will also lead to greater accuracy when reporting culture conditions in protocols, aiding experimental reproducibility, and allowing more precise comparison of results between different systems. In this review we provide an analysis of the different factors involved in the development of benchtop flow bioreactors and their potential biological impacts across a range of applications.

Dynamic Culture of Mesenchymal Stromal/Stem Cell Spheroids and Secretion of Paracrine Factors

In recent years, conditioned medium (CM) obtained from the culture of mesenchymal stromal/stem cells (MSCs) has been shown to effectively promote tissue repair and modulate the immune response in vitro and in different animal models, with potential for application in regenerative medicine. Using CM offers multiple advantages over the implantation of MSCs themselves: 1) simpler storage, transport, and preservation requirements, 2) avoidance of the inherent risks of cell transplantation, and 3) potential application as a ready-to-go biologic product. For these reasons, a large amount of MSCs research has focused on the characterization of the obtained CM, including soluble trophic factors and vesicles, preconditioning strategies for enhancing paracrine secretion, such as hypoxia, a three-dimensional (3D) environment, and biochemical stimuli, and potential clinical applications. In vitro preconditioning strategies can increase the viability, proliferation, and paracrine properties of MSCs and therefore improve the therapeutic potential of the cells and their derived products. Specifically, dynamic cultivation conditions, such as fluid flow and 3D aggregate culture, substantially impact cellular behaviour. Increased levels of growth factors and cytokines were observed in 3D cultures of MSC grown on orbital or rotatory shaking platforms, in stirred systems, such as spinner flasks or stirred tank reactors, and in microgravity bioreactors. However, only a few studies have established dynamic culture conditions and protocols for 3D aggregate cultivation of MSCs as a scalable and reproducible strategy for CM production. This review summarizes significant advances into the upstream processing, mainly the dynamic generation and cultivation of MSC aggregates, for de CM manufacture and focuses on the standardization of the soluble factor production.

Physical optimization of cell proliferation and differentiation using spinner flask and microcarriers

Abstract

The traditional breeding industry has been increasingly saturated and caused environmental pollution, disease transmission, excessive resource use, and methane emission; however, it still cannot meet the needs of the growing population. To explore other alternatives, researchers focused on cell agriculture and cell-based meat, especially large-scale cell culture. As a prerequisite for production, large-scale culture technology has become an important bottleneck restricting cell-based meat industrialization. In this study, the single-factor variable method was adopted to examine the influence of Cytodex1 microcarrier pretreatment, spinner flask reaction vessel, cell culture medium, serum and cell incubation, and other influencing factors on large-scale cell cultures to identify the optimization parameters suitable for 3D culture environment. Collagen and 3D culture were also prospectively explored to promote myogenesis and cultivate tissue-like muscle fibers that contract spontaneously. This research lays a theoretical foundation and an exploratory practice for large-scale cell cultures and provides a study reference for the microenvironment of myoblast culture in vitro, a feasible direction for the cell therapy of muscular dystrophy, and prerequisites for the industrialized manufacturing of cell-based meat.

Graphical Abstract

Scaffold-free approaches for the fabrication of engineered articular cartilage tissue

Tissue engineered cartilaginous constructs have meet great advances in the past decades as a treatment for osteoarthritis, a degenerative disease affecting people all over the world as the population ages. Scaffold-free tissue engineered constructs are designed and developed in recent years with only cells and cell-derived matrix involved. Scaffold-free tissue constructs do not require cell adherence on exogenous materials and are superior to scaffold-based constructs in (1) relying on only cells to produce matrix, (2) not interfering cell-cell signaling, cell migration or small molecules diffusion after implantation and (3) introducing no exogenous impurities. In this review, three main scaffold-free methodologies for cartilage tissue engineering, the cell sheet technology, the phase transfer cell culture-living hyaline cartilage graft (PTCC-LhCG) system and the cell aggregate-based (bottom-up) methods, were reviewed, covering mold fabrication, decellularization and 3D bioprinting. The recent advances, medical applications, superiority and drawbacks were elaborated in detail.

Perfused Platforms to Mimic Bone Microenvironment at the Macro/Milli/Microscale: Pros and Cons

As life expectancy increases, the population experiences progressive ageing. Ageing, in turn, is connected to an increase in bone-related diseases (i.e., osteoporosis and increased risk of fractures). Hence, the search for new approaches to study the occurrence of bone-related diseases and to develop new drugs for their prevention and treatment becomes more pressing. However, to date, a reliable in vitro model that can fully recapitulate the characteristics of bone tissue, either in physiological or altered conditions, is not available. Indeed, current methods for modelling normal and pathological bone are poor predictors of treatment outcomes in humans, as they fail to mimic the in vivo cellular microenvironment and tissue complexity. Bone, in fact, is a dynamic network including differently specialized cells and the extracellular matrix, constantly subjected to external and internal stimuli. To this regard, perfused vascularized models are a novel field of investigation that can offer a new technological approach to overcome the limitations of traditional cell culture methods. It allows the combination of perfusion, mechanical and biochemical stimuli, biological cues, biomaterials (mimicking the extracellular matrix of bone), and multiple cell types. This review will discuss macro, milli, and microscale perfused devices designed to model bone structure and microenvironment, focusing on the role of perfusion and encompassing different degrees of complexity. These devices are a very first, though promising, step for the development of 3D in vitro platforms for preclinical screening of novel anabolic or anti-catabolic therapeutic approaches to improve bone health.

Using Spheroids as Building Blocks Towards 3D Bioprinting of Tumor Microenvironment

Cancer still ranks as a leading cause of mortality worldwide. Although considerable efforts have been dedicated to anticancer therapeutics, progress is still slow, partially due to the absence of robust prediction models. Multicellular tumor spheroids, as a major three-dimensional (3D) culture model exhibiting features of avascular tumors, gained great popularity in pathophysiological studies and high throughput drug screening. However, limited control over cellular and structural organization is still the key challenge in achieving in vivo like tissue microenvironment. 3D bioprinting has made great strides toward tissue/organ mimicry, due to its outstanding spatial control through combining both cells and materials, scalability, and reproducibility. Prospectively, harnessing the power from both 3D bioprinting and multicellular spheroids would likely generate more faithful tumor models and advance our understanding on the mechanism of tumor progression. In this review, the emerging concept on using spheroids as a building block in 3D bioprinting for tumor modeling is illustrated. We begin by describing the context of the tumor microenvironment, followed by an introduction of various methodologies for tumor spheroid formation, with their specific merits and drawbacks. Thereafter, we present an overview of existing 3D printed tumor models using spheroids as a focus. We provide a compilation of the contemporary literature sources and summarize the overall advancements in technology and possibilities of using spheroids as building blocks in 3D printed tissue modeling, with a particular emphasis on tumor models. Future outlooks about the wonderous advancements of integrated 3D spheroidal printing conclude this review.

Artificial tissue creation under microgravity conditions: Considerations and future applications

Traditional tissue engineering methods often fail to promote robust cell growth and differentiation, limiting the development of functioning tissues. However, the microgravity conditions created by rotating wall vessel bioreactors minimize shear stress and unload the gravitational force usually placed on cells. In a microgravity environment, cell proliferation, cell differentiation, and the 3D organization of cells are altered, potentially encouraging the formation of more biosimilar artificial tissues for certain cell types. Additionally, cells in these engineered tissues display lowered immunogenicity, pointing to the transplantation potential of tissues engineered in microgravity conditions. However, these benefits are not consistent across all cell types, and the long-term impact of microgravity on tissue development and stability remains an unanswered question. Even so, there is potential that with further research, microgravity tissue engineering will have productive clinical applications for medical and pharmaceutical purposes.

De novo neo-hyaline-cartilage from bovine organoids in viscoelastic hydrogels

Regenerative therapies for articular cartilage are currently clinically available. However, they are associated with several drawbacks that require resolution. Optimizing chondrocyte expansion and their assembly, can reduce the time and costs of these therapies and more importantly increase their clinical success. In this study, cartilage organoids were quickly mass produced from bovine chondrocytes with a new suspension expansion protocol. This new approach led to massive cell proliferation, high viability and the self-assembly of organoids. These organoids were composed of collagen type II, type VI, glycosaminoglycans, with Sox9 positive cells, embedded in a pericellular and interterritorial matrix similarly to hyaline cartilage. With the goal of producing large scale tissues, we then encapsulated these organoids into alginate hydrogels with different viscoelastic properties. Elastic hydrogels constrained the growth and fusion of the organoids inhibiting the formation of a tissue. In contrast, viscoelastic hydrogels allowed the growth and fusion of the organoids into a homogenous tissue that was rich in collagen type II and glycosaminoglycans. The encapsulation of organoids to produce in vitro neocartilage also proved to be superior to the conventional method of encapsulating 2D expanded chondrocytes. This study describes a multimodal approach that involves chondrocyte expansion, organoid formation and their assembly into neohyaline-cartilage which proved to be superior to the current standard approaches used in cartilage tissue engineering. STATEMENT OF SIGNIFICANCE: In this manuscript, we describe a new and simple methodology to quickly mass produce self-assembling cartilage organoids. Due to their matrix content and structure similarities with native cartilage, these organoids on their own have the potential to revolutionize cartilage research and the manner in which we study signaling pathways, disease progression, tissue engineering, drug development, etc. Furthermore, these organoids and their fast mass production were combined with a key relatively ignored hydrogel characteristic, viscoelasticity, to demonstrate their fusion into a neo-tissue. This has the potential to open the door for large scale cartilage regeneration such as for entire joint surfaces.

A Novel SimpleDrop Chip for 3D Spheroid Formation and Anti-Cancer Drug Assay

Cell culture is important for the rapid screening of anti-cancer drug candidates, attracting intense interest. Traditional 2D cell culture has been widely utilized in cancer biological research. However, 3D cellular spheroids are able to recapitulate the in vivo microenvironment of tissues or tumors. Thus far, several 3D cell culture methods have been developed, for instance, the hanging drop method, spinner flasks and micropatterned plates. Nevertheless, these methods have been reported to have some disadvantages, for example, medium replacement is inconvenient or causes cellular damage. Here, we report on an easy-to-operate and useful micro-hole culture chip (SimpleDrop) for 3D cellular spheroid formation and culture and drug analysis, which has advantages over the traditional method in terms of its ease of operation, lack of shear force and environmentally friendliness. On this chip, we observed the formation of a 3D spheroid clearly. Three drugs (paclitaxel, cisplatin and methotrexate) were tested by both cell viability assay and drug-induced apoptotic assay. The results show that the three drugs present a similar conclusion: cell viability decreased over time and concentration. Moreover, the apoptotic experiment showed a similar trend to the live/dead cell assay, in that the fraction of the apoptotic and necrotic cells correlated with the concentration and time. All these results prove that our SimpleDrop method is a useful and easy method for the formation of 3D cellular spheroids, which shows its potential for both cell-cell interaction research, tissue engineering and anticancer drug screening.

Fabrication of PNIPAm-based thermoresponsive hydrogel microwell arrays for tumor spheroid formation

Complex three-dimensional (3D) cell cultures are being increasingly implemented in biomedical research as they provide important insights into complex cancer biology, and cell-cell and cell-matrix interactions in the tumor microenvironment. However, most methods used today for 3D cell culture are limited by high cost, the need for specialized skills, low throughput and the use of unnatural culture environments. We report the development of a unique biomimetic hydrogel microwell array platform for the generation and stress-free isolation of cancer spheroids. The poly N-isopropylacrylamide-based hydrogel microwell array (PHMA) has thermoresponsive properties allowing for the attachment and growth of cell aggregates/ spheroids at 37 °C, and their easy isolation at room temperature (RT). The reversible phase transition of the microwell arrays at 35 °C was confirmed visually and by differential scanning calorimetry. Swelling/ shrinking studies and EVOS imaging established that the microwell arrays are hydrophilic and swollen at temperatures <35 °C, while they shrink and are hydrophobic at temperatures >35 °C. Spheroid development within the PHMA was optimized for seeding density, incubation time and cell viability. Spheroids of A549, HeLa and MG-63 cancer cell lines, and human lung fibroblast (HLF) cell line generated within the PHMAs had relatively spherical morphology with hypoxic cores. Finally, using MG-63 cell spheroids as representative models, a proof-of-concept drug response study using doxorubicin hydrochloride was conducted. Overall, we demonstrate that the PHMAs are an innovative alternative to currently used 3D cell culture techniques, for the high-throughput generation of cell spheroids for disease modeling and drug screening applications.

Gingiva-derived Mesenchymal Stem Cells and Their Potential Applications in Oral and Maxillofacial Diseases

BACKGROUND

Stem cells are undifferentiated cells with multilineage differentiation potential. They can be collected from bone marrow, fat, amniotic fluid, and teeth. Stem cell-based therapies have been widely used to treat multiple diseases, such as cardiac disease, and hematological disorders. The cells may also be beneficial for controlling the disease course and promoting tissue regeneration in oral and maxillofacial diseases. Oral-derived gingival mesenchymal stem cells are easy to access and the donor sites heal rapidly without a scar. Such characteristics demonstrate the beneficial role of GMSCs in oral and maxillofacial diseases.

OBJECTIVE

We summarize the features of GMSCs, including their self-renewal, multipotent differentiation, immunomodulation, and anti-inflammation properties. We also discuss their applications in oral and maxillofacial disease treatment and tissue regeneration.

CONCLUSION

GMSCs are easily harvestable adult stem cells with outstanding proliferation, differentiation, and immunomodulation characteristics. A growing body of evidence indicates that GMSCs have strong potential use in accelerating wound healing and promoting the regeneration of bone defects, periodontium, oral neoplasms, salivary glands, peri-implantitis, and nerves. Moreover, alginate, polylactic acid and polycaprolactone can be used as biodegradable scaffolds for GMSC encapsulation. Various growth factors can be applied to the corresponding scaffolds to obtain the desired GMSC differentiation and phenotypes. Three-dimensional spheroid culture systems could optimize GMSC properties and improve the performance of the cells in tissue engineering. The immunomodulatory property of GMSCs in controlling oral and maxillofacial inflammation needs further research.

MicroRNA-23 suppresses osteogenic differentiation of human bone marrow mesenchymal stem cells by targeting the MEF2C-mediated MAPK signaling pathway

BACKGROUND

The present study aimed to determine the role and mechanism of miR-23 with respect to regulating the osteogenic differentiation of human bone marrow mesenchymal stem cells (hBMSCs).

MATERIALS

The expression of miR-23 and MEF2C was measured in osteoporosis (OP) patients and healthy controls by a quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR). The correlation between miR-23 and MEF2C was determined by the Pearson correlation coefficient. Moreover, bioinformatic analysis was performed using public databases. Target gene function and potential pathways were further examined. Then, we used a miR-23 mimic or inhibitor to further explore the potential mechanism of miR-23.

RESULTS

miR-23 is found to be up-regulated and MEF2C is down-regulated in OP patients compared to healthy controls. miR-23 had a negative correlation with MEF2C (r = -0.937, p = 0.001). Bioinformatic analysis revealed that a total of 664 overlapping target genes were found in the TargetScan (http://www.targetscan.org), miRDB (http://mirdb.org) and miRanda (http://www.microrna.org/microrna/home.do) databases. Moreover, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis indicated that miR-23 may regulate the mitogan-activated protein kinase (MAPK) signaling pathway. miR-23 is down-regulated and MEF2C is significantly up-regulated in the osteogenic differentiation of hBMSCs. MEF2C was significantly up-regulated in the osteogenic differentiation of hBMSCs. Overexpression of miR-23 significantly down-regulated alkaline phosphatase (ALP) activity and calcium deposition, whereas the miR-23 inhibitor had the opposite effects. Moreover, overexpression of miR-23 significantly decreased osteoblast-related markers (Runx2, Osx, ALP and OCN). Further experiments confirmed that MEF2C is a direct target of miR-23. Moreover, the miR-23 mimic enhanced the expression of p-p38 but had no effect on p-JNK.

CONCLUSIONS

miR-23 decreases the osteogenic differentiation of hBMSCs through the MEF2C/MAPK signaling pathway.

Role of offset and gradient architectures of 3-D melt electrowritten scaffold on differentiation and mineralization of osteoblasts

BACKGROUND

Cell-scaffold based therapies have the potential to offer an efficient osseous regenerative treatment and PCL has been commonly used as a scaffold, however its effectiveness is limited by poor cellular retention properties. This may be improved through a porous scaffold structure with efficient pore arrangement to increase cell entrapment. To facilitate this, melt electrowriting (MEW) has been developed as a technique able to fabricate cell-supporting scaffolds with precise micro pore sizes via predictable fibre deposition. The effect of the scaffold's architecture on cellular gene expression however has not been fully elucidated.

METHODS

The design and fabrication of three different uniform pore structures (250, 500 and 750 μm), as well as two offset scaffolds with different layout of fibres (30 and 50%) and one complex scaffold with three gradient pore sizes of 250-500 - 750 μm, was performed by using MEW. Calcium phosphate modification was applied to enhance the PCL scaffold hydrophilicity and bone inductivity prior to seeding with osteoblasts which were then maintained in culture for up to 30 days. Over this time, osteoblast cell morphology, matrix mineralisation, osteogenic gene expression and collagen production were assessed.

RESULTS

The in vitro findings revealed that the gradient scaffold significantly increased alkaline phosphatase activity in the attached osteoblasts while matrix mineralization was higher in the 50% offset scaffolds. The expression of osteocalcin and osteopontin genes were also upregulated compared to other osteogenic genes following 30 days culture, particularly in offset and gradient scaffold structures. Immunostaining showed significant expression of osteocalcin in offset and gradient scaffold structures.

CONCLUSIONS

This study demonstrated that the heterogenous pore sizes in gradient and fibre offset PCL scaffolds prepared using MEW significantly improved the osteogenic potential of osteoblasts and hence may provide superior outcomes in bone regeneration applications.

Dynamic formation of cellular aggregates of chondrocytes and mesenchymal stem cells in spinner flask

OBJECTIVES

Cellular aggregates are readily applicable in cell-based therapy. The effects of agitation and inoculation density on the aggregation of cells in spinner flask and the molecular mechanism of aggregation were investigated.

MATERIALS AND METHODS

The aggregation kinetics of cells in spinner flask was evaluated with bovine articular chondrocytes (bACs), rabbit bone marrow-derived mesenchymal stem cells (rMSCs) and their mixture. The morphology of cellular aggregates was studied with scanning electron microscopy and gene expression of cell adhesion-related molecules was analysed.

RESULTS

It was shown that suspension culture in spinner flask induced the aggregation of bACs and rMSCs. Both cells exhibited increased aggregation rate and aggregate size with decreasing agitation rate and increasing cell inoculation density. Additionally, aggregate size increased with extended culture time. By analysing gene expression of integrin β1 and cadherin, it was indicated that these molecules were potentially involved in the aggregation process of bACs and rMSCs, respectively. Aggregates composed of both bACs and rMSCs were also prepared, showing rMSCs in the core and bACs in the periphery.

CONCLUSIONS

Cellular aggregates were prepared in dynamic suspension culture using spinner flask, the key parameters to the aggregation process were identified, and the molecular mechanism of aggregation was revealed. This would lay a solid foundation for the large-scale production of cellular aggregates for cell-based therapy, such as cartilage regeneration.