A comprehensive analysis of human dental pulp cell spheroids in a three-dimensional pellet culture system

Scaffold-free 3D culture systems for stem cell-based tissue regeneration

Recent advances in scaffold-free three-dimensional (3D) culture methods have significantly enhanced the potential of stem cell-based therapies in regenerative medicine. This cutting-edge technology circumvents the use of exogenous biomaterial and prevents its associated complications. The 3D culture system preserves crucial intercellular interactions and extracellular matrix support, closely mimicking natural biological niches. Therefore, stem cells cultured in 3D formats exhibit distinct characteristics, showcasing their capabilities in promoting angiogenesis and immunomodulation. This review aims to elucidate foundational technologies and recent breakthroughs in 3D scaffold-free stem cell engineering, offering comprehensive guidance for researchers to advance this technology across various clinical applications. We first introduce the various sources of stem cells and provide a comparative analysis of two-dimensional (2D) and 3D culture systems. Given the advantages of 3D culture systems, we delve into the specific fabrication and harvesting techniques for cell sheets and spheroids. Furthermore, we explore their applications in pre-clinical studies, particularly in large animal models and clinical trials. We also discuss multidisciplinary strategies to overcome existing limitations such as insufficient efficacy, hostile microenvironments, and the need for scalability and standardization of stem cell-based products.

A review of the therapeutic potential of dental stem cells as scaffold-free models for tissue engineering application

In the realm of regenerative medicine, tissue engineering has introduced innovative approaches to facilitate tissue regeneration. Specifically, in pulp tissue engineering, both scaffold-based and scaffold-free techniques have been applied. Relevant articles were meticulously chosen from PubMed, Scopus, and Google Scholar databases through a comprehensive search spanning from October 2022 to December 2022. Despite the inherent limitations of scaffolding, including inadequate mechanical strength for hard tissues, insufficient vents for vessel penetration, immunogenicity, and suboptimal reproducibility-especially with natural polymeric scaffolds-scaffold-free tissue engineering has garnered significant attention. This methodology employs three-dimensional (3D) cell aggregates such as spheroids and cell sheets with extracellular matrix, facilitating precise regeneration of target tissues. The choice of technique aside, stem cells play a pivotal role in tissue engineering, with dental stem cells emerging as particularly promising resources. Their pluripotent nature, non-invasive extraction process, and unique properties render them highly suitable for scaffold-free tissue engineering. This study delves into the latest advancements in leveraging dental stem cells and scaffold-free techniques for the regeneration of various tissues. This paper offers a comprehensive summary of recent developments in the utilization of dental stem cells and scaffold-free methods for tissue generation. It explores the potential of these approaches to advance tissue engineering and their effectiveness in therapies aimed at tissue regeneration.

Three-Dimensional Cell Cultures: The Bridge between In Vitro and In Vivo Models

Although historically, the traditional bidimensional in vitro cell system has been widely used in research, providing much fundamental information regarding cellular functions and signaling pathways as well as nuclear activities, the simplicity of this system does not fully reflect the heterogeneity and complexity of the in vivo systems. From this arises the need to use animals for experimental research and in vivo testing. Nevertheless, animal use in experimentation presents various aspects of complexity, such as ethical issues, which led Russell and Burch in 1959 to formulate the 3R (Replacement, Reduction, and Refinement) principle, underlying the urgent need to introduce non-animal-based methods in research. Considering this, three-dimensional (3D) models emerged in the scientific community as a bridge between in vitro and in vivo models, allowing for the achievement of cell differentiation and complexity while avoiding the use of animals in experimental research. The purpose of this review is to provide a general overview of the most common methods to establish 3D cell culture and to discuss their promising applications. Three-dimensional cell cultures have been employed as models to study both organ physiology and diseases; moreover, they represent a valuable tool for studying many aspects of cancer. Finally, the possibility of using 3D models for drug screening and regenerative medicine paves the way for the development of new therapeutic opportunities for many diseases.

3D Organoids for Regenerative Endodontics

Apical periodontitis is the inflammation and destruction of periradicular tissues, mediated by microbial factors originating from the infected pulp space. This bacteria-mediated inflammatory disease is known to interfere with root development in immature permanent teeth. Current research on interventions in immature teeth has been dedicated to facilitating the continuation of root development as well as regenerating the dentin-pulp complex, but the fundamental knowledge on the cellular interactions and the role of periapical mediators in apical periodontitis in immature roots that govern the disease process and post-treatment healing is limited. The limitations in 2D monolayer cell culture have a substantial role in the existing limitations of understanding cell-to-cell interactions in the pulpal and periapical tissues. Three-dimensional (3D) tissue constructs with two or more different cell populations are a better physiological representation of in vivo environment. These systems allow the high-throughput testing of multi-cell interactions and can be applied to study the interactions between stem cells and immune cells, including the role of mediators/cytokines in simulated environments. Well-designed 3D models are critical for understanding cellular functions and interactions in disease and healing processes for future therapeutic optimization in regenerative endodontics. This narrative review covers the fundamentals of (1) the disease process of apical periodontitis; (2) the influence and challenges of regeneration in immature roots; (3) the introduction of and crosstalk between mesenchymal stem cells and macrophages; (4) 3D cell culture techniques and their applications for studying cellular interactions in the pulpal and periapical tissues; (5) current investigations on cellular interactions in regenerative endodontics; and, lastly, (6) the dental-pulp organoid developed for regenerative endodontics.

In Vitro Bone Differentiation of 3D Microsphere from Dental Pulp-Mesenchymal Stem Cells

Bone defects lead to the structural loss of normal architecture, and those in the field of bone tissue engineering are searching for new alternatives to aid bone regeneration. Dental pulp-mesenchymal stem cells (DP-MSC) could provide a promising alternative to repair bone defects, principally due to their multipotency and capacity to fabricate three-dimensional (3D) spheroids. The present study aimed to characterize the 3D DP-MSC microsphere and the osteogenic differentiation capacity potential cultured by a magnetic levitation system. To achieve this, the 3D DP-MSC microsphere was grown for 7, 14, and 21 days in an osteoinductive medium and compared to 3D human fetal osteoblast (hFOB) microspheres by examining the morphology, proliferation, osteogenesis, and colonization onto PLA fiber spun membrane. Our results showed good cell viability for both 3D microspheres with an average diameter of 350 μm. The osteogenesis examination of the 3D DP-MSC microsphere revealed the lineage commitment, such as the hFOB microsphere, as evidenced by ALP activity, the calcium content, and the expression of osteoblastic markers. Finally, the evaluation of the surface colonization exhibited similar patterns of cell-spreading over the fibrillar membrane. Our study demonstrated the feasibility of forming a 3D DP-MSC microsphere structure and the cell-behavior response as a strategy for the applications of bone tissue guiding.

Therapeutic potential of dental pulp stem cells and their derivatives: Insights from basic research toward clinical applications

For more than 20 years, researchers have isolated and identified postnatal dental pulp stem cells (DPSCs) from different teeth, including natal teeth, exfoliated deciduous teeth, healthy teeth, and diseased teeth. Their mesenchymal stem cell (MSC)-like immunophenotypic characteristics, high proliferation rate, potential for multidirectional differentiation and biological features were demonstrated to be superior to those of bone marrow MSCs. In addition, several main application forms of DPSCs and their derivatives have been investigated, including stem cell injections, modified stem cells, stem cell sheets and stem cell spheroids. In vitro and in vivo administration of DPSCs and their derivatives exhibited beneficial effects in various disease models of different tissues and organs. Therefore, DPSCs and their derivatives are regarded as excellent candidates for stem cell-based tissue regeneration. In this review, we aim to provide an overview of the potential application of DPSCs and their derivatives in the field of regenerative medicine. We describe the similarities and differences of DPSCs isolated from donors of different ages and health conditions. The methodologies for therapeutic administration of DPSCs and their derivatives are introduced, including single injections and the transplantation of the cells with a support, as cell sheets, or as cell spheroids. We also summarize the underlying mechanisms of the regenerative potential of DPSCs.

Scaffold-free 3D culturing enhance pluripotency, immunomodulatory factors, and differentiation potential of Wharton's jelly-mesenchymal stem cells

Mesenchymal stem cells (MSCs) show a decline in pluripotency and differentiation with increased cell culture passages in 2D cultures. The 2D monolayer culture fails to correctly imitate the architecture and microenvironments of in-vivo cell models. Alternatively, 3D culture may improve the simulations of in-vivo cell microenvironments with wide applications in cell culture and drug discovery. In the present study, we compared various 3D culturing techniques such as 3D micro-well (3D-S), hanging drop (HD), and ultra-low attachment (ULA) plate-based spheroid culture to study their effect on morphology, viability, pluripotency, cell surface markers, immunomodulatory factors, and differentiation capabilities of Wharton's jelly-mesenchymal stem cells (WJ-MSCs). The cell morphology, viability, and senescence of 3D cultured WJ-MSCs were comparable to cells in 2D culture. The expression of pluripotency markers (OCT4, SOX2, and NANOG) was enhanced upto 2-8 fold in 3D cultured WJ-MSCs when compared to 2D culture. Moreover, the immunomodulatory factors (IDO, IL-10, LIF, ANG1, and VEGF) were significantly elevated in ULA based 3D cultured WJ-MSCs. Furthermore, significant enhancement in the differentiation potential of WJ-MSCs towards adipocyte (ADP and C/EBP-α), osteocyte (OPN and RUNX2), and definitive endodermal (SOX17, FOXA2, and CXCR4) lineages in 3D culture conditions were observed. Additionally, the osteogenic and adipogenic differentiation potential of WJ-MSCs over the time points 7 days, 14 days, and 28 days was also significantly increased in 3D culture groups. Our study demonstrates that stemness properties of WJ-MSCs were significantly enhanced in 3D cultures and ULA-based culture outperformed other methods with high pluripotency gene expression and enhanced differentiation potential. This study indicates the efficacy of 3D cultures to bridge the gap between 2D cell culture and animal models in regenerative medicine.

Priming strategies for controlling stem cell fate: Applications and challenges in dental tissue regeneration

Mesenchymal stromal cells (MSCs) have attracted intense interest in the field of dental tissue regeneration. Dental tissue is a popular source of MSCs because MSCs can be obtained with minimally invasive procedures. MSCs possess distinct inherent properties of self-renewal, immunomodulation, proangiogenic potential, and multilineage potency, as well as being readily available and easy to culture. However, major issues, including poor engraftment and low survival rates in vivo, remain to be resolved before large-scale application is feasible in clinical treatments. Thus, some recent investigations have sought ways to optimize MSC functions in vitro and in vivo. Currently, priming culture conditions, pretreatment with mechanical and physical stimuli, preconditioning with cytokines and growth factors, and genetic modification of MSCs are considered to be the main strategies; all of which could contribute to improving MSC efficacy in dental regenerative medicine. Research in this field has made tremendous progress and continues to gather interest and stimulate innovation. In this review, we summarize the priming approaches for enhancing the intrinsic biological properties of MSCs such as migration, antiapoptotic effect, proangiogenic potential, and regenerative properties. Challenges in current approaches associated with MSC modification and possible future solutions are also indicated. We aim to outline the present understanding of priming approaches to improve the therapeutic effects of MSCs on dental tissue regeneration.

3D Cell Culture Technology – A New Insight Into in Vitro Research – A Review

Most in vitro cell-based research is based on two-dimensional (2D) systems where growth and development take place on a flat surface, which does not reflect the natural environment of the cells. The imperfection and limitations of culture in 2D systems eventually led to the creation of three-dimensional (3D) culture models that more closely reproduce the actual conditions of physiological cell growth. Since the inception of 3D culture technology, many culture models have been developed, such as technologies of multicellular spheroids, organoids, and organs on chips in the technology of scaffolding, hydrogels, bio-printing and liquid media. In this review we will focus on the advantages and disadvantages of the 2D vs. 3D cell cultures technologies. We will also try to sum up available 3D culture systems and materials for building 3D scaffolds.

Comparison of Osteogenic Potentials of Dental Pulp and Bone Marrow Mesenchymal Stem Cells Using the New Cell Transplantation Platform, CellSaic, in a Rat Congenital Cleft-Jaw Model

Scaffolds stimulate cell proliferation and differentiation and play major roles in providing growth and nutrition factors in the repair of bone defects. We used the recombinant peptide Cellnest™ to prepare the three-dimensional stem cell complex, CellSaic, and evaluated whether CellSaic containing rat dental pulp stem cells (rDPSCs) was better than that containing rat bone marrow stem cells (rBMSCs). rDPSC-CellSaic or rBMSC-CellSaic, cultured with or without osteogenic induction medium, formed the experimental and control groups, respectively. Osteoblast differentiation was evaluated in vitro and transplanted into a rat model with a congenital jaw fracture. Specimens were collected and evaluated by microradiology and histological analysis. In the experimental group, the amount of calcium deposits, expression levels of bone-related genes (RUNX2, ALP, BSP, and COL1), and volume of mineralized tissue, were significantly higher than those in the control group (p < 0.05). Both differentiated and undifferentiated rDPSC-CellSaic and only the differentiated rBMSC-CellSaic could induce the formation of new bone tissue. Overall, rBMSC-CellSaic and rDPSC-CellSaic made with Cellnest™ as a scaffold, provide excellent support for promoting bone regeneration in rat mandibular congenital defects. Additionally, rDPSC-CellSaic seems a better source for craniofacial bone defect repair than rBMSC-CellSaic, suggesting the possibility of using DPSCs in bone tissue regenerative therapy.

Optimizing Conditions for Spheroid Formation of Dental Pulp Cells in Cell Culture

BACKGROUND/AIM

Spheroid formation is a well-known feature of stem/progenitor cells. Dental pulp cells (DPCs) cultured in serum-free medium can also form spheroids. However, the success rate varies largely depending on various factors. This study aimed to explore these factors and optimize the conditions.

MATERIALS AND METHODS

Primary DPCs were obtained from 6 wisdom teeth. Possible influencing factors including donor teeth, concentrations of the KnockOut Serum Replacement (KSR), seeding density (regarding surface and volume), passage and freezing were tested.

RESULTS

DPCs from all 6 donor teeth formed spheroids in serum-free medium. Number, size, and total area of spheroids varied among different donor teeth. Optimal concentration of the KSR and seeding densities also varied from tooth to tooth. Generally, high KSR and high cell density lead to better spheroid formation. However, very high KSR and cell density can also lead to cell death and the fusion of spheroids to irregular aggregates.

CONCLUSION

An initial setting can be recommended as: Serum-free MEM plus 10-15% KSR and seeding densities of 1-2×10⁵ cells/ml and 2×10⁵ cells/cm² These parameters provide a direction for optimizing the condition for obtaining spheroids from human DPCs.

Three-dimensional Spheroid Culture Enhances Multipotent Differentiation and Stemness Capacities of Human Dental Pulp-derived Mesenchymal Stem Cells by Modulating MAPK and NF-kB Signaling Pathways

BACKGROUND

Three-dimensional (3D) culture of mesenchymal stem cells has become an important research and development topic. However, comprehensive analysis of human dental pulp-derived mesenchymal stem cells (DPSCs) in 3D-spheroid culture remains unexplored. Thus, we evaluated the cellular characteristics, multipotent differentiation, gene expression, and related-signal transduction pathways of DPSCs in 3D-spheroid culture via magnetic levitation (3DM), compared with 2D-monolayer (2D) and 3D-aggregate (3D) cultures.

METHODS

The gross morphology and cellular ultrastructure were observed in the 2D, 3D, and 3DM experimental groups using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Surface markers and trilineage differentiation were evaluated using flow cytometry and staining analysis. Quantitative reverse transcription-polymerase chain reaction and immunofluorescence staining (IF) were performed to investigate the expression of differentiation and stemness markers. Signaling transduction pathways were evaluated using western blot analysis.

RESULTS

The morphology of cell aggregates and spheroids was largely influenced by the types of cell culture plates and initial cell seeding density. SEM and TEM experiments confirmed that the solid and firm structure of spheroids was quickly formed in the 3DM-medium without damaging cells. In addition, these three groups all expressed multilineage differentiation capabilities and surface marker expression. The trilineage differentiation capacities of the 3DM-group were significantly superior to the 2D and 3D-groups. The osteogenesis, angiogenesis, adipogenesis, and stemness-related genes were significantly enhanced in the 3D and 3DM-groups. The IF analysis showed that the extracellular matrix expression, osteogenesis, and angiogenesis proteins of the 3DM-group were significantly higher than those in the 2D and 3D-groups. Finally, 3DM-culture significantly activated the MAPK and NF-kB signaling transduction pathways and ameliorated the apoptosis effects of 3D-culture.

CONCLUSIONS

This study confirmed that 3DM-spheroids efficiently enhanced the therapeutic efficiency of DPSCs.

Comparison of 2- and 3-Dimensional Cultured Periodontal Ligament Stem Cells; a Pilot Study

This study compared the characteristics of periodontal ligament stem cells (PDLSCs) cultured using 3-dimensional (3D) versus conventional 2-dimensional (2D) methods. PDLSCs were cultured in either a 3D culture with a non-adhesive culture plate (Stemfit 3D®) or a conventional 2D culture using a 6-well plate. Morphology, viability, proliferation ability, and osteogenic differentiation were analyzed to characterize the differences induced in identical PDLSCs by 3D and 2D culture environments. In addition, gene expression was analyzed using RNA sequencing to further characterize the functional differences. The diameter and the viability of the 3D-cultured PDLSCs decreased over time, but the shape of the spheroid was maintained for 20 days. Although osteogenic differentiation occurred in both the 2D- and 3D-cultured PDLSCs, compared to the control group it was 20.8 and 1.6 higher in the 3D- and 2D-cultured cells, respectively. RNA sequencing revealed that PDLSCs cultured using 2D and 3D methods have different gene expression profiles. The viability of the 3D-cultured cells was decreased, but they showed superior osteogenic differentiation compared to 2D-cultured cells. Within the limitations of this study, the results demonstrate that the structure and function of PDLSCs are influenced by the cell culture method.

Distinct differences in hypoxic responses between human oral mucosa and skin fibroblasts in a 3D collagen matrix

The differences between oral mucosa and skin wound healing involving hypoxic responses of fibroblasts are poorly elucidated. In this study, we aimed to study the different hypoxic responses between oral and skin fibroblasts embedded in a three-dimensional (3D) collagen matrix to address the early stage of wound healing. Primary oral mucosa fibroblasts (OMFs) obtained from the retromolar area and skin fibroblasts (SFs) obtained from the abdomen were cultured in the 3D 'floating model' under either 21%, 5% or 1% O₂ for 2 days. Cell viability under hypoxia was higher in the OMFs than in the SFs. Collagen gel contraction was suppressed under hypoxic conditions in both fibroblasts, consistent with the reduction of alpha smooth muscle actin expression, except for SFs under 1% O₂. Subsequently, their gene expression profiles between 21 and 1% O₂ concentrations were compared via microarray technology, and the expression profiles of the extracellular matrix (ECM)-associated proteins, including matrix metalloproteinases and collagens, were evaluated. The OMFs were more susceptible to 1% O₂, and more of their genes were downregulated than the SFs'. Although the production and expression levels of ECM-associated proteins in both fibroblasts diminished under hypoxia, those levels in OMFs were significantly higher than those in SFs. In the case of single origin OMFs and SFs, our findings suggest that OMFs possess a higher baseline production capacity of several ECM-associated proteins than SFs, except type III collagen. The intrinsic hypoxic responses of OMFs may be attributed to a more favourable wound healing in oral mucosa.

In Vitro Characterization of Dental Pulp Stem Cells Cultured in Two Microsphere-Forming Culture Plates

Various three-dimensional (3D) culture methods have been introduced to overcome the limitations of in vitro culture and mimic in vivo conditions. This study aimed to evaluate two microsphere-forming culture methods and a monolayer culture method. We evaluated cell morphology, viability, osteo-, adipo-, and chondrogenic differentiation potential of dental pulp stem cells (DPSCs) cultured in 3D culture plates: ultra-low attachment (ULA) and U-bottomed StemFit 3D (SF) plates, and a two-dimensional (2D) monolayer plate. RNA sequencing (RNA-seq) revealed differentially expressed gene (DEG) profiles of the DPSCs. In contrast to an increasing pattern in the 2D group, cell viability in 3D groups (ULA and SF) showed a decreasing pattern; however, high multilineage differentiation was observed in both the 3D groups. RNA-seq showed significantly overexpressed gene ontology categories including angiogenesis, cell migration, differentiation, and proliferation in the 3D groups. Hierarchical clustering analysis revealed a similar DEG regulation pattern between the 3D groups; however, a comparatively different DEG was observed between the 2D and 3D groups. Taken together, this study shows that DPSCs cultured in microsphere-forming plates present superior multilineage differentiation capacities and demonstrate higher DEG expression in regeneration-related gene categories compared to that in DPSCs cultured in a conventional monolayer plate.

Impaired angiogenic differentiation of dental pulp stem cells during exposure to the resinous monomer triethylene glycol dimethacrylate

OBJECTIVE

Dental pulp stem cells (DPSCs) can differentiate into tissue specific lineages to support dental pulp regeneration after injuries. Triethylene glycol dimethacrylate (TEGDMA) is a widely used co-monomer in restorative dentistry with adverse effects on cellular metabolism. Aim of this study was to analyze the impact of TEGDMA on the angiogenic differentiation potential of DPSCs.

METHODS

DPSCs were characterized by flow cytometry. Short-term (max. 72h) cytotoxicity of TEGDMA was assessed by MTT assay. To evaluate TEGDMA effects on angiogenic differentiation, DPSCs were cultivated in angiogenic differentiation medium (ADM) in the presence or absence of short-term non-toxic TEGDMA concentrations (0.1mM and 0.25mM). Subsequently, angiogenic differentiation was analyzed by qRT-PCR analysis of mRNA markers and in vitro spheroid sprouting assays.

RESULTS

DPSCs treated with 0.25mM TEGDMA revealed downregulation of angiogenesis-related marker genes PECAM1 (max. 3.8-fold), VEGF-A (max. 2.4-fold) and FLT1 (max. 2.9-fold) compared to respective untreated control. In addition, a reduction of the sprouting potential of DPSCs cultured in the presence of 0.25mM TEGDMA was detectable. Larger spheroidal structures were detectable in the untreated control in comparison to cells treated with 0.25mM TEGDMA. In contrast, TEGDMA at 0.1mM was not affecting angiogenic potential in the investigated time period (up to 28 days).

SIGNIFICANCE

The results of the present study show that TEGDMA concentration dependently impair the angiogenic differentiation potential of DPSCs and may affect wound healing and the formation of granulation tissue.