Aggregation of human dental pulp cells into 3D spheroids enhances their migration ability after reseeding

Tissue engineering approaches for dental pulp regeneration: The development of novel bioactive materials using pharmacological epigenetic inhibitors

The drive for minimally invasive endodontic treatment strategies has shifted focus from technically complex and destructive root canal treatments towards more conservative vital pulp treatment. However, novel approaches to maintaining dental pulp vitality after disease or trauma will require the development of innovative, biologically-driven regenerative medicine strategies. For example, cell-homing and cell-based therapies have recently been developed in vitro and trialled in preclinical models to study dental pulp regeneration. These approaches utilise natural and synthetic scaffolds that can deliver a range of bioactive pharmacological epigenetic modulators (HDACis, DNMTis, and ncRNAs), which are cost-effective and easily applied to stimulate pulp tissue regrowth. Unfortunately, many biological factors hinder the clinical development of regenerative therapies, including a lack of blood supply and poor infection control in the necrotic root canal system. Additional challenges include a need for clinically relevant models and manufacturing challenges such as scalability, cost concerns, and regulatory issues. This review will describe the current state of bioactive-biomaterial/scaffold-based engineering strategies to stimulate dentine-pulp regeneration, explicitly focusing on epigenetic modulators and therapeutic pharmacological inhibition. It will highlight the components of dental pulp regenerative approaches, describe their current limitations, and offer suggestions for the effective translation of novel epigenetic-laden bioactive materials for innovative therapeutics.

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.

Cellulosic/Polyvinyl Alcohol Composite Hydrogel: Synthesis, Characterization and Applications in Tissue Engineering

The biomedical field still requires composite materials for medical devices and tissue engineering model design. As part of the pursuit of non-animal and non-proteic scaffolds, we propose here a cellulose-based material. In this study, 9%, 18% and 36% dialdehyde-functionalized microcrystalline celluloses (DAC) were synthesized by sodium periodate oxidation. The latter was subsequently coupled to PVA at ratios 1:2, 1:1 and 2:1 by dissolving in N-methyl pyrrolidone and lithium chloride. Moulding and successive rehydration in ethanol and water baths formed soft hydrogels. While oxidation effectiveness was confirmed by dialdehyde content determination for all DAC, we observed increasing hydrolysis associated with particle fragmentation. Imaging, FTIR and XDR analysis highlighted an intertwined DAC/PVA network mainly supported by electrostatic interactions, hemiacetal and acetal linkage. To meet tissue engineering requirements, an interconnected porosity was optimized using 0-50 µm salts. While the role of DAC in strengthening the hydrogel was identified, the oxidation ratio of DAC showed no distinct trend. DAC 9% material exhibited the highest indirect and direct cytocompatibility creating spheroid-like structures. DAC/PVA hydrogels showed physical stability and acceptability in vivo that led us to propose our DAC 9%/PVA based material for soft tissue graft application.

Dental-Derived Mesenchymal Stem Cells: State of the Art

Mesenchymal stem cells (MSCs) could be identified in mammalian teeth. Currently, dental-derived MSCs (DMSCs) has become a collective term for all the MSCs isolated from dental pulp, periodontal ligament, dental follicle, apical papilla, and even gingiva. These DMSCs possess similar multipotent potential as bone marrow-derived MSCs, including differentiation into cells that have the characteristics of odontoblasts, cementoblasts, osteoblasts, chondrocytes, myocytes, epithelial cells, neural cells, hepatocytes, and adipocytes. Besides, DMSCs also have powerful immunomodulatory functions, which enable them to orchestrate the surrounding immune microenvironment. These properties enable DMSCs to have a promising approach in injury repair, tissue regeneration, and treatment of various diseases. This review outlines the most recent advances in DMSCs' functions and applications and enlightens how these advances are paving the path for DMSC-based therapies.

Physically-cross-linked poly(vinyl alcohol) cell culture plate coatings facilitate preservation of cell-cell interactions, spheroid formation, and stemness

We employed aqueous solutions of highly-hydrolyzed (>99+%) poly(vinyl alcohol), PVA, to coat plastic dishes as a method to efficiently induce three-dimensional (3D) culturing of cells. The coatings were prepared by simple evaporation of 3 wt/vol% solutions of PVA in water and require no additional processing steps after air drying under sterile conditions. The coating allows spheroids to form in solution. Spheroid formation is usually preferable to two-dimensional (2D) culturing as it creates a more realistic ex vivo model of some human tissues and tumors. Using PVA-coated cell culture plates, we demonstrated that we can grow reproducibly sized spheroids using several human glioma cell lines, including LN229, U87 MG, and Gli36, and the embryonic kidney cell line, 293T. Spheroids formed on PVA-coated plates grow as well as on other commercially-available, low-attachment plates, and have excellent optical imaging properties. As spheroids, LN229 cells express markers of cancer stem cells. Finally, we confirmed that spheroids generated on PVA-coated plates are sensitive to molecular perturbations, as increased expression of the cell adhesion molecule PTPμ significantly increased the size of spheroids. The PVA hydrogel layer is an effective tool for creating a more realistic ex vivo culture system than traditional 2D culture and can be used to generate cell spheroids for potential application in drug screening and personalized medicine for diseases such as cancer.

Spheroid formation of human keratinocyte: Balancing between cell-substrate and cell-cell interaction

BACKGROUND

The formation of spheroids is tightly regulated by intrinsic cell-cell and cell-substrate interactions.

OBJECTIVE

The chitosan (CS)-coating was applied to investigate the driven force directed the spheroid formation.

METHODS

The effects of CS on cell functions were studied. Atomic force microscopy was employed to measure the cell- biomaterial interplay at single cell level.

RESULTS

HaCaT cells shifted from their flattened sheet to a compact 3D spheroidal morphology when increasing CS-coating concentration. The proliferative capacity of HaCaT was preserved in the spheroid. The expression and activation of integrin β1 (ITGB1) were enhanced on CS modified surfaces, while the active to total ratio of ITGB1 was decreased. The adhesive force of a single HaCaT cell to the tissue culture plate (TCP) was 4.84±0.72 nN. It decreased on CS-coated surfaces as CS concentration increased, from 2.16±0.26 nN to 0.96±0.17 nN. The adhesive force between the single HaCaT cell to its neighbor cell increased as CS concentration increased, from 1.15±0.09 nN to 2.60±0.51 nN.

CONCLUSIONS

Conclusively, the decreased cell- substrate adhesion was the main driven force in the spheroid formation. This finding might serve as a design criterion for biomaterials facilitating the formation of epithelial spheroids.

Contraction dynamics of dental pulp cell rod microtissues

OBJECTIVES

The factors that contribute to the morphological changes of dental pulp cell-derived microtissues are unknown. Here, we investigated the contraction dynamics of rod-shaped microtissues derived from dental pulp cells and examined the underlying cell signaling pathways.

METHODS

Human dental pulp cells were seeded into agarose molds to assemble into rod-shaped microtissues. Resazurin- and tetrazolium-based cytotoxicity assays, Live/Dead staining, and hematoxylin and eosin staining for histological evaluation of rods were performed. Rod contraction was evaluated and measured for a period of 10 days. The role of TGF-β, phosphoinositide 3-kinase (PI3K)/AKT, and mitogen-activated protein kinase (MAPK) signaling pathway was analyzed.

RESULTS

Dental pulp cells readily assembled into rods, maintaining the geometric shape for 48 h. Following this period, they condensed to form stable spheroidal structures that remained vital for 10 days from seeding. Inhibition of phosphoinositide 3-kinase signaling pathway by LY294002 significantly prolonged the diminution in the length of rods formed by dental pulp cells. TGF-β and pharmacological inhibition of TGF-β signaling did not show pronounced effects.

CONCLUSION

Overall, dental pulp cells readily formed rod-shaped patterns of microtissues which, over a period of time, condensed into more stable spheroidal structures. Hence, technologies like bioprinting, using direct fabrication of microtissues need to consider the contraction dynamics.

CLINICAL RELEVANCE

The field of regenerative endodontology will benefit from our findings as it can be applied as a novel platform to test the impact of pharmacological agents, biomaterials, and regenerative approaches including bioprinting.