Investigation of Human Dental Pulp Cells on a Potential Injectable Poly(lactic-co-glycolic acid) Microsphere Scaffold

Dental pulp regeneration strategies: A review of status quo and recent advances

Microorganisms, physical factors such as temperature or mechanical injury, and chemical factors such as free monomers from composite resin are the main causes of dental pulp diseases. Current clinical treatment methods for pulp diseases include the root canal therapy, vital pulp therapy and regenerative endodontic therapy. Regenerative endodontic therapy serves the purpose of inducing the regeneration of new functional pulp tissues through autologous revascularization or pulp tissue engineering. This article first discusses the current clinical methods and reviews strategies as well as the research outcomes regarding the pulp regeneration. Then the in vivo models, the prospects and challenges for regenerative endodontic therapy were further discussed.

Carbon Dot-Based Photo-Cross-Linked Gelatin Methacryloyl Hydrogel Enables Dental Pulp Regeneration: A Preliminary Study

An essential factor in tooth nutritional deficits and aberrant root growth is pulp necrosis. Removing inflammatory or necrotic pulp tissue and replacing it with an inert material are the most widely used therapeutic concepts of endodontic treatment. However, pulp loss can lead to discoloration, increased fracture risk, and the reinfection of the damaged tooth. It is now anticipated that the pulp-dentin complex will regenerate through a variety of application methods based on human dental pulp stem cells (hDPSC). In order to create a photo-cross-linked gelatinized methacrylate hydrogel, GelMA/EUO-CDs-E (ECE), that is biodegradable and injectable for application, we created a novel nanoassembly of ECE based on eucommia carbon dots (EUO-CDs) and epigallocatechin gallate (EGCG). We then loaded it onto gelatin methacryloyl (GelMA) hydrogel. We have evaluated the material and examined its in vivo and in vitro angiogenesis-promoting potential as well as its dentin differentiation-enabling characteristics. The outcomes of the experiment demonstrated that GelMA/ECE was favorable to cell proliferation and enhanced hDPSC's capacity for angiogenesis and dentin differentiation. The regeneration of vascular-rich pulp-like tissues was found to occur in vivo when hDPSC-containing GelMA/ECE was injected into cleaned human root segments (RS) for subcutaneous implantation in nude mice. This suggests that the injectable bioscaffold is appropriate for clinical use in pulp regenerative medicine.

Dental-derived stem cells in tissue engineering: the role of biomaterials and host response

Dental-derived stem cells (DSCs) are attractive cell sources due to their easy access, superior growth capacity and low immunogenicity. They can respond to multiple extracellular matrix signals, which provide biophysical and biochemical cues to regulate the fate of residing cells. However, the direct transplantation of DSCs suffers from poor proliferation and differentiation toward functional cells and low survival rates due to local inflammation. Recently, elegant advances in the design of novel biomaterials have been made to give promise to the use of biomimetic biomaterials to regulate various cell behaviors, including proliferation, differentiation and migration. Biomaterials could be tailored with multiple functionalities, e.g., stimuli-responsiveness. There is an emerging need to summarize recent advances in engineered biomaterials-mediated delivery and therapy of DSCs and their potential applications. Herein, we outlined the design of biomaterials for supporting DSCs and the host response to the transplantation.

Hydrogels for Oral Tissue Engineering: Challenges and Opportunities

Oral health is crucial to daily life, yet many people worldwide suffer from oral diseases. With the development of oral tissue engineering, there is a growing demand for dental biomaterials. Addressing oral diseases often requires a two-fold approach: fighting bacterial infections and promoting tissue growth. Hydrogels are promising tissue engineering biomaterials that show great potential for oral tissue regeneration and drug delivery. In this review, we present a classification of hydrogels commonly used in dental research, including natural and synthetic hydrogels. Furthermore, recent applications of these hydrogels in endodontic restorations, periodontal tissues, mandibular and oral soft tissue restorations, and related clinical studies are also discussed, including various antimicrobial and tissue growth promotion strategies used in the dental applications of hydrogels. While hydrogels have been increasingly studied in oral tissue engineering, there are still some challenges that need to be addressed for satisfactory clinical outcomes. This paper summarizes the current issues in the abovementioned application areas and discusses possible future developments.

Advances in Scaffolds Used for Pulp-Dentine Complex Tissue Engineering - A Narrative Review

Pulp necrosis in immature teeth disrupts root development and predisposes roots to fracture as a consequence of their thin walls and open apices. Regenerative endodontics is a developing treatment modality whereby necrotic pulps are replaced with newly formed healthy tissue inside the root canal. Many clinical studies have demonstrated the potential of this strategy to stimulate root maturation and apical root-end closure. However, clinical outcomes are patient-dependent and unpredictable. The development of predictable clinical protocols is achieved through the interplay of the three classical elements of tissue engineering, namely, stem cells, signaling molecules, and scaffolds. Scaffolds provide structural support for cells to adhere and proliferate and also regulate cell differentiation and metabolism. Hence, designing and fabricating an appropriate scaffold is a crucial step in tissue engineering. In this review, four main classes of scaffolds used to engineer pulp-dentine complexes, including bioceramic-based scaffolds, synthetic polymer-based scaffolds, natural polymer-based scaffolds, and composite scaffolds, are covered. Additionally, recent advances in the design, fabrication, and application of such scaffolds are analysed along with their advantages and limitations. Finally, the importance of vascular network establishment in the success of pulp-dentine complex regeneration and strategies used to create scaffolds to address this challenge are discussed.

Functional microspheres for tissue regeneration

As a new type of injectable biomaterials, functional microspheres have attracted increasing attention in tissue regeneration because they possess some advantageous properties compared to other biomaterials, including hydrogels. A variety of bio-inspired microspheres with unique structures and properties have been developed as cellular carriers and drug delivery vehicles in recent years. In this review, we provide a comprehensive summary of the progress of functional and biodegradable microspheres that have been used for tissue regeneration over the last two decades. First, we briefly introduce the biomaterials and general methods for microsphere fabrication. Next, we focus on the newly developed technologies for preparing functional microspheres, including macroporous microspheres, nanofibrous microspheres, hollow microspheres, core-shell structured microspheres, and surface-modified functional microspheres. After that, we discuss the application of functional microspheres for tissue regeneration, specifically for bone, cartilage, dental, neural, cardiac, and skin tissue regeneration. Last, we present our perspectives and future directions of functional microspheres as injectable carriers for the future advancement of tissue regeneration.

Scaffold-based developmental tissue engineering strategies for ectodermal organ regeneration

Tissue engineering (TE) is a multidisciplinary research field aiming at the regeneration, restoration, or replacement of damaged tissues and organs. Classical TE approaches combine scaffolds, cells and soluble factors to fabricate constructs mimicking the native tissue to be regenerated. However, to date, limited success in clinical translations has been achieved by classical TE approaches, because of the lack of satisfactory biomorphological and biofunctional features of the obtained constructs. Developmental TE has emerged as a novel TE paradigm to obtain tissues and organs with correct biomorphology and biofunctionality by mimicking the morphogenetic processes leading to the tissue/organ generation in the embryo. Ectodermal appendages, for instance, develop in vivo by sequential interactions between epithelium and mesenchyme, in a process known as secondary induction. A fine artificial replication of these complex interactions can potentially lead to the fabrication of the tissues/organs to be regenerated. Successful developmental TE applications have been reported, in vitro and in vivo, for ectodermal appendages such as teeth, hair follicles and glands. Developmental TE strategies require an accurate selection of cell sources, scaffolds and cell culture configurations to allow for the correct replication of the in vivo morphogenetic cues. Herein, we describe and discuss the emergence of this TE paradigm by reviewing the achievements obtained so far in developmental TE 3D scaffolds for teeth, hair follicles, and salivary and lacrimal glands, with particular focus on the selection of biomaterials and cell culture configurations.

hDPSC-laden GelMA microspheres fabricated using electrostatic microdroplet method for endodontic regeneration

The microsphere system has attracted considerable attention as a stem-cell delivery vehicle in regeneration medicine owing to its injectability, fast substance transfer ability, and mimicry of the three-dimensional native environment. However, suitable biomaterials for preparation of microspheres optimal for endodontic regeneration are still being explored. Owing to its excellent bioactivity and biodegradability, gelatin methacryloyl (GelMA) was used to fabricate hydrogel microspheres by the electrostatic microdroplet method, and the potential of GelMA microspheres applied in endodontic regeneration was studied. The average size of GelMA microspheres encapsulating human dental pulp stem cells (hDPSCs) was ~200 μm, and the Young's modulus was approximately 582.8 ± 66.0 Pa, which was close to that of the natural human dental pulp. The encapsulated hDPSCs could effectively adhere, spread, proliferate, and secrete extracellular matrix proteins in the microspheres, and tended to occupy the outer layer. Moreover, the cell-laden GelMA microsphere system could withstand cryopreservation, and the thawed cells exhibited normal functions. After subcutaneous implantation in a nude mouse model, more vascularized pulp-like tissues were generated in the cell-laden GelMA microsphere group compared with that in the cell-laden bulk GelMA group, and this was accompanied by a suitable degradation rate. The GelMA microspheres showed remarkable performances and great potential as cell delivery vehicles in endodontic regeneration.

Hydrogels and Dentin-Pulp Complex Regeneration: From the Benchtop to Clinical Translation

Dentin-pulp complex is a term which refers to the dental pulp (DP) surrounded by dentin along its peripheries. Dentin and dental pulp are highly specialized tissues, which can be affected by various insults, primarily by dental caries. Regeneration of the dentin-pulp complex is of paramount importance to regain tooth vitality. The regenerative endodontic procedure (REP) is a relatively current approach, which aims to regenerate the dentin-pulp complex through stimulating the differentiation of resident or transplanted stem/progenitor cells. Hydrogel-based scaffolds are a unique category of three dimensional polymeric networks with high water content. They are hydrophilic, biocompatible, with tunable degradation patterns and mechanical properties, in addition to the ability to be loaded with various bioactive molecules. Furthermore, hydrogels have a considerable degree of flexibility and elasticity, mimicking the cell extracellular matrix (ECM), particularly that of the DP. The current review presents how for dentin-pulp complex regeneration, the application of injectable hydrogels combined with stem/progenitor cells could represent a promising approach. According to the source of the polymeric chain forming the hydrogel, they can be classified into natural, synthetic or hybrid hydrogels, combining natural and synthetic ones. Natural polymers are bioactive, highly biocompatible, and biodegradable by naturally occurring enzymes or via hydrolysis. On the other hand, synthetic polymers offer tunable mechanical properties, thermostability and durability as compared to natural hydrogels. Hybrid hydrogels combine the benefits of synthetic and natural polymers. Hydrogels can be biofunctionalized with cell-binding sequences as arginine-glycine-aspartic acid (RGD), can be used for local delivery of bioactive molecules and cellularized with stem cells for dentin-pulp regeneration. Formulating a hydrogel scaffold material fulfilling the required criteria in regenerative endodontics is still an area of active research, which shows promising potential for replacing conventional endodontic treatments in the near future.

Injectable Highly Tunable Oligomeric Collagen Matrices for Dental Tissue Regeneration

Current stem cell transplantation approaches lack efficacy, because they limit cell survival and retention and, more importantly, lack a suitable cellular niche to modulate lineage-specific differentiation. Here, we evaluate the intrinsic ability of type I oligomeric collagen matrices to modulate dental pulp stem cells (DPSCs) endothelial and odontogenic differentiation as a potential stem cell-based therapy for regenerative endodontics. DPSCs were encapsulated in low-stiffness (235 Pa) and high-stiffness (800 Pa) oligomeric collagen matrices and then evaluated for long-term cell survival, as well as endothelial and odontogenic differentiation following in vitro cell culture. Moreover, the effect of growth factor incorporation, i.e., vascular endothelial growth factor (VEGF) into 235 Pa oligomeric collagen or bone morphogenetic protein (BMP2) into the 800 Pa oligomeric collagen counterpart on endothelial or odontogenic differentiation of encapsulated DPSCs was investigated. DPSCs-laden oligomeric collagen matrices allowed long-term cell survival. Real time polymerase chain reaction (RT-PCR) data showed that the DPSCs cultured in 235 Pa matrices demonstrated an increased expression of endothelial markers after 28 days, and the effect was enhanced upon VEGF incorporation. There was a significant increase in alkaline phosphatase (ALP) activity at Day 14 in the 800 Pa DPSCs-laden oligomeric collagen matrices, regardless of BMP2 incorporation. However, Alizarin S data demonstrated higher mineralization by Day 21 and the effect was amplified in BMP2-modified matrices. Herein, we present key data that strongly support future research aimed at clinical translation of an injectable oligomeric collagen system for delivery and fate regulation of DPSCs to enable pulp and dentin regeneration at specific locations of the root canal system.

Polymer-Based Instructive Scaffolds for Endodontic Regeneration

The challenge of endodontic regeneration is modulated by clinical conditions which determine five kinds of tissue requirements: pulp connective-tissue formation, dentin formation, revascularization, reinnervation and radicular edification. Polymer scaffolds constitute keystone of the different endodontic regenerative strategies. Indeed, scaffolds are crucial for carrying active molecules and competent cells which optimize the regeneration. Hydrogels are very beneficial for controlling viscosity and porosity of endodontic scaffolds. The nanofibrous and microporous scaffolds mimicking extracellular matrix are also of great interest for promoting dentin-pulp formation. Two main types of polymer scaffolds are highlighted: collagen and fibrin. Collagen scaffolds which are similar to native pulp tissue, are adequate for pulp connective tissue formation. Functionnalization by active biomolecules as BMP, SDF-1, G-CSF enhances their properties. Fibrin or PRF scaffolds present the advantage of promoting stem cell differentiation and concomitant revascularisation. The choice of the type of polymers (polypeptide, PCL, chitosan) can depend on its ability to deliver the active biomolecule or to build as suitable hydrogel as possible. Since 2010s, proposals to associate different types of polymers in a same scaffold have emerged for adding advantages or for offsetting a disadvantage of a polymer. Further works would study the synergetic effects of different innovative polymers composition.

Novel Calcium Phosphate Cement with Metformin-Loaded Chitosan for Odontogenic Differentiation of Human Dental Pulp Cells

Metformin is an old and widely accepted first-line drug for treating type 2 diabetes. Our previous studies demonstrate that metformin can stimulate the osteo/odontogenic differentiation of human-induced pluripotent stem cell-derived mesenchymal stem cells and human dental pulp cells (DPCs). Due to the rapid dilution of metformin from the defect area, the aim of this study was to develop a drug delivery system with controlled release of metformin to promote cell viability and odontogenic differentiation of DPCs favoring dentin regeneration. Calcium phosphate cement (CPC) containing chitosan and metformin as a scaffold was synthesized. DPCs were seeded onto the scaffold, and the viability and proliferation were evaluated at several time points. For osteogenic differentiation analysis, alkaline phosphatase (ALP) activity was tested, cells were stained with Alizarin Red, and the expression of odontogenic markers was evaluated by real-time polymerase chain reaction. DPCs remained viable and attached well to the CPC-chitosan composite scaffold. Moreover, the addition of metformin to the CPC-chitosan composite did not adversely affect cell proliferation, compared to that of CPC control. Our data further revealed that the novel CPC-chitosan-metformin composite enhanced the odontogenic differentiation of DPCs, as evidenced by higher ALP activity, elevated expression of odontoblastic markers, and strong mineral deposition. These results suggest that the new CPC-chitosan-metformin composite is a highly promising scaffold with the potential for tissue engineering applications including dentin regeneration.

Metformin Enhances the Differentiation of Dental Pulp Cells into Odontoblasts by Activating AMPK Signaling

INTRODUCTION

Metformin is a first-line drug for treating type 2 diabetes that regulates the differentiation of mesenchymal stem cells. Its effects on human dental pulp cells (DPCs) remain unknown. This study aimed to investigate the effects of metformin on the proliferation and differentiation of DPCs.

METHODS

A live/dead viability assay kit was used to examine the effects of metformin on the cell viability of DPCs. Cell proliferation was analyzed using a cell counting kit (CCK-8; Dojindo, Tokyo, Japan). Levels of phosphorylated and unphosphorylated adenosine 5'-monophosphate-activated protein kinase (AMPK) were quantified by Western blot analysis in response to metformin and the AMPK signaling inhibitor Compound C (EMD Chemicals, San Diego, CA). The effects of Compound C on the metformin-induced odontoblast differentiation of DPCs were determined by alkaline phosphatase activity assay and von Kossa staining, and the expression of odontoblastic markers was evaluated by reverse-transcription polymerase chain reaction analysis.

RESULTS

DPCs exhibited mesenchymal stem cell characteristics using flow cytometry. Different doses of metformin were shown to be cytocompatible with DPCs, yielding >90% cell viability. None of the concentrations of metformin up to 50 μmol/L affected cell proliferation. The Western blot assay showed that DPCs express functional organic cation transporter 1, a transmembrane protein that mediates the intracellular uptake of metformin. Metformin significantly activated the AMPK pathway in a dose-dependent manner. In addition, it stimulated alkaline phosphatase activity; enhanced mineralized nodule formation; and increased the expression of odontoblastic markers including dentin sialophosphoprotein, dentin matrix protein 1, runt-related transcription factor 2, and osteocalcin. Moreover, pretreatment with Compound C, a specific AMPK inhibitor, markedly reversed metformin-induced odontoblastic differentiation and cell mineralization.

CONCLUSIONS

This study shows that metformin can induce DPC differentiation and mineralization in an AMPK-dependent manner and that this well-tolerated antidiabetic drug has potential in regenerative endodontics as well as in other regenerative applications.