Modulation of Dental Pulp Stem Cell Odontogenesis in a Tunable PEG-Fibrinogen Hydrogel System

Guidance for evaluating biomaterials' properties and biological potential for dental pulp tissue engineering and regeneration research

BACKGROUND

Dental pulp regeneration is a complex and advancing field that requires biomaterials capable of supporting the pulp's diverse functions, including immune defense, sensory perception, vascularization, and reparative dentinogenesis. Regeneration involves orchestrating the formation of soft connective tissues, neurons, blood vessels, and mineralized structures, necessitating materials with tailored biological and mechanical properties. Numerous biomaterials have entered clinical practice, while others are being developed for tissue engineering applications. The composition and a broad range of material properties, such as surface characteristics, degradation rate, and mechanical strength, significantly influence cellular behavior and tissue outcomes. This underscores the importance of employing robust evaluation methods and ensuring precise and comprehensive reporting of findings to advance research and clinical translation.

AIMS

This article aims to present the biological foundations of dental pulp tissue engineering alongside potential testing methodologies and their advantages and limitations. It provides guidance for developing research protocols to evaluate the properties of biomaterials and their influences on cell and tissue behavior, supporting progress toward effective dental pulp regeneration strategies.

Preparation and characterization of bovine dental pulp-derived extracellular matrix hydrogel for regenerative endodontic applications: an in vitro study

BACKGROUND

The use of biological scaffolds in regenerative endodontics has gained much attention in recent years. The search for a new biomimetic scaffold that contains tissue-specific cell homing factors could lead to more predictable tissue regeneration. The aim of this study was to prepare and characterize decellularized bovine dental pulp-derived extracellular matrix (P-ECM) hydrogels for regenerative endodontic applications.

METHODS

Freshly extracted bovine molar teeth were collected. Bovine dental pulp tissues were harvested, and stored at -40º C. For decellularization, a 5-day protocol was implemented incorporating trypsin/EDTA, deionized water and DNase treatment. Decellularization was evaluated by DNA quantification and histological examination to assess collagen and glycosaminoglycans (GAGs) content. This was followed by the preparation of P-ECM hydrogel alone or combined with hyaluronic acid gel (P-ECM + HA). The fabricated scaffolds were then characterized using protein quantification, hydrogel topology and porosity, biodegradability, and growth factor content using Enzyme-linked immunosorbent assay (ELISA): transforming growth factor beta-1(TGF-β1), basic fibroblast growth factor (bFGF), bone morphogenetic protein 2 (BMP-2) and vascular endothelial growth factor (VEGF).

RESULTS

Decellularization was histologically confirmed, and DNA content was below (50 ng/mg tissue). P-ECM hydrogel was prepared with a final ECM concentration of 3.00 mg/ml while P-ECM + HA hydrogel was prepared with a final ECM concentration of 1.5 mg/ml. Total protein content in P-ECM hydrogel was found to be (439.0 ± 123.4 µg/µl). P-ECM + HA showed sustained protein release while the P-ECM group showed gradual decreasing release. Degradation was higher in P-ECM + HA which had a significantly larger fiber diameter, while P-ECM had a larger pore area percentage. ELISA confirmed the retention and release of growth factors where P-ECM hydrogel had higher BMP-2 release, while P-ECM + HA had higher release of TGF-β1, bFGF, and VEGF.

CONCLUSIONS

Both P-ECM and P-ECM + HA retained their bioactive properties demonstrating a potential role as functionalized scaffolds for regenerative endodontic procedures.

The role of biophysical cues and their modulated exosomes in dental diseases: from mechanism to therapy

Dental diseases such as caries and periodontitis have been common public health problems. Dental disease treatment can be achieved through stem cell-based dental regeneration. Biophysical cues determine the fate of stem cells and govern the success of dental regeneration. Some studies have manifested exosomes derived from stem cells could not only inherit biophysical signals in microenvironment but also evade some issues in the treatment with stem cells. Nowadays, biophysical cue-regulated exosomes become another promising therapy in dental regenerative medicine. However, methods to improve the efficacy of exosome therapy and the underlying mechanisms are still unresolved. In this review, the association between biophysical cues and dental diseases was summarized. We retrospected the role of exosomes regulated by biophysical cues in curing dental diseases and promoting dental regeneration. Our research also delved into the mechanisms by which biophysical cues control the biogenesis, release, and uptake of exosomes, as well as potential methods to enhance the effectiveness of exosomes. The aim of this review was to underscore the important place biophysical cue-regulated exosomes occupy in the realm of dentistry, and to explore novel targets for dental diseases.

Dental pulp stem cells - A basic research and future application in regenerative medicine

Dental pulp is a valuable and accessible source of stem cells (DPSCs) with characteristics similar to mesenchymal stem cells. DPSCs can regenerate a range of tissues and their potential for clinical application in regenerative medicine is promising. DPSCs have been found to express low levels of Class II HLA-DR (MHC) molecules, making them potential candidates for allogeneic transplantation without matching the donor's tissue. Research on the correlation between non-coding RNAs (ncRNAs) and human dental pulp stem cells (DPSCs) provides promising insights into the use of these cells in clinical settings for a wide range of medical conditions. It is possible to use a number of ncRNAs in order to restore the functional role of downregulated ncRNAs that are correlated with osteoblastogenesis, or to suppress the functional role of overexpressed ncRNAs associated with osteoclast differentiation in some cases.

Controlled release of vancomycin from PEGylated fibrinogen polyethylene glycol diacrylate hydrogel

Surgical site infection (SSI) is a common issue post-surgery which often prolongs hospitalization and can lead to serious complications such as sternal wound infection following cardiac surgery via median sternotomy. Controlled release of suitable antibiotics could allow maximizing drug efficacy and safety, and therefore achieving a desired therapeutic response. In this study, we have developed a vancomycin laden PEGylated fibrinogen-polyethylene glycol diacrylate (PF-PEGDA) hydrogel system that can release vancomycin at a controlled and predictable rate to be applied in SSI prevention. Two configurations were developed to study effect of the hydrogel on drug release, namely, vancomycin laden hydrogel and vancomycin solution on top of blank hydrogel. The relationship between the rigidity of the hydrogel and drug diffusion was found to comply with a universal power law, i.e., softer hydrogels result in a greater diffusion coefficient hence faster release rate. Besides, vancomycin laden hydrogels exhibited burst release, whereas the vancomycin solution on top of blank hydrogels exhibited lag release. A mathematical model was developed to simulate vancomycin permeation through the hydrogels. The permeation of vancomycin can be predicted accurately by using the mathematical model, which provided a useful tool to customize drug loading, hydrogel thickness and stiffness for personalized medication to manage SSI. To evaluate the potential of hydrogels for bone healing applications in cardiovascular medicine, we performed a proof-of-concept median sternotomy in rabbits and applied the hydrogels. The hydrogel formulations accelerated the onset of osteo-genetic processes in rabbits, demonstrating its potential to be used in human.

Modulus-dependent effects on neurogenic, myogenic, and chondrogenic differentiation of human mesenchymal stem cells in three-dimensional hydrogel cultures

Human mesenchymal stromal cells (hMSCs) are of significant interest as a renewable source of therapeutically useful cells. In tissue engineering, hMSCs are implanted within a scaffold to provide enhanced capacity for tissue repair. The present study evaluates how mechanical properties of that scaffold can alter the phenotype and genotype of the cells, with the aim of augmenting hMSC differentiation along the myogenic, neurogenic or chondrogenic linages. The hMSCs were grown three-dimensionally (3D) in a hydrogel comprised of poly(ethylene glycol) (PEG)-conjugated to fibrinogen. The hydrogel's shear storage modulus (G'), which was controlled by increasing the amount of PEG-diacrylate cross-linker in the matrix, was varied in the range of 100-2000 Pascal (Pa). The differentiation into each lineage was initiated by a defined culture medium, and the hMSCs grown in the different modulus hydrogels were characterized using gene and protein expression. Materials having lower storage moduli (G' = 100 Pa) exhibited more hMSCs differentiating to neurogenic lineages. Myogenesis was favored in materials having intermediate modulus values (G' = 500 Pa), whereas chondrogenesis was favored in materials with a higher modulus (G' = 1000 Pa). Enhancing the differentiation pathway of hMSCs in 3D hydrogel scaffolds using simple modifications to mechanical properties represents an important achievement toward the effective application of these cells in tissue engineering.

Mesenchymal stromal cell exosomes enhance dental pulp cell functions and promote pulp-dentin regeneration

Mesenchymal stromal/stem cell (MSC) therapies are currently being explored for dental pulp regeneration. As the therapeutic effects of MSCs in tissue repair are mediated mainly through the release of extracellular vesicles (EVs) including exosomes, we investigated here the cellular processes and molecular mechanisms modulated by MSC exosomes in dental pulp regeneration. Using dental pulp cell (DPC) cultures, we demonstrated that MSC exosomes could increase DPC migration, proliferation, and odontogenic differentiation. The enhancement of these cellular processes was mediated through exosomal CD73-mediated adenosine receptor activation of AKT and ERK signaling. Consistent with these observations, MSC exosomes increased the expression of dentin matrix proteins and promoted the formation of dentin-like tissue and bridge-like structures in a rat pulp defect model. These effects were comparable to that of mineral trioxide aggregate (MTA) treatment. MSC exosomes also yielded recellularized pulp-dentin tissues in the root canal of endodontically-treated human premolars, following subcutaneous implantation in the mouse dorsum. Together, our findings suggest that MSC exosomes could exert a multi-faceted effect on DPC functions including migration, proliferation and odontogenic differentiation to promote dental pulp regeneration. This study provides the basis for development of MSC exosomes as a cell-free MSC therapeutic alternative for pulp-dentin regeneration.

Fabrication and characterization of a novel injectable human amniotic membrane hydrogel for dentin-pulp complex regeneration

OBJECTIVE

Injectable biomaterials that can completely fill the root canals and provide an appropriate environment will have potential application for pulp regeneration in endodontics. This study aimed to fabricate and characterize a novel injectable human amniotic membrane (HAM) hydrogel scaffold crosslinked with genipin, enabling the proliferation of Dental Pulp Stem Cells (DPSCs) and optimizing pulp regeneration.

METHODS

HAM extracellular matrix (ECM) hydrogels (15, 22.5, and 30 mg/ml) crosslinked with different genipin concentrations (0, 0.1, 0.5, 1, 5, and 10 mM) were evaluated for mechanical properties, tooth discoloration, cell viability, and proliferation of DPSCs. The hydrogels were subcutaneously injected in rats to assess their immunogenicity. The hydrogels were applied in a root canal model and subcutaneously implanted in rats to determine their regenerative potential for eight weeks, and histological and immunostaining analyses were performed.

RESULTS

Hydrogels crosslinked with low genipin concentration demonstrated low tooth discoloration, but 0.1 mM genipin crosslinked hydrogels were excluded due to their unfavourable mechanical properties. The degradation ratio was lower in hydrogels crosslinked with 0.5 mM genipin. The 30 mg/ml-0.5 mM crosslinked hydrogel exhibited a microporous structure, and the modulus of elasticity was 1200 PA. In vitro, cell culture showed maximum viability and proliferation in 30 mg/ml-0.5 mM crosslinked hydrogel. All groups elicited minimum immunological responses, and highly vascularized pulp-like tissue was formed in human tooth roots in both groups with/without DPSCs.

SIGNIFICANCE

Genipin crosslinking improved the biodegradability of injectable HAM hydrogels and conferred higher biocompatibility. Hydrogels encapsulated with DPSCs can support stem cell viability and proliferation. In addition, highly vascularized pulp-like tissue formation by this biomaterial displayed potential for pulp regeneration.

New Challenges and Prospective Applications of Three-Dimensional Bioactive Polymeric Hydrogels in Oral and Craniofacial Tissue Engineering: A Narrative Review

Regenerative medicine, and dentistry offers enormous potential for enhancing treatment results and has been fueled by bioengineering breakthroughs over the previous few decades. Bioengineered tissues and constructing functional structures capable of healing, maintaining, and regenerating damaged tissues and organs have had a broad influence on medicine and dentistry. Approaches for combining bioinspired materials, cells, and therapeutic chemicals are critical in stimulating tissue regeneration or as medicinal systems. Because of its capacity to maintain an unique 3D form, offer physical stability for the cells in produced tissues, and replicate the native tissues, hydrogels have been utilized as one of the most frequent tissue engineering scaffolds during the last twenty years. Hydrogels' high water content can provide an excellent conditions for cell viability as well as an architecture that mimics real tissues, bone, and cartilage. Hydrogels have been used to enable cell immobilization and growth factor application. This paper summarizes the features, structure, synthesis and production methods, uses, new challenges, and future prospects of bioactive polymeric hydrogels in dental and osseous tissue engineering of clinical, exploring, systematical and scientific applications.

The development of a dental light curable PRFe-loaded hydrogel as a potential scaffold for pulp-dentine complex regeneration: An in vitro study

AIM

The study aimed to develop a bicomponent bioactive hydrogel formed in situ and enriched with an extract of platelet-rich fibrin (PRFe) and to assess its potential for use in pulp-dentine complex tissue engineering via cell homing.

METHODOLOGY

A bicomponent hydrogel based on photo-activated naturally derived polymers, methacrylated chitosan (ChitMA) and methacrylated collagen (ColMA), plus PRFe was fabricated. The optimized formulation of PRFe-loaded bicomponent hydrogel was determined by analysing the mechanical strength, swelling ratio and cell viability simultaneously. The physical, mechanical, rheological and morphological properties of the optimal hydrogel with and without PRFe were determined. Additionally, MTT, phalloidin/DAPI and live/dead assays were carried out to compare the viability, cytoskeletal morphology and migration ability of stem cells from the apical papilla (SCAP) within the developed hydrogels with and without PRFe, respectively. To further investigate the effect of PRFe on the differentiation of encapsulated SCAP, alizarin red S staining, RT-PCR analysis and immunohistochemical detection were performed. Statistical significance was established at p <  .05.

RESULTS

The optimized formulation of PRFe-loaded bicomponent hydrogel can be rapidly photocrosslinked using available dental light curing units. Compared to bicomponent hydrogels without PRFe, the PRFe-loaded hydrogel exhibited greater viscoelasticity and higher cytocompatibility to SCAP. Moreover, it promoted cell proliferation and migration in vitro. It also supported the odontogenic differentiation of SCAP as evidenced by its promotion of biomineralization and upregulating the gene expression for ALP, COL I, DSPP and DMP1 as well as facilitated angiogenesis by enhancing VEGFA gene expression.

CONCLUSIONS

The new PRFe-loaded ChitMA/ColMA hydrogel developed within this study fulfils the criteria of injectability, cytocompatibility, chemoattractivity and bioactivity to promote odontogenic differentiation, which are fundamental requirements for scaffolds used in pulp-dentine complex regeneration via cell-homing approaches.

Research Advances on Hydrogel-Based Materials for Tissue Regeneration and Remineralization in Tooth

Tissue regeneration and remineralization in teeth is a long-term and complex biological process, including the regeneration of pulp and periodontal tissue, and re-mineralization of dentin, cementum and enamel. Suitable materials are needed to provide cell scaffolds, drug carriers or mineralization in this environment. These materials need to regulate the unique odontogenesis process. Hydrogel-based materials are considered good scaffolds for pulp and periodontal tissue repair in the field of tissue engineering due to their inherent biocompatibility and biodegradability, slow release of drugs, simulation of extracellular matrix, and the ability to provide a mineralized template. The excellent properties of hydrogels make them particularly attractive in the research of tissue regeneration and remineralization in teeth. This paper introduces the latest progress of hydrogel-based materials in pulp and periodontal tissue regeneration and hard tissue mineralization and puts forward prospects for their future application. Overall, this review reveals the application of hydrogel-based materials in tissue regeneration and remineralization in teeth.

Regenerating the Dental Pulp-Scaffold Materials and Approaches

Novel technologies and platforms have allowed significant breakthroughs in dental pulp tissue engineering. The development of injectable scaffolds that can be combined with stem cells, growth factors, or other bioactive compounds has enabled the regeneration of functional dental pulps able to secrete dentin in preclinical and clinical studies. Similarly, cell-homing technologies and scaffold-free strategies aim to modulate dental pulp self-regeneration mediated by resident stem cells and can evade some of the technical challenges related to cell-based tissue engineering strategies. This article will discuss emerging technologies and platforms for the clinical applications of dental pulp tissue engineering.

In-vitro models of biocompatibility testing for restorative dental materials: From 2D cultures to organs on-a-chip

Dental caries is a biofilm-mediated, diet-modulated, multifactorial and dynamic disease that affects more than 90% of adults in Western countries. The current treatment for decayed tissue is based on using materials to replace the lost enamel or dentin. More than 500 million dental restorations are placed annually worldwide, and materials used for these purposes either directly or indirectly interact with dentin and pulp tissues. The development and understanding of the effects of restorative dental materials are based on different in-vitro and in-vivo tests, which have been evolving with time. In this review, we first discuss the characteristics of the tooth and the dentin-pulp interface that are unique for materials testing. Subsequently, we discuss frequently used in-vitro tests to evaluate the biocompatibility of dental materials commonly used for restorative procedures. Finally, we present our perspective on the future directions for biological research on dental materials using tissue engineering and organs on-a-chip approaches. STATEMENT OF SIGNIFICANCE: Dental caries is still the most prevalent infectious disease globally, requiring more than 500 million restorations to be placed every year. Regrettably, the failure rates of such restorations are still high. Those rates are partially based on the fact that current platforms to test dental materials are somewhat inaccurate in reproducing critical components of the complex oral microenvironment. Thus, there is a collective effort to develop new materials while evolving the platforms to test them. In this context, the present review critically discusses in-vitro models used to evaluate the biocompatibility of restorative dental materials and brings a perspective on future directions for tissue-engineered and organs-on-a-chip platforms for testing new dental materials.

A critical analysis of research methods and biological experimental models to study pulp regeneration

With advances in knowledge and treatment options, pulp regeneration is now a clear objective in clinical dental practice. For this purpose, many methodologies have been developed in attempts to address the putative questions raised both in research and in clinical practice. In the first part of this review, laboratory‐based methods will be presented, analysing the advantages, disadvantages, and benefits of cell culture methodologies and ectopic/semiorthotopic animal studies. This will also demonstrate the need for alignment between two‐dimensional and three‐dimensional laboratory techniques to accomplish the range of objectives in terms of cell responses and tissue differentiation. The second part will cover observations relating to orthotopic animal studies, describing the current models used for this purpose and how they contribute to the translation of regenerative techniques to the clinic.

Materials for Dentoalveolar Bioprinting: Current State of the Art

Although current treatments can successfully address a wide range of complications in the dentoalveolar region, they often still suffer from drawbacks and limitations, resulting in sub-optimal treatments for specific problems. In recent decades, significant progress has been made in the field of tissue engineering, aiming at restoring damaged tissues via a regenerative approach. Yet, the translation into a clinical product is still challenging. Novel technologies such as bioprinting have been developed to solve some of the shortcomings faced in traditional tissue engineering approaches. Using automated bioprinting techniques allows for precise placement of cells and biological molecules and for geometrical patient-specific design of produced biological scaffolds. Recently, bioprinting has also been introduced into the field of dentoalveolar tissue engineering. However, the choice of a suitable material to encapsulate cells in the development of so-called bioinks for bioprinting dentoalveolar tissues is still a challenge, considering the heterogeneity of these tissues and the range of properties they possess. This review, therefore, aims to provide an overview of the current state of the art by discussing the progress of the research on materials used for dentoalveolar bioprinting, highlighting the advantages and shortcomings of current approaches and considering opportunities for further research.

Polymeric Scaffolds for Dental, Oral, and Craniofacial Regenerative Medicine

Dental, oral, and craniofacial (DOC) regenerative medicine aims to repair or regenerate DOC tissues including teeth, dental pulp, periodontal tissues, salivary gland, temporomandibular joint (TMJ), hard (bone, cartilage), and soft (muscle, nerve, skin) tissues of the craniofacial complex. Polymeric materials have a broad range of applications in biomedical engineering and regenerative medicine functioning as tissue engineering scaffolds, carriers for cell-based therapies, and biomedical devices for delivery of drugs and biologics. The focus of this review is to discuss the properties and clinical indications of polymeric scaffold materials and extracellular matrix technologies for DOC regenerative medicine. More specifically, this review outlines the key properties, advantages and drawbacks of natural polymers including alginate, cellulose, chitosan, silk, collagen, gelatin, fibrin, laminin, decellularized extracellular matrix, and hyaluronic acid, as well as synthetic polymers including polylactic acid (PLA), polyglycolic acid (PGA), polycaprolactone (PCL), poly (ethylene glycol) (PEG), and Zwitterionic polymers. This review highlights key clinical applications of polymeric scaffolding materials to repair and/or regenerate various DOC tissues. Particularly, polymeric materials used in clinical procedures are discussed including alveolar ridge preservation, vertical and horizontal ridge augmentation, maxillary sinus augmentation, TMJ reconstruction, periodontal regeneration, periodontal/peri-implant plastic surgery, regenerative endodontics. In addition, polymeric scaffolds application in whole tooth and salivary gland regeneration are discussed.

Which experimental models and explorations to use in regenerative endodontics? A comprehensive review on standard practices

Since the discovery of dental pulp stem cells, a lot of teams have expressed an interest in dental pulp regeneration. Many approaches, experimental models and biological explorations have been developed, each including the use of stem cells and scaffolds with the final goal being clinical application in humans. In this review, the authors' objective was to compare the experimental models and strategies used for the development of biomaterials for tissue engineering of dental pulp with stem cells. Electronic queries were conducted on PubMed using the following terms: pulp regeneration, scaffold, stem cells, tissue engineering and biomaterial. The extracted data included the following information: the strategy envisaged, the type of stem cells, the experimental models, the exploration or analysis methods, the cytotoxicity or viability or proliferation cellular tests, the tests of scaffold antibacterial properties and take into account the vascularization of the regenerated dental pulp. From the 71 selected articles, 59% focused on the "cell-transplantation" strategy, 82% used in vitro experimentation, 58% in vivo animal models and only one described an in vivo in situ human clinical study. 87% used dental pulp stem cells. A majority of the studies reported histology (75%) and immunohistochemistry explorations (66%). 73% mentioned the use of cytotoxicity, proliferation or viability tests. 48% took vascularization into account but only 6% studied the antibacterial properties of the scaffolds. This article gives an overview of the methods used to regenerate dental pulp from stem cells and should help researchers create the best development strategies for research in this field.

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.

Ultrasound-targeted microbubble destruction optimized HGF-overexpressing bone marrow stem cells to repair fibrotic liver in rats

BACKGROUND/AIMS

Bone marrow mesenchymal stem cells (BMSCs) have shown their therapeutic potential in cytotherapy for liver fibrosis. However, the insufficient homing of BMSCs and undefined proliferation of BMSCs represent a significant challenge and largely limit the effective implementation. The aims of the present study were to determine whether stable expression of hepatic growth factor (HGF) in BMSCs coupled with ultrasound-targeted microbubble destruction (UTMD) technique could effectively and definitely alleviating carbon tetrachloride (CCl4)-induced liver fibrosis in rats.

MATERIALS AND METHODS

A rat model of liver fibrosis was acquired by injection of carbon tetrachloride (CCl4). The experimental rats were randomly assigned to the four groups: normal, CCl4, BMSCs-HGF/US, and BMSCs-HGF/UTMD groups. The BMSCs, transfected by recombinant adeno-associated virus vector encoding human genome sequence of HGF (BMSCs-HGF), were transplanted in rat via the tail vein. The homing efficiency of BMSCs was observed by immunofluorescence staining. The liver function and its morphological changes were analyzed by biochemical tests and liver histology. The expression of liver fibrosis markers including α-smooth muscle actin (α-SMA), collagen I, and vimentin were examined by immunohistochemistry and quantitative real-time polymerase chain reaction.

RESULTS

The homing efficiency of BMSCs in the fibrotic liver was significantly greater with the application of UTMD. The biochemical markers of liver function and histopathological results showed significantly better improvement in BMSCs-HGF/UTMD group than the other groups, and the serum levels of biochemical markers returned to normal ranges in 12 weeks in this group. Furthermore, the expression levels of liver fibrosis markers (α-SMA, collagen I, and Vimentin) were all significantly lower in BMSCs-HGF/UTMD group in comparison with other groups.

CONCLUSIONS

Our findings have demonstrated that stable expression of HGF in BMSCs and application of the UTMD technique facilitate the homing of BMSCs, and more importantly, which could further improve their alleviation of liver fibrosis. Therefore, these findings have an important clinical implication that AAV-BMSCs-HGF and UTMD hold promise as a novel therapeutic approach for liver fibrosis.

Pulp-Dentin Tissue Healing Response: A Discussion of Current Biomedical Approaches

Dental pulp tissue exposed to mechanical trauma or cariogenic process results in root canal and/or periapical infections, and conventionally treated with root canal procedures. The more recent regenerative endodontic procedure intends to achieve effective root canal disinfection and adequate pulp–dentin tissue regeneration; however, numerous limitations are reported. Because tooth is composed of vital soft pulp enclosed by the mineralized hard tissue in a highly organized structure, complete pulp–dentin tissue regeneration has been challenging to achieve. In consideration of the limitations and unique dental anatomy, it is important to understand the healing and repair processes through inflammatory-proliferative-remodeling phase transformations of pulp–dentin tissue. Upon cause by infectious and mechanical stimuli, the innate defense mechanism is initiated by resident pulp cells including immune cells through chemical signaling. After the expansion of infection and damage to resident pulp–dentin cells, consequent chemical signaling induces pluripotent mesenchymal stem cells (MSCs) to migrate to the injury site to perform the tissue regeneration process. Additionally, innovative biomaterials are necessary to facilitate the immune response and pulp–dentin tissue regeneration roles of MSCs. This review highlights current approaches of pulp–dentin tissue healing process and suggests potential biomedical perspective of the pulp–dentin tissue regeneration.

The effect of hyaluronic acid hydrogels on dental pulp stem cells behavior

Dental caries and trauma, particularly in childhood, are among the most prevalent teeth problems, which result in the creation of cavities and probably tooth loss. Thus, novel regenerative approaches with high efficiency and less toxicity are required. Stem cell therapy along with the implementation of scaffolds has provided excellent opportunities in the regeneration of teeth structure. Hyaluronic acid (HA) hydrogels have enticed great attention in the field of regenerative medicine. The unique chemical and structural properties of HA and its derivatives have enabled their application in tissue engineering. Several factors such as the location and type of the lesion, teeth age, the type of capping materials determine the success rate of pulp therapy. HA hydrogels have been considered as biocompatible and safe scaffold supports in human dental cell therapies.

Taguchi's methods to optimize the properties and bioactivity of 3D printed polycaprolactone/mineral trioxide aggregate scaffold: Theoretical predictions and experimental validation

Mineral trioxide aggregate (MTA) can provide bioactivity to poly-caprolactone (PCL), which is an inert polymer used to print scaffolds. However, testing all combinations of scaffold characteristics (e.g., composition, pore size, and distribution) to optimize properties of scaffolds is time-consuming and costly. The Taguchi's methods can identify characteristics that have major influences on the properties of complex designs, hence decreasing the number of combinations to be tested. The objective was to assess the potential of Taguchi's methods as a predictive tool for the optimization of bioactive scaffold printed using electro-hydro dynamic jetting. A three-level approach assessed the influence of PCL/MTA proportion, pore size, fiber dimension and number of layers in pH, degradation rate, porosity, yield strength, and Young's modulus. Data were analyzed using Tukey's honest significant difference test, analysis of mean and signal-to-noise ratio (S/N) test. Cytocompatibility and differentiation potential were assessed for 5 and 30 days using dental pulp stem cells and analyzed with one-way analysis of variance (proliferation) or Mann-Whitney (qPCR). The S/N ratio and analysis of mean showed that fiber diameter and composition were the most influential characteristics in all properties. The experimental data confirmed that the addition of MTA to PCL increased the pH and scaffold degradation. Only PCL and PCL with 4% MTA allowed cell proliferation. The latter increased the genetic expression of ALP, COL-1, OCN, and MSX-1. The theoretical predictions were confirmed by the experiments. The Taguchi's identified the inputs that can be disregarded to optimize 3D printed meshed bioactive scaffolds.

Graphene-Induced Osteogenic Differentiation Is Mediated by the Integrin/FAK Axis

Graphene is capable of promoting osteogenesis without chemical induction. Nevertheless, the underlying mechanism(s) remain largely unknown. The objectives here were: (i) to assess whether graphene scaffolds are capable of supporting osteogenesis in vivo and; (ii) to ascertain the participation of the integrin/FAK mechanotransduction axis during the osteogenic differentiation induced by graphene. MSC-impregnated graphene scaffolds (n = 6) were implanted into immunocompromised mice (28 days). Alternatively, MSCs were seeded onto PDMS substrates (modulus of elasticity = 130, 830 and 1300 kPa) coated with a single monomolecular layer of graphene and cultured in basal medium (10 days). The ensuing expressions of FAK-p397, integrin, ROCK1, F-actin, Smad p1/5, RUNX2, OCN and OPN were evaluated by Western blot (n = 3). As controls, MSCs were plated onto uncoated PDMS in the presence of mechanotransduction inhibitors (echistatin, Y27632 and DMH1). MSC-impregnated graphene scaffolds exhibited positive immunoexpression of bone-related markers (RUNX2 and OPN) without the assistance of osteogenic inducers. In vitro, regardless of the stiffness of the underlying PDMS substrate, MSCs seeded onto graphene-coated PDMS substrates demonstrated higher expressions of all tested osteogenic and integrin/FAK proteins tested compared to MSCs seeded onto PDMS alone. Hence, graphene promotes osteogenesis via the activation of the mechanosensitive integrin/FAK axis.

Use of 0.4-Tesla static magnetic field to promote reparative dentine formation of dental pulp stem cells through activation of p38 MAPK signalling pathway

AIM

To investigate whether static magnetic fields (SMFs) have a positive effect on the migration and dentinogenesis of dental pulp stem cells (DPSCs) to promote reparative dentine formation.

METHODOLOGY

In vitro scratch assays and a traumatic pulp exposure model were performed to evaluate the effect of 0.4-Tesla (T) SMF on DPSC migration. The cytoskeletons of the DPSCs were identified by fluorescence immunostaining and compared with those of a sham-exposed group. Dentinogenic evaluation was performed by analysing the expressions of DMP-1 and DSPP marker genes using a quantitative real-time polymerase chain reaction (qRT-PCR) process. Furthermore, the formation of calcified deposits was examined by staining the dentinogenic DPSCs with Alizarin Red S dye. Finally, the role played by the p38 MAPK signalling pathway in the migration and dentinogenesis of DPSCs under 0.4-T SMF was investigated by incorporating p38 inhibitor (SB203580) into the in vitro DPSC experiments. The Student's t-test and the Kruskal-Wallis test followed by Dunn's post hoc test with a significance level of P < 0.05 were used for statistical analysis.

RESULTS

The scratch assay results revealed that the application of 0.4-T SMF enhanced DPSCs migration towards the scratch wound (P < 0.05). The cytoskeletons of the SMF-treated DPSCs were found to be aligned perpendicular to the scratch wound. After 20 days of culture, the SMF-treated group had a greater number of out-grown cells than the sham-exposed group (nonmagnetized control). For the SMF-treated group, the DMP-1 (P < 0.05) and DSPP genes (P < 0.05), analysed by qRT-PCR, exhibited a higher expression. The distribution of calcified nodules was also found to be denser in the SMF-treated group when stained with Alizarin Red S dye (P < 0.05). Given the incorporation of p38 inhibitor SB203580 into the DPSCs, cell migration and dentinogenesis were suppressed. No difference was found between the SMF-treated and sham-exposed cells (P > 0.05).

CONCLUSION

0.4-T SMF enhanced DPSC migration and dentinogenesis through the activation of the p38 MAPK-related pathway.

Graphene-Based Nanomaterials for Tissue Engineering in the Dental Field

The world of dentistry is approaching graphene-based nanomaterials as substitutes for tissue engineering. Apart from its exceptional mechanical strength, electrical conductivity and thermal stability, graphene and its derivatives can be functionalized with several bioactive molecules. They can also be incorporated into different scaffolds used in regenerative dentistry, generating nanocomposites with improved characteristics. This review presents the state of the art of graphene-based nanomaterial applications in the dental field. We first discuss the interactions between cells and graphene, summarizing the available in vitro and in vivo studies concerning graphene biocompatibility and cytotoxicity. We then highlight the role of graphene-based nanomaterials in stem cell control, in terms of adhesion, proliferation and differentiation. Particular attention will be given to stem cells of dental origin, such as those isolated from dental pulp, periodontal ligament or dental follicle. The review then discusses the interactions between graphene-based nanomaterials with cells of the immune system; we also focus on the antibacterial activity of graphene nanomaterials. In the last section, we offer our perspectives on the various opportunities facing the use of graphene and its derivatives in associations with titanium dental implants, membranes for bone regeneration, resins, cements and adhesives as well as for tooth-whitening procedures.

Effects of substrate stiffness on dental pulp stromal cells in culture

Dental pulp stromal cells (DPSCs) can be differentiated down lineages known to either express bone or dentin specific protein markers. Since the differentiation of cells can be heavily influenced by their environment, it may be possible to influence the osteogenic/odontogenic potential of DPSCs by modulating the mechanical properties of substrate on which they are grown. In this study, human DPSCs were grown with and without hydroxyapatite (HA) microparticles on a range of substrates including fibronectin-coated hydrogels and glass substrates, which represented an elastic moduli range of approximately 3 kPa-50 GPa, over a 21-day period. Alkaline phosphatase activity, osteopontin production, and mineralization were monitored. The presence of HA microparticles increased the relative degree of mineralized matrix produced by the cells relative to those in the same substrate and media condition without the HA microparticles. In addition, cultures with cells grown on stiffer substrates had higher ALP activity and higher degree of mineralization than those grown on softer substrates. This study shows that DPSCs are affected by the mechanical properties of their underlying growth substrate and by the presence of HA microparticles. In addition, relatively stiff substrates (>75 kPa) may be required for significant mineralization of these cultures. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 1789-1797, 2018.

Progress in the use of dental pulp stem cells in regenerative medicine

The field of tissue engineering is emerging as a multidisciplinary area with promising potential for regenerating new tissues and organs. This approach requires the involvement of three essential components: stem cells, scaffolds and growth factors. To date, dental pulp stem cells have received special attention because they represent a readily accessible source of stem cells. Their high plasticity and multipotential capacity to differentiate into a large array of tissues can be explained by its neural crest origin, which supports applications beyond the scope of oral tissues. Many isolation, culture and cryopreservation protocols have been proposed that are known to affect cell phenotype, proliferation rate and differentiation capacity. The clinical applications of therapies based on dental pulp stem cells demand the development of new biomaterials suitable for regenerative purposes that can act as scaffolds to handle, carry and implant stem cells into patients. Currently, the development of xeno-free culture media is emerging as a means of standardization to improve safe and reproducibility. The present review aims to describe the current knowledge of dental pulp stem cells, considering in depth the key aspects related to the characterization, establishment, maintenance and cryopreservation of primary cultures and their involvement in the multilineage differentiation potential. The main clinical applications for these stem cells and their combination with several biomaterials is also covered.

Stiffness regulates the proliferation and osteogenic/odontogenic differentiation of human dental pulp stem cells via the WNT signalling pathway

OBJECTIVES

Researches showed that stiffness of the extracellular matrix can affect the differentiation of many stem cells. Dental pulp stem cells (DPSCs) are a promising type of adult stem cell. However, we know little about whether and how the behaviour of DPSCs is influenced by stiffness.

MATERIALS AND METHODS

We carried out a study that cultured DPSCs on tunable elasticity polydimethylsiloxane substrates to investigate the influence on morphology, proliferation, osteogenic/odontogenic differentiation and its possible mechanism.

RESULTS

Soft substrates changed the cell morphology and inhibited the proliferation of DPSCs. Expression of markers related to osteogenic/odontogenic differentiation was significantly increased as the substrate stiffness increased, including ALP (alkaline phosphatase), OCN (osteocalcin), OPN (osteopontin), RUNX-2 (runt-related transcription factor-2), BMP-2 (bone morphogenetic protein-2), DSPP (dentin sialophosphoprotein) and DMP-1 (dentin matrix protein-1). Mechanical properties promote the function of DPSCs related to the Wnt signalling pathway.

CONCLUSIONS

Our results showed that mechanical factors can regulate the proliferation and differentiation of DPSCs via the WNT signalling pathway. This provides theoretical basis to optimize dental or bone tissue regeneration through increasing stiffness of extracelluar matrix.

Graphene: A Versatile Carbon-Based Material for Bone Tissue Engineering

The development of materials and strategies that can influence stem cell attachment, proliferation, and differentiation towards osteoblasts is of high interest to promote faster healing and reconstructions of large bone defects. Graphene and its derivatives (graphene oxide and reduced graphene oxide) have received increasing attention for biomedical applications as they present remarkable properties such as high surface area, high mechanical strength, and ease of functionalization. These biocompatible carbon-based materials can induce and sustain stem cell growth and differentiation into various lineages. Furthermore, graphene has the ability to promote and enhance osteogenic differentiation making it an interesting material for bone regeneration research. This paper will review the important advances in the ability of graphene and its related forms to induce stem cells differentiation into osteogenic lineages.