An Optimized Injectable Hydrogel Scaffold Supports Human Dental Pulp Stem Cell Viability and Spreading

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.

Advances on Hydrogels for Oral Science Research

Hydrogels are biocompatible polymer systems, which have become a hotspot in biomedical research. As hydrogels mimic the structure of natural extracellular matrices, they are considered as good scaffold materials in the tissue engineering area for repairing dental pulp and periodontal damages. Combined with different kinds of stem cells and growth factors, various hydrogel complexes have played an optimistic role in endodontic and periodontal tissue engineering studies. Further, hydrogels exhibit biological effects in response to external stimuli, which results in hydrogels having a promising application in local drug delivery. This review summarized the advances of hydrogels in oral science research, in the hopes of providing a reference for future applications.

Innovative Approach in the Cryogenic Freezing Medium for Mesenchymal Stem Cells

The physical stresses during cryopreservation affect stem cell survival and further proliferation. To minimize or prevent cryoinjury, cryoprotective agents (CPAs) are indispensable. Despite the widespread use of 10% dimethyl sulfoxide (DMSO), there are concerns about its potential adverse effects. To bypass those effects, combinations of CPAs have been investigated. This study aimed to verify whether high-molecular-hyaluronic acid (HMW-HA) serves as a cryoprotectant when preserving human mesenchymal stem cells (hMSCs) to reduce the DMSO concentration in the cryopreservation medium. We studied how 0.1% or 0.2% HMW-HA combined with reduced DMSO concentrations (from 10% to 5%, and 3%) affected total cell count, viability, immunophenotype, and differentiation potential post-cryopreservation. Immediately after cell revival, the highest total cell count was observed in 10% DMSO-stored hMSC. However, two weeks after cell cultivation an increased cell count was seen in the HMW-HA-stored groups along with a continued increase in hMSCs stored using 3% DMSO and 0.1% HMW-HA. The increased total cell count corresponded to elevated expression of stemness marker CD49f. The HA-supplemented cryomedium did not affect the differential potential of hMSC. Our results will participate in producing a ready-to-use product for cryopreservation of mesenchymal stem cells.

A narrative overview of utilizing biomaterials to recapitulate the salient regenerative features of dental-derived mesenchymal stem cells

Tissue engineering approaches have emerged recently to circumvent many limitations associated with current clinical practices. This elegant approach utilizes a natural/synthetic biomaterial with optimized physiomechanical properties to serve as a vehicle for delivery of exogenous stem cells and bioactive factors or induce local recruitment of endogenous cells for in situ tissue regeneration. Inspired by the natural microenvironment, biomaterials could act as a biomimetic three-dimensional (3D) structure to help the cells establish their natural interactions. Such a strategy should not only employ a biocompatible biomaterial to induce new tissue formation but also benefit from an easily accessible and abundant source of stem cells with potent tissue regenerative potential. The human teeth and oral cavity harbor various populations of mesenchymal stem cells (MSCs) with self-renewing and multilineage differentiation capabilities. In the current review article, we seek to highlight recent progress and future opportunities in dental MSC-mediated therapeutic strategies for tissue regeneration using two possible approaches, cell transplantation and cell homing. Altogether, this paper develops a general picture of current innovative strategies to employ dental-derived MSCs combined with biomaterials and bioactive factors for regenerating the lost or defective tissues and offers information regarding the available scientific data and possible applications.

Low Molecular Weight Hyaluronic Acid Effect on Dental Pulp Stem Cells In Vitro

Hyaluronic acid (HA) and dental pulp stem cells (DPSCs) are attractive research topics, and their combined use in the field of tissue engineering seems to be very promising. HA is a natural extracellular biopolymer found in various tissues, including dental pulp, and due to its biocompatibility and biodegradability, it is also a suitable scaffold material. However, low molecular weight (LMW) fragments, produced by enzymatic cleavage of HA, have different bioactive properties to high molecular weight (HMW) HA. Thus, the impact of HA must be assessed separately for each molecular weight fraction. In this study, we present the effect of three LMW-HA fragments (800, 1600, and 15,000 Da) on DPSCs in vitro. Discrete biological parameters such as DPSC viability, morphology, and cell surface marker expression were determined. Following treatment with LMW-HA, DPSCs initially presented with an acute reduction in proliferation (p < 0.0016) and soon recovered in subsequent passages. They displayed significant size reduction (p = 0.0078, p = 0.0019, p = 0.0098) while maintaining high expression of DPSC markers (CD29, CD44, CD73, CD90). However, in contrast to controls, a significant phenotypic shift (p < 0.05; CD29, CD34, CD90, CD106, CD117, CD146, CD166) of surface markers was observed. These findings provide a basis for further detailed investigations and present a strong argument for the importance of HA scaffold degradation kinetics analysis.

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.

The effect of polyethylenglycol gel on the delivery and osteogenic differentiation of homologous tooth germ-derived stem cells in a porcine model

OBJECTIVES

The aim of this study was to investigate if bone regeneration can be promoted by homologous transplantation of STRO-1 sorted (STRO-1+) porcine tooth germ mesenchymal stem cells (TGSCs) with the combination of polyethylenglycol (PEG)-based hydrogel and biphasic calcium phosphate (BCP) scaffolds.

MATERIAL AND METHODS

TGSCs were isolated from impacted third molars of domestic pigs. Nine critical-sized defects were created as (1) untreated defect; filled with (2) autogenous bone; (3) BCP + PEG; (4) BCP + PEG + unsorted TGSCs; (5) BCP + unsorted TGSCs; (6) BCP + PEG + STRO-1-sorted TGSCs; (7) BCP + STRO-1-sorted TGSCs; (8) BCP + PEG + osteogenic induced unsorted TGSCs; and (9) BCP + PEG + osteogenic induced STRO-1-sorted TGSCs in 20 domestic pigs. CM-DiI labelling was used to track cells in vivo. Histomorphometric assessment of new bone formation was achieved by toluidine blue O staining and microradiography after 1, 2, 4 and 12 weeks posttransplantation.

RESULTS

Complete healing was achieved in all defects although defects with PEG hydrogel presented better bone formation while STRO-1+ and unsorted TGSCs showed similar ability to form new bone after 12 weeks. Transplanted cells were seen in defects where PEG hydrogel was used as carriers in contrast to defects treated with cells and only bone grafts.

CONCLUSIONS

PEG hydrogel is an efficient carrier for homologous stem cell transplantation. TGSCs are capable of promoting bone healing in critical-sized defects in combination with bone graft and PEG hydrogel.

CLINICAL RELEVANCE

This study provides information about the importance of the delivery vehicle for future translational stem cell delivery approaches.

Injectable Biomaterials for Dental Tissue Regeneration

Injectable biomaterials scaffolds play a pivotal role for dental tissue regeneration, as such materials are highly applicable in the dental field, particularly when compared to pre-formed scaffolds. The defects in the maxilla-oral area are normally small, confined and sometimes hard to access. This narrative review describes different types of biomaterials for dental tissue regeneration, and also discusses the potential use of nanofibers for dental tissues. Various studies suggest that tissue engineering approaches involving the use of injectable biomaterials have the potential of restoring not only dental tissue function but also their biological purposes.

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.

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.

Medical Applications of Collagen and Hyaluronan in Regenerative Medicine

In order to develop and commercialize for the regenerative medicinal products, smart biomaterials with biocompatibility must be needed. In this chapter, we introduce collagen and hyaluronic acid (HA) as extracellular matrix as well as deal with the molecular mechanism as microenvironment, mechanistic effects, and gene expression. Application of collagen and HA have been reviewed in the area of orthopedics, orthopedics, ophthalmology, dermatology and plastic surgery. Finally, the ongoing and commercial products of collagen and HA for regenerative medicine have been introduced.

Injectable co-gels of collagen and decellularized vascular matrix improve MSC-based therapy for acute kidney injury

Transplantation of mesenchymal stem cells (MSCs) is promising for treatment of acute kidney injury (AKI), but their therapeutic effects are often limited under normal conditions. In this study, we prepared the co-gels of decellularized vascular matrix and collagen, and investigated whether the co-gels increase the therapeutic potentials of MSCs on AKI. In vitro studies indicated that the co-gels enhanced the paracrine effects of MSCs, and significantly reduced the apoptosis of MSCs under oxidative environments. When the co-gels were co-transplanted with MSCs into the kidney of model rats with ischemia-reperfusion (I/R)-induced AKI, the survival and paracrine effects of MSCs were enhanced in the injured kidney. More importantly, the co-gels increased the therapeutic effects of MSCs for AKI, as indicated by cell apoptosis, tissue damage, vascularization and renal function. Therefore, the co-gels of decellularized vascular matrix and collagen improved the therapeutic effects of MSCs, and might be promising for AKI treatment.

[Gelatin/alginate hydrogel scaffolds prepared by 3D bioprinting promotes cell adhesion and proliferation of human dental pulp cells in vitro]

OBJECTIVE

To evaluate the cytotoxicity of gelatin/alginate hydrogel scaffolds prepared by 3D bioprinting in human dental pulp cells (HDPCs) and compare the cell adhesion and proliferation of the cells seeded in the biomaterial using two different methods.

METHODS

HDPCs isolated by tissue block culture and enzyme digestion were cultured and passaged. Gelatin/alginate hydrogel scaffolds were printed using a bioplotter, and the cytotoxicity of the aqueous extracts of the scaffold material was tested in the third passage of HDPCs using cell counting kit-8. Scanning electron microscopy and trypan blue were used to assess the adhesion and proliferation of the cells seeded in the scaffold material at a low or high concentration.

RESULTS

The aqueous extract of the scaffolds at different concentrations showed no obvious cytotoxicity and promoted the proliferation of HDPCs. The scaffolds had a good biocompatibility and HDPCs seeded in the scaffold showed good cell growth. Cell seeding at a high concentration in the scaffold better promoted the adhesion of HDPCs and resulted in a greater cell number on the scaffold surface compared with low-concentration cell seeding after a 5-day culture (P<0.05).

CONCLUSION

Gelatin<alginate hydrogel scaffolds prepared by 3D bioprinting has a good biocompatibility and promotes the proliferation of HDPCs, and can be used as a scaffold material for tooth regeneration. Cell seeding at a high concentration can better promote cell adhesion to the scaffold material.