Co-culture of Human Dental Pulp Stem Cells and Endothelial Cells Using Porous Biopolymer Microcarriers: A Feasibility Study for Bone Tissue Engineering

The Diamond Concept Enigma: Recent Trends of Its Implementation in Cross-linked Chitosan-Based Scaffolds for Bone Tissue Engineering

An increasing number of publications over the past ten years have focused on the development of chitosan-based cross-linked scaffolds to regenerate bone tissue. The design of biomaterials for bone tissue engineering applications relies heavily on the ideals set forth by a polytherapy approach called the "Diamond Concept". This methodology takes into consideration the mechanical environment, scaffold properties, osteogenic and angiogenic potential of cells, and benefits of osteoinductive mediator encapsulation. The following review presents a comprehensive summarization of recent trends in chitosan-based cross-linked scaffold development within the scope of the Diamond Concept, particularly for nonload-bearing bone repair. A standardized methodology for material characterization, along with assessment of in vitro and in vivo potential for bone regeneration, is presented based on approaches in the literature, and future directions of the field are discussed.

3D Organoids for Regenerative Endodontics

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

Spatial patterning of PCL µ-scaffolds directs 3D vascularized bio-construct morphogenesis in vitro

Modular tissue engineering (mTE) strategies aim to build three-dimensional tissue analogues in vitro by the sapient combination of cells, micro-scaffolds (μ-scaffs) and bioreactors. The translation of these newly engineered tissues into current clinical approaches is, among other things, dependent on implant-to-host microvasculature integration, a critical issue for cells and tissue survival in vivo. In this work we reported, for the first time, a computer-aided modular approach suitable to build fully vascularized hybrid (biological/synthetic) constructs (bio-constructs) with micro-metric size scale control of blood vessels growth and orientation. The approach consists of four main steps, starting with the fabrication of polycaprolactone μ-scaffs by fluidic emulsion technique, which exhibit biomimetic porosity features. In the second step, layers of μ-scaffs following two different patterns, namely ordered and disordered, were obtained by a soft lithography-based process. Then, the as obtained μ-scaff patterns were used as template for human dermal fibroblasts and human umbilical vein endothelial cells co-culture, aiming to promote and guide the biosynthesis of collagenous extracellular matrix and the growth of new blood vessels within the mono-layered bio-constructs. Finally, bi-layered bio-constructs were built by the alignment, stacking and fusion of two vascularized mono-layered samples featuring ordered patterns. Our results demonstrated that, if compared to the disordered pattern, the ordered one provided better control over bio-constructs shape and vasculature architecture, while minor effect was observed with respect to cell colonization and new tissue growth. Furthermore, by assembling two mono-layered bio-constructs it was possible to build 1-mm thick fully vascularized viable bio-constructs and to study tissue morphogenesis during 1 week of in vitro culture. In conclusion, our results highlighted the synergic role of μ-scaff architectural features and spatial patterning on cells colonization and biosynthesis, and pay the way for the possibility to create in silico designed vasculatures within modularly engineered bio-constructs.

Application of dental stem cells in three-dimensional tissue regeneration

Dental stem cells can differentiate into different types of cells. Dental pulp stem cells, stem cells from human exfoliated deciduous teeth, periodontal ligament stem cells, stem cells from apical papilla, and dental follicle progenitor cells are five different types of dental stem cells that have been identified during different stages of tooth development. The availability of dental stem cells from discarded or removed teeth makes them promising candidates for tissue engineering. In recent years, three-dimensional (3D) tissue scaffolds have been used to reconstruct and restore different anatomical defects. With rapid advances in 3D tissue engineering, dental stem cells have been used in the regeneration of 3D engineered tissue. This review presents an overview of different types of dental stem cells used in 3D tissue regeneration, which are currently the most common type of stem cells used to treat human tissue conditions.

Culturing and Scaling up Stem Cells of Dental Pulp Origin Using Microcarriers

Ectomesenchymal stem cells derived from the dental pulp are of neural crest origin, and as such are promising sources for cell therapy and tissue engineering. For safe upscaling of these cells, microcarrier-based culturing under dynamic conditions is a promising technology. We tested the suitability of two microcarriers, non-porous Cytodex 1 and porous Cytopore 2, for culturing well characterized dental pulp stem cells (DPSCs) using a shake flask system. Human DPSCs were cultured on these microcarriers in 96-well plates, and further expanded in shake flasks for upscaling experiments. Cell viability was measured using the alamarBlue assay, while cell morphology was observed by conventional and two-photon microscopies. Glucose consumption of cells was detected by the glucose oxidase/Clark-electrode method. DPSCs adhered to and grew well on both microcarrier surfaces and were also found in the pores of the Cytopore 2. Cells grown in tissue culture plates (static, non-shaking conditions) yielded 7 × 105 cells/well. In shake flasks, static preincubation promoted cell adhesion to the microcarriers. Under dynamic culture conditions (shaking) 3 × 107 cells were obtained in shake flasks. The DPSCs exhausted their glucose supply from the medium by day seven even with partial batch-feeding. In conclusion, both non-porous and porous microcarriers are suitable for upscaling ectomesenchymal DPSCs under dynamic culture conditions.

A core-shell guanosine diphosphate crosslinked chitosan scaffold as a potential co-encapsulation platform

Recent engineering strategies to better mimic native tissue architecture involve co-encapsulation of cell lineages and/or growth factors in multi-compartmental scaffolds. This study introduces a core-shell platform based on a rapidly gelling guanosine diphosphate cross-linked chitosan scaffold for co-culture. The core-shell sponge is fabricated through combination of chitosan and guanosine diphosphate in 3 steps with each shell layer deposited around the previous layer. Co-encapsulation of pre-osteoblastic MC-3T3 cells and growth factors in the core-shell sponge showed similar microstructure to the standard sponge with high pore connectivity and low closed porosity (<0.4 %). A viable cell population was maintained over time with enhanced cellular functionality when ascorbic acid was added in the same compartment. Co-culture was explored with a proof-of-concept study shown for MC-3T3 and endothelial cells showing homogeneous distribution of cells in their intended compartment. Overall, this core-shell scaffold shows potential as a platform for the regeneration of multiple tissues.

Dental stem cells: The role of biomaterials and scaffolds in developing novel therapeutic strategies

Dental stem cells (DSCs) are self-renewable cells that can be obtained easily from dental tissues, and are a desirable source of autologous stem cells. The use of DSCs for stem cell transplantation therapeutic approaches is attractive due to their simple isolation, high plasticity, immunomodulatory properties, and multipotential abilities. Using appropriate scaffolds loaded with favorable biomolecules, such as growth factors, and cytokines, can improve the proliferation, differentiation, migration, and functional capacity of DSCs and can optimize the cellular morphology to build tissue constructs for specific purposes. An enormous variety of scaffolds have been used for tissue engineering with DSCs. Of these, the scaffolds that particularly mimic tissue-specific micromilieu and loaded with biomolecules favorably regulate angiogenesis, cell-matrix interactions, degradation of extracellular matrix, organized matrix formation, and the mineralization abilities of DSCs in both in vitro and in vivo conditions. DSCs represent a promising cell source for tissue engineering, especially for tooth, bone, and neural tissue restoration. The purpose of the present review is to summarize the current developments in the major scaffolding approaches as crucial guidelines for tissue engineering using DSCs and compare their effects in tissue and organ regeneration.

Cell-cell interaction in a coculture system consisting of CRISPR/Cas9 mediated GFP knock-in HUVECs and MG-63 cells in alginate-GelMA based nanocomposites hydrogel as a 3D scaffold

The interaction between osteogenic and angiogenic cells through a coculturing system in biocompatible materials has been considered for successfully engineering vascularized bone tissue equivalents. In this study, we developed a hydrogel-blended scaffold consisted of gelatin methacryloyl (GelMA) and alginate enriched with hydroxyapatite nanoparticles (HAP) to model an in vitro prevascularized bone construct. The hydrogel-based scaffold revealed a higher mechanical stiffness than those of pure (GelMA), alginate, and (GelMA+ HAP) hydrogels. In the present study, we generated a green fluorescent protein (GFP) knock-in umbilical vein endothelial cells (HUVECs) cell line using the CRISPR/Cas9 technology. The GFP was inserted into the human-like ROSA locus of HUVECs genome. HUVECs expressing GFP were cocultured with OB-like cells (MG-63) within three-dimensionally (3D) fabricated hydrogel to investigate the response of cocultured osteoblasts and endothelial cells in a 3D structure. Cell viability under the 3D cocultured gel was higher than the 3D monocultured. Compared to the 3D monocultured condition, the cells were aligned and developed into the vessel-like structures. During 14 days of culture periods, the cells displayed actin protrusions by the formation of spike-like filopodia in the 3D cocultured model. Angiogenic and osteogenic-related genes such as CD31, vWF, and osteocalcin showed higher expression in the cocultured versus the monocultured. These results have collectively indicated that the 3D cocultured hydrogel facilitates interaction among cells, thereby having a greater effect on angiogenic and osteogenic properties in the absence of induction media.

Development of a functional airway-on-a-chip by 3D cell printing

We used 3D cell printing to emulate an airway coupled with a naturally-derived blood vessel network in vitro. Decellularized extracellular matrix bioink derived from porcine tracheal mucosa (tmdECM) was used to encapsulate and print endothelial cells and fibroblasts within a designated polycarprolactone (PCL) frame. Providing a niche that emulates conditions in vivo, tmdECM gradually drives endothelial re-orientation, which leads to the formation of a lumen and blood vessel network. A fully-differentiated in vitro airway model was assembled with the printed vascular platform, and collectively reproduced a functional interface between the airway epithelium and the vascular network. The model presented respiratory symptoms including asthmatic airway inflammation and allergen-induced asthma exacerbation in physiological context. Because of the adaptable and automated nature of direct 3D cell printing, we expect that this will have relevance in vivo and high reproducibility for production of high-content platforms for preclinical trials in biomedical research.

Improved vasculogenesis and bone matrix formation through coculture of endothelial cells and stem cells in tissue-specific methacryloyl gelatin-based hydrogels

The coculture of osteogenic and angiogenic cells and the resulting paracrine signaling via soluble factors are supposed to be crucial for successfully engineering vascularized bone tissue equivalents. In this study, a coculture system combining primary human adipose-derived stem cells (hASCs) and primary human dermal microvascular endothelial cells (HDMECs) within two types of hydrogels based on methacryloyl-modified gelatin (GM) as three-dimensional scaffolds was examined for its support of tissue specific cell functions. HDMECs, together with hASCs as supporting cells, were encapsulated in soft GM gels and were indirectly cocultured with hASCs encapsulated in stiffer GM hydrogels additionally containing methacrylate-modified hyaluronic acid and hydroxyapatite particles. After 14 days, the hASC in the stiffer gels (constituting the "bone gels") expressed matrix proteins like collagen type I and fibronectin, as well as bone-specific proteins osteopontin and alkaline phosphatase. After 14 days of coculture with HDMEC-laden hydrogels, the viscoelastic properties of the bone gels were significantly higher compared with the gels in monoculture. Within the soft vascularization gels, the formed capillary-like networks were significantly longer after 14 days of coculture than the structures in the control gels. In addition, the stability as well as the complexity of the vascular networks was significantly increased by coculture. We discussed and concluded that osteogenic and angiogenic signals from the culture media as well as from cocultured cell types, and tissue-specific hydrogel composition all contribute to stimulate the interplay between osteogenesis and angiogenesis in vitro and are a basis for engineering vascularized bone.

Double intratibial injection of human tonsil-derived mesenchymal stromal cells recovers postmenopausal osteoporotic bone mass

BACKGROUND AND AIMS

Osteoporosis, which is a disease characterized by weakening of the bone, affects a large portion of the senior population. The current therapeutic options for osteoporosis have side effects, and there is no effective treatment for severe osteoporosis. Thus, we urgently need new treatment strategies, such as topical therapies and/or safe and effective stem cell therapies.

METHODS

We investigated the therapeutic potential of directly injecting human tonsil-derived mesenchymal stem cells (TMSC) into the right proximal tibias of ovariectomized postmenopausal osteoporosis model mice. Injections were given once (1×) or twice (2×) during the 3-month experimental period. At the end of the experiment, micro-computed tomographic images revealed some improvement in the proximal tibias and more significant improvement in the femoral heads of treated mice.

RESULTS

Osteogenic effect was qualitatively and quantitatively more pronounced in TMSC/2×-treated mice. Furthermore, TMSC/2× mice exhibited significant recovery of the serum osteocalcin level, which is pathologically elevated in osteoporosis, and increased serum alkaline phosphatase, which indicates bone formation. TMSC therapy was generally well tolerated and caused no apparent toxicity in the experimental mice. Moreover, TMSC therapy reduced visceral fat.

CONCLUSION

Our results demonstrate that double injection of TMSC directly into the proximal tibia triggers recovery of osteoporosis, and thus could be a potential therapeutic approach for severe bone loss.