An ECM-Mimicking, Mesenchymal Stem Cell-Embedded Hybrid Scaffold for Bone Regeneration. Biomed Res Int. 2017;2017:8591073. [PMID: 29270436 PMCID: PMC5706071 DOI: 10.1155/2017/8591073]

Hybrid 3D-Printed and Electrospun Scaffolds Loaded with Dexamethasone for Soft Tissue Applications

BACKGROUND

To make the regenerative process more effective and efficient, tissue engineering (TE) strategies have been implemented. Three-dimensional scaffolds (electrospun or 3D-printed), due to their suitable designed architecture, offer the proper location of the position of cells, as well as cell adhesion and the deposition of the extracellular matrix. Moreover, the possibility to guarantee a concomitant release of drugs can promote tissue regeneration.

METHODS

A PLA/PCL copolymer was used for the manufacturing of electrospun and hybrid scaffolds (composed of a 3D-printed support coated with electrospun fibers). Dexamethasone was loaded as an anti-inflammatory drug into the electrospun fibers, and the drug release kinetics and scaffold biological behavior were evaluated.

RESULTS

The encapsulation efficiency (EE%) was higher than 80%. DXM embedding into the electrospun fibers resulted in a slowed drug release rate, and a slower release was seen in the hybrid scaffolds. The fibers maintained their nanometric dimensions (less than 800 nm) even after deposition on the 3D-printed supports. Cell adhesion and proliferation was favored in the DXM-loading hybrid scaffolds.

CONCLUSIONS

The hybrid scaffolds that were developed in this study can be optimized as a versatile platform for soft tissue regeneration.

Osteogenic differentiation of adipose-derived canine mesenchymal stem cells seeded in porous calcium-phosphate scaffolds

Introduction

Engineered bone graft substitutes are a promising alternative and supplement to autologous bone grafts as treatments for bone healing impairment. Advances in human medicine extend an invitation to pursue these biomimetic strategies in animal patients, substantiated by the theory that specialized scaffolds, multipotent cells, and biological cues may be combined into a bioactive implant intended for the enhancement of tissue regeneration.

Methods

This proof-of-concept study was designed to evaluate and validate the feasibility of beta-tricalcium phosphate foam scaffolds seeded with canine mesenchymal stem cells derived from adipose tissue. Cell-inoculated samples and sham controls were cultured statically for 72 hours in complete growth medium to evaluate seeding capacity, while a subset of loaded scaffolds was further induced with osteogenic culture medium for 21 days. Produced implants were characterized and validated with a combination of immunofluorescence and reflection confocal microscopy, scanning electron microscopy, and polymerase chain reaction to confirm osteogenic differentiation in tridimensional-induced samples.

Results

After 72 hours of culture, all inoculated scaffolds presented widespread yet heterogeneous surface seeding, distinctively congregating stem cells around pore openings. Furthermore, at 21 days of osteogenic culture conditions, robust osteoblastic differentiation of the seeded cells was confirmed by the change of cell morphology and evident deposition of extra-cellular matrix, accompanied by mineralization and scaffold remodeling; furthermore, all induced cell-loaded implants lost specific stemness immunophenotype expression and simultaneously upregulated genomic expression of osteogenic genes Osterix and Ostecalcin.

Conclusions

β-TCP bio-ceramic foam scaffolds proved to be suitable carriers and hosts of canine adipose-derived MSCs, promoting not only surface attachment and proliferation, but also demonstrating strong in-vitro osteogenic potential. Although this research provides satisfactory in-vitro validation for the conceptualization and feasibility of a canine bio-active bone implant, further testing such as patient safety, large-scale reproducibility, and quality assessment are needed for regulatory compliance in future commercial clinical applications.

Loss of Vlk in Prx1+ Cells Delays the Initial Steps of Endochondral Bone Formation and Fracture Repair in the Limb

Vertebrate lonesome kinase (Vlk) is a secreted tyrosine kinase important for normal skeletogenesis during embryonic development. Vlk null mice (Vlk^-/- ) are born with severe craniofacial and limb skeletal defects and die shortly after birth. We used a conditional deletion model to remove Vlk in limb bud mesenchyme (Vlk-Prx1 cKO) to assess the specific requirement for Vlk expression by skeletal progenitor cells during endochondral ossification, and an inducible global deletion model (Vlk-Ubq iKO) to address the role of Vlk during fracture repair. Deletion of Vlk with Prx1-Cre recapitulated the limb skeletal phenotype of the Vlk^-/- mice and enabled us to study the postnatal skeleton as Vlk-Prx1 cKO mice survived to adulthood. In Vlk-Prx1 cKO adult mice, limbs remained shorter with decreased trabecular and cortical bone volumes. Both Vlk-Prx1 cKO and Vlk-Ubq iKO mice had a delayed fracture repair response but eventually formed bridging calluses. Furthermore, levels of phosphorylated osteopontin (OPN) were decreased in tibias of Vlk-Ubq iKO, establishing OPN as a Vlk substrate in bone. In summary, our data indicate that Vlk produced by skeletal progenitor cells influences the timing and extent of chondrogenesis during endochondral bone formation and fracture repair. © 2022 American Society for Bone and Mineral Research (ASBMR).

Fibrous Polymer-Based Composites Obtained by Electrospinning for Bone Tissue Engineering

Currently, the significantly developing fields of tissue engineering related to the fabrication of polymer-based materials that possess microenvironments suitable to provide cell attachment and promote cell differentiation and proliferation involve various materials and approaches. Biomimicking approach in tissue engineering is aimed at the development of a highly biocompatible and bioactive material that would most accurately imitate the structural features of the native extracellular matrix consisting of specially arranged fibrous constructions. For this reason, the present research is devoted to the discussion of promising fibrous materials for bone tissue regeneration obtained by electrospinning techniques. In this brief review, we focus on the recently presented natural and synthetic polymers, as well as their combinations with each other and with bioactive inorganic incorporations in order to form composite electrospun scaffolds. The application of several electrospinning techniques in relation to a number of polymers is touched upon. Additionally, the efficiency of nanofibrous composite materials intended for use in bone tissue engineering is discussed based on biological activity and physiochemical characteristics.

Bone Scaffolds: An Incorporation of Biomaterials, Cells, and Biofactors

Large injuries to bones are still one of the most challenging musculoskeletal problems. Tissue engineering can combine stem cells, scaffold biomaterials, and biofactors to aid in resolving this complication. Therefore, this review aims to provide information on the recent advances made to utilize the potential of biomaterials for making bone scaffolds and the assisted stem cell therapy and use of biofactors for bone tissue engineering. The requirements and different types of biomaterials used for making scaffolds are reviewed. Furthermore, the importance of stem cells and biofactors (growth factors and extracellular vesicles) in bone regeneration and their use in bone scaffolds and the key findings are discussed. Lastly, some of the main obstacles in bone tissue engineering and future trends are highlighted.

Clinical Applications of Cell-Scaffold Constructs for Bone Regeneration Therapy

Bone tissue engineering (BTE) is a process of combining live osteoblast progenitors with a biocompatible scaffold to produce a biological substitute that can integrate into host bone tissue and recover its function. Mesenchymal stem cells (MSCs) are the most researched post-natal stem cells because they have self-renewal properties and a multi-differentiation capacity that can give rise to various cell lineages, including osteoblasts. BTE technology utilizes a combination of MSCs and biodegradable scaffold material, which provides a suitable environment for functional bone recovery and has been developed as a therapeutic approach to bone regeneration. Although prior clinical trials of BTE approaches have shown promising results, the regeneration of large bone defects is still an unmet medical need in patients that have suffered a significant loss of bone function. In this present review, we discuss the osteogenic potential of MSCs in bone tissue engineering and propose the use of immature osteoblasts, which can differentiate into osteoblasts upon transplantation, as an alternative cell source for regeneration in large bone defects.

Resistance Training Modulates the Matrix Metalloproteinase-2 Activity in Different Trabecular Bones in Aged Rats

Background

Aging decreases osteogenic ability, inducing harmful effects on the bone extracellular matrix (ECM), while exercise training has been indicated as a tool to counteract bone disorders related to advancing age. The modulation of bone ECM is regulated by several types of matrix metalloproteinase (MMP); however, MMP-2 activity in different trabecular bones in response to resistance training (RT) has been neglected. Remodeling differs in different bones under the application of the same mechanical loading. Thus, we investigated the effects of 12 weeks of RT on MMP-2 activity in the lumbar vertebra (L6), tibia, and femur of young (3 months) and older rats (21 months).

Methods

Twenty Wistar rats were divided into four groups (five animals per group): young sedentary or trained and older sedentary or trained. The 12-week RT consisted of climbing a 1.1-m vertical ladder three times per week with progressive weights secured to the animals’ tails. The animals were killed 48 h after the end of the experimental period. The MMP-2 activity was assessed by the zymography method.

Results

The aging process induced lower MMP-2 activity in the lumbar vertebrae and tibia (p=0.01). RT upregulated pro, intermediate, and active MMP-2 activity in the tibia of young rats (p=0.001). RT also upregulated pro and active MMP-2 activity in the lumbar vertebrae and tibia with advancing age (p=0.01). There was no significant difference (p>0.05) between groups for MMP-2 of the femur, regardless of age and RT.

Conclusion

The aging process impairs MMP-2 activity, but RT is a potential therapeutic approach to minimize the deleterious effects of ECM degeneration in different aged bones. Distinct MMP-2 responses to exercise training may result in specific remodeling processes.

Electrospun Nanofibers of Natural and Synthetic Polymers as Artificial Extracellular Matrix for Tissue Engineering

Many types of polymer nanofibers have been introduced as artificial extracellular matrices. Their controllable properties, such as wettability, surface charge, transparency, elasticity, porosity and surface to volume proportion, have attracted much attention. Moreover, functionalizing polymers with other bioactive components could enable the engineering of microenvironments to host cells for regenerative medical applications. In the current brief review, we focus on the most recently cited electrospun nanofibrous polymeric scaffolds and divide them into five main categories: natural polymer-natural polymer composite, natural polymer-synthetic polymer composite, synthetic polymer-synthetic polymer composite, crosslinked polymers and reinforced polymers with inorganic materials. Then, we focus on their physiochemical, biological and mechanical features and discussed the capability and efficiency of the nanofibrous scaffolds to function as the extracellular matrix to support cellular function.

Development of Arabinoxylan-Reinforced Apple Pectin/Graphene Oxide/Nano-Hydroxyapatite Based Nanocomposite Scaffolds with Controlled Release of Drug for Bone Tissue Engineering: In-Vitro Evaluation of Biocompatibility and Cytotoxicity against MC3T3-E1

Fabrication of reinforced scaffolds to repair and regenerate defected bone is still a major challenge. Bone tissue engineering is an advanced medical strategy to restore or regenerate damaged bone. The excellent biocompatibility and osteogenesis behavior of porous scaffolds play a critical role in bone regeneration. In current studies, we synthesized polymeric nanocomposite material through free-radical polymerization to fabricate porous nanocomposite scaffolds by freeze drying. Functional group, surface morphology, porosity, pore size, and mechanical strength were examined through Fourier Transform Infrared Spectroscopy (FTIR), Single-Electron Microscopy (SEM), Brunauer-Emmet-Teller (BET), and Universal Testing Machine (UTM), respectively. These nanocomposites exhibit enhanced compressive strength (from 4.1 to 16.90 MPa), Young’s modulus (from 13.27 to 29.65 MPa) with well appropriate porosity and pore size (from 63.72 ± 1.9 to 45.75 ± 6.7 µm), and a foam-like morphology. The increasing amount of graphene oxide (GO) regulates the porosity and mechanical behavior of the nanocomposite scaffolds. The loading and sustained release of silver-sulfadiazine was observed to be 90.6% after 260 min. The in-vitro analysis was performed using mouse pre-osteoblast (MC3T3-E1) cell lines. The developed nanocomposite scaffolds exhibited excellent biocompatibility. Based on the results, we propose these novel nanocomposites can serve as potential future biomaterials to repair defected bone with the load-bearing application, and in bone tissue engineering.

Metamorphosis in Insect Muscle: Insights for Engineering Muscle-Based Actuators

One of the major limitations to advancing the development of soft robots is the absence of lightweight, effective soft actuators. While synthetic systems, such as pneumatics and shape memory alloys, have created important breakthroughs in soft actuation, they typically rely on large external power sources and some rigid components. Muscles provide an ideal actuator for soft constructs, as they are lightweight, deformable, biodegradable, silent, and powered by energy-dense hydrocarbons such as glucose. Vertebrate cell lines and embryonic cultures have allowed critical foundational work to this end, but progress there is limited by the difficulty of identifying individual pathways in embryonic development, and the divergence of immortal cell lines from these normal developmental programs. An alternative to culturing muscles from embryonic cells is to exploit the advantages of species with metamorphic stages. In these animals, muscles develop from a predefined pool of myoblasts with well-characterized contacts to other tissues. In addition, the endocrine triggers for development into adult muscles are often known and tractable for experimental manipulation. This is particularly true for metamorphic muscle development in holometabolous insects, which provide exciting new avenues for tissue engineering. Using insect tissues for actuator development confers additional benefits; insect muscles are more robust to varying pH, temperature, and oxygenation than are vertebrate cells. Given that biohybrid robots are likely to be used in ambient conditions and changing environments, this sort of hardiness is likely to be required for practical use. In this study, we summarize key processes and signals in metamorphic muscle development, drawing attention to those pathways that offer entry points for manipulation. By focusing on lessons learned from in vivo insect development, we propose that future culture designs will be able to use more systematic, hypothesis-driven approaches to optimizing engineered muscle. Impact statement This review summarizes our current understanding of metamorphic muscle development in insects. It provides a framework for engineering muscle-based actuators that can be used in robotic applications in a wide range of ambient conditions. The focus is on identifying key processes that might be manipulated to solve current challenges in controlling tissue development such as myoblast proliferation, myotube formation and fusion, cytoskeletal alignment, myotendinous attachment and full differentiation. An important goal is to gather findings that cross disciplinary boundaries and to promote the development of better bioactuators for nonclinical applications.

Effect of β-carotene on the differentiation potential of ciliary epithelium-derived MSCs isolated from mouse eyes on alginate-based scaffolds

Retinal degenerative diseases are considered a major challenge all over the world, and stem cell therapy is a promising approach to restore degenerative cells due to RD. MSCs are multipotent stem cells found in a variety of tissues. They are capable of differentiating into various retinal cell types, so it can be a good candidate for various degenerative disorders like retinal degenerations. β-carotene is an antioxidant that could accelerate the stem cell differentiation while using the proper scaffold. In this study, we evaluated the effect of β-carotene on the differentiation potential of ciliary epithelium-derived MSCs isolated from mouse eyes on alginate-based scaffolds. MSCs were isolated from mouse ciliary epithelium, cultured in DMEM medium supplemented with 10% FBS, and identified by detecting their surface antigens. Three 3D culture systems, alginate, alginate/gelatin, and gelatin hydrogels were prepared, and their structures were checked via SEM. MSCs were cultured on 3D and 2D culture system scaffolds following treated with differentiation medium containing 50 μM β-mercaptoethanol, 1 × minimum essential medium-nonessential amino acids and 20% of knockout serum replacement and β-carotene. MSCs viability and differentiation ability were examined by MTT and ICC, respectively. The expression changes of several retinal specific genes (Nestin, RPE65, and Rhodopsin) were also evaluated by qPCR. Over 80% of cells isolated from mouse ciliary epithelium were positive for MSC-specific markers. The viability rates of MSCs grown on all alginate-based scaffolds were above 70%. MSCs cultured on alginate-based scaffold in the differentiation medium containing β-carotene expressed higher levels of rhodopsin protein compared to a 2D culture. Also, the expressions of Nestin, Rhodopsin, and RPE65 genes were upregulated in β-carotene-treated MSCs grown on alginate-based scaffolds. Our results indicate that the addition of β-carotene to the differentiation medium, along with applying alginate-based scaffolds, could induce higher differentiation in mouse ciliary epithelium-derived MSCs into specialized retinal cells.

Human Adipose-Derived Mesenchymal Stem Cells-Incorporated Silk Fibroin as a Potential Bio-Scaffold in Guiding Bone Regeneration

Recently, stem cell-based bone tissue engineering (BTE) has been recognized as a preferable and clinically significant strategy for bone repair. In this study, a pure 3D silk fibroin (SF) scaffold was fabricated as a BTE material using a lyophilization method. We aimed to investigate the efficacy of the SF scaffold with and without seeded human adipose-derived mesenchymal stem cells (hASCs) in facilitating bone regeneration. The effectiveness of the SF-hASCs scaffold was evaluated based on physical characterization, biocompatibility, osteogenic differentiation in vitro, and bone regeneration in critical rat calvarial defects in vivo. The SF scaffold demonstrated superior biocompatibility and significantly promoted osteogenic differentiation of hASCs in vitro. At six and twelve weeks postimplantation, micro-CT showed no statistical difference in new bone formation amongst all groups. However, histological staining results revealed that the SF-hASCs scaffold exhibited a better bone extracellular matrix deposition in the defect regions compared to other groups. Immunohistochemical staining confirmed this result; expression of osteoblast-related genes (BMP-2, COL1a1, and OCN) with the SF-hASCs scaffold treatment was remarkably positive, indicating their ability to achieve effective bone remodeling. Thus, these findings demonstrate that SF can serve as a potential carrier for stem cells, to be used as an osteoconductive bioscaffold for BTE applications.

Enhancing survival, engraftment, and osteogenic potential of mesenchymal stem cells

Mesenchymal stem cells (MSCs) are promising candidates for bone regeneration therapies due to their plasticity and easiness of sourcing. MSC-based treatments are generally considered a safe procedure, however, the long-term results obtained up to now are far from satisfactory. The main causes of these therapeutic limitations are inefficient homing, engraftment, and osteogenic differentiation. Many studies have proposed modifications to improve MSC engraftment and osteogenic differentiation of the transplanted cells. Several strategies are aimed to improve cell resistance to the hostile microenvironment found in the recipient tissue and increase cell survival after transplantation. These strategies could range from a simple modification of the culture conditions, known as cell-preconditioning, to the genetic modification of the cells to avoid cellular senescence. Many efforts have also been done in order to enhance the osteogenic potential of the transplanted cells and induce bone formation, mainly by the use of bioactive or biomimetic scaffolds, although alternative approaches will also be discussed. This review aims to summarize several of the most recent approaches, providing an up-to-date view of the main developments in MSC-based regenerative techniques.

Recent Trends in Decellularized Extracellular Matrix Bioinks for 3D Printing: An Updated Review

The promise of regenerative medicine and tissue engineering is founded on the ability to regenerate diseased or damaged tissues and organs into functional tissues and organs or the creation of new tissues and organs altogether. In theory, damaged and diseased tissues and organs can be regenerated or created using different configurations and combinations of extracellular matrix (ECM), cells, and inductive biomolecules. Regenerative medicine and tissue engineering can allow the improvement of patients' quality of life through availing novel treatment options. The coupling of regenerative medicine and tissue engineering with 3D printing, big data, and computational algorithms is revolutionizing the treatment of patients in a huge way. 3D bioprinting allows the proper placement of cells and ECMs, allowing the recapitulation of native microenvironments of tissues and organs. 3D bioprinting utilizes different bioinks made up of different formulations of ECM/biomaterials, biomolecules, and even cells. The choice of the bioink used during 3D bioprinting is very important as properties such as printability, compatibility, and physical strength influence the final construct printed. The extracellular matrix (ECM) provides both physical and mechanical microenvironment needed by cells to survive and proliferate. Decellularized ECM bioink contains biochemical cues from the original native ECM and also the right proportions of ECM proteins. Different techniques and characterization methods are used to derive bioinks from several tissues and organs and to evaluate their quality. This review discusses the uses of decellularized ECM bioinks and argues that they represent the most biomimetic bioinks available. In addition, we briefly discuss some polymer-based bioinks utilized in 3D bioprinting.

Synthetic Biodegradable Aliphatic Polyester Nanocomposites Reinforced with Nanohydroxyapatite and/or Graphene Oxide for Bone Tissue Engineering Applications

This paper provides review updates on the current development of bionanocomposites with polymeric matrices consisting of synthetic biodegradable aliphatic polyesters reinforced with nanohydroxyaptite (nHA) and/or graphene oxide (GO) nanofillers for bone tissue engineering applications. Biodegradable aliphatic polyesters include poly(lactic acid) (PLA), polycaprolactone (PCL) and copolymers of PLA-PGA (PLGA). Those bionanocomposites have been explored for making 3D porous scaffolds for the repair of bone defects since nHA and GO enhance their bioactivity and biocompatibility by promoting biomineralization, bone cell adhesion, proliferation and differentiation, thus facilitating new bone tissue formation upon implantation. The incorporation of nHA or GO into aliphatic polyester scaffolds also improves their mechanical strength greatly, especially hybrid GO/nHA nanofilllers. Those mechanically strong nanocomposite scaffolds can support and promote cell attachment for tissue growth. Porous scaffolds fabricated from conventional porogen leaching, and thermally induced phase separation have many drawbacks inducing the use of organic solvents, poor control of pore shape and pore interconnectivity, while electrospinning mats exhibit small pores that limit cell infiltration and tissue ingrowth. Recent advancement of 3D additive manufacturing allows the production of aliphatic polyester nanocomposite scaffolds with precisely controlled pore geometries and large pores for the cell attachment, growth, and differentiation in vitro, and the new bone formation in vivo.

Morphological and Molecular Analysis of Osteoblasts Differentiated from Mesenchymal Stem Cells in Polycaprolactone/Magnesium Oxide/Graphene Oxide Scaffold

BACKGROUND

The loss or dysfunction of bone tissue that observed after bone tumor resections and severe nonunion fractures afflicts 200 million people worldwide. Bone tissue engineering is a promising approach to repair osteoporotic fractures.

OBJECTIVE

In this paper, polycaprolactone (PCL)/magnesium oxide (MgO)/graphene oxide (GO) nanofibrous scaffold was fabricated by electrospining method, and its biocompatibility and osteogenic differentiation of adipose-derived mesenchymal stem cells (MSCs) on this scaffold were evaluated and compared with pure PCL nanofibrous scaffold.

METHODS

SEM analysis, DAPI staining and MTT assay were used to evaluation biocompatibility of PCL/MgO/GO composite scaffold. In addition by ALP assay and proteomic approach, osteostimulatory effect of electrospun composite scaffold was investigated and the expression level of osteogenic markers including Runt-related transcription factor cbfa1/runx2 (runx2), collagen type I (Col1a1) and osteopontin (OPN) in MSCs seeded on PCL/MgO/GO composite scaffold was determined and compared with pure PCL scaffold. Then, RT-PCR technique was used to validate the level expression of these genes.

RESULTS

The obtained results showed that adhesion, viability and ALP activity of MSCs on PCL/MgO/GO scaffold considerably enhanced compared with pure PCL. As well as proteomic and real-time analysis illustrated the expression of osteogenic markers including runx2, Col1a1 and OPN increased (>2-fold) in cells seeded on PCL/MgO/GO composite scaffold.

CONCLUSION

It was concluded that MgO and GO nanoparticles could improve the biocompatibility of PCL scaffold and enhance the osteogenic differentiation of MSCs.

Mesenchymal Stromal Cell-Seeded Biomimetic Scaffolds as a Factory of Soluble RANKL in Rankl-Deficient Osteopetrosis

Biomimetic scaffolds are extremely versatile in terms of chemical composition and physical properties, which can be defined to accomplish specific applications. One property that can be added is the production/release of bioactive soluble factors, either directly from the biomaterial, or from cells embedded within the biomaterial. We reasoned that pursuing this strategy would be appropriate to setup a cell‐based therapy for RANKL‐deficient autosomal recessive osteopetrosis, a very rare skeletal genetic disease in which lack of the essential osteoclastogenic factor RANKL impedes osteoclast formation. The exogenously administered RANKL cytokine is effective in achieving osteoclast formation and function in vitro and in vivo, thus, we produced murine Rankl^−/− mesenchymal stromal cells (MSCs) overexpressing human soluble RANKL (hsRL) following lentiviral transduction (LVhsRL). Here, we described a three‐dimensional (3D) culture system based on a magnesium‐doped hydroxyapatite/collagen I (MgHA/Col) biocompatible scaffold closely reproducing bone physicochemical properties. MgHA/Col‐seeded murine MSCs showed improved properties, as compared to two‐dimensional (2D) culture, in terms of proliferation and hsRL production, with respect to LVhsRL‐transduced cells. When implanted subcutaneously in Rankl^−/− mice, these cell constructs were well tolerated, colonized by host cells, and intensely vascularized. Of note, in the bone of Rankl^−/− mice that carried scaffolds with either WT or LVhsRL‐transduced Rankl^−/− MSCs, we specifically observed formation of TRAP⁺ cells, likely due to sRL released from the scaffolds into circulation. Thus, our strategy proved to have the potential to elicit an effect on the bone; further work is required to maximize these benefits and achieve improvements of the skeletal pathology in the treated Rankl^−/− mice. Stem Cells Translational Medicine2019;8:22–34