Stem cells combined with bone graft substitutes in skeletal tissue engineering

Research Progress of Design Drugs and Composite Biomaterials in Bone Tissue Engineering

Bone, like most organs, has the ability to heal naturally and can be repaired slowly when it is slightly injured. However, in the case of bone defects caused by diseases or large shocks, surgical intervention and treatment of bone substitutes are needed, and drugs are actively matched to promote osteogenesis or prevent infection. Oral administration or injection for systemic therapy is a common way of administration in clinic, although it is not suitable for the long treatment cycle of bone tissue, and the drugs cannot exert the greatest effect or even produce toxic and side effects. In order to solve this problem, the structure or carrier simulating natural bone tissue is constructed to control the loading or release of the preparation with osteogenic potential, thus accelerating the repair of bone defect. Bioactive materials provide potential advantages for bone tissue regeneration, such as physical support, cell coverage and growth factors. In this review, we discuss the application of bone scaffolds with different structural characteristics made of polymers, ceramics and other composite materials in bone regeneration engineering and drug release, and look forward to its prospect.

Bone Regeneration Using Mesenchymal Stromal Cells and Biocompatible Scaffolds: A Concise Review of the Current Clinical Trials

Bone regenerative medicine is a clinical approach combining live osteoblast progenitors, such as mesenchymal stromal cells (MSCs), with a biocompatible scaffold that can integrate into host bone tissue and restore its structural integrity. Over the last few years, many tissue engineering strategies have been developed and thoroughly investigated; however, limited approaches have been translated to clinical application. Consequently, the development and clinical validation of regenerative approaches remain a centerpiece of investigational efforts towards the clinical translation of advanced bioengineered scaffolds. The aim of this review was to identify the latest clinical trials related to the use of scaffolds with or without MSCs to regenerate bone defects. A revision of the literature was performed in PubMed, Embase, and Clinicaltrials.gov from 2018 up to 2023. Nine clinical trials were analyzed according to the inclusion criteria: six presented in the literature and three reported in Clinicaltrials.gov. Data were extracted covering background trial information. Six of the clinical trials added cells to scaffolds, while three used scaffolds alone. The majority of scaffolds were composed of calcium phosphate ceramic alone, such as β-tricalcium phosphate (TCP) (two clinical trials), biphasic calcium phosphate bioceramic granules (three clinical trials), and anorganic bovine bone (two clinical trials), while bone marrow was the primary source of the MSCs (five clinical trials). The MSC expansion was performed in GMP facilities, using human platelet lysate (PL) as a supplement without osteogenic factors. Only one trial reported minor adverse events. Overall, these findings highlight the importance and efficacy of cell-scaffold constructs in regenerative medicine under different conditions. Despite the encouraging clinical results obtained, further studies are needed to assess their clinical efficacy in treating bone diseases to optimize their application.

Human Mesenchymal Stem Cells as a Carrier for a Cell-Mediated Drug Delivery

A number of preclinical and clinical studies have demonstrated the efficiency of mesenchymal stromal cells to serve as an excellent base for a cell-mediated drug delivery system. Cell-based targeted drug delivery has received much attention as a system to facilitate the uptake a nd transfer of active substances to specific organs and tissues with high efficiency. Human mesenchymal stem cells (MSCs) are attracting increased interest as a promising tool for cell-based therapy due to their high proliferative capacity, multi-potency, and anti-inflammatory and immunomodulatory properties. In particular, these cells are potentially suitable for use as encapsulated drug transporters to sites of inflammation. Here, we studied the in vitro effects of incorporating synthetic polymer microcapsules at various microcapsule-to-cell ratios on the morphology, ultrastructure, cytokine profile, and migration ability of human adipose-derived MSCs at various time points post-phagocytosis. The data show that under appropriate conditions, human MSCs can be efficiently loaded with synthesized microcapsules without damaging the cell’s structural integrity with unexpressed cytokine secretion, retained motility, and ability to migrate through 8 μm pores. Thus, the strategy of using human MSCs as a delivery vehicle for transferring microcapsules, containing bioactive material, across the tissue–blood or tumor–blood barriers to facilitate the treatment of stroke, cancer, or inflammatory diseases may open a new therapeutic perspective.

Identification of circRNA Expression Profiles in BMSCs from Glucocorticoid-Induced Osteoporosis Model

Background. Circular RNAs (circRNAs) contribute to the regulation of many diseases. However, little is known about the role of circRNAs in the development of glucocorticoid-induced osteoporosis (GIOP). The present study is aimed at systematically characterizing the circRNA expression profiles in GIOP and predict the potential functions of the associated regulatory networks. Methods. A small animal GIOP model was developed in Sprague-Dawley rats given daily intraperitoneal doses of the synthetic glucocorticoid dexamethasone. Micro-CT and bone histomorphometry were performed to characterize the bone loss. Alizarin red S (ARS) staining and alkaline phosphatase (ALP) activity were assessed to determine the osteogenic differentiation potential of BMSCs. RNA sequencing was performed to identify differentially expressed circRNAs in BMSCs between the GIOP and normal groups, which were validated by qRT-PCR. siRNA interference experiments were used to demonstrate their function. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were performed to predict the functions of differentially expressed circRNAs. The microRNA (miRNA) targets of the circRNAs and circRNA-miRNA interactions were predicted. Results. Micro-CT and bone histomorphometry confirmed the rat GIOP model. Both ARS intensity and ALP activity were decreased in GIOP BMSCs. Seventeen circRNAs were identified by $\text{fold}\text{change}=2.0$ , $p<0.05$ , and $\text{false}\text{discovery}\text{rate}<0.05$ , of which 7 were upregulated and 10 were downregulated. The qRT-PCR results of the selected circRNAs were consistent with the RNA-seq results and showed that circARSB and circAKT3 were significantly upregulated, while circPTEN and circTRPM7 were downregulated in the GIOP group. Further functional experiments found that downregulation of circARSB and circPTEN expression resulted in a corresponding change in osteogenic differentiation, suggesting that circARSB negatively, while circPTEN positively, regulates BMSC osteogenic differentiation. Analysis of circRNA-targeted miRNAs predicted that miR-135a-5p was associated with circARSB and circAKT3, and miR-881-3p was associated with circPTEN and circTRPM7. Furthermore, the signalling pathways associated with these differentially expressed circRNAs were predicted. Conclusions. The present study identified circARSB, circAKT3, circPTEN, and circTRPM7 as being associated with osteogenic differentiation during GIOP through a circRNA-targeted miRNA-mRNA axis, which might provide insight into the pathophysiological mechanism of GIOP.

Mesenchymal stem cells plus bone repair materials as a therapeutic strategy for abnormal bone metabolism: Evidence of clinical efficacy and mechanisms of action implied

The regeneration process of human bones is very complicated, the management and treatment of bone damage caused by diseases are the main problems faced by clinicians worldwide. It is known that cell-based stem cell therapy together with biomaterials is a fast-developing method of tissue regeneration. This review focuses on the different types and main characteristics of scaffolds and stem cells suitable for bone regeneration, and aims to provide a state-of-the-art description of the current treatment of common bone metabolism related diseases such as osteoarthritis, osteoporosis and osteosarcoma and the strategies based on stem cell biological scaffolds used in bone tissue engineering. This method may provide a new treatment option for the treatment of common bone metabolism-related diseases that cannot be cured by ordinary and routine applications. Three databases (PubMed, CNKI and Web of Science) search terms used to write this review are: "arthritis", "osteoporosis", "osteosarcoma", "bone tissue engineering", "mesenchymal stem cells", "materials", "bioactive scaffolds" and their combinations, and the most relevant studies are selected. As a conclusion, it needs to be emphasized that despite the encouraging results, further development is needed due to the need for more in-depth research, standardization of stem cell manufacturing processes, large-scale development of clinical methods for bone tissue engineering, and market regulatory approval. Although the research and application of tissue regeneration technology and stem cells are still in their infancy, the application prospect is broad and it is expected to solve the current clinical problems.

Repair of long bone defects of large size using a tissue-engineered periosteum in a rabbit model

Tissue engineering is a promising approach for bone regeneration. In this study, we aimed to investigate whether tissue engineered periosteum (TEP), which was fabricated by combining osteogenically-induced mesenchymal stem cells (MSCs) with porcine small intestinal submucosa (SIS), could restore long bone defects of large size in rabbits. Twenty-four adult New Zealand white rabbits (NZWRs) were used in the experiments. Long bone defects of large size (30 mm-50 mm; average, 40 mm) were established on both sides of NZWRs' radii. The defects were treated with TEP (Group A), allogeneic deproteinized bone (DPB, Group B), TEP combined with DPB (Group C), and pure SIS (Group D). The healing outcome was evaluated by radiography and histological examination at 4, 8, and 12 weeks post-treatment. The radiographical findings showed that bone defects of large size were all repaired in Groups A, B and C within 12 weeks, whereas Group D (pure SIS group) failed to result in defect healing at 4, 8, and 12 weeks. Although there was some new bone regeneration connecting the allografts and bone ends, as observed under radiographical and histological observations, bone defects of large sizes were restored primarily by structurally allografted DPB within 12 weeks. The TEP groups (Groups A and C) showed partial or total bone regeneration upon histological inspection. Based on 12-week histological examinations, significantly more bone was formed in Group A than Group C (P < 0.05), and both groups formed significantly more bone than in Groups B and D. The results indicated that long bone defects of a large size could be restored by TEP or TEP combined with the DPB scaffold, and such materials provide an alternative approach to resolving pathological bone defects in clinical settings.

RNF213 gene silencing upregulates transforming growth factor β1 expression in bone marrow-derived mesenchymal stem cells and is involved in the onset of Moyamoya disease

Moyamoya disease (MMD) is a chronic and progressive cerebrovascular occlusion disease, the precise etiology of which is poorly understood. Ring finger protein 213 (RNF213) has been previously identified as a susceptibility gene that serves an important role in angiogenesis, where it has been shown to be closely associated with the onset of MMD. Patients with MMD exhibit increased expression levels of various pro-inflammatory molecules and angiogenic factors. Under certain conditions, bone marrow mesenchymal stem cells (BMSCs) have the ability to differentiate to form neuron-like and microglia-like cells. In the present study, a total of 40 MMD patients and 40 healthy individuals were enrolled. ELISA assays revealed that the expression of serum vascular endothelial growth factor (VEGF) and transforming growth factor β1 (TGF-β1) were higher than that in healthy controls. Furthermore, rat BMSCs (rBMSCs) were isolated and cultured using the whole bone marrow adherence method, which were then phenotyped using flow cytometry. Osteogenic and adipogenic differentiation were determined by using Alizarin red and oil red O staining, respectively. RNF213 was knocked-down using a lentivirus-mediated short hairpin RNA system in passage three rBMSCs, and successful transfection of the RNF213 was confirmed by RT-qPCR and fluorescence imaging. The expression levels of VEGF and TGF-β1 in these rBMSCs were measured on days 7 and 14, respectively. The results demonstrated that RNF213 knockdown upregulated TGF-β1 at both protein and mRNA levels, but did not exert any effect on VEGF gene expression. In conclusion, these findings suggested that that RNF213 knockdown may contribute to aberrant TGF-β1 expression via a pathway that remains to be unidentified, indicating that quantitative changes in RNF213 gene expression may serve an important role in the pathogenesis of MMD.

Bone Regeneration Improves with Mesenchymal Stem Cell Derived Extracellular Vesicles (EVs) Combined with Scaffolds: A Systematic Review

Scaffolds associated with mesenchymal stem cell (MSC) derivatives, such as extracellular vesicles (EVs), represent interesting carriers for bone regeneration. This systematic review aims to analyze in vitro and in vivo studies that report the effects of EVs combined with scaffolds in bone regeneration. A methodical review of the literature was performed from PubMed and Embase from 2012 to 2020. Sixteen papers were analyzed; of these, one study was in vitro, eleven were in vivo, and four were both in vitro and in vivo studies. This analysis shows a growing interest in this upcoming field, with overall positive results. In vitro results were demonstrated as both an effect on bone mineralization and proangiogenic ability. The interesting in vitro outcomes were confirmed in vivo. Particularly, these studies showed positive effects on bone regeneration and mineralization, activation of the pathway for bone regeneration, induction of vascularization, and modulation of inflammation. However, several aspects remain to be elucidated, such as the concentration of EVs to use in clinic for bone-related applications and the definition of the real advantages.

Calcium Chelidonate: Semi-Synthesis, Crystallography, and Osteoinductive Activity In Vitro and In Vivo

Calcium chelidonate [Ca(ChA)(H₂O)₃]_n was obtained by semi-synthesis using natural chelidonic acid. The structure of the molecular complex was determined by X-ray diffraction analysis. The asymmetric unit of [Ca(ChA)(H₂O)₃]_n includes chelidonic acid coordinated through three oxygen atoms, and three water ligands. The oxygen atoms of acid and oxygen atoms of water from each asymmetric unit are also coordinated to the calcium of another one, forming an infinite linear complex. Calcium geometry is close to the trigonal dodecahedron (D2d). The intra-complex hydrogen bonds additionally stabilize the linear species, which are parallel to the axis. In turn the linear species are packed into the 3D structure through mutual intercomplex hydrogen bonds. The osteogenic activity of the semi-synthetic CaChA was studied in vitro on 21-day hAMMSC culture and in vivo in mice using ectopic (subcutaneous) implantation of CaP-coated Ti plates saturated in vitro with syngeneic bone marrow. The enhanced extracellular matrix ECM mineralization in vitro and ectopic bone tissue formation in situ occurred while a water solution of calcium chelidonate at a dose of 10 mg/kg was used. The test substance promotes human adipose-derived multipotent mesenchymal stromal/stem cells (hAMMSCs), as well as mouse MSCs to differentiate into osteoblasts in vitro and in vivo, respectively. Calcium chelidonate is non-toxic and can stimulate osteoinductive processes.

Rifapentine Polylactic Acid Sustained-Release Microsphere Complex for Spinal Tuberculosis Therapy: Preparation, in vitro and in vivo Studies

Purpose

Spinal tuberculosis has been a common clinical extrapulmonary tuberculosis in recent years. The general anti-tuberculosis drug treatment cycle is long, with unsatisfactory efficacy. This study focused on the preparation and evaluation of rifapentine polylactic acid sustained-release microsphere complex for spinal tuberculosis therapy.

Methods

Rifapentine polylactic acid sustained-release microspheres (RPSMs) were prepared through the double emulsion solvent evaporation method, and RPSMs were combined with hydroxyapatite/β-tricalcium phosphate (HA/β-TCP) composite material to obtain drug-loaded, sustained-release complex. We evaluated the complex for dynamics of drug release and osteogenic ability using in vitro release test, alkaline phosphatase and alizarin red staining, real-time PCR and Western blot. A rabbit model of a spinal tuberculosis defect was established and repaired using HA/β-TCP or complex. The ability of anti-tuberculosis and tissue repair effects of the complex were evaluated through in vivo experiments.

Results

The complex constructed of RPSMs and HA/β-TCP demonstrated a long drug release time, with no significant inhibition of cell osteogenic differentiation in vitro experiments. Postoperative macroscopic observation, immunohistochemical staining and Nilsson histological scores showed that the complex has good effects on the tissue repair. Moreover, the erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), important indexes of inflammation, decreased to normal levels in the complex group.

Conclusion

In vitro and in vivo experiments demonstrated that the complex constructed of RPSMs and HA/β-TCP effectively treated spinal tuberculosis. Therefore, the complex represents a promising approach for the treatment of spinal tuberculosis.

Combination of optimized tissue engineering bone implantation with heel-strike like mechanical loading to repair segmental bone defect in New Zealand rabbits

In this study, effects of combining optimized tissue engineering bone (TEB) implantation with heel-strike like mechanical loading to repair segmental bone defect in New Zealand rabbits were investigated. Physiological characteristics of bone marrow mesenchymal stem cells (BMMSCs), compact bone cells (CBCs), and bone marrow and compact bone coculture cells (BMMSC-CBCs) were compared to select the optimal seed cells for optimized TEB construction. Rabbits with segmental bone defects were treated in different ways (cancellous bone scaffold for group A, cancellous bone scaffold and mechanical loading for group B, optimized TEB for group C, optimized TEB and mechanical loading for group D, n = 4), and the bone repair were compared. BMMSC-CBCs showed better proliferation capacity than CBCs (p < 0.01) and stronger osteogenic differentiation ability than BMMSCs (p < 0.05). Heel-strike like mechanical loading improved proliferation and osteogenic differentiation ability and expression levels of TGFβ1 as well as BMP2 of seed cells in vitro (p < 0.05). At week 12 post-operation, group D showed the best bone repair, followed by groups B and C, while group A finished last (p < 0.05). During week 4 to 12 post-operation, group D peaked in terms of expression levels of TGFβ1, BMP2, and OCN, followed by groups B and C, while group A finished last (p < 0.05). Thus, BMMSC-CBCs showed good proliferation and osteogenic differentiation ability, and they were thought to be better as seed cells than BMMSCs and CBCs. The optimized TEB implantation combined with heel-strike like mechanical loading had a synergistic effect on bone defect healing, and enhanced expression of TGFβ1 and BMP2 played an important role in this process.

Periosteum Mimetic Coating on Structural Bone Allografts via Electrospray Deposition Enhances Repair and Reconstruction of Segmental Defects

Structural bone allograft transplantation remains one of the common strategies for repair and reconstruction of large bone defects. Due to the loss of periosteum that covers the outer surface of the cortical bone, the healing and incorporation of allografts is extremely slow and limited. To enhance the biological performance of allografts, herein, we report a novel and simple approach for engineering a periosteum mimetic coating on the surface of structural bone allografts via polymer-mediated electrospray deposition. This approach enables the coating on allografts with precisely controlled composition and thickness. In addition, the periosteum mimetic coating can be tailored to achieve desired drug release profiles by making use of an appropriate biodegradable polymer or polymer blend. The efficacy study in a murine segmental femoral bone defect model demonstrates that the allograft coating composed of poly(lactic-co-glycolic acid) and bone morphogenetic protein-2 mimicking peptide significantly improves allograft healing as evidenced by decreased fibrotic tissue formation, increased periosteal bone formation, and enhanced osseointegration. Taken together, this study provides a platform technology for engineering a periosteum mimetic coating which can greatly promote bone allograft healing. This technology could eventually result in an off-the-shelf and multifunctional structural bone allograft for highly effective repair and reconstruction of large segmental bone defects. The technology can also be used to ameliorate the performance of other medical implants by modifying their surfaces.

Costimulatory Effect of Rough Calcium Phosphate Coating and Blood Mononuclear Cells on Adipose-Derived Mesenchymal Stem Cells In Vitro as a Model of In Vivo Tissue Repair

Calcium phosphate (CaP) materials do not always induce ectopic vascularization and bone formation; the reasons remain unclear, and there are active discussions of potential roles for post-implantation hematoma, circulating immune and stem cells, and pericytes, but studies on adipose-derived stem cells (AMSCs) in this context are lacking. The rough (average surface roughness R_a = 2-5 µm) scaffold-like CaP coating deposited on pure titanium plates by the microarc oxidation method was used to investigate its subcutaneous vascularization in CBA/CaLac mice and in vitro effect on cellular and molecular crosstalk between human blood mononuclear cells (hBMNCs) and AMSCs (hAMSCs). Postoperative hematoma development on the CaP surface lasting 1-3 weeks may play a key role in the microvessel elongation and invasion into the CaP relief at the end of the 3rd week of injury and BMNC migration required for enhanced wound healing in mice. Satisfactory osteogenic and chondrogenic differentiation but poor adipogenic differentiation of hAMSCs on the rough CaP surface were detected in vitro by differential cell staining. The fractions of CD73⁺ (62%), CD90⁺ (0.24%), and CD105⁺ (0.41%) BMNCs may be a source of autologous circulating stem/progenitor cells for the subcutis reparation, but allogenic hBMNC participation is mainly related to the effects of CD4⁺ T cells co-stimulated with CaP coating on the in vitro recruitment of hAMSCs, their secretion of angiogenic and osteomodulatory molecules, and the increase in osteogenic features within the period of in vivo vascularization. Cellular and molecular crosstalk between BMNCs and AMSCs is a model of effective subcutis repair. Rough CaP surface enhanced angio- and osteogenic signaling between cells. We believe that preconditioning and/or co-transplantation of hAMSCs with hBMNCs may broaden their potential in applications related to post-implantation tissue repair and bone bioengineering caused by microarc CaP coating.

Zn- or Cu-containing CaP-Based Coatings Formed by Micro-Arc Oxidation on Titanium and Ti-40Nb Alloy: Part II-Wettability and Biological Performance

This work describes the wettability and biological performance of Zn- and Cu-containing CaP-based coatings prepared by micro-arc oxidation on pure titanium (Ti) and novel Ti-40Nb alloy. Good hydrophilic properties of all the coatings were demonstrated by the low contact angles with liquids, not exceeding 45°. An increase in the applied voltage led to an increase of the coating roughness and porosity, thereby reducing the contact angles to 6° with water and to 17° with glycerol. The free surface energy of 75 ± 3 mJ/m² for all the coatings were determined. Polar component was calculated as the main component of surface energy, caused by the presence of strong polar PO₄³⁻ and OH⁻ bonds. In vitro studies showed that low Cu and Zn amounts (~0.4 at.%) in the coatings promoted high motility of human adipose-derived multipotent mesenchymal stromal cells (hAMMSC) on the implant/cell interface and subsequent cell ability to differentiate into osteoblasts. In vivo study demonstrated 100% ectopic bone formation only on the surface of the CaP coating on Ti. The Zn- and Cu-containing CaP coatings on both substrates and the CaP coating on the Ti-40Nb alloy slightly decreased the incidence of ectopic osteogenesis down to 67%. The MAO coatings showed antibacterial efficacy against Staphylococcus aureus and can be arranged as follows: Zn-CaP/Ti > Cu-CaP/TiNb, Zn-CaP/TiNb > Cu-CaP/Ti.

Mineral-Coated Microparticles Enhance mRNA-Based Transfection of Human Bone Marrow Cells

The regenerative potential of bone marrow cells could be harnessed for tissue engineering applications. Bone marrow can be easily collected from patients, providing a valuable autologous source of therapeutic cells. However, years of delivery of bone marrow cells have highlighted the need for their genetic manipulation to overcome heterogeneity and to confer specificity to the regenerative process. In this study, we optimized the use of condensed mRNA as a non-viral alternative. As a proof of concept, we used mRNA encoding for reporter proteins such as EGFP or Firefly luciferase, which was condensed by complexing agents and delivered to human bone marrow cells using mineral-coated microparticles. We demonstrated that human bone marrow cells could be transfected with complexed mRNA, and that this approach was more efficient than the delivery of complexed plasmid DNA. In addition, human bone marrow cells were vulnerable to the toxicity of mRNA complexing agents, but these deleterious effects were mitigated by using mineral-coated microparticles as a carrier of complexed mRNA. Microparticle-mediated delivery of complexed mRNA also enabled higher cell metabolic activity and higher transfection in multiple in vitro culture conditions, including suspension culture and three-dimensional culture.

Enhanced osteogenic differentiation of mesenchymal stem cells in ankylosing spondylitis: a study based on a three-dimensional biomimetic environment

The mechanism of pathological osteogenesis in Ankylosing spondylitis (AS) is largely unknown. Our previous studies demonstrated that the imbalance between BMP-2 and Noggin secretion induces abnormal osteogenic differentiation of marrow-derived mesenchymal stem cells (MSCs) from AS patients in a two-dimensional culture environment. In this study, HA/β-TCP scaffolds were further used as a three-dimensional (3D) biomimetic culture system to mimic the bone microenvironment in vivo to determine the abnormal osteogenic differentiation of AS-MSCs. We demonstrated that when cultured in HA/β-TCP scaffolds, AS-MSCs had a stronger osteogenic differentiation capacity than that of MSCs from healthy donors (HD-MSCs) in vitro and in vivo. This dysfunction resulted from BMP2 overexpression in AS-MSCs, which excessively activated the Smad1/5/8 and ERK signalling pathways and finally led to enhanced osteogenic differentiation. Both the signalling pathway inhibitors and siRNAs inhibiting BMP2 expression could rectify the enhanced osteogenic differentiation of AS-MSCs. Furthermore, BMP2 expression in ossifying entheses was significantly higher in AS patients. In summary, our study demonstrated that AS-MSCs possess enhanced osteogenic differentiation in HA/β-TCP scaffolds as a 3D biomimetic microenvironment because of BMP2 overexpression, but not Noggin. These results provide insights into the mechanism of pathological osteogenesis, which can aid in the development of niche-targeting medications for AS.

Bone marrow-derived stem/stromal cells (BMSC) 3D microtissues cultured in BMP-2 supplemented osteogenic induction medium are prone to adipogenesis

Bone marrow-derived mesenchymal stem/stromal cells (BMSC) may facilitate bone repair through secretion of factors that stimulate endogenous repair processes or through direct contribution to new bone through differentiation into osteoblast-like cells. BMSC microtissue culture and differentiation has been widely explored recently, with high-throughput platforms making large-scale manufacture of microtissues increasingly feasible. Bone-like BMSC microtissues could offer an elegant method to enhance bone repair, especially in small-volume non-union defects, where small diameter microtissues could be delivered orthoscopically. Using a high-throughput microwell platform, our data demonstrate that (1) BMSC in 3D microtissue culture result in tissue compaction, rather than growth, (2) not all mineralised bone-like matrix is incorporated in the bulk microtissue mass and (3) a significant amount of lipid vacuole formation is observed in BMSC microtissues exposed to BMP-2. These factors should be considered when optimising BMSC osteogenesis in microtissues or developing BMSC microtissue-based therapeutic delivery processes.

Layer-by-layer nanofiber-enabled engineering of biomimetic periosteum for bone repair and reconstruction

Periosteum plays an indispensable role in bone repair and reconstruction. To recapitulate the remarkable regenerative capacity of periosteum, a biomimetic tissue-engineered periosteum (TEP) was constructed via layer-by-layer bottom-up strategy utilizing polycaprolactone (PCL), collagen, and nano-hydroxyapatite composite nanofiber sheets seeded with bone marrow stromal cells (BMSCs). When combined with a structural bone allograft to repair a 4 mm segmental bone defect created in the mouse femur, TEP restored donor-site periosteal bone formation, reversing the poor biomechanics of bone allograft healing at 6 weeks post-implantation. Further histologic analyses showed that TEP recapitulated the entire periosteal bone repair process, as evidenced by donor-dependent formation of bone and cartilage, induction of distinct CD31^high type H endothelium, reconstitution of bone marrow and remodeling of bone allografts. Compared to nanofiber sheets without BMSC seeding, TEP eliminated the fibrotic tissue capsule elicited by nanofiber sheets, leading to a marked improvement of osseointegration at the compromised periosteal site. Taken together, our study demonstrated a novel layer-by-layer engineering platform for construction of a versatile biomimetic periosteum, enabling further assembly of a multi-component and multifunctional periosteum replacement for bone defect repair and reconstruction.

<i>In Vitro</i> Comparative Study of Osteogenic Differentiation Ability between Adipose and Bone Marrow Mesenchymal Stem Cell Applied to Bovine Demineralized Bone Matrix

Ideal bone graft must possess the desirable trait such as osteoconductive, osteoinductive and osteogenesis. Demineralized Bone Matrix (DBM) provides both osteoconductive and osteoinductive trait. Referring to the tissue engineering principle, the addition of mesenchymal stem cell would add the osteogenic trait to this procedure. The design of this study is experimental using Bovine DBM. Bone Marrow Mesenchymal Stem Cell (BMSCs) and Adipose Mesenchymal Stem Cells (ASCs) were taken from New Zealand white rabbit. There are two groups of treatment, divided into DBM implanted with BMSCs and DBM implanted with ASCs. Each BMSCs and ASCs groups is incubated in the normal and osteogenic culture plate. Evaluation is performed by counting the osteoblast and immunohistochemistry stain using Alkaline Phosphate and Osteocalcin. After 4 weeks of incubation, we found that the osteoblast count in BMSCs groups is higher compared to the ASCs groups in both culture condition (p<0.01) along with Alkaline Phosphate staining (p<0.05), while the Osteocalcin staining showed insignificant differences (p>0.05). This study revealed that xenogenic bovine DBM can act as the potential osteoinductive scaffold for the MSCs to differentiate. The tissue engineering application by combining MSCs and Bovine DBM can be considered as an alternative in managing bone defect cases.

Harnessing extracellular vesicles to direct endochondral repair of large bone defects

Large bone defects remain a tremendous clinical challenge. There is growing evidence in support of treatment strategies that direct defect repair through an endochondral route, involving a cartilage intermediate. While culture-expanded stem/progenitor cells are being evaluated for this purpose, these cells would compete with endogenous repair cells for limited oxygen and nutrients within ischaemic defects. Alternatively, it may be possible to employ extracellular vesicles (EVs) secreted by culture-expanded cells for overcoming key bottlenecks to endochondral repair, such as defect vascularization, chondrogenesis, and osseous remodelling. While mesenchymal stromal/stem cells are a promising source of therapeutic EVs, other donor cells should also be considered. The efficacy of an EV-based therapeutic will likely depend on the design of companion scaffolds for controlled delivery to specific target cells. Ultimately, the knowledge gained from studies of EVs could one day inform the long-term development of synthetic, engineered nanovesicles. In the meantime, EVs harnessed from in vitro cell culture have near-term promise for use in bone regenerative medicine. This narrative review presents a rationale for using EVs to improve the repair of large bone defects, highlights promising cell sources and likely therapeutic targets for directing repair through an endochondral pathway, and discusses current barriers to clinical translation. Cite this article: E. Ferreira, R. M. Porter. Harnessing extracellular vesicles to direct endochondral repair of large bone defects. Bone Joint Res 2018;7:263-273. DOI: 10.1302/2046-3758.74.BJR-2018-0006.

Effect of mechanical strain on the pluripotency of murine embryonic stem cells seeded in a collagen-I scaffold

The use of embryonic stem cells (ESC) in regenerative medicine is restricted due to the possibility of tumorigenicity after inefficient or incomplete differentiation. Studies from our group, and others, suggest that mechanical stimuli may have a suppressive effect on the pluripotency/tumorigenesis of murine ESC (mESC). Furthermore, we have demonstrated that mESC seeded in a type I collagen scaffold, and transplanted into a murine bone fracture model, demonstrated repair without tumor formation. However, it remains unknown if mechanical factors were involved in blocking tumorigenicity of the mESC. Therefore, the aims of the current study were: (i) to characterize the mechanical environment within the transplanted construct (mESC-Col I) in an in vivo murine fracture model using computational analyses; and (ii) to reproduce this mechanical environment in vitro to elucidate the role of these mechanical factors on mESC pluripotent gene expression. It was predicted that the mESC-Col I construct was subjected to an average octahedral shear strain of ∼3.8% and a compressive strain of ∼3.1% within the fracture in vivo when the murine tibia was subjected to an axial compression load of 4 N (1 Hz). When a similar strain environment was replicated experimentally in vitro, the expression patterns of marker genes for pluripotency (Oct 4, Sox 2, Nanog, Rex 1, and oncogene ERas) were significantly down-regulated. This suggests that the local micro-mechanical environment within the fracture site in vivo may be involved in regulating stem cell fate after transplantation, and that these physical factors should be considered when developing regenerative medicine strategies. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:799-807, 2018.

Ectopic bone formation by aggregated mesenchymal stem cells from bone marrow and adipose tissue: A comparative study

Tissue engineered constructs (TECs) based on spheroids of bone marrow mesenchymal stromal cells (BM-MSCs) combined with calcium phosphate microparticles and enveloped in a platelet-rich plasma hydrogel showed that aggregation of MSCs improves their ectopic bone formation potential. The stromal vascular fraction (SVF) and adipose-derived MSCs (ASCs) have been recognized as an interesting MSC source for bone tissue engineering, but their ectopic bone formation is limited. We investigated whether aggregation of ASCs could similarly improve ectopic bone formation by ASCs and SVF cells. The formation of aggregates with BM-MSCs, ASCs and SVF cells was carried out and gene expression was analysed for osteogenic, chondrogenic and vasculogenic genes in vitro. Ectopic bone formation was evaluated after implantation of TECs in immunodeficient mice with six conditions: TECs with ASCs, TECs with BM-MSC, TECs with SVF cells (with and without rhBMP2), no cells and no cells with rhBMP2. BM-MSCs showed consistent compact spheroid formation, ASCs to a lesser extent and SVF showed poor spheroid formation. Aggregation of ASCs induced a significant upregulation of the expression of osteogenic markers like alkaline phosphatase and collagen type I, as compared with un-aggregated ASCs. In vivo, ASC and SVF cells both generated ectopic bone in the absence of added morphogenetic proteins. The highest incidence of bone formation was seen with BM-MSCs (7/9) followed by SVF + rhBMP2 (4/9) and no cells + rhBMP2 (2/9). Aggregation can improve ectopic bone tissue formation by adipose-derived cells, but is less efficient than rhBMP2. A combination of both factors should now be tested to investigate an additive effect.

In vivo investigation of tissue-engineered periosteum for the repair of allogeneic critical size bone defects in rabbits

Aim: The aim of the study was to evaluate the efficacy of tissue-engineered periosteum (TEP) in repairing allogenic bone defects in the long term. Materials & methods: TEP was biofabricated with osteoinduced rabbit bone marrow mesenchymal stem cells and porcine small intestinal submucosa (SIS). A total of 24 critical sized defects were created bilaterally in radii of 12 New Zealand White rabbits. TEP/SIS was implanted into the defect site. Bone defect repair was evaluated with radiographic and histological examination at 4, 8 and 12 weeks. Results: Bone defects were structurally reconstructed in the TEP group with mature cortical bone and medullary canals, however this was not observed in the SIS group at 12 weeks. Conclusion: The TEP approach can effectively restore allogenic critical sized defects, and achieve maturity of long-bone structure in 12 weeks in rabbit models.

The Hair Follicle: An Underutilized Source of Cells and Materials for Regenerative Medicine

The hair follicle is one of only two structures within the adult body that selectively degenerates and regenerates, making it an intriguing organ to study and use for regenerative medicine. Hair follicles have been shown to influence wound healing, angiogenesis, neurogenesis, and harbor distinct populations of stem cells; this has led to cells from the follicle being used in clinical trials for tendinosis and chronic ulcers. In addition, keratin produced by the follicle in the form of a hair fiber provides an abundant source of biomaterials for regenerative medicine. In this review, we provide an overview of the structure of a hair follicle, explain the role of the follicle in regulating the microenvironment of skin and the impact on wound healing, explore individual cell types of interest for regenerative medicine, and cover several applications of keratin-based biomaterials.

Minipig-BMSCs Combined with a Self-Setting Calcium Phosphate Paste for Bone Tissue Engineering

Calcium phosphate cements (CPCs) are a new generation of bone repair materials with good biocompatibility for various stem cells. The minipig is a recommended large animal model for bone engineering research. This study aimed to evaluate the feasibility of utilizing CPC scaffolds for the adhesion, proliferation, and osteogenic differentiation of minipig's bone marrow mesenchymal stem cells (pBMSCs). Passage 3 pBMSCs were seeded on the CPC scaffold and cultured with osteogenic culture medium (osteogenic group) or normal medium (control group). The density of viable cells increased in both groups, and pBMSCs firmly attached and spread well on the CPC scaffold. The alkaline phosphatase (ALP) activity in the osteogenic group had significantly increased on day 7 (D7) and peaked on D14. qRT-PCR revealed that mRNA levels of ALP and three osteogenic marker genes were significantly higher on D4, D7, and D14 in the osteogenic group. Alizarin Red S staining showed a significantly higher degree of bone mineralization from D7, D14 to D21 in the osteogenic group. These results indicated that pBMSCs can attach, proliferate well on CPC scaffold, and be successfully induced to differentiate into osteogenic cells. Our findings may be helpful for bone tissue engineering and the studies of bone regeneration.

Bone tissue engineering using polyetherketoneketone scaffolds combined with autologous mesenchymal stem cells in a sheep calvarial defect model

Polyetherketoneketone (PEKK) a high performance thermoplastic polymer that is FDA-approved for cranio- and maxillo-facial as well as spineal surgery. We studied the viability, growth and osteogenic differentiation of bone marrow-derived human and sheep mesenchymal stem cells (MSC) in combination with a 3D scaffold made of PEKK using different cell-based assays. To investigate if autologous MSC, either undifferentiated or osteogenically pre-differentiated, augmented bone formation after implantation, we implanted cell-seeded 3D PEKK scaffolds into calvarial defects in sheep for 12 weeks. The volume and quality of newly formed bone were investigated using micro-computer tomography (micro-CT) and histological stainings. Our results show that the 3D PEKK scaffolds were cyto- and bio-compatible. They allowed for adherence, growth and osteogenic differentiation of human and ovine MSC. However, bone healing seemed unaffected by whether the scaffolds were seeded with MSC. Considerable amounts of newly formed bone were found in all PEKK treated groups, but a fibrous capsule was formed around the implants regardless of cell seeding with MSC.

Regionally-derived cell populations and skeletal stem cells from human foetal femora exhibit specific osteochondral and multi-lineage differentiation capacity in vitro and ex vivo

Background

Adult skeletal stem cells (SSCs) often exhibit limited in vitro expansion with undesirable phenotypic changes and loss of differentiation capacity. Foetal tissues offer an alternative cell source, providing SSCs which exhibit desirable differentiation capacity over prolonged periods, ideal for extensive in vitro and ex vivo investigation of fundamental bone biology and skeletal development.

Methods

We have examined the derivation of distinct cell populations from human foetal femora. Regionally isolated populations including epiphyseal and diaphyseal cells were carefully dissected. Expression of the SSC marker Stro-1 was also found in human foetal femora over a range of developmental stages and subsequently utilised for immuno-selection.

Results

Regional populations exhibited chondrogenic (epiphyseal) and osteogenic (diaphyseal) phenotypes following in vitro and ex vivo characterisation and molecular analysis, indicative of native SSC maturation during skeletal development. However, each population exhibited potential for induced multi-lineage differentiation towards bone (bone nodule formation), cartilage (proteoglycan and mucopolysaccharide deposition) and fat (lipid deposition), suggesting the presence of a shared stem cell sub-population. This shared sub-population may be comprised of Stro-1+ cells, which were later identified and immuno-selected from whole foetal femora exhibiting multi-lineage differentiation capacity in vitro and ex vivo.

Conclusions

Distinct populations were isolated from human foetal femora expressing osteochondral differentiation capacity. Stro-1 immuno-selected SSCs were isolated from whole femora expressing desirable multi-lineage differentiation capacity over prolonged in vitro expansion, superior to their adult-derived counterparts, providing a valuable cell source with which to study bone biology and skeletal development.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-015-0247-2) contains supplementary material, which is available to authorized users.

Skeletal tissue engineering using mesenchymal or embryonic stem cells: clinical and experimental data

INTRODUCTION

Mesenchymal stem cells (MSCs) can be obtained from a wide variety of tissues for bone tissue engineering such as bone marrow, adipose, birth-associated, peripheral blood, periosteum, dental and muscle. MSCs from human fetal bone marrow and embryonic stem cells (ESCs) are also promising cell sources.

AREAS COVERED

In vitro, in vivo and clinical evidence was collected using MEDLINE® (1950 to January 2014), EMBASE (1980 to January 2014) and Google Scholar (1980 to January 2014) databases.

EXPERT OPINION

Enhanced results have been found when combining bone marrow-derived mesenchymal stem cells (BMMSCs) with recently developed scaffolds such as glass ceramics and starch-based polymeric scaffolds. Preclinical studies investigating adipose tissue-derived stem cells and umbilical cord tissue-derived stem cells suggest that they are likely to become promising alternatives. Stem cells derived from periosteum and dental tissues such as the periodontal ligament have an osteogenic potential similar to BMMSCs. Stem cells from human fetal bone marrow have demonstrated superior proliferation and osteogenic differentiation than perinatal and postnatal tissues. Despite ethical concerns and potential for teratoma formation, developments have also been made for the use of ESCs in terms of culture and ideal scaffold.

Spatiotemporal Analyses of Osteogenesis and Angiogenesis via Intravital Imaging in Cranial Bone Defect Repair

Osteogenesis and angiogenesis are two integrated components in bone repair and regeneration. A deeper understanding of osteogenesis and angiogenesis has been hampered by technical difficulties of analyzing bone and neovasculature simultaneously in spatiotemporal scales and in 3D formats. To overcome these barriers, a cranial defect window chamber model was established that enabled high-resolution, longitudinal, and real-time tracking of angiogenesis and bone defect healing via multiphoton laser scanning microscopy (MPLSM). By simultaneously probing new bone matrix via second harmonic generation (SHG), neovascular networks via intravenous perfusion of fluorophore, and osteoblast differentiation via 2.3-kb collagen type I promoter-driven GFP (Col2.3GFP), we examined the morphogenetic sequence of cranial bone defect healing and further established the spatiotemporal analyses of osteogenesis and angiogenesis coupling in repair and regeneration. We showed that bone defect closure was initiated in the residual bone around the edge of the defect. The expansion and migration of osteoprogenitors into the bone defect occurred during the first 3 weeks of healing, coupled with vigorous microvessel angiogenesis at the leading edge of the defect. Subsequent bone repair was marked by matrix deposition and active vascular network remodeling within new bone. Implantation of bone marrow stromal cells (BMSCs) isolated from Col2.3GFP mice further showed that donor-dependent bone formation occurred rapidly within the first 3 weeks of implantation, in concert with early angiogenesis. The subsequent bone wound closure was largely host-dependent, associated with localized modest induction of angiogenesis. The establishment of a live imaging platform via cranial window provides a unique tool to understand osteogenesis and angiogenesis in repair and regeneration, enabling further elucidation of the spatiotemporal regulatory mechanisms of osteoprogenitor cell interactions with host bone healing microenvironment.

microRNA-21 promotes osteogenic differentiation of mesenchymal stem cells by the PI3K/β-catenin pathway

Osteogenesis of mesenchymal stem cells (MSCs) is essential for bone repair. Recently, microRNAs have been proven to play an important role in the regulation of MSC differentiation, including osteogenesis. Here, the function of microRNA-21 (miR-21) in the osteogenic differentiation of human umbilical cord mesenchymal stem cells (hUMSCs) was investigated. Briefly, the miR-21 mimics (m-miR-21) and the antisense miR-21 (as-miR-21) were transfected to hUMSCs, and the capacity of miR-21 for the osteogenic differentiation of hUMSCs was evaluated by the expression of osteogenic markers encoding alkaline phosphatase (ALP), runt-related gene-2 (RUNX-2) and osteocalcin (OCN), as well as by Alizarin red S staining. The results indicated that the overexpression of miR-21 elevated the expression level of the osteogenesis-related genes of hUMSCs. During this process, the PI3K-AKT signaling pathway activity had an increasing tendency responding to miR-21 up-regulation. This enhancement promoted the phosphorylation of GSK-3β, leading to the stabilization and high concentration accumulation of β-catenin in cytoplasm to activate the transcription of RUNX-2, and finally increased the osteogenesis of hUMSCs. This work demonstrated that miR-21 and its target PI3K-AKT-GSK3β pathway played an important role in the osteogenic differentiation of hUMSCs by stabilizing β-catenin.

Osteogenic differentiation of human mesenchymal stem cells in mineralized alginate matrices

Mineralized biomaterials are promising for use in bone tissue engineering. Culturing osteogenic cells in such materials will potentially generate biological bone grafts that may even further augment bone healing. Here, we studied osteogenic differentiation of human mesenchymal stem cells (MSC) in an alginate hydrogel system where the cells were co-immobilized with alkaline phosphatase (ALP) for gradual mineralization of the microenvironment. MSC were embedded in unmodified alginate beads and alginate beads mineralized with ALP to generate a polymer/hydroxyapatite scaffold mimicking the composition of bone. The initial scaffold mineralization induced further mineralization of the beads with nanosized particles, and scanning electron micrographs demonstrated presence of collagen in the mineralized and unmineralized alginate beads cultured in osteogenic medium. Cells in both types of beads sustained high viability and metabolic activity for the duration of the study (21 days) as evaluated by live/dead staining and alamar blue assay. MSC in beads induced to differentiate in osteogenic direction expressed higher mRNA levels of osteoblast-specific genes (RUNX2, COL1AI, SP7, BGLAP) than MSC in traditional cell cultures. Furthermore, cells differentiated in beads expressed both sclerostin (SOST) and dental matrix protein-1 (DMP1), markers for late osteoblasts/osteocytes. In conclusion, Both ALP-modified and unmodified alginate beads provide an environment that enhance osteogenic differentiation compared with traditional 2D culture. Also, the ALP-modified alginate beads showed profound mineralization and thus have the potential to serve as a bone substitute in tissue engineering.

Bone environment is essential for osteosarcoma development from transformed mesenchymal stem cells

The cellular microenvironment plays a relevant role in cancer development. We have reported that mesenchymal stromal/stem cells (MSCs) deficient for p53 alone or together with RB (p53(-/-)RB(-/-)) originate leiomyosarcoma after subcutaneous (s.c.) inoculation. Here, we show that intrabone or periosteal inoculation of p53(-/-) or p53(-/-)RB(-/-) bone marrow- or adipose tissue-derived MSCs originated metastatic osteoblastic osteosarcoma (OS). To assess the contribution of bone environment factors to OS development, we analyzed the effect of the osteoinductive factor bone morphogenetic protein-2 (BMP-2) and calcified substrates on p53(-/-)RB(-/-) MSCs. We show that BMP-2 upregulates the expression of osteogenic markers in a WNT signaling-dependent manner. In addition, the s.c. coinfusion of p53(-/-)RB(-/-) MSCs together with BMP-2 resulted in appearance of tumoral osteoid areas. Likewise, when p53(-/-)RB(-/-) MSCs were inoculated embedded in a calcified ceramic scaffold composed of hydroxyapatite and tricalciumphosphate (HA/TCP), tumoral bone formation was observed in the surroundings of the HA/TCP scaffold. Moreover, the addition of BMP-2 to the ceramic/MSC implants further increased the tumoral osteoid matrix. Together, these data indicate that bone microenvironment signals are essential to drive OS development.

Endochondral ossification for enhancing bone regeneration: converging native extracellular matrix biomaterials and developmental engineering in vivo

Autologous bone grafting (ABG) remains entrenched as the gold standard of treatment in bone regenerative surgery. Consequently, many marginally successful bone tissue engineering strategies have focused on mimicking portions of ABG's "ideal" osteoconductive, osteoinductive, and osteogenic composition resembling the late reparative stage extracellular matrix (ECM) in bone fracture repair, also known as the "hard" or "bony" callus. An alternative, less common approach that has emerged in the last decade harnesses endochondral (EC) ossification through developmental engineering principles, which acknowledges that the molecular and cellular mechanisms involved in developmental skeletogenesis, specifically EC ossification, are closely paralleled during native bone healing. EC ossification naturally occurs during the majority of bone fractures and, thus, can potentially be utilized to enhance bone regeneration for nearly any orthopedic indication, especially in avascular critical-sized defects where hypoxic conditions favor initial chondrogenesis instead of direct intramembranous ossification. The body's native EC ossification response, however, is not capable of regenerating critical-sized defects without intervention. We propose that an underexplored potential exists to regenerate bone through the native EC ossification response by utilizing strategies which mimic the initial inflammatory or fibrocartilaginous ECM (i.e., "pro-" or "soft" callus) observed in the early reparative stage of bone fracture repair. To date, the majority of strategies utilizing this approach rely on clinically burdensome in vitro cell expansion protocols. This review will focus on the confluence of two evolving areas, (1) native ECM biomaterials and (2) developmental engineering, which will attempt to overcome the technical, business, and regulatory challenges that persist in the area of bone regeneration. Significant attention will be given to native "raw" materials and ECM-based designs that provide necessary osteo- and chondro-conductive and inductive features for enhancing EC ossification. In addition, critical perspectives on existing stem cell-based therapeutic strategies will be discussed with a focus on their use as an extension of the acellular ECM-based designs for specific clinical indications. Within this framework, a novel realm of unexplored design strategies for bone tissue engineering will be introduced into the collective consciousness of the regenerative medicine field.

Optimized cell survival and seeding efficiency for craniofacial tissue engineering using clinical stem cell therapy

Traumatic injuries involving the face are very common, yet the clinical management of the resulting craniofacial deficiencies is challenging. These injuries are commonly associated with missing teeth, for which replacement is compromised due to inadequate jawbone support. Using cell therapy, we report the upper jaw reconstruction of a patient who lost teeth and 75% of the supporting jawbone following injury. A mixed population of bone marrow-derived autologous stem and progenitor cells was seeded onto β-tricalcium phosphate (β-TCP), which served as a scaffold to deliver cells directly to the defect. Conditions (temperature, incubation time) to achieve the highest cell survival and seeding efficiency were optimized. Four months after cell therapy, cone beam computed tomography and a bone biopsy were performed, and oral implants were placed to support an engineered dental prosthesis. Cell seeding efficiency (>81%) of the β-TCP and survival during the seeding process (94%) were highest when cells were incubated with β-TCP for 30 minutes, regardless of incubation temperature; however, at 1 hour, cell survival was highest when incubated at 4°C. Clinical, radiographic, and histological analyses confirmed that by 4 months, the cell therapy regenerated 80% of the original jawbone deficiency with vascularized, mineralized bone sufficient to stably place oral implants. Functional and aesthetic rehabilitation of the patient was successfully completed with installation of a dental prosthesis 6 months following implant placement. This proof-of-concept clinical report used an evidence-based approach for the cell transplantation protocol used and is the first to describe a cell therapy for craniofacial trauma reconstruction.

Advanced nanocomposites for bone regeneration

The field of orthopedic tissue engineering is quickly expanding with the development of novel materials and strategies designed for rapid bone regeneration. While autologous bone grafts continue to be the standard of care, drawbacks include donor-site morbidity and short tissue supplies. Herein we report a novel nanocomposite sponge composed of poly(1,8-octanediol-co-citrate) (POC) and the bioactive ceramic β-tricalcium phosphate (TCP). We show that these nanocomposite sponges can be used as a depot for bone-producing (a.k.a. osteogenic) growth factors. In vitro bioactivity is demonstrated by significant upregulation of osteogenic genes, osteopontin (∼3 fold increase), osteocalcin (∼22 fold increase), alkaline phosphatase (∼10 fold increase), and transcription factor, RUNX2 (∼5 fold increase) over basal expression levels in mesenchymal stem cells. In vivo osteogenicity and biocompatibility is demonstrated in a standard subcutaneous implant model in rat. Results show that the nanocomposite sponge supports complete cell infiltration, minimal adverse foreign body response, positive cellular proliferation, and cellular expression of osteogenic markers in subcutaneous tissue. The results shown herein are encouraging and support the use of this sponge for future bone tissue engineering efforts.

Effect of calcium phosphate materials on multipotent mesenchymal cells from exfoliated deciduous teeth (SHED cells) in vitro

Various calcium phosphate ceramic materials were created and their effect on cultured mesenchymal cells from exfoliated deciduous tooth pulp was evaluated. Tricalcium phosphate ceramics provides best cell survival and is an optimal material for bone tissue engineering. Analysis of the effects of tricalcium phosphate ceramics on osteogenic differentiation of SHED cells suggests that this material potentiated dexamethasone-induced osteogenic differentiation, which manifested in the increased number of ossification foci and enhanced extracellular matrix production by cells. Thus, the tricalcium phosphate ceramics created by us is a promising biomedical material that can be used for tissue-engineered bone analogs.

The application of induced pluripotent stem cells for bone regeneration: current progress and prospects

Loss of healthy bone tissue and dysosteogenesis are still common and significant problems in clinics. Cell-based therapy using mesenchymal stem cells (MSCs) has been performed in patients for quite some time, but the inherent drawbacks of these cells, such as the reductions in proliferation rate and osteogenic differentiation potential that occur with aging, greatly limit their further application. Moreover, embryonic stem cells (ESCs) have brought new hope to osteoregenerative medicine because of their full pluripotent differentiation potential and excellent performance in bone regeneration. However, the ethical issues involved in destroying human embryos and the immune reactions that occur after transplantation are two major stumbling blocks impeding the clinical application of ESCs. Instead, induced pluripotent stem cells (iPSCs), which are ESC-like pluripotent cells that are reprogrammed from adult somatic cells using defined transcription factors, are considered a more promising source of cells for regenerative medicine because they present no ethical or immunological issues. Here, we summarize the primary technologies for generating iPSCs and the biological properties of these cells, review the current advances in iPSC-based bone regeneration and, finally, discuss the remaining challenges associated with these cells, particularly safety issues and their potential application for osteoregenerative medicine.

Construction of adipose scaffold for bone repair with gene engineering bone cells

The bone defect repairing is still a challenge in orthopedics. As the gene engineering bones have been used in the bone repairing clinic, the scaffold construction is a critical fact to be considered. This study aims to construct optimal scaffolds using adipose tissue in the bone repair together with the gene engineering osteocytes. Rat adipose stem cells (ASC) were prepared; the cells were transduced with the OCT-4 gene carrying lentiviral vectors (OCT-4-Lv). Artificial bone defects were created in the rat femoral bone. The bone defects were filled up with adipose scaffolds and shaped by using surrounding muscles and supported with orthopedic splints. ASCs with or without transducing the OCT-4-Lv were injected into the adipose scaffolds. The rats were sacrificed 12 weeks after the surgery. After receiving the OCT-4-Lv, the expressions of OCT-4, RUNX2 and osteocalcin were detected in the ASCs. X-ray examination showed that rats received the OCT-4-Lv transduced ASCs together with the adipose pad had new bone formation in the defect area; none of the control rats showed any new bone formation in situ. The results were supported by histological assessment. Using adipose scaffold and OCT-4-modified ASC transplantation can repair bone defects.