Critical-size calvarial bone defects healing in a mouse model with silk scaffolds and SATB2-modified iPSCs

Murine iPSC-Loaded Scaffold Grafts Improve Bone Regeneration in Critical-Size Bone Defects

In certain situations, bones do not heal completely after fracturing. One of these situations is a critical-size bone defect where the bone cannot heal spontaneously. In such a case, complex fracture treatment over a long period of time is required, which carries a relevant risk of complications. The common methods used, such as autologous and allogeneic grafts, do not always lead to successful treatment results. Current approaches to increasing bone formation to bridge the gap include the application of stem cells on the fracture side. While most studies investigated the use of mesenchymal stromal cells, less evidence exists about induced pluripotent stem cells (iPSC). In this study, we investigated the potential of mouse iPSC-loaded scaffolds and decellularized scaffolds containing extracellular matrix from iPSCs for treating critical-size bone defects in a mouse model. In vitro differentiation followed by Alizarin Red staining and quantitative reverse transcription polymerase chain reaction confirmed the osteogenic differentiation potential of the iPSCs lines. Subsequently, an in vivo trial using a mouse model (n = 12) for critical-size bone defect was conducted, in which a PLGA/aCaP osteoconductive scaffold was transplanted into the bone defect for 9 weeks. Three groups (each n = 4) were defined as (1) osteoconductive scaffold only (control), (2) iPSC-derived extracellular matrix seeded on a scaffold and (3) iPSC seeded on a scaffold. Micro-CT and histological analysis show that iPSCs grafted onto an osteoconductive scaffold followed by induction of osteogenic differentiation resulted in significantly higher bone volume 9 weeks after implantation than an osteoconductive scaffold alone. Transplantation of iPSC-seeded PLGA/aCaP scaffolds may improve bone regeneration in critical-size bone defects in mice.

Mesenchymal stem cells osteogenic differentiation by ZnO nanoparticles and polyurethane bimodal foam nanocomposites

Mesenchymal stem cells with tissue repair capacity involve in regenerative medicine. MSCs can promote bone repair when employed with nano scaffolds/particles. Here, the MTT and Acridine Orange assay enabled the cytotoxic concentration of Zinc oxide nanoparticles and Polyurethane evaluation. Following culturing adipose tissue-derived MSCs, ADSCs' proliferation, growth, and osteogenic differentiation in the presence of PU with and without ZnO NPs is tracked by a series of biological assays, including Alkaline Phosphatase activity, Calcium deposition, alizarin red staining, RT-PCR, scanning electron microscope, and immunohistochemistry. The results showed boosted osteogenic differentiation of ADSCs in the presence of 1% PU scaffold and ZnO NPS and can thus apply as a new bone tissue engineering matrix. The expression level of Osteonectin, Osteocalcin, and Col1 increased in PU-ZnO 1% on the 7th and 14th days. There was an increase in the Runx2 gene expression on the 7th day of differentiation in PU-ZnO 1%, while it decreased on day 14th. In conclusion, Polyurethane nano scaffolds supported the MSCs' growth and rapid osteogenic differentiation. The PU-ZnO helps not only with cellular adhesion and proliferation but also with osteogenic differentiation.

Bone health in SATB2-associated syndrome: Results from a large prospective cohort and recommendations for surveillance

Alterations in SATB2 result in SATB2-associated syndrome (SAS; Glass syndrome, OMIM 612313), an autosomal dominant multisystemic disorder predominantly characterized by developmental delay, craniofacial anomalies, and growth retardation. The bone phenotype of SAS has been less explored until recently and includes a variety of skeletal deformities, increased risk of low bone mineral density (BMD) with a propensity to fractures, and other biochemical abnormalities that suggest elevated bone turnover. We present the results of ongoing surveillance of bone health from 32 individuals (47% females, 3-18 years) with molecularly-confirmed SAS evaluated at a multidisciplinary clinic. Five individuals (5/32, 16%) were documented to have BMD Z-scores by DXA scans of -2.0 SD or lower and 7 more (7/32, 22%) had Z-scores between -1 and - 2 SD at the lumbar spine or the total hip. Alkaline phosphatase levels were found to be elevated in 19 individuals (19/30, 63%) and determined to correspond to bone-specific alkaline phosphatase elevations when measured (11/11, 100%). C-telopeptide levels were found to be elevated when adjusted by age and gender in 6 individuals (6/14, 43%). Additionally, the two individuals who underwent bone cross-sectional geometry evaluation by peripheral quantitative computed tomography were documented to have low cortical bone density for age and sex despite concurrent DXA scans that did not have this level of decreased density. While we could not identify particular biochemical abnormalities that predicted low BMD, the frequent elevations in markers of bone formation and resorption further confirmed the increased bone turnover in SAS. Based on our results and other recently published studies, we propose surveillance guidelines for the skeletal phenotype of SAS.

Regeneration of Critical-Sized Mandibular Defects Using 3D-Printed Composite Scaffolds: A Quantitative Evaluation of New Bone Formation in In Vivo Studies

Mandibular tissue engineering aims to develop synthetic substitutes for the regeneration of critical size defects (CSD) caused by a variety of events, including tumor surgery and post-traumatic resections. Currently, the gold standard clinical treatment of mandibular resections (i.e., autologous fibular flap) has many drawbacks, driving research efforts toward scaffold design and fabrication by additive manufacturing (AM) techniques. Once implanted, the scaffold acts as a support for native tissue and facilitates processes that contribute to its regeneration, such as cells infiltration, matrix deposition and angiogenesis. However, to fulfil these functions, scaffolds must provide bioactivity by mimicking natural properties of the mandible in terms of structure, composition and mechanical behavior. This review aims to present the state of the art of scaffolds made with AM techniques that are specifically employed in mandibular tissue engineering applications. Biomaterials chemical composition and scaffold structural properties are deeply discussed, along with strategies to promote osteogenesis (i.e., delivery of biomolecules, incorporation of stem cells, and approaches to induce vascularization in the constructs). Finally, a comparison of in vivo studies is made by taking into consideration the amount of new bone formation (NB), the CSD dimensions, and the animal model.

Exosomes derived from mesenchymal stromal cells promote bone regeneration by delivering miR-182-5p-inhibitor

Exosomes, small extracellular vesicles that function as a key regulator of cell-to-cell communication, are emerging as a promising candidate for bone regeneration. Here, we aimed to investigate the effect of exosomes from pre-differentiated human alveolar bone-derived bone marrow mesenchymal stromal cells (AB-BMSCs) carrying specific microRNAs on bone regeneration. Exosomes secreted from AB-BMSCs pre-differentiated for 0 and 7 days were cocultured with BMSCs in vitro to investigate their effect on the differentiation of the BMSCs. MiRNAs from AB-BMSCs at different stages of osteogenic differentiation were analyzed. BMSCs seeded on poly-L-lactic acid(PLLA) scaffolds were treated with miRNA antagonist-decorated exosomes to verify their effect on new bone regeneration. Exosomes pre-differentiated for 7 days effectively promoted the differentiation of BMSCs. Bioinformatic analysis revealed that miRNAs within the exosomes were differentially expressed, including the upregulation of osteogenic miRNAs (miR-3182, miR-1468) and downregulation of anti-osteogenic miRNAs (miR-182-5p, miR-335-3p, miR-382-5p), causing activation of the PI3K/Akt signaling pathway. The treatment of BMSC-seeded scaffolds with anti-miR-182-5p decorated exosomes demonstrated enhanced osteogenic differentiation and efficient formation of new bone. In conclusion, Osteogenic exosomes secreted from pre-differentiated AB-BMSCs were identified and the gene modification of exosomes provides great potential as a bone regeneration strategy. DATA AVAILABILITY STATEMENT: Data generated or analyzed in this paper partly are available in the GEO public data repository(http://www.ncbi.nlm.nih.gov/geo).

AdipoRon accelerates bone repair of calvarial defect in diet-induced obesity mice

Objectives

To investigate the role of AdipoRon in bone wound healing of calvaria critical-sized defects (CSD) in diet-induced obesity (DIO) mice.

Materials and methods

After establishing the calvaria CSD in normal-chow (NC), DIO and Adiponectin knockout (APNKO) mice, AdipoRon or vehicle was orally gavaged for 3 weeks. The bone defects were analyzed by micro-CT and H&E staining. The expression of osteogenesis-related factor in the defect area, and the chemotactic gradient of SDF-1 between bone marrow and bone defect area were further analyzed.

Results

AdipoRon downregulated body weight and alleviated fasting blood glucose level of DIO mice after treatment with AdipoRon in 14 and 21 days. Newly formed bone was significantly increased in the defect area of DIO and APNKO mice after treatment with AdipoRon compared with vehicle treatment. No significant difference was shown in NC mice. Furthermore, compared with NC mice, a significant decrease of BV/TV%, Tb.N value and formed bone percentage were shown in DIO and APNKO mice. The treatment with AdipoRon could reverse of decreased value and increase the newly formed bone in those mice. AdipoRon promoted col-1α expression in wound sites in DIO and APNKO mice. AdipoRon nearly quadrupled the chemotactic gradient of SDF-1 by decreasing SDF-1 expression in bone marrow and increasing it in the bone defect area in APNKO and DIO treated mice.

Conclusion

AdipoRon alleviates the obesity status in DIO mice with calvarial defect and increase new bone formation in calvarial defects in DIO and APNKO mice by modulating chemotactic gradient of SDF-1.

A Comprehensive Review on Silk Fibroin as a Persuasive Biomaterial for Bone Tissue Engineering

Bone tissue engineering (BTE) utilizes a special mix of scaffolds, cells, and bioactive factors to regulate the microenvironment of bone regeneration and form a three-dimensional bone simulation structure to regenerate bone tissue. Silk fibroin (SF) is perhaps the most encouraging material for BTE given its tunable mechanical properties, controllable biodegradability, and excellent biocompatibility. Numerous studies have confirmed the significance of SF for stimulating bone formation. In this review, we start by introducing the structure and characteristics of SF. After that, the immunological mechanism of SF for osteogenesis is summarized, and various forms of SF biomaterials and the latest development prospects of SF in BTE are emphatically introduced. Biomaterials based on SF have great potential in bone tissue engineering, and this review will serve as a resource for future design and research.

Bone Tissue and the Nervous System: What Do They Have in Common?

Degenerative diseases affecting bone tissues and the brain represent important problems with high socio-economic impact. Certain bone diseases, such as osteoporosis, are considered risk factors for the progression of neurological disorders. Often, patients with neurodegenerative diseases have bone fractures or reduced mobility linked to osteoarthritis. The bone is a dynamic tissue involved not only in movement but also in the maintenance of mineral metabolism. Bone is also associated with the generation of both hematopoietic stem cells (HSCs), and thus the generation of the immune system, and mesenchymal stem cells (MSCs). Bone marrow is a lymphoid organ and contains MSCs and HSCs, both of which are involved in brain health via the production of cytokines with endocrine functions. Hence, it seems clear that bone is involved in the regulation of the neuronal system and vice versa. This review summarizes the recent knowledge on the interactions between the nervous system and bone and highlights the importance of the interaction between nerve and bone cells. In addition, experimental models that study the interaction between nerve and skeletal cells are discussed, and innovative models are suggested to better evaluate the molecular interactions between these two cell types.

Temporal Modulation of DNA Methylation and Gene Expression in Monolayer and 3D Spheroids of Dental Pulp Stem Cells during Osteogenic Differentiation: A Comparative Study

BACKGROUND

Human mesenchymal stem cells are being used for various regenerative applications in past decades. This study chronicled a temporal profile of the transcriptional pattern and promoter methylation status of the osteogenic related gene in dental pulp stem cells (DPSCs) derived from 3-dimensional spheroid culture (3D) vis a vis 2-dimensional (2D) monolayer culture upon osteogenic induction.

METHODS

Biomimetic properties of osteogenesis were determined by alkaline phosphatase assay and alizarin red staining. Gene expression and promoter methylation status of osteogenic genes such as runt-related transcription factor-2, collagen1α1, osteocalcin (OCN), and DLX5 (distal-homeobox) were performed by qPCR assay and bisulfite sequencing, respectively. Furthermore, µ-Computed tomography (micro-CT) was performed to examine the new bone formation in critical-sized rat calvarial bone defect model.

RESULTS

Our results indicated a greater inclination of spheroid culture-derived DPSCs toward osteogenic lineage than the monolayer culture. The bisulfite sequencing of the promoter region of osteogenic genes revealed sustenance of low methylation levels in DPSCs during the progression of osteogenic differentiation. However, the significant difference in the methylation pattern between 2D and 3D derived DPSCs were identified only for OCN gene promoter. We observed differences in the mRNA expression pattern of epigenetic writers such as DNA methyltransferases (DNMTs) and methyl-cytosine dioxygenases (TET) between the two culture conditions. Further, the DPSC spheroids showed enhanced new bone formation ability in an animal model of bone defect compared to the cells cultivated in a 2D platform which further substantiated our in-vitro observations.

CONCLUSION

The distinct cellular microenvironment induced changes in DNA methylation pattern and expression of epigenetic regulators such as DNMTs and TETs genes may lead to increase expression of osteogenic markers in 3D spheroid culture of DPSCs which make DPSCs spheroids suitable for osteogenic regeneration compared to monolayers.

Stem cells and common biomaterials in dentistry: a review study

Stem cells exist as normal cells in embryonic and adult tissues. In recent years, scientists have spared efforts to determine the role of stem cells in treating many diseases. Stem cells can self-regenerate and transform into some somatic cells. They would also have a special position in the future in various clinical fields, drug discovery, and other scientific research. Accordingly, the detection of safe and low-cost methods to obtain such cells is one of the main objectives of research. Jaw, face, and mouth tissues are the rich sources of stem cells, which more accessible than other stem cells, so stem cell and tissue engineering treatments in dentistry have received much clinical attention in recent years. This review study examines three essential elements of tissue engineering in dentistry and clinical practice, including stem cells derived from the intra- and extra-oral sources, growth factors, and scaffolds.

Fabrication and Effect of Strontium-Substituted Calcium Silicate/Silk Fibroin on Bone Regeneration In Vitro and In Vivo

Achieving rapid osteogenesis and angiogenesis was the key factor for bone regeneration. In the present study, the strontium-substituted calcium silicate (SrCS)/silk fibroin (SF) composite materials have been constructed by combining the different functional component ratios of SrCS (12.5 wt%, 25 wt%) and SF. Then, the effects of SrCS/SF materials on proliferation, osteogenic differentiation, and angiogenic factor secretion of rat bone marrow-derived mesenchymal stromal cells (rBMSCs) were first evaluated in vitro. Moreover, the in vivo effect of osteogenesis was evaluated in a critical-sized rat calvarial defect model. In vitro studies showed that SrCS/SF significantly enhanced the cell proliferation, alkaline phosphatase (ALP) activity, and the expression of osteogenic and angiogenic factors of rBMSCs as compared with the SF and CS/SF, and the optimum proportion ratio was 25 wt%. Besides, the results also showed that CS/SF achieved enhanced effects on rBMSCs as compared with SF. The in vivo results showed that 25 wt% SrCS/SF could obviously promote new bone formation more than SF and CS/SF. The present study revealed that SrCS could significantly promote the osteogenic and angiogenic activities of SF, and SrCS/SF might be a good scaffold material for bone regeneration.

Osteoconductive Effect of a Nanocomposite Membrane Treated with UV Radiation

Modulation of the bio-regenerative characteristics of materials is an indispensable requirement in tissue engineering. Particularly, in bone tissue engineering, the promotion of the osteoconductive phenomenon determines the elemental property of a material be used therapeutically. In addition to the chemical qualities of the constituent materials, the three-dimensional surface structure plays a fundamental role that various methods are expected to modulate in a number of ways, one most promising of which is the use of different types of radiation. In the present manuscript, we demonstrate in a calvarial defect model, that treatment with ultraviolet irradiation allows modification of the osteoconductive characteristics in a biomaterial formed by gelatin and chitosan, together with the inclusion of hydroxyapatite and titanium oxide nanoparticles.

A Narrative Review of Cell-Based Approaches for Cranial Bone Regeneration

Current cranial repair techniques combine the use of autologous bone grafts and biomaterials. In addition to their association with harvesting morbidity, autografts are often limited by insufficient quantity of bone stock. Biomaterials lead to better outcomes, but their effectiveness is often compromised by the unpredictable lack of integration and structural failure. Bone tissue engineering offers the promising alternative of generating constructs composed of instructive biomaterials including cells or cell-secreted products, which could enhance the outcome of reconstructive treatments. This review focuses on cell-based approaches with potential to regenerate calvarial bone defects, including human studies and preclinical research. Further, we discuss strategies to deliver extracellular matrix, conditioned media and extracellular vesicles derived from cell cultures. Recent advances in 3D printing and bioprinting techniques that appear to be promising for cranial reconstruction are also discussed. Finally, we review cell-based gene therapy approaches, covering both unregulated and regulated gene switches that can create spatiotemporal patterns of transgenic therapeutic molecules. In summary, this review provides an overview of the current developments in cell-based strategies with potential to enhance the surgical armamentarium for regenerating cranial vault defects.

Osteogenic effects of microRNA-335-5p/lipidoid nanoparticles coated on titanium surface

OBJECTIVE

In this study, we aimed to investigate the therapeutic potential of miR-335-5p lipidoid nanocomplexes coated on Titanium (Ti) SLActive surface by lyophilization.

DESIGN

In our model, we coated miR-335-5p/Lipidoid nanoparticles on titanium implant, seeded GFP-labelled mouse bone marrow stromal cells (BMSCs) onto the functionalized Ti implant surface, and analyzed the transfection efficiency, cell adhesion, proliferation, and osteogenic activity of the bone-implant interface.

RESULTS

The Ti SLActive surface displayed a suitable hydrophilicity ability and provided a large surface area for miRNA loading, enabling spatial retention of the miRNAs within the nanopores until cellular delivery. We demonstrated a high transfection efficiency of miR-335-5p lipidoid nanoparticles in BMSCs seeded onto the Ti SLActive surface, even after 14 days. Alkaline phosphatase (ALP) activity and cell vitality were significantly increased in BMSCs transfected with miR-335-5p at 7 and 14 days as opposed to cells transfected with negative controls. When miR-335-5p transfected BMSCs were induced to undergo osteogenic differentiation, we detected increased mRNA expression of osteogenic markers including Alkaline phosphatase (ALP), collagen I (COL1), osteocalcin (OCN) and bone sialoprotein (BSP) at 7 and 14 days as compared with negative controls.

CONCLUSION

MiR-335-5p lipidoid nanoparticles could be used as a new cost-effective methodology to increase the osteogenic capacity of biomedical Ti implants.

Novel cell sources for bone regeneration

A plethora of both acute and chronic conditions, including traumatic, degenerative, malignant, or congenital disorders, commonly induce bone disorders often associated with severe persisting pain and limited mobility. Over 1 million surgical procedures involving bone excision, bone grafting, and fracture repair are performed each year in the U.S. alone, resulting in immense levels of public health challenges and corresponding financial burdens. Unfortunately, the innate self-healing capacity of bone is often inadequate for larger defects over a critical size. Moreover, as direct transplantation of committed osteoblasts is hindered by deficient cell availability, limited cell spreading, and poor survivability, an urgent need for novel cell sources for bone regeneration is concurrent. Thanks to the development in stem cell biology and cell reprogramming technology, many multipotent and pluripotent cells that manifest promising osteogenic potential are considered the regenerative remedy for bone defects. Considering these cells' investigation is still in its relative infancy, each of them offers their own particular challenges that must be conquered before the large-scale clinical application.

Establishment of a C57BL/6 Mandibular Critical-Size Bone Defect Model

PURPOSE

The goal of this study was to identify bone defects of critical size in C57BL/6 mouse mandibles.

MATERIALS AND METHODS

Twenty-four male mice were included in this study. All mice underwent surgeries on their left mandibles. Mandibular defects of 1.0 mm (n = 8), 1.6 mm (n = 8), and 2.3 mm (n = 8) were created. For the investigation of bone healing after an 8-week period, micro-computed tomography scans and histomorphology were performed.

RESULTS

Mandibular bone nonunions were seen 0/8 in the 1.0-mm group, 6/8 in the 1.6-mm group, and 8/8 in the 2.3-mm group. The outcome of micro-computed tomography showed that, after 8 weeks, the bone mineral density and the bone volume to total volume ratio were significantly different among the 3 groups. The defect gaps in the nonunion 1.6- and 2.3-mm groups were filled with connective tissue, and no obvious bone formation was found. Additionally, in quantitative analysis, according to the new bone fill calculations, the percentages were 91.85% ± 8.03% in the 1.0-mm group, 59.84% ± 20.60% in the 1.6-mm group, and 15.36% ± 8.28% in the 2.3-mm group, which indicated statistically significantly lower defect healing in the 2.3-mm group.

CONCLUSIONS

The creation of 2.3-mm mandibular defects produces osseous nonunion in C57BL/6 mice.

Effect of a plasma synthesized polypyrrole coverage on polylactic acid/hydroxyapatite scaffolds for bone tissue engineering

Composite biomaterials are solids that contain two or more different materials, combining the properties of their components to restore or improve the function of tissues. In this study, we report the generation of electrospun matrices with osteoconductive properties and porosity using the combination of a biodegradable polyester, polylactic acid (PLA), and hydroxyapatite (HA). Additionally, we report the effects of modifying these matrices through plasma polymerization of pyrrole on the growth and osteogenic differentiation of rabbit bone marrow stem cells. Cells were isolated, seeded and cultured on biomaterials for periods between 7 and 28 days. The matrices we obtained were formed by nano and microfibers containing up to 35.7 wt% HA, presenting a variety of apparent pore sizes to allow for the passage of nutrients to bone cells. Scanning electron microscopy showed that the fibers were coated with polypyrrole doped with iodine, and MTT assay demonstrated this increased cell proliferation and significantly improved cell viability due to the adhesive properties of the polymer. Our results show that PLA/HA/Pyrrole/Iodine matrices are favorable for bone tissue engineering.

Special AT-rich sequence-binding protein 2 (Satb2) synergizes with Bmp9 and is essential for osteo/odontogenic differentiation of mouse incisor mesenchymal stem cells

OBJECTIVES

Mouse incisor mesenchymal stem cells (MSCs) have self-renewal ability and osteo/odontogenic differentiation potential. However, the mechanism controlling the continuous self-renewal and osteo/odontogenic differentiation of mouse incisor MSCs remains unclear. Special AT-rich sequence-binding protein 2 (SATB2) positively regulates craniofacial patterning, bone development and regeneration, whereas SATB2 deletion or mutation leads to craniomaxillofacial dysplasia and delayed tooth and root development, similar to bone morphogenetic protein (BMP) loss-of-function phenotypes. However, the detailed mechanism underlying the SATB2 role in odontogenic MSCs is poorly understood. The aim of this study was to investigate whether SATB2 can regulate self-renewal and osteo/odontogenic differentiation of odontogenic MSCs.

MATERIALS AND METHODS

Satb2 expression was detected in the rapidly renewing mouse incisor mesenchyme by immunofluorescence staining, quantitative RT-PCR and Western blot analysis. Ad-Satb2 and Ad-siSatb2 were constructed to evaluate the effect of Satb2 on odontogenic MSCs self-renewal and osteo/odontogenic differentiation properties and the potential role of Satb2 with the osteogenic factor bone morphogenetic protein 9 (Bmp9) in vitro and in vivo.

RESULTS

Satb2 was found to be expressed in mesenchymal cells and pre-odontoblasts/odontoblasts. We further discovered that Satb2 effectively enhances mouse incisor MSCs self-renewal. Satb2 acted synergistically with the potent osteogenic factor Bmp9 in inducing osteo/odontogenic differentiation of mouse incisor MSCs in vitro and in vivo.

CONCLUSIONS

Satb2 promotes self-renewal and osteo/odontogenic differentiation of mouse incisor MSCs. Thus, Satb2 can cooperate with Bmp9 as a new efficacious bio-factor for osteogenic regeneration and tooth engineering.

The role of PHF8 and TLR4 in osteogenic differentiation of periodontal ligament cells in inflammatory environment

BACKGROUND

Histone methylation is considered to play an important role in the occurrence and development of periodontitis. Plant homeodomain finger protein 8 (PHF8), a histone demethylase, has been shown to regulate inflammation and osteogenic differentiation of bone marrow stromal cells (BMSCs). This study aimed to detect the functions of PHF8 and TLR4 in osteogenic differentiation in an inflammatory environment induced by Porphyromonas gingivalis lipopolysaccharide (Pg-LPS) METHODS: A periodontitis mouse model was established, and the mice were treated with TAK-242. Immunohistochemical staining was used to detect the expression of PHF8 in periodontal tissue. Periodontal ligament cells (PDLCs) were treated with mineralization induction medium supplemented with Pg-LPS and/or TAK-242, and a Cell Counting Kit-8 (CCK-8) assay was used to detect the proliferation of PDLCs. Real-time PCR and western blotting were used to detect the mRNA and protein expression levels, respectively, of PHF8, toll-like receptor 4 (TLR4) and the other osteogenic markers alkaline phosphatase (ALP), osteocalcin (OCN), Special AT-rich sequence-binding protein 2 (Satb2) and Runt-related transcription factor 2 (Runx2) RESULTS: Periodontitis reduced PHF8 expression in periodontal tissue, and TAK-242 partially reversed this downregulation. An in vitro experiment revealed that the mRNA and protein expression levels of PHF8 were significantly upregulated during the osteogenic differentiation of PDLCs. Alizarin red staining showed that the mineralized nodules of PDLCs in osteogenic induction group were more than those in control group. Real-time PCR and western blot results indicated that Pg-LPS inhibited PHF8 expression and upregulated TLR4 expression in PDLCs. TAK-242 inhibited TLR4 and partially reversed the inhibition of PHF8 expression and osteogenic differentiation induced by Pg-LPS in PDLCs CONCLUSION: PHF8 and TLR4 play important roles in periodontitis. Pg-LPS inhibits the expression of PHF8 via upregulation of TLR4 and might further inhibit the osteogenic differentiation of PDLCs. However, the specific mechanisms involved remain to be explored.

Bone Microvasculature: Stimulus for Tissue Function and Regeneration

Bone is a highly vascularized organ, providing structural support to the body, and its development, regeneration, and remodeling depend on the microvascular homeostasis. Loss or impairment of vascular function can develop diseases, such as large bone defects, avascular necrosis, osteoporosis, osteoarthritis, and osteopetrosis. In this review, we summarize how vasculature controls bone development and homeostasis in normal and disease cases. A better understanding of this process will facilitate the development of novel disease treatments that promote bone regeneration and remodeling. Specifically, approaches based on tissue engineering components, such as stem cells and growth factors, have demonstrated the capacity to induce bone microvasculature regeneration and mineralization. This knowledge will have relevant clinical implications for the treatment of bone disorders by developing novel pharmaceutical approaches and bone grafts. Finally, the tissue engineering approaches incorporating vascular components may widely be applied to treat other organ diseases by enhancing their regeneration capacity. Impact statement Bone vasculature is imperative in the process of bone development, regeneration, and remodeling. Alterations or disruption of the bone vasculature leads to loss of bone homeostasis and the development of bone diseases. In this study, we review the role of vasculature on bone diseases and how vascular tissue engineering strategies, with a detailed emphasis on the role of stem cells and growth factors, will contribute to bone therapeutics.

SATB2: A versatile transcriptional regulator of craniofacial and skeleton development, neurogenesis and tumorigenesis, and its applications in regenerative medicine

SATB2 (special AT-rich sequence-binding protein 2) is a member of the special AT-rich binding protein family. As a transcription regulator, SATB2 mainly integrates higher-order chromatin organization. SATB2 expression appears to be tissue- and stage-specific, and is governed by several cellular signaling molecules and mediators. Expressed in branchial arches and osteoblast-lineage cells, SATB2 plays a significant role in craniofacial pattern and skeleton development. In addition to regulating osteogenic differentiation, SATB2 also displays versatile functions in neural development and cancer progression. As an osteoinductive factor, SATB2 holds great promise in improving bone regeneration toward bone defect repair. In this review, we have summarized our current understanding of the physiological and pathological functions of SATB2 in craniofacial and skeleton development, neurogenesis, tumorigenesis and regenerative medicine.

Metal-based nanoparticles for bone tissue engineering

Tissue is vital to the organization of multicellular organisms, because it creates the different organs and provides the main scaffold for body shape. The quest for effective methods to allow tissue regeneration and create scaffolds for new tissue growth has intensified in recent years. Tissue engineering has recently used some promising alternatives to existing conventional scaffold materials, many of which have been derived from nanotechnology. One important example of these is metal nanoparticles. The purpose of this review is to cover novel tissue engineering methods, paying special attention to those based on the use of metal-based nanoparticles. The unique physiochemical properties of metal nanoparticles, such as antibacterial effects, shape memory phenomenon, low cytotoxicity, stimulation of the proliferation process, good mechanical and tensile strength, acceptable biocompatibility, significant osteogenic potential, and ability to regulate cell growth pathways, suggest that they can perform as novel types of scaffolds for bone tissue engineering. The basic principles of various nanoparticle-based composites and scaffolds are discussed in this review. The merits and demerits of these particles are critically discussed, and their importance in bone tissue engineering is highlighted.

Induced Pluripotent Stem Cells in Dental and Nondental Tissue Regeneration: A Review of an Unexploited Potential

Cell-based therapies currently represent the state of art for tissue regenerative treatment approaches for various diseases and disorders. Induced pluripotent stem cells (iPSCs), reprogrammed from adult somatic cells, using vectors carrying definite transcription factors, have manifested a breakthrough in regenerative medicine, relying on their pluripotent nature and ease of generation in large amounts from various dental and nondental tissues. In addition to their potential applications in regenerative medicine and dentistry, iPSCs can also be used in disease modeling and drug testing for personalized medicine. The current review discusses various techniques for the production of iPSC-derived osteogenic and odontogenic progenitors, the therapeutic applications of iPSCs, and their regenerative potential in vivo and in vitro. Through the present review, we aim to explore the potential applications of iPSCs in dental and nondental tissue regeneration and to highlight different protocols used for the generation of different tissues and cell lines from iPSCs.

The Impact of Bioceramic Scaffolds on Bone Regeneration in Preclinical In Vivo Studies: A Systematic Review

Bioceramic scaffolds are appealing for alveolar bone regeneration, because they are emerging as promising alternatives to autogenous and heterogenous bone grafts. The aim of this systematic review is to answer to the focal question: in critical-sized bone defects in experimental animal models, does the use of a bioceramic scaffolds improve new bone formation, compared with leaving the empty defect without grafting materials or using autogenous bone or deproteinized bovine-derived bone substitutes? Electronic databases were searched using specific search terms. A hand search was also undertaken. Only randomized and controlled studies in the English language, published in peer-reviewed journals between 2013 and 2018, using critical-sized bone defect models in non-medically compromised animals, were considered. Risk of bias assessment was performed using the SYRCLE tool. A meta-analysis was planned to synthesize the evidence, if possible. Thirteen studies reporting on small animal models (six studies on rats and seven on rabbits) were included. The calvarial bone defect was the most common experimental site. The empty defect was used as the only control in all studies except one. In all studies the bioceramic materials demonstrated a trend for better outcomes compared to an empty control. Due to heterogeneity in protocols and outcomes among the included studies, no meta-analysis could be performed. Bioceramics can be considered promising grafting materials, though further evidence is needed.

Poly(Dopamine) Coating on 3D-Printed Poly-Lactic-Co-Glycolic Acid/β-Tricalcium Phosphate Scaffolds for Bone Tissue Engineering

Bone defects caused by osteoporosis, bone malignant tumors, and trauma are very common, but there are many limiting factors in the clinical treatment of them. Bone tissue engineering is the most promising treatment and is considered to be the main strategy for bone defect repair. We prepared polydopamine-coated poly-(lactic-co-glycolic acid)/β-tricalcium phosphate composite scaffolds via 3D printing, and a series of characterization and biocompatibility tests were carried out. The results show that the mechanical properties and pore-related parameters of the composite scaffolds are not affected by the coatings, and the hydrophilicities of the surface are obviously improved. Scanning electron microscopy and micro-computed tomography display the nanoscale microporous structure of the bio-materials. Biological tests demonstrate that this modified surface can promote cell adhesion and proliferation and improve osteogenesis through the increase of polydopamine (PDA) concentrations. Mouse cranial defect experiments are conducted to further verify the conclusion that scaffolds with a higher content of PDA coatings have a better effect on the formation of new bones. In the study, the objective of repairing critical-sized defects is achieved by simply adding PDA as coatings to obtain positive results, which can suggest that this modification method with PDA has great potential.

Nanocellulose/bioactive glass cryogels as scaffolds for bone regeneration

A major challenge exists in the preparation of scaffolds for bone regeneration, namely, achieving simultaneously bioactivity, biocompatibility, mechanical performance and simple manufacturing. Here, cellulose nanofibrils (CNF) are introduced for the preparation of scaffolds taking advantage of their biocompatibility and ability to form strong 3D porous networks from aqueous suspensions. CNF are made bioactive for bone formation through a simple and scalable strategy that achieves highly interconnected 3D networks. The resultant materials optimally combine morphological and mechanical features and facilitate hydroxyapatite formation while releasing essential ions for in vivo bone repair. The porosity and roughness of the scaffolds favor several cell functions while the ions act in the expression of genes associated with cell differentiation. Ion release is found critical to enhance the production of the bone morphogenetic protein 2 (BMP-2) from cells within the fractured area, thus accelerating the in vivo bone repair. Systemic biocompatibility indicates no negative effects on vital organs such as the liver and kidneys. The results pave the way towards a facile preparation of advanced, high performance CNF-based scaffolds for bone tissue engineering.

Calcium Phosphate Incorporated Bacterial Cellulose-Polyvinylpyrrolidone Based Hydrogel Scaffold: Structural Property and Cell Viability Study for Bone Regeneration Application

This work focuses on the analysis of structural and functional properties of calcium phosphate (CaP) incorporated bacterial cellulose (BC)-polyvinylpyrrolidone (PVP) based hydrogel scaffolds referred to as “CaP/BC-PVP”. CaP is incorporated in the scaffolds in the form of hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP) in different concentrations (β-TCP: HA (w/w) = 20:80, 40:60, and 50:50). The scaffolds were characterized on the basis of porosity, thermal, biodegradation, mechanical, and cell viability/cytocompatibility properties. The structural properties of all the hydrogel scaffolds show significant porosity. The biodegradation of “CaP/BC-PVP” scaffold was evaluated following hydrolytic degradation. Weight loss profile, pH change, scanning electron microscopy (SEM), and Fourier Transform Infrared Spectroscopy (FTIR) study confirm the significant degradability of the scaffolds. It is observed that a 50:50_CaP/BC-PVP scaffold has the highest degree of degradation. On the other hand, the compressive strengths of CaP/BC-PVP hydrogel scaffolds are found between 0.21 to 0.31 MPa, which is comparable with the human trabecular bone. The cell viability study is performed with a human osteosarcoma Saos-2 cell line, where significant cell viability is observed in all the hydrogel scaffolds. This indicated their ability to facilitate cell growth and cell proliferation. Considering all these substantial properties, CaP/BC-PVP hydrogel scaffolds can be suggested for detailed investigation in the context of bone regeneration application.

BMP-2 Gene Delivery-Based Bone Regeneration in Dentistry

Bone morphogenetic protein-2 (BMP-2) is a potent growth factor affecting bone formation. While recombinant human BMP-2 (rhBMP-2) has been commercially available in cases of non-union fracture and spinal fusion in orthopaedics, it has also been applied to improve bone regeneration in challenging cases requiring dental implant treatment. However, complications related to an initially high dosage for maintaining an effective physiological concentration at the defect site have been reported, although an effective and safe rhBMP-2 dosage for bone regeneration has not yet been determined. In contrast to protein delivery, BMP-2 gene transfer into the defect site induces BMP-2 synthesis in vivo and leads to secretion for weeks to months, depending on the vector, at a concentration of nanograms per milliliter. BMP-2 gene delivery is advantageous for bone wound healing process in terms of dosage and duration. However, safety concerns related to viral vectors are one of the hurdles that need to be overcome for gene delivery to be used in clinical practice. Recently, commercially available gene therapy has been introduced in orthopedics, and clinical trials in dentistry have been ongoing. This review examines the application of BMP-2 gene therapy for bone regeneration in the oral and maxillofacial regions and discusses future perspectives of BMP-2 gene therapy in dentistry.

Satb2 expression in Foxc1-promoted osteogenic differentiation of MC3T3-E1 cells is negatively regulated by microRNA-103-3p

The forkhead transcription factor C1 (Foxc1) is a cell-fate-determining factor that controls cranial bone development and osteogenic differentiation. Previously, it was demonstrated that various microRNAs (miRNAs) play important roles in osteogenesis and regulate the complex process of osteogenic differentiation. However, it remains unclear how miRNA expression changes during Foxc1-promoted osteogenic differentiation. In this study, we successfully overexpressed the Foxc1 gene in MC3T3-E1 cells and investigated the alterations in the miRNA expression profile on day 3 after osteogenic induction by using a miRNA microarray. Nine downregulated miRNAs and eight upregulated miRNAs were found to be differentially expressed. Among these miRNAs, miR-103-3p was consistently downregulated in the Foxc1-overexpressing MC3T3-E1 cells and was identified as a negative regulator of osteogenic differentiation by using a gain- and lose-of-function assay. The special AT-rich sequence-binding protein 2 (Satb2), a pivotal osteogenic transcription factor, was identified as the miR-103-3p targeting gene and was verified by real-time polymerase chain reaction, western blot analysis, and luciferase assay. Overexpression of miR-103-3p markedly inhibited the expression of Satb2 and attenuated Foxc1-promoted osteogenic differentiation. Taken together, our results elucidated the miRNA expression profiles of MC3T3-E1 cells in the early stage of Foxc1-promoted osteogenic differentiation and suggested that miR-103-3p acts as a negative regulator of the osteogenic differentiation of MC3T3-E1 cells by directly targeting Satb2.

Effect of Porous Chitosan Microspheres Loaded with Platelet-Rich Plasma and Bone Marrow-Derived Mesenchymal Stem Cells on Regeneration of Tibia Defect

Objective. Repair of bone defects represents a grave clinical challenge because of the tremendous difficulties in the recovery of bone function and regeneration of bone loss. Therefore, we investigated the effects of platelet-rich plasma-loaded (PRP) porous chitosan microspheres (PCMs) on the differentiation of bone marrow-derived mesenchymal stem cells (BMSCs) and the proliferation and differentiation potential of BMSCs loaded by PCMs in vitro. We also established the model of bone defect repair in rat tibia to further explore the effects of PCMs loaded with PRP and BMSCs on bone regeneration. Methods. MTT assay was used to detect the proliferative ability of BMSCs after hypoxia/reoxygenation (H/R) treatment and the proliferative ability of BMSCs loaded by PCMs; polymerase chain reaction (PCR) was used to detect the expression of alkaline phosphatase (ALP), type I collagen (Col I), and type II collagen (Col II) in BMSCs after hypoxia and in BMSCs induced by PRP-loaded PCMs; PCR was used to detect the expression of Runt-associated transcription factor 2 (Runx2) and osteocalcin (OC) in the newly generated bone tissue; micro-CT scanning was applied to measure the bone mineral density and bone volume of the newly generated bone tissue in rats. Results. BMSCs still have the normal potential of proliferation and differentiation after H/R treatment. PCMs can provide a larger surface for the attachment of BMSCs, facilitating cell proliferation. Loaded by PCMs, PRP can be slowly released, effectively stimulating the differentiation of BMSCs. PCM/PRP/BMSC composites increased the expression levels of Runx2 and OC in the newly generated bone in rat tibia defect and the bone mineral density. Moreover, the composites improved the rate of regenerated bone volume. Conclusion. The application of PCM/PRP/BMSC composites is promising in the repair of tibia defects.

Tailored Biomaterials for Therapeutic Strategies Applied in Periodontal Tissue Engineering

Several therapeutic strategies are currently in development for severe periodontitis and other associated chronic inflammatory diseases. Guided tissue regeneration of the periodontium is based on surgical implantation of natural or synthetic polymers conditioned as membranes, injectable biomaterials (hydrogels), or three-dimensional (3D) matrices. Combinations of biomaterials with bioactive factors represent the next generation of regenerative strategy. Cell delivery strategy based on scaffold-cell constructs showed potential in periodontitis treatment. Bioengineering of periodontal tissues using cell sheets and genetically modified stem cells is currently proposed to complete existing (pre)clinical procedures for periodontal regeneration. 3D structures can be built using computer-assisted manufacturing technologies to improve the implant architecture effect on new tissue formation. The aim of this review was to summarize the advantages and drawbacks of biomimetic composite matrices used as biomaterials for periodontal tissue engineering. Their conditioning as two-dimensional or 3D scaffolds using conventional or emerging technologies was also discussed. Further biotechnologies are required for developing novel products tailored to stimulate periodontal regeneration. Additional preclinical studies will be useful to closely investigate the mechanisms and identify specific markers involved in cell-implant interactions, envisaging further clinical tests. Future therapeutic protocols will be developed based on these novel procedures and techniques.

Calcium phosphate cement scaffold with stem cell co-culture and prevascularization for dental and craniofacial bone tissue engineering

OBJECTIVE

Calcium phosphate cements (CPCs) mimic nanostructured bone minerals and are promising for dental, craniofacial and orthopedic applications. Vascularization plays a critical role in bone regeneration. This article represents the first review on cutting-edge research on prevascularization of CPC scaffolds to enhance bone regeneration.

METHODS

This article first presented the prevascularization of CPC scaffolds. Then the co-culture of two cell types in CPC scaffolds was discussed. Subsequently, to further enhance the prevascularization efficacy, tri-culture of three different cell types in CPC scaffolds was presented.

RESULTS

(1) Arg-Gly-Asp (RGD) incorporation in CPC bone cement scaffold greatly enhanced cell affinity and bone prevascularization; (2) By introducing endothelial cells into the culture of osteogenic cells (co-culture of two different cell types, or bi-culture) in CPC scaffold, the bone defect area underwent much better angiogenic and osteogenic processes when compared to mono-culture; (3) Tri-culture with an additional cell type of perivascular cells (such as pericytes) resulted in a substantially enhanced prevascularization of CPC scaffolds in vitro and more new bone and blood vessels in vivo, compared to bi-culture. Furthermore, biological cell crosstalk and capillary-like structure formation made critical contributions to the bi-culture system. In addition, the pericytes in the tri-culture system substantially promoted stability and maturation of the primary vascular network.

SIGNIFICANCE

The novel approach of CPC scaffolds with stem cell bi-culture and tri-culture is of great significance in the regeneration of dental, craniofacial and orthopedic defects in clinical practice.

High mannoronic acid containing alginate affects the differentiation of Wharton's jelly-derived stem cells to hepatocyte-like cell

For transplantation of cell into injured tissues, cells should be transferred to the damaged site through an adequate carrier. Nevertheless, the nutrient-limited and hypoxic condition in the carrier can bring about broad cell death. This study set to assess the impact of alginate concentrations on the differentiation and the proliferation of cells encapsulated in alginate hydrogels. Human Wharton's Jelly-derived Mesenchymal Stem Cells (HWJ-MSCs) were encapsulated in two concentrations of alginate hydrogel. Then, the proliferation and the hepatic differentiation were evaluated with an MTT assay and the enzyme-linked immunosorbent assay software and urea production. The results demonstrated that the proliferation of cell and urea production in 1.5% alginate concentration was higher than in 2.5% alginate concentration in the hydrogels of alginate. We deduce that the optimized alginate hydrogel concentration is necessary for achieving comparable cell activities in three-dimensional culture.

Bioceramic akermanite enhanced vascularization and osteogenic differentiation of human induced pluripotent stem cells in 3D scaffolds in vitro and vivo

A growing number of studies suggest that the modulation of cell differentiation by biomaterials is critical for tissue engineering. In previous work, we demonstrated that human induced pluripotent stem cells (iPSCs) are remarkably promising seed cells for bone tissue engineering. In addition, we found that the ionic products of akermanite (Aker) are potential inducers of osteogenic differentiation of iPSCs. Furthermore, composite scaffolds containing polymer and bioceramics have more interesting properties compared to pure bioceramic scaffolds for bone tissue engineering. The characteristic of model biomaterials in bone tissue engineering is their ability to control the osteogenic differentiation of stem cells and simultaneously induce the angiogenesis of endothelia cells. Thus, this study aimed at investigating the effects of poly(lactic-co-glycolic acid)/Aker (PLGA-Aker) composite scaffolds on angiogenic and osteogenic differentiation of human iPSCs in order to optimize the scaffold compositions. The results from Alizarin Red S staining, qRT-PCR analysis of osteogenic genes (BMP2, RUNX2, ALP, COL1 and OCN) and angiogenic genes (VEGF and CD31) demonstrated that PLGA/Aker composite scaffolds containing 10% Aker exhibited the highest stimulatory effects on the osteogenic and angiogenic differentiation of human iPSCs among all scaffolds. After the scaffolds were implanted in nu/nu mice subcutaneous pockets and calvarial defects, H&E staining, BSP immunostaining, qRT-PCR analysis and micro-CT analysis (BMD, BV/TV) indicated that PLGA + 10% Aker scaffolds enhanced the vascularization and osteogenic differentiation of human iPSCs and stimulated the repair of bone defects. Taken together, our work indicated that combining scaffolds containing silicate bioceramic Aker and human iPSCs is a promising approach for the enhancement of bone regeneration.

Bioceramics akermanite enhanced vascularization and osteogenic differentiation of human iPSCs in 3D scaffolds in vitro and vivo.

Quantification of the mandibular defect healing by micro-CT morphometric analysis in rats

PURPOSE

The goal of this study was the evaluation of the bone tissue structural characteristics over the time course of mandibular defect healing using micro-CT technique, as well as determination of the inter-relationships between different micro-CT parameters used for assessment of the bone regeneration process and the patterns of their dynamic changes.

MATERIALS AND METHODS

The body and ramus of the mandible was exposed in 24 Wistar rats. A 2-mm full thickness bony defect was created. Animals were randomized into four groups, which were ended 3, 6, 12 and 24 weeks after operation. The mandible was excised and underwent micro-CT analysis. For statistical evaluation, the Mann-Whitney U test, polynomial or exponential regression and Spearman analysis were applied.

RESULTS

The absolute volume of the bone regenerate increased from 1.69 ± 0.53 mm3 (3 weeks) to 3.36 mm3 ± 0.56 (6 months), as well as percentage of bone volume, increased significantly from 12.5 ± 2.3% at the 3-week term to 26.4 ± 8.7% at the 3-month term or 23.1 ± 8.7% at the 6-month term. Structural (trabecular) thickness gradually increased from 0.13 ± 0.007 mm at the 3-week term to 0.3 ± 0.11 mm at the 6-month term. The structural model index was 0.79 ± 0.46 in the early phase after trauma and then decreased to negative values.

CONCLUSION

The bone regeneration process was characterized by a significant increase (p < 0.05) in bone volume, percentage of bone volume, structural thickness and bone mineral density, and a decrease in bone surface-to-volume ratio and volume of pore space from the 3-week term to the 6-month term. These changes can be mathematically described by nonlinear exponential regression models.

Lentivirus‑mediated microRNA‑26a overexpression in bone mesenchymal stem cells facilitates bone regeneration in bone defects of calvaria in mice

Repair of bone defects presents a serious clinical challenge as it is difficult to restore bone function and regenerate bone loss. In the present study, the effects of lentivirus-mediated transfection of bone marrow mesenchymal stem cells (BMSCs) with microRNA (miR)-26a on bone regeneration were investigated in a mouse bone defect repair model. Marker of proliferation Ki67 (Ki67) staining was employed to detect the cell proliferation capacity and alkaline phosphatase (ALP) staining was used to investigate osteogenic differentiation. A mouse model of cranial bone defects was established. β-tricalcium phosphate biomaterials co-cultured with the transfected BMSCs were implanted into the defect areas of mouse models. Micro-computed tomography, and hematoxylin and eosin and toluidine blue staining, were used to detect bone regeneration in the defect areas and the degradation of scaffolds. miR-26a expression, and the mRNA and protein expression of osteogenesis-associated cytokines, were detected using reverse transcription-quantitative polymerase chain reaction and western blot analysis. Separated and cultured BMSCs highly expressed CD29 and CD105, but not CD34 and CD45, as determined by flow cytometry. miR-26a expression and the positive cell rate of Ki67 and ALP staining in BMSCs transfected with pLVTHM-miR-26a were increased. The BMSC and negative control-transfected BMSC groups exhibited increased bone regeneration in the defect areas, increased bone volume of newly formed bones, and elevated mRNA and protein expression of runt-related transcription factor 2 (Runx2) and osteocalcin (OC), compared with the blank group. However, the miR-26a-transfected BMSC group exhibited further increases in bone regeneration and the volume of newly formed bones, and further elevations of the mRNA and protein expression levels of Runx2 and OC. The present findings demonstrated that lentivirus-mediated modification of BMSCs enhanced bone regeneration during the repair of cranial bone defects in mice.

Mesenchymal Stem Cell Therapy for Bone Regeneration

Mesenchymal stem cells (MSCs) have been used in clinic for approximately 20 years. During this period, various new populations of MSCs have been found or manipulated. However, their characters and relative strength for bone regeneration have not been well known. For a comprehensive understanding of MSCs, we reviewed the literature on the multipotent cells ranging from the definition to the current research progress for bone regeneration. Based on our literature review, bone marrow MSCs have been most widely studied and utilized in clinical settings. Among other populations of MSCs, adipose-derived MSCs and perivascular MSCs might be potential candidates for bone regeneration, whose efficacy and safety still require further investigation.

Nanosurfaces modulate the mechanism of peri-implant endosseous healing by regulating neovascular morphogenesis

Nanosurfaces have improved clinical osseointegration by increasing bone/implant contact. Neovascularization is considered an essential prerequisite to osteogenesis, but no previous reports to our knowledge have examined the effect of surface topography on the spatio-temporal pattern of neovascularization during peri-implant healing. We have developed a cranial window model to study peri-implant healing intravitally over clinically relevant time scales as a function of implant topography. Quantitative intravital confocal imaging reveals that changing the topography (but not chemical composition) of an implant profoundly affects the pattern of peri-implant neovascularization. New vessels develop proximal to the implant and the vascular network matures sooner in the presence of an implant nanosurface. Accelerated angiogenesis can lead to earlier osseointegration through the delivery of osteogenic precursors to, and direct formation of bone on, the implant surface. This study highlights a critical aspect of peri-implant healing, but also informs the biological rationale for the surface design of putative endosseous implant materials.

A novel Lipidoid-MicroRNA formulation promotes calvarial bone regeneration

Specific microRNAs (miRs) and the Wnt signaling pathway play critical roles in regulating bone development and homeostasis. Our previous studies revealed the ability of miR-335-5p to promote osteogenic differentiation by downregulating Wnt antagonist Dickkopf-1 (DKK1). The purpose of this study was to use nano-materials to efficiently deliver miR-335-5p into osteogenic cells for tissue engineering applications. We synthesized and screened a library of 12 candidate nano-lipidoids，of which L8 was identified as the preferred biodegradable lipidoid for miRNA molecule delivery into cells. We then investigated whether a lipidoid-miRNA formulation of miR-335-5-p (LMF-335) could successfully deliver miR-335-5-p into cells to promote osteogenesis in vitro and calvarial bone healing in vivo. Transfection of C3H10T1/2 cells and bone marrow stromal cells (BMSCs) with LMF-335 led to decreased expression of DKK1 and increased expression of the key osteogenic genes. LMF-335 and LMF-335-transfected BMSCs were then used in combination with silk scaffolds to evaluate healing of critical-size calvarial bone defects in mice. The results revealed significant new bone formation in the defects in LMF-335 groups as compared with control groups. In conclusion, this first report supports the notion that lipidoid delivery of miRNA can be used to induce osteogenic differentiation of stem cells and bone regeneration.

A review of biomaterials in bone defect healing, remaining shortcomings and future opportunities for bone tissue engineering: The unsolved challenge

Despite its intrinsic ability to regenerate form and function after injury, bone tissue can be challenged by a multitude of pathological conditions. While innovative approaches have helped to unravel the cascades of bone healing, this knowledge has so far not improved the clinical outcomes of bone defect treatment. Recent findings have allowed us to gain in-depth knowledge about the physiological conditions and biological principles of bone regeneration. Now it is time to transfer the lessons learned from bone healing to the challenging scenarios in defects and employ innovative technologies to enable biomaterial-based strategies for bone defect healing. This review aims to provide an overview on endogenous cascades of bone material formation and how these are transferred to new perspectives in biomaterial-driven approaches in bone regeneration.

Cite this article: T. Winkler, F. A. Sass, G. N. Duda, K. Schmidt-Bleek. A review of biomaterials in bone defect healing, remaining shortcomings and future opportunities for bone tissue engineering: The unsolved challenge. Bone Joint Res 2018;7:232–243. DOI: 10.1302/2046-3758.73.BJR-2017-0270.R1.

Soybean Lecithin-Mediated Nanoporous PLGA Microspheres with Highly Entrapped and Controlled Released BMP-2 as a Stem Cell Platform

Injectable polymer microsphere-based stem cell delivery systems have a severe problem that they do not offer a desirable environment for stem cell adhesion, proliferation, and differentiation because it is difficult to entrap a large number of hydrophilic functional protein molecules into the core of hydrophobic polymer microspheres. In this work, soybean lecithin (SL) is applied to entrap hydrophilic bone morphogenic protein-2 (BMP-2) into nanoporous poly(lactide-co-glycolide) (PLGA)-based microspheres by a two-step method: SL/BMP-2 complexes preparation and PLGA/SL/BMP-2 microsphere preparation. The measurements of their physicochemical properties show that PLGA/SL/BMP-2 microspheres had significantly higher BMP-2 entrapment efficiency and controlled triphasic BMP-2 release behavior compared with PLGA/BMP-2 microspheres. Furthermore, the in vitro and in vivo stem cell behaviors on PLGA/SL/BMP-2 microspheres are analyzed. Compared with PLGA/BMP-2 microspheres, PLGA/SL/BMP-2 microspheres have significantly higher in vitro and in vivo stem cell attachment, proliferation, differentiation, and matrix mineralization abilities. Therefore, injectable nanoporous PLGA/SL/BMP-2 microspheres can be potentially used as a stem cell platform for bone tissue regeneration. In addition, SL can be potentially used to prepare hydrophilic protein-loaded hydrophobic polymer microspheres with highly entrapped and controlled release of proteins.

MicroRNA-99a is a novel regulator of KDM6B-mediated osteogenic differentiation of BMSCs

Skeletal tissue originates from mesenchymal stem cells (MSCs) with differentiation potential into the osteoblast lineage regulated by essential transcriptional and post‐transcriptional mechanisms. Recently, miRNAs and histone modifications have been identified as novel key regulators of osteogenic differentiation of MSCs. Here, we identified miR‐99a and its target lysine (K)‐specific demethylase 6B (KDM6B) gene as novel modulators of osteogenic differentiation of bone mesenchymal stem cells (BMSCs). Microarray profiling and further validation by quantitative real‐time RT‐PCR revealed that miR‐99a was up‐regulated during osteoblastic differentiation of BMSCs, and decreased in differentiated osteoblasts. Transfection of miR‐99a mimics inhibited osteoblastic commitment and differentiation of BMSCs, whereas inhibition of miR‐99a by inhibitors enhances these processes. KDM6B was determined as one of important targets of miR‐99a, which was further confirmed by luciferase assay of 3′‐UTR of KDM6B. Moreover, HOX gene level decreased after transfection of miR‐99a mimics in BMSCs, which indicated that KDM6B is a bona fide target of miR‐99a. Furthermore, in a model of in vivo bone regeneration, osteoblast‐specific gain‐ and loss‐of‐function experiments performed using cranial bone defects revealed that miR‐99a mimics‐transfected BMSCs reduced bone formation, and conversely, miR‐99a inhibitors‐transfected BMSCs increased in vivo bone formation. Tissue‐specific inhibition of miR‐99a may be a potential novel therapeutic approach for enhancing BMSCs‐based bone formation and regeneration.

Overexpression of MiR-335-5p Promotes Bone Formation and Regeneration in Mice

MicroRNAs (miRNAs) and the Wnt signaling pathway play critical roles in regulating bone development and homeostasis. Our previous study revealed high expression of miR-335-5p in osteoblasts and hypertrophic chondrocytes in mouse embryos and the ability of miR-335-5p to promote osteogenic differentiation by downregulating Wnt antagonist Dickkopf-1 (DKK1). The purpose of this study was to investigate the effects of miR-335-5p constitutive overexpression on bone formation and regeneration in vivo. To that end, we generated a transgenic mouse line specifically overexpressing miR-335-5p in osteoblasts lineage by the osterix promoter and characterized its bone phenotype. Bone histomorphometry and μCT analysis revealed higher bone mass and increased parameters of bone formation in transgenic mice than in wild-type littermates. Increased bone mass in transgenic mice bones also correlated with enhanced expression of osteogenic differentiation markers. Upon osteogenic induction, bone marrow stromal cells (BMSCs) isolated from transgenic mice displayed higher mRNA expression of osteogenic markers than wild-type mice BMSCs cultures. Protein expression of Runx2 and Osx was also upregulated in BMSC cultures of transgenic mice upon osteogenic induction, whereas that of DKK1 was downregulated. Most important, BMSCs from transgenic mice were able to repair craniofacial bone defects as shown by μCT analysis, H&E staining, and osteocalcin (OCN) immunohistochemistry of newly formed bone in defects treated with BMSCs. Taken together, our results demonstrate constitutive overexpression of miR-335-5p driven by an osterix promoter in the osteoblast lineage induces osteogenic differentiation and bone formation in mice and support the potential application of miR-335-5p-modified BMSCs in craniofacial bone regeneration. © 2017 American Society for Bone and Mineral Research.

Chitosan-Graphene Oxide 3D scaffolds as Promising Tools for Bone Regeneration in Critical-Size Mouse Calvarial Defects

Limited self-regenerating capacity of human skeleton makes the reconstruction of critical size bone defect a significant challenge for clinical practice. Aimed for regenerating bone tissues, this study was designed to investigate osteogenic differentiation, along with bone repair capacity of 3D chitosan (CHT) scaffolds enriched with graphene oxide (GO) in critical-sized mouse calvarial defect. Histopathological/histomorphometry and scanning electron microscopy(SEM) analysis of the implants revealed larger amount of new bone in the CHT/GO-filled defects compared with CHT alone (p < 0.001). When combined with GO, CHT scaffolds synergistically promoted the increase of alkaline phosphatase activity both in vitro and in vivo experiments. This enhanced osteogenesis was corroborated with increased expression of bone morphogenetic protein (BMP) and Runx-2 up to week 4 post-implantation, which showed that GO facilitates the differentiation of osteoprogenitor cells. Meanwhile, osteogenesis was promoted by GO at the late stage as well, as indicated by the up-regulation of osteopontin and osteocalcin at week 8 and overexpressed at week 18, for both markers. Our data suggest that CHT/GO biomaterial could represent a promising tool for the reconstruction of large bone defects, without using exogenous living cells or growth factors.

Reconstruction of Craniomaxillofacial Bone Defects Using Tissue-Engineering Strategies with Injectable and Non-Injectable Scaffolds

Engineering craniofacial bone tissues is challenging due to their complex structures. Current standard autografts and allografts have many drawbacks for craniofacial bone tissue reconstruction; including donor site morbidity and the ability to reinstate the aesthetic characteristics of the host tissue. To overcome these problems; tissue engineering and regenerative medicine strategies have been developed as a potential way to reconstruct damaged bone tissue. Different types of new biomaterials; including natural polymers; synthetic polymers and bioceramics; have emerged to treat these damaged craniofacial bone tissues in the form of injectable and non-injectable scaffolds; which are examined in this review. Injectable scaffolds can be considered a better approach to craniofacial tissue engineering as they can be inserted with minimally invasive surgery; thus protecting the aesthetic characteristics. In this review; we also focus on recent research innovations with different types of stem-cell sources harvested from oral tissue and growth factors used to develop craniofacial bone tissue-engineering strategies.

Estrogen regulates stemness and senescence of bone marrow stromal cells to prevent osteoporosis via ERβ-SATB2 pathway

Decline of pluripotency in bone marrow stromal cells (BMSCs) associated with estrogen deficiency leads to a bone formation defect in osteoporosis. Special AT-rich sequence binding protein 2 (SATB2) is crucial for maintaining stemness and osteogenic differentiation of BMSCs. However, whether SATB2 is involved in estrogen-deficiency associated-osteoporosis is largely unknown. In this study, we found that estrogen mediated pluripotency and senescence of BMSCs, primarily through estrogen receptor beta (ERβ). BMSCs from the OVX rats displayed increased senescence and weaker SATB2 expression, stemness, and osteogenic differentiation, while estrogen could rescue these phenotypes. Inhibition of ERβ or ERα confirmed that SATB2 was associated with ERβ in estrogen-mediated pluripotency and senescence of BMSCs. Furthermore, estrogen mediated the upregulation of SATB2 through the induction of ERβ binding to estrogen response elements (ERE) located at -488 of the SATB2 gene. SATB2 overexpression alleviated senescence and enhanced stemness and osteogenic differentiation of OVX-BMSCs. SATB2-modified BMSCs transplantation could prevent trabecular bone loss in an ovariectomized rat model. Collectively, our study revealed the role of SATB2 in stemness, senescence, and osteogenesis of OVX-BMSCs. These results indicate that estrogen prevents osteoporosis by promoting stemness and osteogenesis, and inhibiting senescence of BMSCs through an ERβ-SATB2 pathway. Therefore, SATB2 is a novel anti-osteoporosis target gene.

SATB2-Nanog axis links age-related intrinsic changes of mesenchymal stem cells from craniofacial bone

Bone mesenchymal stem cells (BMSCs) senescence contributes to age-related bone loss. The alveolar bone in jaws originates from neural crest cells and possesses significant site- and age-related properties. However, such intrinsic characteristics of BMSCs from alveolar bone (AB-BMSCs) and the underlying regulatory mechanisms still remain unknown. Here, we found that the expression of special AT-rich binding protein 2 (SATB2) in human AB-BMSCs significantly decreased with aging. SATB2 knockdown on AB-BMSCs from young donors displayed these aging-related phenotypes in vitro. Meanwhile, enforced SATB2 overexpression could rejuvenate AB-BMSCs from older donors. Importantly, satb2 gene- modified BMSCs therapy could prevent the alveolar bone loss during the aging of rats. Mechanistically, the stemness regulator Nanog was identified as the direct transcriptional target of SATB2 in BMSCs and functioned as a downstream mediator of SATB2. Collectively, our data reveal that SATB2 in AB-BMSCs associates with their age-related properties, and prevents AB-BMSCs senescence via maintaining Nanog expression. These findings highlight the translational potential of transcriptional factor-based cellular reprogramming for anti-aging therapy.

Loss of mechanosensitive sclerostin may accelerate cranial bone growth and regeneration

OBJECTIVE

Cranial defects can result from trauma, infection, congenital malformations, and iatrogenic causes and represent a surgical challenge. The current standard of care is cranioplasty, with either autologous or allogeneic material. In either case, the intrinsic vascularity of the surrounding tissues allows for bone healing. The objective of this study was to determine if mechanotransductive gene manipulation would yield non-weight-bearing bone regeneration in a critical size calvarial defect in mice.

METHODS

A mouse model of Sost deletion in Sost knockout (KO) mice was created in which the osteocytes do not express sclerostin. A critical size calvarial defect (4 mm in diameter) was surgically created in the parietal bone in 8-week-old wild-type (n = 8) and Sost KO (n = 8) male mice. The defects were left undisturbed (no implant or scaffold) to simulate a traumatic calvariectomy model. Eight weeks later, the animals were examined at necropsy by planimetry, histological analysis of new bone growth, and micro-CT scanning of bone thickness.

RESULTS

Defects created in wild-type mice did not fill with bone over the study period of 2 months. Genetic downregulation of sclerostin yielded animals that were able to regenerate 40% of the initial critical size defect area 8 weeks after surgery. A thin layer of bone covered a significant portion of the original defect in all Sost KO animals. A statistically significant increase in bone volume (p < 0.05) was measured in Sost KO mice using radiodensitometric analysis. Immunohistochemical analysis also confirmed that this bone regeneration occurred through the Wnt pathway and originated from the edge of the defect; BMP signaling did not appear to be affected by sclerostin.

CONCLUSIONS

Mechanical loading is an important mechanism of bone formation in the cranial skeleton and is poorly understood. This is partially due to the fact that it is difficult to load bone in the craniomaxillofacial skeleton. This study suggests that modulation of the Wnt pathway, as is able to be done with monoclonal antibodies, is a potentially efficacious method for bone regeneration that requires further study.