Effects of low dose FGF-2 and BMP-2 on healing of calvarial defects in old mice

Depletion of MicroRNA-100-5p Promotes Osteogenesis Via Lysine(K)-Specific Demethylase 6B

Senescence and osteogenic differentiation potential loss limited bone nonunion treatment effects of bone marrow-derived mesenchymal stem cells (BMSCs). MiR-100-5p/Lysine(K)-specific demethylase 6B (KDM6B) can inhibit osteogenesis, but their effects on bone union remain unclear. This study aims to investigate the effects of miR-100-5p/KDM6B on osteogenic differentiation and bone defects. Wild-type or microRNA 100 (miR-100) knockdown mice underwent critical-size defect (CSD) cranial surgery and collagen I/poly-γ-glutamic acid scaffold treatment. The crania was observed using microcomputed tomography, hematoxylin and eosin staining, Masson staining, alkaline phosphatase (ALP) staining, immunohistochemistry, and immunofluorescence. Primary-cultured BMSCs transfected with miR-100-5p mimic/inhibitor and KDM6B cDNA were evaluated for osteogenic differentiation using Alizarin Red staining, ALP activity detection, and Western blot analysis. Genetic transcription levels were detected using quantitative reverse transcription polymerase chain reaction. This study found that miR-100 depletion promotes defect healing in mouse calvaria, increases the proportion of new bone and osteoblasts in calvaria, and activates the expression of KDM6B and osteocalcin (OCN) proteins, promoting the transcription of bone morphogenetic protein-2, Runt-related transcription factor 2 (Runx2), OCN, and KDM6B, while methylation of lysine 27 on histone H3 (H3K27me3) decreased. Furthermore, miR-100-5p mimics suppressed osteogenic differentiation by inhibiting KDM6B with increased H3K27me3, ALP, Runx2, OCN, and osteopontin protein expression, while miR-100-5p inhibitors have opposite effects. Moreover, KDM6B can reverse miR-100-5p mimic effects. Notably, scaffolds carrying miR-100-5p mimics/inhibitors transfected BMSCs were placed in CSD mice and found that miR-100-5p inhibitors have a better effect on CSD healing and increase new bone without inflammatory cell infiltration. This study proved that miR-100-5p depletion promotes bone union and osteogenic differentiation of BMSCs via KDM6B/H3K27me3.

Injectable phase-separated tetra-armed poly(ethylene glycol) hydrogel scaffold allows sustained release of growth factors to enhance the repair of critical bone defects

With the rising prevalence of bone-related injuries, it is crucial to improve treatments for fractures and defects. Tissue engineering offers a promising solution in the form of injectable hydrogel scaffolds that can sustain the release of growth factors like bone morphogenetic protein-2 (BMP-2) for bone repair. Recently, we discovered that tetra-PEG hydrogels (Tetra gels) undergo gel-gel phase separation (GGPS) at low polymer content, resulting in hydrophobicity and tissue affinity. In this work, we examined the potential of a newer class of gel, the oligo-tetra-PEG gel (Oligo gel), as a growth factor-releasing scaffold. We investigated the extent of GGPS occurring in the two gels and assessed their ability to sustain BMP-2 release and osteogenic potential in a mouse calvarial defect model. The Oligo gel underwent a greater degree of GGPS than the Tetra gel, exhibiting higher turbidity, hydrophobicity, and pore formation. The Oligo gel demonstrated sustained protein or growth factor release over a 21-day period from protein release kinetics and osteogenic cell differentiation studies. Finally, BMP-2-loaded Oligo gels achieved complete regeneration of critical-sized calvarial defects within 28 days, significantly outperforming Tetra gels. The easy formulation, injectability, and capacity for sustained release makes the Oligo gel a promising candidate therapeutic biomaterial.

Biomimetic Hematoma as a Novel Delivery Vehicle for rhBMP-2 to Potentiate the Healing of Nonunions and Bone Defects

SUMMARY

The management of bone defects and nonunions creates unique clinical challenges. Current treatment alternatives are often insufficient and frequently require multiple surgeries. One promising option is bone morphogenetic protein-2 (BMP-2), which is the most potent inducer of osteogenesis. However, its use is associated with many side effects, related to the delivery and high doses necessary. To address this need, we developed an ex vivo biomimetic hematoma (BH), replicating naturally healing fracture hematoma, using whole blood and the natural coagulants calcium and thrombin. It is an autologous carrier able to deliver reduced doses of rhBMP-2 to enhance bone healing for complex fractures. More than 50 challenging cases involving recalcitrant nonunions and bone defects have already been treated using the BH delivering reduced doses of rhBMP-2, to evaluate both the safety and efficacy. Preliminary data suggest the BH is currently the only clinically used carrier able to effectively deliver reduced doses (∼70% less) of rhBMP-2 with high efficiency, rapidly and robustly initiating the bone repair cascade to successfully reconstruct complex bone injuries without side effects. The presented case provides a clear demonstration of this technology's ability to significantly alter the clinical outcome in extremely challenging scenarios where other treatment options have failed or are considered unsuitable. A favorable safety profile would portend considerable promise for BH as an alternative to bone grafts and substitutes. Although further studies regarding its clinical efficacy are still warranted, this novel approach nevertheless has tremendous potential as a favorable treatment option for bone defects, open fractures, and recalcitrant nonunions.

Enhanced Bone Formation by Rapidly Formed Bony Wall over the Bone Defect Using Dual Growth Factors

BACKGROUND

In guided bone regeneration (GBR), there are various problems that occur in the bone defect after the wound healing period. This study aimed to investigate the enhancement of the osteogenic ability of the dual scaffold complex and identify the appropriate concentration of growth factors (GF) for new bone formation based on the novel GBR concept that is applying rapid bone forming GFs to the membrane outside of the bone defect.

METHODS

Four bone defects with a diameter of 8 mm were formed in the calvaria of New Zealand white rabbits each to perform GBR. Collagen membrane and biphasic calcium phosphate (BCP) were applied to the bone defects with the four different concetration of BMP-2 or FGF-2. After 2, 4, and 8 weeks of healing, histological, histomorphometric, and immunohistochemical analyses were conducted.

RESULTS

In the histological analysis, continuous forms of new bones were observed in the upper part of bone defect in the experimental groups, whereas no continuous forms were observed in the control group. In the histomorphometry, The group to which BMP-2 0.5 mg/ml and FGF-2 1.0 mg/ml was applied showed statistically significantly higher new bone formation. Also, the new bone formation according to the healing period was statistically significantly higher at 8 weeks than at 2, 4 weeks.

CONCLUSION

The novel GBR method in which BMP-2, newly proposed in this study, is applied to the membrane is effective for bone regeneration. In addition, the dual scaffold complex is quantitatively and qualitatively advantageous for bone regeneration and bone maintenance over time.

Polymeric and Composite Carriers of Protein and Non-Protein Biomolecules for Application in Bone Tissue Engineering

Conventional intake of drugs and active substances is most often based on oral intake of an appropriate dose to achieve the desired effect in the affected area or source of pain. In this case, controlling their distribution in the body is difficult, as the substance also reaches other tissues. This phenomenon results in the occurrence of side effects and the need to increase the concentration of the therapeutic substance to ensure it has the desired effect. The scientific field of tissue engineering proposes a solution to this problem, which creates the possibility of designing intelligent systems for delivering active substances precisely to the site of disease conversion. The following review discusses significant current research strategies as well as examples of polymeric and composite carriers for protein and non-protein biomolecules designed for bone tissue regeneration.

Biomimetic hematoma delivers an ultra-low dose of rhBMP-2 to successfully regenerate large femoral bone defects in rats

Successful repair of large bone defects remains a clinical challenge. Following fractures, a bridging hematoma immediately forms as a crucial step that initiates bone healing. In larger bone defects the micro-architecture and biological properties of this hematoma are compromised, and spontaneous union cannot occur. To address this need, we developed an ex vivo Biomimetic Hematoma that resembles naturally healing fracture hematoma, using whole blood and the natural coagulants calcium and thrombin, as an autologous delivery vehicle for a very reduced dose of rhBMP-2. When implanted into a rat femoral large defect model, complete and consistent bone regeneration with superior bone quality was achieved with 10-20× less rhBMP-2 compared to that required with the collagen sponges currently used. Moreover, calcium and rhBMP-2 demonstrated a synergistic effect enhancing osteogenic differentiation, and fully restored mechanical strength 8 weeks after surgery. Collectively, these findings suggest the Biomimetic Hematoma provides a natural reservoir for rhBMP-2, and that retention of the protein within the scaffold rather than its sustained release might be responsible for more robust and rapid bone healing. Clinically, this new implant, using FDA-approved components, would not only reduce the risk of adverse events associated with BMPs, but also decrease treatment costs and nonunion rates.

Osteogenic Potential of Sheep Mesenchymal Stem Cells Preconditioned with BMP-2 and FGF-2 and Seeded on an nHAP-Coated PCL/HAP/β-TCP Scaffold

Mesenchymal stem cells (MSCs) attract interest in regenerative medicine for their potential application in bone regeneration. However, direct transplantation of cells into damaged tissue is not efficient enough to regenerate large bone defects. This problem could be solved with a biocompatible scaffold. Consequently, bone tissue engineering constructs based on biomaterial scaffolds, MSCs, and osteogenic cytokines are promising tools for bone regeneration. The aim of this study was to evaluate the effect of FGF-2 and BMP-2 on the osteogenic potential of ovine bone marrow-derived MSCs seeded onto an nHAP-coated PCL/HAP/β-TCP scaffold in vitro and its in vivo biocompatibility in a sheep model. In vitro analysis revealed that cells preconditioned with FGF-2 and BMP-2 showed a better capacity to adhere and proliferate on the scaffold than untreated cells. BM-MSCs cultured in an osteogenic medium supplemented with FGF-2 and BMP-2 had the highest osteogenic differentiation potential, as assessed based on Alizarin Red S staining and ALP activity. qRT-PCR analysis showed increased expression of osteogenic marker genes in FGF-2- and BMP-2-treated BM-MSCs. Our pilot in vivo research showed that the implantation of an nHAP-coated PCL/HAP/β-TCP scaffold with BM-MSCs preconditioned with FGF-2 and BMP-2 did not have an adverse effect in the sheep mandibular region and induced bone regeneration. The biocompatibility of the implanted scaffold-BM-MSC construct with sheep tissues was confirmed by the expression of early (collagen type I) and late (osteocalcin) osteogenic proteins and a lack of an elevated level of proinflammatory cytokines. These findings suggest that FGF-2 and BMP-2 enhance the osteogenic differentiation potential of MSCs grown on a scaffold, and that such a tissue engineering construct may be used to regenerate large bone defects.

The role of proteoglycan form of DMP1 in cranial repair

Background

The cranial region is a complex set of blood vessels, cartilage, nerves and soft tissues. The reconstruction of cranial defects caused by trauma, congenital defects and surgical procedures presents clinical challenges. Our previous data showed that deficiency of the proteoglycan (PG) form of dentin matrix protein 1 (DMP1-PG) could lead to abnormal cranial development. In addition, DMP1-PG was highly expressed in the cranial defect areas. The present study aimed to investigate the potential role of DMP1-PG in intramembranous ossification in cranial defect repair.

Methods

Mouse cranial defect models were established by using wild- type (WT) and DMP1-PG point mutation mice. Microcomputed tomography (micro-CT) and histological staining were performed to assess the extent of repair. Immunofluorescence assays and real-time quantitative polymerase chain reaction (RT‒qPCR) were applied to detect the differentially expressed osteogenic markers. RNA sequencing was performed to probe the molecular mechanism of DMP1-PG in regulating defect healing.

Results

A delayed healing process and an abnormal osteogenic capacity of primary osteoblasts were observed in DMP1-PG point mutation mice. Furthermore, impaired inflammatory signaling pathways were detected by using RNA transcription analysis of this model.

Conclusions

Our data indicate that DMP1-PG is an indispensable positive regulator during cranial defect healing.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12860-022-00443-4.

A combined cell and growth factor delivery for the repair of a critical size tibia defect using biodegradable hydrogel implants

The ability to repair critical‐sized long‐bone injuries using growth factor and cell delivery was investigated using hydrogel biomaterials. Physiological doses of the recombinant human bone morphogenic protein‐2 (rhBMP2) were delivered in a sustained manner from a biodegradable hydrogel containing peripheral human blood‐derived endothelial progenitor cells (hEPCs). The biodegradable implants made from polyethylene glycol (PEG) and denatured fibrinogen (PEG‐fibrinogen, PF) were loaded with 7.7 μg/ml of rhBMP2 and 2.5 × 10⁶ cells/ml hEPCs. The safety and efficacy of the implant were tested in a rodent model of a critical‐size long‐bone defect. The hydrogel implants were formed ex‐situ and placed into defects in the tibia of athymic nude rats and analyzed for bone repair after 13 weeks following surgery. The hydrogels containing a combination of 7.7 μg/ml of rhBMP2 and 2.5 × 10⁶ cells/ml hEPCs were compared to control hydrogels containing 7.7 μg/ml of rhBMP2 only, 2.5 × 10⁶ cells/ml hEPCs only, or bare hydrogels. Assessments of bone repair include histological analysis, bone formation at the site of implantation using quantitative microCT, and assessment of implant degradation. New bone formation was detected in all treated animals, with the highest amounts found in the treatments that included animals that combined the PF implant with rhBMP2. Moreover, statistically significant increases in the tissue mineral density (TMD), trabecular number and trabecular thickness were observed in defects treated with rhBMP2 compared to non‐rhBMP2 defects. New bone formation was significantly higher in the hEPC‐treated defects compared to bare hydrogel defects, but there were no significant differences in new bone formation, trabecular number, trabecular thickness or TMD at 13 weeks when comparing the rhBMP2 + hEPCs‐treated defects to rhBMP2‐treated defects. The study concludes that the bone regeneration using hydrogel implants containing hEPCs are overshadowed by enhanced osteogenesis associated with sustained delivery of rhBMP2.

Tissue Engineered Neurovascularization Strategies for Craniofacial Tissue Regeneration

Craniofacial tissue injuries, diseases, and defects, including those within bone, dental, and periodontal tissues and salivary glands, impact an estimated 1 billion patients globally. Craniofacial tissue dysfunction significantly reduces quality of life, and successful repair of damaged tissues remains a significant challenge. Blood vessels and nerves are colocalized within craniofacial tissues and act synergistically during tissue regeneration. Therefore, the success of craniofacial regenerative approaches is predicated on successful recruitment, regeneration, or integration of both vascularization and innervation. Tissue engineering strategies have been widely used to encourage vascularization and, more recently, to improve innervation through host tissue recruitment or prevascularization/innervation of engineered tissues. However, current scaffold designs and cell or growth factor delivery approaches often fail to synergistically coordinate both vascularization and innervation to orchestrate successful tissue regeneration. Additionally, tissue engineering approaches are typically investigated separately for vascularization and innervation. Since both tissues act in concert to improve craniofacial tissue regeneration outcomes, a revised approach for development of engineered materials is required. This review aims to provide an overview of neurovascularization in craniofacial tissues and strategies to target either process thus far. Finally, key design principles are described for engineering approaches that will support both vascularization and innervation for successful craniofacial tissue regeneration.

Endogenous FGF-2 levels impact FGF-2/BMP-2 growth factor delivery dosing in aged murine calvarial bone defects

Bone repair in elderly mice has been shown to be improved or negatively impacted by supplementing the highly osteogenic bone morphogenetic protein-2 (BMP-2) with fibroblast growth factor-2 (FGF-2). To better predict the outcome of FGF-2 supplementation, we investigated whether endogenous levels of FGF-2 play a role in optimal dosing of FGF-2 for augmenting BMP-2 activity in elderly mice. In vivo calvarial bone defect studies in Fgf2 knockout mice with wildtype controls were conducted with the growth factors delivered in a highly localized manner from a biomimetic calcium phosphate/polyelectrolyte multilayer coating applied to a bone graft substitute. Endogenous FGF-2 levels were measured in old mice versus young and found to decrease with age. Optimal dosing for improving bone defect repair correlated with levels of endogenous FGF-2, with a larger dose of FGF-2 required to have a positive effect on bone healing in the Fgf2 knockout mice. The same dose in wildtype old mice, with higher levels of FGF-2, promoted chondrogenesis and increased osteoclast activity. The results suggest a personalized medicine approach, based on a knowledge of endogenous levels of FGF-2, should guide FGF-2 supplementation in order to avoid provoking excessive bone resorption and cartilage formation, both of which inhibited calvarial bone repair.

The biological applications of DNA nanomaterials: current challenges and future directions

DNA, a genetic material, has been employed in different scientific directions for various biological applications as driven by DNA nanotechnology in the past decades, including tissue regeneration, disease prevention, inflammation inhibition, bioimaging, biosensing, diagnosis, antitumor drug delivery, and therapeutics. With the rapid progress in DNA nanotechnology, multitudinous DNA nanomaterials have been designed with different shape and size based on the classic Watson-Crick base-pairing for molecular self-assembly. Some DNA materials could functionally change cell biological behaviors, such as cell migration, cell proliferation, cell differentiation, autophagy, and anti-inflammatory effects. Some single-stranded DNAs (ssDNAs) or RNAs with secondary structures via self-pairing, named aptamer, possess the ability of targeting, which are selected by systematic evolution of ligands by exponential enrichment (SELEX) and applied for tumor targeted diagnosis and treatment. Some DNA nanomaterials with three-dimensional (3D) nanostructures and stable structures are investigated as drug carrier systems to delivery multiple antitumor medicine or gene therapeutic agents. While the functional DNA nanostructures have promoted the development of the DNA nanotechnology with innovative designs and preparation strategies, and also proved with great potential in the biological and medical use, there is still a long way to go for the eventual application of DNA materials in real life. Here in this review, we conducted a comprehensive survey of the structural development history of various DNA nanomaterials, introduced the principles of different DNA nanomaterials, summarized their biological applications in different fields, and discussed the current challenges and further directions that could help to achieve their applications in the future.

Current Biomaterial-Based Bone Tissue Engineering and Translational Medicine

Bone defects cause significant socio-economic costs worldwide, while the clinical "gold standard" of bone repair, the autologous bone graft, has limitations including limited graft supply, secondary injury, chronic pain and infection. Therefore, to reduce surgical complexity and speed up bone healing, innovative therapies are needed. Bone tissue engineering (BTE), a new cross-disciplinary science arisen in the 21st century, creates artificial environments specially constructed to facilitate bone regeneration and growth. By combining stem cells, scaffolds and growth factors, BTE fabricates biological substitutes to restore the functions of injured bone. Although BTE has made many valuable achievements, there remain some unsolved challenges. In this review, the latest research and application of stem cells, scaffolds, and growth factors in BTE are summarized with the aim of providing references for the clinical application of BTE.

Engineered bridge protein with dual affinity for bone morphogenetic protein-2 and collagen enhances bone regeneration for spinal fusion

The revolutionizing efficacy of recombinant human bone morphogenetic protein (rhBMP-2) for clinical spinal fusion is hindered by safety issues associated with the high dose required. However, it continues to be widely used, for example, in InFUSE Bone Graft (Medtronic). Here, we developed a translational protein engineering-based approach to reduce the dose and thereby improve the safety of rhBMP-2 delivered in a collagen sponge, as in InFUSE Bone Graft. We engineered a bridge protein with high affinity for rhBMP-2 and collagen that can be simply added to the product's formulation, demonstrating improved efficacy at low dose of rhBMP-2 in two mouse models of bone regeneration, including a newly developed spinal fusion model. Moreover, the bridge protein can control the retention of rhBMP-2 from endogenous collagenous extracellular matrix of tissue. Our approach may be generalizable to other growth factors and collagen-based materials, for use in many other applications in regenerative medicine.

Polyelectrolyte multilayer composite coating on 316 L stainless steel for controlled release of dual growth factors accelerating restoration of bone defects

A composite coating of polyelectrolyte multilayers (PEMs) consisting of collagen, a chitosan barrier, and poly-γ-glutamic acid was fabricated using a spin coating technique to investigate and overcome the limited osseointegration capacity of 316 L stainless steel (316 L SS). To further enhance the biocompatibility, bone morphogenetic protein 2 (BMP-2) and basic fibroblast growth factor-2 (FGF-2) were loaded separately as dual growth factors, allowing for progressive drug release following the natural process of bone regeneration. The first burst release of FGF-2 triggered the proliferation of surrounding cells, and the subsequent release of BMP-2 stimulated their differentiation. The microstructure, surface potential, hardness, reduced Young's modulus, and wettability were assessed using scanning electron microscopy, nanoindentation, and water contact angle. The formation of apatite layers after immersion in simulated body fluid confirmed the bioactivity of this PEM. PEMs loaded with BMP-2 and FGF-2 showed a long sustained release of growth factors for up to 48 days. The biological properties were studied in vitro with rat bone mesenchymal stem cells (rBMSCs) and in vivo using a rat critical-sized calvarial defect model. PEMs loaded with growth factors further stimulated the proliferation and osteogenic differentiation of rBMSCs and the histology results indicated that new bone tissues could directly grow onto the PEMs. These findings suggest that PEM composite coating possesses significant potential for surface modification and long-term drug release of metallic implants to assist with bone restoration.

Endogenous Mechanisms of Craniomaxillofacial Repair: Toward Novel Regenerative Therapies

In the fields of oral and craniomaxillofacial surgery, regeneration of multiple tissue types-including bone, skin, teeth, and mucosal soft tissue-is often a desired outcome. However, limited endogenous capacity for regeneration, as well as predisposition of many tissues to fibrotic healing, may prevent recovery of normal form and function for patients. Recent basic science research has advanced our understanding of molecular and cellular pathways of repair in the oral/craniofacial region and how these are influenced by local microenvironment and embryonic origin. Here, we review the current state of knowledge in oral and craniomaxillofacial tissue repair/regeneration in four key areas: bone (in the context of calvarial defects and mandibular regeneration during distraction osteogenesis); skin (in the context of cleft lip/palate surgery); oral mucosa (in the context of minimally scarring repair of mucosal injuries); and teeth (in the context of dental disease/decay). These represent four distinct healing processes and outcomes. We will discuss both divergent and conserved pathways of repair in these contexts, with an eye toward fundamental mechanisms of regeneration vs. fibrosis as well as translational research directions. Ultimately, this knowledge can be leveraged to develop new cell-based and molecular treatment strategies to encourage bone and soft tissue regeneration in oral and craniomaxillofacial surgery.

The Potential of FGF-2 in Craniofacial Bone Tissue Engineering: A Review

Bone is a hard-vascularized tissue, which renews itself continuously to adapt to the mechanical and metabolic demands of the body. The craniofacial area is prone to trauma and pathologies that often result in large bone damage, these leading to both aesthetic and functional complications for patients. The "gold standard" for treating these large defects is autologous bone grafting, which has some drawbacks including the requirement for a second surgical site with quantity of bone limitations, pain and other surgical complications. Indeed, tissue engineering combining a biomaterial with the appropriate cells and molecules of interest would allow a new therapeutic approach to treat large bone defects while avoiding complications associated with a second surgical site. This review first outlines the current knowledge of bone remodeling and the different signaling pathways involved seeking to improve our understanding of the roles of each to be able to stimulate or inhibit them. Secondly, it highlights the interesting characteristics of one growth factor in particular, FGF-2, and its role in bone homeostasis, before then analyzing its potential usefulness in craniofacial bone tissue engineering because of its proliferative, pro-angiogenic and pro-osteogenic effects depending on its spatial-temporal use, dose and mode of administration.

Collagen Type I Biomaterials as Scaffolds for Bone Tissue Engineering

Collagen type I is the main organic constituent of the bone extracellular matrix and has been used for decades as scaffolding material in bone tissue engineering approaches when autografts are not feasible. Polymeric collagen can be easily isolated from various animal sources and can be processed in a great number of ways to manufacture biomaterials in the form of sponges, particles, or hydrogels, among others, for different applications. Despite its great biocompatibility and osteoconductivity, collagen type I also has some drawbacks, such as its high biodegradability, low mechanical strength, and lack of osteoinductive activity. Therefore, many attempts have been made to improve the collagen type I-based implants for bone tissue engineering. This review aims to summarize the current status of collagen type I as a biomaterial for bone tissue engineering, as well as to highlight some of the main efforts that have been made recently towards designing and producing collagen implants to improve bone regeneration.

Biological Characteristics and Osteogenic Differentiation of Ovine Bone Marrow Derived Mesenchymal Stem Cells Stimulated with FGF-2 and BMP-2

Cell-based therapies using mesenchymal stem cells (MSCs) are a promising tool in bone tissue engineering. Bone regeneration with MSCs involves a series of molecular processes leading to the activation of the osteoinductive cascade supported by bioactive factors, including fibroblast growth factor-2 (FGF-2) and bone morphogenetic protein-2 (BMP-2). In this study, we examined the biological characteristics and osteogenic differentiation potential of sheep bone marrow MSCs (BM-MSCs) treated with 20 ng/mL of FGF-2 and 100 ng/mL BMP-2 in vitro. The biological properties of osteogenic-induced BM-MSCs were investigated by assessing their morphology, proliferation, phenotype, and cytokine secretory profile. The osteogenic differentiation was characterized by Alizarin Red S staining, immunofluorescent staining of osteocalcin and collagen type I, and expression levels of genetic markers of osteogenesis. The results demonstrated that BM-MSCs treated with FGF-2 and BMP-2 maintained their primary MSC properties and improved their osteogenic differentiation capacity, as confirmed by increased expression of osteocalcin and collagen type I and upregulation of osteogenic-related gene markers BMP-2, Runx2, osterix, collagen type I, osteocalcin, and osteopontin. Furthermore, sheep BM-MSCs produced a variety of bioactive factors involved in osteogenesis, and supplementation of the culture medium with FGF-2 and BMP-2 affected the secretome profile of the cells. The results suggest that sheep osteogenic-induced BM-MSCs may be used as a cellular therapy to study bone repair in the preclinical large animal model.

Nonviral Gene Delivery Embedded in Biomimetically Mineralized Matrices for Bone Tissue Engineering

Research in bone tissue engineering aims to design materials that are effective at generating bone without causing significant side effects. The osteogenic potential of combining matrices and protein growth factors has been well documented, however, improvements are necessary to achieve optimal therapeutic benefits upon clinical translation. In this article, rat calvarial defects were treated with gene-activated matrices (GAMs). The GAMs used were collagen sponges mineralized with a simulated body fluid (SBF) containing a nonviral gene delivery system. Both in vitro and in vivo studies were performed to determine the optimal mode of gene delivery. After 6 weeks, the defects were extracted to assess bone formation and tissue quality through histological and microcomputed tomography analyses. The optimal GAM consisted of a collagen sponge with polyethylenimine plasmid DNA (PEI-pDNA) complexes embedded in a calcium phosphate coating produced by SBF, which increased total bone formation by 39% compared with 19% for control samples. A follow-up in vivo study was performed to optimize the ratio of growth factors included in the GAM. The optimal ratio for supporting bone formation after 6 weeks of implantation was five parts of pBMP-2 to three parts pFGF-2. These studies demonstrated that collagen matrices biomimetically mineralized and activated with plasmids encoding fibroblast growth factor-2 (FGF-2) and bone morphogenetic protein-2 (BMP-2) can optimally improve bone regeneration outcomes. Impact statement Bone tissue engineering has explored both nonviral gene delivery and the concept of biomimetic mineralization. In this study, we combined these two concepts to further enhance bone regeneration outcomes. We demonstrated that embedding polyethylenimine (PEI)-based gene delivery within a mineral layer formed from simulated body fluid (SBF) immersion can increase bone formation rates. We also demonstrated that the ratio of growth factors utilized for matrix fabrication can impact the amount of bone formed in the defect site. This research highlights a combined approach using SBF and nonviral gene delivery both in vitro and in vivo and prepares the way for future optimization of synthetic gene activated matrices.

Human salivary histatin-1 (Hst1) promotes bone morphogenetic protein 2 (BMP2)-induced osteogenesis and angiogenesis

Large‐volume bone defects can result from congenital malformation, trauma, infection, inflammation and cancer. At present, it remains challenging to treat these bone defects with clinically available interventions. Allografts, xenografts and most synthetic materials have no intrinsic osteoinductivity, and so an alternative approach is to functionalize the biomaterial with osteoinductive agents, such as bone morphogenetic protein 2 (BMP2). Because it has been previously demonstrated that human salivary histatin‐1 (Hst1) promotes endothelial cell adhesion, migration and angiogenesis, we examine here whether Hst1 can promote BMP2‐induced bone regeneration. Rats were given subcutaneous implants of absorbable collagen sponge membranes seeded with 0, 50, 200 or 500 μg Hst1 per sample and 0 or 2 μg BMP2 per sample. At 18 days postsurgery, rats were sacrificed, and implanted regional tissue was removed for micro computed tomography (microCT) analyses of new bone (bone volume, trabecular number and trabecular separation). Four samples per group were decalcified and subjected to immunohistochemical staining to analyze osteogenic and angiogenic markers. We observed that Hst1 increased BMP2‐induced new bone formation in a dose‐dependent manner. Co‐administration of 500 μg Hst1 and BMP2 resulted in the highest observed bone volume and trabecular number, the lowest trabecular separation and the highest expression of osteogenic markers and angiogenic markers. Our results suggest that coadministration of Hst1 may enhance BMP2‐induced osteogenesis and angiogenesis, and thus may have potential for development into a treatment for large‐volume bone defects.

Smart Hydrogels for the Augmentation of Bone Regeneration by Endogenous Mesenchymal Progenitor Cell Recruitment

The treatment of bone defects with recombinant bone morphogenetic protein-2 (BMP-2) requires high doses precluding broad clinical application. Here, a bioengineering approach is presented that strongly improves low-dose BMP-2-based bone regeneration by mobilizing healing-associated mesenchymal progenitor cells (MPCs). Smart synthetic hydrogels are used to trap and study endogenous MPCs trafficking to bone defects. Hydrogel-trapped and prospectively isolated MPCs differentiate into multiple lineages in vitro and form bone in vivo. In vitro screenings reveal that platelet-derived growth factor BB (PDGF-BB) strongly recruits prospective MPCs making it a promising candidate for the engineering of hydrogels that enrich endogenous MPCs in vivo. However, PDGF-BB inhibits BMP-2-mediated osteogenesis both in vitro and in vivo. In contrast, smart two-way dynamic release hydrogels with fast-release of PDGF-BB and sustained delivery of BMP-2 beneficially promote the healing of bone defects. Collectively, it is shown that modulating the dynamics of endogenous progenitor cells in vivo by smart synthetic hydrogels significantly improves bone healing and holds great potential for other advanced applications in regenerative medicine.

The Significance and Utilisation of Biomimetic and Bioinspired Strategies in the Field of Biomedical Material Engineering: The Case of Calcium Phosphat-Protein Template Constructs

This review provides a summary of recent research on biomimetic and bioinspired strategies applied in the field of biomedical material engineering and focusing particularly on calcium phosphate-protein template constructs inspired by biomineralisation. A description of and discussion on the biomineralisation process is followed by a general summary of the application of the biomimetic and bioinspired strategies in the fields of biomedical material engineering and regenerative medicine. Particular attention is devoted to the description of individual peptides and proteins that serve as templates for the biomimetic mineralisation of calcium phosphate. Moreover, the review also presents a description of smart devices including delivery systems and constructs with specific functions. The paper concludes with a summary of and discussion on potential future developments in this field.

Potential therapeutic use of relaxin in accelerating closure of cranial bone defects in mice

Bone fractures are associated with considerable morbidity and increased mortality. A major limitation to healing is lack of bone blood flow, which is impaired by physical disruption of intraskeletal and/or periosteal vasculature by the fracture. Thus, pharmacological interventions are needed to improve osseous blood flow, thereby accelerating bone fracture closure. Relaxin is secreted by the ovary and circulates in rodents and humans during pregnancy. Because relaxin might benefit bone fracture healing by stimulating angiogenesis, vasculogenesis (and potentially osteogenesis) through mobilization and activation of bone marrow progenitor cells, and by increasing blood flow via vasodilation, we investigated whether relaxin administration would accelerate closure of a calvarial defect in mice. Whether administered systemically by osmotic pump or locally by collagen scaffolds for ~2 week period after lesioning, relaxin did not accelerate bone healing. Despite implementing relaxin doses that reached plasma concentrations spanning the physiological to supraphysiological range, testing the closure of two different sizes of calvarial lesions, allowing for different intervals of time from instigation of cranial lesion to euthanasia, and investigating mice of different ages, we did not observe a significant benefit of relaxin in bone lesion healing. Nor did we observe stimulation of blood vessel formation in the bone lesion by the hormone. An incidental finding was that relaxin appeared to enhance trabecular bone growth in an uninjured control bone (femur). Although the results of this study were not supportive of a therapeutic benefit for relaxin on calvarial defect closure, future investigation is needed employing different animal species and experimental models of bone fracture.

Interleukin-10 Does Not Augment Osseous Regeneration in the Scarred Calvarial Defect Achieved with Low-Dose Biopatterned BMP2

BACKGROUND

Large calvarial defects represent a major reconstructive challenge, as they do not heal spontaneously. Infection causes inflammation and scarring, further reducing the healing capacity of the calvaria. Bone morphogenetic protein-2 (BMP2) has been shown to stimulate osteogenesis but has significant side effects in high doses. BMP2 has not been tested in combination with antiinflammatory cytokines such as interleukin-10.

METHODS

Sixteen New Zealand White rabbits underwent 15 × 15-mm flap calvarectomies. The flap was incubated in Staphylococcus aureus and replaced, and infection and scarring were allowed to develop. The flap was subsequently removed and the wound débrided. A 15 × 15-mm square of acellular dermal matrix biopatterned with low-dose BMP2, interleukin-10, or a combination was implanted. Computed tomographic scans were taken over 42 days. Rabbits were then killed and histology was performed.

RESULTS

Defects treated with BMP2 showed significantly (p < 0.05) greater osseous regeneration than untreated controls. Interleukin-10 did not significantly augment the healing achieved with BMP2, and interleukin-10 alone did not significantly increase healing compared with controls. Histology showed evidence of bone formation in defects treated with BMP2. Untreated controls and defects treated with interleukin-10 alone showed only fibrous tissue in the defect site.

CONCLUSIONS

Low-dose BMP2 delivered directly to the scarred calvarial defect augments bony healing. Interleukin-10 at the dose applied did not significantly augment healing alone or in combination with BMP2. Healing had not finished at 42 days and analysis at later time points or the use of higher doses of BMP2 may yield greater healing.

Reconstruction of a Calvarial Wound Complicated by Infection: Comparing the Effects of Biopatterned Bone Morphogenetic Protein 2 and Vascular Endothelial Growth Factor

Bone morphogenetic protein 2 (BMP2) bioprinted on biological matrix induces osseous regeneration in large calvarial defects in rabbits, both uncomplicated and scarred. Healing in unfavorable defects scarred from previous infection is decreased due in part to the lack of vascularity. This impedes the access of mesenchymal stem cells, key to osseous regeneration and the efficacy of BMP2, to the wound bed. The authors hypothesized that bioprinted vascular endothelial growth factor (VEGF) would augment the osseous regeneration achieved with low dose biopatterned BMP2 alone. Thirteen New Zealand white rabbits underwent subtotal calvariectomy using a dental cutting burr. Care was taken to preserve the underlying dura. A 15 mm × 15 mm flap of bone was cut away and incubated in a 1 × 108 cfu/mL planktonic solution of S aureus before reimplantation. After 2 weeks of subsequent infection the flap was removed and the surgical wound debrided followed by 10 days of antibiotic treatment. On postoperative day 42 the calvarial defects were treated with acellular dermal matrix bioprinted with nothing (control), VEGF, BMP2, BMP2/VEGF combined. Bone growth was analyzed with serial CT and postmortem histology. Defects treated with BMP2 (BMP2 alone and BMP2/VEGF combination) showed significantly greater healing than control and VEGF treated defect (P < 0.5). Vascular endothelial growth factor treated defect demonstrated less healing than control and VEGF/BMP2 combination treatments achieved less healing than BMP2 alone though these differences were nonsignificant. Low dose BMP2-patterned acellular dermal matrix improves healing of scarred calvarial defects. Vascular endothelial growth factor at the doses applied in this study failed to increase healing.

Tuning the bioactivity of bone morphogenetic protein-2 with surface immobilization strategies

Bone morphogenetic protein-2 (BMP-2) involved therapy is of great potential for bone regeneration. However, its clinical application is restricted due to the undesirable bioactivity and relevant complications in vivo. Immobilization of recombinant BMP-2 (rhBMP-2) is an efficient strategy to mimic natural microenvironment and retain its bioactivity. Herein, we present evidences indicating that osteoinductive capacity of rhBMP-2 can be regulated via variant immobilizing approaches. Three representative superficial immobilizing models were employed to fabricate rhBMP-2-immobilized surfaces including physical adsorption (Au/rhBMP-2), covalent grafting (rhBMP-2-SAM-Au) and heparin binding (Hep-SAM-Au/rhBMP-2) (SAM: self-assembled monolayer). Loading capacity, releasing behavior, osteogenic differentiation and signaling pathways involved, as well as the cellular recognition of rhBMP-2 under various immobilization modes were systematically investigated. As a result, disparate immobilizing approaches not only have effects on loading capacity, but also lead to disparity of osteoinduction at the same dosage. Notably, heparin could reinforce the recognition between rhBMP-2 and its receptors (BMPRs) whereas weaken its binding to its antagonist Noggin. Owing to this "selective" binding feature, the favorable osteoinduction and maximum ectopic bone formation can be achieved with the heparin-binding approach. In particular, manipulation of orientation-mediated BMP-2-cell recognition efficiency may be a potential target to design more therapeutic efficient rhBMP-2 delivery system. STATEMENT OF SIGNIFICANCE: Bone morphogenetic protein-2 (BMP-2) is crucial in bone regeneration. However, its clinical application is challenged due to its shorten half-life and supra-physiological dose associated complications. In this study, three representative superficial immobilizing patterns were fabricated through physical adsorption, covalent grafting and electrostatic interaction with heparin respectively. We provided evidences indicating an dose-dependent osteoinductive capacity of immobilized BMP-2. Further, a possible mechanism of rhBMP-2-cell recognition at the interface was presented, highlighting the superior effect of heparin on rhBMP-2 bioactivity. Finally, We proposed a dual mechanism of tuning the bioactivity of immobilized rhBMP-2 through surface immobilization approaches: regulation of the saturated loading capacity and orientation-mediated rhBMP-2-cell recognition. These results provide novel insights into designing criterion of efficient delivery vehicle for rhBMP-2.

Dual release of growth factor from nanocomposite fibrous scaffold promotes vascularisation and bone regeneration in rat critical sized calvarial defect

A promising strategy for augmenting bone formation involves the local delivery of multiple osteoinductive and vasculogenic growth factors. However, success depends on sustained growth factor release and its appropriate combination to induce stem cells and osteogenic cells at the bony site. Herein, we have developed a nanocomposite fibrous scaffold loaded with fibroblast growth factor 2 (FGF2), vascular endothelial growth factor (VEGF) and bone morphogenetic protein 2 (BMP2) and its ability to promote vascularisation and bone regeneration in critical sized calvarial defect was compared to the scaffold with VEGF + BMP2 and FGF2 + BMP2. Simple loading of growth factors on the scaffold could provide a differential release pattern, both in vitro and in vivo (VEGF release for 1 week where as BMP2 and FGF2 release for 3 weeks). Among all the groups, dual growth factor loaded scaffold (VEGF + BMP2 & FGF2 + BMP2) enhanced vascularisation and new bone formation, but there was no difference between FGF2 and VEGF loaded scaffolds although its release pattern was different. FGF2 mainly promoted stem cell migration, whereas VEGF augmented new blood vessel formation at the defect site. This study suggests that biomimetic nanocomposite scaffold is a promising growth factor delivery vehicle to improve bone regeneration in critical sized bone defects.

STATEMENT OF SIGNIFICANCE

Many studies have shown the effect of growth factors like VEGF-BMP2 or FGF2-BMP2 in enhancing bone formation in critical sized defects, but there are no reports that demonstrate the direct comparison of VEGF-BMP2 and FGF2-BMP2. In this study, we have developed a nanocomposite fibrous scaffold that could differentially release growth factors like VEGF, BMP2 and FGF2 (VEGF release for 1 week where as BMP2 and FGF2 release for 3 weeks), which in turn promoted neovascularisation and new bone formation in critical sized defects. There was no difference in vascularisation and bone formation induced by VEGF + BMP2 or FGF2 + BMP2. The growth factor was loaded in a simple manner, which would ensure ease of use for the end-user, especially for the surgeons treating a patient in an operating room.

Combined delivery of bone morphogenetic protein-2 and insulin-like growth factor-1 from nano-poly (γ-glutamic acid)/β-tricalcium phosphate-based calcium phosphate cement and its effect on bone regeneration in vitro

In this study, nano-doped calcium phosphate cement delivery systems (poly (γ-glutamic acid)/β-tricalcium phosphate/calcium phosphate ceramics and nano (γ-glutamic acid)/β-tricalcium phosphate/calcium phosphate ceramic) were fabricated, and low doses (10 µg/g) of two growth factors, insulin-like growth factor-1 and bone morphogenetic protein-2, were encapsulated then sequentially released. We characterized the delivery systems using Fourier transform infrared spectroscopy and X-ray diffraction and measured washout resistance and compressive strength, and thus optimized the most appropriate proportioning of delivery systems for the two growth factors. One of the growth factors was absorbed by the nano-poly (γ-glutamic acid)/β-tricalcium phosphate, which was then mixed into the calcium phosphate ceramic solid phase to create a new solid phase calcium phosphate ceramic. Nano-poly (γ-glutamic acid)/β-tricalcium phosphate/calcium phosphate ceramic carriers were then prepared by blending the new calcium phosphate ceramic solid phase powder with a solution of the remaining growth factor. The effects of different release patterns (studying sequential behavior) of insulin-like growth factor-1 and bone morphogenetic protein-2 on osteogenic proliferation and differentiation of the MC3t3-E1 mouse osteoblast cell were investigated. This combinational delivery system provided a controlled release of the two growth factors, in which nano-doping significantly affected their release kinetics. The incorporation of dual growth factors could potentially stimulate bone healing and promoting bone ingrowth processes at a low dose.

Fibroblast Growth Factor 2 and Its Receptors in Bone Biology and Disease

The fibroblast growth factor (FGF) regulatory axis is phylogenetically ancient, evolving into a large mammalian/human gene family of 22 ligands that bind to four receptor tyrosine kinases for a complex physiologic system controlling cell growth, differentiation, and metabolism. The tissue targets for the primary FGF function are mainly in cartilage and in bone for morphogenesis, mineralization, and metabolism. A multitude of complexities in the FGF ligand-receptor signaling pathways have made translation into therapies for FGF-related bone disorders such as osteomalacia, osteoarthritis, and osteoporosis difficult but not impossible.

miR-450b Promotes Osteogenic Differentiation In Vitro and Enhances Bone Formation In Vivo by Targeting BMP3

Osteoporosis is characterized by deterioration of bone microarchitecture and low bone mass. One of the primary causes of osteoporosis is the decrease in the osteogenic differentiation of mesenchymal stem cells (MSCs). Tissue engineering therapy with genetically modified MSCs has attracted much attention in the study of bone regeneration. In this study, we found that the expression level of miR-450b was upregulated during osteogenic differentiation of human adipose-derived mesenchymal stem cells (hADSCs). To explore the effect of miR-450b on the osteogenesis of hADSCs, we performed a series of gain- and loss-of-function analyses and demonstrated that miR-450b not only promoted the process of hADSC differentiation to osteoblasts in vitro but also enhanced ectopic bone formation in vivo. Bone morphogenetic protein 3 (BMP3), the most abundant BMP member in bone, was identified as a direct target of miR-450b. Downregulation of the endogenous expression of BMP3 could mimic the effect of miR-450b upregulation on the osteogenic differentiation of hADSCs. Overall, our study first demonstrated that a novel microRNA miR-450b was essential for hADSC differentiation, which could promote osteogenic differentiation in vitro and enhance bone formation in vivo by directly suppressing BMP3.

Targeted delivery of FGF2 to subchondral bone enhanced the repair of articular cartilage defect

It is reported that growth factor (GF) is able to enhance the repair of articular cartilage (AC) defect, however underlying mechanisms of which are not fully elucidated yet. Moreover, the strategy for delivering GF needs to be optimized. The crosstalk between AC and subchondral bone (SB) play important role in the homeostasis and integrity of AC, therefore SB targeted delivery of GF represents one promising way to facilitate the repair of AC defect. In this study, we firstly investigated the effects and mechanism of FGF2 on surrounding SB and cartilage of detect defects in rabbits by using a homogenous collagen-based membranes. It was found that FGF2 had a modulating effect on the defect-surrounding SB via upregulation of bone morphogenetic protein (BMP)-2, BMP4 and SOX9 at the early stage. Low dose FGF2 improved the repair upon directly injected to SB. Inhibition of BMP signaling pathway compromised the beneficial effects of FGF2, which indicated the pivotal roles of BMP in the process. To facilitate SB targeted FGF2 delivery, a double-layered inhomogeneous collagen membrane was prepared and it induced increase of BMP2 and BMP4 in the synovial fluid, and subsequent successful repair of AC defect. Taken together, this targeted delivery of FGF2 to SB provides a promising strategy for AC repair owing to the relatively clear mechanism, less amount of it, and short duration of delivery.

STATEMENT OF SIGNIFICANCE

Articular cartilage (AC) and subchondral bone (SB) form an integral functional unit. The homeostasis and integrity of AC depend on its crosstalk with the SB. However, the function of the SB in AC defect repair is not completely understood. The application of growth factors to promote the repair articular cartilage defect is a promising strategy, but still under the optimization. Our study demonstrate that SB plays important roles in the repair of AC defect. Particularly, SB is the effective target of fibroblast growth factor 2 (FGF2), and targeted delivery of FGF2 can modulate SB and thus significantly enhances the repair of AC defect. Therefore, targeted delivery of growth factor to SB is a novel promising strategy to improve the repair of AC defect.

Functionalization of PCL-3D Electrospun Nanofibrous Scaffolds for Improved BMP2-Induced Bone Formation

Bone morphogenic protein 2 (BMP2) is a key growth factor for bone regeneration, possessing FDA approval for orthopedic applications. BMP2 is often required in supratherapeutic doses clinically, yielding adverse side effects and substantial treatment costs. Considering the crucial role of materials for BMPs delivery and cell osteogenic differentiation, we devote to engineering an innovative bone-matrix mimicking niche to improve low dose of BMP2-induced bone formation. Our previous work describes a novel technique, named thermally induced nanofiber self-agglomeration (TISA), for generating 3D electrospun nanofibrous (NF) polycaprolactone (PCL) scaffolds. TISA process could readily blend PCL with PLA, leading to increased osteogenic capabilities in vitro, however, these bio-inert synthetic polymers produced limited BMP2-induced bone formation in vivo. We therefore hypothesize that functionalization of NF 3D PCL scaffolds with bone-like hydroxyapatite (HA) and BMP2 signaling activator phenamil will provide a favorable osteogenic niche for bone formation at low doses of BMP2. Compared to PCL-3D scaffolds, PCL/HA-3D scaffolds demonstrated synergistically enhanced osteogenic differentiation capabilities of C2C12 cells with phenamil. Importantly, in vivo studies showed this synergism was able to generate significantly increased new bone in an ectopic mouse model, suggesting PCL/HA-3D scaffolds act as a favorable synthetic extracellular matrix for bone regeneration.

Comparison of primary human gingival fibroblasts from an older and a young donor on the evaluation of cytotoxicity of denture adhesives

Denture adhesives (DA) improve the retention and stability of ill-fitting dentures, especially for older adults. These materials should be biocompatible, i.e., they cannot cause undesired biological responses and be non-cytotoxic to oral tissues. However, in vitro testing of DA biocompatibility employing primary cell culture may possibly be affected by other factors, such as the donor age.

* Calvarial Bone Regeneration Is Enhanced by Sequential Delivery of FGF-2 and BMP-2 from Layer-by-Layer Coatings with a Biomimetic Calcium Phosphate Barrier Layer

A drug delivery coating for synthetic bone grafts has been developed to provide sequential delivery of multiple osteoinductive factors to better mimic aspects of the natural regenerative process. The coating is composed of a biomimetic calcium phosphate (bCaP) layer that is applied to a synthetic bone graft and then covered with a poly-l-Lysine/poly-l-Glutamic acid polyelectrolyte multilayer (PEM) film. Bone morphogenetic protein-2 (BMP-2) was applied before the coating process directly on the synthetic bone graft and then, bCaP-PEM was deposited followed by adsorption of fibroblast growth factor-2 (FGF-2) into the PEM layer. Cells access the FGF-2 immediately, while the bCaP-PEM temporally delays the cell access to BMP-2. In vitro studies with cells derived from mouse calvarial bones demonstrated that Sca-1 and CD-166 positive osteoblast progenitor cells proliferated in response to media dosing with FGF-2. Coated scaffolds with BMP-2 and FGF-2 were implanted in mouse calvarial bone defects and harvested at 1 and 3 weeks. After 1 week in vivo, proliferation of cells, including Sca-1+ progenitors, was observed with low dose FGF-2 and BMP-2 compared to BMP-2 alone, indicating that in vivo delivery of FGF-2 activated a similar population of cells as shown by in vitro testing. At 3 weeks, FGF-2 and BMP-2 delivery increased bone formation more than BMP-2 alone, particularly in the center of the defect, confirming that the proliferation of the Sca-1 positive osteoprogenitors by FGF-2 was associated with increased bone healing. Areas of bone mineralization were positive for double fluorochrome labeling of calcium and alkaline phosphatase staining of osteoblasts, along with increased TRAP+ osteoclasts, demonstrating active bone formation distinct from the bone-like collagen/hydroxyapatite scaffold. In conclusion, the addition of a bCaP layer to PEM delayed access to BMP-2 and allowed the FGF-2 stimulated progenitors to populate the scaffold before differentiating in response to BMP-2, leading to improved bone defect healing.

* Calvarial Defects: Cell-Based Reconstructive Strategies in the Murine Model

Calvarial defects pose a continued clinical dilemma for reconstruction. Advancements within the fields of stem cell biology and tissue engineering have enabled researchers to develop reconstructive strategies using animal models. We review the utility of various animal models and focus on the mouse, which has aided investigators in understanding cranial development and calvarial bone healing. The murine model has also been used to study regenerative approaches to critical-sized calvarial defects, and we discuss the application of stem cells such as bone marrow-derived mesenchymal stromal cells, adipose-derived stromal cells, muscle-derived stem cells, and pluripotent stem cells to address deficient bone in this animal. Finally, we highlight strategies to manipulate stem cells using various growth factors and inhibitors and ultimately how these factors may prove crucial in future advancements within calvarial reconstruction using native skeletal stem cells.

Synergistic effects of fibroblast growth factor-2 and bone morphogenetic protein-2 on bone induction

The present study investigated the synergistic effect of co-administering fibroblast growth factor-2 (FGF-2) and bone morphogenetic protein-2 (BMP-2) on osteoblastic differentiation in C2C12 cells and in rats. C2C12 murine myoblast cells represent a well-accepted in vitro model system to study the ability of BMP-2 to alter cell lineage from the myogenic to the osteogenic phenotype. The osteoblastic differentiation potency was determined by alkaline phosphatase (ALP) and Alizarin red S staining. ALP activity and calcium concentrations were colorimetrically measured. Simultaneous administration of 4 µg/ml recombinant human BMP-2 with 2 ng/ml FGF-2 markedly enhanced ALP activity (an early marker of osteogenesis) of C2C12 cells. This combination also increased extracellular signal-regulated kinase1/2 mitogen activated protein kinase signaling that is involved in the promoting effect of FGF-2 on BMP-2-induced osteoblastic differentiation in C2C12 cells. Calcium deposition (a late marker of osteogenesis) and the expression of CD34 (a marker of new vessels) were promoted optimally by simultaneous local sustained administration of FGF-2 and BMP-2 using collagen and chitosan-coated antigen-extracted porcine cancellous implants in a rat ectopic implantation model. The synergistic effects of a combination of BMP-2 and FGF-2 may have potential for bone regenerative therapeutics.

Role of fibroblast growth factors in bone regeneration

Bone is a metabolically active organ that undergoes continuous remodeling throughout life. However, many complex skeletal defects such as large traumatic bone defects or extensive bone loss after tumor resection may cause failure of bone healing. Effective therapies for these conditions typically employ combinations of cells, scaffolds, and bioactive factors. In this review, we pay attention to one of the three factors required for regeneration of bone, bioactive factors, especially the fibroblast growth factor (FGF) family. This family is composed of 22 members and associated with various biological functions including skeletal formation. Based on the phenotypes of genetically modified mice and spatio-temporal expression levels during bone fracture healing, FGF2, FGF9, and FGF18 are regarded as possible candidates useful for bone regeneration. The role of these candidate FGFs in bone regeneration is also discussed in this review.

Insulin-like growth factor-1 (IGF-1) enhances the osteogenic activity of bone morphogenetic protein-6 (BMP-6) in vitro and in vivo, and together have a stronger osteogenic effect than when IGF-1 is combined with BMP-2

Bone morphogenetic protein-2 (BMP-2) is widely used in orthopedic surgery and bone tissue engineering because of its strong osteogenic activity. However, BMP-2 treatments have several drawbacks and many groups are actively exploring alternatives. Since BMP-6 has been demonstrated to be more osteoinductive, its use, either alone or together with other growth factors, might be an interesting option. In this work, we have compared the effect of BMP-2, BMP-6, or insulin-like growth factor-1 (IGF-1), either alone or in combination. Murine preosteoblasts were treated with 15 nM IGF-1 and/or 6 nM BMP-2 or -6 and the expression of osteogenic marker genes, proliferation, and alkaline phosphatase (ALP) activity in vitro were analyzed. The results showed that IGF-1 greatly enhanced the BMP-induced osteogenic differentiation of these cells in general and that the ALP activity in the cultures was higher when the combination was made with BMP-6 than with BMP-2. Furthermore, we tested the osteogenic potential of these treatments in vivo by loading 25 pmoles of IGF-1 and/or 10 pmoles of BMP-2 or -6 onto absorbable collagen sponges and implanting them into an ectopic bone formation model in rats. This study revealed that only BMP-6 was able to induce bone formation at the used dose and that the addition of IGF-1 contributed to an increase of the mineralization in the implants. Hence, the combination of BMP-6 with IGF-1 might be a better alternative than BMP-2 for orthopedic surgery or bone tissue engineering approaches. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1867-1875, 2017.

Biomimetic calcium phosphate/polyelectrolyte multilayer coatings for sequential delivery of multiple biological factors

Combinations of growth factors synergistically enhance tissue regeneration, but typically require sequential, rather than co-delivery from biomaterials for maximum efficacy. Polyelectrolyte multilayer (PEM) coatings can deliver multiple factors without loss of activity; however, sequential delivery from PEM has been limited due to interlayer diffusion that results in co-delivery of the factors. This study shows that addition of a biomimetic calcium phosphate (bCaP) barrier layer to a PEM coating effectively prevents interlayer diffusion and enables sequential delivery of two different biomolecules via direct cell access. A simulated body fluid method was used to deposit a layer of bCaP followed by 30 bilayers of PEM made with poly-l-Lysine (+) and poly l-Glutamic acid (-) (bCaP-PEM). Measurements of MC3T3-E1 proliferation and viability over time on bCaP-PEM were used to demonstrate the sequential delivery kinetics of a proliferative factor [fibroblast growth factor-2 (FGF-2)] followed by a cytotoxic factor (antimycin A, AntiA). FGF-2 and AntiA both retained their bioactivity within bCaP-PEM, yet no release of FGF-2 or AntiA from bCaP-PEM was observed when cells were absent indicating a cell-mediated, local delivery process. This coating technique is useful for a variety of applications that would benefit from highly localized, sequential delivery of multiple biomolecules governed by cell initiated degradation that avoids off-target effects associated with diffusion-based release. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1500-1509, 2017.

A Novel Regenerative Technique Combining Bone Morphogenetic Protein-2 With Fibroblast Growth Factor-2 for Circumferential Defects in Dog Incisors

BACKGROUND

Periodontal regeneration of incisors is necessary for esthetic recovery. A novel regenerative method combining bone morphogenetic protein (BMP)-2 and fibroblast growth factor (FGF)-2 was developed. The purpose of this study is to evaluate periodontal healing, including root coverage, in circumferential defects of incisors.

METHODS

Fifty incisors in five beagles were used. After circumferential defects were surgically created, each group, consisting of ten recipient sites, received: 1) a double layer with FGF-2 (2 μg)/collagen as inner layer and BMP-2 (4 μg)/collagen as outer layer (FB-DL group); 2) collagen impregnated with both FGF-2 (2 μg) and BMP-2 (4 μg) (FB-M group); 3) BMP-2 (4 μg)/collagen (B group); 4) FGF-2 (4 μg)/collagen (F group); or 5) collagen (C group). Dogs were sacrificed 8 weeks post-surgery, and healing was evaluated histologically.

RESULTS

The three groups treated with BMP-2 showed enhanced new bone formation compared with control and F groups (P < 0.05). Furthermore, connective tissue attachment with cementum regeneration in the FB-DL group was significantly greater than in FB-M and B groups (P <0.05). Ankylosis in the FB-DL group was significantly less than in FB-M and B groups (P <0.05). Gingival recession was inhibited significantly better in FB-DL and FB-M groups compared with control and B groups.

CONCLUSION

These data support development of a double-layer method combining BMP-2 and FGF-2 as a therapeutic approach to periodontal regeneration at incisors with horizontal circumferential defects.