Evaluation of angiogenesis and osteogenesis

Convergence of scaffold-guided bone regeneration principles and microvascular tissue transfer surgery

A preclinical evaluation using a regenerative medicine methodology comprising an additively manufactured medical-grade ε-polycaprolactone β-tricalcium phosphate (mPCL-TCP) scaffold with a corticoperiosteal flap was undertaken in eight sheep with a tibial critical-size segmental bone defect (9.5 cm³, M size) using the regenerative matching axial vascularization (RMAV) approach. Biomechanical, radiological, histological, and immunohistochemical analysis confirmed functional bone regeneration comparable to a clinical gold standard control (autologous bone graft) and was superior to a scaffold control group (mPCL-TCP only). Affirmative bone regeneration results from a pilot study using an XL size defect volume (19 cm³) subsequently supported clinical translation. A 27-year-old adult male underwent reconstruction of a 36-cm near-total intercalary tibial defect secondary to osteomyelitis using the RMAV approach. Robust bone regeneration led to complete independent weight bearing within 24 months. This article demonstrates the widely advocated and seldomly accomplished concept of "bench-to-bedside" research and has weighty implications for reconstructive surgery and regenerative medicine more generally.

Protocol for the BONE-RECON trial: a single-arm feasibility trial for critical sized lower limb BONE defect RECONstruction using the mPCL-TCP scaffold system with autologous vascularised corticoperiosteal tissue transfer

INTRODUCTION

Reconstruction of critical bone defects is challenging. In a substantial subgroup of patients, conventional reconstructive techniques are insufficient. Biodegradable scaffolds have emerged as a novel tissue engineering strategy for critical-sized bone defect reconstruction. A corticoperiosteal flap integrates the hosts' ability to regenerate bone and permits the creation of a vascular axis for scaffold neo-vascularisation (regenerative matching axial vascularisation-RMAV). This phase IIa study evaluates the application of the RMAV approach alongside a custom medical-grade polycaprolactone-tricalcium phosphate (mPCL-TCP) scaffold (Osteopore) to regenerate bone sufficient to heal critical size defects in lower limb defects.

METHODS AND ANALYSIS

This open-label, single-arm feasibility trial will be jointly coordinated by the Complex Lower Limb Clinic (CLLC) at the Princess Alexandra Hospital in Woolloongabba (Queensland, Australia), the Australian Centre for Complex Integrated Surgical Solutions (Queensland, Australia) and the Faculty of Engineering, Queensland University of Technology in Kelvin Grove (Queensland, Australia). Aiming for limb salvage, the study population (n=10) includes any patient referred to the CLLC with a critical-sized bone defect not amenable to conventional reconstructive approaches, after discussion by the interdisciplinary team. All patients will receive treatment using the RMAV approach using a custom mPCL-TCP implant. The primary study endpoint will be safety and tolerability of the reconstruction. Secondary end points include time to bone union and weight-bearing status on the treated limb. Results of this trial will help shape the role of scaffold-guided bone regenerative approaches in complex lower limb reconstruction where current options remain limited.

ETHICS AND DISSEMINATION

Approval was obtained from the Human Research Ethics Committee at the participating centre. Results will be submitted for publication in a peer-reviewed journal.

TRIAL REGISTRATION NUMBER

ACTRN12620001007921.

Construction of Vascularized Tissue Engineered Bone with nHA-Coated BCP Bioceramics Loaded with Peripheral Blood-Derived MSC and EPC to Repair Large Segmental Femoral Bone Defect

The regenerative repair of segmental bone defect (SBD) is an urgent problem in the field of orthopedics. Rapid induction of angiogenesis and osteoinductivity after implantation of scaffold is critical. In this study, a unique tissue engineering strategy with mixture of peripheral blood-derived mesenchymal stem cells (PBMSC) and endothelial progenitor cells (PBEPC) was applied in a 3D-printed biphasic calcium phosphate (BCP) scaffold with highly bioactive nano hydroxyapatite (nHA) coating (nHA/BCP) to construct a novel vascularized tissue engineered bone (VTEB) for rabbit femoral SBD repair. The 2D coculture of PBMSC and PBEPC showed that they could promote the osteogenic or angiogenic differentiation of the cells from each other, especially in the group of PBEPC/PBMSC = 75:25. Besides, the 3D coculture results exhibited that the nHA coating could further promote PBEPC/PBMSC adhesion, proliferation, and osteogenic and angiogenic differentiation on the BCP scaffold. In vivo experiments showed that among the four groups (BCP, BCP-PBEPC/PBMSC, nHA/BCP, and nHA/BCP-PBEPC/PBMSC), the nHA/BCP-PBEPC/PBMSC group induced the best formation of blood vessels and new bone and, thus, the good repair of SBD. It revealed the synergistic effect of nHA and PBEPC/PBMSC on the angiogenesis and osteogenesis of the BCP scaffold. Therefore, the construction of VTEB in this study could provide a possibility for the regenerative repair of SBD.

Promoting angiogenesis and diabetic wound healing through delivery of protein transduction domain-BMP2 formulated nanoparticles with hydrogel

Decreased angiogenesis contributes to delayed wound healing in diabetic patients. Recombinant human bone morphogenetic protein-2 (rhBMP2) has also been demonstrated to promote angiogenesis. However, the short half-lives of soluble growth factors, including rhBMP2, limit their use in wound-healing applications. To address this limitation, we propose a novel delivery model using a protein transduction domain (PTD) formulated in a lipid nanoparticle (LNP). We aimed to determine whether a gelatin hydrogel dressing loaded with LNP-formulated PTD-BMP2 (LNP-PTD-BMP2) could enhance the angiogenic function of BMP2 and improve diabetic wound healing. In vitro, compared to the control and rhBMP2, LNP-PTD-BMP2 induced greater tube formation in human umbilical vein endothelial cells and increased the cell recruitment capacity of HaCaT cells. We inflicted large, full-thickness back skin wounds on streptozotocin-induced diabetic mice and applied gelatin hydrogel (GH) cross-linked by microbial transglutaminase containing rhBMP2, LNP-PTD-BMP2, or a control to these wounds. Wounds treated with LNP-PTD-BMP2-loaded GH exhibited enhanced wound closure, increased re-epithelialization rates, and higher collagen deposition than those with other treatments. Moreover, LNP-PTD-BMP2-loaded GH treatment resulted in more CD31- and α-SMA-positive cells, indicating greater neovascularization capacity than rhBMP2-loaded GH or GH treatments alone. Furthermore, in vivo near-infrared fluorescence revealed that LNP-PTD-BMP2 has a longer half-life than rhBMP2 and that BMP2 localizes around wounds. In conclusion, LNP-PTD-BMP2-loaded GH is a viable treatment option for diabetic wounds.

A Medical-Grade Polycaprolactone and Tricalcium Phosphate Scaffold System With Corticoperiosteal Tissue Transfer for the Reconstruction of Acquired Calvarial Defects in Adults: Protocol for a Single-Arm Feasibility Trial

Background

Large skull defects present a reconstructive challenge. Conventional cranioplasty options include autologous bone grafts, vascularized bone, metals, synthetic ceramics, and polymers. Autologous options are affected by resorption and residual contour deformities. Synthetic materials may be customized via digital planning and 3D printing, but they all carry a risk of implant exposure, failure, and infection, which increases when the defect is large. These complications can be a threat to life. Without reconstruction, patients with cranial defects may experience headaches and stigmatization. The protection of the brain necessitates lifelong helmet use, which is also stigmatizing.

Objective

Our clinical trial will formally study a hybridized technique's capacity to reconstruct large calvarial defects.

Methods

A hybridized technique that draws on the benefits of autologous and synthetic materials has been developed by the research team. This involves wrapping a biodegradable, ultrastructured, 3D-printed scaffold made of medical-grade polycaprolactone and tricalcium phosphate in a vascularized, autotransplanted periosteum to exploit the capacity of vascularized periostea to regenerate bone. In vitro, the scaffold system supports cell attachment, migration, and proliferation with slow but sustained degradation to permit host tissue regeneration and the replacement of the scaffold. The in vivo compatibility of this scaffold system is robust—the base material has been used clinically as a resorbable suture material for decades. The importance of scaffold vascularization, which is inextricably linked to bone regeneration, is underappreciated. A variety of methods have been described to address this, including scaffold prelamination and axial vascularization via arteriovenous loops and autotransplanted flaps. However, none of these directly promote bone regeneration.

Results

We expect to have results before the end of 2023. As of December 2020, we have enrolled 3 participants for the study.

Conclusions

The regenerative matching axial vascularization technique may be an alternative method of reconstruction for large calvarial defects. It involves performing a vascularized free tissue transfer and using a bioresorbable, 3D-printed scaffold to promote and support bone regeneration (termed the regenerative matching axial vascularization technique). This technique may be used to reconstruct skull bone defects that were previously thought to be unreconstructable, reduce the risk of implant-related complications, and achieve consistent outcomes in cranioplasty. This must now be tested in prospective clinical trials.

Trial Registration

Australian New Zealand Clinical Trials Registry ACTRN12620001171909; https://tinyurl.com/4rakccb3

International Registered Report Identifier (IRRID)

DERR1-10.2196/36111

EGFL6 regulates angiogenesis and osteogenesis in distraction osteogenesis via Wnt/β-catenin signaling

Background

Osteogenesis is tightly coupled with angiogenesis during bone repair and regeneration. However, the underlying mechanisms linking these processes remain largely undefined. The present study aimed to test the hypothesis that epidermal growth factor-like domain-containing protein 6 (EGFL6), an angiogenic factor, also functions in bone marrow mesenchymal stem cells (BMSCs), playing a key role in the interaction between osteogenesis and angiogenesis.

Methods

We evaluated how EGFL6 affects angiogenic activity of human umbilical cord vein endothelial cells (HUVECs) via proliferation, transwell migration, wound healing, and tube-formation assays. Alkaline phosphatase (ALP) and Alizarin Red S (AR-S) were used to assay the osteogenic potential of BMSCs. qRT-PCR, western blotting, and immunocytochemistry were used to evaluate angio- and osteo-specific markers and pathway-related genes and proteins. In order to determine how EGFL6 affects angiogenesis and osteogenesis in vivo, EGFL6 was injected into fracture gaps in a rat tibia distraction osteogenesis (DO) model. Radiography, histology, and histomorphometry were used to quantitatively evaluate angiogenesis and osteogenesis.

Results

EGFL6 stimulated both angiogenesis and osteogenic differentiation through Wnt/β-catenin signaling in vitro. Administration of EGFL6 in the rat DO model promoted CD31^hiEMCN^hi type H-positive capillary formation associated with enhanced bone formation. Type H vessels were the referred subtype involved during DO stimulated by EGFL6.

Conclusion

EGFL6 enhanced the osteogenic differentiation potential of BMSCs and accelerated bone regeneration by stimulating angiogenesis. Thus, increasing EGFL6 secretion appeared to underpin the therapeutic benefit by promoting angiogenesis-coupled bone formation. These results imply that boosting local concentrations of EGFL6 may represent a new strategy for the treatment of compromised fracture healing and bone defect restoration.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02487-3.

Vascularization Strategies in Bone Tissue Engineering

Bone is a highly vascularized tissue, and its development, maturation, remodeling, and regeneration are dependent on a tight regulation of blood vessel supply. This condition also has to be taken into consideration in the context of the development of artificial tissue substitutes. In classic tissue engineering, bone-forming cells such as primary osteoblasts or mesenchymal stem cells are introduced into suitable scaffolds and implanted in order to treat critical-size bone defects. However, such tissue substitutes are initially avascular. Because of the occurrence of hypoxic conditions, especially in larger tissue substitutes, this leads to the death of the implanted cells. Therefore, it is necessary to devise vascularization strategies aiming at fast and efficient vascularization of implanted artificial tissues. In this review article, we present and discuss the current vascularization strategies in bone tissue engineering. These are based on the use of angiogenic growth factors, the co-implantation of blood vessel forming cells, the ex vivo microfabrication of blood vessels by means of bioprinting, and surgical methods for creating surgically transferable composite tissues.

Comparison of Freshly Isolated Adipose Tissue-derived Stromal Vascular Fraction and Bone Marrow Cells in a Posterolateral Lumbar Spinal Fusion Model

STUDY DESIGN

Rat posterolateral lumbar fusion model.

OBJECTIVE

The aim of this study was to compare the efficacy of freshly isolated adipose tissue-derived stromal vascular fraction (A-SVF) and bone marrow cells (BMCs) cells in achieving spinal fusion in a rat model.

SUMMARY OF BACKGROUND DATA

Adipose tissue-derived stromal cells (ASCs) offer advantages as a clinical cell source compared to bone marrow-derived stromal cells (BMSCs), including larger available tissue volumes and reduced donor site morbidity. While pre-clinical studies have shown that ex vivo expanded ASCs can be successfully used in spinal fusion, the use of A-SVF cells better allows for clinical translation.

METHODS

A-SVF cells were isolated from the inguinal fat pads, whereas BMCs were isolated from the long bones of syngeneic 6- to 8-week-old Lewis rats and combined with Vitoss (Stryker) bone graft substitute for subsequent transplantation. Posterolateral spinal fusion surgery at L4-L5 was performed on 36 female Lewis rats divided into three experimental groups: Vitoss bone graft substitute only (VO group); Vitoss + 2.5 × 106 A-SVF cells/side; and, Vitoss + 2.5 × 106 BMCs/side. Fusion was assessed 8 weeks post-surgery via manual palpation, micro-computed tomography (μCT) imaging, and histology.

RESULTS

μCT imaging analyses revealed that fusion volumes and μCT fusion scores in the A-SVF group were significantly higher than in the VO group; however, they were not significantly different between the A-SVF group and the BMC group. The average manual palpation score was highest in the A-SVF group compared with the BMC and VO groups. Fusion masses arising from cell-seeded implants yielded better bone quality than nonseeded bone graft substitute.

CONCLUSION

In a rat model, A-SVF cells yielded a comparable fusion mass volume and radiographic rate of fusion to BMCs when combined with a clinical-grade bone graft substitute. These results suggest the feasibility of using freshly isolated A-SVF cells in spinal fusion procedures.Level of Evidence: N/A.

Light rare earth elements hinder bone development via inhibiting type H vessels formation in mice

Light rare earth elements (LREEs) are widely used in medical, industrial, and agricultural fields. Wide application of light rare earth and exposure to these elements in human society leads to increasing accumulation of LREE in human skeletal system. However, the effects of LREEs on human bone health is not clear. In this study, we found that LREE reduced CD31highEmcnhigh endothelial cell mediated type H vessels formation at the metaphyseal sites, resulting in reduced bone mass and low bone quality in mouse bone development. To explore the underlying mechanism, we induced bone marrow macrophages (BMMs) to preosteoclasts (pOCs) with exposure of LREE (Pr3+, Nd3+, Sm3+). The cytotoxicity of LREE was evaluated by CCK-8. Platelet-derived growth factor (PDGF-BB) is the cytokine secreted by pOCs that most responsible for inducing Type H vessel formation. We used ELISA kit to determine the PDGF-BB level in pOC supernatant, and mouse serum finding that the PDGF-BB level was reduced by LREEs treatment. Then we tested the ability of migration and tube formation of HUVECs using condition medium from pOCs. The migration and tube formation ability of HUVECs were both suppressed with LREEs pretreatment. We concluded that LREEs hinder mouse bone development by suppressing type H vessels associated bone formation. DATA AND MATERIALS AVAILABILITY: All data generated or analyzed during this study are included in this article. Please contact the corresponding author for unique material requests. Some material used in the reported research may require requests to collaborators and agreements with both commercial and non-profit institutions, as specified in the paper. Requests are reviewed by Third Military Medical University to verify whether the request is subject to any intellectual property or confidentiality obligations. Any material that can be shared will be released via a Material Transfer Agreement.

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.

Bioprinting: From Tissue and Organ Development to in Vitro Models

Bioprinting techniques have been flourishing in the field of biofabrication with pronounced and exponential developments in the past years. Novel biomaterial inks used for the formation of bioinks have been developed, allowing the manufacturing of in vitro models and implants tested preclinically with a certain degree of success. Furthermore, incredible advances in cell biology, namely, in pluripotent stem cells, have also contributed to the latest milestones where more relevant tissues or organ-like constructs with a certain degree of functionality can already be obtained. These incredible strides have been possible with a multitude of multidisciplinary teams around the world, working to make bioprinted tissues and organs more relevant and functional. Yet, there is still a long way to go until these biofabricated constructs will be able to reach the clinics. In this review, we summarize the main bioprinting activities linking them to tissue and organ development and physiology. Most bioprinting approaches focus on mimicking fully matured tissues. Future bioprinting strategies might pursue earlier developmental stages of tissues and organs. The continuous convergence of the experts in the fields of material sciences, cell biology, engineering, and many other disciplines will gradually allow us to overcome the barriers identified on the demanding path toward manufacturing and adoption of tissue and organ replacements.

Bioactive Glasses: A Promising Therapeutic Ion Release Strategy for Enhancing Wound Healing

The morbidity, mortality, and burden of burn victims and patients with severe diabetic wounds are still high, which leads to an extensively growing demand for novel treatments with high clinical efficacy. Biomaterial-based wound treatment approaches have progressed over time from simple cotton wool dressings to advanced skin substitutes containing cells and growth factors; however, no wound care approach is yet completely satisfying. Bioactive glasses are materials with potential in many areas that exhibit unique features in biomedical applications. Today, bioactive glasses are not only amorphous solid structures that can be used as a substitute in hard tissue but also are promising materials for soft tissue regeneration and wound healing applications. Biologically active elements such as Ag, B, Ca, Ce, Co, Cu, Ga, Mg, Se, Sr, and Zn can be incorporated in glass networks; hence, the superiority of these multifunctional materials over current materials results from their ability to release multiple therapeutic ions in the wound environment, which target different stages of the wound healing process. Bioactive glasses and their dissolution products have high potency for inducing angiogenesis and exerting several biological impacts on cell functions, which are involved in wound healing and some other features that are valuable in wound healing applications, namely hemostatic and antibacterial properties. In this review, we focus on skin structure, the dynamic process of wound healing in injured skin, and existing wound care approaches. The basic concepts of bioactive glasses are reviewed to better understand the relationship between glass structure and its properties. We illustrate the active role of bioactive glasses in wound repair and regeneration. Finally, research studies that have used bioactive glasses in wound healing applications are summarized and the future trends in this field are elaborated.

Advancements in Hydrogel-Based Drug Sustained Release Systems for Bone Tissue Engineering

Bone defects caused by injury, disease, or congenital deformity remain a major health concern, and efficiently regenerating bone is a prominent clinical demand worldwide. However, bone regeneration is an intricate process that requires concerted participation of both cells and bioactive factors. Mimicking physiological bone healing procedures, the sustained release of bioactive molecules plays a vital role in creating an optimal osteogenic microenvironment and achieving promising bone repair outcomes. The utilization of biomaterial scaffolds can positively affect the osteogenesis process by integrating cells with bioactive factors in a proper way. A high water content, tunable physio-mechanical properties, and diverse synthetic strategies make hydrogels ideal cell carriers and controlled drug release reservoirs. Herein, we reviewed the current advancements in hydrogel-based drug sustained release systems that have delivered osteogenesis-inducing peptides, nucleic acids, and other bioactive molecules in bone tissue engineering (BTE).

Convergence of Scaffold-Guided Bone Reconstruction and Surgical Vascularization Strategies-A Quest for Regenerative Matching Axial Vascularization

The prevalent challenge facing tissue engineering today is the lack of adequate vascularization to support the growth, function, and viability of tissue engineered constructs (TECs) that require blood vessel supply. The research and clinical community rely on the increasing knowledge of angiogenic and vasculogenic processes to stimulate a clinically-relevant vascular network formation within TECs. The regenerative matching axial vascularization approach presented in this manuscript incorporates the advantages of flap-based techniques for neo-vascularization yet also harnesses the in vivo bioreactor principle in a more directed "like for like" approach to further assist regeneration of the specific tissue type that is lost, such as a corticoperiosteal flap in critical sized bone defect reconstruction.

Bioinspired surface modification of orthopedic implants for bone tissue engineering

Biomedical implants have been widely used in various orthopedic treatments, including total hip arthroplasty, joint arthrodesis, fracture fixation, non-union, dental repair, etc. The modern research and development of orthopedic implants have gradually shifted from traditional mechanical support to a bioactive graft in order to endow them with better osteoinduction and osteoconduction. Inspired by structural and mechanical properties of natural bone, this review provides a panorama of current biological surface modifications for facilitating the interaction between medical implants and bone tissue and gives a future outlook for fabricating the next-generation multifunctional and smart implants by systematically biomimicking the physiological processes involved in formation and functioning of bones.

CD34+ cells seeded in collagen scaffolds promote bone formation in a mouse calvarial defect model

Bone tissue engineering (BTE) holds promise for managing the clinical problem of large bone defects. However, clinical adoption of BTE is limited due to limited vascularization of constructs, which could be circumvented by pre-cultivation of osteogenic and endothelial derived cells in natural-based polymer scaffolds. However, until now not many studies compared the effect of mono- and cocultures pre-seeded in collagen before implantation. We utilized a mouse calvarial defect model and compared five groups of collagen scaffolds: a negative control of a collagen scaffold alone, a positive control treated with BMP-7, monocultures of either human osteoblasts (hOBs) or CD34+ cells, and a coculture of hOB and CD34⁺ cells. Each pre-seeded collagen scaffold was implanted in mice. After 6 weeks mice were sacrificed and their skulls prepared for volumetric and histologic analysis. We found that a monoculture of CD34⁺ cells and a coculture of hOB and CD34⁺ cells pre-cultured in the collagen scaffold increased bone regeneration to a similar extend. In these groups, greater amounts of new bone were found compared with hOB monocultures. Interestingly, monoculture of CD34⁺ cells demonstrated better fracture healing than monoculture of hOBs, emphasizing the possible role of angiogenesis. Our results are promising regarding a cellular based collagen BTE construct, but more work is needed to understand the complex interaction between the osteogenic and endothelial cells. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1505-1516, 2018.

Biofabrication and Bone Tissue Regeneration: Cell Source, Approaches, and Challenges

The growing occurrence of bone disorders and the increase in aging population have resulted in the need for more effective therapies to meet this request. Bone tissue engineering strategies, by combining biomaterials, cells, and signaling factors, are seen as alternatives to conventional bone grafts for repairing or rebuilding bone defects. Indeed, skeletal tissue engineering has not yet achieved full translation into clinical practice because of several challenges. Bone biofabrication by additive manufacturing techniques may represent a possible solution, with its intrinsic capability for accuracy, reproducibility, and customization of scaffolds as well as cell and signaling molecule delivery. This review examines the existing research in bone biofabrication and the appropriate cells and factors selection for successful bone regeneration as well as limitations affecting these approaches. Challenges that need to be tackled with the highest priority are the obtainment of appropriate vascularized scaffolds with an accurate spatiotemporal biochemical and mechanical stimuli release, in order to improve osseointegration as well as osteogenesis.

Engineering prevascularized composite cell sheet by light-induced cell sheet technology

Light-induced cell sheet technology based on light-responsive TiO₂ nanodots film realized an optimal and transferable prevascularized MSC–EC composite cell sheet.

Human Bone Progenitor Cells for Clinical Application: What Kind of Immune Reaction Does Fetal Xenograft Tissue Trigger in Immunocompetent Rats?

The potential of human fetal bone cells for successful bone regeneration has been shown in vivo. In particular, it has been demonstrated that the seeding of these cells in porous poly-(l-lactic acid)/β-tricalcium phosphate scaffolds improved the bone formation compared to cell-free scaffolds in skulls of rats. However, even if the outcome is an improvement of bone formation, a thorough analysis concerning any immune responses, due to the implantation of a xenograft tissue, is not known. As the immune response and skeletal system relationship may contribute to either the success or failure of an implant, we were interested in evaluating the presence of any immune cells and specific reactions of human fetal cells (also called human bone progenitor cells) once implanted in femoral condyles of rats. For this purpose, (1) cell-free scaffolds, (2) human bone progenitor cells, or (3) osteogenic human bone progenitor cells within scaffolds were implanted over 3, 7, 14 days, and 12 weeks. The key finding is that human bone progenitor cells and osteogenic human bone progenitor cells do not trigger any particular specific immune reactions in immunocompetent rats but are noted to delay some bone formation.

Biodegradable Mg-Cu alloys with enhanced osteogenesis, angiogenesis, and long-lasting antibacterial effects

A series of biodegradable Mg-Cu alloys is designed to induce osteogenesis, stimulate angiogenesis, and provide long-lasting antibacterial performance at the same time. The Mg-Cu alloys with precipitated Mg2Cu intermetallic phases exhibit accelerated degradation in the physiological environment due to galvanic corrosion and the alkaline environment combined with Cu release endows the Mg-Cu alloys with prolonged antibacterial effects. In addition to no cytotoxicity towards HUVECs and MC3T3-E1 cells, the Mg-Cu alloys, particularly Mg-0.03Cu, enhance the cell viability, alkaline phosphatase activity, matrix mineralization, collagen secretion, osteogenesis-related gene and protein expressions of MC3T3-E1 cells, cell proliferation, migration, endothelial tubule forming, angiogenesis-related gene, and protein expressions of HUVECs compared to pure Mg. The favorable osteogenesis and angiogenesis are believed to arise from the release of bioactive Mg and Cu ions into the biological environment and the biodegradable Mg-Cu alloys with osteogenesis, angiogenesis, and long-term antibacterial ability are very promising in orthopedic applications.

Comparison of growth & function of endothelial progenitor cells cultured on deproteinized bovine bone modified with covalently bound fibronectin and bound vascular endothelial growth factor

OBJECTIVES

The objective of this study was to assess and compare the growth and function of Endothelial Progenitor Cells (EPCs) cultured on covalently bonded Vascular Endothelial Growth Factor (VEGF) and covalently bonded Fibronectin (FN) coating on deproteinized bovine bone (DBB) (test samples), compared to non-modified DBB blocks (control sample).

MATERIALS AND METHODS

The test samples were prepared by plasma polymerization of allylamine onto DBB blocks. Group1 of test samples were prepared with VEGF coating (VEGF-DBB) where as the Group2 test samples were coated with FN (FN-DBB). Non-modified DBB blocks served as a Control. EPCs were isolated and cultivated from buffy coats of peripheral blood of healthy volunteers and cultivated in the different samples and examined at time intervals of 24 h, 3 days, and 7 days. Evaluation of growth by cell count and cell morphology was done using Confocal Laser Scanning Electron Microscopy; vitality and function of cells was assessed using MTT assay and RT-PCR and ELISA for eNOS and iNOS respectively.

RESULTS

The results of the study show that both VEGF and FN could be successfully immobilized by plasma polymerization onto a complex, porous, three-dimensional structure of DBB. When comparing vital cell coverage, proliferation and function of EPCs, FN-DBB provided more positive values followed by VEGF-DBB as compared to DBB samples. eNOS level were significant higher in VEGF-DBB and FN-DBB when compared to DBB (P = 0.019 and P = 0.002). The difference between VEGF-DBB and FN-DBB was not significant.

CONCLUSIONS

Biomimetic coatings of Fibronectin may clinically relate to faster angiogenesis and earlier healing potential.

Tissue engineering strategies for promoting vascularized bone regeneration

This review focuses on current tissue engineering strategies for promoting vascularized bone regeneration. We review the role of angiogenic growth factors in promoting vascularized bone regeneration and discuss the different therapeutic strategies for controlled/sustained growth factor delivery. Next, we address the therapeutic uses of stem cells in vascularized bone regeneration. Specifically, this review addresses the concept of co-culture using osteogenic and vasculogenic stem cells, and how adipose derived stem cells compare to bone marrow derived mesenchymal stem cells in the promotion of angiogenesis. We conclude this review with a discussion of a novel approach to bone regeneration through a cartilage intermediate, and discuss why it has the potential to be more effective than traditional bone grafting methods.

Biofabrication of bone tissue: approaches, challenges and translation for bone regeneration

The rising incidence of bone disorders has resulted in the need for more effective therapies to meet this demand, exacerbated by an increasing ageing population. Bone tissue engineering is seen as a means of developing alternatives to conventional bone grafts for repairing or reconstructing bone defects by combining biomaterials, cells and signalling factors. However, skeletal tissue engineering has not yet achieved full translation into clinical practice as a consequence of several challenges. The use of additive manufacturing techniques for bone biofabrication is seen as a potential solution, with its inherent capability for reproducibility, accuracy and customisation of scaffolds as well as cell and signalling factor delivery. This review highlights the current research in bone biofabrication, the necessary factors for successful bone biofabrication, in addition to the current limitations affecting biofabrication, some of which are a consequence of the limitations of the additive manufacturing technology itself.

Hydrogel biophysical properties instruct coculture-mediated osteogenic potential

Cell-based approaches for bone formation require instructional cues from the surrounding environment. As an alternative to pharmacological strategies or transplanting single cell populations, one approach is to coimplant populations that can establish a new vasculature and differentiate to bone-forming osteoblasts. Mesenchymal stem/stromal cells (MSCs) possess osteogenic potential and produce numerous angiogenic growth factors. Endothelial colony-forming cells (ECFCs) are a subpopulation of endothelial progenitor cells capable of vasculogenesis in vivo and may provide endogenous cues to support MSC function. We investigated the contribution of the carrier biophysical properties to instruct entrapped human MSCs and ECFCs to simultaneously promote their osteogenic and proangiogenic potential. Compared with gels containing MSCs alone, fibrin gels engineered with increased compressive stiffness simultaneously increased the osteogenic and proangiogenic potential of entrapped cocultured cells. ECFCs produced bone morphogenetic protein-2 (BMP-2), a potent osteoinductive molecule, and increases in BMP-2 secretion correlated with gel stiffness. Coculture of MSCs with ECFCs transduced to knockdown BMP-2 production abrogated the osteogenic response to levels observed with MSCs alone. These results demonstrate that physical properties of engineered hydrogels modulate the function of cocultured cells in the absence of inductive cues, thus increasing the translational potential of coimplantation to speed bone formation and repair.

Multifunctional hydroxyapatite and poly(D,L-lactide-co-glycolide) nanoparticles for the local delivery of cholecalciferol

Cholecalciferol, vitamin D3, plays an important role in bonemetabolism by regulating extracellular levels of calcium. Presented here is a study on the effects of the local delivery of cholecalciferol (D3) using nanoparticulate carriers composed of hydroxyapatite (HAp) and poly(D,L-lactide-co-glycolide) (PLGA). Multifunctional nanoparticulate HAp-based powders were prepared for the purpose of: (a) either fast or sustained, local delivery of cholecalciferol, and (b) the secondary, osteoconductive and defect-filling effect of the carrier itself. Two types of HAp-based powders with particles of narrowly dispersed sizes in the nano range were prepared and tested in this study: HAp nanoparticles as direct cholecalciferol delivery agents and HAp nanoparticles coated with cholecalciferol-loaded poly(D,L)-lactide-co-glycolide (HAp/D3/PLGA). Satisfying biocompatibility of particulate systems, when incubated in contact with MC3T3-E1 osteoblastic cells in vitro, was observed for HAp/D3/PLGA and pure HAp. In contrast, an extensively fast release of cholecalciferol from the system comprising HAp nanoparticles coated with cholecalciferol (HAp/D3) triggered necrosis of the osteoblastic cells in vitro. Artificial defects induced in the osteoporotic bone of the rat mandible were successfully reconstructed following implantation of cholecalciferol-coated HAp nanoparticles as well as those comprising HAp nanoparticles coated with cholecalciferol-loaded PLGA (HAp/D3/PLGA). The greatest levels of enhanced angiogenesis, vascularization, osteogenesis and bone structure differentiation were achieved upon the implementation of HAp/D3/PLGA systems.

Analyzing Structure and Function of Vascularization in Engineered Bone Tissue by Video-Rate Intravital Microscopy and 3D Image Processing

Vascularization is a key challenge in tissue engineering. Three-dimensional structure and microcirculation are two fundamental parameters for evaluating vascularization. Microscopic techniques with cellular level resolution, fast continuous observation, and robust 3D postimage processing are essential for evaluation, but have not been applied previously because of technical difficulties. In this study, we report novel video-rate confocal microscopy and 3D postimage processing techniques to accomplish this goal. In an immune-deficient mouse model, vascularized bone tissue was successfully engineered using human bone marrow mesenchymal stem cells (hMSCs) and human umbilical vein endothelial cells (HUVECs) in a poly (D,L-lactide-co-glycolide) (PLGA) scaffold. Video-rate (30 FPS) intravital confocal microscopy was applied in vitro and in vivo to visualize the vascular structure in the engineered bone and the microcirculation of the blood cells. Postimage processing was applied to perform 3D image reconstruction, by analyzing microvascular networks and calculating blood cell viscosity. The 3D volume reconstructed images show that the hMSCs served as pericytes stabilizing the microvascular network formed by HUVECs. Using orthogonal imaging reconstruction and transparency adjustment, both the vessel structure and blood cells within the vessel lumen were visualized. Network length, network intersections, and intersection densities were successfully computed using our custom-developed software. Viscosity analysis of the blood cells provided functional evaluation of the microcirculation. These results show that by 8 weeks, the blood vessels in peripheral areas function quite similarly to the host vessels. However, the viscosity drops about fourfold where it is only 0.8 mm away from the host. In summary, we developed novel techniques combining intravital microscopy and 3D image processing to analyze the vascularization in engineered bone. These techniques have broad applicability for evaluating vascularization in other engineered tissues as well.

Inosculation potential of angiopoietin-4-immobilized pHEMA-based bone scaffolds

Although angiopoietin-1has potential therapeutic use in angiogenesis, the biological role of angiopoietin-4, especially in its immobilized form, is already unknown. In this study, vascularization potential of angiopoietin-4 either alone or in combination with vascular endothelial growth factor (VEGF) was investigated following its immobilization onto the poly(2-hydroxyethyl methacrylate)-based bone scaffolds. Poly(2-hydroxyethyl methacrylate) (pHEMA)-based superporous hydrogels (SPHs) were synthesized by radical polymerization of hydroxyethyl methacrylate in the presence of gelatin or chitosan and the porosity was achieved by gas foaming. However, only pHEMA-gelatin SPHs fulfill the structural and biological characteristics of a bone scaffold. Therefore, angiopoietin-4 and/or VEGF were immobilized successfully onto the pHEMA–gelatin SPHs using carbodiimide chemistry. The cell culture studies that were performed with human umbilical vein endothelial cells (HUVECs) for 28 days showed that immobilized angiopoietin-4 supported sprout formation more than that of other groups, while the immobilized VEGF including scaffolds promoted proliferation of HUVECs.

Engineering clinically relevant volumes of vascularized bone

Vascularization remains one of the most important challenges that must be overcome for tissue engineering to be consistently implemented for reconstruction of large volume bone defects. An extensive vascular network is needed for transport of nutrients, waste and progenitor cells required for remodelling and repair. A variety of tissue engineering strategies have been investigated in an attempt to vascularize tissues, including those applying cells, soluble factor delivery strategies, novel design and optimization of bio-active materials, vascular assembly pre-implantation and surgical techniques. However, many of these strategies face substantial barriers that must be overcome prior to their ultimate translation into clinical application. In this review recent progress in engineering vascularized bone will be presented with an emphasis on clinical feasibility.

Evaluating 3D-printed biomaterials as scaffolds for vascularized bone tissue engineering

There is an unmet need for a consistent set of tools for the evaluation of 3D-printed constructs. A toolbox developed to design, characterize, and evaluate 3D-printed poly(propylene fumarate) scaffolds is proposed for vascularized engineered tissues. This toolbox combines modular design and non-destructive fabricated design evaluation, evaluates biocompatibility and mechanical properties, and models angiogenesis.

The use of total human bone marrow fraction in a direct three-dimensional expansion approach for bone tissue engineering applications: focus on angiogenesis and osteogenesis

Current approaches in bone tissue engineering have shown limited success, mostly owing to insufficient vascularization of the construct. A common approach consists of co-culture of endothelial cells and osteoblastic cells. This strategy uses cells from different sources and differentiation states, thus increasing the complexity upstream of a clinical application. The source of reparative cells is paramount for the success of bone tissue engineering applications. In this context, stem cells obtained from human bone marrow hold much promise. Here, we analyzed the potential of human whole bone marrow cells directly expanded in a three-dimensional (3D) polymer matrix and focused on the further characterization of this heterogeneous population and on their ability to promote angiogenesis and osteogenesis, both in vitro and in vivo, in a subcutaneous model. Cellular aggregates were formed within 24 h and over the 12-day culture period expressed endothelial and bone-specific markers and a specific junctional protein. Ectopic implantation of the tissue-engineered constructs revealed osteoid tissue and vessel formation both at the periphery and within the implant. This work sheds light on the potential clinical use of human whole bone marrow for bone regeneration strategies, focusing on a simplified approach to develop a direct 3D culture without two-dimensional isolation or expansion.

Improved repair of bone defects with prevascularized tissue-engineered bones constructed in a perfusion bioreactor

Vascularization of tissue-engineered bones is critical to achieving satisfactory repair of bone defects. The authors investigated the use of prevascularized tissue-engineered bone for repairing bone defects. The new bone was greater in the prevascularized group than in the non-vascularized group, indicating that prevascularized tissue-engineered bone improves the repair of bone defects. [Orthopedics. 2014; 37(10):685-690.].

Cellular and molecular bases of skeletal regeneration: what can we learn from genetic mouse models?

Although bone repairs through a very efficient regenerative process in 90% of the patients, many factors can cause delayed or impaired healing. To date, there are no reliable biological parameters to predict or diagnose bone repair defects. Orthopedic surgeons mostly base their diagnoses on radiographic analyses. With the recent progress in our understanding of the bone repair process, new methods may be envisioned. Animal models have allowed us to define the key steps of bone regeneration and the biological and mechanical factors that may influence bone healing in positive or negative ways. Most importantly, small animal models such as mice have provided powerful tools to apprehend the genetic bases of normal and impaired bone healing. The current review presents a state of the art of the genetically modified mouse models that have advanced our understanding of the cellular and molecular components of bone regeneration and repair. The review illustrates the use of these models to define the role of inflammation, skeletal cell lineages, signaling pathways, the extracellular matrix, osteoclasts and angiogenesis. These genetic mouse models promise to change the field of orthopedic surgery to help establish genetic predispositions for delayed repair, develop models of non-union that mimic the human conditions and elaborate new therapeutic approaches to enhance bone regeneration.

Biomaterials in co-culture systems: towards optimizing tissue integration and cell signaling within scaffolds

Most natural tissues consist of multi-cellular systems made up of two or more cell types. However, some of these tissues may not regenerate themselves following tissue injury or disease without some form of intervention, such as from the use of tissue engineered constructs. Recent studies have increasingly used co-cultures in tissue engineering applications as these systems better model the natural tissues, both physically and biologically. This review aims to identify the challenges of using co-culture systems and to highlight different approaches with respect to the use of biomaterials in the use of such systems. The application of co-culture systems to stimulate a desired biological response and examples of studies within particular tissue engineering disciplines are summarized. A description of different analytical co-culture systems is also discussed and the role of biomaterials in the future of co-culture research are elaborated on. Understanding the complex cell-cell and cell-biomaterial interactions involved in co-culture systems will ultimately lead the field towards biomaterial concepts and designs with specific biochemical, electrical, and mechanical characteristics that are tailored towards the needs of distinct co-culture systems.

Increased extracellular matrix and proangiogenic factor transcription in endothelial cells after cocultivation with primary human osteoblasts

The most promising strategies in bone engineering have concentrated on providing sufficient vascularization to support the newly forming tissue. In this context, recent research in the field has focused on studying the complex interactions between bone forming and endothelial cells. Our previous work has demonstrated that direct contact cocultivation of human umbilical vein endothelial cells (HUVECs) with primary human osteoblasts (hOBs) induces the osteogenic phenotype and survival of hOBs. In order to investigate the mechanisms that lead to this effect, we performed microarray gene expression profiling on HUVECs following cocultivation with hOBs. Our data reveal profound transcriptomic changes that are dependent on direct cell contact between these cell populations. Pathway analysis using the MetaCore™ platform and literature research suggested a striking upregulation of transcripts related to extracellular matrix and cell-matrix interactions. Upregulation of a number of major angiogenetic factors confirms previous observations that HUVECs enter a proangiogenic state upon cocultivation with osteoblasts. Interestingly, the downregulated transcripts clustered predominantly around cell cycle-related processes. The microarray data were confirmed by quantitative real-time RT-PCR on selected genes. Taken together, this study provides a platform for further inquiries in complex interactions between endothelial cells and osteoblasts.

Cell interactions between human progenitor-derived endothelial cells and human mesenchymal stem cells in a three-dimensional macroporous polysaccharide-based scaffold promote osteogenesis

Several studies have reported the benefits of mesenchymal stem cells (MSCs) for bone tissue engineering. However, vascularization remains one of the main obstacles that must be overcome to reconstruct large bone defects. In vitro prevascularization of the three-dimensional (3-D) constructs using co-cultures of human progenitor-derived endothelial cells (PDECs) with human bone marrow mesenchymal stem cells (HBMSCs) appeared as a potential strategy. However, the crosstalk between the two lineages has been studied in two-dimensional (2-D), but remains unknown in 3-D. The aim of this study is to investigate the cell interactions between PDECs and HBMSCs in a porous matrix composed of polysaccharides. This biodegradable scaffold promotes cell interactions by inducing multicellular aggregates composed of HBMSCs surrounded by PDECs. Cell aggregation contributes to the formation of junctional proteins composed of Connexin43 (Cx43) and VE-cadherin, and an activation of osteoblastic differentiation of HBMSCs stimulated by the presence of PDECs. Inhibition of Cx43 by mimetic peptide 43GAP27 induced a decrease in mRNA levels of Cx43 and all the bone-specific markers. Finally, subcutaneous implantations for 3 and 8 weeks in NOG mice revealed an increase in osteoid formation with the tissue-engineered constructs seeded with HBMSCs/PDECs compared with those loaded with HBMSCs alone. Taking together, these results demonstrate that this 3-D microenvironment favored cell communication, osteogenesis and bone formation.

Bone tissue engineering: recent advances and challenges

The worldwide incidence of bone disorders and conditions has trended steeply upward and is expected to double by 2020, especially in populations where aging is coupled with increased obesity and poor physical activity. Engineered bone tissue has been viewed as a potential alternative to the conventional use of bone grafts, due to their limitless supply and no disease transmission. However, bone tissue engineering practices have not proceeded to clinical practice due to several limitations or challenges. Bone tissue engineering aims to induce new functional bone regeneration via the synergistic combination of biomaterials, cells, and factor therapy. In this review, we discuss the fundamentals of bone tissue engineering, highlighting the current state of this field. Further, we review the recent advances of biomaterial and cell-based research, as well as approaches used to enhance bone regeneration. Specifically, we discuss widely investigated biomaterial scaffolds, micro- and nano-structural properties of these scaffolds, and the incorporation of biomimetic properties and/or growth factors. In addition, we examine various cellular approaches, including the use of mesenchymal stem cells (MSCs), embryonic stem cells (ESCs), adult stem cells, induced pluripotent stem cells (iPSCs), and platelet-rich plasma (PRP), and their clinical application strengths and limitations. We conclude by overviewing the challenges that face the bone tissue engineering field, such as the lack of sufficient vascularization at the defect site, and the research aimed at functional bone tissue engineering. These challenges will drive future research in the field.

How smart do biomaterials need to be? A translational science and clinical point of view

Over the last 4 decades innovations in biomaterials and medical technology have had a sustainable impact on the development of biopolymers, titanium/stainless steel and ceramics utilized in medical devices and implants. This progress was primarily driven by issues of biocompatibility and demands for enhanced mechanical performance of permanent and non-permanent implants as well as medical devices and artificial organs. In the 21st century, the biomaterials community aims to develop advanced medical devices and implants, to establish techniques to meet these requirements, and to facilitate the treatment of older as well as younger patient cohorts. The major advances in the last 10 years from a cellular and molecular knowledge point of view provided the scientific foundation for the development of third-generation biomaterials. With the introduction of new concepts in molecular biology in the 2000s and specifically advances in genomics and proteomics, a differentiated understanding of biocompatibility slowly evolved. These cell biological discoveries significantly affected the way of biomaterials design and use. At the same time both clinical demands and patient expectations continued to grow. Therefore, the development of cutting-edge treatment strategies that alleviate or at least delay the need of implants could open up new vistas. This represents the main challenge for the biomaterials community in the 21st century. As a result, the present decade has seen the emergence of the fourth generation of biomaterials, the so-called smart or biomimetic materials. A key challenge in designing smart biomaterials is to capture the degree of complexity needed to mimic the extracellular matrix (ECM) of natural tissue. We are still a long way from recreating the molecular architecture of the ECM one to one and the dynamic mechanisms by which information is revealed in the ECM proteins in response to challenges within the host environment. This special issue on smart biomaterials lists a large number of excellent review articles which core is to present and discuss the basic sciences on the topic of smart biomaterials. On the other hand, the purpose of our review is to assess state of the art and future perspectives of the so called "smart biomaterials" from a translational science and specifically clinical point of view. Our aim is to filter out and discuss which biomedical advances and innovations help us to achieve the objective to translate smart biomaterials from bench to bedside. The authors predict that analyzing the field of smart biomaterials from a clinical point of view, looking back 50 years from now, it will show that this is our heritage in the 21st century.

Controlled release strategies for bone, cartilage, and osteochondral engineering--Part II: challenges on the evolution from single to multiple bioactive factor delivery

The development of controlled release systems for the regeneration of bone, cartilage, and osteochondral interface is one of the hot topics in the field of tissue engineering and regenerative medicine. However, the majority of the developed systems consider only the release of a single growth factor, which is a limiting step for the success of the therapy. More recent studies have been focused on the design and tailoring of appropriate combinations of bioactive factors to match the desired goals regarding tissue regeneration. In fact, considering the complexity of extracellular matrix and the diversity of growth factors and cytokines involved in each biological response, it is expected that an appropriate combination of bioactive factors could lead to more successful outcomes in tissue regeneration. In this review, the evolution on the development of dual and multiple bioactive factor release systems for bone, cartilage, and osteochondral interface is overviewed, specifically the relevance of parameters such as dosage and spatiotemporal distribution of bioactive factors. A comprehensive collection of studies focused on the delivery of bioactive factors is also presented while highlighting the increasing impact of platelet-rich plasma as an autologous source of multiple growth factors.

Prevascularisation with endothelial progenitor cells improved restoration of the architectural and functional properties of newly formed bone for bone reconstruction

PURPOSE

The aim of this study was to examine whether the addition of endothelial progenitor cells (EPCs) contributes to restoring the architectural and functional properties of newly formed bone for reconstruction of bone defects.

METHODS

Bone marrow-derived EPCs and mesenchymal stem cells (MSCs) were co-seeded onto demineralized bone matrix (DBM) as a prevascularized tissue-engineered bone (TEB) for the repair of segmental bone defects to evaluate the effects of prevascularization of TEB on ameliorating morphological, haemodynamic and mechanical characteristics.

RESULTS

The restoration of the intraosseous vasculature and medullary cavity was improved markedly compared to the non-prevascularized groups. The blood supply, biomechanical strength, and bone mineral density of the prevascularized group were significantly higher than those of the non-prevascularized groups during bone reconstruction.

CONCLUSIONS

The present study indicates that EPC-dependent prevascularization contributes to bone healing with structural reconstruction and functional recovery and may improve the understanding of correlation between angiogenesis and osteogenesis.

In vivo bone generation via the endochondral pathway on three-dimensional electrospun fibers

A new concept of generating bone tissue via the endochondral route might be superior to the standard intramembranous ossification approach. To implement the endochondral approach, suitable scaffolds are required to provide a three-dimensional (3-D) substrate for cell population and differentiation, and eventually for the generation of osteochondral tissue. Therefore, a novel wet-electrospinning system, using ethanol as the collecting medium, was exploited in this study to fabricate a cotton-like poly(lactic-co-glycolic acid)/poly(ε-caprolactone) scaffold that consisted of a very loose and uncompressed accumulation of fibers. Rat bone marrow cells were seeded on these scaffolds and chondrogenically differentiated in vitro for 4 weeks followed by subcutaneous implantation in vivo for 8 weeks. Cell pellets were used as a control. A glycosaminoglycan assay and Safranin O staining showed that the cells infiltrated throughout the scaffolds and deposited an abundant cartilage matrix after in vitro chondrogenic priming. Histological analysis of the in vivo samples revealed extensive new bone formation through the remodeling of the cartilage template. In conclusion, using the wet-electrospinning method, we are able to create a 3-D scaffold in which bone tissue can be formed via the endochondral pathway. This system can be easily processed for various assays and histological analysis. Consequently, it is more efficient than the traditional cell pellets as a tool to study endochondral bone formation for tissue engineering purposes.

Influence of architecture of β-tricalcium phosphate scaffolds on biological performance in repairing segmental bone defects

BACKGROUND

Although three-dimensional (3D) β-tricalcium phosphate (β-TCP) scaffolds serve as promising bone graft substitutes for the segmental bone defect treatment, no consensus has been achieved regarding their optimal 3D architecture.

METHODS

In this study, we has systematically compared four types of β-TCP bone graft substitutes with different 3D architectures, including two types of porous scaffolds, one type of tubular scaffolds and one type of solid scaffolds, for their efficacy in treating segmental bone defect in a rabbit model.

RESULTS

Our study has demonstrated that when compared to the traditional porous and solid scaffolds, tubular scaffolds promoted significantly higher amount of new bone formation in the defect regions as shown by X-ray, micro CT examinations and histological analysis, restored much greater mechanical properties of the damaged bone evidenced by the biomechanical testing, and eventually achieved the complete union of segmental defect. Moreover, the implantation of tubular scaffolds enhanced the neo-vascularization at the defect region with higher bone metabolic activities than others, as indicated by the bone scintigraphy assay.

CONCLUSIONS

This study has further the current knowledge regarding the profound influence of overall 3D architecture of β-TCP scaffolds on their in vivo defect healing performance and illuminated the promising potential use of tubular scaffolds as effective bone graft substitute in treating large segmental bone defects.

Whatever their differentiation status, human progenitor derived - or mature - endothelial cells induce osteoblastic differentiation of bone marrow stromal cells

Association of the bone-forming osteoblasts (OBs) and vascular endothelial cells (ECs) into a biomaterial composite provides a live bone graft substitute that can repair the bone defect when implanted. An intimate functional relationship exists between these cell types. This communication is crucial to the coordinated cell behaviour necessary for bone development and remodelling. Previous studies have shown that direct co-culture of primary human osteoprogenitors (HOPs) with primary human umbilical vein endothelial cells (HUVECs) stimulates HOPs differentiation and induces tubular-like networks. The present work aims to test the use of human bone marrow stromal cells (HBMSCs) co-cultured with human endothelial progenitor cells in order to assess whether progenitor-derived ECs (PDECs) could support osteoblastic differentiation as mature ECs do. Indeed, data generated from the literature by different laboratories considering these co-culture systems appear difficult to compare. Monocultures of HUVECs, HOPs, HBMSCs (in a non-orientated lineage), PDECs (from cord blood) were used as controls and four combinations of co-cultures were undertaken: HBMSCs-PDECs, HBMSCs-HUVECs, HOPs-PDECs, HOPs-HUVECs with ECs (mature or progenitor) for 6 h to 7 days. At the end of the chosen co-culture time, intracellular alkaline phosphatase (ALP) activity was detected in HOPs and HBMSCs and quantified in cell extracts. Quantitative real-time polymerase chain reaction (qPCR) of ALP was performed over time and vascular endothelial growth factor (VEGF) was measured. After 21 days, calcium deposition was observed, comparing mono- and co-cultures. We confirm that ECs induce osteoblastic differentiation of mesenchymal stem cells in vitro. Moreover, HUVECs can be replaced by PDECs, the latter being of great interest in tissue engineering.

Salvianolic acid B prevents bone loss in prednisone-treated rats through stimulation of osteogenesis and bone marrow angiogenesis

Glucocorticoid (GC) induced osteoporosis (GIO) is caused by the long-term use of GC for treatment of autoimmune and inflammatory diseases. The GC related disruption of bone marrow microcirculation and increased adipogenesis contribute to GIO development. However, neither currently available anti-osteoporosis agent is completely addressed to microcirculation and bone marrow adipogenesis. Salvianolic acid B (Sal B) is a polyphenolic compound from a Chinese herbal medicine, Salvia miltiorrhiza Bunge. The aim of this study was to determine the effects of Sal B on osteoblast bone formation, angiogenesis and adipogenesis-associated GIO by performing marrow adipogenesis and microcirculation dilation and bone histomorphometry analyses. (1) In vivo study: Bone loss in GC treated rats was confirmed by significantly decreased BMD, bone strength, cancellous bone mass and architecture, osteoblast distribution, bone formation, marrow microvessel density and diameter along with down-regulation of marrow BMPs expression and increased adipogenesis. Daily treatment with Sal B (40 mg/kg/d) for 12 weeks in GC male rats prevented GC-induced cancellous bone loss and increased adipogenesis while increasing cancellous bone formation rate with improved local microcirculation by capillary dilation. Treatment with Sal B at a higher dose (80 mg/kg/d) not only prevented GC-induced osteopenia, but also increased cancellous bone mass and thickness, associated with increase of marrow BMPs expression, inhibited adipogenesis and further increased microvessel diameters. (2) In vitro study: In concentration from 10⁻⁶ mol/L to 10⁻⁷ mol/L, Sal B stimulated bone marrow stromal cell (MSC) differentiation to osteoblast and increased osteoblast activities, decreased GC associated adipogenic differentiation by down-regulation of PPARγ mRNA expression, increased Runx2 mRNA expression without osteoblast inducement, and, furthermore, Sal B decreased Dickkopf-1 and increased β-catenin mRNA expression with or without adipocyte inducement in MSC. We conclude that Sal B prevented bone loss in GC-treated rats through stimulation of osteogenesis, bone marrow angiogenesis and inhibition of adipogenesis.