Angiogenesis and bone repair

Friend or foe? Inflammation and the foreign body response to orthopedic biomaterials

The use of biomaterials and implants for joint replacement, fracture fixation, spinal stabilization and other orthopedic indications has revolutionized patient care by reliably decreasing pain and improving function. These surgical procedures always invoke an acute inflammatory reaction initially, that in most cases, readily subsides. Occasionally, chronic inflammation around the implant develops and persists; this results in unremitting pain and compromises function. The etiology of chronic inflammation may be specific, such as with infection, or be unknown. The histological hallmarks of chronic inflammation include activated macrophages, fibroblasts, T cell subsets, and other cells of the innate immune system. The presence of cells of the adaptive immune system usually indicates allergic reactions to metallic haptens. A foreign body reaction is composed of activated macrophages, giant cells, fibroblasts, and other cells often distributed in a characteristic histological arrangement; this reaction is usually due to particulate debris and other byproducts from the biomaterials used in the implant. Both chronic inflammation and the foreign body response have adverse biological effects on the integration of the implant with the surrounding tissues. Strategies to mitigate chronic inflammation and the foreign body response will enhance the initial incorporation and longevity of the implant, and thereby, improve long-term pain relief and overall function for the patient. The seminal research performed in the laboratory of Dr. James Anderson and co-workers has provided an inspirational and driving force for our laboratory's work on the interactions and crosstalk among cells of the mesenchymal, immune, and vascular lineages, and orthopedic biomaterials. Dr. Anderson's delineation of the fundamental biologic processes and mechanisms underlying acute and chronic inflammation, the foreign body response, resolution, and eventual functional integration of implants in different organ systems has provided researchers with a strategic approach to the use of biomaterials to improve health in numerous clinical scenarios.

Promoting a Cobalt Complex of Qingzhuan Dark Tea Polysaccharides on Fracture Healing in Rats

Fractures occur commonly with multiple injuries, and their incidence has increased in recent years. Trace amounts of cobalt are necessary for many living organisms as it stimulates hematopoiesis and improves bone health. However, cobalt is also toxic, as it might cause allergic reactions and tissue destruction. These factors limit the application of cobalt in some medical fields. We studied the tea polysaccode-cobalt complex (TPS-Co) prepared from Qingzhuan Dark Tea polysaccharides. We used 6-week-old Sprague-Dawley rats to establish a femoral fracture model and evaluated the effects of CoCl2 and TPS-Co on the healing of femoral fractures. In this study, treatment with TPS-Co for the same content of cobalt intake decreased the side effects associated with CoCl2 treatment and accelerated the healing of femoral fractures in rats. This treatment method promoted angiogenesis by upregulating the expression of vascular endothelial growth factor and hypoxia-inducible factor. Bone formation was promoted via the upregulation of the expression of bone morphogenetic protein 2 and serum bone alkaline phosphatase. TPS-Co was found to actively regulate bone and vascular systems, resulting in significant bone regeneration effects. Therefore, the Qingzhuan Dark Tea polysaccharide cobalt complex might be used as an additive or drug to promote fracture healing, and thus, it might have a huge market value.

Artificial Intelligence-Based 3D Printing Strategies for Bone Scaffold Fabrication and Its Application in Preclinical and Clinical Investigations

3D printing has become increasingly popular in the field of bone tissue engineering. However, the mechanical properties, biocompatibility, and porosity of the 3D printed bone scaffolds are major requirements for tissue regeneration and implantation as well. Designing the scaffold architecture in accordance with the need to create better mechanical and biological stimuli is necessary to achieve unique scaffold properties. To accomplish this, different 3D designing strategies can be utilized with the help of the scaffold design library and artificial intelligence (AI). The implementation of AI to assist the 3D printing process can enable it to predict, adapt, and control the parameters on its own, which lowers the risk of errors. This Review emphasizes 3D design and fabrication of bone scaffold using different materials and the use of AI-aided 3D printing strategies. Also, the adaption of AI to 3D printing helps to develop patient-specific scaffolds based on different requirements, thus providing feedback and adequate data for reproducibility, which can be improvised in the future. These printed scaffolds can also serve as an alternative to preclinical animal test models to cut costs and prevent immunological interference.

Synthetic Calcium-Phosphate Materials for Bone Grafting

Synthetic bone grafting materials play a significant role in various medical applications involving bone regeneration and repair. Their ability to mimic the properties of natural bone and promote the healing process has contributed to their growing relevance. While calcium-phosphates and their composites with various polymers and biopolymers are widely used in clinical and experimental research, the diverse range of available polymer-based materials poses challenges in selecting the most suitable grafts for successful bone repair. This review aims to address the fundamental issues of bone biology and regeneration while providing a clear perspective on the principles guiding the development of synthetic materials. In this study, we delve into the basic principles underlying the creation of synthetic bone composites and explore the mechanisms of formation for biologically important complexes and structures associated with the various constituent parts of these materials. Additionally, we offer comprehensive information on the application of biologically active substances to enhance the properties and bioactivity of synthetic bone grafting materials. By presenting these insights, our review enables a deeper understanding of the regeneration processes facilitated by the application of synthetic bone composites.

Infrared Thermography-A Novel Tool for Monitoring Fracture Healing: A Critically Appraised Topic With Evidence-Based Recommendations for Clinical Practice

CLINICAL SCENARIO

Stress fractures are one of the most common injuries in athletes. Unfortunately, they are hard to diagnose, require multiple radiology exams and follow-up which leads to more exposure to radiation and an increase in cost. Stress fractures that are mismanaged can lead to serious complications and poorer outcomes for the athlete. During the rehabilitation process, it would be beneficial to be able to monitor the healing of fractures to know when it is safe to gradually allow a patient to a return to sport because the return to activity is not usually objective and based on pain level.

CLINICAL QUESTION

Can infrared thermography (IRT) be a useful tool to measure the pathophysiological state of the fracture healing? The aim of this critically appraised topic is to analyze the current evidence of IRT for measuring the temperature change in fractures to provide recommendations for medical practitioners.

SUMMARY OF KEY FINDINGS

For this critically appraised topic, we examined 3 articles that compared medical imaging and IRT over multiple time points during the follow-up. The 3 articles concluded that a 1 °C asymmetry in temperature followed by a return to normal (less than 0.3 °C) temperature during the healing process of fractures can be monitored using IRT.

CLINICAL BOTTOM LINE

Once the patient has been diagnosed with a fracture, IRT can safely be used to monitor the evolution of a fracture. When the thermogram progresses from a hot thermogram to a cold thermogram, the healing is considered good enough to return to sport.

STRENGTH OF RECOMMENDATION

Grade 2 evidence exists to support IRT being used by clinicians to monitor fracture healing. Due to the limited research and novelty of the technology, the current recommendations are for following the treatment of the fracture once the initial diagnosis is made.

Microfibril-Associated Glycoprotein-2 Promoted Fracture Healing via Integrin αvβ3/PTK2/AKT Signaling

Fracture healing is a complex physiological process in which angiogenesis plays an essential role. Microfibril-associated glycoprotein-2 (MAGP2) has been reported to possess a proangiogenic activity via integrin αvβ3, yet its role in bone repair is unexplored. In this study, a critical-sized femoral defect (2 mm) was created in mice, followed by the delivery of an adenovirus-based MAGP2 overexpression vector or its negative control at the fracture site. At days 7, 14, 21, and 28 postfracture, bone fracture healing was evaluated by radiography, micro-computed tomography, and histopathologic analysis. Adenovirus-based MAGP2 overexpression vector-treated mice exhibited increased bone mineral density and bone volume fraction. MAGP2 overexpression contributed to an advanced stage of endochondral ossification and induced cartilage callus into the bony callus. Further analysis indicated that MAGP2 was associated with enhanced angiogenesis, as evidenced by marked MAGP2 and integrin αvβ3 costaining and increased endothelial cell markers such as endomucin and CD31 levls, as well as elevated phosphorylation of protein tyrosine kinase 2 (PTK2) and AKT serine/threonine kinase 1 (AKT) in the callus. In vitro, recombinant human MAGP2 treatment enhanced the viability, migration, and tube formation ability of human microvascular endothelial cells, which was partially reversed by integrin αvβ3 inhibition or MK-2206, a specific AKT inhibitor. Inhibition of integrin αvβ3 abolished MAGP2-induced PTK2 and AKT activation. Taken together, our data provide the first evidence that MAGP2 promotes angiogenesis and bone formation by activating the integrin αvβ3/PTK2/AKT signaling pathway.

Recent advances on 3D-printed PCL-based composite scaffolds for bone tissue engineering

Population ageing and various diseases have increased the demand for bone grafts in recent decades. Bone tissue engineering (BTE) using a three-dimensional (3D) scaffold helps to create a suitable microenvironment for cell proliferation and regeneration of damaged tissues or organs. The 3D printing technique is a beneficial tool in BTE scaffold fabrication with appropriate features such as spatial control of microarchitecture and scaffold composition, high efficiency, and high precision. Various biomaterials could be used in BTE applications. PCL, as a thermoplastic and linear aliphatic polyester, is one of the most widely used polymers in bone scaffold fabrication. High biocompatibility, low cost, easy processing, non-carcinogenicity, low immunogenicity, and a slow degradation rate make this semi-crystalline polymer suitable for use in load-bearing bones. Combining PCL with other biomaterials, drugs, growth factors, and cells has improved its properties and helped heal bone lesions. The integration of PCL composites with the new 3D printing method has made it a promising approach for the effective treatment of bone injuries. The purpose of this review is give a comprehensive overview of the role of printed PCL composite scaffolds in bone repair and the path ahead to enter the clinic. This study will investigate the types of 3D printing methods for making PCL composites and the optimal compounds for making PCL composites to accelerate bone healing.

Composite Nanocoatings of Biomedical Magnesium Alloy Implants: Advantages, Mechanisms, and Design Strategies

The rapid degradation of magnesium (Mg) alloy implants erodes mechanical performance and interfacial bioactivity, thereby limiting their clinical utility. Surface modification is among the solutions to improve corrosion resistance and bioefficacy of Mg alloys. Novel composite coatings that incorporate nanostructures create new opportunities for their expanded use. Particle size dominance and impermeability may increase corrosion resistance and thereby prolong implant service time. Nanoparticles with specific biological effects may be released into the peri-implant microenvironment during the degradation of coatings to promote healing. Composite nanocoatings provide nanoscale surfaces to promote cell adhesion and proliferation. Nanoparticles may activate cellular signaling pathways, while those with porous or core-shell structures may carry antibacterial or immunomodulatory drugs. Composite nanocoatings may promote vascular reendothelialization and osteogenesis, attenuate inflammation, and inhibit bacterial growth, thus increasing their applicability in complex clinical microenvironments such as those of atherosclerosis and open fractures. This review combines the physicochemical properties and biological efficiency of Mg-based alloy biomedical implants to summarize the advantages of composite nanocoatings, analyzes their mechanisms of action, and proposes design and construction strategies, with the purpose of providing a reference for promoting the clinical application of Mg alloy implants and to further the design of nanocoatings.

Histologic Evidence of Oral and Periodontal Regeneration Using Recombinant Human Platelet-Derived Growth Factor

Human histology provides critical information on the biological potential of various regenerative protocols and biomaterials, which is vital to advancing the field of periodontal regeneration, both in research and clinical practice. Outcomes of histologic studies are particularly valuable when interpreted considering additional evidence available from pre-clinical and clinical studies. One of the best-documented growth factors areproven to have positive effects on a myriad of oral regenerative procedures is recombinant human platelet-derived growth factor—BB (rhPDGF-BB). While a systematic review of clinical studies evaluating rhPDGF in oral regenerative procedures has been recently completed, a review article that focuses on the histologic outcomes is needed. Hence, this communication discusses the histologic effects of rhPDGF-BB on oral and periodontal regenerative procedures, including root coverage and soft tissue augmentation, intrabony defects, furcation defects, peri-implant bone augmentation, and guided bone regeneration. Studies from 1989 to 2022 have been included in this review.

Autologous Tooth Graft: Innovative Biomaterial for Bone Regeneration. Tooth Transformer® and the Role of Microbiota in Regenerative Dentistry. A Systematic Review

Different biomaterials, from synthetic products to autologous or heterologous grafts, have been suggested for the preservation and regeneration of bone. The aim of this study is to evaluate the effectiveness of autologous tooth as a grafting material and examine the properties of this material and its interactions with bone metabolism. PubMed, Scopus, Cochrane Library, and Web of Science were searched to find articles addressing our topic published from 1 January 2012 up to 22 November 2022, and a total of 1516 studies were identified. Eighteen papers in all were considered in this review for qualitative analysis. Demineralized dentin can be used as a graft material, since it shows high cell compatibility and promotes rapid bone regeneration by striking an ideal balance between bone resorption and production; it also has several benefits, such as quick recovery times, high-quality newly formed bone, low costs, no risk of disease transmission, the ability to be performed as an outpatient procedure, and no donor-related postoperative complications. Demineralization is a crucial step in the tooth treatment process, which includes cleaning, grinding, and demineralization. Since the presence of hydroxyapatite crystals prevents the release of growth factors, demineralization is essential for effective regenerative surgery. Even though the relationship between the bone system and dysbiosis has not yet been fully explored, this study highlights an association between bone and gut microbes. The creation of additional scientific studies to build upon and enhance the findings of this study should be a future objective of scientific research.

Emerging role of mesenchymal stem/stromal cells (MSCs) and MSCs-derived exosomes in bone- and joint-associated musculoskeletal disorders: a new frontier

Exosomes are membranous vesicles with a 30 to 150 nm diameter secreted by mesenchymal stem/stromal cells (MSCs) and other cells, such as immune cells and cancer cells. Exosomes convey proteins, bioactive lipids, and genetic components to recipient cells, such as microRNAs (miRNAs). Consequently, they have been implicated in regulating intercellular communication mediators under physiological and pathological circumstances. Exosomes therapy as a cell-free approach bypasses many concerns regarding the therapeutic application of stem/stromal cells, including undesirable proliferation, heterogeneity, and immunogenic effects. Indeed, exosomes have become a promising strategy to treat human diseases, particularly bone- and joint-associated musculoskeletal disorders, because of their characteristics, such as potentiated stability in circulation, biocompatibility, low immunogenicity, and toxicity. In this light, a diversity of studies have indicated that inhibiting inflammation, inducing angiogenesis, provoking osteoblast and chondrocyte proliferation and migration, and negative regulation of matrix-degrading enzymes result in bone and cartilage recovery upon administration of MSCs-derived exosomes. Notwithstanding, insufficient quantity of isolated exosomes, lack of reliable potency test, and exosomes heterogeneity hurdle their application in clinics. Herein, we will deliver an outline respecting the advantages of MSCs-derived exosomes-based therapy in common bone- and joint-associated musculoskeletal disorders. Moreover, we will have a glimpse the underlying mechanism behind the MSCs-elicited therapeutic merits in these conditions.

Research Progress of Macrophages in Bone Regeneration

Bone tissue regeneration plays an increasingly important role in contemporary clinical treatment. The reconstruction of bone defects remains a huge challenge for clinicians. Bone regeneration is regulated by the immune system, in which inflammation is an important regulating factor in bone formation and remodeling. As the main cells involved in inflammation, macrophages play a key role in osteogenesis by polarizing into different phenotypes during different stages of bone regeneration. Considering this, this review mainly summarizes the function of macrophage in bone regeneration based on mesenchymal stem cells (MSCs), osteoblasts, osteoclasts, and vascular cells. In conclusion, anti-inflammatory macrophages (M2) have a greater potentiality to promote bone regeneration than M0 and classically activated proinflammatory macrophages (M1). In the fracture and bone defect models, tissue engineering materials can induce the transition from M1 to M2, alter the bone microenvironment, and promote bone regeneration through interactions with bone-related cells and blood vessels. The review provides a further understanding of macrophage polarization behavior in the evolving field of bone immunology.

A comparative study of bone bioactivity and osteogenic potential of different bioceramics in methacrylated collagen hydrogels

Biomimetic scaffolds composed of bioactive ceramic-based materials incorporated within a polymeric framework have shown immense promise for use in bone tissue engineering (BTE) applications. However, studies on direct comparison of the efficacy of different bioceramics on bone bioactivity and osteogenic differentiation are lacking. Herein, we performed an in vitro direct comparison of three different bioceramics-Bioglass 45S5 (BG), Laponite XLG (LAP), and β-Tricalcium Phosphate (TCP)-on the physical properties and bone bioactivity of methacrylated collagen (CMA) hydrogels (10% w/w bioceramic:CMA). In addition, human MSCs (hMSCs) were encapsulated in bioceramic-laden CMA hydrogels and the effect of different bioceramics on osteogenic differentiation of hMSCs was investigated in two different culture medium-osteoconductive (without dexamethasone [DEX]) and osteoinductive (with DEX). Results showed that the stability of CMA hydrogels was maintained upon bioceramic addition. Compression testing revealed that BG incorporation significantly decreased (p < 0.05) the modulus of photochemically crosslinked CMA hydrogels. Incubation of TCP-CMA and LAP-CMA hydrogels in simulated body fluid showed deposition of hydroxycarbonate apatite layer on the surface indicating that these hydrogels may be more bone bioactive than BG-CMA and CMA only hydrogels. Cell cytoskeleton staining results showed greater cell spreading in TCP-CMA hydrogels. Furthermore, TCP incorporation significantly increased alkaline phosphatase activity (ALP; p < 0.05) in hMSCs. Together, these results indicate that TCP has superior osteogenic potential compared with BG and LAP and hence should be considered as a bioceramic of preferred choice for use in the biomimetic design of cell-laden hydrogels for BTE applications.

Rapid fabrication and screening of tailored functional 3D biomaterials: Validation in bone tissue repair - Part II

Regenerative medicine strategies place increasingly sophisticated demands on 3D biomaterials to promote tissue formation at sites where tissue would otherwise not form. Ideally, the discovery/fabrication of the 3D scaffolds needs to be high-throughput and uniform to ensure quick and in-depth analysis in order to pinpoint appropriate chemical and mechanical properties of a biomaterial. Herein we present a versatile technique to screen new potential biocompatible acrylate-based 3D scaffolds with the ultimate aim of application in tissue repair. As part of this process, we identified an acrylate-based 3D porous scaffold that promoted cell proliferation followed by accelerated tissue formation, pre-requisites for tissue repair. Scaffolds were fabricated by a facile freeze-casting and an in-situ photo-polymerization route, embracing a high-throughput synthesis, screening and characterization protocol. The current studies demonstrate the dependence of cellular growth and vascularization on the porosity and intrinsic chemical nature of the scaffolds, with tuneable 3D scaffolds generated with large, interconnected pores suitable for cellular growth applied to skeletal reparation. Our studies showed increased cell proliferation, collagen and ALP expression, while chorioallantoic membrane assays indicated biocompatibility and demonstrated the angiogenic nature of the scaffolds. VEGRF2 expression in vivo observed throughout the 3D scaffolds in the absence of growth factor supplementation demonstrates a potential for angiogenesis. This novel platform provides an innovative approach to 3D scanning of synthetic biomaterials for tissue regeneration.

EGFL7 Secreted By Human Bone Mesenchymal Stem Cells Promotes Osteoblast Differentiation Partly Via Downregulation Of Notch1-Hes1 Signaling Pathway

BACKGROUND

Epidermal growth factor-like domain protein 7 (EGFL7) is a secreted protein that is differentially expressed in the bone microenvironment; however, the effect of EGFL7 on the osteogenesis of human bone marrow mesenchymal stem cells (hBMSCs) is largely unknown.

METHODS

EGFL7 expression in the fracture microenvironment was analyzed based on the Gene Expression Omnibus (GEO) database. Knockdown of EGFL7 by small interfering RNA (siRNA) and in vitro stimulation with recombinant human EGFL7 (rhEGFL7) protein were used to assess alterations in downstream signaling and changes in the osteogenic differentiation and proliferation of hBMSCs. A γ-secretase inhibitor was used to further explore whether inhibition of Notch signaling rescued the osteogenic-inhibitory effect of EGFL7 knockdown in hBMSCs. A femoral defect model was established to verify the effect of recombinant mouse EGFL7 on bone healing in vivo.

RESULTS

EGFL7 expression increased during hBMSC osteogenesis. Knockdown of EGFL7 impaired hBMSC osteogenesis and activated Notch1/NICD/Hes1 signaling. rhEGFL7 promoted hBMSC osteogenesis and downregulated Notch1 signaling. The osteoblast-inhibitory effect of EGFL7 knockdown was rescued by Notch1 signaling inhibition. Recombinant EGFL7 led to enhanced bone healing in mice with femoral defects.

CONCLUSIONS

EGFL7 promotes osteogenesis of hBMSCs partly via downregulation of Notch1 signaling.

Influence of the contact area of the sub-antral space with sinus bone and the Schneiderian membrane on osteogenesis in lateral window sinus elevation surgery: a prospective experiment

BACKGROUND

Osteogenesis of lateral window sinus elevation surgery is the key to placement of the subsequent implant, excessive collapse of the sub-antral space may adversely affect long-term stability of implants. At present, few studies focus on the influence of the contact area of the sub-antral space on osteogenesis. This study evaluated whether the change in the contact area of the sub-antral space with maxillary sinus bone and the Schneiderian membrane can affect osteogenesis.

METHODS

Cone beam computed tomography (CBCT) images were collected of patients requiring maxillary sinus floor elevation (residual bone height < 6 mm) for standard-length implant placement before surgery, after surgery, and at 6-month follow-up visits. The postoperative sub-antral space volume (V₁) and surface area (S₁), and the remaining volume after six months of healing (V₂) were measured. Then, the contact area of sub-antral space with maxillary sinus bone (S_bc) and the Schneiderian membrane (S_mc), the absorbed volume during healing (V_a), and the percentage of remaining volume (V₂%) and absorbed volume (V_a%) were calculated. The correlation between anatomical parameters was analyzed using multiple linear regression.

RESULTS

A total of 62 maxillary sinuses from 56 patients were augmented, of which 57 were considered for the final analysis (5 withdrew due to perforation). Multiple linear regression results demonstrated that S_bc was significantly positively correlated with V_a (β coefficient = 0.141, p < 0.01) without correlation between S_mc and V_a (β coefficient =  - 0.046, p = 0.470). There was a positive correlation between S_bc and V₂% (β coefficient = 2.269, p < 0.05).

CONCLUSIONS

This study confirmed that the size of the S_bc in lateral window sinus elevation surgery affected osteogenesis after six months of healing. Clinicians should assess the sinus contour type preoperatively, then consider whether it is necessary to expand the range of the Schneiderian membrane elevation to avoid excessive collapse of the sub-antral space.

TRIAL REGISTRATION

Chinese Clinical Trial Registry (ChiCTR), ChiCTR2200057924. Registered 22 March 2022-Retrospectively registered.

Advancement in the Treatment of Osteoporosis and the Effects on Bone Healing

Osteoporosis (OP) is a major global health concern, with aging being one of the most important risk factors. Osteoarthritis (OA) is also an age-related disorder. Patients with OP and/or OA may be treated surgically for fractures or when their quality of life is impaired. Poor bone quality due to OP can seriously complicate the stability of a bone fixation construct and/or surgical fracture treatment. This review summarizes the current knowledge on the pathophysiology of normal and osteoporotic bone healing, the effect of a bone fracture on bone turnover markers, the diagnosis of a low bone mineral density (BMD) before surgical intervention, and the effect of available anti-osteoporosis treatment. Interventions that improve bone health may enhance the probability of favorable surgical outcomes. Fracture healing and the treatment of atypical femoral fractures are also discussed.

Role of the Hypoxic-Secretome in Seed and Soil Metastatic Preparation

During tumor growth, the delivery of oxygen to cells is impaired due to aberrant or absent vasculature. This causes an adaptative response that activates the expression of genes that control several essential processes, such as glycolysis, neovascularization, immune suppression, and the cancer stemness phenotype, leading to increased metastasis and resistance to therapy. Hypoxic tumor cells also respond to an altered hypoxic microenvironment by secreting vesicles, factors, cytokines and nucleic acids that modify not only the immediate microenvironment but also organs at distant sites, allowing or facilitating the attachment and growth of tumor cells and contributing to metastasis. Hypoxia induces the release of molecules of different biochemical natures, either secreted or inside extracellular vesicles, and both tumor cells and stromal cells are involved in this process. The mechanisms by which these signals that can modify the premetastatic niche are sent from the primary tumor site include changes in the extracellular matrix, recruitment and activation of different stromal cells and immune or nonimmune cells, metabolic reprogramming, and molecular signaling network rewiring. In this review, we will discuss how hypoxia might alter the premetastatic niche through different signaling molecules.

Next-generation finely controlled graded porous antibacterial bioceramics for high-efficiency vascularization in orbital reconstruction

Eyeball loss due to severe ocular trauma, intraocular malignancy or infection often requires surgical treatment called orbital implant reconstruction to rehabilitate the orbital volume and restore the aesthetic appearance. However, it remains a challenge to minimize the postoperative exposure and infection complications due to the inert nature of conventional orbital implants. Herein, we developed a novel Ca–Zn-silicate bioceramic implant with multi-functions to achieve the expected outcomes. The porous hardystonite (Ca₂ZnSi₂O₇) scaffolds with triply periodic minimal surfaces (TPMS)-based pore architecture and graded pore size distribution from center to periphery (from 500 to 800 μm or vice versa) were fabricated through the digital light processing (DLP) technique, and the scaffolds with homogeneous pores (500 or 800 μm) were fabricated as control. The graded porous scaffolds exhibited a controlled bio-dissolving behavior and intermediate mechanical strength in comparison with the homogeneous counterparts, although all of porous implants presented significant antibacterial potential against S. aureus and E. coli. Meanwhile, the pore size-increasing scaffolds indicated more substantial cell adhesion, cell viability and angiogenesis-related gene expression in vitro. Furthermore, the gradually increasing pore feature exhibited a stronger blood vessel infiltrating potential in the dorsal muscle embedding model, and the spherical implants with such pore structure could achieve complete vascularization within 4 weeks in the eyeball enucleation rabbit models. Overall, our results suggested that the novel antibacterial hardystonite bioceramic with graded pore design has excellent potential as a next-generation orbital implant, and the pore topological features offer an opportunity for the improvement of biological performances in orbital reconstruction.

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The graded porous bioceramics were fabricated through computer-assisted design and digital light processing technique.

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The graded pore architecture could control the biodegradation and mechanical behavior of porous bioceramics.

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The porous Ca-Zn-silicate bioceramics exhibited significant antibacterial potentials against S. aureus and E. coli.

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The gradually increasing pore size feature of scaffolds contributes to cell activity and vascular infiltration.

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The graded porous bioceramics implants achieved complete vascularization within 4 weeks in the enucleation animal model.

Systematic review on the application of 3D-bioprinting technology in orthoregeneration: current achievements and open challenges

BACKGROUND

Joint degeneration and large or complex bone defects are a significant source of morbidity and diminished quality of life worldwide. There is an unmet need for a functional implant with near-native biomechanical properties. The potential for their generation using 3D bioprinting (3DBP)-based tissue engineering methods was assessed. We systematically reviewed the current state of 3DBP in orthoregeneration.

METHODS

This review was performed using PubMed and Web of Science. Primary research articles reporting 3DBP of cartilage, bone, vasculature, and their osteochondral and vascular bone composites were considered. Full text English articles were analyzed.

RESULTS

Over 1300 studies were retrieved, after removing duplicates, 1046 studies remained. After inclusion and exclusion criteria were applied, 114 articles were analyzed fully. Bioink material types and combinations were tallied. Cell types and testing methods were also analyzed. Nearly all papers determined the effect of 3DBP on cell survival. Bioink material physical characterization using gelation and rheology, and construct biomechanics were performed. In vitro testing methods assessed biochemistry, markers of extracellular matrix production and/or cell differentiation into respective lineages. In vivo proof-of-concept studies included full-thickness bone and joint defects as well as subcutaneous implantation in rodents followed by histological and µCT analyses to demonstrate implant growth and integration into surrounding native tissues.

CONCLUSIONS

Despite its relative infancy, 3DBP is making an impact in joint and bone engineering. Several groups have demonstrated preclinical efficacy of mechanically robust constructs which integrate into articular joint defects in small animals. However, notable obstacles remain. Notably, researchers encountered pitfalls in scaling up constructs and establishing implant function and viability in long term animal models. Further, to translate from the laboratory to the clinic, standardized quality control metrics such as construct stiffness and graft integration metrics should be established with investigator consensus. While there is much work to be done, 3DBP implants have great potential to treat degenerative joint diseases and provide benefit to patients globally.

New use for old drug: Local delivery of puerarin facilitates critical-size defect repair in rats by promoting angiogenesis and osteogenesis

Objectives

Methods

Results

Conclusion

The Translational Potential of this Article

Recent advances and trends in the applications of MXene nanomaterials for tissue engineering and regeneration

MXene, as a new two-dimensional nanomaterial, is endowed with lots of particular properties, such as large surface area, excellent conductivity, biocompatibility, biodegradability, hydrophilicity, antibacterial activity, and so on. In the past few years, MXene nanomaterials have become a rising star in biomedical fields including biological imaging, tumor diagnosis, biosensor, and tissue engineering. In this review, we sum up the recent applications of MXene nanomaterials in the field of tissue engineering and regeneration. First, we briefly introduced the synthesis and surface modification engineering of MXene. Then we focused on the application and development of MXene and MXene-based composites in skin, bone, nerve and heart tissue engineering. Uniquely, we also paid attention to some research on MXene with few achievements at present but might become a new trend in tissue engineering and regeneration in the future. Finally, this paper will also discuss several challenges faced by MXene nanomaterials in the clinical application of tissue engineering.

Vascular Endothelial Growth Factor Mimetic Peptide and Parathyroid Hormone (1-34) Delivered via a Blue-Light-Curable Hydrogel Synergistically Accelerate Bone Regeneration

Safe and effective biomaterials are in urgent clinical need for tissue regeneration and bone repair. While numerous advances have been made on hydrogels promoting osteogenesis in bone formation, co-stimulation of the angiogenic pathways in this process remains to be exploited. Here, we have developed a gelatin-based blue-light-curable hydrogel system, functionalized with an angiogenic vascular endothelial growth factor (VEGF) mimetic peptide, KLTWQELYQLKYKGI (KLT), and an osteoanabolic peptide, parathyroid hormone (PTH) 1-34. We have discovered that the covalent modification of gelatin scaffold with peptides can modulate the physical properties and biological activities of the produced hydrogels. Furthermore, we have demonstrated that those two peptides orchestrate synergistically and promote bone regeneration in a rat cranial bone defect model with remarkable efficacy. This dual-peptide-functionalized hydrogel system may serve as a promising lead to functional biomaterials in bone repair and tissue engineering.

Tracking Strain-Specific Morphogenesis and Angiogenesis of Murine Calvaria with Large-Scale Optoacoustic and Ultrasound Microscopy

Skull bone development is a dynamic and well-coordinated process playing a key role in maturation and maintenance of the bone marrow (BM), fracture healing, and progression of diseases such as osteoarthritis or osteoporosis. At present, dynamic transformation of the growing bone (osteogenesis) as well as its vascularization (angiogenesis) remain largely unexplored due to the lack of suitable in vivo imaging techniques capable of noninvasive visualization of the whole developing calvaria at capillary-level resolution. We present a longitudinal study on skull bone development using ultrasound-aided large-scale optoacoustic microscopy (U-LSOM). Skull bone morphogenesis and microvascular growth patterns were monitored in three common mouse strains (C57BL/6J, CD-1, and Athymic Nude-Foxn1nu) at the whole-calvaria scale over a 3-month period. Strain-specific differences in skull development were revealed by quantitative analysis of bone and vessel parameters, indicating the coupling between angiogenesis and osteogenesis during skull bone growth in a minimally invasive and label-free manner. The method further enabled identifying BM-specific sinusoidal vessels, and superficial skull vessels penetrating into BM compartments. Our approach furnishes a new high-throughput longitudinal in vivo imaging platform to study morphological and vascular skull alterations in health and disease, shedding light on the critical links between blood vessel formation, skull growth, and regeneration. © 2022 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Developing a novel calcium magnesium silicate/graphene oxide incorporated silk fibroin porous scaffold with enhanced osteogenesis, angiogenesis and inhibited osteoclastogenesis

Recently, biofunctional ions (Mg2+, Si4+, etc.) and graphene derivatives are proved to be promising in stimulating bone formation. In this study, a novel inorganic/organic composite porous scaffold based on silk fibroin (SF), graphene oxide (GO), and calcium magnesium silicate (CMS) was developed for bone repair. The porous scaffolds obtained by lyophilization showed a little difference in pore structure while GO and CMS displayed a good interaction with SF matrix. The addition of CMS with good mineralization potential and sustainedly release ability of biofunctional ions (Ca2+, Mg2+ and Si4+) increased the strength of SF scaffolds a little and facilitated the osteogenic differentiation of bone mesenchymal stem cells (BMSCs) by upregulating bone formation-related genes (ALP, COL1, OC and Runx2). The further incorporation of GO in SF scaffolds enhanced the compressive strength and water retention, and also remarkably promoted the osteogenic differentiation of BMSCs. Besides, the angiogenesis of human umbilical vein endothelial cells was significantly promoted by CMS/GO/SF scaffold extract through the upregulation of angiogenesis genes (eNOs and bFGF). Moreover, the osteoclastic formation ability of RAW264.7 cells was suppressed by the released ions from CMS/GO/SF scaffold through the down-regulation of CAK, MMP9 and TRAP. The promoted osteogenesis, angiogenesis and inhibited osteoclastogenesis functions of CMS/GO/SF composite scaffold may enable it as a novel therapy for bone repair and regeneration.

Low-Intensity Pulsed Ultrasound Stimulation for Bone Fractures Healing: A Review

Low-intensity pulsed ultrasound (LIPUS) is a developing technology, which has been proven to improve fracture healing process with minimal thermal effects. This noninvasive treatment accelerates bone formation through various molecular, biological, and biomechanical interactions with tissues and cells. Although LIPUS treatment has shown beneficial effects on different bone fracture locations, only very few studies have examined its effects on deeper bones. This study provides an overview on therapeutic ultrasound for fractured bones, possible mechanisms of action, clinical evidences, current limitations, and its future prospects.

Effect of Inter-Fragmentary Gap Size on Neovascularization During Bone Healing: A Micro-CT Imaging Study

Introduction: Neovascularization of the fracture site is of great importance for bone healing and could be influenced by local mechanical environment such as fixation stability and inter-fragmentary gap size. This study aims to reconstruct the neovascularization of the fracture site and explore the effect of inter-fragmentary gap size on the spatiotemporal structure of vascularity during bone healing.

Methods: Osteotomy was performed on 36 Sprague–Dawley (SD) rats on the right tibial diaphysis, and the fracture was given stable fixation with two different inter-fragmentary gap sizes. SD rats received stable fixation with either a small-sized inter-fragmentary gap (FSF1, 1 mm, n = 18) or a large-sized one (FSF3, 3 mm, n = 18). The left hind limbs were treated as the control group (CON). The animals were killed at different time points (2, 4, and 6 weeks postoperatively, n = 6, respectively) for vascular perfusion and micro-CT imaging.

Results: (a) At week 2 and 4, FSF1 group showed significantly higher vessel volume ratio (VV/TV) and vessel surface density (VS/TV) values than both CON and FSF3 group; there was no significant difference in either VV/TV or VS/TV values between CON and FSF3 groups. (b) At week 6, both FSF1 and FSF3 groups showed significantly higher VV/TV and VS/TV values than CON group; FSF3 group had a significantly higher VV/TV value than FSF1 group.

Conclusion: Different inter-fragmentary gap sizes greatly affect the timing of angiogenesis at the fracture site. Stable fixation with a small inter-fragmentary gap (1 mm) benefits neovascularization at the early stages during bone healing and reconstruction, while stable fixation with a large inter-fragmentary gap (3 mm) delays the occurrence of angiogenesis to a later phase.

The vascularization paradox of non-union formation

Despite major research efforts to elucidate mechanisms of non-union formation, failed fracture healing remains a common complication in orthopedic surgery. Adequate vascularization has been recognized as a crucial factor for successful bone regeneration, as newly formed microvessels guarantee the supply of the callus tissue with vital oxygen, nutrients, and growth factors. Accordingly, a vast number of preclinical studies have focused on the development of vascularization strategies to stimulate fracture repair. However, recent evidence suggests that stimulation of blood vessel formation is an oversimplified approach to support bone regeneration. This review discusses the role of vascularization during bone regeneration and delineates a phenomenon, for which we coin the term “the vascularization paradox of non-union-formation”. This view is based on the results of a variety of experimental studies that suggest that the callus tissue of non-unions is indeed densely vascularized and that pro-angiogenic mediators, such as vascular endothelial growth factor, are sufficiently expressed at the facture site. By gaining further insights into the molecular and cellular basis of non-union vascularization, it may be possible to develop more optimized treatment approaches or even prevent the non-union formation in the future.

Does new bone formation vary in different sites within the same maxillary sinus after lateral augmentation? A prospective histomorphometric study

OBJECTIVE

The aim of this study was to evaluate histomorphometric outcomes of lateral maxillary sinus augmentation in different areas of the same cavity and to correlate results to bucco-palatal sinus width (SW) and residual bone height (RBH).

MATERIAL AND METHODS

Patients needing maxillary sinus floor elevation (RBH <5 mm) to insert two nonadjacent implants were treated with lateral augmentation using a composite graft. Six months later, two bone-core biopsies (mesial/distal) were retrieved in implant insertion sites. SW and RBH were measured on cone beam computed tomography, and correlations between histomorphometric and anatomical parameters were evaluated by multivariate linear regression analysis.

RESULTS

Twenty patients underwent sinus augmentation, and eighteen were included in the final analysis (two dropouts for membrane perforation). Mean newly formed mineralized tissue percentage (%NFMT) after 6 months in mesial and distal sites was 17.5 ± 4.7 and 11.6 ± 4.7, respectively (p = .0004). Multivariate linear regression showed a strong negative correlation between SW and %NFMT (β coefficient=-.774, p < .0001) and no correlation between RBH and %NFMT (β coefficient =-.038, p = .825).

CONCLUSIONS

The present study confirms that %NFMT after lateral sinus augmentation occurs at different rates in different anatomical areas of the same maxillary sinus, showing a strong negative correlation with SW, whereas no influence of RBH was observed. Clinicians should regard SW as a guide for graft selection and to decide duration of the healing period. Researchers should consider SW as a predictor variable, when comparing regenerative outcomes of different biomaterials by using maxillary sinus as an experimental model.

OUP accepted manuscript

Cells of the stromal vascular fraction (SVF) of human adipose tissue have the capacity to generate osteogenic grafts with intrinsic vasculogenic properties. However, cultured adipose-derived stromal cells (ASCs), even after minimal monolayer expansion, lose osteogenic capacity in vivo. Communication between endothelial and stromal/mesenchymal cell lineages has been suggested to improve bone formation and vascularization by engineered tissues. Here, we investigated the specific role of a subpopulation of SVF cells positive for T-cadherin (T-cad), a putative endothelial marker. We found that maintenance during monolayer expansion of a T-cad-positive cell population, composed of endothelial lineage cells (ECs), is mandatory to preserve the osteogenic capacity of SVF cells in vivo and strongly supports their vasculogenic properties. Depletion of T-cad-positive cells from the SVF totally impaired bone formation in vivo and strongly reduced vascularization by SVF cells in association with decreased VEGF and Adiponectin expression. The osteogenic potential of T-cad-depleted SVF cells was fully rescued by co-culture with ECs from a human umbilical vein (HUVECs), constitutively expressing T-cad. Ectopic expression of T-cad in ASCs stimulated mineralization in vitro but failed to rescue osteogenic potential in vivo, indicating that the endothelial nature of the T-cad-positive cells is the key factor for induction of osteogenesis in engineered grafts based on SVF cells. This study demonstrates that crosstalk between stromal and T-cad expressing endothelial cells within adipose tissue critically regulates osteogenesis, with VEGF and adiponectin as associated molecular mediators.

Lotus root and osteons-inspired channel structural scaffold mediate cell biomineralization and vascularized bone tissue regeneration

The interconnectivity of porous scaffold is vital for cell and tissue infiltration, and vascular networks formation, determining the successful bone regeneration in large bone defects. Here, inspired by the lotus-root and Haversian system of natural bone, a nano-hydroxyapatite/polyurethane (n-HA/PU) lotus root-like scaffold inlaid with micro holes on the wall of the adjacent channel was utilized to mediate cell biomineralization and vascularized bone tissue regeneration. Such a particular lotus-type structure remarkably promoted cells to proliferate and infiltrate into the center of the entire scaffold, serving as a clue to account for regulating cell alignment and differentiation physically. In vitro studies suggested that apatite accumulated dramatically on the channel wall in the lotus-type scaffold, probably promoting specific osteogenic differentiation of cells by the orientated channels, even in the absence of osteogenic factors. In vivo creation of critical bone defects (15-mm segments) was done in the radius of rabbits and implanted with the scaffold of different geometry to assess the structural parameters on the efficacy of new bone regeneration. The more extensive positive staining of BMP-2, more considerable amount of infiltrated capillary, more robust new bone formation, particularly the biomechanical strength of lotus-type scaffold group could reach the level of the control group without surgery, indicating that the lotus-type scaffold was more favorable for new bone tissue formation along tube-like channels. These results highlighted the potential of this biomimetic scaffold for cell and tissue infiltration and thus repair large bony defects.

Advanced PLGA hybrid scaffold with a bioactive PDRN/BMP2 nanocomplex for angiogenesis and bone regeneration using human fetal MSCs

Biodegradable polymers have been used with various systems for tissue engineering. Among them, poly(lactic-co-glycolic) acid (PLGA) has been widely used as a biomaterial for bone regeneration because of its great biocompatibility and biodegradability properties. However, there remain substantial cruxes that the by-products of PLGA result in an acidic environment at the implanting site, and the polymer has a weak mechanical property. In our previous study, magnesium hydroxide (MH) and bone extracellular matrix are combined with a PLGA scaffold (PME) to improve anti-inflammation and mechanical properties and osteoconductivity. In the present study, the development of a bioactive nanocomplex (NC) formed along with polydeoxyribonucleotide and bone morphogenetic protein 2 (BMP2) provides synergistic abilities in angiogenesis and bone regeneration. This PME hybrid scaffold immobilized with NC (PME/NC) achieves outstanding performance in anti-inflammation, angiogenesis, and osteogenesis. Such an advanced PME/NC scaffold suggests an integrated bone graft substitute for bone regeneration.

Collagen-based biocomposites inspired by bone hierarchical structures for advanced bone regeneration: ongoing research and perspectives

Bone is a hard-connective tissue composed of matrix, cells and bioactive factors with a hierarchical structure, where the matrix is mainly composed of type I collagen and hydroxyapatite. Collagen fibers assembled by collagen are the template for mineralization and make an important contribution to bone formation and the bone remodeling process. Therefore, collagen has been widely clinically used for bone/cartilage defect regeneration. However, pure collagen implants, such as collagen scaffolds or sponges, have limitations in the bone/cartilage regeneration process due to their poor mechanical properties and osteoinductivity. Different forms of collagen-based composites prepared by incorporating natural/artificial polymers or bioactive inorganic substances are characterized by their interconnected porous structure and promoting cell adhesion, while they improve the mechanical strength, structural stability and osteogenic activities of the collagen matrix. In this review, various forms of collagen-based biocomposites, such as scaffolds, sponges, microspheres/nanoparticles, films and microfibers/nanofibers prepared by natural/synthetic polymers, bioactive ceramics and carbon-based materials compounded with collagen are reviewed. In addition, the application of collagen-based biocomposites as cytokine, cell or drug (genes, proteins, peptides and chemosynthetic) delivery platforms for proangiogenesis and bone/cartilage tissue regeneration is also discussed. Finally, the potential application, research and development direction of collagen-based biocomposites in future bone/cartilage tissue regeneration are discussed.

Towards in silico Models of the Inflammatory Response in Bone Fracture Healing

In silico modeling is a powerful strategy to investigate the biological events occurring at tissue, cellular and subcellular level during bone fracture healing. However, most current models do not consider the impact of the inflammatory response on the later stages of bone repair. Indeed, as initiator of the healing process, this early phase can alter the regenerative outcome: if the inflammatory response is too strongly down- or upregulated, the fracture can result in a non-union. This review covers the fundamental information on fracture healing, in silico modeling and experimental validation. It starts with a description of the biology of fracture healing, paying particular attention to the inflammatory phase and its cellular and subcellular components. We then discuss the current state-of-the-art regarding in silico models of the immune response in different tissues as well as the bone regeneration process at the later stages of fracture healing. Combining the aforementioned biological and computational state-of-the-art, continuous, discrete and hybrid modeling technologies are discussed in light of their suitability to capture adequately the multiscale course of the inflammatory phase and its overall role in the healing outcome. Both in the establishment of models as in their validation step, experimental data is required. Hence, this review provides an overview of the different in vitro and in vivo set-ups that can be used to quantify cell- and tissue-scale properties and provide necessary input for model credibility assessment. In conclusion, this review aims to provide hands-on guidance for scientists interested in building in silico models as an additional tool to investigate the critical role of the inflammatory phase in bone regeneration.

Troxerutin Stimulates Osteoblast Differentiation of Mesenchymal Stem Cell and Facilitates Bone Fracture Healing

Troxerutin (TRX), a semi-synthetic derivative of the natural bioflavonoid rutin, is a bioactive flavonoid widely abundant in various fruits and vegetables. Known as vitamin P4, TRX has been demonstrated to have several activities including anti-inflammation, anti-oxidants, vasoprotection, and immune support in various studies. Although rutin, the precursor of troxerutin, was reported to have a protective role against bone loss, the function of TRX in skeletal system remains unknown. In the present study, we found that TRX promoted osteogenic differentiation of human mesenchymal stem cells (MSCs) in a concentration-dependent manner by stimulating the alkaline phosphatase (ALP) activity, calcium nodule formation and osteogenic marker genes expression in vitro. The further investigation demonstrated that TRX stimulated the expression of the critical transcription factor β-catenin and several downstream target genes of Wnt signaling, thus activated Wnt/β-catenin signaling. Using a femur fracture rats model, TRX was found to stimulate new bone formation and accelerate the fracture healing in vivo. Collectively, our data demonstrated that TRX could promote osteogenesis in vitro and facilitate the fracture healing in vivo, indicating that TRX may be a promising therapeutic candidate for bone fracture repair.

Spatiotemporal blood vessel specification at the osteogenesis and angiogenesis interface of biomimetic nanofiber-enabled bone tissue engineering

While extensive research has demonstrated an interdependent role of osteogenesis and angiogenesis in bone tissue engineering, little is known about how functional blood vessel networks are organized to initiate and facilitate bone tissue regeneration. Building upon the success of a biomimetic composite nanofibrous construct capable of supporting donor progenitor cell-dependent regeneration, we examined the angiogenic response and spatiotemporal blood vessel specification at the osteogenesis and angiogenesis interface of cranial bone defect repair utilizing high resolution multiphoton laser scanning microscopy (MPLSM) in conjunction with intravital imaging. We demonstrate here that the regenerative vasculature can be specified as arterial and venous capillary vessels based upon endothelial surface markers of CD31 and Endomucin (EMCN), with CD31⁺EMCN^- vessels exhibiting higher flowrate and higher oxygen tension (pO₂) than CD31⁺EMCN⁺ vessels. The donor osteoblast clusters are uniquely coupled to the sprouting CD31⁺EMCN⁺ vessels connecting to CD31⁺EMCN^- vessels. Further analyses reveal differential vascular response and vessel type distribution in healing and non-healing defects, associated with changes of gene sets that control sprouting and morphogenesis of blood vessels. Collectively, our study highlights the key role of spatiotemporal vessel type distribution in bone tissue engineering, offering new insights for devising more effective vascularization strategies for bone tissue engineering.

Gene activated scaffolds incorporating star-shaped polypeptide-pDNA nanomedicines accelerate bone tissue regeneration in vivo

Increasingly, tissue engineering strategies such as the use of biomaterial scaffolds augmented with specific biological cues are being investigated to accelerate the regenerative process. For example, significant clinical challenges still exist in efficiently healing large bone defects which are above a critical size. Herein, we describe a cell-free, biocompatible and bioresorbable scaffold incorporating a novel star-polypeptide biomaterial as a gene vector. This gene-loaded scaffold can accelerate bone tissue repair in vivo in comparison to a scaffold alone at just four weeks post implantation in a critical sized bone defect. This is achieved via the in situ transfection of autologous host cells which migrate into the implanted collagen-based scaffold via gene-loaded, star-shaped poly(l-lysine) polypeptides (star-PLLs). In vitro, we demonstrate that star-PLL nanomaterials designed with 64 short poly(l-lysine) arms can be used to functionalise a range of collagen based scaffolds with a dual therapeutic cargo (pDual) of the bone-morphogenetic protein-2 plasmid (pBMP-2) and vascular endothelial growth factor plasmid (pVEGF). The versatility of this polymeric vector is highlighted in its ability to transfect Mesenchymal Stem Cells (MSCs) with both osteogenic and angiogenic transgenes in a 3D environment from a range of scaffolds with various macromolecular compositions. In vivo, we demonstrate that a bone-mimetic, collagen-hydroxyapatite scaffold functionalized with star-PLLs containing either 32- or 64- poly(l-lysine) arms can be used to successfully deliver this pDual cargo to autologous host cells. At the very early timepoint of just 4 weeks, we demonstrate the 64-star-PLL-pDual functionalised scaffold as a particularly efficient platform to accelerate bone tissue regeneration, with a 6-fold increase in new bone formation compared to a scaffold alone. Overall, this article describes for the first time the incorporation of novel star-polypeptide biomaterials carrying two therapeutic genes into a cell free scaffold which supports accelerated bone tissue formation in vivo.

A self-powered implantable and bioresorbable electrostimulation device for biofeedback bone fracture healing

Electrostimulation has been recognized as a promising nonpharmacological treatment in orthopedics to promote bone fracture healing. However, clinical applications have been largely limited by the complexity of equipment operation and stimulation implementation. Here, we present a self-powered implantable and bioresorbable bone fracture electrostimulation device, which consists of a triboelectric nanogenerator for electricity generation and a pair of dressing electrodes for applying electrostimulations directly toward the fracture. The device can be attached to irregular tissue surfaces and provide biphasic electric pulses in response to nearby body movements. We demonstrated the operation of this device on rats and achieved effective bone fracture healing in as short as 6 wk versus the controls for more than 10 wk to reach the same healing result. The optimized electrical field could activate relevant growth factors to regulate bone microenvironment for promoting bone formation and bone remodeling to accelerate bone regeneration and maturation, with statistically significant 27% and 83% improvement over the control groups in mineral density and flexural strength, respectively. This work provided an effective implantable fracture therapy device that is self-responsive, battery free, and requires no surgical removal after fulfilling the biomedical intervention.

Mechanosensitive Piezo1 in endothelial cells promotes angiogenesis to support bone fracture repair

Piezo1, a calcium-permeable non-selective cationic channel that senses mechanical stimulation in multicellular organisms, mediates various biological processes, including angiogenesis. The supply of nutrients and oxygen through newly formed blood vessels at the fractured lesion is critical for bone fracture repair. The elucidation of the underlying mechanisms involved in angiogenesis and bone repair can aid in improving fracture healing. Here, mice with endothelial cell-specific deletion of Piezo1 channels were used to examine the role of Piezo1 in the initiation of fracture healing. The expression and distribution of Piezo1 was explored in the vasculature of the bone. The deletion of endothelial Piezo1 resulted in impaired bone fracture repair, downregulation of calcium-activated proteolytic calpain activity during vascularization, inhibition of osteoblast maturation and ossification, downregulation of phosphorylated PI3K-AKT, and impaired Notch signaling during bone fracture union. These findings indicated that Piezo1 protein is a potential target for enhancing bone regeneration and treating delayed or nonunion bone fractures.

Multi-Dimensional Printing for Bone Tissue Engineering

The development of 3D printing has significantly advanced the field of bone tissue engineering by enabling the fabrication of scaffolds that faithfully recapitulate desired mechanical properties and architectures. In addition, computer-based manufacturing relying on patient-derived medical images permits the fabrication of customized modules in a patient-specific manner. In addition to conventional 3D fabrication, progress in materials engineering has led to the development of 4D printing, allowing time-sensitive interventions such as programed therapeutics delivery and modulable mechanical features. Therapeutic interventions established via multi-dimensional engineering are expected to enhance the development of personalized treatment in various fields, including bone tissue regeneration. Here, recent studies utilizing 3D printed systems for bone tissue regeneration are summarized and advances in 4D printed systems are highlighted. Challenges and perspectives for the future development of multi-dimensional printed systems toward personalized bone regeneration are also discussed.

Use of Osteobiologics for Fracture Management: The When, What, and How

Osteobiologics are defined as a group of natural and synthetic materials used to augment bone healing. The selection of the most appropriate osteobiologic from the growing list of available options can be a challenging task. In selecting a material, surgeons should weigh a variety of considerations, including the indication for their use (the when), the most suitable substance (the what), and the correct mode of application (the how). This summary reviews these considerations and seeks to provide the surgeon with a basis for informed clinical evidence-based decision-making in their choice of a successful option.

Proangiogenic Effect of 2A-Peptide Based Multicistronic Recombinant Constructs Encoding VEGF and FGF2 Growth Factors

Coronary artery disease remains one of the primary healthcare problems due to the high cost of treatment, increased number of patients, poor clinical outcomes, and lack of effective therapy. Though pharmacological and surgical treatments positively affect symptoms and arrest the disease progression, they generally exhibit a limited effect on the disease outcome. The development of alternative therapeutic approaches towards ischemic disease treatment, especially of decompensated forms, is therefore relevant. Therapeutic angiogenesis, stimulated by various cytokines, chemokines, and growth factors, provides the possibility of restoring functional blood flow in ischemic tissues, thereby ensuring the regeneration of the damaged area. In the current study, based on the clinically approved plasmid vector pVax1, multigenic constructs were developed encoding vascular endothelial growth factor (VEGF), fibroblast growth factors (FGF2), and the DsRed fluorescent protein, integrated via picornaviruses' furin-2A peptide sequences. In vitro experiments demonstrated that genetically modified cells with engineered plasmid constructs expressed the target proteins. Overexpression of VEGF and FGF2 resulted in increased levels of the recombinant proteins. Concomitantly, these did not lead to a significant shift in the general secretory profile of modified HEK293T cells. Simultaneously, the secretome of genetically modified cells showed significant stimulating effects on the formation of capillary-like structures by HUVEC (endothelial cells) in vitro. Our results revealed that when the multicistronic multigene vectors encoding 2A peptide sequences are created, transient transgene co-expression is ensured. The results obtained indicated the mutual synergistic effects of the growth factors VEGF and FGF2 on the proliferation of endothelial cells in vitro. Thus, recombinant multicistronic multigenic constructs might serve as a promising approach for establishing safe and effective systems to treat ischemic diseases.

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.

Natural medicine delivery from biomedical devices to treat bone disorders: A review

With an increasing life expectancy and aging population, orthopedic defects and bone graft surgeries are increasing in global prevalence. Research to date has advanced the understanding of bone biology and defect repair mechanism, leading to a marked success in the development of synthetic bone substitutes. Yet, the quest for functionalized bone grafts prompted the researchers to find a viable alternative that regulates cellular activity and supports bone regeneration and healing process without causing serious side-effects. Recently, researchers have introduced natural medicinal compounds (NMCs) in bone scaffold that enables them to release at a desirable rate, maintains a sustained release allowing sufficient time for tissue in-growth, and guides bone regeneration process with minimized risk of tissue toxicity. According to World Health Organization (WHO), NMCs are gaining popularity in western countries for the last two decades and are being used by 80% of the population worldwide. Compared to synthetic drugs, NMCs have a broader range of safety window and thus suitable for prolonged localized delivery for bone regeneration. There is limited literature focusing on the integration of bone grafts and natural medicines that provides detailed scientific evidences on NMCs, their toxic limits and particular application in bone tissue engineering, which could guide the researchers to develop functionalized implants for various bone disorders. This review will discuss the emerging trend of NMC delivery from bone grafts, including 3D-printed structures and surface-modified implants, highlighting the significance and potential of NMCs for bone health, guiding future paths toward the development of an ideal bone tissue engineering scaffold. STATEMENT OF SIGNIFICANCE: To date, additive manufacturing technology provids us with many advanced patient specific or defect specific bone constructs exhibiting three-dimensional, well-defined microstructure with interconnected porous networks for defect-repair applications. However, an ideal scaffold should also be able to supply biological signals that actively guide tissue regeneration while simultaneously preventing post-implantation complications. Natural biomolecules are gaining popularity in tissue engineering since they possess a safer, effective approach compared to synthetic drugs. The integration of bone scaffolds and natural biomolecules exploits the advantages of customized, multi-functional bone implants to provide localized delivery of biochemical signals in a controlled manner. This review presents an overview of bone scaffolds as delivery systems for natural biomolecules, which may provide prominent advancement in bone development and improve defect-healing caused by various musculoskeletal disorders.

Functionalization of Synthetic Bone Substitutes

Bone substitutes have been applied to treat osseous defects for a long time. To prevent implant related infection (IRI) and enhance bone healing functionalized biomaterials, antibiotics and osteoinductive substances have been introduced. This study gives an overview of the current available surface-coated bone substitutes and provides an outlook for future perspectives.

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.

Bifunctional hydrogel for potential vascularized bone tissue regeneration

Most of the synthetic polymer-based hydrogels lack the intrinsic properties needed for tissue engineering applications. Here, we describe a biomimetic approach to induce the mineralization and vascularization of poly(ethylene glycol) (PEG)-based hydrogel to template the osteogenic activities. The strategy involves the covalent functionalization of oligo[poly(ethylene glycol) fumarate] (OPF) with phosphate groups and subsequent treatment of phosphorylated-OPF (Pi-OPF) hydrogels with alkaline phosphatase enzyme (ALP) and calcium. Unlike previously reported studies for ALP induced mineralization, in this study, the base polymer itself was modified with the phosphate groups for uniform mineralization of hydrogels. In addition to improvement of mechanical properties, enhancement of MC3T3-E1 cell attachment and proliferation, and promotion of mesenchymal stem cells (MSC) differentiation were observed as the intrinsic benefits of such mineralization. Current bone tissue engineering (BTE) research endeavors are also extensively focused on vascular tissue regeneration due to its inherent advantages in bone regeneration. Taking this into account, we further functionalized the mineralized hydrogels with FG-4592, small hypoxia mimicking molecule. The functionalized hydrogels elicited upregulated in vitro angiogenic activities of human umbilical vein endothelial cells (HUVEC). In addition, when implanted subcutaneously in rats, enhanced early vascularization activities around the implantation site were observed as demonstrated by the immunohistochemistry results. This further leveraged the formation of calcified tissues at the implantation site at later time points evident through X-ray imaging. The overall results here show the perspectives of bifunctional OPF hydrogels for vascularized BTE.

Mechanisms of bone blood flow regulation in humans

Bone is a highly vascularized tissue. However, despite the importance of appropriate circulation for bone health, regulation of bone blood flow remains poorly understood. Invasive animal studies suggest that sympathetic activity plays an important role in bone flow control. However, it remains unknown if bone vasculature evidences robust vasoconstriction in response to sympathoexcitatory stimuli. Here, we characterized bone blood flow in young healthy individuals [n = 13, (four females)] in response to isometric handgrip exercise (IHE) and cold pressor test (CPT). These provide a strong stimulus for active vasoconstriction in the inactive muscle, and perhaps also in the bone. During sustained IHE to fatigue and CPT, we measured blood pressure, whole leg blood flow, and tibial perfusion using near-infrared spectroscopy. Tibia perfusion was determined as oxy- and deoxyhemoglobin. For both stimuli, tibial metabolism remained constant (i.e., no change in deoxyhemoglobin) and thus tibial arterial perfusion was represented by oxyhemoglobin. During IHE, oxyhemoglobin declined (beginning -0.20 ± 1.04 μM; end -1.13 ± 3.71 μM, both P < 0.01) slower than whole leg blood flow (beginning -0.85 ± 1.02 cm/s; end -2.72 ± 1.64 cm/s, both P < 0.01). However, during CPT, both oxyhemoglobin (beginning -0.46 ± 1.43 μM; end -0.60 ± 1.59 μM, both P < 0.01) and whole leg blood flow (beginning -1.52 ± 1.63 cm/s; end -0.69 ± 1.51 cm/s, both P < 0.01) declined with a similar timecourse, even though the magnitudes of decline were smaller than during IHE. These responses are likely due to the different timecourses of sympathetically mediated vasoconstriction in bone and muscle. These results indicate that sympathetic innervation of the bone vasculature serves a functional role in the control of flow in young healthy individuals.NEW & NOTEWORTHY The current study is the first one to noninvasively investigate control of bone blood perfusion in vivo in humans, on a moment-by-moment basis. Our results indicate that tibial bone vasculature demonstrates active vasoconstriction in response to sympathoexcitatory stimuli in young healthy individuals. Compared with whole leg vasculature, bone vasoconstrictor response seems to be smaller, delayed, and more variable.

Comparison and Contrast of Bone and Dentin in Genetic Disorder, Morphology and Regeneration: A Review

The bone and dentin have distinct healing processes. The healing process of bones is regenerative, as newly formed tissues are morphologically and functionally similar to the original bone structures. In contrast, the healing process of dentin is reparative due to its failure to replicate some of its key morphological features. In this review, we compare and contrast the healing processes of bone and dentin. We describe how distinct morphological and physiological structures of the 2 tissues translate into different signaling molecules, growth factors, and matrix protein secretion.