Evaluation of the osteo-inductive potential of hollow three-dimensional magnesium-strontium substitutes for the bone grafting application

Bone Tissue Engineering with Adipose-Derived Stem Cells in Polycaprolactone/Graphene Oxide/Dexamethasone 3D-Printed Scaffolds

We fabricated three-dimensional (3D)-printed polycaprolactone (PCL) and PCL/graphene oxide (GO) (PGO) scaffolds for bone tissue engineering. An anti-inflammatory and pro-osteogenesis drug dexamethasone (DEX) was adsorbed onto GO and a 3D-printed PGO/DEX (PGOD) scaffold successfully improved drug delivery with a sustained release of DEX from the scaffold up to 1 month. The physicochemical properties of the PCL, PGO, and PGOD scaffolds were characterized by various analytical techniques. The biological response of these scaffolds was studied for adherence, proliferation, and osteogenic differentiation of seeded rabbit adipose-derived stem cells (ASCs) from DNA assays, alkaline phosphatase (ALP) production, calcium quantification, osteogenic gene expression, and immunofluorescence staining of osteogenic marker proteins. The PGOD scaffold was demonstrated to be the best scaffold for maintaining cell viability, cell proliferation, and osteogenic differentiation of ASCs in vitro. In vivo biocompatibility of PGOD was confirmed from subcutaneous implantation in nude mice where ASC-seeded PGOD can form ectopic bones, demonstrated by microcomputed tomography (micro-CT) analysis and immunofluorescence staining. Furthermore, implantation of PGOD/ASCs constructs into critical-sized cranial bone defects in rabbits form tissue-engineered bones at the defect site, observed using micro-CT and histological analysis.

A comprehensive review on the role of strontium in biodegradable metals

Biodegradable metals, including magnesium, iron, and zinc alloys, have attracted extensive attention due to their good biodegradability and biocompatibility. However, the mechanical properties and corrosion rates of most biodegradable metallic materials have not yet reached the ideal level required for clinical applications. Strontium, as an element of Group IIA in the periodic table of elements, has similar chemical and biological properties to calcium. It can promote bone tissue development and increase bone strength. In addition, strontium can also promote angiogenesis and facilitate the repair of infarcted heart activity. Thus, strontium is commonly used as one of the most alloying elements to improve the in vitro and in vivo properties of biodegradable metals. Besides, strontium is also widely used in various bioactive coatings to improve the comprehensive properties of biodegradable metals. This paper outlines the role of strontium in the human body and summarizes recent research and applications of strontium-containing biodegradable metallic materials. Finally, this paper also provides an outlook on the challenges faced in applying and researching strontium in biodegradable metals.

Towards Stem Cell Therapy for Critical-Sized Segmental Bone Defects: Current Trends and Challenges on the Path to Clinical Translation

The management and reconstruction of critical-sized segmental bone defects remain a major clinical challenge for orthopaedic clinicians and surgeons. In particular, regenerative medicine approaches that involve incorporating stem cells within tissue engineering scaffolds have great promise for fracture management. This narrative review focuses on the primary components of bone tissue engineering-stem cells, scaffolds, the microenvironment, and vascularisation-addressing current advances and translational and regulatory challenges in the current landscape of stem cell therapy for critical-sized bone defects. To comprehensively explore this research area and offer insights for future treatment options in orthopaedic surgery, we have examined the latest developments and advancements in bone tissue engineering, focusing on those of clinical relevance in recent years. Finally, we present a forward-looking perspective on using stem cells in bone tissue engineering for critical-sized segmental bone defects.

Resveratrol facilitates bone formation in high-glucose conditions

Periodontitis is known to be affected by high-glucose conditions, which poses a challenge to periodontal tissue regeneration, particularly in bone formation. In this study, the potential effects of resveratrol (3,5,4'-trihydroxystilbene, RSV) in facilitating bone formation under high-glucose conditions after periodontitis has been investigated. We focused on the analysis of osteoblasts and periodontal ligament cells, which are essential for bone formation including cell proliferation and differentiation. And we aimed to investigate the impact of RSV on bone healing, employed diabetic mouse model induced by streptozotocin and confirmed through histological observation. High-glucose conditions adversely affected cell proliferation and ALP activity in both MC3T3-E1 and hPDLF in vitro, with more significant impact on MC3T3-E1 cells. RSV under high-glucose conditions had positive effects on both, showing early-stage effects for MC3T3-E1 cells and later-stage effects for hPDLF cells. RSV seemed to have a more pronounced rescuing role in MC3T3-E1 cells. Increased ALP activity was observed and the expression levels of significant genes, such as Col 1, TGF-β1, ALP, and OC, in osteogenic differentiation were exhibited stage-specific expression patterns. Upregulated Col 1 and TGF-β1 were detected in the early stage, and then ALP and OC expressions became more pronounced in the later stages. Similarly, stronger positive reactions against RUNX2 were detected in the RSV-treated group compared to the control. Furthermore, in in vivo experiment, RSV stimulates the growth and differentiation of osteoblasts, thereby promoting bone formation. High-glucose levels have the potential to impair cellular functions and the regenerative capacity to facilitate bone formation with MC3T3-E1 rather than hPDLF cells. Resveratrol appears to facilitate the inherent abilities of MC3T3-E1 cells compared with hPDLF cells, indicating its potential capacity to restore functionality during periodontal regeneration.

An osteogenic magnesium alloy with improved corrosion resistance, antibacterial, and mechanical properties for orthopedic applications

The aim of this study was to develop a novel biodegradable magnesium (Mg) alloy for bone implant applications. We used scandium (Sc; 2 wt %) and strontium (Sr; 2 wt %) as alloying elements due to their high biocompatibility, antibacterial efficacy, osteogenesis, and protective effects against corrosion. In the present work, we also examined the effect of a heat treatment process on the properties of the Mg-Sc-Sr alloy. Alloys were manufactured using a metal casting process followed by heat treatment. The microstructure, corrosion, mechanical properties, antibacterial activity, and osteogenic activity of the alloy were assessed in vitro. The results showed that the incorporation of Sc and Sr elements controlled the corrosion, reduced the hydrogen generation, and enhanced mechanical properties. Furthermore, alloying with Sc and Sr demonstrated a significantly enhanced antibacterial activity and decreased biofilm formation compared to control Mg. Also, culturing Mg-Sc-Sr alloy with human bone marrow-derived mesenchymal stromal cells showed a high degree of biocompatibility (>90% live cells) and a significant increase in osteoblastic differentiation in vitro shown by Alizarin red staining and alkaline phosphatase activity. Based on these results, the Mg-Sc-Sr alloy heat-treated at 400°C displayed optimal mechanical properties, corrosion rate, antibacterial efficacy, and osteoinductivity. These characteristics make the Mg-Sc-Sr alloy a promising candidate for biodegradable orthopedic implants in the fixation of bone fractures such as bone plate-screws or intramedullary nails.

Recent research advances on corrosion mechanism and protection, and novel coating materials of magnesium alloys: a review

Magnesium alloys have achieved a good balance between biocompatibility and mechanical properties, and have great potential for clinical application, and their performance as implant materials has been continuously improved in recent years. However, a high degradation rate of Mg alloys in a physiological environment remains a major limitation before clinical application. In this review, according to the human body's intake of elements, the current mainstream implanted magnesium alloy system is classified and discussed, and the corrosion mechanism of magnesium alloy in vivo and in vitro is described, including general corrosion, localized corrosion, pitting corrosion, and degradation of body fluid environment impact etc. The introduction of methods to improve the mechanical properties and biocorrosion resistance of magnesium alloys is divided into two parts: the alloying part mainly discusses the strengthening mechanisms of alloying elements, including grain refinement strengthening, solid solution strengthening, dislocation strengthening and precipitation strengthening etc.; the surface modification part introduces the ideas and applications of novel materials with excellent properties such as graphene and biomimetic materials in the development of functional coatings. Finally, the existing problems are summarized, and the future development direction is prospected.

Alkaline earth metals for osteogenic scaffolds: From mechanisms to applications

Regeneration of bone defects is a significant challenge today. As alternative approaches to the autologous bone, scaffold materials have remarkable features in treating bone defects; however, the various properties of current scaffold materials still fall short of expectations. Due to the osteogenic capability of alkaline earth metals, their application in scaffold materials has become an effective approach to improving their properties. Furthermore, numerous studies have shown that combining alkaline earth metals leads to better osteogenic properties than applying them alone. In this review, the physicochemical and physiological characteristics of alkaline earth metals are introduced, mainly focusing on their mechanisms and applications in osteogenesis, especially magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba). Furthermore, this review highlights the possible cross-talk between pathways when alkaline earth metals are combined. Finally, some of the current drawbacks of scaffold materials are enumerated, such as the high corrosion rate of Mg scaffolds and defects in the mechanical properties of Ca scaffolds. Moreover, a brief perspective is also provided regarding future directions in this field. It is worth exploring that whether the levels of alkaline earth metals in newly regenerated bone differs from those in normal bone. The ideal ratio of each element in the bone tissue engineering scaffolds or the optimal concentration of each elemental ion in the created osteogenic environment still needs further exploration. The review not only summarizes the research developments in osteogenesis but also offers a direction for developing new scaffold materials.

Biodegradable Mg-Sc-Sr Alloy Improves Osteogenesis and Angiogenesis to Accelerate Bone Defect Restoration

Magnesium (Mg) and its alloys are considered to be biodegradable metallic biomaterials for potential orthopedic implants. While the osteogenic properties of Mg alloys have been widely studied, few reports focused on developing a bifunctional Mg implant with osteogenic and angiogenic properties. Herein, a Mg-Sc-Sr alloy was developed, and this alloy's angiogenesis and osteogenesis effects were evaluated in vitro for the first time. X-ray Fluorescence (XRF), X-ray diffraction (XRD), and metallography images were used to evaluate the microstructure of the developed Mg-Sc-Sr alloy. Human umbilical vein/vascular endothelial cells (HUVECs) were used to evaluate the angiogenic character of the prepared Mg-Sc-Sr alloy. A mix of human bone-marrow-derived mesenchymal stromal cells (hBM-MSCs) and HUVEC cell cultures were used to assess the osteogenesis-stimulating effect of Mg-Sc-Sr alloy through alkaline phosphatase (ALP) and Von Kossa staining. Higher ALP activity and the number of calcified nodules (27% increase) were obtained for the Mg-Sc-Sr-treated groups compared to Mg-treated groups. In addition, higher VEGF expression (45.5% increase), tube length (80.8% increase), and number of meshes (37.9% increase) were observed. The Mg-Sc-Sr alloy showed significantly higher angiogenesis and osteogenic differentiation than pure Mg and the control group, suggesting such a composition as a promising candidate in bone implants.

Effects of erythropoietin on osteoblast in the tooth extraction socket in mice periodontitis model

Periodontitis is an excessive inflammatory event in tooth-supporting tissues and can cause tooth loss. We used erythropoietin (EPO), which has been reported to play an important role in bone healing and modulation of angiogenesis, as a therapeutic agent in vivo and in vitro experimental models to analyze its effect on periodontitis. First, EPO was applied to in vitro MC3T3-E1 cells and human periodontal ligament fibroblast (hPDLF) cells to examine its function in altered cellular events and gene expression patterns. In vitro cultivation of MC3T3-E1 and hPDLF cells with 10 IU/ml EPO at 24 and 48 h showed an obvious increase in cell proliferation. Interestingly, EPO treatment altered the expression of osteogenesis-related molecules, including alkaline phosphatase (ALP), bone morphogenetic protein-2 (BMP-2), and osteocalcin (OC) in MC3T3-E1 cells but not in hPDLF cells. In particular, MC3T3-E1 cells showed increased expression of ALP, BMP-2, and OC on day 5, while hPDLF cells showed increased expression of BMP-2, and OC on day 14. Based on the in vitro examination, we evaluated the effect of EPO on bone formation using an experimentally-induced animal periodontitis model. After the induction of periodontitis in the maxillary left second M, 10 IU/ml of EPO was locally applied to the extraction tooth sockets. Histomorphological examination using Masson’s trichrome (MTC) staining showed facilitated bone formation in the EPO-treated groups after 14 days. Similarly, stronger positive reactions against vascular endothelial growth factor (VEGF), cluster of differentiation 31 (CD31), runt-related transcription factor 2 (RUNX2), and osteocalcin (OC) were detected in the EPO-treated group compared to the control. Meanwhile, myeloperoxidase, an inflammatory marker, was decreased in the EPO-treated group on days 1 and 5. Overall, EPO facilitates bone healing and regeneration through altered signaling regulation and modulation of inflammation in the osteoblast cell lineage and to a lesser extent in hPDLF cells.

Magnesium for Implants: A Review on the Effect of Alloying Elements on Biocompatibility and Properties

An attempt is made to cover the whole of the topic of biodegradable magnesium (Mg) alloys with a focus on the biocompatibility of the individual alloying elements, as well as shed light on the degradation characteristics, microstructure, and mechanical properties of most binary alloys. Some of the various work processes carried out by researchers to achieve the alloys and their surface modifications have been highlighted. Additionally, a brief look into the literature on magnesium composites as also been included towards the end, to provide a more complete picture of the topic. In most cases, the chronological order of events has not been particularly followed, and instead, this work is concentrated on compiling and presenting an update of the work carried out on the topic of biodegradable magnesium alloys from the recent literature available to us.

The effect of different coatings on bone response and degradation behavior of porous magnesium-strontium devices in segmental defect regeneration

Regeneration of long-bone segmental defects remains a challenge for orthopedic surgery. Current treatment options often require several revision procedures to maintain acceptable alignment and achieve osseous healing. A novel hollow tubular system utilizing magnesium-strontium (Mg-Sr) alloy with autogenous morselized bone filled inside to repair segmental defects was developed. To improve the corrosion and biocompatible properties, two coatings, Ca-P and Sr-P coatings, were prepared on surface of the implants. Feasibility of applying these coated implants was systematically evaluated in vitro and in vivo, and simultaneously to have a better understanding on the relationship of degradation and bone regeneration on the healing process. According to the in vitro corrosion study by electrochemical measurements, greater corrosion resistance was obtained for Ca-P coated sample, and attributed to the double-layer protective structure. The cytotoxicity and alkaline phosphatase (ALP) assays demonstrated enhanced bioactivity for Sr-P coated group because of the long-lasting release of beneficial Sr2+. At 12 weeks post-implantation with Mg-Sr alloy porous device, the segmental defects were effectively repaired with respect to both integrity and continuity. In addition, compared with the Ca-P coated implant, the Sr-P coated implant was more proficient at promoting bone formation and mineralization. In summary, the Sr-P coated implants have bioactive properties and exceptional durability, and promote bone healing that is close to the natural rate, implying their potential application for the regeneration of segmental defects.

Nitrogen-containing bisphosphonate-loaded micro-arc oxidation coating for biodegradable magnesium alloy pellets inhibits osteosarcoma through targeting of the mevalonate pathway

Osteosarcoma (OS) remains one of the most threatening primary malignant human tumors of the bone, especially in the first or second decade of life. Unfortunately, the clinical therapeutic efficacy has not substantially improved over the past four decades. Therefore, to achieve efficient tumor eradication, a new approach to prevent tumor recurrence is urgently needed. Here, we develop a new bisphosphonate (BP)-loaded microarc oxidation (MAO) coated magnesium-strontium (Mg-Sr) alloy pellet that can inhibit OS, and we illuminate the cellular and molecular mechanisms of the inhibiting effect. To generate such pellets, nitrogen-containing BP is chemically conjugated with a MAO coating on hollow Mg-Sr alloys. We demonstrate that BP coated Mg pellet has multiple desired features for OS therapy through in vitro and in vivo studies. At the cellular level, BP coated Mg pellets not only induce apoptosis and necrosis, as well as antitumor invasion of OS cells in the two-dimensional (2D) cell culture environment, but also damage the formation of multicellular tumor spheroids by OS cell lines in the three-dimensional (3D) cell culture environment. At the in vivo level, BP coated Mg pellets can destroy tumors and prevent neoplasm recurrence via synergistic Mg degradation and drug release. It is further suggested that the superior inhibitory effect on OS of our pellet is achieved by inhibiting the mevalonate pathway at the molecular level. Hence, these results collectively show that the BP coated Mg pellet is a promising candidate for future applications in repairing defects after tumor removal in OS therapy.

Challenges in Bone Tissue Regeneration: Stem Cell Therapy, Biofunctionality and Antimicrobial Properties of Novel Materials and Its Evolution

An aging population leads to increasing demand for sustained quality of life with the aid of novel implants. Patients expect fast healing and few complications after surgery. Increased biofunctionality and antimicrobial behavior of implants, in combination with supportive stem cell therapy, can meet these expectations. Recent research in the field of bone implants and the implementation of autologous mesenchymal stem cells in the treatment of bone defects is outlined and evaluated in this review. The article highlights several advantages, limitations and advances for metal-, ceramic- and polymer-based implants and discusses the future need for high-throughput screening systems used in the evaluation of novel developed materials and stem cell therapies. Automated cell culture systems, microarray assays or microfluidic devices are required to efficiently analyze the increasing number of new materials and stem cell-assisted therapies. Approaches described in the literature to improve biocompatibility, biofunctionality and stem cell differentiation efficiencies of implants range from the design of drug-laden nanoparticles to chemical modification and the selection of materials that mimic the natural tissue. Combining suitable implants with mesenchymal stem cell treatment promises to shorten healing time and increase treatment success. Most research studies focus on creating antibacterial materials or modifying implants with antibacterial coatings in order to address the increasing number of complications after surgeries that are mostly caused by bacterial infections. Moreover, treatment of multiresistant pathogens will pose even bigger challenges in hospitals in the future, according to the World Health Organization (WHO). These antibacterial materials will help to reduce infections after surgery and the number of antibiotic treatments that contribute to the emergence of new multiresistant pathogens, whilst the antibacterial implants will help reduce the amount of antibiotics used in clinical treatment.

Ex vivo determination of chitosan/curdlan/hydroxyapatite biomaterial osseointegration with the use of human trabecular bone explant: New method for biocompatibility testing of bone implants reducing animal tests

Permanent orthopedic/dental implants should reveal good osseointegration, which is defined as an ability of the biomaterial to form a direct connection with the surrounding host bone tissue after its implantation into the living organism. Currently, biomaterial osseointegration is confirmed exclusively with the use of in vivo animal tests. This study presents for the first time ex vivo determination of osseointegration process using human trabecular bone explant that was drilled and filled with the chitosan/curdlan/hydroxyapatite biomaterial, followed by its long-term culture under in vitro conditions. Within this study, it was clearly proved that tested biomaterial allows for the formation of the connection with bone explant since osteoblasts, having ability to produce bone extracellular matrix (type I collagen, fibronectin), were detected at a bone-implant interface by confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). Importantly, in this research it was demonstrated by Live/Dead staining and CLSM imaging that human bone explants may stay alive for a long period of time (at least approx. 50 days) during their culture under in vitro conditions. Therefore, ex vivo bone explant, which is a heterogeneous tissue containing many different cell types, may serve as an excellent model to test biomaterial osseointegration during comparative and preliminary studies, reducing animal tests which is compatible with the principles of '3Rs', aiming to Replace, Reduce and Refine the use of animals wherever possible.

Strontium enhances proliferation and osteogenic behavior of bone marrow stromal cells of mesenchymal and ectomesenchymal origins in vitro

Obejective

To investigate the effect of increasing Strontium (Sr) concentrations on the growth and osteogenic behavior of human bone marrow stromal cells (BMSCs) from mesenchymal (i.e., fibula) and ectomesenchymal (i.e., mandible) embryonic origins.

Materials and methods

Fibula and mandible BMSCs were cultured in media without (Ctrl) or with Sr in four diverse concentrations: Sr1, 11.3 × 10⁻³ mg/L, human seric physiological level; Sr2, 13 mg/L, human seric level after strontium ranelate treatment; Sr3, 130 mg/L, and Sr4, 360 mg/L. Proliferation rate (1, 3, and 7 days), osteogenic behavior (alkaline phosphatase [ALP] activity, 7 and 14 days; expression of osteogenic genes (ALP, osteopontin, and osteocalcin at 7, 14, and 21 days), and formation of mineralized nodules (14 and 21 days) of the BMSCs were assessed. Data was compared group‐ and period‐wise using analysis of variance tests.

Results

Fibula and mandible BMSCs cultured with Sr4 showed increased proliferation rate, and osteocalcin and osteopontin gene expression together with more evident formation of mineralized nodules, compared all other Sr concentrations. For both cell populations, Sr4 led to lower ALP activity, and ALP gene expression, compared with the other Sr concentrations.

Conclusion

BMSCs from mesenchymal (i.e., fibula) and ectomesenchymal (i.e., mandible) embryonic origins showed increased cellular proliferation and osteogenic behavior when cultured with Sr4, in vitro.

Stem cells in Osteoporosis: From Biology to New Therapeutic Approaches

Osteoporosis is a systemic disease that affects the skeleton, causing reduction of bone density and mass, resulting in destruction of bone microstructure and increased risk of bone fractures. Since osteoporosis is a disease affecting the elderly and the aging of the world's population is constantly increasing, it is expected that the incidence of osteoporosis and its financial burden on the insurance systems will increase continuously and there is a need for more understanding this condition in order to prevent and/or treat it. At present, available drug therapy for osteoporosis primarily targets the inhibition of bone resorption and agents that promote bone mineralization, designed to slow disease progression. Safe and predictable pharmaceutical means to increase bone formation have been elusive. Stem cell therapy of osteoporosis, as a therapeutic strategy, offers the promise of an increase in osteoblast differentiation and thus reversing the shift towards bone resorption in osteoporosis. This review is focused on the current views regarding the implication of the stem cells in the cellular and physiologic mechanisms of osteoporosis and discusses data obtained from stem cell-based therapies of osteoporosis in experimental animal models and the possibility of their future application in clinical trials.

Bone regeneration of hollow tubular magnesium‑strontium scaffolds in critical-size segmental defects: Effect of surface coatings

Segmental defects are formidable challenges for orthopedic surgeons that are caused by large osseous defects such as open injury, comminuted fracture as well as other severe traumas and infection. Current treatment options have practical and clinical shortcomings, calling for innovative bone graft materials. This study is related to hollow tubular magnesium‑strontium (MgSr) alloy scaffolds with autologous morselized bone filled inside and three different coatings were individually applied on MgSr scaffolds, respectively, to study the effects of degradation and bioactivity of the grafts on new bone growth. The optimal coating method was screened using immersion tests, cell proliferation and adhesion, alkaline phosphatase (ALP) assay in vitro, and 4 weeks' implantation in a critical-size segmental defect in vivo. More new bone formation was observed by radiographic tests and histology along the ulna defects, when magnesium scaffold grafts were implanted. Meanwhile, depression occurred for blank control group with only autologous morselized bone filled, because of rapid absorption rate of morselized bone during initial implantation. Therefore, biodegradable MgSr alloy grafts showed their potential application in treating the critical-size segmental defects. As for different coating methods, CaP chemically deposited (CaP) coated sample showed least H₂ evolution in vivo, demonstrating highest corrosion resistance and relative stable interfaces, however, the least beneficial ion release meanwhile. Micro-arc oxidation coating (MAO) degraded faster comparing with CaP, while with the main composition of MgO. They both indicate insufficient bioactivity in bone formation. The results suggest superior combination of bioactive surface, beneficial ions release and appropriate corrosion rate of Strontium phosphate conversion (SrP) coating, indicating superior comprehensive oeteoconductive and osteoinductive properties of coatings on hollow tubular MgSr alloy scaffold.

Regulation of osteogenesis and osteoclastogenesis by zoledronic acid loaded on biodegradable magnesium-strontium alloy

Inhibiting osteoclasts and osteoclast precursors to reduce bone resorption is an important strategy to treat osteoclast-related diseases, such as peri-prosthetic osteolysis. In this study, our objective was to study the role of zoledronic acid (ZA), as a highly potent and nitrogen-containing bisphosphonate, in promoting osteogenesis and inhibiting osteoclastogenesis properties of magnesium (Mg)-based implants. ZA was chemically associated with calcium phosphate (CaP) deposited on magnesium-strontium (Mg-Sr) alloy, which was confirmed by the morphological observation, phase composition and drug releasing via SEM, XRD spectrum and High Performance Liquid Chromatography (HPLC), respectively. The in vitro performances indicated that ZA-CaP bilayer coating Mg-Sr alloy could enhance the proliferation and the osteogenic differentiation as well as the mineralization of pre-osteoblasts, however, induce the apoptosis and inhibit the osteoclast differentiation. We further investigated the possible molecular mechanisms by using Quantitative real-time PCR (qRT-PCR) and Western Blotting, and the results showed that ZA-CaP bilayer coating Mg-Sr alloy could regulate the osteogenesis and osteoclastogenesis through the Estrogen Receptor α (ERα) and NF-κB signaling pathway. Moreover, ZA-CaP bilayer coating Mg-Sr alloy could regulate the cross talk of osteoblast-osteoclast and increase the ratio of OPG: RANKL in the co-culture system through OPG/RANKL/RANK signaling pathway, which promoting the balance of bone remodeling process. Therefore, these promising results suggest the potential clinical applications of ZA pretreated Mg-Sr alloys for bone defect repairs and periprosthetical osteolysis due to the excessive differentitation and maturation of osteoclasts.

The summary of the most important cell-biomaterial interactions that need to be considered during in vitro biocompatibility testing of bone scaffolds for tissue engineering applications

Tissue engineered products (TEPs), which mean biomaterials containing either cells or growth factors or both cells and growth factors, may be used as an alternative to the autografts taken directly from the bone of the patients. Nevertheless, the use of TEPs needs much more understanding of biointeractions between biomaterials and eukaryotic cells. Despite the possibility of the use of in vitro cellular models for initial evaluation of the host response to the implanted biomaterial, it is observed that most researchers use cell cultures only for the evaluation of cytotoxicity and cell proliferation on the biomaterial surface, and then they proceed to animal models and in vivo testing of bone implants without fully utilizing the scientific potential of in vitro models. In this review, the most important biointeractions between eukaryotic cells and biomaterials were discussed, indicating molecular mechanisms of cell adhesion, proliferation, and biomaterial-induced activation of immune cells. The article also describes types of cellular models which are commonly used for biomaterial testing and highlights the possibilities and drawbacks of in vitro tests for biocompatibility evaluation of novel scaffolds. Finally, the review summarizes recent findings concerning the use of adult mesenchymal stem cells for TEP generation and compares the potential of bone marrow- and adipose tissue-derived stem cells in regenerative medicine applications.

Molecular and cellular mechanisms for zoledronic acid-loaded magnesium-strontium alloys to inhibit giant cell tumors of bone

Giant Cell Tumors of Bone (GCTB) are benign but aggressive and metastatic tumors. Surgical removal cannot eradicate GCTB due to the subsequent recurrence and osteolysis. Here we developed Zoledronic acid (ZA)-loaded magnesium-strontium (Mg-Sr) alloys that can inhibit GCTB and studied the molecular and cellular mechanisms of such inhibition. We first formed a calcium phosphate (CaP) coating on the Mg-1.5 wt%Sr implants by coprecipitation and then loaded ZA on the CaP coating. We examined the response of GCTB cells to the ZA-loaded alloys. At the cellular level, the alloys not only induced apoptosis and oxidative stress of GCTB cells, and suppressed their resultant pre-osteoclast recruitment, but also inhibited their migration. At the molecular level, the alloys could significantly activate the mitochondrial pathway and inhibit the NF-κB pathway in the GCTB cells. These collectively enable the ZA-loaded alloys to suppress GCTB cell growth and osteolysis, and thus improve our understanding of the materials-induced tumor inhibition. Our study shows that ZA-loaded alloys could be a potential implant in repairing the bone defects after tumor removal in GCTB therapy.

STATEMENT OF SIGNIFICANCE

In clinics, giant cell tumors of bone (GCTB) are removed by surgery. However, the resultant defects in bone still contain aggressive and metastatic GCTB cells that can recruit osteoclasts to damage bone, leading to new GCTB tumor growth and bone damage after tumor surgery. Hence, it is of high demand in developing a material that can not only fill the bone defects as an implant but also inhibit GCTB in the defect area as a therapeutic agent. More importantly, the molecular and cellular mechanism by which such a material inhibits GCTB growth has never been explored. To solve these two problems, we prepared a new biomaterial, the Mg-Sr alloys that were first coated with calcium phosphate and then loaded with a tumor-inhibiting molecule (Zoledronic acid, ZA). Then, by using a variety of molecular and cellular biological assays, we studied how the ZA-loaded alloys induced the death of GCTB cells (derived from patients) and inhibited their growth at the molecular and cellular level. At the cellular level, our results showed that ZA-loaded Mg-Sr alloys not only induced apoptosis and oxidative stress of GCTB cells, and suppressed their induced pre-osteoclast recruitment, but also inhibited their migration. At the molecular level, our data showed that ZA released from the ZA-loaded Mg-Sr alloys could significantly activate the mitochondrial pathway and inhibit the NF-κB pathway in the GCTB cells. Both mechanisms collectively induced GCTB cell death and inhibited GCTB cell growth. This work showed how a biomaterial inhibit tumor growth at the molecular and cellular level, increasing our understanding in the fundamental principle of materials-induced cancer therapy. This work will be interesting to readers in the fields of metallic materials, inorganic materials, biomaterials and cancer therapy.

Integrating 3D-printed PHBV/Calcium sulfate hemihydrate scaffold and chitosan hydrogel for enhanced osteogenic property

We developed the 3D-printed poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/calcium sulfate hemihydrate (PHBV/CaSH) scaffolds by using fused deposition modelling (FDM) technique and then coated the scaffolds with chitosan (CS) acetic acid solution. After drying and neutralization, CS hydrogel was formed on the surface of the scaffolds. The resultant PHBV/CaSH/CS scaffolds could promote the adhesion and proliferation of rat bone marrow stromal cells (rBMSCs) and enhance the osteogenesis of rBMSCs by up-regulating the expression level of osteogenic genes compared to the PHBV and PHBV/CaSH scaffolds. In vivo studies further demonstrated the PHBV/CaSH/CS scaffolds could effectively promote new bone formation. Therefore, integrating 3D-printed PHBV/CaSH scaffold and CS hrydogel represents a novel strategy to promote osteogensis property, showing full potential for bone defects repair.

Effects of solidification cooling rate on the corrosion resistance of a biodegradable β-TCP/Mg-Zn-Ca composite

Biodegradable beta-tricalcium phosphate (β-TCP) particle reinforced magnesium metal matrix composites (Mg-MMC) have attracted increasing interest for application as implant materials. This investigation was conducted to study the effect of cooling rate on the microstructure and corrosion behavior of a biodegradable β-TCP/Mg-Zn-Ca composite. The composite was fabricated under a series of cooling rates using a wedge-shaped casting mold. The microstructure of the composite was examined by optical and scanning electron microscopy, and the corrosion behavior was investigated using an electrochemical workstation and immersion tests in a simulated body fluid (SBF). Faster cooling rates were shown to refine the secondary phase and grain size, and produce a more homogenous microstructure. The refined microstructure resulted in a more uniform distribution of β-TCP particles, which is believed to be beneficial in the formation of a stable and compact corrosion product layer, leading to improved corrosion resistance for the composite.

Highly dispersed lithium doped mesoporous silica nanospheres regulating adhesion, proliferation, morphology, ALP activity and osteogenesis related gene expressions of BMSCs

Lithium (Li) doped mesoporous silica nanospheres (LMSNs) were synthesized by incorporation of 5 wt% Li into mesoporous silica nanospheres (MSNs) using sol-gel method. The results showed that LMSNs with a mean size of approximate 300 nm exhibited uniform and highly dispersed spherical morphology, which was similar to the morphology of MSNs. Moreover, the degradability of MSNs was significantly increased after the incorporation of Li, and LMSNs could release both silicon (Si) and Li ions in a sustained manner. Due to the release of Li ions, LMSNs showed higher stimulatory effects on the attachment and proliferation of bone marrow mesenchymal stem cells (BMSCs) than MSNs. In addition, LMSNs could also enhance the ALP activity of BMSCs as well as improving osteogenesis related genes (OPN, ALP, Runx2 and OCN) expression of BMSCs. In summary, LMSNs have shown the capability of being a carrier of biologically active ions, which exhibit great potential in bone repair/regeneration applications.