Magnesium promotes osteogenesis via increasing OPN expression and activating CaM/CaMKIV/CREB1 pathway.

Magnesium (Mg) based alloy has been used as a biodegradable implant for fracture repair with considerable efficacy, and it has been proved that magnesium ion (Mg2+ ), one of the degradation products, could stimulate osteogenesis. Here, we investigated the osteogenesis property of magnesium both in vitro and in vivo, and to identify the cellular and molecular mechanisms that mediate these effects. Results showed that magnesium exerts a dose-dependent increase in the proliferation of MC3T3 and MG63 cells, and in the expression of osteopontin (OPN), a promising biomarker of osteogenesis. Subsequently, the protein-protein interaction (PPI) network analysis showed the interactions between calmodulin (CaM) and calmodulin-dependent protein kinase (CaMK) and CREB1. The ratio of p-CaMKIV/CaMKIV and p-CREB1/CREB were increased at protein level in MC3T3 and MG63 cells after treatment with Mg2+ . Dual-luciferase reporter gene assay showed that p-CREB1 could directly bind to OPN promoter and up-regulate the transcription of OPN after nuclear entry. Meanwhile, the expression of OPN and p-CREB1, which increased after Mg2+ treatment, was down-regulated by sh-CaMKIV or sh-CREB1. Moreover, the mineralized deposit and expression of OPN were reduced after treatment with an inhibitor of CaMKIV, KN93. In addition, massive cavities in the cortical bone around the Mg screw were showed in vivo after injection of KN93. These data indicated that the osteogenic effect of Mg is related to the activation OPN through CaM/CaMKIV/CREB1 signaling pathway.

Loading comparison of two structures in the moving tube of a non-invasive prosthesis.

BACKGROUND: The treatment of adolescent patients with distal femoral cancer has always been a concern. The limb-salvage, regarded as a mainstream treatment, had been developed in recent years, but its application in children still remains challenging. This is because it can lead to potential limb-length discrepancy from the continued normal growth of the contralateral lower body. The extendable prosthesis could solve this problem. The principle is that it can artificially control the length of the prosthesis, making it consistent with the length of the side of the lower limbs. However, this prosthesis has some complications. The extendable prosthesis is classified into invasive and minimally invasive, which extends the prosthesis with each operation. OBJECTIVE: We designed a new non-invasive prosthesis that can be extended in the body. Based on the non-invasive and extendable characteristics, we need to verify the supporting performance of this prosthesis. METHODS: We carried out a mechanical testing method and finite element analysis simulation. CONCLUSION: The support performance and non-invasively extension of this prosthesis were verified.

Microstructure controls the corrosion behavior of a lean biodegradable Mg-2Zn alloy.

Microstructural design was a long-term sustainable development method to improve the biodegradability and mechanical properties of low alloyed biomedical Mg alloys. In this study, the microstructural features (including grain size, deformation twin, deformed grains, sub-grains, and recrystallized grains) of the MZ2 ((Mg-2Zn (wt%)) alloy were controlled by different single-passed rolling reductions at high temperature. Besides the effect of grain size, we found that deformation twins and deformed grains influenced corrosion performance. Grain refinement with uniform distribution, meanwhile reducing the content of deformation twins, deformed grains, and sub-grains, was a practical method to improve both corrosion resistance and mechanical properties of MZ2 alloy. This finding proposed a better understanding of the development of lean biomedical Mg alloys with superior mechanical properties and favorable corrosion resistance. STATEMENT OF SIGNIFICANCE: Current research and development of biomedical Mg focused on alloying methods. The lean biodegradable Mg, which reduced the materials' compositional complexity, was the benefit of development for long-term sustainability. Here, our work revealed the relationship between microstructural features and corrosion resistance of a lean Mg-2Zn alloy during the different single-passed rolling processes. We found that recrystallized fine grains with partially ultra-fine grains could improve both strength and corrosion resistance. This study could give a new understanding of the development of lean biodegradable Mg alloys by using microstructural design to improve the overall performance of biomedical applications.

Biodegradable Mg Implants Suppress the Growth of Ovarian Tumor.

The common treatment of epithelial ovarian cancer is aggressive surgery followed by platinum-based cytotoxic chemotherapy. However, residual tumor cells are resistant to chemotherapeutic drugs during postoperative recurrence. The treatment of ovarian cancer requires breakthroughs and advances. In recent years, magnesium alloy has been widely developed as a new biodegradable material because of its great potential in the field of medical devices. From the degradation products of magnesium, biodegradable magnesium implants have great potential in antitumor. According to the disease characteristics of ovarian cancer, we choose it to study the antitumor characteristics of biodegradable magnesium. We tested the anti-ovarian tumor properties of Mg through both in vivo and in vitro experiments. According to the optical in vivo imaging and relative tumor volume statistics of mice, high-purity Mg wires significantly inhibited the growth of SKOV3 cells in vivo. We find that the degradation products of Mg, Mg2+, and H2 significantly inhibit the growth of SKOV3 cells and promote their apoptosis. Our study suggests a good promise for the treatment of ovarian cancer.

Local intragranular misorientation accelerates corrosion in biodegradable Mg.

Mg-based implants are used in biomedical applications predominantly because of their degradable property. In this paper, the effect of local misorientations (intragranular misorientation) on the corrosion behavior of high-purity Mg (HPM) was systematically investigated according to microstructure characterization and corrosion measurements. The results showed that local misorientation introduced into grains by deformation could result in corrosion around the grain boundary (GB), which ultimately reduces the corrosion resistance of HPM. After removing the local misorientation by annealing, the corrosion around GB could be eliminated. This work is expected to inspire better control over the degradation behaviors of biomedical Mg through microstructure design to be used for various biomedical applications. STATEMENT OF SIGNIFICANCE: 1. Fine grains, fine grains with large local misorientation, and coarse grains could be obtained, respectively, in high-purity Mg by sequential hot rolling, compression deformation, and annealing treatments. 2. Large local misorientation introduced into grains could lead to corrosion around the grain boundary and ultimately reduce corrosion resistance. 3. In the absence of local misorientation, refining grain size could improve the corrosion resistance of Mg.

Crevice corrosion - A newly observed mechanism of degradation in biomedical magnesium.

Crevice-induced corrosion is not desirable to occur in metallic magnesium (Mg) during many industrial applications. However, orthopedic implants made of Mg alloys have been demonstrated to degrade faster between the joining surface of bone plates and screws after implantation, suggesting the crevice corrosion may occur in the physiological environment. In this paper, a resin device is designed to parallel high purity magnesium (HP-Mg) plates with closely spaced slits. After a standard corrosion test in the phosphate-buffered saline (PBS) solution, the paralleled HP-Mg samples embedded in the custom-made resin device corrode faster than those without the resin device. The corrosion morphology of Mg with the resin device exhibits features of crevice corrosion with many deep holes and river-like texture. Moreover, implantation of the bone plate and screws in vivo demonstrates similar corrosion morphology as that of the in vitro test, suggesting the occurrence of crevice-enhanced corrosion in the bone-bone plate interface, as well as the contact area between the bone plate and the screws. STATEMENT OF SIGNIFICANCE: Understanding the corrosion behavior of Mg and Mg alloys after implantation is one of the main challenges for developing desirable biodegradable Mg alloys or effective methods to adjust the corrosion rate of Mg-based implants. In this paper, we attempted to understand the corrosion behaviors of HP-Mg at the joining surface between HP-Mg plates or HP-Mg screws and bone tissues after implantation. We designed an in vitro setup to mimic the crevice environment of the in vivo joining surface and found that the crevices existing on the HP-Mg would significantly accelerate the corrosion rate and change the corrosion morphology of HP-Mg plates. The in vivo implantation also showed similar corrosion morphology caused by crevice corrosion, which appeared at the joining surface between HP-Mg plates or HP-Mg screws and bone tissues. Then, we proposed a new corrosion mechanism of Mg-based alloys inside the crevice. The findings of this study can help us broaden our cognition on the corrosion behavior of Mg and Mg alloy-based orthopedic implants.

Translational status of biomedical Mg devices in China.

Magnesium (Mg) and its alloys as temporary medical implants with biodegradable and properly mechanical properties have been investigated for a long time. There are already three kinds of biodegradable Mg implants which are approved by Conformite Europeene (CE) or Korea Food and Drug Administration (KFDA), but not China Food and Drug Administration (CFDA, now it is National Medical Products Administration, NMPA). As we know, Chinese researchers, surgeons, and entrepreneurs have tried a lot to research and develop biodegradable Mg implants which might become other new approved implants for clinical applications. So in this review, we present the representative Mg implants of three categories, orthopedic implants, surgical implants, and intervention implants and provide an overview of current achievement in China from academic publications and Chinese patents. We would like to provide a systematic way to translate Mg and its alloy implants from experiment designs to clinical products.

High-Purity Magnesium Staples Suppress Inflammatory Response in Rectal Anastomoses.

Magnesium-based materials are promising biodegradable implants, although the impact of magnesium on rectal anastomotic inflammation is poorly understood. Thus, we investigated the inflammatory effects of high-purity Mg staples in rectal anastomoses by in vivo luciferase reporter gene expression in transgenic mice, hematoxylin-eosin staining, immunohistochemistry, and Western blotting. As expected, strong IL-1ß-mediated inflammation and inflammatory cell infiltration were observed 1 day after rectal anastomoses were stapled with high-purity Mg or Ti. However, inflammation and inflammatory cell infiltration decreased more robustly 4-7 days postoperation in tissues stapled with high-purity Mg. This rapid reduction in inflammation was confirmed by immunohistochemical analysis of IL-6 and TNF-α. Western blot also suggested that the reduced inflammatory response is due to suppressed TLR4/NF-κB signaling. In contrast, MCP-1, uPAR, and VEGF were abundantly expressed, in line with the notion that expression of these proteins is regulated by feedback between the VEGF and NF-κB pathways. In vitro expression of MCP-1, uPAR, and VEGF was also similarly high in primary rectal mucosal epithelial cells exposed to extracts from Mg staples, as measured by antibody array. Collectively, the results suggest that high-purity Mg staples suppress the inflammatory response during rectal anastomoses via TLR4/NF-κB and VEGF signaling.

Accelerating Corrosion of Pure Magnesium Co-implanted with Titanium in Vivo.

Magnesium is a type of reactive metal, and is susceptible to galvanic corrosion. In the present study, the impact of coexistence of Ti on the corrosion behavior of high purity Mg (HP Mg) was investigated both in vitro and in vivo. Increased corrosion rate of HP Mg was demonstrated when Mg and Ti discs were not in contact. The in vivo experiments further confirmed accelerating corrosion of HP Mg screws when they were co-implanted with Ti screws into Sprague-Dawley rats' femur, spacing 5 and 10 mm. Micro CT scan and 3D reconstruction revealed severe corrosion morphology of HP Mg screws. The calculated volume loss was much higher for the HP Mg screw co-implanted with Ti screw as compared to that co-implanted with another Mg screw. Consequently, less new bone tissue ingrowth and lower pullout force were found in the former group. It is hypothesized that the abundant blood vessels on the periosteum act as wires to connect the Mg and Ti screws and form a galvanic-like cell, accelerating the corrosion of Mg. Therefore, a certain distance is critical to maintain the mechanical and biological property of Mg when it is co-implanted with Ti.

In vivo and in vitro assessment of the biocompatibility and degradation of high-purity Mg anastomotic staples.

Titanium (Ti) staples are not biodegradable, and anastomotic complications related to Ti staples are reported frequently. In the present study, the biocompatibility and degradation behavior of high-purity magnesium (HP Mg) staples with the small intestine were investigated. HP Mg staples did not affect the relative growth rate, cell cycle and apoptosis of primary rectal mucosal epithelial cells (IEC-6) in vitro. At one, two and three days after immersion in intestinal juice, the weight of the 30 rinsed HP Mg staples reduced by 7.5 ± 1.6, 10.6 ± 2.2 and 13.5 ± 2.1 mg, respectively, and those in the Hanks' solution reduced by 3.9 ± 0.8, 6.1 ± 1.2 and 7.1 ± 2.4 mg. Extracts of HP Mg staples were bio-safe for IEC-6, and the corrosion rate of HP staples was faster in the small intestinal juice than in the Hanks' solution. In the in vivo experiments, the small intestine of the minipigs was anastomosed by HP Mg and Ti staples. HP Mg staples neither affected important bio-chemical parameters nor induced serious inflammation or necrosis in the anastomosis tissues. The residual weight of a HP Mg staples (0.81 ± 0.13 mg) was 89.7% of the original weight (9 ± 0.09 mg) one month after surgery. The in vivo corrosion rate for one HP Mg staple was determined to be∼0.007 ± 0.001 mm·month-1. The preliminary results of the biocompatibility and degradation of high-purity Mg anastomotic staples are promising, and further studies will be initiated to study in more detail.

Reduced antibacterial property of metallic magnesium in vivo.

Magnesium and its alloys have drawn interest as antibacterial biomaterials, owing to their ability to alkalize the surrounding medium during degradation. The antibacterial effect of pure Mg and Mg alloys in vitro has previously been reported. However, the antibacterial property of Mg in vivo might be different because of the apparently dissimilar corrosion characteristics. In this study, pure Mg rods were implanted and bacterial suspension were injected into rat femurs to investigate the antibacterial property of Mg in vivo. The results showed that contrary to the high antibacterial rate in vitro, Mg exhibited a dramatic drop in antibacterial effect in vivo. Bacteria proliferated on the surface of the Mg rods as well as in the femur. Inflammatory cells filled cavities in the cortical bone of the femur, which was demonstrated by histological and micro-CT examination after 2 and 4 weeks of implantation. It is suggested that a reduced corrosion rate in vivo would result in insufficient pH value. In addition, the deposition layer would prevent further corrosion of Mg and provide a favorite site for bacteria adhesion. Hence, the dramatically reduced antibacterial property of Mg needs to be noticed when it is used as a biomaterial.

High-purity magnesium interference screws promote fibrocartilaginous entheses regeneration in the anterior cruciate ligament reconstruction rabbit model via accumulation of BMP-2 and VEGF.

Interference screw in the fixation of autologous tendon graft to the bone tunnel is widely accepted for the reconstruction of anterior cruciate ligament (ACL), but the regeneration of fibrocartilaginous entheses could hardly be achieved with the traditional interference screw. In the present work, biodegradable high-purity magnesium (HP Mg) showed good cytocompatibility and promoted the expression of bone morphogenetic protein-2 (BMP-2) and vascular endothelial growth factor (VEGF), fibrocartilage markers (Aggrecan, COL2A1 and SOX-9), and glycosaminoglycan (GAG) production in vitro. The HP Mg screw was applied to fix the semitendinosus autograft to the femoral tunnel in a rabbit model of ACL reconstruction with titanium (Ti) screw as the control. The femur-tendon graft-tibia complex was retrieved at 3, 6, 9 and 12 weeks. Gross observation and range of motion (ROM) of the animal model reached normal levels at 12 weeks. No sign of host reaction was found in the X-ray scanning. The HP Mg group was comparable to the Ti group with respect to biomechanical properties of the reconstructed ACL, and the ultimate load to failure and stiffness increased 12 weeks after surgery. In the histological analysis, the HP Mg group formed distinct fibrocartilage transition zones at the tendon-bone interface 12 weeks after surgery, whereas a disorganized fibrocartilage layer was found in the Ti group. In the immunohistochemical analysis, highly positive staining of BMP-2, VEGF and the specific receptor for BMP-2 (BMPR1A) was shown at the tendon-bone interface of the HP Mg group compared with the Ti group. Furthermore, the HP Mg group had significantly higher expression of BMP-2 and VEGF than the Ti group in the early phase of tendon-bone healing, followed by enhanced expression of fibrocartilage markers and GAG production. Therefore we proposed that the stimulation of BMP-2 and VEGF by Mg ions was responsible for the fibrochondrogenesis of Mg materials. HP Mg was promising as a biodegradable interference screw with the potential to promote fibrocartilaginous entheses regeneration in ACL reconstruction.

Study of Cell Behaviors on Anodized TiO2 Nanotube Arrays with Coexisting Multi-Size Diameters.

It has been revealed that the different morphologies of anodized TiO2 nanotubes, especially nanotube diameters, triggered different cell behaviors. However, the influence of TiO2 nanotubes with coexisting multi-size diameters on cell behaviors is seldom reported. In this work, coexisting four-diameter TiO2 nanotube samples, namely, one single substrate with the integration of four different nanotube diameters (60, 150, 250, and 350 nm), were prepared by repeated anodization. The boundaries between two different diameter regions show well-organized structure without obvious difference in height. The adhesion behaviors of MC3T3-E1 cells on the coexisting four-diameter TiO2 nanotube arrays were investigated. The results exhibit a significant difference of cell density between smaller diameters (60 and 150 nm) and larger diameters (250 and 350 nm) within 24 h incubation with the coexistence of different diameters, which is totally different from that on the single-diameter TiO2 nanotube arrays. The coexistence of four different diameters does not change greatly the cell morphologies compared with the single-diameter nanotubes. The findings in this work are expected to offer further understanding of the interaction between cells and materials.

Research of a novel biodegradable surgical staple made of high purity magnesium.

Surgical staples made of pure titanium and titanium alloys are widely used in gastrointestinal anastomosis. However the Ti staple cannot be absorbed in human body and produce artifacts on computed tomography (CT) and other imaging examination, and cause the risk of incorrect diagnosis. The bioabsorbable staple made from polymers that can degrade in human body environment, is an alternative. In the present study, biodegradable high purity magnesium staples were developed for gastric anastomosis. U-shape staples with two different interior angles, namely original 90° and modified 100°, were designed. Finite element analysis (FEA) showed that the residual stress concentrated on the arc part when the original staple was closed to B-shape, while it concentrated on the feet for the modified staple after closure. The in vitro tests indicated that the arc part of the original staple ruptured firstly after 7 days immersion, whereas the modified one kept intact, demonstrating residual stress greatly affected the corrosion behavior of the HP-Mg staples. The in vivo implantation showed good biocompatibility of the modified Mg staples, without inflammatory reaction 9 weeks post-operation. The Mg staples kept good closure to the Anastomosis, no leaking and bleeding were found, and the staples exhibited no fracture or severe corrosion cracks during the degradation.

Guided proliferation and bone-forming functionality on highly ordered large diameter TiO2 nanotube arrays.

The significantly enhanced osteoblast adhesion, proliferation and alkaline phosphatase (ALP) activity were observed on TiO2 nanotube surface in recent studies in which the scale of nanotube diameter was restricted under 100 nm. In this paper, a series of highly ordered TiO2 nanotube arrays with larger diameters ranging from 150 nm to 470 nm were fabricated via high voltage anodization. The behaviors of MC3T3-E1 cells in response to the diameter-controlled TiO2 nanotubes were investigated. A contrast between the trend of proliferation and the trend of cell elongation was observed. The highest cell elongation (nearly 10:1) and the lowest cell number were observed on the TiO2 nanotube arrays with 150 nm diameter. While, the lowest cell elongation and highest cell number were achieved on the TiO2 nanotube arrays with 470 nm diameter. Furthermore, the ALP activity peaked on the 150 nm diameter TiO2 nanotube arrays and decreased dramatically with the increase of nanotube diameter. Thus a narrow range of diameter (100-200 nm) that could induce the greatest bone-forming activity is determined. It is expected that more delicate design of orthopedic implant with regional abduction of cell proliferation or bone forming could be achieved by controlling the diameter of TiO2 nanotubes.