In vitro and in vivo evaluation of the surface bioactivity of a calcium phosphate coated magnesium alloy

Bone cells influence the degradation interface of pure Mg and WE43 materials: Insights from multimodal in vitro analysis

In this study, the interaction of pure Mg and WE43 alloy under the presence of osteoblast (OB) and osteoclast (OC) cells and their influence on the degradation of materials have been deeply analyzed. Since OB and OC interaction has an important role in bone remodeling, we examined the surface morphology and dynamic changes in the chemical composition and thickness of the corrosion layers formed on pure Mg and WE43 alloy by direct monoculture and coculture of pre-differentiated OB and OC cells in vitro. Electrochemical techniques examined the corrosion performance. The corrosion products were characterized using a combination of the focused ion beam (FIB), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). Cell viability and morphology were assessed by fluorescent microscopy and SEM. Our findings demonstrate cell spread and attachment variations, which differ depending on the Mg substrates. It was clearly shown that cell culture groups delayed degradation processes with the lowest corrosion rate observed in the presence of OBOC coculture for the WE43 substrate. Ca-P enrichment was observed in the outer-middle region of the corrosion layer but only after 7 days of OBOC coculture on WE43 and after 14 days on the pure Mg specimens. STATEMENT OF SIGNIFICANCE: Magnesium metallic materials that can degrade over time provide distinct opportunities for orthopedic application. However, there is still a lack, especially in elucidating cell-material interface characterization. This study investigated the influence of osteoblast-osteoclast coculture in direct Mg-material contact. Our findings demonstrated that pre-differentiated osteoblasts and osteoclasts cocultured on Mg substrates influenced the chemistry of the corrosion layers. The cell spread and attachment were Mg substrate-dependent. The findings of coculturing bone cells directly on Mg materials within an in vitro model provide an effective approach for studying the dynamic degradation processes of Mg alloys while also elucidating cell behavior and their potential contribution to the degradation of these alloys.

Biocompatibility and osteogenic potential of choline phosphate chitosan-coated biodegradable Zn1Mg

Zinc alloys have demonstrated considerable potentials as implant materials for biodegradable vascular and orthopedic applications. However, the high initial release of Zn2+ can trigger intense immune responses that impede tissue healing. To address this challenge and enhance the osteogenic capacity of zinc alloys, the surface of Zn1Mg was subjected to CO2 plasma modification (Zn1Mg-PP) followed by grafting with choline phosphate chitosan (Zn1Mg-PP-PCCs). This study aims to investigate the in vitro and in vivo biocompatibility of the surface-modified Zn1Mg. The effect of the surface modification on the inflammatory response and osteogenic repair process was investigated. Compared with unmodified Zn1Mg, the degradation rate of Zn1Mg-PP-PCCs was significantly decreased, avoiding the cytotoxicity triggered by the release of large amounts of Zn2+. Moreover, PCCs significantly enhanced the cell-material adhesion, promoted the proliferation of osteoblasts (MC3T3-E1) and upregulated the expression of key osteogenic factors in vitro. Notably, the in vivo experiments revealed that the surface modification of Zn1Mg suppressed inhibited the expression of inflammatory cytokines, promoting the secretion of anti-inflammatory factors, thereby reducing inflammation and promoting bone tissue repair. Furthermore, histological analysis of tissue sections exhibited strong integration between the material and the bone, along with well-defined new bone formation and reduced osteoclast aggregation on the surface. This was attributed to the improved immune microenvironment by PCCs, which promoted osteogenic differentiation of osteoblasts. These findings highlight that the preparation of PCCs coatings on zinc alloy surfaces effectively inhibited ion release and modulated the immune environment to promote bone tissue repair. STATEMENT OF SIGNIFICANCE: Surface modification of biodegradable Zn alloys facilitates the suppression of intense immune responses caused by excessive ion release concentrations from implants. We modified the surface of Zn1Mg with choline phosphate chitosan (PCCs) and investigated the effects of surface modification on the inflammatory response and osteogenic repair process. In vitro results showed that the PCCs coating effectively reduced the degradation rate of Zn1Mg to avoid cytotoxicity caused by high Zn2+ concentration, favoring the proliferation of osteoblasts. In addition, in vivo results indicated that Zn1Mg-PP-PCCs attenuated inflammation to promote bone repair by modulating the release of inflammation-related factors. The surface-modified Zn1Mg implants demonstrated strong osseointegration, indicating that the PCCs coating effectively modulated the immune microenvironment and promoted bone healing.

Polymeric Coatings for Magnesium Alloys for Biodegradable Implant Application: A Review

Magnesium (Mg) alloys are a very attractive material of construction for biodegradable temporary implants. However, Mg alloys suffer unacceptably rapid corrosion rates in aqueous environments, including physiological fluid, that may cause premature mechanical failure of the implant. This necessitates a biodegradable surface barrier coating that should delay the corrosion of the implant until the fractured/damaged bone has healed. This review takes a brief account of the merits and demerits of various existing coating methodologies for the mitigation of Mg alloy corrosion. Since among the different coating approaches investigated, no single coating recipe seems to address the degradation control and functionality entirely, this review argues the need for polymer-based and biodegradable composite coatings.

In vivo and In vitro properties evaluation of curcumin loaded MgO doped 3D printed TCP scaffolds

The lack of site-specific chemotherapeutic agents to treat bone malignancy throws a significant challenge in the design of a delivery vehicle. The major scientific question posed in this study is, can we utilize curcumin-loaded magnesium oxide (MgO) doped 3D printed tricalcium phosphate (TCP) bone grafts as a localized delivery system that improves early stage in vivo osseointegration and in vitro chemoprevention, antibacterial properties? We have utilized curcumin as an alternative natural chemopreventive agent for bone cancer-specific delivery after direct incorporation on the 3D printed tricalcium phosphate (TCP) bone grafts. The addition of MgO as a dopant to TCP leads to ∼1.3 times enhancement in compressive strength. The designed drug delivery system shows up to ∼22% curcumin release in a physiological pH of 7.4 after 30 days. The presence of curcumin leads to up to ∼8.5 times reduction in osteosarcoma viability. In vitro results indicate that these scaffolds significantly enhance bone-forming osteoblast cells while reducing the bone-resorbing osteoclast cells. The in vivo rat distal femur model surgery followed by histological assessment with H&E, vWF, and Movat pentachrome staining results show that the designed scaffolds lead to new bone formation (up to ∼2.5 times higher than the control) after successful implantation. The presence of MgO and curcumin results in up to ∼71% antibacterial efficacy against osteomyelitis causing S. aureus. These 3D printed osteogenic and chemopreventive scaffolds can be utilized in patient-specific low load-bearing defect sites.

Improving Biocompatibility for Next Generation of Metallic Implants

The increasing need for joint replacement surgeries, musculoskeletal repairs, and orthodontics worldwide prompts emerging technologies to evolve with healthcare's changing landscape. Metallic orthopaedic materials have a shared application history with the aerospace industry, making them only partly efficient in the biomedical domain. However, suitability of metallic materials in bone tissue replacements and regenerative therapies remains unchallenged due to their superior mechanical properties, eventhough they are not perfectly biocompatible. Therefore, exploring ways to improve biocompatibility is the most critical step toward designing the next generation of metallic biomaterials. This review discusses methods of improving biocompatibility of metals used in biomedical devices using surface modification, bulk modification, and incorporation of biologics. Our investigation spans multiple length scales, from bulk metals to the effect of microporosities, surface nanoarchitecture, and biomolecules such as DNA incorporation for enhanced biological response in metallic materials. We examine recent technologies such as 3D printing in alloy design and storing surface charge on nanoarchitecture surfaces, metal-on-metal, and ceramic-on-metal coatings to present a coherent and comprehensive understanding of the subject. Finally, we consider the advantages and challenges of metallic biomaterials and identify future directions.

A comprehensive review of properties of the biocompatible thin films on biodegradable Mg alloys

Magnesium (Mg) and its alloys have attracted attention as biodegradable materials for biomedical applications owing to their mechanical properties being comparable to that of bone. Mg is a vital trace element in many enzymes and thus forms one of the essential factors for human metabolism. However, before being used in biomedical applications, the early stage or fast degradation of Mg and its alloys in the physiological environment should be controlled. The degradation of Mg alloys is a critical criterion that can be controlled by a surface modification which is an effective process for conserving their desired properties. Different coating methods have been employed to modify Mg surfaces to provide good corrosion resistance and biocompatibility. This review aims to provide information on different coatings and discuss their physical and biological properties. Finally, the current withstanding challenges have been highlighted and discussed, followed by shedding some light on future perspectives.

Characterization of a Magnesium Fluoride Conversion Coating on Mg-2Y-1Mn-1Zn Screws for Biomedical Applications

MgF₂-coated screws made of a Mg-2Y-1Mn-1Zn alloy, called NOVAMag^® fixation screws (biotrics bioimplants AG), were tested in vitro for potential applications as biodegradable implants, and showed a controlled corrosion rate compared to non-coated screws. While previous studies regarding coated Mg-alloys have been carried out on flat sample surfaces, the present work focused on functional materials and final biomedical products. The substrates under study had a complex 3D geometry and a nearly cylindrical-shaped shaft. The corrosion rate of the samples was investigated using an electrochemical setup, especially adjusted to evaluate these types of samples, and thus, helped to improve an already patented coating process. A MgF₂/MgO coating in the µm-range was characterized for the first time using complementary techniques. The coated screws revealed a smoother surface than the non-coated ones. Although the cross-section analysis revealed some fissures in the coating structure, the electrochemical studies using Hanks' salt solution demonstrated the effective role of MgF₂ in retarding the alloy degradation during the initial stages of corrosion up to 24 h. The values of polarization resistance (Rp) of the coated samples extrapolated from the Nyquist plots were significantly higher than those of the non-coated samples, and impedance increased significantly over time. After 1200 s exposure, the Rp values were 1323 ± 144 Ω.cm² for the coated samples and 1036 ± 198 Ω.cm² for the non-coated samples, thus confirming a significant decrease in the degradation rate due to the MgF₂ layer. The corrosion rates varied from 0.49 mm/y, at the beginning of the experiment, to 0.26 mm/y after 1200 s, and decreased further to 0.01 mm/y after 24 h. These results demonstrated the effectiveness of the applied MgF₂ film in slowing down the corrosion of the bulk material, allowing the magnesium-alloy screws to be competitive as dental and orthopedic solutions for the biodegradable implants market.

Mechanical Properties and Corrosion Behavior of Silica Nanoparticle Reinforced Magnesium Nanocomposite for Bio-Implant Application

In this study, magnesium (Mg)-based nanocomposites reinforced with silica (SiO₂) nanoparticles were developed using the powder metallurgy process, and their mechanical and corrosion behavior were assessed. Mg-alloy AZ31 served as the matrix material, and two different weight percentages of SiO₂ nanoparticles were used as filler. According to the microstructural analysis, the composite generated a Mg₂Si phase as a result of SiO₂ dissociating during the sintering process. The microhardness of the Mg-alloy dramatically enhanced with the addition of 3% nanosilica, although the elastic modulus remained constant. Additionally, the outcomes demonstrated that the Mg₂Si phase's development in the composite constrained the mechanism of deterioration and postponed the pace of degradation, which aided in enhancing the qualities of corrosion resistance. This nanocomposite might, thus, be thought of as a potential replacement for the traditional bio-implant materials.

Effect of pH fluctuations on the biodegradability of nanocomposite Mg-alloy in simulated bodily fluids

According to the National Institute of Health, the biodegradability, non-toxic nature, and remarkable natural and mechanical properties of magnesium and its components make them desirable choices for use in the production of supplies for biomedical implantation. Simulated bodily fluid (SBF) is used as a standard electrolyte for in vitro corrosion research. Each SBF module's independent and synergistic corrosion effects are studied in this study. Artificial pH variations increase degradation, according to the results. This experiment examined the Mg corrosion submerged in a SBF solution. The effect of pH changes on the rate of corrosion of Mg immersed in standard SBF solution was investigated. According to the previously published study, the corrosion process of Mg has been confirmed by scanning electron microscopy observations of damaged surface morphology. Because of these investigations, pH 7 was selected as the pH for bodily fluids since it is neutral.

Insights of Microstructural Features and Their Effect on Degradation and the In Vitro Bioactivity Response of as-Cast Mg-Sn Alloys for Orthopedic Implant Applications

The present work focuses on a deep understanding of microstructural evolution and phase formation in a binary Mg-Sn alloy system. Mg-xSn (x = 1, 5, 10 wt.%) alloys were cast using a squeeze casting technique. Phase identification and microstructural analysis were done using XRD (X-ray Diffraction) and FESEM with EDS (Field Emission Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy), respectively. The mechanical behavior of the alloys under study was evaluated by conducting a compression test. The corrosion behavior of all the alloys were intricately studied using electrochemical corrosion tests and an immersion test in the simulated body fluid (SBF) environment for different immersion periods. The bioactivity response of Mg-Sn alloys systems under this study was investigated by immersing the samples in SBF for 14 days. From the analysis of the results, it was understood that the amount of Sn addition has a large influence on the metallurgical, corrosion, and bioactivity properties. Interesting facts about the intermetallic phase formation and segregation of Sn were observed when the wt.% of Sn was varied in the alloy and the evolution of the microstructure was described clearly. Mechanical properties of Mg-Sn alloys were improved, as the Sn content increased up to 5 wt.% and declined in the case of a 10 wt.% Sn addition. A similar trend was observed even in the case of corrosion resistance and bioactivity properties. Among the alloy compositions studied, Mg with a 5 wt.% addition has proved to be a promising candidate material for orthopedic implant applications with an acceptable elastic modulus, higher corrosion resistance, and an excellent bioactive response.

MAGNESIUM BASED ALLOYS FOR BIODEGRADABLE IMPLANTS APPLICATIONS USING ADDITIVE MANUFACTURING TECHNIQUE: A REVIEW

Biodegradable materials have various advantages compared to nonbiodegradable materials. Developing implants using biodegradable materials eliminates the need for secondary surgery, improves mechanical and biological properties, and improves biocompatibility. Magnesium (Mg) and its alloys are frequently used in orthopedic applications nowadays. However, the rapid degradation of Mg poses a substantial challenge. As a result, for the bone to heal properly, a proper balance between implant degeneration rate and bone healing must be obtained. Mg has certain other drawbacks, such as the need for an inert atmosphere when employing powder metallurgy and casting procedures to manufacture it because of its reactive nature. In this paper, Additive manufacturing (AM) techniques for manufacturing orthopedic biodegradable implants made of Mg and its alloys are discussed which helps in obtaining improved biological and mechanical properties of the implants. These orthopedic implants should have a controlled rate of degradation and antibacterial functional surfaces. There is also a description of the use of several AM processes utilized to enhance the mechanical and biological characteristics of implants employing Mg. This paper also seeks to present the concept of integrating established techniques into a production process to obtain the needed biodegradable implant material for orthopedic applications.

Biodegradable open-porous scaffolds made of sintered magnesium W4 and WZ21 short fibres show biocompatibility in vitro and in long-term in vivo evaluation

Open-porous scaffolds made of W4 and WZ21 fibres were evaluated to analyse their potential as an implant material. WZ21 scaffolds without any surface modification or coating, showed promising mechanical properties which were comparable to the W4 scaffolds tested in previous studies. Eudiometric testing results were dependent on the experimental setup, with corrosion rates differing by a factor of 3. Cytotoxicity testing of WZ21 showed sufficient cytocompatibility. The corrosion behavior of the WZ21 scaffolds in different cell culture media are indicating a selective dealloying of elements from the magnesium scaffold by different solutions. Long term in-vivo studies were using 24 W4 scaffolds and 12 WZ21 scaffolds, both implanted in rabbit femoral condyles. The condyles and important inner organs were explanted after 6, 12 and 24 weeks and analyzed. The in-vivo corrosion rate of the WZ21 scaffolds calculated by microCT-based volume loss was up to 49 times slower than the in-vitro corrosion rate based on weight loss. Intramembranous bone formation within the scaffolds of both alloys was revealed, however a low corrosion rate and formation of gas cavities at initial time points were also detected. No systemic or local toxicity could be observed. Investigations by μ-XRF did not reveal accumulation of yttrium in the neighboring tissue. In summary, the magnesium scaffold´s performance is biocompatible, but would benefit from a surface modification, such as a coating to obtain lower the initial corrosion rates, and hereby establish a promising open-porous implant material for load-bearing applications. STATEMENT OF SIGNIFICANCE: Magnesium is an ideal temporary implant material for non-load bearing applications like bigger bone defects, since it degrades in the body over time. Here we developed and tested in vitro and in a rabbit model in vivo degradable open porous scaffolds made of sintered magnesium W4 and WZ21 short fibres. These scaffolds allow the ingrowth of cells and blood vessels to promote bone healing and regeneration. Both fibre types showed in vitro sufficient cytocompatibility and proliferation rates and in vivo, no systemic toxicity could be detected. At the implantation site, intramembranous bone formation accompanied by ingrowth of supplying blood vessels within the scaffolds of both alloys could be detected.

Potential bioactive coating system for high-performance absorbable magnesium bone implants

Magnesium alloys are considered the most suitable absorbable metals for bone fracture fixation implants. The main challenge in absorbable magnesium alloys is their high corrosion/degradation rate that needs to be controlled. Various coatings have been applied to magnesium alloys to slow down their corrosion rates to match their corrosion rate to the regeneration rate of the bone fracture. In this review, a bioactive coating is proposed to slow down the corrosion rate of magnesium alloys and accelerate the bone fracture healing process. The main aim of the bioactive coatings is to enhance the direct attachment of living tissues and thereby facilitate osteoconduction. Hydroxyapatite, collagen type I, recombinant human bone morphogenetic proteins 2, simvastatin, zoledronate, and strontium are six bioactive agents that show high potential for developing a bioactive coating system for high-performance absorbable magnesium bone implants. In addition to coating, the substrate itself can be made bioactive by alloying magnesium with calcium, zinc, copper, and manganese that were found to promote bone regeneration.

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Bioactive-coated magnesium implant could accelerate bone fracture healing time to match with magnesium degradation.

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Hydroxyapatite, collagen type I, recombinant human bone morphogenetic proteins 2, simvastatin, zoledronate, and strontium are high potential bioactive coating materials.

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The incorporation of Ca, Zn, Cu, Sr, and Mn in Mg base-metal could further enhance bone formation.

Review of the Effect of Surface Coating Modification on Magnesium Alloy Biocompatibility

Magnesium alloy, as an absorbable and implantable biomaterial, has been greatly developed in the application field of biomaterials in recent years due to its excellent biocompatibility and biomechanics. However, due to the poor corrosion resistance of magnesium alloy in the physiological environment, the degradation rate will be unbalanced, which seriously affects the clinical use. There are two main ways to improve the corrosion resistance of magnesium alloy: one is by adding alloying elements, the other is by surface modification technology. Compared with adding alloy elements, the surface coating modification has the following advantages: (1) The surface coating modification is carried out without changing the matrix elements of magnesium alloy, avoiding the introduction of other elements; (2) The corrosion resistance of magnesium alloy can be improved by relatively simple physical, chemical, or electrochemical improvement. From the perspective of corrosion resistance and biocompatibility of biomedical magnesium alloy materials, this paper summarizes the application and characteristics of six different surface coating modifications in the biomedical magnesium alloy field, including chemical conversion method, micro-arc oxidation method, sol-gel method, electrophoretic deposition, hydrothermal method, and thermal spraying method. In the last section, it looks forward to the development prospect of surface coating modification and points out that preparing modified coatings on the implant surface combined with various modification post-treatment technologies is the main direction to improve biocompatibility and realize clinical functionalization.

Electrochemical and In Vitro Biological Evaluation of Bio-Active Coatings Deposited by Magnetron Sputtering onto Biocompatible Mg-0.8Ca Alloy

The use of resorbable magnesium alloys in the design of implants represents a new direction in the healthcare domain. Two main research avenues are currently explored for developing or improving metallic biomaterials: (i) increase of their corrosion resistance by designed compositional and structural modifications, and (ii) functionalization of their surfaces by coating with ceramic or polymeric layers. The main objective of this work was to comparatively assess bio-functional coatings (i.e., highly-crystallized hydroxyapatite and silica-rich glass) deposited by radio-frequency magnetron sputtering (RF-MS) on a biodegradable Mg-0.8Ca alloy (0.8 wt.% of Ca). After probing their morphology (by scanning electron microscopy) and structure (by Fourier transform infrared spectroscopy and grazing incidence X-ray diffraction), the corrosion resistance of the RF-MS coated Mg-0.8Ca substrates was electrochemically tested (in synthetic biological media with different degrees of biomimicry), and their cytocompatibility was assessed in osteoblast and fibroblast cell cultures. By collective assessment, the most promising performances, in terms of mass loss (~7% after 12 days), hydrogen release rate (~6 mL/cm² after 12 days), electrochemical corrosion parameters and cytocompatibility, were obtained for the crystalline HA coating.

Corrosion Resistance and Biocompatibility of Calcium Phosphate Coatings with a Micro-Nanofibrous Porous Structure on Biodegradable Magnesium Alloys

Magnesium (Mg) and its alloys have exhibited great potential for orthopedic applications; however, their poor corrosion resistance and potential cytotoxicity have hindered their further clinical applications. In this study, we prepared a calcium phosphate (Ca-P) coating with a micro-nanofibrous porous structure on the Mg alloy surface by a chemical conversion method. The morphology, composition, and corrosion performance of the coatings were investigated by scanning electron microscope (SEM), energy-dispersive spectrometer (EDS), X-ray diffraction (XRD), immersion tests, and electrochemical measurements. The effects of the preparation temperature of the Ca-P coatings were analyzed, and the results confirmed that the coating obtained at 60 °C had the densest structure and the best corrosion resistance. In addition, a systematic investigation into cell viability, ALP activity, and cell morphology confirmed that the Ca-P coating had excellent biocompatibility, which could effectively promote the proliferation, differentiation, and adhesion of osteoblasts. Hence, the Ca-P coating demonstrates great potential in the field of biodegradable Mg-based orthopedic implant materials.

In vivo and in vitro performances of chitosan-coated Mg-Zn-Zr-Gd-Ca alloys as bone biodegradable materials in rat models

Mg alloys have attracted significant attention as promising biomedical materials, specifically as fixation materials for promoting fracture healing. However, their unsatisfactory corrosion resistances hinder further clinical applications and thus require attention. This study aims to determine the performance of novel chitosan-coated Mg-1Zn-0.3Zr-2Gd-1Ca alloy and its ability to promote the healing of osteoporotic fractures. Moreover, its corrosion resistance and biocompatibility were assessed. Performance degradations of the samples were measured via electrochemical tests, weight loss test and morphological analysis, and the uncoated and chitosan-coated fixations were compared based on their effects on biocompatibility via the cytotoxicity test, X-rays, and hematoxylin and eosin staining. The effect of bone growth and healing was investigated via immunohistochemical test. Results of the electrochemical tests indicated that compared with the bare body, chitosan-coated Mg-Zn-Ca-Zr-Gd alloys improved by one order of magnitude. Additionally, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and weight loss test demonstrated that the corrosion resistance of the chitosan-coated Mg alloy is better than that of the uncoated alloy. In addition, cytotoxicity analysis indicated that the viability and morphology of the chitosan-coated alloy groups were superior to the uncoated groups in vitro. During in vivo analysis, chitosan-coated and uncoated Mg-1Zn-0.3Zr-2Gd-1Ca alloys were implanted into ovariectomized SD female rats with osteoporotic fractures for 1, 2, and 3 weeks. No displacement and shedding were observed through X-rays, and pathological analyses proved that the material was not harmful for liver and kidney tissues. Immunohistochemistry revealed that the chitosan-coated Mg-Zn-Ca-Zr-Gd alloy material contributed to the healing of osteoporotic fractures in the SD rat models. In conclusion, this study demonstrated the chitosan-coated Mg-Zn-Ca-Zr-Gd alloys have improved corrosion resistance and biocompatibility. Moreover, the alloy was found to accelerate the healing of osteoporotic fractures in SD rat models. Therefore, it has significant potential as a fixation material for osteoporotic fractures.

In vitro and in vivo degradation assessment and preventive measures of biodegradable Mg alloys for biomedical applications

Magnesium (Mg) and its alloys have been widely explored as a potential biodegradable implant material. However, the fast degradation of Mg-based alloys under physiological environment has hindered their widespread use for implant applications till date. The present review focuses on in vitro and in vivo degradation of biodegradable Mg alloys, and preventive measures for biomedical applications. Initially, the corrosion assessment approaches to predict the degradation behavior of Mg alloys are discussed along with the measures to control rapid corrosion. Furthermore, this review attempts to explore the correlation between in vitro and in vivo corrosion behavior of different Mg alloys. It was found that the corrosion depends on experimental conditions, materials and the results of different assessment procedures hardly matches with each other. It has been demonstrated the corrosion rate of magnesium can be tailored by alloying elements, surface treatments and heat treatments. Various researches also studied different biocompatible coatings such as dicalcium phosphate dihydrate (DCPD), β-tricalcium phosphate (β-TCP), hydroxyapatite (HA), polycaprolactone (PCL), polylactic acid (PLA), and so on, on Mg alloys to suppress rapid degradation and examine their influence on new bone regeneration as well. This review shows the need for a standard method of corrosion assessment to predict the in vivo corrosion rate based on in vitro data, and thus reducing the in vivo experimentation.

A biodegradable, mechanically tunable micro-arc oxidation AZ91D-based composite implant with calcium phosphate/chitosan coating promotes long-term bone tissue regeneration

BACKGROUND

To reduce the biodegradable rate and develop the long-term osteogenic ability of magnesium (Mg) alloy, we prepared a new biodegradable micro arc oxidation AZ91D-based composite implant with calcium phosphate/chitosan coating (CaP-CS/MAO/AZ91D) and investigated its mechanical property and long-term bone tissue regeneration ability.

MAIN METHODS AND MAJOR RESULTS

The results showed that the binding force and bioactivity of CaP-CS/MAO/AZ91D was better when the ratio of water to ethanol was 4:6 and MAO constant current was 0.1 A cm^-2 . Compressive strengths of 4:6 sample were more than 1300 N when the soaking time was increased to 21 days. CaP-CS/MAO/AZ91D extracts promoted differentiation and proliferation of rat mesenchymal stem cells (RMSC), which achieved higher proliferation rates over 16 days of culture and exhibited early alkaline phosphatase activity and late bone sialoprotein markers.

CONCLUSIONS AND IMPLICATIONS

CaP-CS/MAO/AZ91D was established to promote RMSC osteogenic differentiation within a proper range for at least 90 days through Wnt/β-catenin pathway activation, which would allow sufficient time for bone healing. Collectively, our findings suggest that the CaP-CS/MAO/AZ91D coating could not only reduce the corrosion rate and lead to better long-term biocompatibility but also promote osteogenic mineralization.

Biosafety and biodegradation studies of AZ31B magnesium alloy carotid artery stent in vitro and in vivo

Biosafety of AZ31B magnesium (Mg) alloy and the effect of its degradation products on tissues, organs, and whole systems are highly needed to be evaluated before clinical application. This study serves a wide variety of safety evaluations of biodegradable AZ31B alloy on nerve cells. As a result of this in vitro study, the maximum aluminum (Al) ion and Mg ion concentrations in the medium were estimated to be 22 μmol/L and 2.75 mmol/L, respectively, during degradation. In addition, the corresponding cell mortality was observed to be 36% and lower than 5% according to the resistance curves of the cell to Mg and Al ions. Furthermore, the maximum Al ion and Mg ion concentrations in serum and cerebrospinal fluid were detected to be 26.1 μmol/L and 1.2 mmol/L, respectively, for 5 months implantation. Combining the result of in vivo dialysis with the result of ion tolerance assay experiments, the actual death rate of nerve cells is estimated between 4 and 10% in vivo, which is lower than the result of in vitro cytotoxicity evaluation. Moreover, no psychomotor disability during clinical studies is observed. Consequently, stent made of AZ31B alloy with surface treatment is feasible for carotid artery stenosis, and it is safe in terms of cell viability on the nervous system.

Design approaches and challenges for biodegradable bone implants: a review

Introduction: Biodegradable materials have been at the forefront of cutting-edge research and offer a truly viable option in the designing and manufacturing of bone implants in biomedical engineering. Most research regarding these materials has focused on their biological characteristics and mechanical behavior vis-à-vis nonbiodegradable (NB) materials; but the design aspects and parametric configurations of biodegradable bone implant have somehow not received as much attention as they deserved.Area covered: This review aims to develop insight into the parametrically conceptualized design of biodegradable bone implant and takes into due consideration the characteristics of bone-biodegradable implant interface (BBII), design techniques employed for conventionally used bone implants to optimize parameters using standard test methods, traditional design, and finite element analysis approaches for implant and healing behavior, manufacturing techniques, real-time surgical simulations, and so on.Expert opinion: Some successful and conventionally used NB bone implants do not dissolve or degrade with time and require removal through a complicated surgery after fulfilling the intended objectives. These bone implants should be reconceptualized and designed with an appropriate biodegradable material while paying due attention to all factors/parameters involved and striking a balance between these factors with the ultimate objective of fulfilling all desired orthopedic requirements.

Bio-corrosion impacts on mechanical integrity of ZM21 Mg for orthopaedic implant application processed by equal channel angular pressing

The mechanical integrity of rolled ZM21 Mg was improved by equal channel angular pressing (ECAP) to function as a potential biodegradable bone screw implant. Electron backscattered diffraction (EBSD) revealed deformed grains of 45 µm observed in rolled ZM21 Mg. They were transformed to equiaxed fine grains of 5.4 µm after 4^th pass ECAP. The yield strength of rolled and ECAPed ZM21 Mg alloys were comparable. In contrast, 4^th pass ZM21 Mg exhibited relatively higher elongation when compared to rolled sample. The mechanical properties of rolled and ECAPed ZM21 Mg were dependant on both grain refinement and crystallographic texture. The rolled and 4^th pass ECAPed tensile samples exhibited nonlinear deterioration of mechanical properties when tested after 7, 14, 21 and 28 days immersion in Hank's solution. The evaluation signifies that regardless their processing condition, ZM21 Mg alloys are suitable for surgical areas that requires high mechanical strength. In addition, the 4^th pass ECAP samples were viable to MG-63 cells proving themselves to be promising candidates for future in vivo studies.

Preliminary study on modelling, fabrication by photo-chemical etching and in vivo testing of biodegradable magnesium AZ31 stents

Magnesium metal (Mg) is a promising material for stent applications due to its biocompatibility and ability to be resorbed by the body. Manufacturing of stents by laser cutting has become an industry standard. Our alternative approach uses photo-chemical etching to transfer a pattern of the stent onto a Mg sheet. In this study, we present three stages of creating and validating a stent prototype, which includes design and simulation using finite element analysis (FEA), followed by fabrication based on AZ31 alloy and, finally, in vivo testing in peripheral arteries of domestic pigs. Due to the preliminary character of this study, only six stents were implanted in two domestic farm pigs weighing 25-28 kg and they were evaluated after 28 days, with an interim follow-up on day 14. The left and right superficial femoral, the left iliac, and the right renal artery were selected for this study. The diameters of the stented artery segments were evaluated at the time of implantation, on day 14 and then, finally, on day 28, by quantitative vessel analysis (QVA) using fluoroscopic imaging. Optical Coherence Tomography (OCT) imaging displayed some malposition, breaks, stacking, and protrusion into the lumen at the proximal, distal, and mid-sections of the stented arteries. The stents degraded with time, but simultaneously became embedded in the intima. After 28 days, the animals were euthanized, and explanted vessels were fixed for micro-CT imaging and histology studies. Micro-CT imaging revealed stent morphological and volumetric changes due to the in-body degradation. An in vivo corrosion rate of 0.75 mm/year was obtained by the CT evaluation. The histology suggested no-life threatening effects, although moderate injury, inflammation, and endothelialization scores were observed.

Calcium phosphate coatings enhance biocompatibility and degradation resistance of magnesium alloy: Correlating in vitro and in vivo studies

Magnesium (Mg) and its alloys are promising biodegradable materials for orthopedic applications. However, one of the major problems is their rapid degradation rate with quick evolution of hydrogen gas. To overcome this problem, calcium phosphate (CaP) coatings have been used to improve the degradation resistance and the biocompatibility of Mg materials. This study focuses on the comparison and correlation of the in vitro and in vivo degradation and biocompatibility behaviors of these materials. A CaP coating consisting of dicalcium phosphate dihydrate (DCPD) was deposited on an AZ60 Mg alloy by the chemical conversion method. Then, the in vitro degradation testing including electrochemical and immersion tests, and in vivo implantation of the CaP coated Mg alloy were conducted to compare the degradation behaviors. Next, the in vitro cell behavior and in vivo bone tissue response were also compared on both uncoated and CaP-coated Mg samples. Data showed that the CaP coating provided the Mg alloy with significantly better biodegradation behavior and biocompatibility. The in vitro and in vivo biocompatibility tests exhibited good consistency while not the case for biodegradation. Results showed that the in vitro electrochemical test could be a quick screening tool for the biodegradation rate, while the in vitro immersion degradation rate was often 2-4 folds faster than the in vivo degradation rate.

Alkali-Treated Titanium Coated with a Polyurethane, Magnesium and Hydroxyapatite Composite for Bone Tissue Engineering

The aim of this study was to form a functional layer on the surface of titanium (Ti) implants to enhance their bioactivity. Layers of polyurethane (PU), containing hydroxyapatite (HAp) nanoparticles (NPs) and magnesium (Mg) particles, were deposited on alkali-treated Ti surfaces using a cost-effective dip-coating approach. The coatings were assessed in terms of morphology, chemical composition, adhesion strength, interfacial bonding, and thermal properties. Additionally, cell response to the variably coated Ti substrates was investigated using MC3T3-E1 osteoblast-like cells, including assessment of cell adhesion, cell proliferation, and osteogenic activity through an alkaline phosphatase (ALP) assay. The results showed that the incorporation of HAp NPs enhanced the interfacial bonding between the coating and the alkali-treated Ti surface. Furthermore, the presence of Mg and HAp particles enhanced the surface charge properties as well as cell attachment, proliferation, and differentiation. Our results suggest that the deposition of a bioactive composite layer containing Mg and HAp particles on Ti implants may have the potential to induce bone formation.

Bio-inspired biomaterial Mg-Zn-Ca: a review of the main mechanical and biological properties of Mg-based alloys

The toxicity of alloying elements in magnesium alloys used for biomedical purposes is an interesting and innovative subject, due to the great technological advances that would result from their application in medical devices (MDs) in traumatology. Recently promising results have been published regarding the rates of degradation and mechanical integrity that can support Mg alloys; this has led to an interest in understanding the toxicological features of these emerging biomaterials. The growing interest of different segments of the MD market has increased the determination of different research groups to clarify the behavior of alloying elements in vivo. This review covers the influence of the alloying elements on the body, the toxicity of the elements in Mg-Zn-Ca, as well as the mechanical properties, degradation, processes of obtaining the alloy, medical approaches and future perspectives on the use of the Mg in the manufacture of MDs for various medical applications.

UV-irradiation induced biological activity and antibacterial activity of ZnO coated magnesium alloy

In order to improve the biological activity and antibacterial activity of magnesium alloy, the single zinc oxide (ZnO) coating was prepared on magnesium alloys using microwave aqueous synthesis method and followed heat treatment. Then, the coated magnesium alloys were irradiated with ultraviolet (UV) light for different time and subsequently immersed in simulated body fluids (SBF). The influences of UV-irradiated time on the morphology, composition, in vitro biological activity and antibacterial activity were investigated. The results indicated that the ability of the apatite formation on the ZnO coated magnesium alloys surface was significantly enhanced as UV irradiation time prolonged, and the bone-like apatite was formed after UV irradiation for 24 h and then immersing into SBF for 2 weeks, the newly formed apatite was dense and integrate, implying that UV irradiation could activate ZnO coating to improve the biological activity. Moreover, after immersing in SBF for 2 weeks, the antibacterial experiment results demonstrated that ZnO coated magnesium alloys with UV irradiation time of 24 h exhibited more effective antibacterial activity than those of naked magnesium alloys and ZnO coated magnesium alloys which were not irradiated by ultraviolet (UV) light. This work afforded a surface strategy for designing magnesium alloy implant with desirable osseointegration ability and antibacterial property simultaneously for orthopedic and dental applications.

Fabrication and characterization of silk fibroin coating on APTES pretreated Mg-Zn-Ca alloy

To delay the degradation of magnesium alloys, silk fibroin as a natural organic polymer coating was fabricated on a 3-amino-propyltriethoxysilane (APTES) pretreated Mg-Zn-Ca alloy. APTES pretreatment coated the surface of magnesium alloys with amino groups, which can bond with functional groups in silk fibroin to form a compact coating/substrate interface. The influences of the APTES concentration and drying temperature on the coating adhesion and interface were investigated to explore the optimal parameters in the fabrication process. The nanoporous silk fibroin films completely covered the APTES pretreated Mg-Zn-Ca surface, which reached a thickness of ~7 μm. The chemical states for the coated Mg-Zn-Ca alloy were compared to those of the bare Mg-Zn-Ca alloy and the APTES pretreated Mg-Zn-Ca alloy to illustrate the coating mechanism. During in vitro degradation and electrochemical measurements in simulated body fluid (SBF), the samples with the silk fibroin coating showed remarkably improved corrosion resistance and a slower degradation rate compared to those of the bare samples, suggesting that the silk fibroin coating was an effective protection coating for the substrates and can delay the degradation of magnesium alloys. Moreover, a model for the in vitro degradation was proposed. In vitro cell experiments confirmed the excellent biocompatibility of silk fibroin coated Mg-Zn-Ca structure.

Biological behavior exploration of a paclitaxel-eluting poly-l-lactide-coated Mg–Zn–Y–Nd alloy intestinal stent in vivo

As a new type of intestinal stent, the MAO/PLLA/paclitaxel/Mg–Zn–Y–Nd alloy stent has shown good degradability, although its biocompatibility in vitro and in vivo has not been investigated in detail. In this study, its in vivo biocompatibility was evaluated by animal study. New Zealand white rabbits were implanted with degradable intestinal Mg–Zn–Y–Nd alloy stents that were exposed to different treatments. Stent degradation behavior was observed both macroscopically and using a scanning electron microscope (SEM). Energy dispersion spectrum (EDS) and histological observations were performed to investigate stent biological safety. Macroscopic analysis showed that the MAO/PLLA/paclitaxel/Mg–Zn–Y–Nd stents could not be located 12 days after implantation. SEM observations showed that corrosion degree of the MAO/PLLA/paclitaxel/Mg–Zn–Y–Nd stents implanted in rabbits was significantly lower than that in the PLLA/Mg–Zn–Y–Nd stent group. Both histopathological testing and serological analysis of in vivo biocompatibility demonstrated that the MAO/PLLA/paclitaxel/Mg–Zn–Y–Nd alloy stents could significantly inhibit intestinal tissue proliferation compared to the PLLA/Mg–Zn–Y–Nd alloy stents, thus providing the basis for designing excellent biodegradable drug stents.

Mg–Zn–Y–Nd alloy stents coated with MAO/PLLA/paclitaxel coating were implanted into the New Zealand rabbits intestine to investigate the biocompatibility and degradation behavior.

Biofunctionalization of metallic implants by calcium phosphate coatings

Metallic materials have been extensively applied in clinical practice due to their unique mechanical properties and durability. Recent years have witnessed broad interests and advances on surface functionalization of metallic implants for high-performance biofunctions. Calcium phosphates (CaPs) are the major inorganic component of bone tissues, and thus owning inherent biocompatibility and osseointegration properties. As such, they have been widely used in clinical orthopedics and dentistry. The new emergence of surface functionalization on metallic implants with CaP coatings shows promise for a combination of mechanical properties from metals and various biofunctions from CaPs. This review provides a brief summary of state-of-art of surface biofunctionalization on implantable metals by CaP coatings. We first glance over different types of CaPs with their coating methods and in vitro and in vivo performances, and then give insight into the representative biofunctions, i.e. osteointegration, corrosion resistance and biodegradation control, and antibacterial property, provided by CaP coatings for metallic implant materials.

Magnesium matrix nanocomposites for orthopedic applications: A review from mechanical, corrosion, and biological perspectives

Magnesium (Mg) and some of its alloys have attracted extensive interests for biomedical applications as they exhibit biodegradability and low elastic modulus that is closer to natural bones than the currently used metallic implant materials such as titanium (Ti) and its alloys, stainless steels, and cobalt-chromium (Co-Cr) alloys. However, the rapid degradation of Mg alloys and loss of their mechanical integrity before sufficient bone healing impede their clinical application. Our literature review shows that magnesium matrix nanocomposites (MMNCs) reinforced with nanoparticles possess enhanced strength, high corrosion resistance, and good biocompatibility. This article provides a detailed analysis of the effects of nanoparticle reinforcements on the mechanical properties, corrosion behavior, and biocompatibility of MMNCs as promising biodegradable implant materials. The governing equations to quantitatively predict the mechanical properties and underlying synergistic strengthening mechanisms in MMNCs are elucidated. The potential, recent advances, challenges and future research directions in relation to nanoparticles reinforced MMNCs are highlighted. STATEMENT OF SIGNIFICANCE: Critically reviewing magnesium metal matrix nanocomposites (MMNCs) for the biomedical application. Clear definitions of strengthening mechanisms using reinforcement particle in the magnesium matrix, as there were controversial in governing equations of strengthening parameters. Providing better understanding of the effect of particle size, volume fraction, interfacial bonding, and uniform dispersion of reinforcement particles on MMNCs.

Development of magnesium implants by application of conjoint-based quality function deployment

Biodegradable magnesium-based implants are the subject of a great deal of research for different orthopedic and vascular applications. The targeted design and properties depend on the specific medical function and location in the body. Development of the biomaterial requires a comprehensive understanding of the biological interaction between the implant and the host tissue, as well as of the behavior in the physiological environment in vivo. Research into and the development of innovative magnesium implants entails interdisciplinary research efforts and communication between materials science, bioscience, and medical experts. The present study provides a transparent planning and communication tool for market-oriented implant development processes. The objective was to identify medical needs at an early stage of the development process and to quantify the importance of the engineering characteristics of different research fields that cater to specific implant requirements. The method is demonstrated by the performance of a survey-based conjoint analysis, which was integrated into a quality function deployment approach. Twenty-seven medical professionals and 29 biomaterial scientists assessed the importance of identified medical requirements, whereby the control of mechanical integrity and degradation along with nontoxicity and nonimmunogenicity showed the highest number of preferences. The evaluation of implant options by 31 experts indicated that the engineering characteristic with the highest importance was the condition and sterilization of the surface. These values can be used to set priorities in strategic decisions. Research trials can be aligned to medical preferences, ensuring high product quality and an effective development process. This is the first paper to report on the application of conjoint-based quality function deployment in biomaterial research.

The effect of the nano- bioglass reinforcement on magnesium based composite

Nano-bioceramic particles serving as a reinforcement can improve the mechanical and biological properties of magnesium implants, but they might have some side effects, that must be addressed. In this research, magnesium composites including 10 wt% nano-bioglass (nBG) were fabricated using powder metallurgy (PM10) and spark plasma sintering (SPS10) methods for bone reconstruction purposes. The results of the compression test indicated that the SPS10 sample had higher mechanical properties, in comparison to the PM10 sample, and nBG had more reinforcing effect on the mechanical properties of magnesium matrix. X-ray difractometery indicated that nBG was chemically reacted with magnesium in the PM10 sample, and resulted in some extra phases (MgO and Mg₂Si) formation, while there was no detectable extra phases in the SPS10 sample. However, a higher in vitro degradation rate was observed for PM10 sample, because of multi-phase formation at the magnesium matrix. To inhibit the chemical reaction between magnesium and nBG kinetically, a short time sintering process can be, therefore, recommended.

Surface Activation and Pretreatments for Biocompatible Metals and Alloys Used in Biomedical Applications

To improve the biocompatibility of medical implants, a chemical composition of bone-like material (e.g., hydroxyapatite) can be deposited on the surface of various substrates. When hydroxyapatite is deposited on surfaces of orthopedic implants, several parameters must be addressed including the need of rapid bone ingrowth, high mechanical stability, corrosion resistance, biocompatibility, and osseointegration induction. However, the deposition process can fail due to poor adhesion of the hydroxyapatite coating to the metallic substrate. Increasing adhesion by enhancing chemical bonding and minimizing biocoating degradation can be achieved through surface activation and pretreatment techniques. Surface activation can increase the adhesion of the biocoating to implants, providing protection in the biological environment and restricting the leaching of metal ions in vivo. This review covers the main surface activation and pretreatment techniques for substrates such as titanium and its alloys, stainless steel, magnesium alloys, and CoCrMo alloys. Alkaline, acidic, and anodizing techniques and their effects on bioapatite deposition are discussed for each of the substrates. Other chemical treatment and combination techniques are covered when used for certain materials. For titanium, the surface pretreatments improve the thickness of the TiO₂ passive layer, improving adhesion and bonding of the hydroxyapatite coating. To reduce corrosion and wear rates on the surface of stainless steel, different surface modifications enhance the bonding between the bioapatite coatings and the substrate. The use of surface modifications also improves the morphology of hydroxyapatite coatings on magnesium surfaces and limits the concentration of magnesium ions released into the body. Surface treatment of CoCrMo alloys also decreased the concentration of harmful ions released in vivo. The literature covered in this review is for pretreated surfaces which then undergo deposition of hydroxyapatite using electrodeposition or other wet deposition techniques and mainly limited to the years 2000-2019.

Silk fibroin film-coated MgZnCa alloy with enhanced in vitro and in vivo performance prepared using surface activation

Magnesium and its alloys have generated considerable interest as one of the most promising biodegradable metals for biomedical bone implants. However, the enormous challenges are to improve their rapid corrosion excessively as well as to endow them with biocompatibility and biosafety. Herein, we introduce a natural silk fibroin protein coating to control the corrosion resistance and enhance the biocompatibility of MgZnCa alloy. To obtain a robust and reliable coated structure, different surface-activation processes are employed to increase the available functional groups on MgZnCa surfaces before coating. Compared to oxygen plasma activation, our unique vacuum ultraviolet-ozone (VUV/O₃) activation method is effective in realizing uniform silk fibroin films as a protective barrier on MgZnCa alloy surfaces, and the nanoscratch test verified the superior adhesion strength of the silk fibroin-coated magnesium alloy structure. Long-term immersion results combined with electrochemical tests showed the preferable in vitro anticorrosion behavior and a low degradation rate of coated Mg alloy (1/8 times that of uncoated Mg alloy). Cell adhesion and cytotoxicity tests demonstrated that silk fibroin-coated MgZnCa presented improved biocompatibility with bone marrow mesenchymal stem cells. An animal study involving silk fibroin-coated MgZnCa implanted on one side of a rabbit spine for 180 days showed remarkably improved in vivo corrosion resistance, with 1/18 times the degradation rate of uncoated MgZnCa. These results not only comprehensively confirmed the validity of the VUV/O₃-activation method as a coating strategy but also implied the tremendous potential of the modified Mg alloy for application as a degradable biomedical implant material. STATEMENT OF SIGNIFICANCE: MgZnCa alloy is a promising material in clinical implantation. Silk fibroin (SF) is a natural organic material with biocompatibility and biodegradability. To date, the combination of SF and MgZnCa alloy has exhibited considerable prospects for orthopedic applications. The realization of a direct coating is an enormous challenge because strong chemical bonds cannot be easily formed between organic and inorganic materials. To solve this bottleneck, we proposed a unique vacuum ultraviolet-ozone (VUV/O₃) surface-activation method for the first time to modify the Mg alloy surface before SF coating, which significantly enhanced both in vitro and in vivo performance, such as superior biocompatibility and remarkably improved corrosion resistance of magnesium alloys (∼1/18 the in vivo degradation rate of uncoated MgZnCa).

The Potential of Magnesium Based Materials in Mandibular Reconstruction

The future of biomaterial design will rely on development of bioresorbable implant materials that completely and safely degrade in vivo after the tissues grow, without generating harmful degradation products at the targeted anatomic site. Permanent biomaterials such as Ti6Al4V alloy, 316L stainless steel, and Co-based alloys currently used in mandibular reconstruction often result in stress shielding effects due to mismatch in the Young’s modulus values between the bone and the implant, resulting in implant loosening. Also, allergic responses due to metal ion releases necessitates revision surgery to prevent long term exposure of the body to toxic implant contents. Bioresorbable metals are perceived as revolutionary biomaterials that have transformed the nature of metallic biomaterials from bioinert to bioactive and multi-bio functional (anti-bacterial, anti-proliferation, and anti-cancer). In this aspect, magnesium (Mg)-based materials have recently been explored by the biomedical community as potential materials for mandibular reconstruction, as they exhibit favorable mechanical properties, adequate biocompatibility, and degradability. This article reviews the recent progress that has led to advances in developing Mg-based materials for mandibular reconstruction; correlating with the biomechanics of mandible and types of mandibular defects. Mg-based materials are discussed regarding their mechanical properties, corrosion characteristics, and in vivo performance. Finally, the paper summarizes findings from this review, together with a proposed scope for advancing the knowledge in Mg-based materials for mandibular reconstruction.

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.

Bioactive calcium phosphate materials and applications in bone regeneration

BACKGROUND

Bone regeneration involves various complex biological processes. Many experiments have been performed using biomaterials in vivo and in vitro to promote and understand bone regeneration. Among the many biomaterials, calcium phosphates which exist in the natural bone have been conducted a number of studies because of its bone regenerative property. It can be directly contributed to bone regeneration process or assist in the use of other biomaterials. Therefore, it is widely used in many applications and has been continuously studied.

MAINBODY

Calcium phosphate has been widely used in bone regeneration applications because it shows osteoconductive and in some cases osteoinductive features. The release of calcium and phosphorus ions regulates the activation of osteoblasts and osteoclasts to facilitate bone regeneration. The control of surface properties and porosity of calcium phosphate affects cell/protein adhesion and growth and regulates bone mineral formation. Properties affecting bioactivity vary depending on the types of calcium phosphates such as HAP, TCP and can be utilized in various applications because of differences in ion release, solubility, stability, and mechanical strength. In order to make use of these properties, different calcium phosphates have been used together or mixed with other materials to complement their disadvantages and to highlight their advantages. Calcium phosphate has been utilized to improve bone regeneration in ways such as increasing osteoconductivity for bone ingrowth, enhancing osteoinductivity for bone mineralization with ion release control, and encapsulating drugs or growth factors.

CONCLUSION

Calcium phosphate has been used for bone regeneration in various forms such as coating, cement and scaffold based on its unique bioactive properties and bone regeneration effectiveness. Additionally, several studies have been actively carried out to improve the efficacy of calcium phosphate in combination with various healing agents. By summarizing the properties of calcium phosphate and its research direction, we hope that calcium phosphate can contribute to the clinical treatment approach for bone defect and disease.

The current trends of Mg alloys in biomedical applications-A review

Magnesium (Mg) has emerged as an ideal alternative to the permanent implant materials owing to its enhanced properties such as biodegradation, better mechanical strengths than polymeric biodegradable materials and biocompatibility. It has been under investigation as an implant material both in cardiovascular and orthopedic applications. The use of Mg as an implant material reduces the risk of long-term incompatible interaction of implant with tissues and eliminates the second surgical procedure to remove the implant, thus minimizes the complications. The hurdle in the extensive use of Mg implants is its fast degradation rate, which consequently reduces the mechanical strength to support the implant site. Alloy development, surface treatment, and design modification of implants are the routes that can lead to the improved corrosion resistance of Mg implants and extensive research is going on in all three directions. In this review, the recent trends in the alloying and surface treatment of Mg have been discussed in detail. Additionally, the recent progress in the use of computational models to analyze Mg bioimplants has been given special consideration. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1970-1996, 2019.

Characterization and biological properties of a novel synthesized silicon-substituted hydroxyapatite derived from eggshell

In the present study, the effect of adding different concentrations of silicon on physical, mechanical and biological properties of a synthesized aqueous precipitated eggshell-derived hydroxyapatite (e-HA) was evaluated. No secondary phases were detected by X-ray diffraction for the specimens e-HA and e-HA containing silicon (Si-e-HAs) before and after heating at 1200°C. A reduction in the crystallite size and a-axis as well as an increase in c-axis was occurred when silicon replacement was happened in the structure of e-HA. The presence of Si-O vibrations and carbonate modes for Si-e-HAs was confirmed by Fourier transform infrared spectroscopy analysis. The range of porosity and density was varied from 25% and 2.4 g cm^-3 to 7% and 2.8 g cm^-3 for e-HA and Si-e-HAs. The values of Young's modulus ( E) and compressive strength were varied for e-HA and Si-e-HAs. The porous structure of the samples was reduced when they were heated as e-HA kept the porous microstructure containing some dense areas and Si-e-HAs possessed a rough surface including slight levels of microporosity. The acellular in vitro bioactivity represented different apatite morphologies for e-HA and Si-e-HAs. The G-292 osteoblastic cells were stretched well on the surface with polygon-shaped morphology for 0.8Si-e-HA after 7 days of culture. According to MTT assay and alkaline phosphatase test, the maximum cell activity was related to 0.8Si-e-HA. The minimum inhibitory concentration for 0.8Si-e-HA and e-HA was estimated to be about 3.2 and 4.4 mg/mL, respectively. In overall, the sample 0.8Si-e-HA exhibited a higher bacteriostatic effect than e-HA against gram-negative bacterial strain Escherichia coli.

Degradation and In Vivo Response of Hydroxyapatite-Coated Mg Alloy

Nowadays there is a need for new generation of biodegradable implants, which should be able to stimulate the healing responses of injured tissues at the molecular level. Magnesium alloys attract great attention as perspective bone implants due to their biocompatibility, physical properties and ability to degrade completely under physiological conditions. The main purpose of this research was assessment of in vitro corrosion and surface morphology after short term in vivo implantation of Mg based implant covered by hydroxyapatite (HA). Mg alloys with the addition of Zr (0.65%), Al (1.85%) and Nd (1.25%) were used. In our work, we propose dipping method for hydroxyapatite coatings formation which has been shown to reduce the corrosion rate of magnesium implants in vivo. Simulated body fluid (SBF; pH 7.4) with ion concentrations approximately equal to those of human blood plasma resembling physiological conditions and citrate buffer with pH 5—simulating inflammation were selected as modelling environments for in vitro degradation test. The rod samples were implanted into the tibia bone of rats and after 1 day and 5 days of implantation were taken out to observe cells adhesion on surface samples. SEM was used to assess surface morphology after in vitro and in vivo tests. SBF solution causes some cracks on the surface of HA coatings, while citrate solution at pH 2 caused complete dissolving of the coating. The HA coating favoured cell adhesion and rapid fibrous tissue formation.

Avaliação topográfica e in vitro de superfícies de titânio revestidas com vidro bioativo

Resumo Objetivo Avaliar e comparar a rugosidade superficial e a atividade dos osteoblastos em contato com uma nova superfície bioativa e nanoestruturada de titânio grau 4 revestida com vidro bioativo contendo fosfato de cálcio, sintetizada pelo método sol-gel. Material e método Sessenta e três discos de titânio, medindo 4 mm de diâmetro por 2 mm de altura, foram preparados e divididos em três grupos: microtexturizado (Ticp - controle); revestido com vidro bioativo e seco a vácuo a 37 °C por 10 dias (BGTi37), e revestido com vidro bioativo e aquecido a 600 °C por cinco horas (BGTi600). Três espécimes de cada grupo foram utilizados para avaliação da topografia superficial e 18 espécimes, para cultura celular. Resultado O revestimento de vidro bioativo diminuiu a rugosidade média quando comparado ao titânio microtexturizado. A proporção de células viáveis, a produção de fosfatase alcalina e o grau de mineralização da matriz óssea em contato com os espécimes de titânio do grupo BGTi600 foram significativamente menores em relação aos grupos controle e do titânio microtexturizado. Conclusão Apesar de sua marcante menor rugosidade, a superfície BGTi37 apresentou comportamento biológico semelhante a uma superfície de titânio microtexturizada e moderadamente rugosa. A outra superfície experimental (BGTi600), a de menor rugosidade entre todas as testadas, apresentou os piores resultados de ativação dos osteoblastos.

Microstructure and Corrosion Behavior of Composite Coating on Pure Mg Acquired by Sliding Friction Treatment and Micro-Arc Oxidation

For the purpose of detecting the influence of grain structure of a Mg matrix on the microstructure and corrosion resistance of micro-arc oxidation (MAO) coating, prior to MAO processing, sliding friction treatment (SFT) was adopted to generate a fine-grained (FG) layer on coarse-grained (CG) pure Mg surface. It showed that the FG layer had superior corrosion resistance, as compared to the CG matrix, owing to the grain refinement; furthermore, it successfully survived after MAO treatment. Thus, an excellent FG-MAO coating was gained by combining SFT and MAO. The surface morphology and element composition of FG-MAO and CG-MAO samples did not show significant changes. However, the FG layer favorably facilitated the formation of an excellent MAO coating, which possessed a superior bonding property and greater thickness. Consequently, the modified FG-MAO sample possessed enhanced corrosion resistance, since a lower hydrogen evolution rate, a larger impedance modulus and a lower corrosion current were observed on the FG-MAO sample.