Surface microstructure and in vitro analysis of nanostructured akermanite (Ca2MgSi2O7) coating on biodegradable magnesium alloy for biomedical applications

Clinical translation and challenges of biodegradable magnesium-based interference screws in ACL reconstruction

As one of the most promising fixators developed for anterior cruciate ligament (ACL) reconstruction, biodegradable magnesium (Mg)-based interference screws have gained increasing attention attributed to their appropriate modulus and favorable biological properties during degradation after surgical insertion. However, its fast degradation and insufficient mechanical strength have also been recognized as one of the major causes to limit their further application clinically. This review focused on the following four parts. Firstly, the advantages of Mg or its alloys over their counterparts as orthopaedic implants in the fixation of tendon grafts in ACL reconstruction were discussed. Subsequently, the underlying mechanisms behind the contributions of Mg ions to the tendon-bone healing were introduced. Thirdly, the technical challenges of Mg-based interference screws towards clinical trials were discussed, which was followed by the introduction of currently used modification methods for gaining improved corrosion resistance and mechanical properties. Finally, novel strategies including development of Mg/Titanium (Ti) hybrid fixators and Mg-based screws with innovative structure for achieving clinically customized therapies were proposed. Collectively, the advancements in the basic and translational research on the Mg-based interference screws may lay the foundation for exploring a new era in the treatment of the tendon-bone insertion (TBI) and related disorders.

[Research progress on the biological properties of the surface nanocrystals of typical medical metal materials]

Biomedical metal materials have always been a major biomedical material with a large and wide range of clinical use due to their excellent properties such as high strength and toughness, fatigue resistance, easy forming, and corrosion resistance. They are also the preferred implant material for hard tissues (bones and teeth that need to withstand higher loads) and interventional stents. And nano-medical metal materials have better corrosion resistance and biocompatibility. This article focuses on the changes and improvements in the properties of several typical medical metal materials surfaces after nanocrystallization, and discusses the current problems and development prospects of nano-medical metal materials.

Corrosion Behavior and Biological Activity of Micro Arc Oxidation Coatings with Berberine on a Pure Magnesium Surface

Bone tissue repair materials can cause problems such as inflammation around the implant, slow bone regeneration, and poor repair quality. In order to solve these problems, a coating was prepared by ultrasonic micro-arc oxidation and self-assembly technology on a pure magnesium substrate. We studied the effect of berberine on the performance of the ultrasonic micro-arc oxidation/polylactic acid and glycolic acid copolymer/berberine (UMAO/PLGA/BR) coating. The chemical and morphological character of the coating was analyzed using scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The corrosion properties were studied by potentiodynamic polarization and electrochemical impedance spectroscopy in a simulated body fluid. The cumulative release of drugs was tested by high-performance liquid chromatography. The results indicate that different amounts of BR can seal the corrosion channel to different extents. These coatings have a self-corrosion current density (Icorr) at least one order of magnitude lower than the UMAO coatings. When the BR content is 3.0 g/L, the self-corrosion current density of the UMAO/PLGA/BR coatings is the lowest (3.14 × 10−8 A/cm2) and the corrosion resistance is improved. UMAO/PLGA/BR coatings have excellent biological activity, which can effectively solve the clinical problem of rapid degradation of pure magnesium and easy infection.

Biodegradable Magnesium Bone Implants Coated with a Novel Bioceramic Nanocomposite

Magnesium (Mg) alloys are being investigated as a biodegradable metallic biomaterial because of their mechanical property profile, which is similar to the human bone. However, implants based on Mg alloys are corroded quickly in the body before the bone fracture is fully healed. Therefore, we aimed to reduce the corrosion rate of Mg using a double protective layer. We used a magnesium-aluminum-zinc alloy (AZ91) and treated its surface with micro-arc oxidation (MAO) technique to first form an intermediate layer. Next, a bioceramic nanocomposite composed of diopside, bredigite, and fluoridated hydroxyapatite (FHA) was coated on the surface of MAO treated AZ91 using the electrophoretic deposition (EPD) technique. Our in vivo results showed a significant enhancement in the bioactivity of the nanocomposite coated AZ91 implant compared to the uncoated control implant. Implantation of the uncoated AZ91 caused a significant release of hydrogen bubbles around the implant, which was reduced when the nanocomposite coated implants were used. Using histology, this reduction in the corrosion rate of the coated implants resulted in an improved new bone formation and reduced inflammation in the interface of the implants and the surrounding tissue. Hence, our strategy using a MAO/EPD of a bioceramic nanocomposite coating (i.e., diopside-bredigite-FHA) can significantly reduce the corrosion rate and improve the bioactivity of the biodegradable AZ91 Mg implant.

Assessment of magnesium-based biomaterials: from bench to clinic

This review presents the operation procedures of commonly used standard methods for assessment of Mg-based biomaterials from bench to clinic.

Study on the corrosion resistance and anti-infection of modified magnesium alloy

In this paper, a low-cost and multifunctional hydroxyapatite (HA)/pefloxacin (PFLX) drug eluting layer is coated on magnesium (Mg) alloy through a simple hydrothermal and dip process. The drug PFLX could provide effective prevention for bone infection and inflammation due to its broad-spectrum antibacterial property. And HA would promote the growth of new bone and further improve the biocompatibility of implants. Besides, both PFLX and HA exhibits excellent corrosion protection for Mg alloy substrate. This coating is of great value for improving the application of Mg alloy as biomaterials.

Doped Calcium Silicate Ceramics: A New Class of Candidates for Synthetic Bone Substitutes

Doped calcium silicate ceramics (DCSCs) have recently gained immense interest as a new class of candidates for the treatment of bone defects. Although calcium phosphates and bioactive glasses have remained the mainstream of ceramic bone substitutes, their clinical use is limited by suboptimal mechanical properties. DCSCs are a class of calcium silicate ceramics which are developed through the ionic substitution of calcium ions, the incorporation of metal oxides into the base binary xCaO-ySiO₂ system, or a combination of both. Due to their unique compositions and ability to release bioactive ions, DCSCs exhibit enhanced mechanical and biological properties. Such characteristics offer significant advantages over existing ceramic bone substitutes, and underline the future potential of adopting DCSCs for clinical use in bone reconstruction to produce improved outcomes. This review will discuss the effects of different dopant elements and oxides on the characteristics of DCSCs for applications in bone repair, including mechanical properties, degradation and ion release characteristics, radiopacity, and biological activity (in vitro and in vivo). Recent advances in the development of DCSCs for broader clinical applications will also be discussed, including DCSC composites, coated DCSC scaffolds and DCSC-coated metal implants.

Ion-Doped Silicate Bioceramic Coating of Ti-Based Implant

Titanium and its alloy are known as important load-bearing biomaterials. The major drawbacks of these metals are fibrous formation and low corrosion rate after implantation. The surface modification of biomedical implants through various methods such as plasma spray improves their osseointegration and clinical lifetime. Different materials have been already used as coatings on biomedical implant, including calcium phosphates and bioglass. However, these materials have been reported to have limited clinical success. The excellent bioactivity of calcium silicate (Ca-Si) has been also regarded as coating material. However, their high degradation rate and low mechanical strength limit their further coating application. Trace element modification of (Ca-Si) bioceramics is a promising method, which improves their mechanical strength and chemical stability. In this review, the potential of trace element-modified silicate coatings on better bone formation of titanium implant is investigated.

Effects of Corroded and Non-Corroded Biodegradable Mg and Mg Alloys on Viability, Morphology and Differentiation of MC3T3-E1 Cells Elicited by Direct Cell/Material Interaction

This study investigated the effect of biodegradable Mg and Mg alloys on selected properties of MC3T3-E1 cells elicited by direct cell/material interaction. The chemical composition and morphology of the surface of Mg and Mg based alloys (Mg2Ag and Mg10Gd) were analysed by scanning electron microscopy (SEM) and EDX, following corrosion in cell culture medium for 1, 2, 3 and 8 days. The most pronounced difference in surface morphology, namely crystal formation, was observed when Pure Mg and Mg2Ag were immersed in cell medium for 8 days, and was associated with an increase in atomic % of oxygen and a decrease of surface calcium and phosphorous. Crystal formation on the surface of Mg10Gd was, in contrast, negligible at all time points. Time-dependent changes in oxygen, calcium and phosphorous surface content were furthermore not observed for Mg10Gd. MC3T3-E1 cell viability was reduced by culture on the surfaces of corroded Mg, Mg2Ag and Mg10Gd in a corrosion time-independent manner. Cells did not survive when cultured on 3 day pre-corroded Pure Mg and Mg2Ag, indicating crystal formation to be particular detrimental in this regard. Cell viability was not affected when cells were cultured on non-corroded Mg and Mg alloys for up to 12 days. These results suggest that corrosion associated changes in surface morphology and chemical composition significantly hamper cell viability and, thus, that non-corroded surfaces are more conducive to cell survival. An analysis of the differentiation potential of MC3T3-E1 cells cultured on non-corroded samples based on measurement of Collagen I and Runx2 expression, revealed a down-regulation of these markers within the first 6 days following cell seeding on all samples, despite persistent survival and proliferation. Cells cultured on Mg10Gd, however, exhibited a pronounced upregulation of collagen I and Runx2 between days 8 and 12, indicating an enhancement of osteointegration by this alloy that could be valuable for in vivo orthopedic applications.

Biomineralization and biocompatibility studies of bone conductive scaffolds containing poly(3,4-ethylenedioxythiophene):poly(4-styrene sulfonate) (PEDOT:PSS)

Considering the well-known phenomenon of enhancing bone healing by applying electromagnetic stimulation, manufacturing conductive bone scaffolds is on demand to facilitate the delivery of electromagnetic stimulation to the injured region, which in turn significantly expedites the healing procedure in tissue engineering methods. For this purpose, hybrid conductive scaffolds composed of poly(3,4-ethylenedioxythiophene), poly(4-styrene sulfonate) (

PEDOT

PSS), gelatin (Gel), and bioactive glass (BaG) were produced employing freeze drying technique. Concentration of

PEDOT

PSS were optimized to design the most appropriate conductive scaffold in terms of biocompatibility and cell proliferation. More specifically, scaffolds with four different compositions of 0, 0.1, 0.3 and 0.6% (w/w)

PEDOT

PSS in the mixture of 10% (w/v) Gel and 30% (w/v) BaG were synthesized. Immersing the scaffolds in simulated body fluid (SBF), we evaluated the bioactivity of samples, and the biomineralization were studied in details using scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction analysis and Fourier transform infrared spectroscopy. By performing cytocompatibility analyses for 21 days using adult human mesenchymal stem cells, we concluded that the scaffolds with 0.3% (w/w)

PEDOT

PSS and conductivity of 170 μS/m has the optimized composition and further increasing the

PEDOT

PSS content has inverse effect on cell proliferation. Based on our finding, addition of this optimized amount of

PEDOT

PSS to our composition can increase the cell viability more than 4 times compared to a nonconductive composition.

In vivo biocompatibility of Mg implants surface modified by nanostructured merwinite/PEO

Magnesium (Mg) alloys have been suggested as biodegradable bone implant materials due to their good intrinsic biocompatibility and great mechanical properties. Although magnesium has attractive properties as an orthopedic implant material, its quick degradation and low bioactivity may lead to the loss of mechanical integrity of the implant during the bone healing process. In this paper, we endeavor to surmount the abovementioned defects using the surface coating technique. We have recently coated AZ91 magnesium implants with merwinite (Ca3MgSi2O8) through the coupling of plasma electrolytic oxidation (PEO) and electrophoretic deposition method. In this work, we are specifically focused on the in vivo examinations of the coated implants in comparison with the uncoated one. For the in vivo experiment, the rod samples, including the uncoated and merwinite/PEO coated implants, were imbedded into the greater trochanter of rabbits. The results of the in vivo animal test indicated an improvement in biodegradability including slower implant weight loss, reduction in Mg ion released from the coated implants in the blood plasma, lesser release of hydrogen bubbles and an improvement in biocompatibility including an increase in the amount of bone formation and ultimately a mild bone inflammation after the surgery according to the histological images. In summary, proper surface treatment of magnesium implants such as silicate bioactive ceramics may improve their biocompatibility under physiological conditions to making them suitable and applicable for future clinical applications.

Fabrication of nano-structured calcium silicate coatings with enhanced stability, bioactivity and osteogenic and angiogenic activity

The bioactivity and stability of coatings on alloy implants play critical roles in the fast osseointegration and maintenance of a long-term life span of the implants, respectively. Herein, nano-sheet surface on bioactive calcium silicate (CaSiO3, CS) coatings on metal substrates was fabricated by combining atmosphere plasma spraying (APS) and hydrothermal technology (HT). The glassy phase in CS coatings generated by APS was converted into crystalline sheet-like nano-structures after HT treatment. Compared with the original CS coating samples, HT treatment decreased the degradation rate of the CS coatings. Moreover, the fabricated nano-structured topography of CS coatings increased the apatite mineralization ability and significantly enhanced the cell attachment, proliferation, differentiation, alkaline phosphatase (ALP) activity and expression of osteogenic genes and angiogenic factors of rat bone marrow stromal cells (bMSCs). Our results suggest that the nano-structured CS coatings have immense potential in improving the clinical performance of medical implants.

In vivo assessments of bioabsorbable AZ91 magnesium implants coated with nanostructured fluoridated hydroxyapatite by MAO/EPD technique for biomedical applications

Although magnesium (Mg) is a unique biodegradable metal which possesses mechanical property similar to that of the natural bone and can be an attractive material to be used as orthopedic implants, its quick corrosion rate restricts its actual clinical applications. To control its rapid degradation, we have modified the surface of magnesium implant using fluoridated hydroxyapatite (FHA: Ca10(PO4)6OH2-xFx) through the combined micro-arc oxidation (MAO) and electrophoretic deposition (EPD) techniques, which was presented in our previous paper. In this article, the biocompatibility examinations were conducted on the coated AZ91 magnesium alloy by implanting it into the greater trochanter area of rabbits. The results of the in vivo animal test revealed a significant enhancement in the biocompatibility of FHA/MAO coated implant compared to the uncoated one. By applying the FHA/MAO coating on the AZ91 implant, the amount of weight loss and magnesium ion release in blood plasma decreased. According to the histological results, the formation of the new bone increased and the inflammation decreased around the implant. In addition, the implantation of the uncoated AZ91 alloy accompanied by the release of hydrogen gas around the implant; this release was suppressed by applying the coated implant. Our study exemplifies that the surface coating of magnesium implant using a bioactive ceramic such as fluoridated hydroxyapatite may improve the biocompatibility of the implant to make it suitable as a commercialized biomedical product.

In vivo study of nanostructured akermanite/PEO coating on biodegradable magnesium alloy for biomedical applications

The major issue for biodegradable magnesium alloys is the fast degradation and release of hydrogen gas. In this article, we aim to overcome these disadvantages by using a surface modified magnesium implant. We have recently coated AZ91 magnesium implants by akermanite (Ca2 MgSi2 O7 ) through the combined electrophoretic deposition (EPD) and plasma electrolytic oxidation (PEO) methods. In this work, we performed the in vitro and in vivo examinations of these coated implants using L-929 cell line and rabbit animal model. The in vitro study confirmed the higher cytocompatibility of the coated implants compare to the uncoated ones. For the in vivo experiment, the rod samples were implanted into the greater trochanter of rabbits and monitored for two months. The results indicated a noticeable biocompatibility improvement of the coated implants which includes slower implant weight loss, reduction in Mg ion released from the coated samples in the blood plasma, lower release of hydrogen bubbles, increase in the amount of bone formation and ultimately lower bone inflammation after the surgery according to the histological images. Our data exemplifies that the proper surface treatment of the magnesium implants can improve their biocompatibility under physiological conditions to make them applicable in clinical uses. © 2014 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 103A: 1798-1808, 2015.