Because the bioresorbable scaffold (BRS) could overcome the difficulties caused by traditional nondegradable stents including chronic inflammation, late stent thrombosis, and long-term antiplatelet therapy, BRS is the research focus of interventional medical engineering. Because of both the high supporting strength and bioresorbable feature, the bioresorbable magnesium scaffold (BMS) is the research focus of BRS. In this paper, development process of Biotronik serial magnesium stents along with research progress of our domestic AZ31, JDBM and MgZnYNd stents is reviewed. According to the results of extensive in vitro and in vivo studies, BMS is safe and effective in vivo although its degradation rate is faster than our expectation. Through developing novel alloy system and improving stents' structure, the performance of BMS will be better and it will play more important role on the therapy of cardiovascular disease.

Magnesium and its alloys exhibit high mechanical strength and good biocompatibility, and their modulus is similar to natural cortical bone, which could help to avoid the stress shielding effect. These advantages make them promising candidates for bone repair applications. This paper summarizes the advantages, history, challenges, and the recent research progress of biodegradable Mg alloys for orthopedic application. At last, it gives a detailed introduction of the latest researches of Shanghai Jiao Tong University on biodegradable Mg alloys, and related work to promote their clinical applications.

Magnesium-based metals become novel biodegradable implanting material and present good clinical application prospect due to their good biocompatibility, mechanical properties matching with bone tissue as well as absorbable and biodegradable properties in human body. They are expected to replace traditional medical metals such as stainless steel and titanium alloy in the area of orthopaedics and cardiovascular stent. In this paper, the current research status about the biocompatibility of magnesium based metals both at home and abroad in recent years has been reviewed. In vitro and in vivo cytocompatibility, hemocompatibility and histocompatibility have been mentioned from aspects of alloying and surface modification. The clinical application and development tendencies for magnesium based metals are also proposed.

Bone defects are very challenging in orthopedic practice due to a variety of reasons. Bone repair requires four critical elements, biocompatibility, osteoconduction, osteoinduction and osteogenesis. The autografts still exist some problems for applications such as the limitation of available autogenous bones and post-operative complications, although they are considered as the “gold standard” in bony defect repairs. Generally the synthetic bone substitutes do not possess osteoinductive and osteogenic activities. Therefore, the clinical bone grafts and bone-graft substitutes have their own shortcomings in the repair of bone defects. Biodegradable magnesium-based metals, including pure magnesium and magnesium alloys, have been concerned and studied recently due to their biodegradation, good biocompatibility and similar elastic modulus and density with bone tissue. This paper summarizes the biological behavior of magnesium-based metals for bone defects repair application, including ability of promoting osteogenesis, osteoconduction and potential osteoinduction, as well as some particular biofunctions such as antibacterial and antitumor properties. The great advantages and potentials of magnesium in bone defects repair can not be denied as a promising class of bone substitutes, although further researches are still needed for clinical applications.

In recent years, magnesium and its alloys as biodegradable materials have attracted much attention. Biodegradable MgYREZr, mainly WE43 alloy, with good integrated properties has been studied in favor. In this paper, the microstructure, mechanical properties, biodegradable property and biocompatibility of biodegradable MgYREZr alloy were reviewed, as well as the clinical results of the bone fixation screws developed in Germany using the alloy with similar composition to WE43. MgYREZr alloy presents uniform microstructure and higher mechanical properties after large plastic deformation with the grain size of less than 1 μm. The RE elements can be dissolved and stabilize the corrosion layer, which can decrease the degradation rate of the alloy accompanying with optimized heat treatment. The animal tests showed biocompatibility and good bioactivity. Clinical tests showed the MgYREZr alloy screws presented equivalent to titanium screws for the treatment of mild hallux valgus deformities, however resorption cysts was revealed by X-rays when the acute scaphoid fractures were treated with a double-threaded screw made of MgYREZr, and it was only after 6 months that the fractures were consolidated enough to allow physical work. So for different clinical cases, the degradation and biological behaviors of MgYREZr alloys need to be further studied in vitro and in vivo. To control the degradation rates to meet the different clinical requirements is still a major obstacle for biodegradable MgYREZr alloys to enlarge their clinical application.

Cardiovascular disease has become the first major disease that is harmful to people's health, vascular stents and other percutaneous coronary interventions are considered the most important and effective treatment technology of cardiovascular disease. In this review, the development about percutaneous coronary interventions was simply introduced, through comparing a series of randomized clinical trial data of bioabsorbable vascular stents developed by Abbott of the United States and absorbable magnesium stents developed by Biotronik of Germany, summarizing the shortcomings and analyzing trend in the future of absorbable stents.

During the last two decades, a great amount of researches have been focused on biodegradable metals. Technologies from alloy design to melting, manufacturing and processing, from micro-tube to stent laser processing and drug eluting coating have been improved and optimized continuously. Biodegradable metallic stent has evolved from a concept to a real product and generated three branches of material system. A large amount of animal tests and clinical tests have been carried out to investigate biodegradable magnesium stents. Results of clinical study have indicated that the magnesium stent is feasible, with favourable safety and performance outcomes. More importantly, Biotronik won CE Mark for Magmaris bioresorbable stent in 2016. Researches of biodegradable iron stents are still in the stage of animal tests. The nitrided iron stent possesses excellent mechanical properties. Results showed a good long-term biocompatibility of nitrided iron stent in rabbit and porcine model. Biodegradable zinc stent has only been introduced in recent years. Only a few in vivo studies have been reported with zinc wires implanted in rats. Results showed a good degradation behavior and biocompatibility of zinc wires. In this paper, the current research status of biodegradable metallic stents is reviewed, and the future research and development in mechanical property optimization, drug eluting and intelligence is proposed.

Biomedical titanium alloy materials have become the main raw materials for orthopedic, dental and cardiovascular implants or devices, but their biological and mechanical compatibility remains to be improved to meet the long-term safety and function in services for clinical application. Whether developing the novel medical titanium alloys with high-strength, low-modulus and other finer comprehensive performance, or upgrading and optimizing the traditional medical titanium alloys, it is the foundation and key to ensuring the structure homogeneity, high performance, versatility and low cost of biomedical titanium alloy materials and expanding its clinical application. The design, physical metallurgy, materials process, microstructure and properties, surface modification, advanced manufacturing and the clinical application of biomedical titanium alloys were introduced, and their latest research progress was reviewed in this paper, together with the recent advances in the author's R & D team. Finally, the further research and development trend of biomedical titanium alloys are summarized.

Metal materials are one of the main application materials of medical implants. Due to the objective existence of the defects, such as ion dissolution and biologically inert, how to improve the biocompatibility and tissue suitability of the implant surface has attracted great research interests. Fabricating micro-nano structures on surfaces, which regulates the cell and tissue by the contact-induced mechanism is one of the most important research direction to improve the surface biological function of implantation device. In this paper, the preparation techniques and application progress of various microstructures on metal implanted devices surface were reviewed. In addition, the effects of contact induction on the regulation of osteogenesis to vascular endothelial cells, to tissue growth behavior and induction of stem cell differentiation were also reviewed.

Osteogenic capacity (i.e., properties that promote new bone formation around the implant) has long been a clinical requirement for most orthopedic implants. Recently, anti-infection or antibacterial property has increasingly become critical for orthopedic implants (especially without the use of antibiotics). Orthopedic implant materials with simultaneous osteogenic and anti-infection capacities are extremely promising for orthopedic applications, but such materials are not widely available to date and have only recently been researched. In this review article, the advances in metallic biomaterials with both osteogenic and anti-infection capacities were introduced considering of the wide application of metallic biomaterials in orthopedics. Firstly, numerous attractive metal formulations that exhibit both osteogenic and anti-infection capacities as well as surface modification strategies that enhance such capacities are introduced. Secondly, several possible mechanisms underlying the osteogenic and anti-infection properties are discussed. Finally, an outlook of this field is proposed.

Porous tantalum (PT) is an orthopedics implant material that has been developed rapidly in recent decades. PT exhibits excellent biocompatibility, outstanding comprehensive mechanical properties, initial stability originated from their high friction factor and long term stability from their good osteoinduction, which make it widely applied in clinical practice. In this review, state of the arts and recent deve-lopment in the field of porous tantalum used as orthopedics implant material have been summarized and commented, which consist of introduction of its background, advantages, preparation approaches, biological performance and application status on clinic. The prospects are also described.

Biomedical nickel-free stainless steels acquire better comprehensive properties than the traditional stainless steels, with wide application prospect in medical devices for bone and vascular repair. As a new biomaterial, in recent years, the excellent properties of nickel-free stainless steels are gradually verified, which is meaningful for developing medical devices with higher safety and biocompatibility. In this paper, the research progress on alloy design, mechanical properties, corrosion resistance and biocompatibility of nickel-free stainless steels and the current application status are reviewed, and the future tendency on research and development for this new metallic biomaterial is also proposed.

In recent years, zinc, as an essential trace element, with its alloys has attracted increasing attention as new biodegradable metals because of its appropriate degradation rate and degradation behavior. In this stage, it appears that the fabrication and degradation mechanism of zinc alloys as biodegradable metal still needs abundant systematic study. This review summarizes progress towards biodegradable zinc alloys. It emphasizes the current understanding of physiological and biological benefits of zinc and its biocompatibility. Finally, the review provides an outlook on challenges in designing zinc-based stents of optimal mechanical properties and biodegradation rate.

Magnetic resonance imaging (MRI) is widely used in clinical applications. Metallic medical devices and implants used under MRI normally produce noticeable artifact which seriously affects image quality. Therefore, the artifact is an essential problem that should be solved for metallic biomaterials. Although artifact can be reduced by technical manipulation, it cannot be eliminated completely. This paper summarizes recent studies on MR-compatible alloys such as Zr alloys, Nb alloys and Cu alloys. Compared with normally clinical metallic materials, MR-compatible alloys described in this article can effectively reduce or eliminate artifacts under MRI. MR-compatibility will become an essential property to implant materials and devices. Thus developing metallic biomaterials with low magnetic susceptibility and excellent comprehensive performance becomes more important.

High nitrogen nickel free stainless steel (HNNFSS) has begun to be used in clinic, which possesses excellent mechanical properties, corrosion resistance and biocompatibility. Especially its strength is two times more than that of the conventional 316L stainless steel, but this advantage is not fully used in optimization of both the structure and the size of the implant devices. In this work, the effect of thickness change of HNNFSS bone plate on the biomechanical behavior of bone plate was studied by means of finite element analysis. The result showed that the resistances to bending, tension and compression of HNNFSS plate are all better than those of 316L plate when its thickness is thinned less than 18%. The internal fixation of the lightweight HNNFSS plate was also studied by a 12 weeks rabbit femur fracture model and the result showed that the HNNFSS plate with about 14% thickness thinning could promote the healing and reconstruction of bone fracture of rabbit femur in comparison with 316L plate.

Entering into 21 Century,the degradable Mg and Mg alloy become research focus for the development of Internal fixation material from inert to active metal. The polybasic coating (UMAO-OH-SCA-SF) was prepared by ultrasound micro-arc oxidation (UMAO), alkali treatment (OH), treatment of silicohydride conversion coating (SCA) and the treatment of self-assembly silk fibroin on the surface of magnesium, which can improve the corrosion resistance and bioactivity of pure magnesium. The surface topography, structure, corrosion resistance, cell activity and bone growth in vivo of the coating were studied by SEM, IR spectra, electrochemical measurement, vitro experiment and implant test. The results show that the main phase of coating is MgO. The alkali treatment is beneficial to forming Si-O-Mg film by silicohydride coupling. With the self-assembly silk fibroin time increasing, the silk fibroin structure changes from random coil to β-fold. The polybasic coating self-corrosion is improved and self-corrosion current is reduced by two orders of magnitude. Compared to substrate, the polybasic coating has better proliferation, adherent and differentiation of osteoblast. It has a better bone integration capacity in the bone healing early stage, and which can control magnesium ion dissolving. The UMAO-OH-SCA-SF/1.5h coating has the best property.

Magnesium alloy is now a promising bio-absorbable material. The previous researches on the corrosion and degradation behavior of biomedical magnesium alloy are mainly carried out in static conditions in vitro. However, considering the real physiological flow field of different flow states in vivo, the static degradation experiments can not effectively simulate the real situation. It is important to study the effect of flow field on the corrosion behavior of magnesium alloy and establish the relationship between flow rate and corrosion rate for the research and development of biomedical magnesium alloy. The corrosion behavior of AZ31 magnesium alloy in the flow field was studied using a self-designed dynamic test bench in vitro by electrochemical measurement, tensile method, pH value test of simulated body fluid (SBF) and SEM observation in this work. The relationship between the corrosion rate of magnesium alloy and the flow rate of the flow field was investigated from the perspective of corrosion electrochemistry. The influence of flow state and flow-induced shear stress (FISS) on corrosion behaviors at different positions of magnesium alloy was also studied by ANSYS finite element analysis. The results show that the flow field will accelerate the corrosion of AZ31 magnesium alloy and the corrosion rate increases with the increase of the flow rate. There is a relationship between the corrosion current density i_corr of magnesium alloy and the average flow rate ν during the early corrosion stage, namely \begin{array}{c}{i_{\mathit{corr}}}^{-1}={i_c}^{-1}+A{\nu }^{-1/2}\end{array}, where i_c is the corrosion current density ignoring the influence of diffusion, and A is a constant. With the corrosion time extended, due to the influence of the corrosion products, the experimental results gradually deviate from the calculated linear relationship of i_corr^-1~ν^-1/2. Also, there are significant differences in the fluid flow state and FISS distributions at different positions of the sample. The mass transfer coefficient at the edge of the sample under different flow rates is 4~5 times bigger than that at the middle position. The localized corrosion morphology corresponds well to the FISS distribution and the difference of flow state.

Mg alloy has attracted researchers' attention as applied for novel biomedical material because of its super corrosion property and well biocompatibility. Ultra-fine grain (UFG) Mg alloy has certain advantages in the development of medical devices because of its good plasticity and corrosion resistance. Equal channel angular pressing (ECAP) was performed on Mg-3Sn-0.5Mn alloy successfully. The microstructure and grain size were observed and measured by OM and TEM. The mechanical property was tested by microhardness and tensile test, the texture oriented was experimented by XRD, and the corrosion property was tested by electrochemical experiment. After 4 passes ECAP at 320 ℃, the average grain size of Mg-3Sn-0.5Mn alloy reached 1.65 μm, and local grain size reached 0.8 μm. The grain refinement was caused by severe plastic deformation and recrystallization. The elongation increased from 22.2% to 58.6%, the tensile strength decreased from 242.8 MPa to 195.6 MPa after 4 passes deformation. The mechanical tests showed an improvement in the elongation after 4 passes, which were about 3 times higher than in the as-extruded sample, whereas the tensile strength decreased slightly. The texture of Mg-3Sn-0.5Mn alloy changed obviously which contributed to the actuating of the slip system. This change of texture contributed to the improvement of fracture elongation and decrease of tensile strength. The mechanical property of Mg-3Sn-0.5Mn alloy after ECAP was affected by the texture orientation and grain strengthening.

Magnesium metal matrix composites (MMCs) are hot research spots in recent years because of their adjustable mechanical and corrosion properties. However, the agglomerate particles in MMCs limit its applications in many areas. In order to solve this problem, MgO surface modified hydroxyapatite ceramic nanorods (m-HA) were prepared and added as reinforcement in this work. Mg-3Zn-0.8Zr alloy (MZZ), Mg-3Zn-0.8Zr composites with unmodified (MZZH) and modified (MZZMH) nanorods were produced by high shear mixing technology. Effects of m-HA nanorods on the microstructure, mechanical properties and corrosion properties of Mg-Zn-Zr/m-HA composites were investigated. The results showed that the addition of HA nanorods refined the grain size of MZZ alloy and gave a raise to the mechanical properties and electrochemical corrosion resistance of MZZ alloy. The grain size of MZZMH was smaller than that of MZZH and the distribution of m-HA nanorods in the matrix was more uniform than that of HA nanorods. Moreover, the as-extruded MZZMH composite exhibited a yield tensile strength of 291 MPa and ultimate tensile strength of 325 MPa, greater than that of MZZH. The corrosion potential of MZZMH was approximately 59 mV greater than that of MZZH. The corrosion rate of MZZMH was 5 mm/a after immersion 7 d in SBF, lower than that of MZZH. The corrosion resistance of MZZMH was better than that of MZZH due to the different corrosion mechanism. Surface corrosion products of MZZMH was alternating Mg(OH)₂ and Ca-P compound at the early stage of immersion, but surface corrosion layer of MZZH specimen was always Mg(OH)₂. The mechanical properties and corrosion resistance of Mg-Zn-Zr/m-HA composites were improved by the addition of m-HA.

The Cu-containing titanium alloy has been proved to possess excellent antibacterial performance, which has great potential for clinical application. In this work, the effect of cooling rate on the microstructure, mechanical properties, corrosion resistance and antibacterial property of a Ti6Al4V-5Cu alloy was investigated. Results showed that the furnace-cooled alloy exhibited the best ductility because of the maximum size and volume fraction of the primary α phase in microstructure. The alloys water quenched from 740 and 820 ℃ respectively demonstrated low hardness and yield strength due to the existence of orthorhombic α′′ phase in microstructure. The alloy quenched at 910 ℃ showed the highest hardness and tensile strength, but the lowest plasticity because of the presence of acicular hcp α′ phase. With the increase of heating temperature, the elemental distribution in the alloy became more uniform, and therefore the corrosion resistance increased gradually. However, the cooling rate did not obviously change the antibacterial property of the alloy. The Ti6Al4V-5Cu alloy showed excellent antibacterial property under different cooling rates.

Excellent corrosion resistance, good biocompatibility and relatively low elastic modulus make Ti and Ti alloys fulfill the property requirements in the biomedical field better than other competing materials such as stainless steels. Even so, there still exist some problems to be solved such as the biological toxicity of some alloy elements and the so-called stress shielding effect caused by higher elastic modulus than that of human bone. In response to these issues, several metastable β-type Ti alloys were developed with the advantage of nontoxicity and a much lower elastic modulus. Ti-24Nb-4Zr-8Sn (mass fraction, %, abbreviated Ti2448) alloy is a multifunctional biomedical Ti alloy with high strength and low elastic modulus, which makes it show great application prospect in the field of body implant. It put up obvious nonlinear elasticity and highly localized plastic deformation behavior. Study on deformation behavior of single crystal can help to understand the deformation mechanism of polycrystalline alloy. In this work, Ti2448 single crystal alloy along three different orientations were prepared by optical floating zone method. The plastic deformation behaviors of them under tensile stress were investigated in terms of mechanical properties, slip system and fracture morphology. Results show that Ti2448 single crystal shows obvious anisotropy, the tensile strengths along <100>, <110> and <111> orientations are 650, 642 and 889 MPa, respectively, while the elongations are about 73%, 22% and 13%, respectively. The main plastic deformation mechanism of Ti2448 single crystal alloy is by slip. The appearance of slip bands and its direction relationship with crystal orientation were detailed observed. Under tensile stress, the operated slip systems for <100>, <110> and <111> orientation single crystals are (112)[111]/(112)[111]/(112)[111]/(112)[111], (211)[111]/(211)[111] and (211)[111], respectively. This is in accordance with the law of critical shearing stress. SEM analyses show a fracture surface shape of rectangle, duckbilled and triangle for the <100>, <110> and <111> orientation single crystals, respectively. The intersection angle between fracture surface and loading direction is all about 55 degree, and a lot of dimple was detected that show ductile fracture mode.

Titanium and its alloys are widely used in hard tissue replacements because of their good biocompatibility. However, titanium and its alloys cannot meet all of the clinical requirements. In this work, carbon ions were implanted into the titanium surfaces using plasma immersion ion implantation and deposition (PIII&D) technology to improve the mechanical properties, corrosion resistance, and biological and antibacterial activities. Influences of the injected carbon on the surface morphology, composition and structure of titanium were investigated. Hydrophilicity, surface potential, surface mechanical properties, corrosion resistance, bacterial adhesion and biocompatibility of the modified titanium surfaces were evaluated, and the effects which the structure and composition of the modified layer have on their biological properties were elaborated preliminarily. Experimental results show that the modified layer treated by carbon plasma immersion ion implantation and deposition (C-PIII&D) is mainly composed of amorphous carbon. The surface morphology of the modified titanium has no obvious change. However, its surface turns to be more hydrophobic and electronegative, and the surface mechanical properties and corrosion resistance are improved. Cell adhesion, spreading and proliferation on the modified surface are in good condition while the adhesion of E. coli is inhibited to a certain extent.

Bacterial biofilm contained with proteins and polysaccharides, which made it have the potential to mimic extracellular matrix for tissue repair. It also has the properties to attach the substrate firmly. In order to regulate the bioactivity of titanium metal, inactivated bacterial biofilm was hybridized on the metal surfaces. Staphylococcus aureus (S.aureus) was cultured for 5 d on pure titanium metal (P-Ti) and that subjected to acid-alkali treatment (AA-Ti), and then the bacteria was inactivated at 121 ℃ and 0.13 MPa for 30 min to get hybridized titanium metals BP-Ti and BAA-Ti respectively. BCA (bicinchoninic acid) assay and phenol-sulfuric acid analysis showed the extracellular matrix (ECM) in the biofilm on BAA-Ti contented less polysaccharide and more protein than that on BP-Ti. Enzyme immunoassay showed the staphylococcal enterotoxins in both biofilms were lower than the threshold value. SBF (simulated body fluid) soaking experiments showed both BAA-Ti and BP-Ti could induce apatite formation after 5 d, and BAA-Ti induced less apatite than the BP-Ti did. The AA-Ti could induce apatite formation at 1 d, but there is no apatite formation on P-Ti even after 5 d. It indicated that the biofilm decreased the bioactivity of BAA-Ti, but increased the bioactivity of BP-Ti. This effect might depend on the roles of proteins and polysaccharide in the biofilms which could restrain the apatite formation for the former, and accelerate the apatite formation for the later. When osteosarcoma cell MG-63 was cultured on the metals for 3 d, the cell proliferation ability on the metals followed by the order of BAA-Ti