Biodegradable Mg alloys for orthopedic implants——A review

The last decade has seen a significant growth in the market for alloys used for implants,especially for those intended for orthopedic implants.Research into biodegradable magnesium-based alloys has made great strides in this period,so huge progress has been made in their use in the medical industry.The important factors that led to the intensification of research in this regard,were social but also economic,wanting to improve the quality of life,by reducing the use of conventionally permanent metallic implants(stainless steel,cobalt-based alloys,and titanium alloys)which involve the second implant removal surgery and other undesirable effects(stress shielding and metal ion releases),with a negative impact on the emotional and physical condition of patients,and by significantly reducing the costs for both the patient and the health system in the field of orthopedics.This paper refers to the impact and importance of biodegradable Mg alloys,reviewing the beginning of their development,the significant characteristics that make them so desirable for such applications(orthopedic implants)but also the characteristics that must be modulated(corrosion rate and mechanical properties)to arrive at the ideal product for the targeted application.It highlights,in detail,the mechanism and aspects related to the corrosion behaviour of Mg alloys,electrochemical characterization techniques/methods,as well as strategies to improve the corrosion behaviour and mechanical properties of these types of biodegradable alloys.The means of optimization,the category and the effect of the alloying elements,the design criteria,the requirements that the implants of biodegradable alloys Mg-based must meet and the aspects related to their efficiency are also presented.Finally,the potential applications in the specialized clinics,as well as the final products currently used and made by important prestigious companies in the world are approached.

Carbon fiber cannot always reduce the wear of PEEK for orthopedic implants under DPPC lubrication

Excellent wear resistance is an important feature of orthopedic implants.However,although pure polyetheretherketone(PEEK)is outperformed by carbon fiber-reinforced PEEK(CF-PEEK)for stability and durability under laboratory conditions,it is not clear whether CF-PEEK should be preferred in all real-world applications.Results indicate that,under dipalmitoylphosphatidylcholine(DPPC)lubrication,the wear rates of PEEK are 35%-80%lower than the wear rates of CF-PEEK for different implant materials,speeds,loadings,and DPPC concentrations.Molecular dynamics calculations confirm that DPPC self-assembles on the PEEK surface to form an easily adsorbed continuous phospholipid lubricating film.In contrast,the carbon fibers on the CF-PEEK surface hinder the formation of the protective DPPC film and the CF-PEEK surface is thus subject to faster wear.

Burden of routine orthopedic implant removal a single center retrospective study

BACKGROUND Open reduction and internal fixation represent prevalent orthopedic procedures,sparking ongoing discourse over whether to retain or remove asymptomatic implants.Achieving consensus on this matter is paramount for orthopedic surgeons.This study aims to quantify the impact of routine implant removal on patients and healthcare facilities.A retrospective analysis of implant removal cases from 2016 to 2022 at King Fahad Hospital of the University(KFHU)was conducted and subjected to statistical scrutiny.Among these cases,44%necessitated hospitalization exceeding one day,while 56%required only a single day.Adults exhibited a 55%need for extended hospital stays,contrasting with 22.8%among the pediatric cohort.The complication rate was 6%,with all patients experiencing at least one complication.Notably,34.1%required sick leave and 4.8%exceeded 14 d.General anesthesia was predominant(88%).Routine implant removal introduces unwarranted complications,particularly in adults,potentially prolonging hospitalization.This procedure strains hospital resources,tying up the operating room that could otherwise accommodate critical surgeries.Clearly defined institutional guidelines are imperative to regulate this practice.AIM To measure the burden of routine implant removal on the patients and hospital.METHODS This is a retrospective analysis study of 167 routine implant removal cases treated at KFHU,a tertiary hospital in Saudi Arabia.Data were collected in the orthopedic department at KFHU from February 2016 to August 2022,which includes routine asymptomatic implant removal cases across all age categories.Nonroutine indications such as infection,pain,implant failure,malunion,nonunion,restricted range of motion,and prominent hardware were excluded.Patients who had external fixators removed or joints replaced were also excluded.RESULTS Between February 2016 and August 2022,360 implants were retrieved;however,only 167 of those who met the inclusion criteria were included in this study.The remaining implants were rejected due to exclusion criteria.Among the cases,44%required more than one day in the hospital,whereas 56%required only one day.55%of adults required more than one day of hospitalization,while 22.8%of pediatric patients required more than one day of inpatient care.The complication rate was 6%,with each patient experiencing at least one complication.Sick leave was required in 34.1%of cases,with 4.8%requiring more than 14 d.The most common type of anesthesia used in the surgeries was general anesthesia(88%),and the mean(SD)surgery duration was 77.1(54.7)min.CONCLUSION Routine implant removal causes unnecessary complications,prolongs hospital stays,depletes resources and monopolizing operating rooms that could serve more critical procedures.

A trilogy antimicrobial strategy for multiple infections of orthopedic implants throughout their life cycle

Bacteria-associated infection represents one of the major threats for orthopedic implants failure during their life cycles.However,ordinary antimicrobial treatments usually failed to combat multiple waves of infections during arthroplasty and prosthesis revisions etc.As these incidents could easily introduce new microbial pathogens in/onto the implants.Herein,we demonstrate that an antimicrobial trilogy strategy incorporating a sophisticated multilayered coating system leveraging multiple ion exchange mechanisms and fine nanotopography tuning,could effectively eradicate bacterial infection at various stages of implantation.Early stage bacteriostatic effect was realized via nano-topological structure of top mineral coating.Antibacterial effect at intermediate stage was mediated by sustained release of zinc ions from doped CaP coating.Strong antibacterial potency was validated at 4 weeks post implantation via an implanted model in vivo.Finally,the underlying zinc titanate fiber network enabled a long-term contact and release effect of residual zinc,which maintained a strong antibacterial ability against both Staphylococcus aureus and Escherichia coli even after the removal of top layer coating.Moreover,sustained release of Sr2+and Zn2+during CaP coating degradation substantially promoted implant osseointegration even under an infectious environment by showing more peri-implant new bone formation and substantially improved bone-implant bonding strength.

Orthopedic implants and devices for bone fractures and defects:Past,present and perspective

Bone is a unique tissue that is capable of repairing itself after damage.However,there are certain instances of fractures and defects that require clinical intervention for proper alignment and healing.As with any implant,careful consideration of the material used to create the implants to treat these problems is needed.If the incorrect material is chosen,the implants themselves can lead to bone fractures or defects,or bone healing may not take place at all.All three classes of biomaterials-metals,ceramics,and polymers-have been used in the treatment of both bone fractures and bone defects,and each has its own unique benefits and limitations for its applications.Furthermore,composites of these different materials have also been created to try to take advantage of all the different benefits offered by each different material.This review highlights different materials that have been used for the development of internal fixators and bone graft substitutes to treat fracture and bone defects as well as their limitations and needed future research.

Accelerated fracture healing by osteogenic Ti45Nb implants through the PI3K–Akt signaling pathway

The key to managing fracture is to achieve stable internal fixation,and currently,biologically and mechanically appropriate internal fixation devices are urgently needed.With excellent biocompatibility and corrosion resistance,titanium–niobium alloys have the potential to become a new generation of internal fixation materials for fractures.However,the role and mechanism of titanium–niobium alloys on promoting fracture healing are still undefined.Therefore,in this study,we systematically evaluated the bone-enabling properties of Ti45Nb via in vivo and in vitro experiments.In vitro,we found that Ti45Nb has an excellent ability to promote MC3T3-E1 cell adhesion and proliferation without obvious cytotoxicity.Alkaline phosphatase(ALP)activity and alizarin red staining and semiquantitative analysis showed that Ti45Nb enhanced the osteogenic differentiation of MC3T3-E1 cells compared to the Ti6Al4V control.In the polymerase chain reaction experiment,the expression of osteogenic genes in the Ti45Nb group,such as ALP,osteopontin(OPN),osteocalcin(OCN),type 1 collagen(Col-1)and runt-related transcription factor-2(Runx2),was significantly higher than that in the control group.Meanwhile,in the western blot experiment,the expression of osteogenic-related proteins in the Ti45Nb group was significantly increased,and the expression of PI3K–Akt-related proteins was also higher,which indicated that Ti45Nb might promote fracture healing by activating the PI3K–Akt signaling pathway.In vivo,we found that Ti45Nb implants accelerated fracture healing compared to Ti6Al4V,and the biosafety of Ti45Nb was confirmed by histological evaluation.Furthermore,immunohistochemical staining confirmed that Ti45Nb may promote osteogenesis by upregulating the PI3K/Akt signaling pathway.Our study demonstrated that Ti45Nb exerts an excellent ability to promote fracture healing as well as enhance osteoblast differentiation by activating the PI3K/Akt signaling pathway,and its good biosafety has been confirmed,which indicates its clinical translation potential.

Insight of magnesium alloys and composites for orthopedic implant applications-a review

Magnesium(Mg)and its alloys have been widely researched for orthopedic applications recently.Mg alloys have stupendous advantages over the commercially available stainless steel,Co-Cr-Ni alloy and titanium implants.Till date,extensive mechanical,in-vitro and in-vivo studies have been done to improve the biomedical performance of Mg alloys through alloying,processing conditions,surface modification etc.This review comprehensively describes the strategies for improving the mechanical and degradation performance of Mg alloys through properly tailoring the composition of alloying elements,reinforcements and processing techniques.It also highlights the status and progress of research in to(i)the selection of nutrient elements for alloying,reinforcement and its effects(ii)type of Mg alloy system(binary,ternary and quaternary)and composites(iii)grain refinement for strengthening through severe plastic deformation techniques.Furthermore it also emphasizes on the importance of Mg composites with regard to hard tissue applications.

Study of the degradation behavior and the biocompatibility of Mg-0.8Ca alloy for orthopedic implant applications

Mg-Ca alloys have recently attracted great attention towards the research in the field of orthopedic biodegradable implants.This study presents an in vitro degradation assessment of Mg-0.8Ca(0.8 wt.%of Ca)alloy in Hank’s balanced salt solution(HBSS).Immersion,hydrogen evolution and electrochemical behavior was studied as well as the cytotoxicity of the degradation products.Morphology and phase composition of the corrosion products were studied using SEM,EDX and XRD techniques.Degradation in HBSS resulted in the formation of the needle-shaped carbonated hydroxyapatite which was similar to the biological apatite in the human bone.Degradation kinetics showed that Mg-0.8Ca alloy had approximately 3-fold faster degradation rate than the pure Mg(1.08±0.38 mm/year for Mg-0.8Ca and 0.35±0.17 mm/year for pure Mg),as observed in two independent experiments.Both,pure Mg and Mg-0.8Ca alloy were biocompatible,generating no cytotoxic degradation products against human-derived HEK 293 cells.Thus,the Mg-0.8Ca alloy was found to be a promising biodegradable implant in terms of bioactivity and compatibility with human cell lines.Depending on the application of the implant and the estimated healing time of the bone,the desired degradation rate of an implant can be controlled by the Mg-Ca composition of such alloys.

Magnesium based implants for functional bone tissue regeneration–A review

Magnesium(Mg)has emerged as one of the third-generation biomaterials for regeneration and support of functional bone tissue.Mg is a better choice over permanent implants such as titanium,stainless steel,cobalt-chrome as magnesium is biodegradable and does not require a second surgery for its removal after bone tissue recovery.It also reduces the risk of stress shielding as its elastic modulus is closer to human bone in comparison to permanent implants and other biodegradable metallic implants based on Iron and Zinc.Most importantly,Mg is osteoconductive thus stimulates new bone formation and possess anti-bacterial properties hence reducing the risk of failure due to infection.Despite its advantages,a major concern with pure Mg is its rapid bio-corrosion in presence of body fluids due to which the mechanical integrity of the implant deteriorates before healing of the tissue is complete.Mechanical properties of Mg-based implants can be enhanced by mechanical processing,alloying,and topology optimization.To reduce the corrosion/degradation rate,Mg has been alloyed with metals,reinforced with ceramics,and surface coatings have been applied so that the degradation rate of Mg-based implant matches with that of healing rate of bone tissue.The present review discusses the effect of alloying elements and reinforcing ceramics on microstructure,mechanical,and corrosion properties of Mg-based orthopedic implants.In addition,the biocompatibility of Mg-based alloys,composites,and coatings applied on Mg implants has been highlighted.Further,different methods of fabricating porous implants have been highlighted as making the implant porous facilitates the growth of new bone tissue through the pores.

Approaches to promoting bone marrow mesenchymal stem cell osteogenesis on orthopedic implant surface

Bone marrow-derived mesenchymal stem cells(BMSCs)play a critical role in the osseointegration of bone and orthopedic implant.However,osseointegration between the Ti-based implants and the surrounding bone tissue must be improved due to titanium’s inherent defects.Surface modification stands out as a versatile technique to create instructive biomaterials that can actively direct stem cell fate.Here,we summarize the current approaches to promoting BMSC osteogenesis on the surface of titanium and its alloys.We will highlight the utilization of the unique properties of titanium and its alloys in promoting tissue regeneration,and discuss recent advances in understanding their role in regenerative medicine.We aim to provide a systematic and comprehensive review of approaches to promoting BMSC osteogenesis on the orthopedic implant surface.

Layer-by-layer self-assembly and clinical application in orthopedics

Orthopedic implants for the treatment of bone defects from various causes have been challenged by insufficient osseointegration,bacterial infection,oxidative stress,immune rejection,and insufficient individualized treatment.These challenges not only impact treatment outcomes but also severely impact patients’daily lives.Layer-by-Layer(LbL)serves as a simple surface coating technique,in simple terms,to functionalize implants by sequentially adsorbing oppositely charged materials onto a substrate.In orthopaedics,LbL self-assembly technology solves some of the challenges by loading various drugs or biological agents on the implant surface and controlling their release precisely to the site of bone defects in a personalized way.This review will introduce the basic principle and the development of LbL in orthopaedics,review and analyze the chemical strategy of LbL in the preparation of bone implants to ensure the stability of the implant,and introduce the use of LbL bone implants in orthopaedics in recent years.The application of LbL includes the realization of programmed drug delivery and sustained release,thereby promoting osseointegration and the formation of new blood vessels,antibacterial,antioxidant,etc.This review focuses on the LbL technology,involving the technology selection for the preparation of bone implants,the chemical strategies of the stability guarantee of LbL implants,the pharmacological properties,loading and release mechanisms of loaded drugs,and the molecular mechanisms of osteogenesis and angiogenesis.The aim of this review is to provide an overview of current research advances,and a prospect in this field was also described.

Innovations in osteomyelitis research:A review of animal models

Infection of bone tissue,or osteomyelitis,has become a growing concern in modern healthcare due in no small part to a rise in antibiotic resistance among bacteria,notably Staphylococcus aureus.The current standard of care involves aggressive,prolonged antibiotic therapy combined with surgical debridement of infected tissues.While this treatment may be sufficient for resolving a portion of cases,recurrences of the infection and associated risks including toxicity with long-term antibiotic usage have been reported.Therefore,there exists a need to produce safer,more efficacious options of treatment for osteomyelitis.In order to test treatment regimens,animal models that closely mimic the clinical condition and allow for accurate evaluation of therapeutics are necessary.Establishing a model that replicates features of osteomyelitis in humans continues to be a challenge to scientists,as there are many variables involved,including choosing an appropriate species and method to establish infection.This review addresses the refinement of animal models of osteomyelitis to reflect the clinical disease and test prospective therapeutics.The aim of this review is to explore studies regarding the use of animals for osteomyelitis therapeutics research and encourage further development of such animal models for the translation of results from the animal experiment to human medicine.

Construction of tantalum/poly(ether imide)coatings on magnesium implants with both corrosion protection and osseointegration properties

Poly(ether imide)(PEI)has shown satisfactory corrosion protection capability with good adhesion strength as a coating for magnesium(Mg),a potential candidate of biodegradable orthopedic implant material.However,its innate hydrophobic property causes insufficient osteoblast affinity and a lack of osseointegration.Herein,we modify the physical and chemical properties of a PEI-coated Mg implant.A plasma immersion ion implantation technique is combined with direct current(DC)magnetron sputtering to introduce biologically compatible tantalum(Ta)onto the surface of the PEI coating.The PEI-coating layer is not damaged during this process owing to the extremely short processing time(30 s),retaining its high corrosion protection property and adhesion stability.The Ta-implanted layer(roughly 10-nm-thick)on the topmost PEI surface generates long-term surface hydrophilicity and favorable surface conditions for pre-osteoblasts to adhere,proliferate,and differentiate.Furthermore,in a rabbit femur study,the Ta/PEI-coated Mg implant demonstrates significantly enhanced bone tissue affinity and osseointegration capability.These results indicate that Ta/PEI-coated Mg is promising for achieving early mechanical fixation and long-term success in biodegradable orthopedic implant applications.

Surface Modification on Biodegradable Magnesium Alloys as Orthopedic Implant Materials to Improve the Bio-adaptability:A Review

Magnesium （Mg） and its alloys as a novel kind of biodegradable material have attracted much funda- mental research and valuable exploration to develop its clinical application, Mg alloys degrade too fast at the early stage after implantation, thus commonly leading to some problems such as osteolysis, early fast mechanical loss, hydric bubble aggregation, gap formation between the implants and the tissue. Surface modification is one of the effective methods to control the degradation property of Mg alloys to adapt to the need of organism. Some coatings with bioactive elements have been developed, especially for the micro-arc oxidation coating, which has high adhesion strength and can be added with Ca, P, and Sr elements. Chemical deposition coating including bio-mimetic deposition coating, electro-deposition coating and chemical conversion coating can provide good anticorrosion property as well as better bioactivity with higher Ca and P content in the coating. From the biodegradation study, it can be seen that surface coating protected the Mg alloys at the early stage providing the Mg alloy substrate with lower degra-dation rate. The biocompatibility study showed that the surface modification could provide the cell and tissue stable and weak alkaline surface micro-environment adapting to the cell adhesion and tissue growth. The surface modification also decreased the mechanical loss at the early stage adapting to the load- bearing requirement at this stage. From the interface strength between Mg alloys implants and the surrounding tissue study, it can be seen that the surface modification improved the bio-adhesion of Mg alloys with the surrounding tissue, which is believed to be contributed to the tissue adaptability of the surface modification. Therefore, the surface modification adapts the biodegradable magnesium alloys to the need of hiodegradation, biocompatibility and mechanical loss property. For the different clinical application, different surface modification methods can be provided to adapt to the clinical requirements for the Mg alloy implants.

Bone infection site targeting nanoparticle-antibiotics delivery vehicle to enhance treatment efficacy of orthopedic implant related infection

Orthopedic implants account for 99%of orthopedic surgeries,however,orthopedic implant-related infection is one of the most serious complications owing to the potential for limb-threatening sequelae and mortality.Current antibiotic treatments still lack the capacity to target bone infection sites,thereby resulting in unsatisfactory therapeutic effects.Here,the bone infection site targeting efficacy of D6 and UBI29-41 peptides was investigated,and bone-and-bacteria dual-targeted nanoparticles(NPs)with D6 and UBI29-41 peptides were first fabricated to target bone infection site and control the release of vancomycin in bone infection site.The results of this study demonstrated that the bone-and-bacteria dual-targeted mesoporous silica NPs exhibit excellent bone and bacteria targeting efficacy,excellent biocompatibility and effective antibacterial properties in vitro.Furthermore,in a rat model of orthopedic implant-related infection with methicillin-resistant Staphylococcus aureus,the growth of bacteria was evidently inhibited without cytotoxicity,thus realizing the early treatment of implant-related infection.Hence,the bone-and-bacteria dual-targeted molecule-modified NPs may target bacteria-infected bone sites and act as ideal candidates for the therapy of orthopedic implant-related infections.

Accelerated biodegradation of iron-based implants via tantalum-implanted surface nanostructures

In recent years,pure iron(Fe)has attracted significant attention as a promising biodegradable orthopedic implant material due to its excellent mechanical and biological properties.However,in physiological conditions,Fe has an extremely slow degradation rate with localized and irregular degradation,which is problematic for practical applications.In this study,we developed a novel combination of a nanostructured surface topography and galvanic reaction to achieve uniform and accelerated degradation of an Fe implant.The target-ion induced plasma sputtering(TIPS)technique was applied on the Fe implant to introduce biologically compatible and electrochemically noble tantalum(Ta)onto its surface and develop surface nano-galvanic couples.Electrochemical tests revealed that the uniformly distributed nano-galvanic corrosion cells of the TIPS-treated sample(nano Ta-Fe)led to relatively uniform and accelerated surface degradation compared to that of bare Fe.Furthermore,the mechanical properties of nano Ta-Fe remained almost constant during a long-term in vitro immersion test(~40 weeks).Biocompatibility was also assessed on surfaces of bare Fe and nano Ta-Fe using in vitro osteoblast responses through direct and indirect contact assays and an in vivo rabbit femur medullary cavity implantation model.The results revealed that nano Ta-Fe not only enhanced cell adhesion and spreading on its surface,but also exhibited no signs of cellular or tissue toxicity.These results demonstrate the immense potential of Ta-implanted surface nanostructures as an effective solution for the practical application of Fe-based orthopedic implants,ensuring long-term biosafety and clinical efficacy.

300 MPa grade biodegradable high-strength ductile low-alloy(BHSDLA)Zn-Mn-Mg alloys:An in vitro study

300 MPa grade biodegradable Zn-(0.6,0.8)Mn-(<0.1)Mg alloys with yield strengths>300 MPa and elongations>15%have been developed,which are designated as Zn06Mn006Mg(HE)and Zn08Mn005Mg(HE)in as-extruded state.They are the newest members of a small group of biodegradable Zn alloys with mechanical properties beyond the generally accepted benchmark for orthopedic implants.Immersed in simulated body fluid for 30 days,Zn06Mn006Mg(HE)and Zn08Mn005Mg(HE)exhibit corrosion rates of 38 and 53μm y^(-1),respectively.They show high antibacterial rates of 93%-97%against E.coli.In 25%-75%extracts of both the alloys,MC3T3-E1 cell viabilities for 1 day and 3 days are all over 100%,indicating complete cytocompatibility.In 100%extracts for 3 days,both alloys show non-toxicity.After a longtime room temperature storage of 72 weeks,natural embrittling alike Zn-Mg alloys does not happen.The Zn-Mn-Mg alloys still have mechanical properties exceeding the benchmark by a large margin.The in vitro study shows the newly developed BHSDLA Zn-Mn-Mg alloys are promising candidates for orthopedic implants.

Advanced surface engineering of titanium materials for biomedical applications:From static modification to dynamic responsive regulation

Titanium(Ti)and its alloys have been widely used as orthopedic implants,because of their favorable mechanical properties,corrosion resistance and biocompatibility.Despite their significant success in various clinical applications,the probability of failure,degradation and revision is undesirably high,especially for the patients with low bone density,insufficient quantity of bone or osteoporosis,which renders the studies on surface modification of Ti still active to further improve clinical results.It is discerned that surface physicochemical properties directly influence and even control the dynamic interaction that subsequently determines the success or rejection of orthopedic implants.Therefore,it is crucial to endow bulk materials with specific surface properties of high bioactivity that can be performed by surface modification to realize the osseointegration.This article first reviews surface characteristics of Ti materials and various conventional surface modification techniques involving mechanical,physical and chemical treatments based on the formation mechanism of the modified coatings.Such conventional methods are able to improve bioactivity of Ti implants,but the surfaces with static state cannot respond to the dynamic biological cascades from the living cells and tissues.Hence,beyond traditional static design,dynamic responsive avenues are then emerging.The dynamic stimuli sources for surface functionalization can originate from environmental triggers or physiological triggers.In short,this review surveys recent developments in the surface engineering of Ti materials,with a specific emphasis on advances in static to dynamic functionality,which provides perspectives for improving bioactivity and biocompatibility of Ti implants.

Surface integrity of ball burnished bioresorbable magnesium alloy

Magnesium alloys are potential biodegradable and biocompatible implant materials because of their excellent biological properties. Recently, interest in these alloys as a promising alternative for temporary orthopedic implants has grown owing to their desirable biological, mechanical, and physical properties. However, the application of magnesium alloys is hindered by their rapid degradation and low corrosion resistance in physiological fluids, leading to the failure of implants. Thus, the current challenge is to enhance the corrosion resistance and control the degradation rate of magnesium under physiological conditions. The rapid degradation of magnesium alloys can be controlled by improving their surface integrity, such as surface roughness and microhardness. The present study aims to improve the surface integrity of the Mg Ze41A alloy by the ball burnishing technique. The surface roughness improved by 94.90% from 0.941 μm to 0.048 μm with a burnishing force of 50 N, burnishing speed of 1 300 r/min, burnishing feed of 130 mm/min, and three passes. Similarly, the microhardness improved by 50.62% from 75.2 HV to 113.27 HV with a burnishing force of 60 N, burnishing speed of 1 100 r/min, burnishing feed of 100 mm/min, and five passes. The variations in microhardness, which were observed up to 400 μm beneath the surface, exhibited a linear nature. These variations may be attributed to the movement of dislocations, formation of new dislocations, nanocrystal structures, metastable phases and subgrains, and lattice distortion or grain refinement. The surface features obtained from optical images demonstrated the fundamental mechanisms involved in the ball burnishing process. The concept of burnishing maps and zones will assist in the design of the ball burnishing parameters of a material with an equivalent yield strength of 140 MPa. The significant improvement in the surface integrity of the Mg Ze41A alloy by the ball burnishing technique is expected to improve its functional performance.

In vitro and in vivo degradation behavior of Mg-2Sr-Ca and Mg-2Sr-Zn alloys

Magnesium alloys with integration of degradability and good mechanical performance are desired for orthopedic implants.In this paper,Mg-2Sr-Ca and Mg-2Sr-Zn alloys were prepared and the degradation as well as the bone response were investigated.Compared with the binary Mg-2Sr alloys,the addition of Ca and Zn improved the in vitro and in vivo corrosion resistance.Mg-2Sr-Ca and Mg-2Sr-Zn alloys exhibited more uniform corrosion and maintained the configuration of the implants 4 weeks post-implantation.The in vivo corrosion rates were 0.85 mm/yr for Mg-2Sr-Zn and 1.10 mm/yr for Mg-2Sr-Ca in comparison with 1.37 mm/yr for Mg-2Sr.The in vitro cell tests indicated that Mg-2Sr-Ca and Mg-2Sr-Zn alloys exhibited higher MG63 cell viability than Mg-2Sr alloy.Furthermore,these two alloys can promote the mineralization and new bone formation without inducing any significant adverse effects and this sound osteogenic properties suggest its attractive clinical potential.