Breaking piezoelectric limits of molecules for biodegradable implants

In the quest for optimizing biodegradable implants,the exploration of piezoelectric materials stands at the forefront of biomedical engineering research.Traditional piezoelectric materials often suffer from limitations in biocompatibility and biodegradability,significantly impeding their in vivo study and further biomedical application.By leveraging molecular engineering and structural design,a recent innovative approach transcends the conventional piezoelectric limits of the molecules designed for biodegradable implants.The biodegradable molecular piezoelectric implants may open new avenues for their applications in bioenergy harvesting/sensing,implanted electronics,transient medical devices and tissue regeneration.

Graphene-calcium carbonate coating to improve the degradation resistance and mechanical integrity of a biodegradable implant

Biodegradable implants are critical for regenerative orthopaedic procedures,but they may suffer from too fast corrosion in human-body environment.This necessitates the synthesis of a suitable coating that may improve the corrosion resistance of these implants without compromising their mechanical integrity.In this study,an AZ91 magnesium alloy,as a representative for a biodegradable Mg implant material,was modified with a thin reduced graphene oxide(RGO)-calcium carbonate(CaCO_(3))composite coating.Detailed analytical and in-vitro electrochemical characterization reveals that this coating significantly improves the corrosion resistance and mechanical integrity,and thus has the potential to greatly extend the related application field.

Interplay of laser power and pore characteristics in selective laser melting of ZK60 magnesium alloys:A study based on in-situ monitoring and image analysis

This study offers significant insights into the multi-physics phenomena of the SLM process and the subsequent porosity characteristics of ZK60 Magnesium(Mg)alloys.High-speed in-situ monitoring was employed to visualise process signals in real-time,elucidating the dynamics of melt pools and vapour plumes under varying laser power conditions specifically between 40 W and 60 W.Detailed morphological analysis was performed using Scanning-Electron Microscopy(SEM),demonstrating a critical correlation between laser power and pore formation.Lower laser power led to increased pore coverage,whereas a denser structure was observed at higher laser power.This laser power influence on porosity was further confirmed via Optical Microscopy(OM)conducted on both top and cross-sectional surfaces of the samples.An increase in laser power resulted in a decrease in pore coverage and pore size,potentially leading to a denser printed part of Mg alloy.X-ray Computed Tomography(XCT)augmented these findings by providing a 3D volumetric representation of the sample internal structure,revealing an inverse relationship between laser power and overall pore volume.Lower laser power appeared to favour the formation of interconnected pores,while a reduction in interconnected pores and an increase in isolated pores were observed at higher power.The interplay between melt pool size,vapour plume effects,and laser power was found to significantly influence the resulting porosity,indicating a need for effective management of these factors to optimise the SLM process of Mg alloys.

Influence of bimodal grain size distribution on the corrosion behavior of friction stir processed biodegradable AZ31 magnesium alloy

In the present study,AZ31 magnesium alloy sheets were processed by friction stir processing(FSP)to investigate the effect of the grain refinement and grain size distribution on the corrosion behavior.Grain refinement from a starting size of 16.4±6.8µm to 3.2±1.2µm was attained after FSP.Remarkably,bimodal grain size distribution was observed in the nugget zone with a combination of coarse(11.62±8.4µm)and fine grains(3.2±1.2µm).Due to the grain refinement,a slight improvement in the hardness was found in the nugget zone of FSPed AZ31.The bimodal grain size distribution in the stir zone showed pronounced influence on the corrosion rate of FSPed AZ31 as observed from the immersion and electrochemical tests.From the X-ray diffraction analysis,more amount of Mg(OH)_(2) was observed on FSPed AZ31 compared with the unprocessed AZ31.Polarization measurements demonstrated the higher corrosion current density for FSPed AZ31(8.92×10^(−5)A/cm^(2))compared with the unprocessed condition(2.90×10^(−5)A/cm^(2))that can be attributed to the texture effect and large variations in the grain size which led to non-uniform galvanic intensities.

Effects of heat treatment on the corrosion behavior and mechanical properties of biodegradable Mg alloys

Biodegradable magnesium(Mg)alloys exhibit great potential for use as temporary structures in tissue engineering applications.Such degradable implants require no secondary surgery for their removal.In addition,their comparable mechanical properties with the human bone,together with excellent biocompatibility,make them a suitable candidate for fracture treatments.Nevertheless,some challenges remain.Fast degradation of the Mg-based alloys in physiological environments leads to a loss of the mechanical support that is needed for complete tissue healing and also to the accumulation of hydrogen gas bubbles at the interface of the implant and tissue.Among different methods used to improve the performance of the biodegradable Mg alloys to address these challenges,it appears that heat treatment is the most effective way to modify the microstructure and thus the corrosion behavior and mechanical properties without changing the composition or shape of the alloys.A desirable combination of corrosion and mechanical properties can be obtained through a precise control of the heat treatment parameters.In this report,the effects of different heat treatments(T4 and T6)on the microstructure,corrosion behavior,and mechanical properties of some of the most important heat-treatable biodegradable Mg alloys(Mg-Zn,Mg-Gd,Mg-Y,Mg-Nd,Mg-Al and Mg-Ag)are examined as well as new perspectives to enhance their clinical implementation.

Calcium phosphate conversion technique:A versatile route to develop corrosion resistant hydroxyapatite coating over Mg/Mg alloys based implants

Globally,vast research interest is emerging towards the development of biodegradable orthopedic implants as it overcomes the toxicity exerted by non-degradable implants when fixed in the human body for a longer period.In this context,magnesium(Mg)plays a major role in the production of biodegradable implants owing to their characteristic degradation nature under the influence of body fluids.Also,Mg is one of the essential nutrients required to perform various metabolic activities by the human cells,and therefore,the degraded Mg products will be readily absorbed by the nearby tissues.Nevertheless,the higher corrosion rate in the biological environment is the primary downside of using Mg implants that liberate H2gas resulting in the formation of cavities.Further,in certain cases,Mg undergoes complete degradation before the healing of damaged bone tissue and cannot serve the purpose of providing mechanical support.So,many studies have been focused on the development of different strategies to improve the corrosion-resistant behavior of Mg according to the requirement.In this regard,the present review focused on the limitations of using pure Mg and Mg alloys for the fabrication of medical implants and how the calcium phosphate conversion coating alters the corrosive tendency through the formation of hydroxyapatite protective films for enhanced performance in medical implant applications.

In silico studies of magnesium-based implants: A review of the current stage and challenges

In silico methods to study biodegradable implants have recently received increasing attention due to their potential in reducing experimental time and cost. An important application case for in silico methods are magnesium(Mg)-based biodegradable implants, as they represent a powerful alternative to traditional materials used for temporary orthopaedic applications. Controlling Mg alloy degradation is critical to designing an implant that supports the bone healing process. To simulate different aspects of this biodegradation process, several mathematical models have been proposed with the ultimate aim of replacing laboratory experiments with computational modeling. In this review, we provide a comprehensive and critical discussion of the published models and their performance with respect to capturing the complexity of the biodegradation process. This complexity is presented initially. Additionally, the present review discusses the different approaches of optimizing and quantifying the different sources of errors and uncertainties within the proposed models.

Study of the effect of magnetic fields on static degradation of Fe and Fe-12Mn-1.2C in balanced salts modified Hanks’solution

Iron and its alloys are attractive as biodegradable materials because of their low toxicity and suitable mechanical properties;however,they generally have a slow degradation rate.Given that corrosion is an electrochemical phenomenon where an exchange of electrons takes place,the application of magnetic fields from outside the body may accelerate the degradation of a ferrous temporary implant.In the present study,we have investigated the effect of alternating and direct low magnetic field(H=6.5 kA/m)on the corrosion process of pure iron(Fe)and an iron-manganese alloy(FeMnC)in modified Hanks’solution.A 14-day static immersion test was performed on the materials.The corrosion rate was assessed by mass and cross-sectional loss measurements,scanning electron microscopy,X-ray diffractometry,Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy before and after degradation.The results show that the presence of magnetic fields significantly accelerates the degradation rate of both materials,with the corrosion rate being twice as high in the case of Fe and almost three times as high for FeMnC.In addition,a homogenous degradation layer is formed over the entire surface and the chemical composition of the degradation products is the same regardless of the presence of a magnetic field.

Concerting magnesium implant degradation facilitates local chemotherapy in tumor-associated bone defect

Effective management of malignant tumor-induced bone defects remains challenging due to severe systemic side effects,substantial tumor recurrence,and long-lasting bone reconstruction post tumor resection.Magnesium and its alloys have recently emerged in clinics as orthopedics implantable metals but mostly restricted to mechanical devices.Here,by deposition of calcium-based bilayer coating on the surface,a Mg-based composite implant platform is developed with tailored degradation characteristics,simultaneously integrated with chemotherapeutic(Taxol)loading capacity.The delicate modulation of Mg degradation occurring in aqueous environment is observed to play dual roles,not only in eliciting desirable osteoinductivity,but allows for modification of tumor microenvironment(TME)owing to the continuous release of degradation products.Specifically,the sustainable H2 evolution and Ca2+from the implant is distinguished to cooperate with local Taxol delivery to achieve superior antineoplastic activity through activating Cyt-c pathway to induce mitochondrial dysfunction,which in turn leads to significant tumor-growth inhibition in vivo.In addition,the local chemotherapeutic delivery of the implant minimizes toxicity and side effects,but markedly fosters osteogenesis and bone repair with appropriate structure degradation in rat femoral defect model.Taken together,a promising intraosseous administration strategy with biodegradable Mg-based implants to facilitate tumor-associated bone defect is proposed.

Severe plastic deformation (SPD) of biodegradable magnesium alloys and composites: A review of developments and prospects

The use of magnesium in orthopedic and cardiovascular applications has been widely attracted by diminishing the risk of abnormal interaction of the implant with the body tissue and eliminating the second surgery to remove it from the body.Nevertheless,the fast degradation rate and generally inhomogeneous corrosion subsequently caused a decline in the mechanical strength of Mg during the healing period.Numerous researches have been conducted on the influences of various severe plastic deformation(SPD)processes on magnesium bioalloys and biocomposites.This paper strives to summarize the various SPD techniques used to achieve magnesium with an ultrafine-grained(UFG)structure.Moreover,the effects of various severe plastic deformation methods on magnesium microstructure,mechanical properties,and corrosion behavior have been discussed.Overall,this review intends to clarify the different potentials of applying SPD processes to the magnesium alloys and composites to augment their usage in biomedical applications.

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.

Mechanical and degradation behaviour of biodegradable magnesium-zinc/hydroxyapatite composite with different powder mixing

Magnesium-based biomaterials have recently gained great attention as promising candidates for the new generation of biodegradable implants.This study investigated the mechanical performance and biodegradation behaviour of magnesium-zinc/hydroxyapatite(Mg-Zn/HA)composites fabricated by different powder mixing techniques.A single step mixing process involved mechanical alloying or mechanical milling techniques,while double step processing involved a combination of both mechanical alloying and mechanical milling.Optimum mechanical properties of the composite were observed when the powders were prepared using single step processing via mechanical alloying technique.However,Mg-Zn/HA composite fabricated through single step processing via mechanical milling technique was found to have the most desirable low degradation rate coupled with highest bioactivity.The composite achieved the lowest degradation rate of 0.039×10^−3 mm/year as measured by immersion test and 0.0230 mm/year as measured by electrochemical polarization.Ca:P ratio of the composite also slightly more than enough to aid the initial bone mineralization,that is 1:1.76,as the required Ca:P ratio for initial bone mineralization is between 1:1 and 1:1.67.

Understanding the effects of excimer laser treatment on corrosion behavior of biodegradable Mg-1Ca alloy in simulated body fluid

In this study,a KrF excimer laser was used to modify the biodegradable Mg-1Ca alloy and the time-evolution degradation behavior of the alloy before and after laser treatment was investigated in simulated body fluid(SBF)solution using immersion tests and electrochemical impedance spectroscopy(EIS).A 5μm melted layer with a homogeneous microstructure and an MgO film on the surface were achieved by laser radiation.Corrosion observations(hydrogen evolution,morphology and corrosion products)and EIS results revealed an improvement of corrosion resistance after laser treatment for 48 h.It was found a two-layer structure developed after 2 h immersion on both the untreated and laser-treated alloys,but the sequence of forming the two layers was opposite and greatly influenced by the laser-treated layer.The time-evolution corrosion processes on the untreated and laser-treated alloys were discussed,providing a better understanding of corrosion behavior of biodegradable Mg alloys modified by excimer laser.

Assessing the microstructure and in vitro degradation behavior of Mg-xGd screw implants using μCT

Biodegradable implants are taking an increasingly important role in the area of orthopedic implants with the aim to replace permanent implants for temporary bone healing applications.During the implant preparation process,the material’s surface and microstructure are being changed by stresses induced by machining.Hence degradable metal implants need to be fully characterized in terms of the influence of machining on the resulting microstructure and corrosion performance.In this study,micro-computed tomography(μCT)is used for the quantification of the degradation rate of biodegradable implants.To our best knowledge,for the first time quantitative measures are introduced to describe the degradation homogeneity in 3D.This information enables a prediction in terms of implant stability during the degradation in the body.Two magnesium gadolinium alloys,Mg-5Gd and Mg-10 Gd(all alloy compositions are given in weight%unless otherwise stated),in the shape of M2 headless screws have been investigated for their microstructure and their degradation performance up to 56 days.During the microstructure investigations particular attention was paid to the localized deformation of the alloys,due to the machining process.In vitro immersion testing was performed to assess the degradation performance quantified by subsequent weight loss and volume loss(usingμCT)measurements.Although differences were observed in the degree of screw’s near surface microstructure being influenced from machining,the degradation rates of both materials appeared to be suitable for application in orthopedic implants.From the degradation homogeneity point of view no obvious contrast was detected between both alloys.However,the higher degradation depth ratios between the crests and roots of Mg-5Gd ratios may indicated a less homogeneous degradation of the screws of these alloys on contract to the ones made of Mg-10Gd alloys.Due to its lower degradation rates,its more homogeneous microstructure,its weaker texture and better degradation performance extruded Mg-10Gd emerged more suitable as implant material than Mg-5Gd.

Corrosion and corrosion-fatigue behavior of magnesium metal matrix composites for bio-implant applications:A review

Recently,the topic of bioresorbable metals,with much focus on magnesium for bone implant applications,has been an area of considerable investigation.Indeed,it could be argued that magnesium is the most promising biodegradable material currently being studied for use as an orthopedic skeletal fixation and joint replacement hardware.However,the fast degradation rate of magnesium-based materials in the physiological environment negatively affects their mechanical integrity and hence limits their biomedical use.The most critical conditions may occur when the implant is subjected to a corrosive physiological environment and a fluctuating load during daily activities.Hence,numerous studies have been published on the synthesis,alloying,and coating of magnesium to control degradation rate and increase strength and durability.Among the materials and strategies employed to achieve these goals,magnesium-based biocomposites have exhibited superior mechanical properties and acceptable biocompatibility.However,there is a lack of understanding of their corrosion and corrosion-fatigue behavior.Such understanding is necessary to qualify these new materials for various bio-implant applications.To this end,this paper reviews the recent advances in the corrosion and corrosion-fatigue behavior of magnesium-based biocomposites.It also provides a comprehensive discussion of different factors that influence the biocompatibility,corrosion,fatigue,and corrosion-fatigue of magnesium-based biocomposites as potential implant materials.This study emphasizes that despite the abundance of various studies on the corrosion behavior of magnesium-based biocomposites,there is an imperative need for more fatigue and corrosion-fatigue studies.

Detailing the influence of PEO-coated biodegradable Mg-based implants on the lacuno-canalicular network in sheep bone:A pilot study

An increasing prevalence of bone-related injuries and aging geriatric populations continue to drive the orthopaedic implant market.A hierarchical analysis of bone remodelling after material implantation is necessary to better understand the relationship between implant and bone.Osteocytes,which are housed and communicate through the lacuno-canalicular network(LCN),are integral to bone health and remodelling processes.Therefore,it is essential to examine the framework of the LCN in response to implant materials or surface treatments.Biodegradable materials offer an alternative solution to permanent implants,which may require revision or removal surgeries.Magnesium alloys have resurfaced as promising materials due to their bone-like properties and safe degradation in vivo.To further tailor their degradation capabilities,surface treatments such as plasma electrolytic oxidation(PEO)have demonstrated to slow degradation.For the first time,the influence of a biodegradable material on the LCN is investigated by means of non-destructive 3D imaging.In this pilot study,we hypothesize noticeable variations in the LCN caused by altered chemical stimuli introduced by the PEO-coating.Utilising synchrotron-based transmission X-ray microscopy,we have characterised morphological LCN differences around uncoated and PEO-coated WE43 screws implanted into sheep bone.Bone specimens were explanted after 4,8,and 12 weeks and regions near the implant surface were prepared for imaging.Findings from this investigation indicate that the slower degradation of PEO-coated WE43 induces healthier lacunar shapes within the LCN.However,the stimuli perceived by the uncoated material with higher degradation rates induces a greater connected LCN better prepared for bone disturbance.

Radiofrequency induced heating of biodegradable orthopaedic screw implants during magnetic resonance imaging

Magnesium(Mg)-based implants have re-emerged in orthopaedic surgery as an alternative to permanent implants.Literature reveals little information on how the degradation of biodegradable implants may introduce safety implications for patient follow-up using medical imaging.Magnetic resonance imaging(MRI)benefits post-surgery monitoring of bone healing and implantation sites.Previous studies demonstrated radiofrequency(RF)heating of permanent implants caused by electromagnetic fields used in MRI.Our investigation is the first to report the effect of the degradation layer on RF-induced heating of biodegradable orthopaedic implants.WE43 orthopaedic compression screws underwent in vitro degradation.Imaging techniques were applied to assess the corrosion process and the material composition of the degraded screws.Temperature measurements were performed to quantify implant heating with respect to the degradation layer.For comparison,a commercial titanium implant screw was used.Strongest RF induced heating was observed for non-degraded WE43 screw samples.Implant heating had shown to decrease with the formation of the degradation layer.No statistical differences were observed for heating of the non-degraded WE43 material and the titanium equivalent.The highest risk of implant RF heating is most pronounced for Mg-based screws prior to degradation.Amendment to industry standards for MRI safety assessment is warranted to include biodegradable materials.

Microstructural, mechanical and corrosion characterization of an as-cast Mg-3Zn-0.4Ca alloy for biomedical applications

The as-cast Mg-3Zn-0.4Ca alloy shows a great potential to be used in biomedical applications due to its composition,mechanical properties and biodegradability.Zn and Ca appear naturally in the organism accomplishing vital functions.The alloy consists of an a-Mg matrix and a eutectic composed of a-Mg4-Ca2Mg6Zn3.The eutectic product enhances the mechanical properties of the studied alloy,causing strengthening and providing superior hardness values.In this alloy,cracks initiate at the intermetallic compounds and progress through the matrix because of the open network formed by the eutectics.Attending to the corrosion results,the eutectic product presents a noble potential compared to the a-Mg phase.For this reason,the corrosion progresses preferentially through the matrix,avoiding the(α-Mg+Ca2Mg6Zri3)eutectic product,when the alloy is in direct contact to Hank's solution.

Effect of heat treatment on the mechanical and biocorrosion behaviour of two Mg-Zn-Ca alloys

The effect of heat treatment on the mechanical and biocorrosion behaviour of the Mg-1 wt.%Zn-1 wt.%Ca(ZX11)and Mg-3 wt.%Zn-0.4 wt.%Ca(ZX30)alloys was evaluated.For this purpose,three-point bending tests as well as electrochemical and immersion tests in Hank’s solution were performed on both alloys in four different thermal conditions:as-cast,solution-treated,peak-aged and over-aged.Microstructural examinations revealed that the as-cast ZX11 and ZX30 alloys exhibit a microstructure composed ofα-Mg grains separated by large Mg_(2)Ca and Ca_(2)Mg_(6)Zn_(3) particles and by large Ca_(2)Mg_(6)Zn_(3) particles,respectively.During solution treatment,the Ca_(2)Mg_(6)Zn_(3) precipitates at the grain boundaries(GBs)are fully dissolved in the ZX11 alloy,but mainly redistributed to form a more connected configuration in the ZX30 alloy,showing a poor age-hardening response.Consequently,after solution-treatment,galvanic corrosion and corrosion rate decreases in the former,but increases in the latter.The peak-aged condition displays the highest corrosion rate for both alloys,maybe due to an excessive number density of fine Ca_(2)Mg_(6)Zn_(3) particles acting as cathodic sites.However,the over-aged condition shows the lowest corrosion rate for the ZX11 alloy and a very similar one to that of the as-cast sample for the ZX30 alloy.The ZX11 alloy shows generally better biocorrosion behaviour than the ZX30 alloy to its lower content in the Ca_(2)Mg_(6)Zn_(3) phase and thus reduced galvanic corrosion.The Mg_(2)Ca phase present in the studied ZX11 alloy has been proved to exhibit an increased corrosion potential,which has been related to an observed enrichment with Zn.

The current performance of biodegradable magnesium-based implants in magnetic resonance imaging:A review

Magnesium-based implants are re-emerging as a substantial amendment to standard orthopaedic implants.A brief introduction of magnesium(Mg)as a biodegradable material and basic magnetic resonance imaging(MRI)principles are discussed.This review aims to highlight the current performance of these implants during examinations with MRI.We also aim to summarise comparisons between Mg-based implants with current standards to emphasise the promotion of biodegradable implants in clinical practice.A comprehensive search of current literature on Mg-based implants and the utilisation of MRI in the studies was performed.Additionally,recorded artefact behaviour of Mg-based implants during MRI was investigated.A total of nine studies were included in which MRI was employed to image Mg-based implants.Of those studies,four of the nine discuss artefact production caused by the implants.MRI successfully imaged regions of interest over all and produced fewer artefacts than other materials used in the studies.MRI was employed in contrast angiography,bone growth observation,bone infection healing,and blood perfusion.Imaging capabilities of an implant material are vital to translating products into clinical application.Positive findings presented in this review suggest and support the use of Mg-based implants due to their successful visual compatibility with MRI techniques.