Materials For Biodegradable Implants Research Articles

Enhanced Experimental Setup and Methodology for the Investigation of Corrosion Fatigue in Metallic Biodegradable Implant Materials.

Biodegradable implants as bone fixations may present a safe alternative to traditional permanent implants, reducing the risk of infections, promoting bone healing, and eliminating the need for removal surgeries. Structural integrity is an important consideration when choosing an implant material. As a biodegradable implant is being resorbed, until the natural bone has regrown, the implant material needs to provide mechanical stability. However, the corrosive environment of the human body may affect the fatigue life of the material. Conversely, mechanical stress can have an effect on electrochemical corrosion processes. This is known as corrosion fatigue. In the presented work, an experimental setup and methodology was established to analyze the corrosion fatigue of experimental bioresorbable materials while simultaneously monitoring the electrochemical processes. A double-walled measurement cell was constructed for a three-point bending test in Dulbecco's Phosphate-Buffered Saline (DPBS- -), which was used as simulated body fluid (SBF), at 37 ± 1 °C. The setup was combined with a three-electrode setup for corrosion measurements. Rod-shaped zinc samples were used to validate the setup's functionality. Preliminary static and dynamic bending tests were carried out as per the outlined methodology to determine the test parameters. Open-circuit as well as potentiostatic polarization measurements were performed with and without mechanical loading. For the control, fatigue tests were performed in an air environment. The tested zinc samples were inspected via scanning electron microscopy (SEM). Based on the measured mechanical and electrochemical values as well as the SEM images, the effects of the different environments were investigated, and the setup's functionality was verified. An analysis of the data showed that a comprehensive investigation of corrosion fatigue characteristics is feasible with the outlined approach. Therefore, this novel methodology shows great potential for furthering our understanding of the effects of corrosion on the fatigue of biodegradable implant materials.

Nanoparticle-Enabled Zn-0.1Mg Alloy with Long-Term Stability, Refined Degradation, and Favorable Biocompatibility for Biodegradable Implant Devices.

Zinc-based alloys, specifically Zn-Mg, have garnered considerable attention as promising materials for biodegradable implants due to their favorable mechanical strength, appropriate corrosion rate, and biocompatibility. Nevertheless, the alloy's lack of mechanical stability and integrity, resulting from ductility loss induced by age hardening at room temperature, hampers its practical bioapplication. In this study, ceramic nanoparticles have been successfully incorporated into the Zn-Mg alloy system, leading to a significant improvement in long-term stability as well as mechanical strength and ductility. In addition, this study represents the first investigation of Zn-based nanocomposites both in vitro and in vivo to comprehend the influence of nanoparticles on the degradation behavior and biocompatibility of the Zn system. The findings indicate that the incorporation of WC nanoparticles effectively refines and stabilizes the degradation behavior of Zn-Mg without negatively impacting the cytocompatibility of the alloy. The subcutaneous implantation and femoral implantation further prove the benefits of nanoparticle incorporation and found no negative effects. Collectively, Zn-Mg-WC nanocomposites yield great potential for implant usage.

Fostering biomineralization and biodegradation: nano-hydroxyapatite reinforced iron composites for biodegradable implant application

Iron (Fe) is regarded as a candidate material for biodegradable metallic implants due to its biocompatibility and ability to degrade in physiological environemnt. However, the degradation rate in the physiological environment is too slow for clinical applications. It is necessary to accelerate the rate such that the degradation is compatible with tissue growth. Furthermore, the implant material needs to be bioactive for promoting osteointegration, osteoconductivity, cell proliferation and biological apatite formation. Nano-sized bioactive hydroxyapatite (nHA) was incorporated into a porous Fe matrix to enhance the bioactivity and degradation rate. Electrochemical studies in biomemtic NaCl solution, revealed that incorporation of nHA in porous Fe can increase the degradation by 2.5 times compared to the pure iron counterparts with similar porosity. Furthermore, immersion tests in simulated body fluid (SBF) revealed that nHA added samples displayed enhanced biomineralization and degraded at a rate three times faster than pure iron in this environment. The incorporation of nHA into the iron matrix aided in the formation of biomineralized hydroxyapatite. The composite surface promoted the cell adhesion and proliferation and the L929 fibroblast cells exhibited good cell viability. It is proposed that porous morphology incorporated with nHA can improve biomineralization and tailor the degradation rate of Fe-based materials in physiological environment.

Quasi-"In Situ" Analysis of the Reactive Liquid-Solid Interface during Magnesium Corrosion Using Cryo-Atom Probe Tomography.

The early stages of corrosion occurring at liquid-solid interfaces control the evolution of the material's degradation process, yet due to their transient state, their analysis remains a formidable challenge. Here corrosion tests are performed on a MgCa alloy, a candidate material for biodegradable implants using pure water as a model system. The corrosion reaction is suspended by plunge freezing into liquid nitrogen. The evolution of the early-stage corrosion process on the nanoscale by correlating cryo-atom probe tomography (APT) with transmission-electron microscopy (TEM) and spectroscopy, is studied. The outward growth of Mg hydroxide Mg(OH)2 and the inward growth of an intermediate corrosion layer consisting of hydrloxides of different compositions, mostly monohydroxide Mg(OH) instead of the expected MgO layer, are observed. In addition, Ca partitions to these newly formed hydroxides and oxides. Density-functional theory calculations suggest a domain of stability for this previously experimental unreported Mg(OH) phase. This new approach and these new findings advance the understanding of the early stages of magnesium corrosion, and in general reactions and processes at liquid-solid interfaces, which can further facilitate the development of corrosion-resistant materials or better control of the biodegradation rate of future implants.

Corrosion Activity of Ultrafine-Grained Pure Magnesium and ZK60 Magnesium Alloy in Phosphate Buffered Saline Solution.

The magnesium alloy ZK60 is a promising candidate as a material for biodegradable implants. One of the most important factors for biodegradable implants is the modification of their corrosion behavior to match the requirements for the healing bone or tissue. The corrosion behavior can be influenced by different factors, among them the grain size, which can be changed by severe plastic deformation processes such as High Pressure Torsion Extrusion (HPTE). This study focuses on the corrosion behavior of samples of pure magnesium and ZK60 before and after HPTE, and the influence of the microstructure on the corrosion activity. The samples are subjected to immersion tests in phosphate buffered saline solution (PBS). The corrosion activity is defined by the emerging hydrogen volume from the corrosion process which is collected and by subsequently observing the resulting sample surfaces. The findings of this study suggest that pure magnesium shows lower corrosion activities than ZK60 and that HPTE processing leads to higher corrosion activities in PBS.

Development and characterization of Zn[sbnd]xCu[sbnd]yTi[sbnd]zMo alloys for biomedical applications: A high-throughput gradient continuous casting approach

The limited mechanical properties of pure Zn, such as its low strength and ductility, hinder its application as a material for biodegradable implants. Addressing this challenge, the current study focuses on the development of biodegradable Zn-based alloys, employing innovative alloy design and processing strategies. Here, alloys with compositions ranging from 0.02 to 0.10 weight percent (wt%) Cu, 1.22 to 1.80 wt% Ti, and 0.04 to 0.06 wt% Mo were produced utilizing a high-throughput gradient continuous casting process. This study highlights three specific alloys: Zn1.82Cu0.10Ti0.05Mo (HR8), Zn0.08Cu1.86Ti0Mo (HR7), and Zn1.26Cu0.13Ti0.06Mo (HR6), which were extensively evaluated for their microstructure, mechanical properties, electrochemical performance, potential as bioimplants, and cytotoxicity. These alloys were found to exhibit enhanced mechanical strength, optimal degradation rates, and superior biocompatibility, evidenced by in-vivo experiments with SD rats, positioning them as promising candidates for medical implants. This research not only introduces a significant advancement in biodegradable alloy development but also proposes an efficient method for their production, marking a pivotal step forward in biomedical engineering. Statement of significanceThe limited mechanical properties of pure Zn have hindered its application in biodegradable implants. Our research primarily focuses on the alloy design and process strategies of biodegradable Zn-based alloys. We explore the ZnCuxTixMox alloys. This study introduces a high-throughput experimental approach for efficient screening of multi-component alloy systems with optimal properties. The ZnCuxTixMox alloys were designed and processed through gradient continuous casting, followed by homogenization and hot rolling. Our findings indicate that the Zn1.82Cu0.10Ti0.05Mo alloy demonstrates superior tensile, mechanical, and corrosion properties post hot rolling. The study suggests that Zn0.13Cu1.26Ti0.06Mo, Zn0.08Cu1.86Ti0Mo, and Zn1.82Cu0.10Ti0.05Mo alloys hold significant potential as biodegradable materials.

Investigation on microstructures, mechanical properties, and corrosion behavior of novel biodegradable Zn-xCu-xTi alloys after hot rolling fabricated by self-developed newly gradient continuous casting

The poor mechanical properties exhibited by pure Zn effectively prohibit its utilization as a viable material for biodegradable implants. Hence, the primary area of interest has been directed towards alloy design and process strategies of biodegradable Zn alloys. To this end, novel biodegradable Zn-xCu-xTi (Cu: x = 0.001–2.72 and Ti: x = 0.03–1.21) alloys were designed and fabricated using a gradient continuous casting method followed by homogenization and rolling. The fabricated samples were then investigated in terms of their microstructures, mechanical properties, and corrosion behavior. The results showed that the as-cast Zn-0.001Cu-0.037Ti and Zn-1.50Cu-1.06Ti alloys possess better mechanical properties and corrosion resistance. The yield strength, elongation, and highest charge transfer resistance (Rct) of Zn-0.001Cu-0.037Ti were 137 MPa, 60 %, and 2227.9 Ω, respectively. On the other hand, the Zn-1.50Cu-1.06Ti alloy exhibited 250 MPa yield strength, 12.7.% elongation, and 11113.0 Ω Rct, respectively. Higher Cu and Ti content also led to larger second phases. However, as-hot rolled Zn-1.50Cu-1.06Ti alloy displayed better mechanical properties as compared to the Zn-0.001Cu-0.037Ti alloy due to a very fine nanocrystalline structure. Furthermore, the hot-rolled Zn-xCu-xTi alloys demonstrated superior corrosion resistance compared to their as-cast counterparts, as evidenced by the analysis of the potentiodynamic polarization and electrochemical impedance spectroscopy data. This improved corrosion resistance is attributed to the refined grain size, fractured second phases which reduce both the anode and cathode areas, and the formation of protective oxide layers. Lastly, the corrosion products primarily consisted of carbon, phosphorus, calcium, and oxygen, suggesting the presence of Zn(OH)2, carbonates, and phosphates.

Comparison of Time-Zero Primary Stability Between a Biodegradable Magnesium Bone Staple and Metal Bone Staples for Knee Ligament Fixation: A Biomechanical Study in a Porcine Model.

Bone staples have been shown previously to be a viable modality for cortical tendon graft fixation in ligament knee surgery. However, soft tissue reactions have been reported, making implant removal necessary. Magnesium alloys are a promising material for biodegradable orthopaedic implants, with mechanical properties closely resembling those of human bone. To compare the primary stability of a biodegradable bone staple prototype made from magnesium to bone staples made from metal in the cortical fixation of tendon grafts during knee surgery. Controlled laboratory study. Primary stability of peripheral tendon graft fixation was assessed in a porcine model of medial collateral ligament reconstruction. Two commercially available metal bone staples (Richards fixation staple with spikes [Me1] and spiked ligament staple [Me2]) were compared with a magnesium bone staple prototype for soft tissue fixation. Primary stability was assessed using a uniaxial materials testing machine. Cyclic loading at 50 and 100 N was applied for 500 cycles each, followed by load-to-failure testing. After 500 cycles at 50 N, elongation was 1.5 ± 0.5 mm in the Me1 group, 1.9 ± 0.5 mm in the Me2 group, and 1.8 ± 0.4 mm in the magnesium group. After 1000 cycles of loading (500 cycles at 50 N and 500 at 100 N), elongation was 3.6 ± 0.9 mm in the Me1 group, 3.5 ± 0.6 mm in the Me2 group, and 4.1 ± 1.0 mm in the magnesium group. No significant differences regarding elongation were found between the groups. Load to failure was 352 ± 115 N in the Me1 group, 373 ± 77 N in the Me2 group, and 449 ± 92 N in the magnesium group, with no significant difference between the groups. In this study, the magnesium bone staples provided appropriate time-zero biomechanical primary stability in comparison with metal bone staples and may therefore be a feasible alternative for cortical fixation of tendon grafts in knee surgery. The biodegradability of magnesium bone staples would eliminate the need for later implant removal.

A strategy for enhancing bioactivity and osseointegration with antibacterial effect by incorporating magnesium in polylactic acid based biodegradable orthopedic implant

Biodegradable orthopedic implants are essential for restoring the physiological structure and function of bone tissue while ensuring complete degradation after recovery. Polylactic acid (PLA), a biodegradable polymer, is considered a promising material due to its considerable mechanical properties and biocompatibility. However, further improvements are necessary to enhance the mechanical strength and bioactivity of PLA for reliable load-bearing orthopedic applications. In this study, a multifunctional PLA-based composite was fabricated by incorporating tricalcium phosphate (TCP) microspheres and magnesium (Mg) particles homogenously at a volume fraction of 40 %. This approach aims to enhance mechanical strength, accelerate pore generation, and improve biological and antibacterial performance. Mg content was incorporated into the composite at varying values of 1, 3, and 5 vol% (referred to as PLA/TCP-1 Mg, PLA/TCP-3 Mg, and PLA/TCP-5 Mg, respectively). The compressive strength and stiffness were significantly enhanced in all composites, reaching 87.7, 85.9, and 84.1 MPa, and 2.7, 3.0, and 3.1 GPa, respectively. The degradation test indicated faster elimination of the reinforcers as the Mg content increased, resulting in accelerated pore generation to induce enhanced osseointegration. Because PLA/TCP-3 Mg and PLA/TCP-5 Mg exhibited cracks in the PLA matrix due to rapid corrosion of Mg forming corrosion byproducts, to optimize the Mg particle content, PLA/TCP-1 Mg was selected for further evaluation. As determined by in vitro biological and antibacterial testing, PLA/TCP-1 Mg showed enhanced bioactivity with pre-osteoblast cells and exhibited antibacterial properties by suppressing bacterial colonization. Overall, the multifunctional PLA/TCP-Mg composite showed improved mechanobiological performance, making it a promising material for biodegradable orthopedic implants.

Human Body-Fluid-Assisted Fracture of Zinc Alloys as Biodegradable Temporary Implants: Challenges, Research Needs and Way Forward.

Alloys of magnesium, zinc or iron that do not contain toxic elements are attractive as construction material for biodegradable implants, i.e., the type of implants that harmlessly dissolve away within the human body after they have completed their intended task. The synergistic influence of mechanical stress and corrosive human body fluid can cause sudden and catastrophic fracture of bioimplants due to phenomena such as stress corrosion cracking (SCC) and corrosion fatigue (CF). To date, SCC and CF of implants based on Zn have scarcely been investigated. This article is an overview of the challenges, research needs and way forward in understanding human body-fluid-assisted fractures (i.e., SCC and CF) of Zn alloys in human body fluid.

New biodegradable Mg–Zn–Ca bulk metallic glass composite with large plasticity reinforced by SnZn alloy

Mg–Zn–Ca bulk metallic glass exhibits remarkable biocompatibility and biodegradability in human environments, making it a promising material for biodegradable implants. However, the material's brittleness at room temperature limits its applicability. To overcome this limitation, we introduced a non-toxic, highly plastic SnZn alloy as a second phase into Mg–Zn–Ca metallic glass. Our investigation focused on how varying SnZn alloy content affected the composites' microstructure and mechanical properties. The resulting composites exhibited a vein-like pattern, and the SnZn alloy contributed to their plasticity while Mg–Zn–Ca metallic glass provided strength. Our composite achieved a yield strength of 225 MPa with a 17% strain. Furthermore, when the SnZn alloy content exceeded 60%, the composites remained unbroken during compression testing. These results indicate that our Mg–Zn–Ca/SnZn bulk metallic glass composites exhibit excellent mechanical properties and hold promise as an implant material. This study provides a new direction for the development of biodegradable implant materials.

Influence of Polyols on the In Vitro Biodegradation and Bioactivity of 58S Bioactive Sol–Gel Coatings on AZ31B Magnesium Alloys

The mechanical qualities of AZ31B magnesium alloys make them a promising material for biodegradable metallic implants. However, rapid degradation limits the application of these alloys. In the present study, 58S bioactive glasses were synthesized using the sol-gel method and several polyols such as glycerol, ethylene glycol, and polyethylene glycol, were used to improve the sol stability and to control the degradation of AZ31B. The synthesized bioactive sols were dip-coated onto AZ31B substrates and then, characterized by various techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD) and electrochemical techniques (potentiodynamic and electrochemical impedance spectroscopy), among them. FTIR analysis confirmed the formation of a silica, calcium, and phosphate system and the XRD the amorphous nature of the 58S bioactive coatings obtained by sol-gel. The contact angle measurements confirmed that all the coatings were hydrophilic. The biodegradability response under physiological conditions (Hank's solution) was investigated for all the 58S bioactive glass coatings, observing a different behaviour depending on the polyols incorporated. Thus, for 58S PEG coating, an efficient control of the release of H2 gas was observed, and showing a pH control between 7.6 and 7.8 during all the tests. A marked apatite precipitation was also observed on the surface of the 58S PEG coating after the immersion test. Thus, the 58S PEG sol-gel coating is considered a promising alternative for biodegradable magnesium alloy-based medical implants.

Effect of Filler Types on Cellulose-Acetate-Based Composite Used as Coatings for Biodegradable Magnesium Implants for Trauma.

Magnesium alloys are considered one of the most promising materials for biodegradable trauma implants because they promote bone healing and exhibit adequate mechanical strength during their biodegradation in relation to the bone healing process. Surface modification of biodegradable magnesium alloys is an important research field that is analyzed in many publications as the biodegradation due to the corrosion process and the interface with human tissue is improved. The aim of the current preliminary study is to develop a polymeric-based composite coating on biodegradable magnesium alloys by the solvent evaporation method to reduce the biodegradation rate much more than in the case of simple polymeric coatings by involving some bioactive filler in the form of particles consisting of hydroxyapatite and magnesium. Various techniques such as SEM coupled with EDS, FTIR, and RAMAN spectroscopy, and contact angle were used for the structural and morphological characterization of the coatings. In addition, thermogravimetric analysis (TGA) was used to study the effect of filler particles on polymer thermostability. In vitro cytotoxicity assays were performed on MG-63 cells (human osteosarcomas). The experimental analysis highlights the positive effect of magnesium and hydroxyapatite particles as filler for cellulose acetate when they are used alone from biocompatibility and surface analysis points of view, and it is not recommended to use both types of particles (hydroxyapatite and magnesium) as hybrid filling. In future studies focused on implantation testing, we will use only CA-based composite coatings with one filler on magnesium alloys because these composite coatings have shown better results from the in vitro testing point of view for future potential orthopedic biodegradable implants for trauma.

Zinc Matrix Composites Reinforced with Partially Unzipped Carbon Nanotubes as Biodegradable Implant Materials

The activity of zinc is between that of magnesium and iron, and it has a suitable degradation rate and good biocompatibility. It has been regarded as a very promising biodegradable metal material for biomedicine. However, the insufficient mechanical properties of pure Zn limit its practical application in the field of orthopedic implants. In this paper, partially unzipped carbon nanotubes (PUCNTs) obtained by meridionally cutting multi-walled carbon nanotubes (MWCNTs) were used as reinforcements and combined with spark plasma sintering to prepare partially unzipped carbon nanotube reinforced Zn matrix composites. The effects of PUCNT addition on the microstructure and the mechanical properties of Zn matrix composites were investigated. The microstructure analysis showed the good interface bonding between PUCNTs and the Zn matrix. Additionally, the strength of PUCNTs/Zn composites showed a trend of increasing first and then decreasing with the PUCNT content increases. When the PUCNT content was 0.2 wt%, the tensile strength and yield strength of composites were about 78.4% and 64.4% higher than that of pure Zn, respectively, while maintaining a high elongation (62.6%).

Experimental investigations of electrical discharge micro-drilling for Mg-alloy and multi-response optimization using MOGA-ANN

Electric Discharge Drilling (EDD), a spark erosion drilling process, is designed to produce small to large size holes in high-strength and heat-resistant materials with the greatest precision. Magnesium (Mg) based alloy is potential material for biodegradable medical implants, and EDD can be employed to create perforated implants for tissue engineering. The present study was carried out to investigate the EDD process for Mg-alloy using a face-centered central composite design (FCCD) and the effect of input process variables such as discharge current (I p ), spark-on time (T on ), spark-off time (T off ) and work height (WH) have been evaluated on response characteristics; drilling rate (DR), tool wear ratio (TWR) and hole overcut (HO). Analysis of Variance (ANOVA) suggests that Ip, T on , T off and WH are the most significant factor affecting the response characteristics under 95% confidence level. Based on the response surface methodology (RSM), regression equations have been developed between the input process variables and response characteristics. Further, an artificial neural network (ANN) model is developed, and a multi-objective genetic algorithm (MOGA) was utilized to optimize the multi-response objectives. It has been found that the best combination of input parameters while using RSM is: Ip; 4 amp, T on ; 30 µs, T off ; 48 µs, WH: 10 mm, and the predicted values of DR, TWR and HO were Ip; 129.22 mm/min, TWR; 0.142 and HO; 87.26 µm respectively whereas in the Multi-objective Genetic algorithm artificial neural network (MOGA-ANN) hybrid technique, optimal balance results achieved are DR of 142.527 mm/min, with TWR and HO 0.168, 98.258 µm respectively at optimal input parameters. The optimal results obtained with MOGA-ANN are validated experimentally.

The Effect of Mn on the Mechanical Properties and In Vitro Behavior of Biodegradable Zn-2%Fe Alloy

The attractiveness of Zn-based alloys as structural materials for biodegradable implants mainly relates to their excellent biocompatibility, critical physiological roles in the human body and excellent antibacterial properties. Furthermore, in in vivo conditions, they do not tend to produce hydrogen gas (as occurs in the case of Mg-based alloys) or voluminous oxide (as occurs in Fe-based alloys). However, the main disadvantages of Zn-based alloys are their reduced mechanical properties and their tendency to provoke undesirable fibrous encapsulation due to their relatively high standard reduction potential. The issue of fibrous encapsulation was previously addressed by the authors via the development of the Zn-2%Fe alloy that was selected as the base alloy for this study. This development assumed that the addition of Fe to pure Zn can create a microgalvanic effect between the Delta phase (Zn11Fe) and the Zn-matrix that significantly increases the biodegradation rate of the alloy. The aim of the present study is to examine the effect of up to 0.8% Mn on the mechanical properties of biodegradable Zn-2%Fe alloy and to evaluate the corrosion behavior and cytotoxicity performance in in vitro conditions. The selection of Mn as an alloying element is related to its vital role in the synthesis of proteins and the activation of enzyme systems, as well as the fact that Mn is not considered to be a toxic element. Microstructure characterization was carried out by optical microscopy and scanning electron microscopy (SEM), while phase analysis was obtained by X-ray diffraction (XRD). Mechanical properties were examined in terms of hardness and tensile strength, while corrosion performance and electrochemical behavior were assessed by immersion tests, open circuit potential examination, potentiodynamic polarization analysis and impedance spectroscopy. All the in vitro corrosion testing was performed in a simulated physiological environment in the form of a phosphate-buffered saline (PBS) solution. The cytotoxicity performance was evaluated by indirect cell viability analysis, carried out according to the ISO 10993-5/12 standard using Mus musculus 4T1 cells. The obtained results clearly demonstrate the strengthening effect of the biodegradable Zn-2%Fe alloy due to Mn addition. The effect of Mn on in vitro corrosion degradation was insignificant, while in parallel Mn had a favorable effect on indirect cell viability.

Osteogenic and angiogenic bioactive collagen entrapped calcium/zinc phosphates coating on biodegradable Zn for orthopedic implant applications.

Zinc is becoming one of the leading candidate materials for biodegradable orthopedic implants owing to its attractive properties in terms of degradation behavior and mechanical properties. However, the insufficient surface bio-activities postpone its clinical application. In this study, an organic-inorganic collagen entrapped calcium/zinc phosphates coating was constructed on Zn surface to lessen Zn2+ releasing rate and to leverage the surface osteogenic and angiogenic properties. Collagen molecules were immobilized onto Zn substrate and subsequently coordinated with calcium and zinc ions to promote the CaZnP inorganic phase growth, ensuing an intertwined collagen-CaZnP hybrid system. Consequently, the hybrid coating was highly coalesced and compact. Such high quality warranted the contained Zn2+ releasing in a tolerable rate favorable for cells viability. The collagen-CaZnP coated Zn showed remarkedly stronger osteogenicity as compared to the untreated Zn, ascertained by the MC3T3-E1 osteoblast cell proliferation and differentiation assays, such as alkaline phosphatase expression and calcium nodule formation results. In addition, this hybrid coating supported human umbilical vein endothelial cells (HUVECs) migration and tube formation. The enhanced osteogenic and angiogenic properties could be ascribed to the nature of collagen and calcium/zinc phosphate components, the hybrid micro/nano-structure as well as the ability of controlling the Zn2+ release of Zn substrate into a suitable concentration range. Our strategy provides a new avenue to surface modification of biodegradable metals for bone regenerative perspective.

Microstructure evolution, mechanical properties and corrosion behavior of biodegradable Zn-2Cu-0.8Li alloy during room temperature drawing

Biodegradable Zn-based alloys exhibit promising application prospects due to their suitable degradation rates and acceptable biocompatibility. However, unstable mechanical properties during room-temperature storage limit their application potential. In this study, Zn-2Cu-0.8Li (wt%) alloy wires with excellent and stable mechanical properties were prepared by hot extrusion followed by multi-pass cold drawing. For the as-extruded Zn-2Cu-0.8Li alloy of a [1¯21¯0]//ED texture, (Li, Cu)Zn4 phase (volume fraction: 84.4 ± 2.4%) is found to be the matrix, and the remaining phase is Zn-based solid solution (η-Zn phase). During cold drawing, the (Li, Cu)Zn4 phase was continuously elongated, and its original texture gradually evolved into intensive [011¯0]//DD fiber texture. In contrast, the η-Zn phase exhibits an evidently refined grain structure and weakened texture due to dynamic recrystallization (DRX). Accordingly, the ultimate tensile strength was significantly improved from348.1 ± 3.1 MPa (as-extruded rod: Ø 6 mm) to 450.3 ± 8.7 MPa (as-drawn wire: Ø 3 mm), with the elongation decreasing from 37.1 ± 2.1% to 29.5 ± 1.3%. After 6-month natural aging, the as-drawn wire showed desirable mechanical stability, with basically unchanged mechanical properties. The corrosion rate of as-drawn wire with a diameter of 3 mm in c-SBF solution exhibits a 46% increase (from 212.07 ± 10.73 μm/year to 309.81 ± 16.53 μm/year) after cold drawing. Given the excellent mechanical properties and suitable corrosion rate, the Zn-2Cu-0.8Li wires are proposed as a promising material for biodegradable implants.

Fabrication and Properties of Zn-3Mg-1Ti Alloy as a Potential Biodegradable Implant Material.

A Zn-3Mg-1Ti alloy was fabricated by ultrasonic treatment of Zn-Mg alloy melt using a Ti ultrasonic radiation rod. The microstructure, phase structure, mechanical properties, degradation property, and in vitro cytotoxicity were investigated systematically. The obtained Zn-3Mg-1Ti alloy is composed of the Zn, Mg2Zn11, and TiZn16. Owing to the grain refinement and second phase reinforcement, the mechanical properties of Zn-3Mg-1Ti alloy is improved. In addition, the Zn-3Mg-1Ti alloy exhibits minimal cytotoxicity compared to pure Zn and Zn-1Ti alloy. Electrochemical tests show that the Zn-3Mg-1Ti alloy has an appropriate degradation rate in Hank’s solution.

Improving mechanical properties of lean Mg–Zn–Ca alloy for absorbable implants via Double Equal Channel Angular Pressing (D-ECAP)

Mg alloys are suitable materials for biodegradable osteosynthesis implants which stabilize bone fractures as long as the fracture is healing but are absorbed by the human body after they have fulfilled this purpose. However, high degradation rates and/or low strength values can be seen as drawbacks of such alloys. The present study deals with a lean Mg–Zn–Ca alloy which exhibits a desired, low degradation rate and explores the possibilities to improve its mechanical properties by Severe Plastic Deformation (SPD) via Double Equal Channel Angular Pressing (D-ECAP). The effects of different D-ECAP process parameters on the microstructure, mechanical properties and degradation behavior are investigated in detail. The results show that grain refinement during D-ECAP occurs via dynamic recrystallization. Lowering the processing temperature leads to a reduction of the size of the smaller grains of the initial bimodal grain size distribution while a higher degree of deformation (higher number of D-ECAP passes) reduces almost only the area fraction of the larger grains. While the increase in hardness is mainly due to the small size of the recrystallized grains, the tensile strength is additionally determined by the remaining larger grains. Thus, the mechanical properties of the lean Mg–Zn–Ca alloy can be tailored by D-ECAP according to the requirements of the final application. For example, the tensile strength can be increased to more than 370 MPa while maintaining the elongation at fracture at 7%. The degradation rate is not affected by D-ECAP as the process does not change the number or size of intermetallic particles. The optimized mechanical properties, in combination with the low degradation rate, make the D-ECAP-processed alloy very suitable for biomedical applications as absorbable material for osteosynthesis implants.