Stress Corrosion Analysis and Direct Cell Viability of Biodegradable Zn-Fe-Ca Alloy in In-Vitro Conditions

Due to the excellent biocompatibility of Zn and Zn-based alloys, researchers have shown great interest in developing biodegradable implants based on zinc. Furthermore, zinc is an essential component of many enzymes and proteins. The human body requires ~15 mg of Zn per day, and there is minimal concern for systemic toxicity from a small zinc-based cardiovascular implant, such as an arterial stent. However, biodegradable Zn-based implants have been shown to provoke local fibrous encapsulation reactions that may isolate the implant from its surrounding environment and interfere with implant function. The development of biodegradable implants made from Zn-Fe-Ca alloy was designed to overcome the problem of fibrous encapsulation. In a previous study made by the authors, the Zn-Fe-Ca system demonstrated a suitable corrosion rate that was higher than that of pure Zn and Zn-Fe alloy. The Zn-Fe-Ca system also showed adequate mechanical properties and a unique microstructure that contained a secondary Ca-reach phase. This has raised the promise that the tested alloy could serve as a biodegradable implant metal. The present study was conducted to further evaluate this promising Zn alloy. Here, we assessed the material’s corrosion performance in terms of cyclic potentiodynamic polarization analysis and stress corrosion behavior in terms of slow strain rate testing (SSRT). We also assessed the ability of cells to survive on the alloy surface by direct cell culture test. The results indicate that the alloy develops pitting corrosion, but not stress corrosion under phosphate-buffered saline (PBS) and air environment. The direct cell viability test demonstrates the successful adherence and growth of cells on the alloy surface.

Effectiveness of laddered embossed structure in a locking compression plate for biodegradable orthopaedic implants

Locking compression plate (LCP) has conventionally been the most extensively employed plate in internal fixation bone implants used in orthopaedic applications. LCP is usually made up of non-biodegradable materials that have a higher mechanical capability. Biodegradable materials, by and large, have less mechanical strength at the point of implantation and lose strength even more after a few months of continuous degradation in the physiological environment. To attain the adequate mechanical capability of a biodegradable bone implant plate, LCP has been modified by adding laddered – type semicircular filleted embossed structure. This improved design may be named as laddered embossed locking compression plate (LELCP). It is likely to provide additional mechanical strength with the most eligible biodegradable material, namely, Mg-alloy, even after continuous degradation that results in diminished thickness. For mechanical validation and comparison of LELCP made up of Mg-alloy, four-point bending test (4PBT) and axial compressive test (ACT) have been performed on LELCP, LCP and continuously degraded LELCP (CD-LELCP) with the aid of finite element method (FEM) for the assembly of bone segments, plate and screw segments. LELCP, when subjected to the above mentioned two tests, has been observed to provide 26% and 10.4% lower equivalent stress, respectively, than LCP without degradation. It is also observed mechanically safe and capable of up to 2 and 6 months of continuous degradation (uniform reduction in thickness) for 4PBT and ACT, respectively. These results have also been found reasonably accurate through real-time surgical simulations by approaching the most optimal mesh. According to these improved mechanical performance parameters, LELCP may be used or considered as a viable biodegradable implant plate option in the future after real life or in vivo validation.

Investigation on tribological behaviors of biodegradable pure Zn and Zn-X (Li, Cu, Ge) binary alloys

As a potential biodegradable implant material, zinc (Zn) alloys have attracted increasing attention due to their good biocompatibility and moderate degradation rate. Zn and its alloys are expected to become candidate materials for medical devices. The metals implanted in the human body will inevitably undergo friction in the human body before it is completely degraded. Friction and wear are essential factors which may cause medical devices’ service failure. However, there are still few studies on the friction and wear properties of biodegradable Zn-based alloys in the human body, and most studies just focus on the mechanical properties, degradation properties and biocompatibility of the alloys. Thus, it is crucial to study the friction and wear properties of Zn and its alloys. In the present work, we investigated the tribological properties of biodegradable pure Zn and Zn-X (Li, Cu, Ge) alloys. Our study found that under simulated body fluid and dry friction conditions, the addition of alloying elements Li and Cu can improve the friction properties of Zn. Among the four metals, Zn-0.5Li alloy has the lowest friction coefficient and the best wear resistance. Hank’s solution has lubricating and corrosive effects. That is to say, when the alloy is rubbed in Hank’s solution, it can not only be protected by the lubrication of the solution, but also tribocorrosion will occur as well.

Enhancing the Mechanical Properties of Biodegradable Mg Alloys Processed by Warm HPT and Thermal Treatments

In this study, several biodegradable Mg alloys (Mg5Zn, Mg5Zn0.3Ca, Mg5Zn0.15Ca, and Mg5Zn0.15Ca0.15Zr, numbers in wt%) were investigated after thermomechanical processing via high-pressure torsion (HPT) at elevated temperature as well as after additional heat treatments. Indirect and direct analyses of microstructure revealed that the significant strength increases arise not only from dislocations and precipitates but also from vacancy agglomerates. By contrast with former low-temperature processing routes applied by the authors, a significant ductility was obtained because of temperature-induced dynamic recovery. The low initial values of Young’s modulus were not significantly affected by warm HPT-processing. nor by heat treatments afterwards. Also, corrosion resistance did not change or even increase during those treatments. Altogether, the study reveals a viable processing route for the optimization of Mg alloys to provide enhanced mechanical properties while leaving the corrosion properties unaffected, suggesting it for the use as biodegradable implant material.

Recent Advances on Development of Hydroxyapatite Coating on Biodegradable Magnesium Alloys: A Review

The wide application of magnesium alloys as biodegradable implant materials is limited because of their fast degradation rate. Hydroxyapatite (HA) coating can reduce the degradation rate of Mg alloys and improve the biological activity of Mg alloys, and has the ability of bone induction and bone conduction. The preparation of HA coating on the surface of degradable Mg alloys can improve the existing problems, to a certain extent. This paper reviewed different preparation methods of HA coatings on biodegradable Mg alloys, and their effects on magnesium alloys’ degradation, biocompatibility, and osteogenic properties. However, no coating prepared can meet the above requirements. There was a lack of systematic research on the degradation of coating samples in vivo, and the osteogenic performance. Therefore, future research can focus on combining existing coating preparation technology and complementary advantages to develop new coating preparation techniques, to obtain more balanced coatings. Second, further study on the metabolic mechanism of HA-coated Mg alloys in vivo can help to predict its degradation behavior, and finally achieve controllable degradation, and further promote the study of the osteogenic effect of HA-coated Mg alloys in vivo.

In Vivo Imaging of Biodegradable Implants and Related Tissue Biomarkers

Non-invasive longitudinal imaging of osseointegration of bone implants is essential to ensure a comprehensive, physical and biochemical understanding of the processes related to a successful implant integration and its long-term clinical outcome. This study critically reviews the present imaging techniques that may play a role to assess the initial stability, bone quality and quantity, associated tissue remodelling dependent on implanted material, implantation site (surrounding tissues and placement depth), and biomarkers that may be targeted. An updated list of biodegradable implant materials that have been reported in the literature, from metal, polymer and ceramic categories, is provided with reference to the use of specific imaging modalities (computed tomography, positron emission tomography, ultrasound, photoacoustic and magnetic resonance imaging) suitable for longitudinal and non-invasive imaging in humans. The advantages and disadvantages of the single imaging modality are discussed with a special focus on preclinical imaging for biodegradable implant research. Indeed, the investigation of a new implant commonly requires histological examination, which is invasive and does not allow longitudinal studies, thus requiring a large number of animals for preclinical testing. For this reason, an update of the multimodal and multi-parametric imaging capabilities will be here presented with a specific focus on modern biomaterial research.

Experimental Investigation Into the Fabrication of Porous Biodegradable Fe Scaffold by Microwave Sintering of 3D Printed Green Body

Iron has appealing biodegradable properties that makes compatible for biodegradable implant tools applications. Although, the slow corrosion rate of Fe made obsolete for biomedical applications. The incorporation of the porous structure may result in an enhanced degradation rate. The main advantage offer by the porous structure is to allow to flow the body transportation fluid through it and ease to proliferate the new tissue. Therefore, the current work focused on the development of a porous Fe structures using micro-extrusion based three-dimensional printing (ME3DP) and pressure less microwave sintering. The metallic-based polymeric ink used to fabricate the intent design structure. Subsequently, samples were heated in the microwave sintering furnace. The experimentations were done to evaluate the outcomes of different Fe concentrations (91–95 wt.%) on density and compressive yield strength of developed porous parts. Experimental observation deduced that fabricated part ≥ 94.wt.% of Fe concentration has strong bonding strength between the printed layers. Moreover, the mechanical property of 94 wt.% has found greater than 95 wt.% of Fe concentration. The scanning electron microscopic (SEM) image illustrated the presence of porous morphology into the fabricated body. Additionally, XRD (X-ray diffraction) plots exhibited the purity of sample without any contamination residue.