Microstructural and Electrochemical Influence of Zn in MgCaZn Biodegradable Alloys

In Vitro and In Vivo Analysis of the Mg-Ca-Zn Biodegradable Alloys

The objective of this work was to analyze the in vitro and in vivo tests of a novel Mg-based biodegradable alloy-Mg-0.5%Ca-with various amounts of Zn (0.5, 1, 1.5, 2.0, and 3.0 wt.%). In terms of in vitro biocompatibility, MTT and Calcein-AM cell viability assays, performed on the MG-63 cell line through the extract method, revealed that all five alloy extracts are non-cytotoxic at an extraction ratio of 0.025 g alloy per mL of cell culture medium. In the in vivo histological analysis, Mg-0.5Ca-1.5Zn demonstrated exceptional potential for stimulating bone remodeling and showed excellent biocompatibility. It was observed that Mg-0.5Ca-0.5Zn, Mg-0.5Ca-1.5Zn, and Mg-0.5Ca-3Zn displayed good biocompatibility. Furthermore, the histological examination highlighted the differentiation of periosteal cells into chondrocytes and subsequent bone tissue replacement through endochondral ossification. This process highlighted the importance of the initial implant's integrity and the role of the periosteum. In summary, Mg-0.5Ca-1.5Zn stands out as a promising candidate for bone regeneration and osseointegration, supported by both in vitro and in vivo findings.

Structural and temporal dynamics analysis of zinc-based biomaterials: History, research hotspots and emerging trends

Objectives

To examine the 16-year developmental history, research hotspots, and emerging trends of zinc-based biodegradable metallic materials from the perspective of structural and temporal dynamics.

Methods

The literature on zinc-based biodegradable metallic materials in WoSCC was searched. Historical characteristics, the evolution of active topics and development trends in the field of zinc-based biodegradable metallic materials were analyzed using the bibliometric tools CiteSpace and HistCite.

Results

Over the past 16 years, the field of zinc-based biodegradable metal materials has remained in a hotspot stage, with extensive scientific collaboration. In addition, there are 45 subject categories and 51 keywords in different research periods, and 80 papers experience citation bursts. Keyword clustering anchored 3 emerging research subfields, namely, #1 plastic deformation #4 additive manufacturing #5 surface modification. The keyword alluvial map shows that the longest-lasting research concepts in the field are mechanical property, microstructure, corrosion behavior, etc., and emerging keywords are additive manufacturing, surface modification, dynamic recrystallization, etc. The most recent research on reference clustering has six subfields. Namely, #0 microstructure, #2 sem, #3 additive manufacturing, #4 laser powder bed fusion, #5 implant, and #7 Zn-1Mg.

Conclusion

The results of the bibliometric study provide the current status and trends of research on zinc-based biodegradable metallic materials, which can help researchers identify hot spots and explore new research directions in the field.

Investigations on the Degradation Behavior of Processed FeMnSi-xCu Shape Memory Alloys

A new functional Fe-30Mn-5Si-xCu (x = 1.5 and 2 wt%) biomaterial was obtained from the levitation induction melting process and evaluated as a biodegradable material. The degradation characteristics were assessed in vitro using immersion tests in simulated body fluid (SBF) at 37 ± 1 °C, evaluating mass loss, pH variation that occurred in the solution, open circuit potential (OCP), linear and cyclic potentiometry (LP and CP), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and nano-FTIR. To obtain plates as samples, the cast materials were thermo-mechanically processed by hot rolling. Dynamic mechanical analysis (DMA) was employed to evaluate the thermal properties of the smart material. Atomic force microscopy (AFM) was used to show the nanometric and microstructural changes during the hot rolling process and DMA solicitations. The type of corrosion identified was generalized corrosion, and over the first 3-5 days, an increase in mass was observed, caused by the compounds formed at the metal-solution interface. The formed compounds were identified mainly as oxides that passed into the immersion liquid. The degradation rate (DR) was obtained as a function of mass loss, sample surface area and immersion duration. The dynamic mechanical behavior and dimensions of the sample were evaluated after 14 days of immersion. The nanocompounds found on the surface after atmospheric corrosion and immersion in SBF were investigated with the Neaspec system using the nano-FTIR technique.

Biocompatibility and osteogenic potential of choline phosphate chitosan-coated biodegradable Zn1Mg

Zinc alloys have demonstrated considerable potentials as implant materials for biodegradable vascular and orthopedic applications. However, the high initial release of Zn2+ can trigger intense immune responses that impede tissue healing. To address this challenge and enhance the osteogenic capacity of zinc alloys, the surface of Zn1Mg was subjected to CO2 plasma modification (Zn1Mg-PP) followed by grafting with choline phosphate chitosan (Zn1Mg-PP-PCCs). This study aims to investigate the in vitro and in vivo biocompatibility of the surface-modified Zn1Mg. The effect of the surface modification on the inflammatory response and osteogenic repair process was investigated. Compared with unmodified Zn1Mg, the degradation rate of Zn1Mg-PP-PCCs was significantly decreased, avoiding the cytotoxicity triggered by the release of large amounts of Zn2+. Moreover, PCCs significantly enhanced the cell-material adhesion, promoted the proliferation of osteoblasts (MC3T3-E1) and upregulated the expression of key osteogenic factors in vitro. Notably, the in vivo experiments revealed that the surface modification of Zn1Mg suppressed inhibited the expression of inflammatory cytokines, promoting the secretion of anti-inflammatory factors, thereby reducing inflammation and promoting bone tissue repair. Furthermore, histological analysis of tissue sections exhibited strong integration between the material and the bone, along with well-defined new bone formation and reduced osteoclast aggregation on the surface. This was attributed to the improved immune microenvironment by PCCs, which promoted osteogenic differentiation of osteoblasts. These findings highlight that the preparation of PCCs coatings on zinc alloy surfaces effectively inhibited ion release and modulated the immune environment to promote bone tissue repair. STATEMENT OF SIGNIFICANCE: Surface modification of biodegradable Zn alloys facilitates the suppression of intense immune responses caused by excessive ion release concentrations from implants. We modified the surface of Zn1Mg with choline phosphate chitosan (PCCs) and investigated the effects of surface modification on the inflammatory response and osteogenic repair process. In vitro results showed that the PCCs coating effectively reduced the degradation rate of Zn1Mg to avoid cytotoxicity caused by high Zn2+ concentration, favoring the proliferation of osteoblasts. In addition, in vivo results indicated that Zn1Mg-PP-PCCs attenuated inflammation to promote bone repair by modulating the release of inflammation-related factors. The surface-modified Zn1Mg implants demonstrated strong osseointegration, indicating that the PCCs coating effectively modulated the immune microenvironment and promoted bone healing.

The Influence of Potassium Hexafluorophosphate on the Morphology and Anticorrosive Properties of Conversion Coatings Formed on the AM50 Magnesium Alloy by Plasma Electrolytic Oxidation

In this study, conversion coatings were produced on the AM50 magnesium alloy by a plasma electrolytic oxidation (PEO) process in alkaline-silicate electrolyte with the addition of potassium hexafluorophosphate, using a unipolar pulse power source. The coating microstructure and its composition were determined using scanning electron microscopy (SEM) and an X-ray photoelectron spectroscopy (XPS). The corrosion resistance of the conversion coatings was evaluated by means of potentiodynamic polarization tests (PDP) and electrochemical impedance spectroscopy (EIS) in a dilute Harrison solution (DHS). It has been found that the properties (microstructure, composition, and coating thickness) of the obtained layer and, therefore, their anticorrosive resistance strongly depend on the electrolyte composition. The best anticorrosive properties were observed in the layers obtained in the presence of 2.5 g/L KPF6. It was found that the conversion coating produced with the addition of hexafluorophosphate is characterized by a different morphology (sponge-like) and better anticorrosion properties, in comparison to the coating obtained with the addition of fluoride and orthophosphate salts commonly used in PEO synthesis. The sponge-like structure, which is similar to bone structure in combination with the presence of phosphates in the layer, can increase the biocompatibility and the possibility of self-healing of this coating. However, neither Mg(PF6)2, nor any other compounds containing PF6-, have been found in the layers produced.

Influence of Dynamic Strain Sweep on the Degradation Behavior of FeMnSi-Ag Shape Memory Alloys

Iron-based SMAs can be used in the medical field for both their shape memory effect (SME) and biodegradability after a specific period, solving complicated chirurgical problems that are partially now addressed with shape-memory polymers or biodegradable polymers. Iron-based materials with (28-32 wt %) Mn and (4-6 wt %) Si with the addition of 1 and 2 wt % Ag were obtained using levitation induction melting equipment. Addition of silver to the FeMnSi alloy was proposed in order to enhance its antiseptic property. Structural and chemical composition analyses of the newly obtained alloys were performed by X-ray diffraction (confirming the presence of ε phase), scanning electron microscopy (SEM) and energy-dispersive spectroscopy. The corrosion resistance was evaluated through immersion tests and electrolyte pH solution variation. Dynamic mechanical solicitations were performed with amplitude sweep performed on the FeMnSi-1Ag and FeMnSi-2Ag samples, including five deformation cycles at 40 °C, with a frequency of 1 Hz, 5 Hz and 20 Hz. These experiments were meant to simulate the usual behavior of some metallic implants subjected to repetitive mechanical loading. Atomic force microscopy was used to analyze the surface roughness before and after the dynamic mechanical analysis test followed by the characterization of the surface profile change by varying dynamic mechanical stress. Differential scanning calorimetry was performed in order to analyze the thermal behavior of the material in the range of -50-+200 °C. X-ray diffraction and Fourier transform infrared spectroscopy (FTIR) along with Neaspec nano-FTIR experiments were performed to identify and confirm the corrosion compounds (oxides, hydroxides or carbonates) formed on the surface.

Evaluation of Physiochemical and Biological Properties of Biofunctionalized Mg-Based Implants Obtained via Large-Scale PEO Process for Dentistry Applications

An increasing number of tooth replacement procedures ending with implant failure generates a great need for the delivery of novel biomedical solutions with appropriate mechanical characteristics that would mimic natural tissue and undergo biodegradation. This phenomenon constitutes a significant difficulty for scientists, since currently applied biomaterials dedicated for this purpose are based on stainless steel, Ti, and Ti and CoCr alloys. One of the most promising raw materials is magnesium, which has been proven to promote bone regeneration and accelerate the tissue healing process. Nevertheless, its high reactivity with body fluid components is associated with fast and difficult-to-control biocorrosion, which strongly limits the application of Mg implants as medical devices. The achievement of appropriate functionality, both physiochemical and biological, to enable the commercial use of Mg biomaterials is possible only after their superficial modification. Therefore, the obtainment of uniform, reproducible coatings increasing resistance to the aqueous environment of the human body combined with a nanostructured surface that enhances implant-cell behaviors is an extremely important issue. Herein, we present a successful strategy for the modification of Mg implants via the PEO process, resulting in the obtainment of biomaterials with lower corrosion rates and superior biological properties, such as the promotion of extracellular matrix formation and a positive impact on the proliferation of MG-63 cells. The implants were investigated regarding their chemical composition using the FT-IR and XRD methods, which revealed that MgO layer formation, as well as the incorporation of electrolyte components such as fluorine and silica, were responsible for the increased microhardness of the samples. An extensive study of the biomaterials' morphology confirmed that successful surface modification led to a microporous structure suitable for the attachment and proliferation of cells. The three-layer nature of the newly-formed coatings, typical for PEO modification, was confirmed via cross-section analysis. A biocorrosion and biodegradation study proved that applied modification increased their resistance to body fluids. The cell culture study performed herein confirmed that the correct adjustment of modification parameters results in a lack of cytotoxicity of the magnesium implants, cell proliferation enhancement, and improvement in extracellular matrix formation.