Electrochemical Analysis and In Vitro Assay of Mg-0.5Ca-xY Biodegradable Alloys

Long-Term Examination of Degradation and In Vivo Biocompatibility of Some Mg-0.5Ca-xY Alloys in Sprague Dawley Rats

The medical field has undergone constant development in recent years, and a segment of this development is occupied by biodegradable alloys. The most common alloys in this field are those based on Mg, their main advantage being the ability to degrade gradually, without affecting the patient, and also their ability to be fully absorbed by the human body. One of their most important conditions is the regeneration and replacement of human tissue. Tissue can be engineered in different ways, one being tissue regeneration in vivo, which can serve as a template. In vivo remodeling aims to restore tissue or organs. The key processes of tissue formation and maturation are: proliferation (sorting and differentiation of cells), proliferation and organization of the extracellular matrix, biodegradation of the scaffold-remodeling, and potential tissue growth. In the present paper, the design of the alloys in the Mg-Ca-Y system is formed from the beginning using high-purity components, Mg-98.5%, master-alloys: Mg-Y (70 wt.%-30 wt.%) and Mg-Ca (85 wt.%-15 wt.%). After 8 weeks of implantation, the degradation of the implanted material is observed, and only small remaining fragments are found. At the site of implantation, no inflammatory reaction is observed, but it is observed that the process of integration and reabsorption, over time, accentuates the prosaic surface of the material. The aim of the work is to test the biocompatibility of magnesium-based alloys on laboratory rats in order to use these alloys in medical applications. The innovative parts of these analyses are the chemical composition of the alloys used and the tests performed on laboratory animals.

Influence of Surface Roughness on Biodegradability and Cytocompatibility of High-Purity Magnesium

High-purity magnesium (Mg) is a promising biodegradable metal for oral and maxillofacial implants. Appropriate surface roughness plays a critical role in the degradation behavior and the related cellular processes of biodegradable Mg-based metals. Nevertheless, the most optimized surface roughness has been questionable, especially for Mg-based oral and maxillofacial implants. Three representative scales of surface roughness were investigated in this study, including smooth (Sa < 0.5 µm), moderately rough (Sa between 1.0−2.0 µm), and rough (Sa > 2.0 µm). The results indicated that the degradation rate of the Mg specimen in the cell culture medium was significantly accelerated with increased surface roughness. Furthermore, an extract test revealed that Mg with different roughness did not induce an evident cytotoxic effect. Nonetheless, the smooth Mg surface had an adversely affected cell attachment. Therefore, the high-purity Mg with a moderately rough surface exhibited the most optimized balance between biodegradability and overall cytocompatibility.

The Formation of 14H-LPSO in Mg-9Gd-2Y-2Zn-0.5Zr Alloy during Heat Treatment

There is a new long-period stacking ordered structure in Mg-RE-Zn magnesium alloys, namely the LPSO phase, which can effectively improve the yield strength, elongation, and corrosion resistance of Mg alloys. According to different types of Mg-RE-Zn alloy systems, two transformation modes are involved in the heat treatment transformation process. The first is the alloy without LPSO phase in the as-cast alloy, and the Mg_xRE phase changes to 14H-LPSO phase. The second is the alloy containing LPSO phase in the as-cast state, and the 14H-LPSO phase is obtained by the transformations of 6H, 18R, and 24R. The effects of different solution parameters on the second phase of Mg-9Gd-2Y-2Zn-0.5Zr alloy were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The precipitation mechanism of 14H-LPSO phase during solution treatment was further clarified. At a solution time of 13 h, the grain size increased rapidly initially and then decreased slightly with increasing solution temperature. The analysis of the volume fraction of the second phase and lattice constant showed that Gd and Y elements in the alloy precipitated from the matrix and formed 14H-LPSO phase after solution treatment at 490 °C for 13 h. At this time, the hardness of the alloy reached the maximum of 74.6 HV. After solution treatment at 500 °C for 13 h, the solid solution degree of the alloy increases, and the grain size and hardness of the alloy remain basically unchanged.

Corrosion-Resistance Analysis of HA Layer Deposited through Electrophoresis on Ti4Al4Zr Metallic Substrate

An alloy surface with possible applications in the medical field, Ti4A14Zr, was improved through the deposition of a thin hydroxyapatite (HA) layer. In this paper, we analyzed the growth of a HA layer through electrophoresis and the corrosion resistance of the metallic sample covered with the ceramic layer. The substrate surface was processed via chemical procedures before the HA deposition. The state of the metallic surface and that of the layer of HA were investigated using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analysis of the chemical composition. The results indicate a high increase in the corrosion resistance associated with the ceramic layer compared to the metallic basic layer. Moreover, the analysis revealed the formation of a homogeneous TiO2 layer on the surface of the metallic substrate. The titanium oxide layer identified by SEM–EDS and confirmed by EIS was very homogeneous and resistant, with a compact microstructural appearance and submicron dimension. The layer composed of TiO2 and HA provided good corrosion protection.

Microstructural, Electrochemical and In Vitro Analysis of Mg-0.5Ca-xGd Biodegradable Alloys

The subject of Mg-based biodegradable materials, used for medical applications, has been extensively studied throughout the years. It is a known fact that alloying Mg with biocompatible and non-toxic elements improves the biodegradability of the alloys that are being used in the field of surgical applications. The aim of this research is to investigate the aspects concerning the microstructure, electrochemical response (corrosion resistance) and in vitro cytocompatibility of a new experimental Mg-based biodegradable alloy—Mg–0.5%Ca with controlled addition of Gd as follows: 0.5, 1.0, 1.5, 2.0 and 3.0 wt.%—in order to establish improved biocompatibility with the human hard and soft tissues at a stable biodegradable rate. For this purpose, scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), light microscopy (LM) and X-ray diffraction (XRD) were used for determining the microstructure and chemical composition of the studied alloy and the linear polarization resistance (LPR) method was used to calculate the corrosion rate for the biodegradability rate assessment. The cellular response was evaluated using the 3-(4,5-dimethyltiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) test followed by fluorescence microscopy observation. The research led to the discovery of a dendritic α-Mg solid solution, as well as a lamellar Mg2Ca and a Mg5Gd intermetallic compound. The in vivo tests revealed 73–80% viability of the cells registered at 3 days and between 77 and 100% for 5 days, a fact that leads us to believe that the experimental studied alloys do not have a cytotoxic character and are suitable for medical applications.

Long Term Evaluation of Biodegradation and Biocompatibility In-Vivo the Mg-0.5Ca-xZr Alloys in Rats

Biodegradable alloys in Mg have the advantages of traditional metallic materials and those of biodegradable polymers with superior strength, lower density and ideal rigidity for fixing bone fractures. The biocompatibility and biodegradability of the five concentrations of Mg-0.5Ca-xZr alloys used were assessed using clinical and laboratory examinations that followed over time: tissue reaction, histological and imaging (RX, CT and SEM) evolution at 1, 2, 4 and 8 weeks after implant. The main purpose of this study was to investigate in vivo the long-term effect of Mg-0.5Ca-xZr alloys in rats. The results confirmed that Mg-0.5Ca-xZr alloys are biocompatible and biodegradable and are recommended to be used as possible materials for new orthopedics devices.