Maria Lorenza Escudero

Magnesium-based alloys are considered to be promising materials for the fabrication of temporary bone repair medical implants. The AZ31 magnesium-based (AZ31-Mg) alloy contains 3% aluminum and 1% zinc in its microstructure, which gives it mechanical strength and corrosion resistance. Nonetheless, the corrosion rate is high, which can lead to implant failure due to rapid degradation, which triggers the release of harmful metal ions. In the present work, a passive layer was obtained on the AZ31-Mg alloy, and subsequently, a cerium oxide (CeO₂) coating was deposited through a chemical conversion treatment using 0.01 M CeO₂ as a precursor. Based on X-ray photoelectron spectroscopy, the calculated amount of Ce(IV) and Ce(III) present in AZ31-Mg(OH)₂/CeO₂ was 93.6% and 6.4%, respectively. AZ31-Mg(OH)₂/CeO₂ showed improved corrosion resistance compared with the bare sample. The in vitro assessment of MC3T3-E1 pre-osteoblast cell viability showed that AZ31-Mg(OH)₂/CeO₂ was biocompatible after incubation for 24 and 72 h. The results revealed that the CeO₂ coating confers greater electrochemical stability and biocompatibility properties, mostly due to the presence of Ce⁴⁺ ions.

Various surface modifications to increase the lifespan of cobalt–chromium (CoCr) joint prostheses are being studied to reduce the wear rate in bone joint applications. One recently proposed modification involves depositing graphene oxide functionalized with hyaluronic acid (a compound present in joints) on CoCr surfaces, which can act as a solid lubricant. This paper analyzes the biological alterations caused by wear–corrosion phenomena that occur in joints, both from the perspective of the worn surface (in vitro model) and the particles generated during the wear processes (in vivo model). The analysis of the inflammatory response of macrophage was performed on CoCr surfaces modified with graphene oxide and functionalized with hyaluronic acid (CoCr-GO-HA), before and after wear–corrosion processes. The wear particles released during the wear–corrosion tests of the CoCr-GO-HA/CoCr ball pair immersed in 3 g/L hyaluronic acid were intra-articularly injected into the experimental animals. The hematological analysis in vivo was made considering a murine model of intra-articular injection into the left knee in male adult Wistar rats, at increasing concentrations of the collected wear particles dispersed in 0.9% NaCl. Non-significant differences in the inflammatory response to unworn CoCr-GO-HA surfaces and control (polystyrene) were obtained. The wear–corrosion of the CoCr-GO-HA disk increased the inflammatory response at both 72 and 96 h of material exposure compared to the unworn CoCr-GO-HA surfaces, although the differences were not statistically significant. The pro-inflammatory response of the macrophages was reduced on the worn surfaces of the CoCr modified and functionalized with graphene oxide (GO) and hyaluronic acid (HA), compared to the worn surfaces of the unmodified CoCr. The hematological analysis and tissue reactions after intra-articular injection did not reveal pathological damage, with average hematological values recorded, although slight reductions in creatinine and protein within non-pathological ranges were found. Some traces of biomaterial particles in the knee at the highest concentration of injected particles were only found but without inflammatory signs. The results show the potential benefits of using graphene in intra-articular prostheses, which could improve the quality of life for numerous patients.

In this work, impermeable and ultrathin surface nanomodifications for joint applications based on graphene oxide (GO) are assembled on CoCr surfaces via covalent immobilization between GO nanosheets and silane monolayers. Two silane curing temperatures, 45 °C for 24 h and 75 °C for 30 min, on CoCr surfaces and two incubation times for GO suspension, 12 h and 24 h, on silanized CoCr surfaces are prepared. Electrochemical characterization is performed using electrochemical impedance spectroscopy (EIS) in a 3 g/L hyaluronic acid solution. Results show that GO nanosheets immobilized with silane covalent bonding confer impermeability of sp2 networks on GO and strong interfacial adhesion of GO sheets anchored to silanized CoCr via organosilane chemistry, which prevents the permeation of oxidant species at the metal interface. At short GO incubation times (12 h), the Rs values decrease with the immersion time, indicating that small species, such as metal ions, are able to diffuse through the interlayer gaps of nanolayers. Longer GO incubation times (24 h) favor the formation of bonds between the GO and the silane, thus slowing downdiffusion and metal ion release into the medium. EIS data confirm the impermeability of GO nanocoatings with lengthening GO incubation time for medical application of metallic implants.

The presence of a worn surface in the implanted material, as in the case of a replacement of a damaged osteoarticular joint, is the normal condition after implantation. This manuscript focuses precisely on the comparative study of the cellular behavior on worn CoCr surfaces, analyzing the effect of different surface modifications on macrophages’ responses. CoCr surfaces were modified by the deposition of electrochemically reduced graphene oxide (CoCrErGO), followed by additional surface functionalization with hyaluronic acid (CoCrErGOHA). After the wear corrosion processes, the macrophage response was studied. In addition, macrophage supernatants exposed to the surfaces, before and after wear, were also evaluated for osteoblast response through the analysis of the metabolic activity, plasma membrane damage, and phosphatase alkaline activity (ALP). The proteomic analysis and the quantitative TNF-α/IL-10 ratios of the J774A.1 macrophages exposed to the surfaces under study showed a polarization shift from M0 (basal state) to M1, associated with the pro-inflammatory response of all surfaces. A lower M1 polarization was observed upon exposure to the surface modification with ErGO, whereas posterior HA functionalization attenuated, even more, the M1 polarization. The wear corrosion process contributed to inflammation and exacerbated the M1 polarization response on macrophages to CoCr, which was diminished for the ErGO and attenuated the most for the ErGOHA surfaces. Comparative proteomics showed that the pathways related to M1 polarization were downregulated on the surfaces of CoCrErGOHA, which suggests mechanisms for the observed attenuation of M1 polarization. The suitable immuno-modulatory potential induced by the ErGOHA surface, with and without wear, together with the stimulation of ALP activity in osteoblasts induced by macrophage supernatants, promotes the mineralization processes necessary for bone repair. This makes it feasible to consider the adsorption of ErGOHA on CoCr as a recommended surface treatment for the use of biomaterials in osseous joint applications.

Background: The discrepancy among the in vivo results found in the literature regarding graphene’s side effects led us to conduct an in vivo study with graphene. Methods: In vivo tests involving intraperitoneal inoculation of graphene and graphene oxide nanosheets in rats were carried out to assess potential changes in the blood and organs after 15 and 30 days. Graphene and graphene oxide nanosheets at a concentration of 4 mg per kilogram were suspended in an aqueous solution of 0.9% NaCl at a 1:1 proportion (graphene or graphene oxide), i.e., 1 mg/mL. Results: Optical microscopy of liver, kidney, spleen, and lung tissues revealed no visible histological changes. However, particle traces were found in the peritoneal cavity. Thirty days after inoculation, blood samples were collected for hematological analysis. The blood analysis showed changes indicating a hepatic inflammatory process. Hematological changes after 30 days consisted of alterations to the red series, including microcytosis or higher mean hemoglobin concentrations. In addition, changes in prothrombin and thromboplastin caused longer coagulation times. Conclusion: This study contributes to further clarifying the possible toxicity of graphene and its potential biomedical applications.

The durability of metal–metal prostheses depends on achieving a higher degree of lubrication. The beneficial effect of hyaluronic acid (HA) on the friction and wear of both natural and artificial joints has been reported. For this purpose, graphene oxide layers have been electrochemically reduced on CoCr surfaces (CoCrErGO) and subsequently functionalized with HA (CoCrErGOHA). These layers have been evaluated from the point of view of wettability and corrosion resistance in a physiological medium containing HA. The wettability was analyzed by contact angle measurements in phosphate buffer saline-hyaluronic acid (PBS-HA) solution. The corrosion behavior of functionalized CoCr surfaces was studied with electrochemical measurements. Biocompatibility, cytotoxicity, and expression of proteins related to wound healing and repair were studied in osteoblast-like MC3T3-E1 cell cultures. All of the reported results suggest that HA-functionalized CoCr surfaces, through ErGO layers in HA-containing media, exhibit higher hydrophilicity and better corrosion resistance. Related to this increase in wettability was the increase in the expressions of vimentin and ICAM-1, which favored the growth and adhesion of osteoblasts. Therefore, it is a promising material for consideration in trauma applications, with improved properties in terms of wettability for promoting the adhesion and growth of osteoblasts, which is desirable in implanted materials used for bone repair.

In this research work, the corrosion resistance of plate steel used in the construction of cylindrical container tanks of seawater was evaluated. These container tanks are usually used for fighting fires on the coast of the Arequipa-Peru region, where the shortage of drinking water is significant. The study was based on immersion tests of 2 × 2 cm square test plates in 3.5 wt.% NaCl solution. Five paint systems were studied, varying only in the primers: P1-860 (inorganic zinc silicate); P1-ZC (epoxy-zinchromate); P1-850 (organic rich in zinc); P1-600 (reinforced inorganic zinc) and P1-SP1000 (high solids epoxy-amine). All systems consisted of a primer coat, an epoxy middle coat and a polyurethane topcoat. To characterize the behaviour of each system, the electrochemical impedance spectroscopy (EIS) was mostly used. In addition, the scanning Kelvin probe (SKP) and scanning electro­che­mical microscopy (SECM) were used as local techniques. The first three paint systems (P1-860, P1-ZC and P1-850) showed an invariable value of impedance modulus up to 3360 h of immersion in NaCl. The last two paint systems (P1-600 and P1-SP1000) showed a decrease in impedance modulus by more than one order of magnitude. This research provides a clear contribution of results obtained by global electrochemical techniques such as EIS, estab­lishing excellent tools for monitoring the performance of organic anticorrosive coatings.

El objetivo de este trabajo ha sido estudiar si los tratamientos térmicos y de conversión química mejoran la biocompatibilidad de la aleación TiAlV y reducen el crecimiento bacteriano. En primer lugar, se modificó la aleación de TiAlV mediante tratamiento térmico a 650 ºC durante 1 hour. Luego, se llevó a cabo la conversión química en una solución de CeCl3 para generar óxido de cerio. Las superficies modificadas se caracterizaron utilizando AFM y SEM-EDX. La adhesión de osteoblastos y la formación de biopelículas microbianas se midieron in vitro con la línea celular de osteoblastos MC3T3-E1 y Staphylococcus epidermidis ATCC 35983, respectivamente. La viabilidad bacteriana se cuantificó a través del contenido en trifosfato de adenosina (ATP) como medida de la actividad metabólica. La morfología y la proliferación en superficies modificadas se analizaron mediante SEM-EDX. Los resultados revelaron que el TiAlV tratado térmicamente mostró una mayor proliferación osteoblástica asociada con una mayor rugosidad y estructura cristalina del rutilo. Las superficies modificadas no causaron efecto bactericida, pero las superficies de TiAlV con ceria mostraron una disminución en la adhesión bacteriana, es decir, menos proliferación bacteriana y por tanto disminución en la colonización bacteriana.

Improvements in the lubrication of metal–metal joint prostheses are of great clinical interest in order to minimize the particles released during wear–corrosion processes. In this work, electrochemically reduced graphene oxide (ErGO) on CoCr was functionalized with hyaluronic acid (ErGOHA). Functionalization was carried out by soaking for 24 h in phosphate buffer saline (PBS) solution containing 3 g/L hyaluronic acid (HA). The corrosion performance of CoCrErGO and CoCrErGOHA surfaces was studied by electrochemical impedance spectroscopy (EIS) for 7 days in PBS. Biocompatibility and cytotoxicity were studied in mouse macrophages J774A.1 cell line by the measurement of mitochondrial activity (WST-1 assay) and plasma membrane damage (LDH assay). The inflammatory response was examined through TNF-α and IL-10 cytokines in macrophages culture supernatants, used as indicators of pro-inflammatory and anti-inflammatory responses, respectively. EIS diagrams of CoCrErGOHA revealed two time constants: the first one, attributed to the hydration and diffusion processes of the HA layer adsorbed on ErGO, and the second one, the corrosion resistance of ErGOHA/CoCr interface. Macrophage assays showed better behavior on CoCrErGOHA than CoCr and CoCrErGO surfaces based on their biocompatible, cytotoxic, and inflammatory responses. Comparative analysis of IL-10 showed that functionalization with HA induces higher values of anti-inflammatory cytokine, suggesting an improvement in inflammatory behavior.