Comparison of Inflammatory Effects in THP-1 Monocytes and Macrophages after Exposure to Metal Ions

Cobalt and Chromium Ions Impair Macrophage Response to Staphylococcus aureus Infection

Cobalt-chromium-molybdenum (CoCrMo) alloys are routinely used in arthroplasty. CoCrMo wear particles and ions derived from arthroplasty implants lead to macrophage-driven adverse local tissue reactions, which have been linked to an increased risk of periprosthetic joint infection after revision arthroplasty. While metal-induced cytotoxicity is well characterized in human macrophages, direct effects on their functionality have remained elusive. Synchrotron radiation X-ray microtomography and X-ray fluorescence mapping indicated that peri-implant tissues harvested during aseptic revision of different arthroplasty implants are exposed to Co and Cr in situ. Confocal laser scanning microscopy revealed that macrophage influx is predominant in patient tissue. While in vitro exposure to Cr3+ had only minor effects on monocytes/macrophage phenotype, pathologic concentrations of Co2+ significantly impaired both, monocyte/macrophage phenotype and functionality. High concentrations of Co2+ led to a shift in macrophage subsets and loss of surface markers, including CD14 and CD16. Both Co2+ and Cr3+ impaired macrophage responses to Staphylococcus aureus infection, and particularly, Co2+-exposed macrophages showed decreased phagocytic activity. These findings demonstrate the immunosuppressive effects of locally elevated metal ions on the innate immune response and support further investigations, including studies exploring whether Co2+ and Cr3+ or CoCrMo alloys per se expose the patients to a higher risk of infections post-revision arthroplasty.

Plastic response of macrophages to metal ions and nanoparticles in time mimicking metal implant body environment

The paradigm of using metal biomaterials could be viewed from two sides - treatment of wide spectrum of degenerative diseases, and debris release from materials. After implant insertion, metal nanoparticles (NPs) and ions are released not only upon the first contact with cells/tissues, but in continual manner, which is immediately recognized by immune cells. In this work, the effects of metal nanoparticles (TiO2, Ni) and ions (Ni2+, Co2+, Cr3+, Mo6+) on primary human M0 macrophages from the blood samples of osteoarthritic patients undergoing total arthroplasty were studied in order to monitor immunomodulatory effects on the cells in a real-time format. The highest NiNPs concentration of 10 µg/ml had no effect on any of macrophage parameters, while the Ni2+ ions cytotoxicity limit for the cells is 0.5 mM. The cytotoxic effects of higher Ni2+ concentration revealed mitochondrial network fragmentation leading to mitochondrial dysfunction, accompanied by increased lysosomal activity and changes in pro-apoptotic markers. The suppression of M2 cell formation ability was connected to presence of Ni2+ ions (0.5 mM) and TiO2NPs (10 µg/ml). The immunomodulatory effect of Mo6+ ions, controversially, inhibit the formation of the cells with M1 phenotype and potentiate the thread-like shape M2s with increased chaotic cell movement. To summarize, metal toxicity depends on the debris form. Both, metal ions and nanoparticles affect macrophage size, morphological and functional parameters, but the effect of ions is more complex and likely more harmful, which has potential impact on healing and determines post-implantation reactions.

Survivability of Titanium Implant Materials: In Vitro Simulated Inflammatory and Infectious Environment

Titanium-based implants utilized in total joint arthroplasties could restore primary musculoskeletal function to patients suffering from osteoarthritis and other conditions. Implants are susceptible to failure stemming from aseptic loosening and infection at the joint site, eventually requiring revision surgery. We hypothesized that there might be a feedback loop by which metal degradation particles and ions released from the implant decrease cell viability and increase immune response, thereby creating biochemical conditions that increase the corrosion rate and release more metal ions. This study focused on the synergistic process through cell viability assays and electrochemical tests. From the results, inflammatory conditions from ion release resulting in cell death would further increase the corrosion rate at the metal implant site. The synergistic interaction in the implant surroundings in which infectious conditions produce Ti ions that contribute to more infection, creating a potential cycle of accelerating corrosion.

Corrosion Products from Metallic Implants Induce ROS and Cell Death in Human Motoneurons In Vitro

Due to advances in surgical procedures and the biocompatibility of materials used in total joint replacement, more and younger patients are undergoing these procedures. Although state-of-the-art joint replacements can last 20 years or longer, wear and corrosion is still a major risk for implant failure, and patients with these implants are exposed for longer to these corrosive products. It is therefore important to investigate the potential effects on the whole organism. Released nanoparticles and ions derived from commonly used metal implants consist, among others, of cobalt, nickel, and chromium. The effect of these metallic products in the process of osteolysis and aseptic implant loosening has already been studied; however, the systemic effect on other cell types, including neurons, remains elusive. To this end, we used human iPSC-derived motoneurons to investigate the effects of metal ions on human neurons. We treated human motoneurons with ion concentrations regularly found in patients, stained them with MitoSOX and propidium iodide, and analyzed them with fluorescence-assisted cell sorting (FACS). We found that upon treatment human motoneurons suffered from the formation of ROS and subsequently died. These effects were most prominent in motoneurons treated with 500 μM of cobalt or nickel, in which we observed significant cell death, whereas chromium showed fewer ROS and no apparent impairment of motoneurons. Our results show that the wear and corrosive products of metal implants at concentrations readily available in peri-implant tissues induced ROS and subsequently cell death in an iPSC-derived motoneuron cell model. We therefore conclude that monitoring of neuronal impairment is important in patients undergoing total joint replacement.

Does Green Exfoliation of Graphene Produce More Biocompatible Structures?

Graphene has been studied thoroughly for its use in biomedical applications over the last decades. A crucial factor for a material to be used in such applications is its biocompatibility. Various factors affect the biocompatibility and toxicity of graphene structures, including lateral size, number of layers, surface functionalization, and way of production. In this work, we tested that the green production of few-layer bio-graphene (bG) enhances its biocompatibility compared to chemical-graphene (cG). When tested against three different cell lines in terms of MTT assays, both materials proved to be well-tolerated at a wide range of doses. However, high doses of cG induce long-term toxicity and have a tendency for apoptosis. Neither bG nor cG induced ROS generation or cell cycle modifications. Finally, both materials affect the expression of inflammatory proteins such as Nrf2, NF-kB and HO-1 but further research is required for a safe result. In conclusion, although there is little to choose between bG and cG, bG's sustainable way of production makes it a much more attractive and promising candidate for biomedical applications.

Experimental Investigation of Material Transfer on Bearings for Total Hip Arthroplasty—A Retrieval Study on Ceramic and Metallic Femoral Heads

Metallic deposition is a commonly observed phenomenon on the surface of revised femoral heads in total hip arthroplasty and can lead to increased wear due to third bodies. In order to find out the origin and composition of the transfer material, 98 retrieved femoral heads of different materials were examined with regard to the cause of revision, localization, pattern and composition of the transfer material by energy dispersive X-ray spectroscopy. We found that in 53.1%, the deposition was mostly in the region of the equator and the adjacent pole of the femoral heads. The most common cause for revision of heads with metallic deposition was polyethylene wear (43.9%). Random stripes (44.9%), random patches (41.8%) and solid patches (35.7%) were most prevalent on retrieved femoral heads. Random patches were a typical pattern in ceramic-on-ceramic bearing couples. The solid patch frequently occurred in association with dislocation of the femoral head (55%). The elemental analysis of the depositions showed a variety of different materials. In most cases, titanium was an element of the transferred material (76.5%). In addition to metallic components, several non-metallic components were also detected, such as carbon (49%) or sulfur (4.1%). Many of the determined elements could be assigned with regard to their origin with the help of the associated revision cause. Since the depositions lead to an introduction of third-body particles and thus to increased wear, the depositions on the bearing surfaces should be avoided in any case.

Effect of the Size of Titanium Particles Released from Dental Implants on Immunological Response

The techniques used in oral implantology to remove bacterial biofilm from the surface of implants by machining the titanium surface (implantoplasty) or by placing rough dental implants through friction with the cortical bone generate a large release of particles. In this work, we performed a simulation of particle generation following clinical protocols. The particles were characterized for commercially pure titanium with particle sizes of 5, 10, 15, and 30 μm. The aim was to determine the effect of particle size and chemical composition of the implant on the immune response. For this purpose, their morphology and possible contamination were characterized by scanning electron microscopy and X-ray microanalysis. In addition, the granulometry, specific surface area, release of metal ions into the medium, and studies of cytocompatibility, gene expression, and cytokine release linked to the inflammatory process were studied. The release of ions for titanium particles showed levels below 800 ppb for all sizes. Smaller particle sizes showed less cytotoxicity, although particles of 15 μm presented higher levels of cytocompatibility. In addition, inflammatory markers (TNFα and Il-1β) were higher compared to larger titanium. Specifically, particles of 15 μm presented a lower proinflammatory and higher anti-inflammatory response as characterized by gene expression and cytokine release, compared to control or smaller particles. Therefore, in general, there is a greater tendency for smaller particles to produce greater toxicity and a greater proinflammatory response.

Influence of Cu2+ on Osteoclast Formation and Activity In Vitro

Background: Copper-containing biomaterials are increasingly applied for bone regeneration due to their pro-angiogenetic, pro-osteogenetic and antimicrobial properties. Therefore, the effect of Cu²⁺ on osteoclasts, which play a major role in bone remodeling was studied in detail. Methods: Human primary osteoclasts, differentiated from human monocytes were differentiated or cultivated in the presence of Cu²⁺. Osteoclast formation and activity were analyzed by measurement of osteoclast-specific enzyme activities, gene expression analysis and resorption assays. Furthermore, the glutathione levels of the cells were checked to evaluate oxidative stress induced by Cu²⁺. Results: Up to 8 µM Cu²⁺ did not induce cytotoxic effects. Activity of tartrate-resistant acid phosphatase (TRAP) was significantly increased, while other osteoclast specific enzyme activities were not affected. However, gene expression of TRAP was not upregulated. Resorptive activity of osteoclasts towards dentin was not changed in the presence of 8 µM Cu²⁺ but decreased in the presence of extracellular bone matrix. When Cu²⁺ was added to mature osteoclasts TRAP activity was not increased and resorption decreased only moderately. The glutathione level of both differentiating and mature osteoclasts was significantly decreased in the presence of Cu²⁺. Conclusions: Differentiating and mature osteoclasts react differently to Cu²⁺. High TRAP activities are not necessarily related to high resorption.

Bioinstructive Micro-Nanotextured Zirconia Ceramic Interfaces for Guiding and Stimulating an Osteogenic Response In Vitro

Osseous implantology’s material requirements include a lack of potential for inducing allergic disorders and providing both functional and esthetic features for the patient’s benefit. Despite being bioinert, Zirconia ceramics have become a candidate of interest to be used as an alternative to titanium dental and cochlear bone-anchored hearing aid (BAHA) implants, implying the need for endowing the surface with biologically instructive properties by changing basic parameters such as surface texture. Within this context, we propose anisotropic and isotropic patterns (linear microgroove arrays, and superimposed crossline microgroove arrays, respectively) textured in zirconia substrates, as bioinstructive interfaces to guide the cytoskeletal organization of human mesenchymal stem cells (hMSCs). The designed textured micro-nano interfaces with either steep ridges and microgratings or curved edges, and nanoroughened walls obtained by direct femtosecond laser texturing are used to evaluate the hMSC response parameters and osteogenic differentiation to each topography. Our results show parallel micro line anisotropic surfaces are able to guide cell growth only for the steep surfaces, while the curved ones reduce the initial response and show the lowest osteogenic response. An improved osteogenic phenotype of hMSCs is obtained when grown onto isotropic grid/pillar-like patterns, showing an improved cell coverage and Ca/P ratio, with direct implications for BAHA prosthetic development, or other future applications in regenerating bone defects.