The effects of calcium phosphate deposition upon corrosion of CoCr alloys and the potential for implant failure

Influence of cold rolling on in vitro cytotoxicity and electrochemical behaviour of an Fe-Mn-C biodegradable alloy in physiological solutions

The properties of cold-worked Fe-13Mn-1.2C steel, as candidate material for scaffolding and stenting applications, have been investigated. The study of the electrochemical corrosion susceptibility of Fe-13Mn-1.2C alloy in protein bearing and non-protein bearing physiological solutions, revealed that there were no differences between the as-received, 10% and 20% cold worked Fe-13Mn-1.2C samples. Although protein addition reduces the overall corrosion rate in static immersion degradation tests for both the cold worked and non-cold worked alloys, there were no discernible differences in the corrosion rates of samples with different percentages of cold work deformations. Similarly, potentiodynamic testing showed no differences between the corrosion rates in solutions with and without protein addition. Atomic absorption spectroscopy (AAS) results—post static immersion—showed similar values of Fe and Mn concentrations in the electrolyte for all the investigated conditions. Cold working was found to increase Grain Average Misorientation (GAM) and deformation twins within the steel, and, consequently, this led to an increase in the elastic modulus. Hence, cold-rolling may be used to achieve smaller sections (volumes) in order to support the equivalent load of the non-cold worked counterpart, giving a larger surface area to the volume ratio, thereby increasing the corrosion rate, and, in turn, rendering the degradation process shorter. When considering cytocompatibility in vitro, the collected supernatant particulate free Fe-13Mn-1.2C steel electrolytes were seen to be equally cytocompatible with no differences being observed between the different percentage cold work conditions. The presence of solid 80 μm size particles in the seeded elutions were seen to change the results and render the Fe-13Mn-1.2C steel non-cytocompatible.

Content of distinct metals in periprosthetic tissues and pseudosynovial joint fluid in patients with total joint arthroplasty

This prospective study examined the content of metals released from total joint arthroplasty into joint fluid, whole blood and periprosthetic tissues. We determined the levels of Ti, V, Nb, Co, Cr, and Mo, using inductively coupled plasma mass spectrometry, in samples from patients who underwent reoperation of total hip or knee arthroplasty. All of the patients (n = 117) included in the study had either metal on polyethylene or ceramic on polyethylene-bearing pairs. First, our results conclusively showed that the majority of released metals were deposited in periprosthetic tissues. In this context, the bloodstream turned out to be an ineffective biomarker of the effects occurring in local tissues. Second, there was a clear time-dependent nature of metallic accumulation. Based on our extensive dataset, we found significantly elevated levels of the released metals in joint fluid and periprosthetic tissues originating from loosened implants compared to stable ones, as well as recognizable differences between the groups with stable implants and aseptic loosening. Finally, it was proved that the concentrations of metals decreased dependent on the distance of the tissue from the implant. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 107B: 454-462, 2019.

The Cytotoxicity and Genotoxicity of Particulate and Soluble Cobalt in Human Urothelial Cells

Cobalt use is increasing particularly due to its use as one of the primary metals in cobalt-chromium-molybdenum (CoCrMo) metal-on-metal prosthetics. CoCrMo is a high-strength, wear-resistant alloy with reduced risk for prosthetic loosening and device fracture. More than 500,000 people receive hip implants each year in the USA which puts them at potential risk for exposure to metal ions and particles released by the prosthetic implants. Data show cobalt ions released from prosthetics reach the bloodstream and accumulate in the bladder. As patients with failed hip implants show increased urinary and blood cobalt levels, no studies have considered the effects of cobalt on human urothelial cells. Accordingly, we investigated the cytotoxic and genotoxic effects of particulate and soluble cobalt in urothelial cells. Exposure to both particulate and soluble cobalt resulted in a concentration-dependent increase in cytotoxicity, genotoxicity, and intracellular cobalt ions. Based on intracellular cobalt ion levels, we found, when compared to particulate cobalt, soluble cobalt was more cytotoxic, but induced similar levels of genotoxicity. Interestingly, at similar intracellular cobalt ion concentrations, soluble cobalt induced cell cycle arrest indicated by a lack of metaphases not observed after particulate cobalt treatment. These data indicate that cobalt compounds are cytotoxic and genotoxic to human urothelial cells and solubility may play a key role in cobalt-induced toxicity.

Evolution of the degradation mechanism of pure zinc stent in the one-year study of rabbit abdominal aorta model

In the present study, pure zinc stents were implanted into the abdominal aorta of rabbits for 12 months. Multiscale analysis including micro-CT, scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM) and histological stainings was performed to reveal the fundamental degradation mechanism of the pure zinc stent and its biocompatibility. The pure zinc stent was able to maintain mechanical integrity for 6 months and degraded 41.75 ± 29.72% of stent volume after 12 months implantation. No severe inflammation, platelet aggregation, thrombosis formation or obvious intimal hyperplasia was observed at all time points after implantation. The degradation of the zinc stent played a beneficial role in the artery remodeling and healing process. The evolution of the degradation mechanism of pure zinc stents with time was revealed as follows: Before endothelialization, dynamic blood flow dominated the degradation of pure zinc stent, creating a uniform corrosion mode; After endothelialization, the degradation of pure zinc stent depended on the diffusion of water molecules, hydrophilic solutes and ions which led to localized corrosion. Zinc phosphate generated in blood flow transformed into zinc oxide and small amounts of calcium phosphate during the conversion of degradation microenvironment. The favorable physiological degradation behavior makes zinc a promising candidate for future stent applications.

Cobalt toxicity in humans-A review of the potential sources and systemic health effects

Cobalt (Co) and its compounds are widely distributed in nature and are part of numerous anthropogenic activities. Although cobalt has a biologically necessary role as metal constituent of vitamin B₁₂, excessive exposure has been shown to induce various adverse health effects. This review provides an extended overview of the possible Co sources and related intake routes, the detection and quantification methods for Co intake and the interpretation thereof, and the reported health effects. The Co sources were allocated to four exposure settings: occupational, environmental, dietary and medical exposure. Oral intake of Co supplements and internal exposure through metal-on-metal (MoM) hip implants deliver the highest systemic Co concentrations. The systemic health effects are characterized by a complex clinical syndrome, mainly including neurological (e.g. hearing and visual impairment), cardiovascular and endocrine deficits. Recently, a biokinetic model has been proposed to characterize the dose-response relationship and effects of chronic exposure. According to the model, health effects are unlikely to occur at blood Co concentrations under 300μg/l (100μg/l respecting a safety factor of 3) in healthy individuals, hematological and endocrine dysfunctions are the primary health endpoints, and chronic exposure to acceptable doses is not expected to pose considerable health hazards. However, toxic reactions at lower doses have been described in several cases of malfunctioning MoM hip implants, which may be explained by certain underlying pathologies that increase the individual susceptibility for Co-induced systemic toxicity. This may be associated with a decrease in Co bound to serum proteins and an increase in free ionic Co²⁺. As the latter is believed to be the primary toxic form, monitoring of the free fraction of Co²⁺ might be advisable for future risk assessment. Furthermore, future research should focus on longitudinal studies in the clinical setting of MoM hip implant patients to further elucidate the dose-response discrepancies.

The biological response to orthopaedic implants for joint replacement: Part I: Metals

Joint replacement is a commonly performed, highly successful orthopaedic procedure, for which surgeons have a large choice of different materials and implant designs. The materials used for joint replacement must be both biologically acceptable to minimize adverse local tissue reactions, and robust enough to support weight bearing during common activities of daily living. Modern joint replacements are made from metals and their alloys, polymers, ceramics, and composites. This review focuses on the biological response to the different biomaterials used for joint replacement. In general, modern materials for joint replacement are well tolerated by the body as long as they are in bulk (rather than in particulate or ionic) form, are mechanically stable and noninfected. If the latter conditions are not met, the prosthesis will be associated with an acute/chronic inflammatory reaction, peri-prosthetic osteolysis, loosening and failure. This article (Part 1 of 2) is dedicated to the use of metallic devices in orthopaedic surgery including the associated biological response to metallic byproducts is a review of the basic science literature regarding this topic. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 2162-2173, 2017.

Effect of angular displacement amplitude on the torsional fretting corrosion behavior of CoCrMo alloy in different synovial fluid

The wear mechanism of torsional fretting in this paper was mainly the joint action of abrasive wear, corrosion wear and adhesive wear.

Toxicology of wear particles of cobalt-chromium alloy metal-on-metal hip implants Part II: Importance of physicochemical properties and dose in animal and in vitro studies as a basis for risk assessment

The objective of the Part II analysis was to evaluate animal and in vitro toxicology studies of CoCr particles with respect to their physicochemistry and dose relevance to metal-on-metal (MoM) implant patients as derived from Part I. In the various toxicology studies, physicochemical characteristics were infrequently considered and administered doses were orders of magnitude higher than what occurs in patients. Co was consistently shown to rapidly release from CoCr particles for distribution and elimination from the body. CoCr micron sized particles appear more biopersistent in vivo resulting in inflammatory responses that are not seen with similar mass concentrations of nanoparticles. We conclude, that in an attempt to obtain data for a complete risk assessment, future studies need to focus on physicochemical characteristics of nano and micron sized particles and on doses and dose metrics relevant to those generated in patients or in properly conducted hip simulator studies.

Interactions between mammalian cells and nano- or micro-sized wear particles: physico-chemical views against biological approaches

Total joint arthroplasty (TJA) is a more and more frequent approach for the treatment of end-stage osteoarthritis in young and active adults; it successfully relieves joint pain and improves function significantly enhancing the health-related quality of life. Aseptic loosening and other wear-related complications are some of the most recurrent reasons for revision of TJA. This review focuses on current understanding of the biological reactions to prosthetic wear debris comparing in vivo and in vitro results. Mechanisms of interactions of various types of cells with metal, polymeric and ceramic wear particles are summarised. Alternative views based on multidisciplinary approaches are proposed to consider physico-chemical, surface parameters of wear particles (such as: particle size, geometry and charge) and material (particle chemical composition and its nature) with biological effects (cellular responses).

Local and systemic toxicity of nanoscale debris particles in total hip arthroplasty

Over the past 30 years joint replacement prostheses have been developed and refined to enhance durability and reproducibility. Total hip joint arthroplasty is being performed in an increasing number of younger patients; therefore orthopaedic surgeons seek implants with a longer life span. With regards to the progress of mechanical behaviour of the biomaterials used in an arthroplasty, little is known about the long-term biological effects of wear debris. Owing to the composition of the prostheses currently in use, systemic exposure to chromium (Cr), cobalt (Co), nickel (Ni) and aluminium (Al) alloys occurs as a result of the formation of metal wear nano-particles that are released both from metal-on-metal and polyethylene-on-metal bearings, resulting in a postoperative increase in metal ion levels at different organ sites. These particles circulate both locally and systemically, penetrate cell plasma membranes, bind to cellular proteins and enzymes and modulate cytokine expression. Their physiologic effects are poorly understood and their potential toxicity, hypersensitivity and carcinogenicity remain a cause for concern. In this article we will address the issue of whether these nanoscale degradation products are associated with adverse, clinically significant local or systemic toxicologic sequelae.

Effects of soluble cobalt and cobalt incorporated into calcium phosphate layers on osteoclast differentiation and activation

Metal ions originating from mechanical debris and corrosive wear of prosthetic implant alloys accumulate in peri-implant soft tissues, bone mineral, and body fluids. Eventually, metal ions such as cobalt (II) (Co(2+)), which is a major component of cobalt-chromium-based implant alloys and a known activator of osteolysis, are incorporated into the mineral phase of bone. We hypothesize that the accumulation of Co(2+) in the mineral could directly activate osteolysis by targeting osteoclasts. To test this hypothesis, we coated tissue culture plastic with a thin layer of calcium phosphate (CaP) containing added traces of Co(2+), thereby mimicking the bone mineral accumulation of Co(2+). Murine bone marrow osteoclasts formed in the presence of M-CSF and RANKL were cultured on these surfaces to examine the effects of Co(2+) on osteoclast formation and resorptive activity. Treatment conditions with Co(2+) involved incorporation into the CaP layer, adsorption to the mineral surface, or addition to culture media. Micromolar concentrations of Co(2+) delivered to developing osteoclast precursors by all 3 routes increased both osteoclast differentiation and resorptive function. Compared to CaP layers without Co(2+), we observed a maximal 75% increase in osteoclast numbers and a 2.3- to 2.7-fold increase in mineral resorption from the tissue culture wells containing 0.1 microM Co(2+) and 0.1-10 microM Co(2+), respectively. These concentrations are well within the range found in peri-implant tissues in vivo. This direct effect of Co(2+) on osteoclasts appears to act independently of the particulate phagocytosis/inflammation-mediated pathways, thus enhancing osteolysis and aseptic implant loosening.

Orthopaedic metals and their potential toxicity in the arthroplasty patient

The long-term effects of metal-on-metal arthroplasty are currently under scrutiny because of the potential biological effects of metal wear debris. This review summarises data describing the release, dissemination, uptake, biological activity, and potential toxicity of metal wear debris released from alloys currently used in modern orthopaedics. The introduction of risk assessment for the evaluation of metal alloys and their use in arthroplasty patients is discussed and this should include potential harmful effects on immunity, reproduction, the kidney, developmental toxicity, the nervous system and carcinogenesis.

The role of the surface chemistry of CoCr alloy particles in the phagocytosis and DNA damage of fibroblast cells

Surface chemistry of CoCr particles is demonstrated to be fundamental to the process of phagocytosis by fibroblast cells in vitro. Particles preincubated in serum for 5 days and washed in water before addition to cell cultures were phagocytosed less readily than were particles preincubated in minimal essential medium (MEM) for 1 h and washed in water. This was explained by the coating of calcium phosphate and protein on the serum-immersed particles investigated by time-of-flight secondary ion mass spectroscopy. The cells incubated with the serum-immersed particles had a reduced mitotic index when compared with the MEM-immersed particles, indicating that the phagocytosed particles were causing cell cycle arrest. The release of soluble ions measured by electrothermal atomic absorption spectroscopy within the first hour of particle immersion in MEM was identified as the most likely cause for the DNA damage measured by single cell gel electrophoresis ("Comet" assay). Cryofocused ion beam SEM with a spatial resolution of 8 nm was used to cross section cells, to investigate the location of the phagocytosed particles, some of which were found within the nuclear membrane. This paper demonstrated that consideration of the surface chemistry is essential to understand the processes of the effects of orthopedic wear debris.