Significance of Tribocorrosion in Biomedical Applications: Overview and Current Status

Recently, “tribocorrosion,” a research area combining the science of tribology and corrosion, has drawn attention from scientists and engineers belonging to a wide spectrum of research domains. This is due to its practical impact on daily life and also the accompanying economical burdens. It encompasses numerous applications including the offshore, space, and biomedical industry, for instance, in the case of artificial joints (Total Hip Replacement, THR) in orthopedic surgery, where implant metals are constantly exposed to tribological events (joint articulations) in the presence of corrosive solutions, that is, body fluids. Keeping the importance of this upcoming area of research in biomedical applications in mind, it was thought to consolidate the work in this area with some fundamental aspects so that a comprehensive picture of the current state of knowledge can be depicted. Complexity of tribocorrosion processes has been highlighted, as it is influenced by several parameters (mechanical and corrosion) and also due to the lack of an integrated/efficient test system. Finally a review of the recent work in the area of biotribocorrosion is provided, by focusing on orthopedic surgery and dentistry

On the matter of synovial fluid lubrication: implications for Metal-on-Metal hip tribology

Artificial articular joints present an interesting, and difficult, tribological problem. These bearing contacts undergo complex transient loading and multi axes kinematic cycles, over extremely long periods of time (>10 years). Despite extensive research, wear of the bearing surfaces, particularly metal–metal hips, remains a major problem. Comparatively little is known about the prevailing lubrication mechanism in artificial joints which is a serious gap in our knowledge as this determines film formation and hence wear. In this paper we review the accepted lubrication models for artificial hips and present a new concept to explain film formation with synovial fluid. This model, recently proposed by the authors, suggests that interfacial film formation is determined by rheological changes local to the contact and is driven by aggregation of synovial fluid proteins. The implications of this new mechanism for the tribological performance of new implant designs and the effect of patient synovial fluid properties are discussed

The role of surface pre-treatment on the microstructure, corrosion and fretting corrosion of cemented femoral stems

The use of cemented femoral stems is common practice worldwide with strong clinical data supporting their use. Over the years, different surface processing techniques have been employed to enhance the performance of the stem-cement interface. As a result different clinical outcomes and visual presentation at revision has been observed. Whilst research has focussed on increasing adhesion and better load bearing capacity, the effects of surface processing on the degradation of cemented femoral stems has not been investigated. The aims of this study was to investigate the effects of surface processing on the subsurface microstructure, surface chemistry and tribocorrosion degradation mechanisms of cemented tapered femoral stems subjected to polishing and blasting (Vaquasheen) processes. Cemented femoral stems were orientated and loaded according to ISO 7206-4 for 500,000 cycles in 0.9% NaCl at 37 °C. A three-electrode electrochemical cell was integrated into the mechanical test to facilitate in-situ corrosion measurements. The severity and mechanism of damaged were assessed scanning and transmission electron microscopy, X-ray photoelectron spectrometry, solution mass spectrometry and white light interferometry. Surface processing influenced the level of tribocorrosion at the interface with polished surfaces demonstrating higher levels of tribocorrosion and ion release when compared to the blasted surfaces. Surface analysis consistently demonstrated the presence of a SiO2 layer on the vaquasheened stems thought to originate from the glass bead blast matrix. This resulted in lower levels of corrosion both under static and tribocorrosion assessment. In conclusion, blasted surfaces resulted in lower wear induced corrosion when compared to the polished surfaces. However the total metallic ion levels did not follow the same trend. This is thought to be due to the formation of metallic debris and dissolution of debris due to abrasion of the femoral stems

Detailed Inspection of Metal Implants

Detailed visual inspection of metal hips is the first step in retrieval analysis. In this study a systematic visual inspection protocol was developed to quantify bearing surface changes and their associations with material loss was investigated. Simple and multiple linear regression models found that moderate surface scratching, discolouration, haziness and the size of visible wear scars were all significantly associated with material loss (R2 = 5% - 73%, p<0.05). Visual inspection is not a substitute for measurement of material loss but an understanding of bearing surface changes may offer unique clues as to the mechanisms of failure of retrieved hips

Surface and subsurface changes as a result of tribocorrosion at the stem-neck interface of bi-modular prosthesis

This study presents a detailed multi-scale analysis of the degradation processes occurring on both the CoCrMo and TMZF alloy surfaces at different regions across the taper interface. Co-ordinate measurement machine, scanning electron microscopy, transmission electron microscopy and X-ray Diffraction methods have been utilised to identify the roles of degradation from the mm to nm scale. Dependant on the region of interest, varying topographies and subsurface morphologies were observed across both surfaces. In regions where high pressures are expected, retention of the surface topography was seen on the CoCrMo trunnion. This was complimented by gross shear and plastic deformation of the subsurface material. In regions where maximum penetration was seen, evidence of fretting-corrosion was seen and a loss of the nano-crystalline layer. For the TMZF surface, refinement of the alloy was seen in the top 5 μm, with fatigue cracks within the bulk present. Precipitation and formation of oxide species were observed at depths of 2 μm. The degradation of bi-modular prosthesis is a complex multifactorial process. It is hypothesised that this formation of oxide species at the interface and within the bulk alloy play an important role in the degradation through a combined work-hardening and corrosion process

Tribofilms on CoCrMo alloys: Understanding the role of the lubricant

The tribological activation of a passive metal alloy in an aqueous biological environment have been highlighted by many researchers; better known as bio-tribocorrosion. Tribocorrosion processes, which can be found at a number of metal-based biomedical implant interfaces, can be affected by lubricant species such as proteins, amino acids and salts. To date, researchers have quantified how the presence of organic species and the environment affect the tribological and corrosion process. However, the nature of the bio-films is still broadly to be explored. This study aims to understand how the lubricant - surface interactions influence the evolving frictional, corrosion and material volume loss from CoCrMo alloys and how the formation of any tribo-film at the interface may influence the aforementioned processes. This current research uses reciprocating tribocorrosion tests of CoCrMo surfaces in saline, protein, and protein-free cell culture medium lubricants (0.9% NaCl, 25% Foetal Bovine Serum (FBS) diluted in Phosphate Buffered Saline (PBS), Dulbecco's Modified Eagle Medium (DMEM) and 25% FBS in DMEM solutions). Results show the addition of organic constituents give a better tribology and corrosion performances. XPS confirmed that chemical reactions happened on the tested surfaces. Calcium, phosphorus and sulphur are shown to be catalysed to react in tribology-induced processes and have important roles in tribocorrosion. These results contribute to the understanding of protein-metal interactions occurring in tribofilm formation on wearing surfaces

Exposure effects of endotoxin-free titanium-based wear particles to human osteoblasts

Titanium-based materials are widely employed by the biomedical industry in orthopedic and dental implants. However, when placed into the human body, these materials are highly susceptible to degradation processes, such as corrosion, wear, and tribocorrosion. As a consequence, metallic ions or particles (debris) may be released, and although several studies have been conducted in recent years to better understand the effects of their exposure to living cells, a consensual opinion has not yet been obtained. In this work, we produced metallic based wear particles by tribological tests carried out on Ti-6Al-4V and Ti-15Zr-15Mo alloys. They were posteriorly physicochemically characterized according to their crystal structure, size, morphology, and chemical composition and compared to Ti-6Al-4V commercially available particles. Finally, adsorbed endotoxins were removed (by applying a specific thermal treatment) and endotoxin-free particles were used in cell experiments to evaluate effects of their exposure to human osteoblasts (MG-63 and HOb), namely cell viability/metabolism, proinflammatory cytokine production (IL-6 and PGE2), and susceptibility to internalization processes. Our results indicate that tribologically-obtained wear particles exhibit fundamental differences in terms of size (smaller) and morphology (irregular shapes and rough surfaces) when compared to the commercial ones. Consequently, both Ti-6Al-4V and Ti-15Zr-15Mo particles were able to induce more pronounced effects on cell viability (decrease) and cytokine production (increase) than did Ti-6Al-4V commercial particles. Furthermore, both types of wear particles penetrated osteoblast membranes and were internalized by the cells. Influences on cytokine production by endotoxins were also demonstrated.This work was supported by Fundacao de Amparo a Pesquisa do Estado de Sao Paulo - FAPESP (2015/50280-5 and 2017/24300-4), Fundacao para a Ciencia e Tecnologia - FCT (UID/EEA/04436/2013), Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior - CAPES (Finance Code 0001), FCT/CAPES Joint Research Project (99999.008666/2014-08), FCT COMPETE 2020 (POCI-01-0145-FEDER-006941 and POCI-01-0145-FEDER-007265) and M-ERA-NET (0001/2015)

Effects of metal-on-metal wear on the host immune system and infection in hip arthroplasty

Methods We reviewed the available literature on the influence of degradation products of MOM bearings in total hip arthroplasties on infection risk. Results Wear products were found to influence the risk of infection by hampering the immune system, by inhibiting or accelerating bacterial growth, and by a possible antibiotic resistance and heavy metal co-selection mechanism. Interpretation Whether or not the combined effects of MOM wear products make MOM bearings less or more prone to infection requires investigation in the near future

Tribology of Medical Devices

Importance of tribology in a number of medical devices and surgical instruments is reviewed, including artificial joints, artificial teeth, dental implants and orthodontic appliances, cardiovascular devices, contact lenses, artificial limbs and surgical instruments. The current focus and future developments of these medical devices are highlighted from a tribological point of view, together with the underlying mechanisms

Diagnostic guidelines for the histological particle algorithm in the periprosthetic neo-synovial tissue

Background The identification of implant wear particles and non-implant related particles and the characterization of the inflammatory responses in the periprosthetic neo-synovial membrane, bone, and the synovial-like interface membrane (SLIM) play an important role for the evaluation of clinical outcome, correlation with radiological and implant retrieval studies, and understanding of the biological pathways contributing to implant failures in joint arthroplasty. The purpose of this study is to present a comprehensive histological particle algorithm (HPA) as a practical guide to particle identification at routine light microscopy examination. Methods The cases used for particle analysis were selected retrospectively from the archives of two institutions and were representative of the implant wear and non-implant related particle spectrum. All particle categories were described according to their size, shape, colour and properties observed at light microscopy, under polarized light, and after histochemical stains when necessary. A unified range of particle size, defined as a measure of length only, is proposed for the wear particles with five classes for polyethylene (PE) particles and four classes for conventional and corrosion metallic particles and ceramic particles. Results All implant wear and non-implant related particles were described and illustrated in detail by category. A particle scoring system for the periprosthetic tissue/SLIM is proposed as follows: 1) Wear particle identification at light microscopy with a two-step analysis at low (× 25, × 40, and × 100) and high magnification (× 200 and × 400); 2) Identification of the predominant wear particle type with size determination; 3) The presence of non-implant related endogenous and/or foreign particles. A guide for a comprehensive pathology report is also provided with sections for macroscopic and microscopic description, and diagnosis. Conclusions The HPA should be considered a standard for the histological analysis of periprosthetic neo-synovial membrane, bone, and SLIM. It provides a basic, standardized tool for the identification of implant wear and non-implant related particles at routine light microscopy examination and aims at reducing intra-observer and inter-observer variability to provide a common platform for multicentric implant retrieval/radiological/histological studies and valuable data for the risk assessment of implant performance for regional and national implant registries and government agencies