Progress in Wear Resistant Materials for Total Hip Arthroplasty

Multi-functional bioactive silver- and copper-doped diamond-like carbon coatings for medical implants

Diamond-like carbon (DLC) coatings doped with bioactive elements of silver (Ag) and copper (Cu) have been receiving increasing attention in the last decade, particularly in the last 5 years, due to their potential to offer a combination of enhanced antimicrobial and mechanical performance. These multi-functional bioactive DLC coatings offer great potential to impart the next generation of load-bearing medical implants with improved wear resistance and strong potency against microbial infections. This review begins with an overview of the status and issues with current total joint implant materials and the state-of-the art in DLC coatings and their application to medical implants. A detailed discussion of recent advances in wear resistant bioactive DLC coatings is then presented with a focus on doping the DLC matrix with controlled quantities of Ag and Cu elements. It is shown that both Ag and Cu doping can impart strong antimicrobial potency against a range of Gram-positive and Gram-negative bacteria, but this is always accompanied so far by a reduction in mechanical performance of the DLC coating matrix. The article concludes with discussion of potential synthesis methods to accurately control bioactive element doping without jeopardising mechanical properties and gives an outlook to the potential long-term impact of developing a superior multifunctional bioactive DLC coating on implant device performance and patient health and wellbeing. STATEMENT OF SIGNIFICANCE: Multi-functional diamond-like carbon (DLC) coatings doped with bioactive elements of silver (Ag) and copper (Cu) offer great potential to impart the next generation of load-bearing medical implants with improved wear resistance and strong potency against microbial infections. This article provides a critical review of the state-of-the-art in Ag and Cu doped DLC coatings, beginning with an overview of the current applications of DLC coatings in implant technology followed by a detailed discussion of Ag/Cu doped DLC coatings with particular focus on the relationship between their mechanical and antimicrobial performance. Finally, it ends with a discussion on the potential long-term impact of developing a truly multifunctional ultra-hard wearing bioactive DLC coating to extend the lifetime of total joint implants.

Nanoparticle-Containing Hyaluronate Solution for Improved Lubrication of Orthopedic Ceramics

Premature failure caused by inadequate lubrication of an artificial joint is a major problem. Inspired by engine lubrication, in which various additives are used to enforce the oil lubricant, here, a bench test of a biomimetic lubricating fluid containing different substances was carried out. Bovine serum albumin (BSA), in the form of both molecules and nanoparticles, was used as a functional additive. Compared with BSA molecules, BSA nanoparticles dispersed in HA solution served as more effective additives in the biomimetic lubrication fluid to minimize the friction and wear of ceramic orthopedic materials made of zirconium dioxide (ZrO₂). Meanwhile, a tribo-acoustic study indicated that the “squeaking” problem associated with ZrO₂ could be suppressed by the biomimetic fluid. Together with a cytotoxicity assessment, the BSA nanoparticle-incorporated biomimetic fluid was confirmed as a potential reagent for use in the clinic to maintain an even longer service life of artificial joints.

Optimal Design of Ceramic Based Hip Implant Composites Using Hybrid AHP-MOORA Approach

Designing excellent hip implant composite material with optimal physical, mechanical and wear properties is challenging. Improper hip implant composite design may result in a premature component and product failure. Therefore, a hybrid decision-making tool was proposed to select the optimal hip implant composite according to several criteria that are probably conflicting. In varying weight proportions, a series of hip implant composite materials containing different ceramics (magnesium oxide, zirconium oxide, chromium oxide, silicon nitride and aluminium oxide) were fabricated and evaluated for wear and physicomechanical properties. The density, void content, hardness, indentation depth, elastic modulus, compressive strength, wear, and fracture toughness values were used to rank the hip implant composites. It was found that the density and void content of the biocomposites remain in the range of 3.920-4.307 g/cm3 and 0.0021-0.0089%, respectively. The composite without zirconium oxide exhibits the lowest density (3.920 g/cm3), while the void content remains lowest for the composite having no chromium oxide content. The highest values of hardness (28.81 GPa), elastic modulus (291 GPa) and fracture toughness (11.97 MPa.m1/2) with the lowest wear (0.0071 mm3/million cycles) were exhibited by the composites having 83 wt.% of aluminium oxide and 10 wt.% of zirconium oxide. The experimental results are compositional dependent and without any visible trend. As a result, selecting the best composites among a group of composite alternatives becomes challenging. Therefore, a hybrid AHP-MOORA based multi-criteria decision-making approach was adopted to choose the best composite alternative. The AHP (analytic hierarchy process) was used to calculate the criteria weight, and MOORA (multiple objective optimisation on the basis of ratio analysis) was used to rank the composites. The outcomes revealed that the hip implant composite with 83 wt.% aluminium oxide, 10 wt.% zirconium oxide, 5 wt.% silicon nitride, 3 wt.% magnesium oxide, and 1.5 wt.% chromium oxide had the best qualities. Finally, sensitivity analysis was conducted to determine the ranking's robustness and stability concerning the criterion weight.

Role of Interfacial Bonding in Tribochemical Wear

Tribochemical wear of contact materials is an important issue in science and engineering. Understanding the mechanisms of tribochemical wear at an atomic scale is favorable to avoid device failure, improve the durability of materials, and even achieve ultra-precision manufacturing. Hence, this article reviews some of the latest developments of tribochemical wear of typical materials at micro/nano-scale that are commonly used as solid lubricants, tribo-elements, or structural materials of the micro-electromechanical devices, focusing on their universal mechanisms based on the studies from experiments and numerical simulations. Particular focus is given to the fact that the friction-induced formation of interfacial bonding plays a critical role in the wear of frictional systems at the atomic scale.

Improving the Endoprosthesis Design and the Postoperative Therapy as a Means of Reducing Complications Risks after Total Hip Arthroplasty

One of the most high-tech, efficient and reliable surgical procedures is Total Hip Arthroplasty (THA). Due to the increase in average life expectancy, it is especially relevant for older people suffering from chronic joint disease, allowing them to return to an active lifestyle. However, the rejuvenation of such a severe joint disease as osteoarthritis requires the search for new solutions that increase the lifespan of a Total Hip Replacement (THR). Current trends in the development of this area are primarily focused on the creation of new materials used in THR and methods for their processing that meet the requirements of biocompatibility, long-term strength, wear resistance and the absence of an immune system response aimed at rejection. This study is devoted to the substantiation of one of the possible approaches to increase the reliability and durability of THR, based on the improvement of the implant design and postoperative rehabilitation technology, potentially reducing the risk of complications in the postoperative period.

Recent Progress on Wear-Resistant Materials: Designs, Properties, and Applications

There has been tremendous interest in the development of different innovative wear-resistant materials, which can help to reduce energy losses resulted from friction and wear by ≈40% over the next 10-15 years. This paper provides a comprehensive review of the recent progress on designs, properties, and applications of wear-resistant materials, starting with an introduction of various advanced technologies for the fabrication of wear-resistant materials and anti-wear structures with their wear mechanisms. Typical strategies of surface engineering and matrix strengthening for the development of wear-resistant materials are then analyzed, focusing on the development of coatings, surface texturing, surface hardening, architecture, and the exploration of matrix compositions, microstructures, and reinforcements. Afterward, the relationship between the wear resistance of a material and its intrinsic properties including hardness, stiffness, strength, and cyclic plasticity is discussed with underlying mechanisms, such as the lattice distortion effect, bonding strength effect, grain size effect, precipitation effect, grain boundary effect, dislocation or twinning effect. A wide range of fundamental applications, specifically in aerospace components, automobile parts, wind turbines, micro-/nano-electromechanical systems, atomic force microscopes, and biomedical devices are highlighted. This review is concluded with prospects on challenges and future directions in this critical field.

Minimum 15-year results of metasul 28-mm metal-on-metal total hip arthroplasty in patients younger than 50 years of age

Background

Some propitious mid- and long-term studies had been reported for MoM bearings; however, most studies have addressed specific patient groups rather than younger, active patients, who probably represent the most suitable population for investigations on wear and osteolysis. The purpose of this study to evaluate the long-term results of second-generation metal-on-metal cementless total hip arthroplasty (THA) in patients aged <50 years.

Methods

From December 1997 to January 2004, primary THA using a metal-on-metal bearing cementless implant was performed in 63 patients (72 hips) aged <50 years. The mean follow-up duration was 18.6 (range, 15.9–22.1) years, and the mean age at initial operation was 39 (range, 22–49) years. Clinical results, complications, survivorship, osteolysis, and aseptic loosening were evaluated.

Results

The mean Harris hip score and Western Ontario and McMaster Universities Arthritis Index scores were improved from 57.8 (range, 28–69) points and 73.4 (range, 63–94) points preoperatively to 91.7 (range, 80–100) points and 25.5 points (range, 17–38) points, respectively, at the last follow-up. Osteolysis lesions were found in 12 hips (acetabulum, 6 and femur, 6). The notching occurred on the femoral stem neck occurred in 12 hips. The mean serum cobalt and chromium concentrations were 2.3 (range, 0.2–10.6) μg/L and 1.7 (range, 0.4–8.1) μg/L, respectively, at a mean follow-up of 12.7 years in 32 patients (50.1%). The Kaplan-Meier survivorship curve analysis with revision for any reason as the endpoint revealed that 93.1% survived at 18.6 years’ follow-up.

Conclusions

Second-generation metal-on-metal cementless THA was found to produce satisfactory clinical and radiographic results with a low revision rate for osteolysis and aseptic loosening in patients aged less than 50 years.

Mid-term outcomes of the R3™ delta ceramic acetabular system in total hip arthroplasty

Background

Whilst bony fixation of hip replacement has stable solutions, there remains controversy over which bearing best optimizes longevity and function. Ceramic-on-ceramic (CoC) bearing combinations are associated with lower risk of revision due to aseptic loosening and dislocation. Evidence for long-term functional outcomes of modern, 4th generation CoC bearings is limited. The aim of this study was to analyze outcomes and complications of the R3™ Acetabular System (Smith & Nephew, Inc., Cordova, TN, USA) in combination with BIOLOX® Delta ceramic femoral head in patients undergoing primary total hip arthroplasty (THA).

Methods

Between June 2009 and May 2011, 175 patients (178 hips) were enrolled into a prospective, study at 6 sites in Europe and prospectively followed-up at 3 months and 1, 3, 5, and 7 years postoperative.

Results

Total WOMAC score improved from 63 (range, 22–91) preoperative to 8 (range, 0–8) at 1-year follow-up and remained unchanged at 7-year follow-up. Modified Harris hip score improved from 45 (range, 10–87) preoperative to 83 (range, 25–100) at 3 months, 91 (range, 42–100) at 1 year, and 92 (range, 46, 100) at 7 years. UCLA Activity Rating Scale score improved from 3.3 (range, 1–8) preoperative to 6.2 (range, 2–8) at 1 year; it marginally declined to 5.8 (range, 3–8) at 7-year follow-up. There were 4 trochanteric fractures and 5 patients died of unrelated reasons. Three hips were revised (2 periprosthetic fractures and 1 subluxation). The 7-year cumulative survival rate was 98.3%.

Conclusion

Clinical and functional improvements of THA with CoC bearing are maintained at 7 years postoperative.

Trial registration

ClinicalTrials.Gov, NCT03566082, Registered 10 January 2018—retrospectively registered,

Implant Coating Manufactured by Micro-Arc Oxidation and Dip Coating in Resorbable Polylactide for Antimicrobial Applications in Orthopedics

Prophylaxis and the treatment of implant-related infections has become a key focus area for research into improving the outcome of orthopedic implants. Functional resorbable coatings have been developed to provide an antimicrobial surface on the implant and reduce the risk of infection. However, resorbable coatings developed to date still suffer from low adhesive strength and an inadequate release rate of antibiotics. This study presents a novel double-coating of micro-arc oxidation and resorbable polylactide copolymer on a Ti-6Al-4V implant with the aim of reducing the risk of infection post-implantation. The adhesive strength, rate of coating degradation, and antibiotic release rate were investigated. A key finding was that the micro-arc oxidation coating with the addition of antibiotics increased the adhesive strength of the poly-l-lactide-co-ε-caprolactone (PLC) coatings. The adhesive strength was influenced by the concentration of the PLC solution, the surface structure of the titanium substrate, and the composition of the coatings. The antibiotics blended into the PLC coating had a release cycle of approximately 10 days, which would be long enough to reduce the risk of developing an infection after implantation. The double coatings presented in this study have an excellent potential for reducing the incidence and severity of implants-related early infections.

AFM Study on Superlubricity between Ti6Al4V/Polymer Surfaces Achieved with Liposomes

Liposomes have been considered as the boundary lubricant in natural joints. They are also the main component of bionic lubricant. In this study, the tribological properties of liposomes on Ti6Al4V/polymer surface were studied by atomic force microscope (AFM) at the nanoscale. The superlubricity with a friction coefficient of 0.007 was achieved under the maximal pressure of 15 MPa, consisting with the lubrication condition of natural joints. Especially, when the AFM probe was hydrophilically modified and preadsorbed, the friction coefficient and load bearing capacity could be further improved. In addition, the probe with a large radius could maintain the stable lubrication of liposomes in the contact zone. Finally, an optimal lubrication model of liposomes was established and the critical force for superlubricity was also proposed. It was the boundary between elastic deformation and plastic deformation for vesicles. It was also the indicator of the plough effect appearing on the adsorbed layer. This work reveals the interfacial behavior of liposomes and realizes the controllable superlubricity system, providing more guidance for clinical application.

Assessment the Sliding Wear Behavior of Laser Microtexturing Ti6Al4V under Wet Conditions

Laser micro-texturing processes, compared to untreated surfaces, can improve the friction, wear and wettability behavior of sliding parts. This improvement is related to the micro-geometry and the dimensions of the texture which is also dependent on the processing parameters. This research studied the effect of laser textured surfaces on the tribological behavior of titanium alloy Ti6Al4V. The influence of processing parameters was analyzed by changing the scanning speed of the beam and the energy density of pulse. First, the characterization of dimensional and geometrical features of the texturized tracks was carried out. Later, their influence on the wetting behavior was also evaluated through contact angle measurements using water as a contact fluid. Then, the tribological performance of these surfaces was analyzed using a ball-on-flat reciprocating tribometer under wet and dry conditions. Finally, wear mechanisms were identified employing electronic and optical microscopy techniques capable to evaluate the wear tracks on Ti surfaces and WC–Co spheres. These analyses had determined a strong dependence between the wear behavior and the laser patterning parameters. Wear friction effects were reduced by up to a 70% replacing conventional untreated surfaces of Ti6Al4V alloy with laser textured surfaces.