UHMWPE acetabular cup creep deformation during the run-in phase of THA's life cycle

Updates on Biomaterials Used in Total Hip Arthroplasty (THA)

One of the most popular and effective orthopedic surgical interventions for treating a variety of hip diseases is total hip arthroplasty. Despite being a radical procedure that involves replacing bone and cartilaginous surfaces with biomaterials, it produces excellent outcomes that significantly increase the patient's quality of life. Patient factors and surgical technique, as well as biomaterials, play a role in prosthetic survival, with aseptic loosening (one of the most common causes of total hip arthroplasty failure) being linked to the quality of biomaterials utilized. Over the years, various biomaterials have been developed to limit the amount of wear particles generated over time by friction between the prosthetic head (metal alloys or ceramic) and the insert fixed in the acetabular component (polyethylene or ceramic). An ideal biomaterial must be biocompatible, have a low coefficient of friction, be corrosion resistant, and have great mechanical power. Comprehensive knowledge regarding what causes hip arthroplasty failure, as well as improvements in biomaterial quality and surgical technique, will influence the survivability of the prosthetic implant. The purpose of this article was to assess the benefits and drawbacks of various biomaterial and friction couples used in total hip arthroplasties by reviewing the scientific literature published over the last 10 years.

Adaptive Neuro-Fuzzy-Based Models for Predicting the Tribological Properties of 3D-Printed PLA Green Composites Used for Biomedical Applications

Tribological performance is a critical aspect of materials used in biomedical applications, as it can directly impact the comfort and functionality of devices for individuals with disabilities. Polylactic Acid (PLA) is a widely used 3D-printed material in this field, but its mechanical and tribological properties can be limiting. This study focuses on the development of an artificial intelligence model using ANFIS to predict the wear volume of PLA composites under various conditions. The model was built on data gathered from tribological experiments involving PLA green composites with different weight fractions of date particles. These samples were annealed for different durations to eliminate residual stresses from 3D printing and then subjected to tribological tests under varying normal loads and sliding distances. Mechanical properties and finite element models were also analyzed to better understand the tribological results and evaluate the load-carrying capacity of the PLA composites. The ANFIS model demonstrated excellent compatibility and robustness in predicting wear volume, with an average percentage error of less than 0.01% compared to experimental results. This study highlights the potential of heat-treated PLA green composites for improved tribological performance in biomedical applications.

Dynamic finite element analysis of hip replacement edge loading: Balancing precision and run time in a challenging model

An important aspect in evaluating the resilience of hip replacement designs is testing their performance under adverse conditions that cause edge loading of the acetabular liner. The representation of edge loading conditions in finite element models is computationally challenging due to the changing contact locations, need for fine meshes, and dynamic nature of the system. In this study, a combined mesh and mass-scaling sensitivity study was performed to identify an appropriate compromise between convergence and solution time of explicit finite element analysis in investigating edge loading in hip replacement devices. The optimised model was then used to conduct a sensitivity test investigating the effect of different hip simulator features (the mass of the translating fixture and mediolateral spring damping) on the plastic strain in the acetabular liner. Finally, the effect of multiple loading cycles on the progressive accumulation of plastic strain was then also examined using the optimised model. A modelling approach was developed which provides an effective compromise between mass-scaling effects and mesh refinement for a solution time per cycle of less than 1 h. This 'Recommended Mesh' model underestimated the plastic strains by less than 10%, compared to a 'Best Estimate' model with a run time of ∼190 h. Starting with this model setup would therefore significantly reduce any new model development time while also allowing the flexibility to incorporate additional complexities as required. The polyethylene liner plastic strain was found to be sensitive to the simulator mass and damping (doubling the mass or damping had a similar magnitude effect to doubling the swing phase load) and these should ideally be described in future experimental studies. The majority of the plastic strain (99%) accumulated within the first three load cycles.

Evaluating the Performance of 3D-Printed PLA Reinforced with Date Pit Particles for Its Suitability as an Acetabular Liner in Artificial Hip Joints

Off-the-shelf hip joints are considered essential parts in rehabilitation medicine that can help the disabled. However, the failure of the materials used in such joints can cause individual discomfort. In support of the various motor conditions of the influenced individuals, the aim of the current research is to develop a new composite that can be used as an acetabular liner inside the hip joint. Polylactic acid (PLA) can provide the advantage of design flexibility owing to its well-known applicability as a 3D printed material. However, using PLA as an acetabular liner is subject to limitations concerning mechanical properties. We developed a complete production process of a natural filler, i.e., date pits. Then, the PLA and date pit particles were extruded for homogenous mixing, producing a composite filament that can be used in 3D printing. Date pit particles with loading fractions of 0, 2, 4, 6, 8, and 10 wt.% are dispersed in the PLA. The thermal, physical, and mechanical properties of the PLA–date pit composites were estimated experimentally. The incorporation of date pit particles into PLA enhanced the compressive strength and stiffness but resulted in a reduction in the elongation and toughness. A finite element model (FEM) for hip joints was constructed, and the contact stresses on the surface of the acetabular liner were evaluated. The FEM results showed an enhancement in the composite load carrying capacity, in agreement with the experimental results.

Parametric analysis of the effect of impaction load on the stability of head-neck junction in total hip arthroplasty

BACKGROUND

Tribocorrosion at head-neck interface is one of the main causes leading to the failure of hip implants in total hip arthroplasty. Impaction load has been acknowledged as one of the key factors influencing the stability of the taper junction. It is understood that the magnitude of impaction force differs from the surgeon to surgeon in primary total hip arthroplasty or revision. Clinically, it is sufficient enough to keep the male and female tapers inseparable utilizing a low impaction, which seems to contradict previous researches. The objective of this study was to investigate the effect of impaction loads on the stability of taper junction during assembly and gaits.

METHODS

A finite element model with 12/14 taper and the taper mismatch of 4' was developed for investigation. The impaction force profiles were collected from surgeon as the inputs, and then the contact mechanics over one or multiple gaits was further analyzed and validated utilizing hip simulator test.

FINDINGS

Impaction force ranging from 200 to 2000 N could provide the same taper connection effect after the first gait due to the secondary seating. As for impaction loads of 3000 N and above, an increased impaction force would lead to the tighter taper connection.

INTERPRETATION

The effect of impaction load on the stability of head-neck junction is a piecewise function, indicating that the stability of taper junction is not affected by different impaction loads and tends to be consistent while its magnitude is below the threshold. Instead, the stability of taper junction is positively correlated with impaction force.

Mechanical in vitro fatigue testing of implant materials and components using advanced characterization techniques

Implants of different material classes have been used for the reconstruction of damaged hard and soft tissue for decades. The aim is to increase and subsequently maintain the patient's quality of life through implantation. In service, most implants are subjected to cyclic loading, which must be taken particularly into consideration, since the fatigue strength is far below the yield and tensile strength. Inaccurate estimation of the structural strength of implants due to the consideration of yield or tensile strength leads to a miscalculation of the implant's fatigue strength and lifetime, and therefore, to its unexpected early fatigue failure. Thus, fatigue failure of an implant based on overestimated performance capability represents acute danger to human health. The determination of fatigue strength by corresponding tests investigating various stress amplitudes is time-consuming and cost-intensive. This study summarizes four investigation series on the fatigue behavior of different implant materials and components, following a standard and an in vitro short-time testing procedure, which evaluates the material reaction in one enhanced test set-up. The test set-up and the applied characterization methods were adapted to the respective application of the implant with the aim to simulate the surrounding of the human body with laboratory in vitro tests only. It could be shown that by using the short-time testing method the number of tests required to determine the fatigue strength can be drastically reduced. In future, therefore it will be possible to exclude unsuitable implant materials or components before further clinical investigations by using a time-efficient and application-oriented testing method.

Role of tribochemistry reactions of B4C on tribofilm growth at a PEEK–steel interface in simulated body fluids

Hydrolysis of B4C particles triggered by friction and deposition of Ca2+ and phosphate ions dominate formation of the barrier layer. The barrier layer endows the PEEK–metal sliding pair enhanced anti-wear and anti-corrosion performance.

Ultra-High-Molecular-Weight-Polyethylene (UHMWPE) as a Promising Polymer Material for Biomedical Applications: A Concise Review

Ultra-High Molecular Weight Polyethylene (UHMWPE) is used in biomedical applications due to its high wear-resistance, ductility, and biocompatibility. A great deal of research in recent decades has focused on further improving its mechanical and tribological performances in order to provide durable implants in patients. Several methods, including irradiation, surface modifications, and reinforcements have been employed to improve the tribological and mechanical performance of UHMWPE. The effect of these modifications on tribological and mechanical performance was discussed in this review.

Tuning the tribofilm nanostructures of polymer-on-metal joint replacements for simultaneously enhancing anti-wear performance and corrosion resistance

Total joint replacement is currently the most successful clinical treatment for improving the life quality of individuals afflicted with end-stage osteoarthritis of knee or hip joints. However, release of wear and corrosion products from the prostheses is a critical issue causing adverse physiological responses of local issues. β-SiC nanoparticles were dispersed into polyetheretherketone (PEEK) materials and their role in tribocorrosion performance of PEEK-steel joints exposed to simulated body fluid was investigated. It is demonstrated that β-SiC nanoparticles increase greatly the wear resistance of the PEEK materials, and meanwhile mitigate significantly corrosion of the steel counterpart. It is revealed that tribochemical reactions of β-SiC nanoparticles promoted formation of a robust tribofilm having complex structures providing protection and shielding effects. The present work proposes a strategy for developing high-performance polymer-on-metal joint replacement materials of enhanced lifespan and biocompatibility via tuning interface nanostructures. STATEMENT OF SIGNIFICANCE: Adverse tissue responses to metal wear and corrosion products from metal base implants remain a challenge to surgeons and patients. We demonstrated that leaching of metal ions and release of metallic debris are well decreased via tuning interface nanostructures of metal-polymer joint bearings by dispersing β-SiC nanoparticles into polyetheretherketone (PEEK). It is identified that the addition of β-SiC greatly improves the tribological performances of the PEEK materials and mitigated corrosion of the steel. Tribo-chemistry reactions of SiC induce the formation of complex structures which provide protection and shielding effects. Nanostructures of the tribofilm were also comprehensively investigated. These novel findings proposed a potential route for designing high performance metal-polymer joint replacement materials.