The impact of surface and geometry on coefficient of friction of artificial hip joints

Coefficient of friction (COF) tests were conducted on 28-mm and 36-mm-diameter hip joint prostheses for four different material combinations, with or without the presence of Ultra High Molecular Weight Polyethylene (UHMWPE) particles using a novel pendulum hip simulator. The effects of three micro dimpled arrays on femoral head against a polyethylene and a metallic cup were also investigated. Clearance played a vital role in the COF of ceramic on polyethylene and ceramic on ceramic artificial hip joints. Micro dimpled metallic femoral heads yielded higher COF against a polyethylene cup; however, with metal on metal prostheses the dimpled arrays significantly reduced the COF. In situ images revealed evidence that the dimple arrays enhanced film formation, which was the main mechanism that contributed to reduced friction

Advances of Wear Reduction of Artificial Joints: Regenerative Cartilage Artificial Joints

The lifespan is a major concern for artificial joints when more younger patients are taking the total joint replacement operations. Wear is recognized as the main reason for the premature failure of implanted joints. So lowering the wear is one of the most effective way to extend the lifespan, which has attracted much efforts in both academia and industry. Development of new bio-materials is a main approach but contributes less in recent year. The research on surface roughness hasn’t given a definite solution in directing the industrial practice. The surface texturing functions well in improving the friction and wear of artificial joints, but the working mechanism is still ambiguous. Cushion or buffering layer is a promising solution to introduce elastic contact between the bearing surfaces, but cannot totally avoid debonding or shear stresses currently. Latest progress on regeneration of articular cartilage makes it possible to form hyaline cartilage in vitro onto bio-implant surfaces to reproduce the original properties of healthy joints which is definitely the most promising way

Simulated studies of wear and friction in total hip prosthesis components with various ball sizes and surface finishes

Experiments were conducted on a newly designed total hip joint simulator. The apparatus closely simulates the complex motions and loads of the human hip in normal walking. The wear and friction of presently used appliance configurations and materials were determined. A surface treatment of the metal femoral ball specimens was applied to influence wear. The results of the investigation indicate that wear can be reduced by mechanical treatment of metal femoral ball surfaces. A metallographic examination and surface roughness measurements were made

The influence of textured surfaces on the tribological behaviour of hip replacements employing a mass conserving complementarity algorithm

The tribological behaviour of Metal-on-Metal (MoM) hip prostheses is a key factor for their success. In particular, wear is recognized to have a crucial role in the failure of a prosthesis and can have severe consequences on the patient’s health, e.g. pseudo-tumors in MoM implants, [1,2]. The lubrication of the coupling between the prosthetic head and the acetabular cup can affect both the contact behaviour and the wear of the prosthesis [3]. Different contributions exist in the pertinent literature addressing the elastohydrodynamic analysis of the head-acetabulum coupling, but rarely these analysis are performed taking into account the possible fluid cavitation in the contact area between the mating surfaces [4]. In order to improve the tribological performance of hip implants, the use of textured surfaces has been proposed in recent studies [5]. The present contribution focuses on the possible improvement that textured surfaces could give to the hip joint replacement tribological behaviour. Textured surfaces are widely used in mechanics in order to increase the carrying capacity of various kind of joints working in elastohydrodynamic condition [6-8]. Textured surfaces typically show a path of cavitated zones due to the presence of dimples in the contact surfaces. The effect of these cavitated zones can result in a global decreasing of friction and wear [9]. This preliminary contribution aims at studying, by means of preliminary simplified one-dimensional models, the influence of the geometrical parameters of the textures on the tribological behavior of a hip joint coupling. The analysis have been carried out employing a linear complementarity mass-conserving algorithm originally proposed in [10], capable of properly capturing the phenomenon of cavitation

Wear behaviour of Ti6Al4V femoral head surfaces functionalized through ultrasonic vibration turning for drug delivery

La tesi presenta una possibile funzionalizzare di teste di protesi femorali in Ti6Al4V per mezzo di una lavorazione meccanica (l'Ultrasonic Vibration Turning UVT). Tale funzionalizzazione è una potenziale soluzione per risolvere l'infiammazione post-operatoria per mezzo del drug delivery, in quanto permette di creare delle microbuche superficiali, possibili siti di immagazzinamento di medicinale

Master of Science

thesisMore than 285,000 total hip replacement (THR) surgeries are performed in the United States each year. Most prosthetic hip joints consist of a cobalt-chromium (CoCr) femoral head that articulates with a polyethylene acetabular component lubricated with synovial fluid. The statistical survivorship of these metal-on-polyethylene prosthetic hip joints declines significantly after 10 to 15 years of use, primarily as a result of polyethylene wear and wear debris incited disease. The current engineering paradigm to increase the longevity of prosthetic hip joints is to manufacture ultra-smooth articulating surfaces. In contrast, this work shows that adding a patterned microtexture to the ultra-smooth CoCr femoral head reduces friction when articulating with the polyethylene acetabular liner. The microtexture increases the load-carrying capacity and the thickness of the joint lubricant film, which reduces contact between the articulating surfaces. As a result, friction and wear is reduced. A lubrication model is used to design the geometry of the patterned microtexture, and we experimentally demonstrate reduced friction for the microtextured compared to conventional smooth surrogate prosthetic hip joints

Micro-crack characterization for metal-on-metal hip implant of textured surface using electrical discharge machining

In hip implant, it has been proven that surface texturing which is also known as dimples can improve the lubrication performance and reduce friction. However, little attention is paid to the effect of textured surface by assessing the crack formation on the dimple areas. This research focuses on the formation of cracks on dimple edges during manufacturing process using electrical discharge machining (EDM) as higher stress is produced in this area. The crack formation then was observed during operational use of metal-on-metal (MoM) hip implant in the case that the dimples parameters are not fully optimized. For dimple manufacturing on a S45C mild steel material, machining angles was varied at 50°, 70° and 90° using developed workpiece positioning system in this research. The pulse currents were set at 1 A, 2 A and 3 A. Cracks formed on the dimple edge after the machining were observed using Scanning Electron Microscope (SEM) and measured in terms of its length. Then, nine dimples were machined on the samples of acetabular cup part using the chosen EDM parameters. Friction screening on the hip implant samples with femoral head of 28 mm diameter and radial clearance of 30 pm was carried out using four-ball bearing machine. The loads varied up to 250 N, 500 N and 1000 N representing the loading gait in the hip joint. The formation of cracks on the dimple edges for each load was then observed. The experimental results showed that when lowest current 1A was applied, the micro-cracks total length appeared during EDM process increased substantially. For MoM hip implant, it was found that the optimal setting for the EDM machining was 3 A at 90° machining angle, taking into account the curved hip implant surface. However, more than 50% of the cracks formed during machining were removed after loading due to surface grooving. It is suggested that it is suitable to machine the dimples on the hip implant surface using EDM in terms of crack formation. While new cracks formed after the loading were found to be far more dominant than the original cracks due to EDM machining. The cracks were found to be much wider and longer especially with the imposition of the maximum load of 1000 N. The contribution of this study is on the effect of crack formation on hip implant improvement, as well as providing basic data of textured surface in hip implant. This is because the crack formed can cause wear and friction which can lead to wear fatigue in hip implant thus shorten lifespand its lifespan

Lubrication Modelling of Artificial Joint Replacements: Current Status and Future Challenges

This paper reviews the recent advancements in computational modelling of the lubrication of hip and knee joint replacements, especially those concerning Professor Duncan Dowson’s contribution. The review starts with the development of modelling the five key parameters that appeared in the pioneered Hamrock–Dowson formula. Then, the theory and approaches for the mixed lubrication in which the artificial hip and knee joint replacements operate are reviewed. We also discuss the current challenges in modelling the lubrication behaviour of joint replacements and how these challenges could be addressed in future studies. These challenges include the mixed lubrication theory, the numerical complexities due to complicated realistic geometry, material and rheology, and individual physiological diversities

Biotribology of Artificial Hip Joints

Tribology is the science of interacting surfaces; when these surfaces are in a biological system, it is called as biotribology. With the increasing rate of joint replacement operations and need for artificial prosthesis, biotribology is becoming a very important and rapidly growing branch of tribology. Based on this fact, in this chapter, basic tribological concepts are presented in terms of friction, lubrication, and wear; then with these fundamental backgrounds the biotribological behavior of natural and artificial hip joints are discussed in detail. Moreover, material pairs that are used in artificial joint replacements and the application of surface modification for the enhancement of the tribological properties of these materials are handled. Furthermore, the determination of tribological behavior of joint materials such as wear, coefficient of friction, friction torque, and frictional heating by using conventional techniques and hip joint simulator are discussed. Finally, the measurement and analysis of wear in both retrieved prosthesis and experimental studies are discussed referring the latest research articles