Dynamic degradation of porous magnesium under simulated environment of human cancellous bone

Biodegradable metals have been suggested for bone scaffold applications due to their mechanical properties that are better for load bearing applications. Among biodegradable metals, magnesium and its alloy are the most investigated materials due to their mechanical properties which are closer to the cancellous bone and could prevent complications such as an aseptic loosening of stress shielding effects, and potentially to be used as bone scaffolds. Bone adapts the mechanical loading from the physiological activities that induced the movement of bone marrow passing through the porous structure of cancellous bone due to the pressure differences. The aim of this research is to analyse the degradation behaviour of porous magnesium under dynamic degradation test for bone scaffold applications. Interconnected holes of porous magnesium have been developed with various percentages of porosity (30%, 41% and 55%) and are fabricated using computer numerical control (CNC) machine. Dynamic immersion test rigs are specifically designed to simulate environment of human cancellous bone. There are two types of tests that have been conducted in this study: (1) fluid flow with different flowrates (0.025, 0.4 and 0.8 ml/min) and (2) fluid flow integrated cyclic loading (different cyclic loading (1000, 2000 and 3500 με) under constant flowrate of 0.025 ml/min). A dynamic immersion test has been conducted for 24, 48 and 72 hours. The results showed that the specimen with a higher percentage of porosity as well as the exposed surface area degrades faster compared to the others. The degradation product formation and clogging pores phenomenon are influenced by the level of flow rates. The effects of different flow rates towards the mechanical integrity of porous magnesium have shown a huge drop of 95% from their original mechanical properties within 3 days, which have deteriorated in both functions; porosity and degradation time. The variation in flowrates used showed that degradation of the material is seven times higher compared to the static immersion test environment. Furthermore, the influenced of integrating fluid flow and cyclic loading have increased the relative weight loss and degradation rate as high as 61.56% and 93.67%, respectively. Additionally, the mechanical properties have improved and increased from 53% to 87% as compared to dynamic immersion test using the mechanical stimulus of fluid flow only. Therefore, the dynamic immersion test with integrated cyclic loading was more reliable and provides realistic environment for degradation assessment compared to static immersion test for bone scaffold application as this study using the boundary of human cancellous bone environment

Contact pressure analysis of acetabular cup surface with dimple addition on total hip arthroplasty using finite element method

This research aims to analyze the contact pressure on acetabular cup surface with dimple addition and without dimple addition. The main contribution in this research is to explore the influence of dimple addition to contact pressure that affects implant lifetime. The simulation is carried out by giving fully 3D physiological loading of the hip joint under normal walking conditions. Contact pressure analysis conducted on dry contact condition and meshing with the two-pole method performed to provide a comprehensive contact pressure result. The results show that the total hip arthroplasty model with dimple addition can reduce contact pressure for all phases in one full cycle with average decreased by 15.53% which indicates that adding dimple to the contact surface in the total hip arthroplasty bearing can extend the life of implant use

The effect of bottom profile dimples on the femoral head on wear in metal-on-metal total hip arthroplasty

Wear and wear-induced debris is a significant factor in causing failure in implants. Reducing contact pressure by using a textured surface between the femoral head and acetabular cup is crucial to improving the implant’s life. This study presented the effect of surface texturing as dimples on the wear evolution of total hip arthroplasty. It was implemented by developing finite element analysis from the prediction model without dimples and with bottom profile dimples of flat, drill, and ball types. Simulations were carried out by performing 3D physiological loading of the hip joint under normal walking conditions. A geometry update was initiated based on the patient’s daily routine activities. Our results showed that the addition of dimples reduced contact pressure and wear. The bottom profile dimples of the ball type had the best ability to reduce wear relative to the other types, reducing cumulative linear wear by 24.3% and cumulative volumetric wear by 31% compared to no dimples. The findings demonstrated that surface texturing with appropriate dimple bottom geometry on a bearing surface is able to extend the lifetime of hip implants

Finite element analysis of porosity effects on mechanical properties for tissue engineering scaffold

Porosity plays a vital role in the development of tissue engineering scaffolds. It influences the biocompatibility performance of the scaffolds by increasing cell proliferation and allowing the transportation of the nutrients, oxygen, and metabolites in the blood rapidly to generate new tissue structure. However, a high amount of porosity can reduce the mechanical properties of the scaffold. Thus, this study aims to determine the geometry of the porous structure of a scaffold which exhibits good mechanical properties while maintaining its porosity at a percentage of more than 80%. Circle and square geometries were used since they are categorized as simple geometry. A unit cell of 12mm x 12mm x 12mm for square shape and pore area of 25p mm2 for circle shape was modeled and simulated by using Finite Element Analysis. The simulation consists of a compression test that determines which geometry exhibits better Young’s Modulus. Since the circle geometry has better Young’s Modulus, the pore size was furthered varied while maintaining the porosity of the scaffold to be above 80%. The same method of the simulation was done on the models. The result shows that the smallest pore size model has the highest Young’s Modulus, which still able to maintain the porosity at 80%

An overview of ultrasound testing for lesion detection in human kidney

Ultrasound waves are commonly used to produce images of the human internal organs such as kidney. Most kidney cancers are found unexpectedly when patient have an ultrasound or scan for symptoms that turn out to be unrelated. Usually, the first test a medical doctor will do is an ultrasound scan, which is a real-time, moving test used to detect and differentiate between tumours, stones and cysts on the kidney. This paper presents the overview of ultrasound imaging for renal screening to detect renal lesions such as tumor, stone and cyst

Mechanical degradation model of porous fe scaffold: simulation approach

This paper proposes a simple degradation model that estimates morphological changes in pure iron scaffolding due to surface erosion. The main contribution of this work is to estimate the degradation of porous pure iron scaffolding and analyze the impact of morphological changes on mechanical properties. In this study, the pure iron scaffolding model was designed in CAD software with 3 different porosity such as 30%, 41%, and 55% respectively. The geometry images of CAD models with a resolution of 3316 x 5530 pixels are captured layer by layer with a thickness of 0.02 mm. The purpose of this method is to replace the function of the u-CT scanning technique. Two-dimensional morphological erosion is applied to reduce the number of pixels of the image model. This erosion process is adjusted iteratively with increasing number of pixels to erode the image model until the volume of the scaffold after reconstruction matches the volume of the model undergoing mathematical calculations. Their changes in the volume of scaffold geometry and degradation of mechanical properties were evaluated using finite element analysis. This study found that mechanical properties such as elastic modulus and yield strength decreased systematically during the 19 week degradation period. In addition, deformation analysis is performed on models based on finite element analysis

Development of computational wear prediction on total ankle replacement

The computational wear simulation has been widely used to predict wear generated on hip and knee implant but studies related to wear analysis of the ankle are limited. The purpose of this study is to develop finite element analysis on total ankle replacement (TAR) wear prediction. Three-dimensional (3D) models of a right ankle TAR have been created to represent Bologna-Oxford (BOX) TAR model. The model consist of three components; tibial, bearing and talar representing their physiological functions. The joint reaction force profile at ankle joint has applied 25 discrete instants during stance phase of a gait cycle. It is to determine the distribution of contact stress on meniscal bearing surfaces contact with talar component. The sliding distance was obtained from predominate motions of plantar/dorsi flexion. Parametric studies to reduce wear have been conducted to optimize the design of polyethylene joint. The parameters involved are the thickness of the meniscal bearing, the radius of curvature between talar and bearing component, the width and length of meniscal bearing. The value of linear wear depth is 0.01614 mm per million cycles which is in agreement with other studies (0.0081 – 0.0339 mm per million cycles). The relative difference is 9%. The value of volumetric wear after five million cycles is 30.5 mm3 which is in agreement with other studies (16 – 66 mm3). The relative difference is 12%. The best dimension to use for the thickness, radius of curvature, width and length of meniscal bearing are 6 mm, 30 mm, 30 mm and 22 mm, respectively

Study of dynamic degradation behaviour of porous magnesium under physiological environment of human cancellous bone

This study analyse the effect of integrating of physiological environment of human cancellous bone as shown by different level of cyclic compressive on the degradation behaviour of porous magnesium under dynamic immersion for bone scaffold applications. The porous magnesium (30%, 41% and 55% of porosity) were immersed in simulated body fluid (SBF) with flowrate 0.0025 ml/min while having dynamic loading (1000 με 2000 με and 3500 με) for 24, 48 and 72 h. The influenced integrating both boundaries have increased the relative weight loss and degradation rate as high as 61.56% and 93.67%, respectively as compared to dynamic immersion test only

Study of wear prediction on total ankle replacement

Pre-clinical experimental wear testing is very effective to evaluate new ankle replacement in the aspect of design and material used. However, both cost and time can be one of the constraints factors, particularly in the early stage of design or analysis. Numerical method has been addressed as an alternative to predict wear on ankle replacement. The computational wear simulation has been widely used on the hip and knee but very less found in study related to wear analysis of the ankle. The purpose of this research is to develop computational simulation to predict wear on total ankle replacement (TAR). Three dimensional (3D) models of the right ankle TAR were developed using BOX total ankle replacement model. Mobile bearing device was developed consisting of three components tibial, bearing and talar. Each component has different design and purposes representing its physiological behaviour of the ankle. The ankle load applied was based on the joint reaction force profile at the ankle joint. This is to determine the distribution of contact stress on the meniscal bearing surfaces contact with talar component for 25 discrete instant during stance phase of gait cycle. The sliding distance was obtained from predominates motion of plantar/dorsi flexion. The computed linear wear depth and cumulative volumetric wear were 0.01614 mm per million cycles and 30.5 mm3, respectively. The values obtained were proven to be consistent with the previous in vitro result