Investigating Effects of Testing Parameters on Frictional Heating of UHMWPE by Taguchi Method

Frictional heating makes detrimental effects on surrounding tissue and lubricant around the artificial hip joint. For reduction of this thermal damage, testing parameters and their effects were investigated by using the Taguchi method and analysis of variance. Ultra high molecular weight polyethylene (UHMWPE) acetabular liners and CoCrMo femoral head artificial hip joint components were used as samples. Frictional heating measurements of the joints were carried out on a custom made hip joint friction experimental setup. Surface dimples in different sizes were machined on the inner surface of acetabular insert samples. The tests were conducted under different loading conditions with different testing time. Bovine calf serum was used as lubricant with different amount of third body wear particles in it. Temperature rise in acetabular and femoral component was recorded with embedded thermocouples. The experimental results demonstrated that the surface dimples were the major parameter on frictional heating, followed by applied load, amount of third body particles and time. The optimal combination of the testing parameters was predicted and validated by doing experiments

Effect of surface patterning on frictional heating of vitamin E blended UHMWPE

Friction between articulating surfaces cause temperature rise in the acetabular cup and femoral head. This heating may influence the rate of wear, fatigue, creep and oxidative degradation of bearing materials. The objective of this study is to determine the effect of surface patterning on frictional temperature rise of the articulating surfaces of vitamin E blended ultra-high molecular weight polyethylene acetabular component paired with a cobalt-chromium (CoCrMo) femoral component. For this reason concave dimples were formed on inner surface of the acetabular cup with 0.5 mm diameter and 0.5 mm depth. Temperature rise between the bearing surfaces was measured under different loading conditions. Frictional measurements of the joints were carried out on a custom made hip joint friction experimental set up. The prostheses were of 28 mm diameter. Applied static loads were changed from 200 N to 1500 N. In the flexion-extension plane, a simple harmonic oscillatory motion between ±24° was applied to the ultra high molecular weight polyethylene acetabular component. The frequency of motion was 1 Hz and the tests were run up to 11,000 cycles. Temperature rise in acetabular and femoral component was recorded with embedded thermocouples. Lower temperature rise in patterned sample pairs were measured than unpatterned samples. So it can be said that the surface patterning contributes to reduction of frictional heating of sliding surfaces

Evaluating Frictional Temperature Rise in Sliding Surface of Artificial Hip Joint Materials with Different Loading Conditions

Friction between articulating surfaces cause temperature rise in acetabular cup and femoral head. This heating may influence the rate of wear, fatigue, creep, oxidative degradation of bearing materials and may terminate surrounding tissue. The objective of this study is to determine temperature rise with different applied load for the articulating surfaces of conventional ultra high molecular weight polyethylene (UHMWPE) and vitamin E blended ultra high molecular weight polyethylene (VE-UHMWPE) acetabular components paired with a ceramic femoral component in bovine calf serum lubrication condition. Additionally frictional torque between the bearing surfaces was measured and friction coefficient was calculated. Frictional measurements of the joints were carried out on a custom made hip joint friction simulator. Various levels of static loads were applied on 28 mm diameter prostheses. In flexion-extension plane, a simple harmonic oscillatory motion between ± 24° was applied to the UHMWPE acetabular component. The period of motion was 1 Hz and the tests were run up to 12,000 cycles. Temperature rise in acetabular and femoral component was recorded with embedded thermocouples. The results were compared in terms of UHMWPE and vitamin E blended UHMWPE

Surface Texturing of Vitamin E Blended UHMWPE for Reduction of Wear

Ultra high molecular weight polyethylene (UHMWPE) has been the most commonly used bearing material in artificial hip and knee replacements. But wear and wear debris of UHMWPE has been the most important problem which cause aseptic loosening and revision surgery of these replacements. For enhangement of wear resistance, new generation UHMWPE materials have been developed and different surface modification techniques have been tried. The objective of this study is to determine the effect of surface dimples on wear behavior of conventional UHMWPE and vitamin E blended UHMWPE (VE-UHMWPE) in ultra-pure water lubrication conditions. Pin-on-disc tribotester was used for measurement of friction coefficient and wear. 0.5 mm in diameter dimples were machined on the surfaces of UHMWPE and VE-UHMWPE discs. CoCrMo pins were used as counter surface. Results were evaluated in terms of materials and presence of dimples

Measurement of Wear in Orthopedic Prosthesis

Wear in orthopedic prosthesis has been the main limiting factor of total joint replacement's service life. Wear analysis of total joint replacements is essential for determining failure mechanism, prediction of wear and longevity of implants. So it would be possible to improve design, material and manufacturing quality and service life of these devices. Radiographic, gravimetric, volumetric and optical techniques are current methods for measuring of wear in retrieved implants. Gravimetric method is the standardized method for quantifying wear volumes of total joint prosthesis. Although this method is effective for determining experimental wear volume in simulated conditions, it is not suitable for assessing the clinically retrieved prosthesis for which there is no pre-wear data available. Each of the wear measuring methods has advantages and limitations. Researches have been going on for developing effective methods. In this paper the techniques that are currently used for evaluating wear of orthopedic prosthesis like gravimetry, coordinate measuring machine, micro computed tomography, and digital photogrammetry are explained. The literature works and new trends in metrological assessment of wear are reviewed

Measurement of Wear in Orthopedic Prosthesis

Wear in orthopedic prosthesis has been the main limiting factor of total joint replacement's service life. Wear analysis of total joint replacements is essential for determining failure mechanism, prediction of wear and longevity of implants. So it would be possible to improve design, material and manufacturing quality and service life of these devices. Radiographic, gravimetric, volumetric and optical techniques are current methods for measuring of wear in retrieved implants. Gravimetric method is the standardized method for quantifying wear volumes of total joint prosthesis. Although this method is effective for determining experimental wear volume in simulated conditions, it is not suitable for assessing the clinically retrieved prosthesis for which there is no pre-wear data available. Each of the wear measuring methods has advantages and limitations. Researches have been going on for developing effective methods. In this paper the techniques that are currently used for evaluating wear of orthopedic prosthesis like gravimetry, coordinate measuring machine, micro computed tomography, and digital photogrammetry are explained. The literature works and new trends in metrological assessment of wear are reviewed

Current-mode PID controllers employing commercially available active components

This work describes two current-mode (CM) PID controllers using only two commercially active components, namely, current feedback operational amplifier (CFOA), and four passive components, i.e. two capacitors and two resistors. They have appropriate output and input impedance values, allowing them to be utilized in cascade connections without requiring a buffer circuit. Since all capacitors are grounded, it is suitable for integrated circuit (IC) technology. Moreover, the controllers can be easily modified to operate in voltage-mode (VM), transimpedance-mode (TIM), and transadmittance-mode (TAM) PID controllers. Using 0.18 µm CMOS parameters and the PSPICE program, the proposed circuits are simulated to verify the theoretical behavior. To demonstrate the viability of the circuits, experimental tests using commercially available AD844 integrated circuits are performed. The suggested PID circuits are also experimental tested in a closed-loop system as an example. © 2023 Elsevier Gmb

Importance of Measurement Parameters for the Dental Implant Surface Characterization

Pure titanium and its alloys have been widely used in biomedical applications on account of their biological and mechanical properties. Although the mechanical properties of titanium provide acceptable responses under dynamic pressures, surface modifications are needed in order to improve osseointegration between bone-implant interfaces. There are many different surface modification techniques like sand blasting, acid etching, or coating with various materials. Surface characterization is as important as surface modification for dental implants. Although many researchers studied about measurement of surface characteristics of dental implants with similar techniques but with different measurement parameters, there is still no consensus about the optimal surface characteristics values of a successful dental implant. Among many other surface characteristics, surface roughness is one of the most important features for dental implants. In this study, the importance of surface roughness measurement of dental implants is discussed and the need of a standardized procedure for implant surface roughness measurement is emphasized. In our experimental study three different processed surfaces as sand blasted and hydrofluoric acid etched surfaces, sand blasted and nitric acid etched surfaces and blasted surfaces were investigated. Results are compared via each method and each processing technique. It is aimed to highlight the importance of a standardized method for measuring and describing surface characteristics. More definitive, standardized methods are needed to augment the rather existing varied combined measurement parameters which affect the results for the assessment of biomedical surfaces

Importance of Measurement Parameters for the Dental Implant Surface Characterization

Pure titanium and its alloys have been widely used in biomedical applications on account of their biological and mechanical properties. Although the mechanical properties of titanium provide acceptable responses under dynamic pressures, surface modifications are needed in order to improve osseointegration between bone-implant interfaces. There are many different surface modification techniques like sand blasting, acid etching, or coating with various materials. Surface characterization is as important as surface modification for dental implants. Although many researchers studied about measurement of surface characteristics of dental implants with similar techniques but with different measurement parameters, there is still no consensus about the optimal surface characteristics values of a successful dental implant. Among many other surface characteristics, surface roughness is one of the most important features for dental implants. In this study, the importance of surface roughness measurement of dental implants is discussed and the need of a standardized procedure for implant surface roughness measurement is emphasized. In our experimental study three different processed surfaces as sand blasted and hydrofluoric acid etched surfaces, sand blasted and nitric acid etched surfaces and blasted surfaces were investigated. Results are compared via each method and each processing technique. It is aimed to highlight the importance of a standardized method for measuring and describing surface characteristics. More definitive, standardized methods are needed to augment the rather existing varied combined measurement parameters which affect the results for the assessment of biomedical surfaces