Accessible Requires Authentication Published by De Gruyter May 26, 2013

A New Design of Hip Prosthesis Coating using Functionally Graded Material

Neues Design von Hüftendoprothesenbeschichtungen mittels funktioneller gradierter Werkstoffe
Hassan S. Hedia and Noha Fouda
From the journal Materials Testing

Abstract

Titanium and its alloys which have been widely used in many prostheses carry the major joint load and cause stress shielding. Thus, the bone might become osteoporotic due to lack of physiological stress flow in common hip replacement. Therefore, the optimization of hip joint materials is one of the most challenging tasks in prosthetic design. It is found in the literature that there is a great contradiction regarding the use of hydroxyapatite (HAP) coating. In this study a finite element analysis (FEA) and optimization techniques have been carried out in order to find a new design of hip stem coating using functionally graded material (FGM) to reduce stress shielding at the proximal medial part of the femur, as well as reducing the interface shear stress at the interface between the coating and the bone which directly affects the implantation and long-term stability. This work is divided into two parts: in the first part, the gradation of the elastic modulus of the coating material has been changed in the vertical direction, while the second part changes the elastic modulus in the horizontal direction. The optimal design of the first and second models was compared with HAP coating and with homogenous uncoated titanium stem. The design optimization of the first model revealed, using a coating material consisting of HAP at the upper layer of the coating graded to collagen at the lower layer, increases the maximum von Mises stress in bone at the proximal medial part of the femur by 65% and 19% compared to titanium stem and titanium coated with HAP, respectively. The maximum lateral interface shear stress in the bone at the bone/coating interface is reduced by 23% and 12%, respectively. However, the maximum medial interface shear stress in the bone at the bone/coating interface is reduced by 39% and 14% compared to titanium stem and titanium coated with HAP, respectively. The design optimization of the second model revealed, using a coating material consisting of collagen at the inner layer adjacent to stem graded to HAP at the outer layer adjacent to bone, increases the maximum von Mises stress at the proximal medial part of the femur by 60% and 15% compared to titanium stem and titanium coated with HAP, respectively. The maximum lateral interface shear stress is reduced by 18% and 6%, respectively. However, the maximum medial interface shear stress is reduced by 35% and 8% compared to titanium stem and titanium coated with HAP, respectively.

Kurzfassung

Titan und seine Legierungen, die sehr häufig in vielen Prothesen verwendet werden, tragen die Hauptlasten der Gelenke und verursachen eine Spannungsabschirmung. Auf Grund eines fehlenden physiologischen Spannungsflusses in üblichen Hüftersetzungen wird der Knochen osteoporotisch. Daher ist die Optimierung der Hüftgelenkwerkstoffe eine der herausfordernsten Aufgaben des Prothesendesigns. Anhand der Literatur wurde festgestellt, dass es widersprüchliche Auffassungen bezüglich der Verwendung von Hydroxyapatit(HAP)-Beschichtungen gibt. In der diesem Beitrag zugrundeliegenden Studie wurden Finite Elemente Analyse und entsprechende Optimierungstechniken durchgeführt, um ein neues Design für die Prothesenschaftbeschichtung zu finden, wobei mittels Gradientenwerkstoffen (functionally graded material — FGM) sowohl die Spannungsabschirmung im nahe gelegenen mittleren Teil des Oberschenkelknochens als auch die Zwischenlagenschubspannung zwischen der Schicht und dem Knochen reduziert werden sollten, die direkt die Implantierung und die Langzeitstabilität beeinflussen. Die Arbeit gliedert sich in zwei Teile: Im ersten Teil wurde die Graduierung des Elastizitätsmodules in vertikaler Richtung verändert, während sie im zweiten Teil in horizontaler Richtung verändert wurde. Das jeweils optimale Design wurde mit einer HAP-Beschichtung und mit einem homogenen unbeschichteten Schaft verglichen. Als optimales Design für das erste Modell erwies sich die Verwendung eines Schichtmaterials, das in der oberen Schicht aus HAP und in der unteren Schicht aus Kollagen besteht. Dieses erhöht die maximale von Mises Spannung im Knochen im nahe gelegenen mittleren Teil des Oberschenkelknochens um 65% beziehungsweise 19% im Vergleich zu dem Titanschaft und dem HAP-beschichteten Titanschaft. Die maximale laterale Schubspannung in der Zwischenlage ist dabei um 23% bzw. 12% reduziert. Die mittlere Schubspannung in der Zwischenlage ist im Vergleich zu dem Titanschaft und dem HAP-beschichteten Titanschaft um 39% bzw. 14% reduziert. Als optimales Design für das zweite Modell erwies sich, dass die Verwendung eines Schichtmaterials, das aus Kollagen der inneren Schicht dicht am Schaft besteht und das zu HAP in der äußeren Schicht dicht am Knochen graduiert wurde, die von Mises Spannungen im nahe gelegenen mittleren Teil des Oberschenkelknochens um 60%, beziehungsweise um 15% im Vergleich zu dem Titanschaft und dem HAP-beschichteten Titanschaft erhöht. Die maximale laterale Schubspannung in der Zwischenlage verringert sich dabei um 18% bzw. 6%. Die maximale mittlere Schubspannung in der Grenzfläche ist im Vergleich zu dem Titanschaft und dem HAP-beschichteten Titanschaft um 35% beziehungsweise 8% reduziert.


Prof. Dr. Hassan S. Hedia is professor in materials and solid mechanics. He is working in King Abdulaziz University, Saudi Arabia. He was born in Egypt in 1959. He received his BSc in 1981 in Mechanical Engineering from Cairo University, Egypt. He received his MSc in 1989 Production Engineering, Mansoura University, Egypt and his PhD in 1996 in Mechanical Engineering from Leeds University, UK and Mansoura University, Egypt under channel system. His field of interest is advanced materials, fracture mechanics, stress analysis and biomechanics. He has published around 60 papers in an international journals. He is in the editorial board of three international journals: 1- International Journal of Mechanics and Applications (http://journal.sapub.org/MECHANICS), 2- Journal of Control Engineering and Technology (JCET) (http://www.ijcet.org/Home.aspx) 3- Steering Committee Member for an international journal called Information Science and Technology (IST), Journal Website: www.academicpub.org/ist/. He is referees for at least ten international journals, e.g. Journal of Applied Polymer Science (USA), International Journal of Biomechanics (Elsevier), International Journal of Medical Engineering & Physics (Elsevier), International Journal of Engineering Fracture Mechanics (Elsevier), International Journal of Biomaterials (Elsevier), Journal of King Abdulaziz University - Engineering Sciences and WSEAS Conferences as well as Journal Papers

Dr. Noha Fouda, born in 1973, is assistant professor at the Mansoura University, Faculty of Engineering, Mansoura, Egypt. She received her BSc (Production Engineering) in 1995 from Mansoura University, Egypt, and her MSc in 2000. She recieved her PhD in 2006 from Mansoura University, Egypt. Her fields of interest are optimum design, stress analysis and mechanics of materials.


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Published Online: 2013-05-26
Published in Print: 2013-01-01

© 2013, Carl Hanser Verlag, München