T/37 International Polymer Science and Technology, Vol. 31, No. 9, 2004 Muanyag es Gumi, No. 5, 2004, pp. 187 Acetabular cups made from ultrahigh-molecular weight polyethylene and Kevlar for use in medicine G. Zsoldos and Gy. Czel Selected from International Polymer Science and Technology, 31, No. 2, 2004, reference MG 04/05/187; transl. serial no. 15197 Translation submitted by E.A. Inglis 1. INTRODUCTION During the manufacture of internal and external medical prostheses doctors and engineers try to use high-strength materials which are friendly to the environment and the organism. Hip prostheses are being used in increasing numbers by traumatology and orthopaedics professionals to repair hip joints broken as a result of accidents caused by injuries and illnesses. Following the experimental prosthetics first introduced in 1938, nowadays the number of prostheses introduced annually is in excess of 600,000. The Metrimed Surgical Subsidiary Company, making internal prostheses (for hip and knee joints) was founded in Hungary in 1986, and its products are used by the Hungarian medical profession. 2. HIP JOINT PROSTHETIC COMPONENTS Hip joint and other prostheses continuous development firstly serves this aim, that following recovery the prosthesis long term, greater freedom of movement makes possible for the former invalids. In terms of its structure the prosthesis can be divided into three main components (Figure 1). The leg or shank is the largest component, this holds the joint secure in the thigh bone. The head is made of basically the same material as the shank, from a cobalt-based metal alloy or austenite aid- resistant steel. The acetabulum is a spherical cap-shaped component which can be fitted into the bone of the hip prosthesis. Load transmission between the thigh bone and the pelvic bone takes place on the outer spherical surface of the head and the inner surface of the acetabulum. The material employed for the acetabulum is a polyethylene plastic with special properties. Nowadays the material most frequently used for the surgical implant is ultrahigh molecular weight polyethylene (UHMWPE) is used. UHMWPE is a unique material with regard to its physical and mechanical properties [2]. Despite the many successful implants it should be mentioned that the service life of UHMWPE is finite and greatly depends on the conditions of implantation. Together with the normal wear and tear distortion of the UHMWPE acetabulum often necessitate replacement of the prostheses, or “reoperation”. In cases where there is an excessively high load distributed over the spherical surface the acetabulum can also be deformed by the excessive load in addition to the wear. The degree of deformation may be so high that it makes it impossible for the spherical head to fit tightly, and the spherical head hangs loose in the cup. It is a specific requirement that in the case of excessive static and dynamic loading the deformation can approach 1 millimetre. Continuing development of the service life of the acetabulum presupposes an increase in the strength and wear resistance Figure 1. Photo of hip joint prosthesis [1]