Hip Joint Displacement

A total hip joint replacement usually composed of two main components articulating with one another, a polymeric acetabular cup against a metal or ceramic femoral head component [1]. Ultra-high molecular weight polyethylene (UHMWPE) is a key player in the total hip joint replacement as an acetabular cup since more than half a century, due to their unique properties such as high wear resistance, strength and modulus, excellent toughness, chemical resistance and impact, low moisture absorption, good wave transmission, and electrical insulation [2]. This does not preclude that there are many materials have been used for this purpose such as; polytetrafluoroethylene (PTEF), polyarylether ether ketone (PEEK), Polyethylene terephthalate (PET), polyoxymethylene
(POM), and polyamide (PA) [3-7]. The results showed that the failure often occurs in the polymeric cups due to a large aseptic loosening resulted by abrasive and adhesive wear [8]. Also, the results illustrated that UHMWPE had the better wear resistance compared with other polymeric materials [9]. Although the reported results of UHMWPE were Favorable and the listed previous materials considered UHMWPE the most expensive material while POM is the cheapest one [10]. In addition, POM has more strength than UHMWPE, where the strength of POM is 67 MPa and UHMWPE is between 35-55MPa [11-13]. Besides, POM has a very good biocompatibility was motivated for researchers to use it in the biomaterial applications such as removable partial dentures [14]. More of that, POM has a very good tribological characteristic which was the main reason to employ in bearing and gear applications [15-17]. However, the wear behavior of POM still lower than UHMWPE which was leading to large aseptic loosening in osteolysis and was a barrier to use extremely in this application [18]. Therefore, economically and performance, POM is considered the most appropriate alternative for UHMWPE after finding the appropriate solution of lower wear resistance compared by UHMWPE which constrained by good biocompatibility. Currently, carbon nanotubes (CNTs) is using as a nanofiller material to improve the tribological and other behavior of several polymeric materials [19, 20].
This is Because CNTs has unique properties such as high aspect ratio, lightweight, high mechanical strength, good thermal and electrical conductivity and excellent tribological behavior [21]. However, the results were not favorable due to the poor compatibility of POM with other materials as a result of high viscosity, especially with bulk materials [22]. Therefore, Yousef et al. (2013) develop a paraffin oil (PO) dispersion technique to obtain a uniform dispersion. The new dispersion technique summarized on adding a small amount of PO (2-3%Wt.) during the mixing process to decrease the viscosity of POM during the injection process then obtain a uniform dispersion of CNTs inside the matrix [23]. Through the new dispersion technique, Yousef et al. (2015) succeed to produce a real CNTs/POM bulk products had a uniform dispersion, in particular, spur, helical, bevel, and worm gears [24]. The results showed that the new dispersion technique has been successfully utilized to increase the wear resistance of POM by adding 0.02 wt. % of POM by 35% when compared by virgin
POM. Based on these results, this work aims to produce the first nanocomposite POM hip cup in the world reinforced with 0.02 wt. % of functionalized CNTs using paraffin oil dispersion technique and injection process. The wear rate of the new cups was evaluated by using a total leg joint’s simulator, which was particularly designed for this purpose, according to ISO 14242-1 standard [25]. Also, the effect of the functionalization process of the mechanical and thermal behaviors was studied.