Hydroxyapatite and Titanium on Zirconia (HTOZ) is a newly developed zirconia composite material for use in the femoral component of cementless knee prosthesis. The material has a tetragonal zirconia polycrystal (TZP) substrate covered with an arc-spray coating layer of titanium and a flame-spray coating layer of hydroxyapatite on the fixation side. These surface layers provide good conductivity of bone formation and enhance the integration of the ceramic femoral component to living bone. Although the mechanical properties of the TZP substrate is not affected by the manufacturing process of applying the coating layers on the fixation side, processing causes changes to the articulating surface TZP microstructure which makes the surface smoother microscopically and also hydrophobic. In this study, the friction and wear behaviour of the UHMWPE-on-HTOZ sliding pair for the cementless knee prostheses was evaluated using unidirectional pin-on-disk and multidirectional pin-on-plate tests. Results indicated that the UHMWPE-on-HTOZ sliding pair produced favourable tribological characteristics compared to UHMWPE-on-TZP. Friction was lower than that of the conventional UHMWPE-on-TZP sliding pair under the same physiological lubrication conditions. Under multidirectional sliding the wear of polyethylene was, similar to the wear of UHMWPE-on-ceramic. It is postulated that the hydrophobic and microscopically smooth surface of HTOZ contributed to its improved friction and wear behaviour through enhanced fluid film formation compared to conventional TZP. The results support the use of the HTOZ-on-UHMWPE bearing combination for knee prostheses.
|Number of pages||9|
|Publication status||Published - Jan 1 2003|
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