“…Based on all the references compiled in Tables A.2 and A.3 in the Appendix of this article, all the parameters of interest in the design space have been classified into either input or output parameters. The tribo-mechanical properties of PEEK and PEEK composites (output parameters) cannot be altered directly, but can be affected indirectly by tailoring other parameters of interest (input parameters) such as the material's microstructure, its composition, the articulating material coupling, as well as the testing and environmental conditions under which the experiments are performed (Flöck et al, 1999;Unsworth, 2007, 2009;Evans et al, 2014;Cowie et al, 2020;Scholes and Unsworth, 2010;East et al, 2015;Brockett et al, 2017;Grupp et al, 2010;Wang et al, 1998b;Brockett et al, 2012;Polineni et al, 1998;Kandemir et al, 2019;Regis et al, 2018;Wang et al, 1999;Chamberlain et al, 2019;Brockett et al, 2016). The definitions are as follows: input parameters (also known as control parameters) are the ones which can be controlled directly during experiments while the output parameters can be indirectly influenced by adjusting the input parameters but there exists no way to alter them through a direct route.…”