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Chemical evolution of CoCrMo wear particles: an in-situ characterisation study

DOI: 10.1021/acs.jpcc.9b00745 DOI Help

Authors: Mohamed A. Koronfel (Imperial College London) , Angela E. Goode (Imperial College London) , Miguel Angel Gomez-gonzalez (Imperial College London) , Johanna Nelson Weker (Stanford Synchrotron Radiation Lightsource) , Thiago Araujo Simões (University of Leeds) , Rik Brydson (University of Leeds) , Paul Quinn (Diamond Light Source) , Michael F. Toney (Stanford Synchrotron Radiation Lightsource) , Alister Hart (University College London (UCL)) , Alexandra E. Porter (Imperial College London) , Mary P. Ryan (Imperial College London)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: The Journal Of Physical Chemistry C

State: Published (Approved)
Published: April 2019

Abstract: The unexpected high failure rates of CoCrMo hip-implants is associated with the release of a large number of inflammatory wear particles. CoCrMo is nominally a stable material, however, previous chemical speciation studies on CoCrMo wear particles obtained from periprosthetic tissue revealed only trace amounts of Co remaining despite Co being the major component of the alloy. The unexpected high levels of Co dissolution in-vivo raised significant clinical concerns particularly related to the Cr speciation in the dissolution process. At high electrochemical potentials, the alloy’s Cr-rich passive film breaks down (transpassive polarisation) facilitating alloy dissolution. The potential release of the carcinogenic Cr(VI) species in vivo has been a subject of debate. While the large scale Co dissolution observed on in vivo produced particles could indicate a highly oxidising in vivo environment, Cr(VI) species were not previously detected in periprosthetic tissue samples. However, Cr(VI) is likely to be an unstable (transient) species in biological environments and studies on periprosthetic tissue does not provide information on intermediate reaction products nor the exposure history of the wear particles. Here, an in situ spectro-microscopy approach was developed, utilising the high chemical resolution of synchrotron radiation, in order to study CoCrMo reactivity as a function of time and oxidising conditions. The results reveal limited Co dissolution from CoCrMo particles, which increases dramatically at a critical electrochemical potential. Furthermore, in-situ XAS detected only Cr(III) dissolution, even at potentials where Cr(VI) is known to be produced, suggesting that Cr(VI) species are extremely transient in simulated biological environments where the oxidation zone is small.

Subject Areas: Chemistry, Materials

Facility: Stanford Synchrotron Radiation Lightsource