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Amit Bandyopadhyay1 Anish Shivaram1 Murat Isik1 Jose Avila1 Susmita Bose1

1, School of Mechanical and Materials Engineering, Washington State University, Pullman, Washington, United States

Cobalt-chromium-molybdenum (CoCrMo) alloys are widely used in load-bearing implants, specifically in hip, knee, and spinal applications, due to their excellent wear resistance and their being economic compared to titanium-based alloys. However, due to wear induced metal ion release from the implants and poor biocompatibility at implant-tissue interface, there is a significant interest to find an alternative to CoCrMo alloy. We hypothesize that adding calcium phosphate (CaP) based ceramic in the form of hydorxyapatite can minimize metal ion release concerns in CoCrMo alloy.
CoCrMo-CaP composite coatings were processed using a commercial laser-engineered net shaping (LENS™) system. After LENS™ processing, CoCrMo alloy was subjected to laser surface melting (LSM). Samples were investigated for microstructure, phase stability, and wear induced damage. It was found that wear resistance of CoCrMo was enhanced by ~ 5 times due to the formation of an in situ tribofilm of CaPs, and achievement of a fine dendritic microstructure in the case of LSM treated CoCrMo. In vitro cell material interactions study using human osteoblasts cell line was performed. For in vivo, rat and rabbit distal femur models were used for a period of 5 and 12 weeks. In vitro and in vivo study showed improved biological response for surface modified CoCrMo compared to untreated CoCrMo approximately a 5-fold increase in osteoid formation. Our results show that careful surface modification treatments can simultaneously improve wear resistance and in vivo biocompatibility.
The presentation will focus on processing as well as physical, mechanical and biological characterization of 3D printed CaP-CoCrMo composites with a focus on minimizing metal ion release.

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