Understanding wear behavior of 3D-Printed calcium phosphate-reinforced CoCrMo in biologically relevant media

Abstract

Recent advances in the processing of wear-resistant calcium-phosphate reinforced CoCrMo composites for articulating surface applications has necessitated further investigation of performance in biological conditions relevant to patient applications. To this end, CoCrMo composites containing calcium phosphate in the form of hydroxyapatite (HA) were manufactured to study the influence of the reinforcing phase on the tribofilm formation in biologically-relevant conditions. The CoCrMo-HA composites were processed using a laser engineered net shaping (LENS™) additive manufacturing (AM) system with three distinctive compositions: CoCrMo-0%HA, CoCrMo-1%HA, and CoCrMo-3%HA. Extensive wear testing of the CoCrMo-HA composites was carried out in DMEM (cell media) and DMEM + Hyaluronic acid (found naturally in synovial fluid). Wear tests were performed at loads ranging from 5N to 20N, and wear media was measured post-test using ICP-MS techniques to release Co and Cr ions. During testing, all coefficients of friction remained in the 0.15-0.25 range, which was lower than the previously reported 0.50-0.75 range in DI water, indicating that the DMEM + hyaluronic acid media plays a significant role in reducing frictional contact. At loads higher than 15N, the HA-tribofilm exhibited a breakdown resulting in higher wear rates but still lower overall ion release than the CoCrMo control composition. Our results indicate that CoCrMo alloys with HA addition can significantly reduce wear rates and ion release even in the presence of naturally-occurring synovial-fluid friction-reducing media.

Keywords: Cobalt-chromium-molybdenum; Hydroxyapatite; Laser additive manufacturing; Tribofilm; Wear.

Figure 1:

Outline of LENS™ based processing and previous work showing a demonstration of tribofilm formation. LENS™ schematic and contact resistance plot modified from (Bandyopadhyay et al., 2019; Bandyopadhyay and Traxel, 2018), respectively.

Figure 2:

Characteristic COF curves for composites. (A) DMEM-0%HyAcid. (B) DMEM-10%HyAcid. (C) DMEM-50%HyAcid.

Figure 3:

Wear rates and Co + Cr ion release into a solution across all testing conditions.

Figure 4:

Surface damage images of CCM + 3%HA composites at 15N load under the DMEM+50HyAcid environment.

Figure 5:

SEM Micrograph showing an absence of tribofilm in CCM-3HA composite at 20N load under the DMEM+50HyAcid environment.

Figure 6:

Mechanism of action of tribofilm formation in DMEM + HyaA environment.