Fabrication and characterization of DLC coated microdimples on hip prosthesis heads

Abstract

Diamond like carbon (DLC) is applied as a thin film onto substrates to obtain desired surface properties such as increased hardness and corrosion resistance, and decreased friction and wear rate. Microdimple is an advanced surface modification technique enhancing the tribological performance. In this study, DLC coated microdimples were fabricated on hip prosthesis heads and their mechanical, material and surface properties were characterized. An Electro discharge machining (EDM) oriented microdrilling was utilized to fabricate a defined microdimple array (diameter of 300 µm, depth of 70 µm, and pitch of 900 µm) on stainless steel (SS) hip prosthesis heads. The dimpled surfaces were then coated by hydrogenated amorphous carbon (a-C:H) and tetrahedral amorphous carbon (Ta-C) layers by using a magnetron sputtering technology. A preliminary tribology test was conducted on these fabricated surfaces against a ceramic ball in simulated hip joint conditions. It was found that the fabricated dimples were perpendicular to the spherical surfaces and no cutting-tools wear debris was detected inside the individual dimples. The a-C:H and Ta-C coatings increased the hardness at both the dimple edges and the nondimpled region. The tribology test showed a significant reduction in friction coefficient for coated surfaces regardless of microdimple arrays: the lowest friction coefficient was found for the a-C:H samples (µ = 0.084), followed by Ta-C (µ = 0.119), as compared to the SS surface (µ = 0.248).

Tribological investigation of diamond-like carbon coated micro-dimpled surface under bovine serum and osteoarthritis oriented synovial fluid

“…The coating thickness was 1.05–1.15 μ m for DLC coating (figure 2(b)). Previous studies on DLC coating also showed a similar coating thickness value [5, 23]. …”

“…Carbon should be the main composition on the coating layer; it also contains chromium, as it was used as an interlayer during the deposition process in order to increase the bonding strength between coating and titanium alloy substrate [5]. Furthermore, some pores, as well as lighter-colored bumps, may exist on the coating surfaces (figure 2(a)).…”

“…Therefore, a number of studies have been carried out based on different materials and designs to increase the durability of implants by decreasing friction, wear, and corrosion. The bearing clearance, which is the difference between the radius of the prosthesis head and cup, is an important factor of hip joint-bearing performance and stability [4, 5]. The recommended clearance of a modern hip joint prosthesis is usually 50–100 microns [6, 7]; however, it is a big challenge for manufacturers to maintain the clearance with an exact deviation, despite the availability of precise manufacturing facilities.…”

“…One effective technique to do this is fabricating micro-dimples on a Ti–6Al–4V alloy substrate. It was reported previously that micro-dimples exhibit a low coefficient of friction [11, 12] and wear rate [13, 14] because they improve lubrication, trap wear debris generated from the contacting surface, and provide a hydrodynamic pressure [5]. Thus, surface texturing, such as the use of micro-dimples, enhances tribological performance in the presence of a lubricant.…”

Mechanical tests, wear simulation and wear particle analysis of carbon-based nanomultilayer coatings on Ti6Al4V alloys as hip prostheses

“…Our previous studies showed that the sp 2 and sp 3 structure of the nanomultilayer coating determines the high hardness and self-lubricating characteristic, and the selflubrication characteristic of the graphitic coating helps the steady COF. 24,28 The nanomultilayer coatings have a low average COF of 0.1, and it is a lower value compared with other coating such as DLC in literature, 41,42 but the COF may be affected by the testing conditions in different studies. Thus, microstructure and mechanical tests showed that the carbon-based nanomultilayer coatings have desirable mechanical and tribological properties.…”