title: Diamond-like carbon coatings enhance scratch resistance of bearing surfaces for use in joint arthroplasty: hard substrates outperform soft.
abstract: The purpose of this study was to test the hypotheses that diamond-like carbon (DLC) coatings will enhance the scratch resistance of a bearing surface in joint arthroplasty, and that a hard ceramic substrate will further enhance scratch resistance by reducing plastic deformation. We tested these hypotheses by applying a hard DLC coating to medical-grade cobalt chromium alloy (CoCr) and magnesia-stabilized zirconia (Mg-PSZ) femoral heads and performing scratch tests to determine the loads required to cause cohesive and adhesive fracture of the coating. Scratch tracks of DLC-coated and noncoated heads were then scanned by optical profilometry to determine scratch depth, width, and pile-up (raised edges), as measures of susceptibility to scratching. DLC-coated CoCr specimens exhibited cohesive coating fracture as wedge spallation at an average load of 9.74 N, whereas DLC-coated Mg-PSZ exhibited cohesive fracture as arc-tensile cracks and chipping at a significantly higher average load of 41.3 N (p < 0.0001). At adhesive coating fracture, DLC-CoCr delaminated at an average load of 35.2 N, whereas DLC-Mg-PSZ fractured by recovery spallation at a significantly higher average load of 46.8 N (p < 0.05). Both DLC-CoCr and DLC-Mg-PSZ specimens exhibited significantly shallower scratches and less pile-up than did uncoated specimens (p < 0.005 and p < 0.01, respectively). However, the harder ceramic substrate of DLC-Mg-PSZ better resisted plastic deformation, requiring significantly higher loads for cohesive and adhesive coating fracture. These findings supported both of our hypotheses.
authors.affiliation: Missouri Bone & Joint Research Foundation, St. Louis, Missouri 63131.
authors.forename: Marie E
authors.initials: ME
authors.lastname: Roy
authors.affiliation: Missouri Bone & Joint Research Foundation, St. Louis, Missouri 63131.|Signal Medical Corp., St. Louis, Missouri 63131.
authors.forename: Leo A
authors.initials: LA
authors.lastname: Whiteside
authors.affiliation: Signal Medical Corp., St. Louis, Missouri 63131.
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Katerberg
mesh_terms: D002244:Carbon / Q000737:chemistry*; D002858:Chromium Alloys / Q000737:chemistry; D020099:Coated Materials, Biocompatible / Q000737:chemistry*; D003035:Cobalt / Q000737:chemistry; D018130:Diamond / Q000737:chemistry*; D006244:Hardness; D006622:Hip Prosthesis; D006801:Humans; D008277:Magnesium Oxide / Q000737:chemistry; D008422:Materials Testing; D011475:Prosthesis Failure; D013314:Stress, Mechanical; D013499:Surface Properties; D015040:Zirconium / Q000737:chemistry
chemical_list: D002858:Chromium Alloys; D020099:Coated Materials, Biocompatible; D008277:Magnesium Oxide; D003035:Cobalt; D002244:Carbon; D018130:Diamond; D015040:Zirconium; C028541:zirconium oxide