title: In-vitro assessment of the wear development mechanism and stabilization of wear in the Edwards MIRA/Sorin Bicarbon mechanical heart valve orifice ring.
abstract: OBJECTIVE
  Currently, there appears to be no detailed published information specifically describing the early 'wear-in' and stabilization periods of wear in a bileaflet mechanical heart valve. This study presents a detailed morphological description of the early to middle (0 to 200 million cycles) stages of wear in the Carbofilm carbon coating on the Edwards MIRA/Sorin Bicarbon valve housing (orifice ring) pivot slots.
  
  
  METHODS
  Wear testing was performed using a specially designed durability tester that controls the impact load of the occluder against the housing. The control values were determined based on simulated physiological pulsatile flow impact loads. A morphological assessment of the early wear was performed using light microscopy and scanning electron microscopy at intervals of 0.1, 1, 10 and 40 million cycles, and at every 40 million cycles thereafter up to 200 million cycles (five equivalent years). A quantitative assessment of the rate of Carbofilm removal was determined using planimetric methods as a function of cycles.
  
  
  RESULTS
  The morphology of the Carbofilm wear showed first a gradual thinning of the layer in locations in contact with the leaflets, followed by small areas of film removal, culminating in slowly increasing areas of exposed titanium alloy substrate. Initial substrate exposure began typically between 0.1 million and 10 million cycles. The wear rate stabilized at a relatively low value, typically by 40 million cycles.
  
  
  CONCLUSIONS
  The nature of the early wear development of the Edwards MIRA/Sorin Bicarbon valve has been determined as a process of gradual thinning of the Carbofilm layer, followed by a decelerating area increase of exposed titanium alloy substrate. The process is not one of 'flaking' or spalling of relatively large particles. The exposed titanium alloy surface is typically smooth and burnished. The wear rate is well behaved and stabilized by approximately 40 million cycles. Wear area expansion continues at a decreasing rate up to 200 million cycles.
authors.affiliation: Helmholtz-Institute for Biomedical Engineering, Aachen, Germany.
authors.forename: Helmut
authors.initials: H
authors.lastname: Reul
authors.forename: Christoph
authors.initials: C
authors.lastname: Schmitz
authors.forename: Ewald M
authors.initials: EM
authors.lastname: Pfaff
authors.forename: Cornelia
authors.initials: C
authors.lastname: Hohlstein
authors.forename: Paul A
authors.initials: PA
authors.lastname: Schmidt
authors.forename: Günter
authors.initials: G
authors.lastname: Rau
authors.forename: Pietro
authors.initials: P
authors.lastname: Arru
mesh_terms: D002244:Carbon / Q000032:analysis; D020099:Coated Materials, Biocompatible / Q000032:analysis; D020878:Device Removal; D004869:Equipment Safety; D006350:Heart Valve Prosthesis; D006801:Humans; D008422:Materials Testing / Q000379:methods; D011474:Prosthesis Design; D013314:Stress, Mechanical; D014025:Titanium / Q000032:analysis
chemical_list: D020099:Coated Materials, Biocompatible; D002244:Carbon; D014025:Titanium