title: Mechanical characterization of nacre as an ideal-model for innovative new endoprosthesis materials.
abstract: BACKGROUND
  To mimic the impressive mechanical behavior of natural ceramics for technical or biomedical applications, interest has been focused on nacre, a natural composite consisting of imbricated aragonite platelets embedded in a protein matrix. Nacre is an ideal model material for implants, since it possesses favorable strength and toughness properties compared to the component materials of which it is composed. The focus of the present study was to test standardized parameters which are good indicators of the material's suitability as an implant material.
  
  
  METHODS
  A three-point bending test was performed on polished nacre samples according to international standards for Young's modulus, bending strength and fracture toughness. A total of 60 nacre samples were tested, with 5 samples each in 4 states of hydration (dry, distilled water, 0.9% NaCl and sea water). As a basis for comparison, 10 samples of a newly developed bioceramic material were tested for fracture toughness.
  
  
  RESULTS
  The fracture toughness of nacre tended to be higher for specimens conditioned in 0.9% NaCl than for dry specimens (5.3 ± 0.6 vs. 4.3 ± 0.7 MPam(1/2), p = 0.061). The fracture toughness of the bioceramic investigated was observed to be somewhat higher than nacre (5.8 ± 0.4 vs. 4.3 ± 0.7 MPam(1/2), p ≤ 0.001).
  
  
  CONCLUSIONS
  The increase in fracture toughness of hydrated nacre was not as large as would be expected based on the difference in stiffness of the matrix material after hydration that has been reported. Modulus and toughness were similar to published values and the fracture toughness observed was somewhat higher than reported for alumina implant ceramics, which are in use in total hip arthroplasty. In a direct comparison, we found that a newly developed alumina bioceramic material can in fact match nature in terms of fracture toughness.
authors.affiliation: Laboratory for Biomechanics and Biomaterials, Orthopaedic Department, Hannover Medical School, Germany. Berna.Richter@ddh-gruppe.de
authors.forename: Berna Ida
authors.initials: BI
authors.lastname: Richter
authors.forename: Sarah
authors.initials: S
authors.lastname: Kellner
authors.forename: Henning
authors.initials: H
authors.lastname: Menzel
authors.forename: Peter
authors.initials: P
authors.lastname: Behrens
authors.forename: Berend
authors.initials: B
authors.lastname: Denkena
authors.forename: Sven
authors.initials: S
authors.lastname: Ostermeier
authors.forename: Christof
authors.initials: C
authors.lastname: Hurschler
mesh_terms: D040761:Biomimetic Materials; D006245:Hardness Tests; D008422:Materials Testing; D011474:Prosthesis Design