FIGURE 1

1
A USAXS STUDY OF NANOCOMPOSITE POLY(METHYL
METHACRYLATE) BONE CEMENTSMary Turell, Heimo
Schnablegger, David Baker, Lisa Pruitt, Anuj
BellareDepartment of Orthopaedic Surgery,
Brigham and Womens Hospital, Harvard Medical
School, Boston, MA University of Hamburg,
Hamburg, Germany Department of Mechanical
Engineering, University of California at
Berkeley, Berkeley, CA

• SUMMARY OF RESULTS
• Scanning electron microscopy of freeze fracture
  surfaces of CMW1 microcomposite (Fig. 1 left)
  and the CMW1 nanocomposite (Figure 1 right)
  showed that in both cases barium sulfate
  particles were finely dispersed in the cement
  with no large agglomerates present.
• Specific surface, Os, was calculated from the
  USAXS curves (Figure 2)
• Os pK/Q where K Porod constant, and Q
  Invariant
• Guinier approximation was invoked for calculation
  of the invariant in the angular region of 0-qmin
  while Porods law was used to estimate the
  invariant for qmax-infinity for calculation of Os
  (see Table below)
• Fatigue tests showed that, under the processing
  and test conditions used in this study,
  substitution of the micrometer size barium
  sulfate with the 100nm size particles resulted in
  a two-fold increase in the number of cycles to
  failure in CMW1 (Figure 3).

• INTRODUCTION
• Acrylic bone cement is widely used for fixation
  of total joint replacement prostheses. In the
  United States alone, expenditures on orthopaedic
  implants exceeded 1.99 billion dollars in 1999
  1. The lifetime of bone cement is limited by
  fracture associated with fatigue failure which
  can ultimately lead to loosening of the implant,
  and early revision surgery.
• Fractographic studies have shown that cracks are
  associated with defects in the cement, such as
  voids and large agglomerates of radiopacifier
  particles 2, 3. Prevention of such defects is
  therefore expected to improve the fracture
  toughness of bone cement.
• Commercial cements are "microcomposites"
  containing 10 weight barium sulfate
  radiopacifier particles of 1 mm size in a
  polymethyl methacrylate (PMMA) matrix. In this
  study, micrometer size barium sulfate particles
  were replaced with 100nm size barium sulfate
  particles in a commercial cement.
• USAXS was used to quantify the dispersion of
  both microcomposite and nanocomposite PMMA
  cements using specific surface area calculations.
• In vitro fatigue tests were performed to
  evaluate the performance of each bone cement
  under simulated in vivo conditions.
• MATERIALS AND METHODS
• CMW bone cements (Johnson Johnson/Depuy,
  Warsaw, IN) were mixed using a standard
  techniques and molded into dumbbell shaped
  fatigue specimens and 0.5mm thick specimens for
  USAXS.
• 100nm and 1000nm size barium sulfate particles
  were employed as radiopacifiers (Sachtleben,
  Duisberg, Germany) The 100nm barium sulfate
  ultrafine powder contained 2 weight percent
  sodium citrate anticoagulant.
• USAXS was performed on microcomposite,
  nanocomposite and unfilled cement samples at
  UNICAT using 10 KeV x-rays.

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