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Raman Imaging of Str ess Patterns in Biomaterials 315

Standard tribological studies of ceramic-on-ceramic load-bearing
surfaces usually mainly rely on phenomenological parameters for
describing the wear effects, like as surface topography, friction coef-
48
ficient, and loss rates. However, we have shown here that advanced
spectroscopic analyses can be also employed in order to obtain a
deeper understanding of wear mechanisms and load-bearing kinet-
ics. PS Raman analyses can be useful to clarify the actual mechanisms
lying behind the wear behavior of ceramic bearings, which typically
occur in a complex way, hardly predictable by theoretical simulations
and reproducible in artificial joint simulators. Raman spectroscopy
advancements are particularly relevant to the future of ceramic-on-
ceramic bearings, which are considered as the main protagonists in
the new generation of materials for arthroplastic applications.

10.5 Conclusions
A PS Raman technique, based on a microscopy measurement enabled
us to quantitatively assess in situ the microscopic stress fields devel-
oped during fracture at the crack tip of natural and synthetic bioma-
terials. Using the Raman PS technique, crack-tip toughening
mechanisms could be clearly visualized and assessed quantitatively.
This chapter also presents results on microscopic stress analysis of
ceramic biomaterials as collected by Raman microspectroscopy on
the bearing surfaces of artificial hip joints. Based on the current and
previous results, improved designs of more realistic hip joint simula-
tors can be attempted, which take into consideration phenomena
like microseparation and surface microdisplacements. Mechanistic
Raman spectroscopic analyses may help rationalizing the structural
behavior of biomaterials, thus building up new theories that attribute
such behavior to clear factors. The possibility of nondestructively and
quantitatively measuring stress fields, in addition to phase fractions
from Raman spectra of biomaterials definitely offers a chance to
materials scientists to rationally address the best microstructural
design approach to better synthetic biomaterials.

References
1. G. Pezzotti, “Stress Microscopy and Confocal Raman Imaging of Load-Bearing
Surfaces in Artificial Hip Joints,” Expert Review of Medical Devices, 4:165–189,
2007.
2. G. Pezzotti, “Raman Piezo-Spectroscopic Analysis of Natural and Synthetic
Biomaterials,” Analytical and Bioanalytical Chemistry, 381:577–590, 2005.
3. E. E. Lawson, B. W. Barry, A. C. Williams and H. G. M. Edwards, “Biomedical
Applications of Raman Spectroscopy,” Journal of Raman Spectroscopy, 28:111–117,
1998.
4. G. Pezzotti and A. A. Porporati, “Raman Spectroscopic Analysis of Phase-
Transformation and Stress Patterns in Zirconia Hip Joints,” Journal of Biomedical
Optics, 9:372–384, 2004.