Biomedical Engineering Reference
In-Depth Information
Chapter 25
Bone mechanical stimulation with Piezoelectric
materials
J. Reis, C. Frias, F. Silva, J. Potes, J. A. Simões, M. L. Botelho,
C. C. Castro, and A. T. Marques
iNtroduCtioN
Fukada and Yasuda were the first to describe bone piezoelectrical properties, in the
1950s. When submitting dry bone samples to compressive load, an electrical potential
was generated, an occurrence explained by the direct piezoelectric effect (Fukada and
Yasuda, 1957). The nature of the piezoelectric effect is closely related to the occur-
rence of electric dipole moments in solids. In connective tissues such as bone, skin,
tendon and dentine, the dipole moments are probably related to the collagen fibbers,
composed by aligned strongly polar protein molecules (ElMessiery, 1981; Fukada and
Yasuda, 1964; Halperin et al., 2004). The architecture of bone itself, with its aligned
concentric lamellae, concurs for the existence of potentials along bone structure (El-
Messiery, 1981).
Bone piezoelectric constants, that is the polarization generated per unit of mechan-
ical stress, change according to moisture content, maturation state (immature bone has
lower piezoelectric constants when comparing to mature bone) and architectural orga-
nization (samples from osteossarcoma areas show lower values due to the unorganized
neoplastic changes) (Marino and Becker, 1974).
Early studies concentrated on dry bone and because collagen's piezoelectricity
was described as nearly zero with 45% moisture content, there were doubts that wet
bone could, in fact, behave as a piezoelectric material, but further studies confirmed
it in fact does (Fukada and Yasuda, 1957; Marino and Becker, 1974; Reinish and No-
wick, 1975). Some of the published studies reinforce the importance of fluid flow as
the main mechanism for stress generated potentials in bone, and piezoelectricity's role
was, and still is, quite unknown (Pienkowski and Pollack, 1983).
More recently, bone piezoelectrical properties have rouse interest, in the context
of bone physiology and electro-mechanics. It has been associated to bone remodel-
ing mechanisms, and to streaming potential mechanisms (Ahn and Grodzinsky, 2009;
Ramtani, 2008). Piezoelectricity explains why, when under compression, collagen re-
organizes its dipole and shows negative charges on the surface, which attract cations
like calcium. Conversely, if tensed, collagen yields predominance of positive charges,
thus obviously influencing the streaming potential and mineralization process (Noris-Suárez
et al., 2007).
The commercially available biomaterials for bone replacement and reinforce-
ment do not take into account the bone natural piezoelectricity and the mechanism of
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