Acta Microscopica Vol 16 No1-2,(Supp.2)2007
Cusco-Peru September 2007 122
Collagen Piezoelectric effect induce bone healing
Ana Marina Ferreira1, Karem Noris-Suárez1, Joaquín Lira-Olivares2, Jose Luis Feijoo3, Gema Gonzalez4
1: Cellular Biology Department, Simón Bolívar University. Caracas, Venezuela.
2: Center for Surface Engineering Centro, CIS, Simón Bolívar University. Caracas, Venezuela
3: Materials Science Department (Polymer Group), Simón Bolívar University. Caracas, Venezuela
4: Instituto Venezolano de Investigaciones Científicas (IVIC), Lab de Ciencia e Ing. de Materiales. Caracas, Venezuela
E-mail: email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com.
Abstract— The collagen includes 90% of the organic matrix of the bones. Bone healing and growth are
controlled by the rate of deposition of hydroxyapatite (HA). This process have been so far accredited to the
work of osteoblasts, which are attracted by the electrical dipoles produced either by piezoelectricity, due to
deformation of the bone, specially the collagen in it, or due to outside electrical stimuli. The main purpose
of this work was to study the influence of the effect of piezoelectricity of elastically deformed cortical bone
collagen, on the mineralization process without bone cells. The collagen type I was obtained by rabbit’s
bones decalcification using EDTA 0.5 M pH 7.4 treatment. The rectangular samples of bone collagen were
bending to induce piezoelectricity (Figure B) and immersed into Simulated Body Fluid (SBF) using the
biomimetic method for 5 weeks. This effect induces a net negative charge on the compression side which
induces a preferential deposition of mineral on the surface compared with the tension side (net positively
charge), as previously described [Noris-Suárez K. et al., Biom. 8(3): 941-948]. Controls (undeformed) and
deformed samples were analyzed by SEM to verify mineral deposition on both sides. The micrographs of
SEM of the deformed collagen immersed for different periods of time 3, 4 and 5 weeks are shown. Figure
A corresponds to deformed collagen under compression immersed for 31/2 weeks in SBF; it shows the
crosslinks between each collagen fibbers and how the initial process of apatite nucleation on the different
collagen bands occurs. Figure B corresponds to the deformed collagen immersed for 4 weeks in SBF and it
is possible to observe that the mineral deposition is much higher on the compression deformed side than at
the surface under tension deformation. This preferential deposition is attributed to the piezoelectric effect
generated by the mechanical deformation on the collagen, which induces a dipole orientation on the
material, as an effect of the internal reorganization of collagen fibbers. In Figures C.I and C.II we can detail
the mineral growth on the deformed collagen under compression and immersed in SBF for 5 weeks. The
apatite particles cover the fibbers and forms conglomerates, compared with the deformed collagen site
under tension, in same conditions (micrograph C.III), only have a few particles of mineral disperse on the
surface. Probably the mineral deposited in the zone of the collagen of the cortical bone under compression
is an amorphous phase of apatite precursor of crystals of hydroxyapatite. Our results demonstrate that this
piezoelectric effect induced by collagen deformation could act as initiators of the mineralization process.
The results of this study showed that the piezoelectric phenomena of bone collagen promotes
mineralization on the compression side more than on the tension side compared with undeformed surface in
absence of bone cells.
Keywords: cortical bone collagen, piezoelectricity, MEB.
Figure 1: SEM micrographs of deformed bone collagen. A) Compression side immersed in SBF for 31/2 weeks. B)
Samples immersed in SBF for 4 weeks C) Samples immersed in SBF for 5 weeks: I) Compression side: Mineral
growth on collagen surface, II) Compression side: Mineral deposition detailed on collagen fibers, III) Tension
side: collagen fibbers.
Ferreira et al.