Biomedical Engineering Reference
In-Depth Information
streaming potential, and thus its use is accompanied by a break in bone natural electro
physiologic mechanisms.
On the other hand, so far orthopedic implants only perform fulfill primary func-
tions such as mechanical support, eliminating pain and re-establishing mobility and/
or tribologic/articular contact. Arthroplasty is liable to cause intense changes on strain
levels and distribution in the bone surrounding the implant, namely stress shielding.
Metal stiffness is much higher than that of bone, so the rigid stems tend to diminish the
amount of stress transmitted to the surrounding bone and produce stress concentration
in other areas, depending on geometry and fixation technique. Stress shielding leads
to bone resorption, which in turn may cause implant instability and femoral fracture,
and make revision surgery more challenging (Beaulé et al., 2004; Huiskes et al., 1992;
Mintzer et al., 1990; Sumner and Galante, 1992). Ideally, the bone implant should
present sensing capability and the ability to stimulate bone, maintaining physiological
levels of strain at the implant interface.
The work here summarized explores
in vitro
and
in vivo
use of a piezoelectric
polymer for bone mechanical stimulation.
Piezoelectric materials for mechanical stimulation of Bone Cells--the
in
vitro
study
Osteocytes and osteoblasts are essential for mechanosensing and mechanotransduc-
tion, and cell response depends on strain and loading frequency (Kadow-Romacker
et al., 2009; Mosley et al., 1997). We explored the use of piezoelectric materials as a
mean of directly straining bone cells by converse piezoelectric effect.
The MCT3T3-E1 cells were cultured under standard conditions and on the surface
of Polyvinylidene Fluoride (PVDF) films, subjected to static and dynamic conditions,
as described by Frias et al. (2010).
Polymeric piezoelectric films (PVDF) were used as substrate for cell growth. These
thin films consisted of a 12 x 13 mm active area, printed with silver ink electrodes on
both surfaces in a 15 x 40 mm die-cut piezoelectric polymer substrate, polarized along
the thickness. In dynamic conditions the substrates were deformed by applying a 5 V
current, at 1 Hz and 3 Hz for 15 min.
To guarantee adhesion of osteoblasts to the device surface and electric insulation,
the surface was uniformly covered with an electric insulator material. The chosen ma-
terial for covering was an acrylic, poly (methyl methacrylate) (PMMA), (PERFEX®,
International Dental Products, USA), used alone in the first three layers and a in forth
layer along with 4% of Bonelike® (250-500 µm) particles added (kindly offered by
INESC Porto). The coating was performed by dip-coating at constant velocity of 0,
238 mm/sec. Impedance was measured both in saline and culture medium, in non-
coated and coated devices, and electric insulation achieved. The coating procedure
aimed improvement of cell adhesion and electrical insulation. Electrically charged
particles are known to improve osteoblast proliferation and it was important to prevent
cell damage and other means of stimulation other than the mechanical (Dekhtyar et al.,
2008; Kumar et al., 2010; Nakamura, 2009).
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